In this lecture, we're going to talk about alternatives to Bitcoin's existing proof-of-work mining puzzle. Mining puzzles are at the very core of Bitcoin because mining puzzles determine the incentive system in Bitcoin. Bitcoin miners get rewards for the puzzles that they solve. We expect that miners will spend considerable effort trying to find any shortcuts available to them to solve these puzzles faster or more efficiently. There's a faster way to solve puzzles we think they'll take it. Also, if there's extra stuff to do that might help the network but doesn't directly help them solve puzzles any faster, we expect that they might eventually not bother to do so at all. Therefore, the nature of the puzzle plays a very important role in steering and guiding participation in the network. Now, we've talked about some of the basic features that Bitcoin's existing SHA-2 hash-based mining puzzle already satisfies. So for example, it's fairly difficult to solve a whole bunch of puzzle solutions. This makes attacks on the Bitcoin network very costly or unlikely to succeed. On the other hand, puzzle solutions are found at a fairly predictable rate once every 10 minutes by someone. This means that honest miners to participate have some incentive to keep participating and compensate themselves for the resources that they put into the network. If we were going to design a new puzzle system from scratch or modify Bitcoin's puzzle system to be different somehow, what else could we design the puzzle to achieve? What other kinds of behaviors would we like to encourage or disincentivize? In this lecture, we're going to talk about a variety of possible alternative puzzle designs. Some of them are already used in practice and altcoins existing today. Others are research ideas that might turn out to be used in the future. The puzzles that we'll look at can achieve a variety of possible goals, such as ASIC resistance, which means leveling the playing field between users with ordinary computing equipment and users with special optimized custom hardware. We'll also look at puzzles that discourage users from delegating their participation to directors of large centralized pools. And we'll look at useful proofs of work that have some intrinsic social benefit. We'll also talk about some of the essential security requirements for mining puzzles. It doesn't do any good to have some fancy secondary feature if the puzzle doesn't still satisfy the basic requirements that it needs to keep Bitcoin secure. Before going into the alternate puzzle designs, let's talk a little bit about some of the essential requirements that any viable mining puzzle has to satisfy. Now there are many possible requirements. We've talked about some of them before. Mining puzzles need to be cheap to verify the solutions because every node on the network validates all of the puzzle solutions, even ones that aren't involved in mining directly. Puzzles also have to have adjustable difficulty so that the difficulty of the puzzle can be adjusted over time as new users join the network with increasing amounts of hash power contributed. I'm only going to talk in detail right now about one other essential requirement, which is a little bit subtle. This is that the chance of winning a puzzle solution in any unit of time should be roughly proportional to the hash power contributed. In particular, this means that really large miners with very powerful hardware should only have a proportional advantage in being the next miner to find a puzzle solution. Even small players should have some proportional chance of being successful in receiving compensation. To illustrate this point, let me show you an example of a bad puzzle that doesn't satisfy this requirement. Consider a mining puzzle that takes exactly n steps to find a solution. There are examples of puzzles like this, I don't need to go into details though, but consider these a sequential proof of work. A miner would be able to find one of these proof of work solutions by computing n steps in order in a sequence. Once it reaches n steps, finds a solution. Now the problem is that if it takes exactly n steps in a sequence to find a puzzle solution, then the fastest miner in the network will always be the one who wins the next reward. So consider a scenario with two equally powerful miners and a third miner that's slightly faster at making computational steps than the other two. For every step that the small miners take, the large miner takes two steps here. This means that the large miner finds its puzzle solution at the end of n steps while the smaller miners are still computing theirs. In this case, the fastest miner would be the only one who would receive any compensation at all. Therefore none of the other nodes would have any incentive to participate in the first place. So the alternative to this, a good puzzle, is one that gives every miner a chance of winning the next puzzle solution in proportion to the amount of hash power they contribute. This forms a weighted sample of all of the miners. So imagine throwing a dart at a board randomly at a board of different sized targets where the size of the target corresponds to the mining power. The more hash power you contribute, the better your chance of being the node that finds the next puzzle solution. A puzzle that has this property is sometimes called progress free. Now, this was just one of the requirements. There are others, but for now we're going to move on to types of alternative puzzles and we'll discuss essential requirements as they come up. We're going to start by talking about ASIC resistant mining puzzles. These are far and away the most widely discussed and sought after alternative mining puzzles. Now there are several reasons why we might want an ASIC resistant mining puzzle. If you recall from previous lectures, Bitcoin mining used to be done using ordinary computers like CPUs and GPUs. Then eventually moved towards customized FPGA devices. And now mining is mostly conducted using very powerful optimized ASIC chips, which are so vastly more effective than general purpose computing equipment that it doesn't even pay off to use an ordinary computer or a very old generation of mining equipment. But this is too bad in a way because it used to be very appealing that ordinary users could mine bitcoins out of thin air just by leaving their computer on overnight, a computer that they already had. This was really good for a low barrier to entry because it gave a compelling reason for ordinary users around the world to join the Bitcoin mining network and participate. So wouldn't it be nice if we could go back to the good old days when it was possible to mine bitcoins using ordinary general purpose computing equipment? So the approach to go back to this is to come up with a puzzle that reduces the gap between the most cost effective customized hardware and general purpose equipment that ordinary people already have. A separate goal is to try to prevent the very large ASIC manufacturers from dominating the Bitcoin mining game. There are only a few companies that are able to produce large semiconductor fabrication in order to actually produce the ASICs. So this represents a sort of consolidation of power. Now a lot of customers of Bitcoin mining ASICs have this concern that the manufacturers are going to delay the shipment of their mining devices in order for them to the manufacturers to use the mining devices themselves in order to use them for their own benefit to get their own rewards at the expense of their customers. Another concern is that if there is some breakthrough and there is a vastly more efficient ASIC design whoever comes up with that design might keep it a trade secret to themselves and use it to build their own very powerful industrial mining center then they would be able to dominate the network. So the approach here might be to build a puzzle that reduces the gap between potential future hardware ASIC designs and the ASICs that we already have which are largely distributed to ASIC mining customers. We're going to start by talking about the most widely used approach towards having an ASIC resistant puzzle. This is called a memory hard puzzle. Now the premise here is fairly simple and it's based on a well-known phenomena since the 80s about the change in the performance of computing equipment over time. Since the 80s, the performance of processing has increased at an exponential rate. You've probably heard of this referred to as Moore's Law. Now the performance of memory and storage have also increased at an exponential rate but this rate is much slower, much lower rate than that for processors. There's a performance gap between the most efficient processors and the most efficient memory and storage and this gap actually grows over time. This means that if we had a puzzle that required lots of memory to compute rather than just processing circuits then the potential improvement from next generation's optimized hardware and the current generation of optimized hardware or even general purpose computing equipment would be much lower and that's what we want. So we're going to talk now about the most popular instance of a memory hard puzzle. This is called Escript. Escript is actually a memory hard hash function and an Escript based mining puzzle is the same as the Bitcoin mining puzzle just replacing the SHA2 hash with the Escript hash. Escript is memory hard in the sense that it has a constant time memory trade-off. This means that the hash can be computed using a fixed amount of memory. It's possible to compute it using less memory but doing so increases the amount of time that it takes to compute. Now as I mentioned this puzzle is actually widely used in Bitcoin alternatives including the second most popular cryptocurrency Litecoin in a variety of others. One thing that is Descript's advantage is that this hash function is also used in other places in security, especially password hashing which has similar goals to ASIC resistance in Bitcoin mining. This gives extra confidence that if there are security problems with the hash function then other people are looking at them and might find them. Now the basic way that Escript works goes in two steps. The first step involves filling a large block of random access memory with random values and the second step involves reading from this memory in a random order.  Now the goal here is going to be to compute the Escript hash function of an input string x. This is going to be the first step. The goal is to fill a block of memory containing n cells with random values. Here n is 36. Now these values are going to be filled in in sequential order. The first value v1 is simply the hash of the input string x where the hash function h is an ordinary hash function like SHA2. Now the second value v2 is the hash SHA2 of the previous value v1. This is the same as the hash function applied to the input string x twice and so on. The third value v3 is the hash function applied to the input value x three times and so on. After n iterations all in memory cells are filled up with pseudo random values and the last value is the same as the hash function h applied to x n times. Now in the next step we're going to read back the values of memory in random order. Now we're going to begin by having an accumulator value a which involves computing the hash function h one more time on the last value. Now for n iterations we're going to use the current value of the accumulator a to pick an index i out of these n potential memory cells. Then we're going to read that value of memory. XOR with the current accumulator value a take the hash h once more of this value and replace the accumulator's value with this updated value. Now after n iterations the final value of the accumulator a is the output of this hash function. Now let me explain the intuition for why this s-script hash function is memory hard. Now you can compute this by using the n memory cells as described just before. It's also possible to compute the s-script hash value using less memory. Suppose you wanted to cut down the amount of memory you needed by half. You could do this by only storing every other value v in the table. Only the odd values in this case. Now what happens if you need to access one of the even numbered values of v which you aren't storing or you need to compute it from the values of v that you are storing. Now you can always compute vi by computing the hash h of vi minus one. Now this works and you got away with using less memory but you had to compute an extra value for h. Now this intuition holds up. On average if you wanted to reduce the amount of memory by half you would have to increase the amount of computation cycles you need by a factor of one and a half and so on. Now to talk a little bit about s-script used in practice there are a couple of disadvantages. One is that even though it has this advantage of being memory hard to compute the s-script based mining puzzle also requires an amount of memory and n cycles in order to check a proof of work puzzle solution. This puts a constraint on how large you can set n in other words how memory hard you can make it. Now a good question is is this memory hard puzzle actually ASIC resistant? And there's some uncertainty here. S-script ASICs are already available at least the first generation of these and they're at least somewhat faster than what you can do with general purpose computing equipment like CPUs and GPUs. There are several companies competing to make faster s-script ASICs and it's unclear how much better this performance gap will be able to get. There's some concern that in the altcoins that currently use s-script based mining puzzles that the parameter n hasn't been set correctly and this is one of the factors leading to ASICs arriving. Now this general approach of having a memory hard hash function is good because as I mentioned s-script is used in other applications like password hashing and so if there's any future improvements in password hashing then memory hard mining puzzles would be able to use these new password hashing functions and be able to achieve the desired effect. Now I'm going to talk about another approach to having a memory hard proof of work mining puzzle. This puzzle is called cuckoo hash cycles and the main advantage this has over s-script is that it doesn't require any random access memory to check a puzzle solution. Now we're going to look at how this works which involves for every mining attempt we're going to start with a potential solution x which you can think of as a random string and we're going to use the following procedure to determine whether or not x is a puzzle solution. For the first step we're going to select the E pseudo random edges in this graph. Now for each edge we're going to pick a random node from the top set of nodes and a random node from the bottom set of nodes. Now we do this by computing hash values using again the underlying hash value h which can just be an ordinary hash function. Now the edges are filled in the graph as illustrated below. Once the graph's completed we want to determine whether or not there's a cycle in the graph of size k. Now a cycle is a set of edges such that if you align the edges tip to tip or tip to end then they form a complete cycle. So here's what a cycle of size 4 would look like in this illustrated graph. Now k is another parameter of the puzzle. If the graph determined by input x has a cycle of size k then we say that this has a solution and we just output the input value x as well as the evidence that there was a cycle so the k indexes of the edges. Now it's not as intuitive why this is a memory hard function but the explanation is that this is a finding cycles in graphs is a fairly well studied problem and the best known algorithms for doing this do require a large amount of memory. Now what is really clear to see is that this puzzle is very easy to check. The only thing you need to do in order to check the puzzle solution is to re-compute what the edge endpoints would be for each of the k edges provided using the input value x. You only have to compute k hash functions and no random access memory is required. Now there are even more approaches towards building ASIC resistant mining puzzles. I'm only going to describe these really briefly. One is to simply build much more complicated hash functions than the ones that we've talked about so far. One example of this is the mining puzzle based on the x11 hash function which is simply 11 well-known hash functions strung together in a sequence. Another approach is to have a mining puzzle that's a moving target. Here you would have a mining puzzle that actually changes altogether every so often. This means that optimized mining hardware for one puzzle probably wouldn't be good at solving all of the puzzles even after the puzzle changes and customized mining hardware that's only good at solving one instance of the puzzle won't be very useful once the puzzle does change. Now it's unclear exactly how we would change the puzzle every so often in order to maintain the security requirements that we need. Now there's a counter argument that says that there's really no point in trying to make an ASIC resistant puzzle because the SHA-2 based mining puzzle that we already have is already good enough. The SHA-2 circuit is pretty well understood. We have a good idea of what's the optimal way of computing SHA-2. As a result, Bitcoin mining ASICs aren't changing very much and it seems unlikely that there's going to be a breakthrough in computing these proof-of-work solutions any faster. Now even as it is today, mining ASICs consist of multiple copies of the same basic SHA-2 circuit and the only difference between the largest ASICs and the smallest or cheapest ASICs is that they have more copies of the same essential circuit. This means that even the biggest mining ASICs are only a little bit more cost effective than the smaller ASICs. They compute puzzle solutions faster, but they're also more expensive. Now we're going to talk about another possible desired quality for puzzles which is for them to have some sort of socially beneficial intrinsic use. Now there's a sense in which it seems like Bitcoin mining is extremely wasteful. If you recall from previous lectures, we think that Bitcoin mining consumes about 150 to 900 megawatts of power in total and this is comparable to the power output of a really small hydroelectric power plant for example. Now this mining work is put towards computing these SHA-2 mining puzzles which don't serve any purpose outside the Bitcoin mining system. So this raises a very natural question. Is there some way that we could have a puzzle where computing the puzzle solution actually provides some sort of useful benefit to society while still satisfying the basic things that Bitcoin puzzles need? This would amount to something like recycling and it would have advantages such as lowering the overall cost of the Bitcoin system and potentially reducing Bitcoin's environmental impact. Now there are a bunch of natural candidates for this that seem like they might work. The general structure of these possible candidates are problems that involve finding a solution in a potentially very large solution space or the good solutions that you're looking for are very sparse within this space. This is like finding a needle in a haystack. Problems of this sort include protein folding where the goal is to find a 3D configuration of a molecule that has a very low potential energy or searching for aliens and signals from radio signals in space and looking for anomalous patterns that might indicate extraterrestrial life. Now for the same reason these seem like they might work as a Bitcoin mining puzzle these have been successfully used in the past as crowdsource distributed computing projects such as Folding at Home and SETI at Home.  In the cases that I just described at home like Folding at Home and SETI at Home there's a trusted administrator of the distributed computing project that's able to choose which instances of problems all of the participants in the network are supposed to be working on. Now in Bitcoin there is no trusted administrator to choose the problems so instead instances of the problem have to be generated pseudo-randomly from public information such as the hash of the last block that was found. Now in order for these to be useful randomly generated puzzle instances of this sort would have to still be useful and also randomly generated puzzle solutions have to be hard. Now it's not known how to turn any of these problems into such a puzzle scheme. Now there is one example that seems to work and has already been implemented and is somewhat used in practice which is called Primecoin. Now the goal here is to have a mining puzzle where finding a puzzle solution involves finding a chain of very large prime numbers. In particular to find a puzzle solution in Primecoin you have to find a Cunningham chain. Now a Cunningham chain consists of a sequence of prime numbers p where each of the p's is of the form 2 to the power of some number times a constant a plus 1. Now each p in the sequence has to be a large probable prime where whether or not it's a probable prime uses a probabilistic prime checking algorithm. And also the first instance of the prime number p has to be a multiple of the hash function of the metadata for the block such as the hash of the previous block, the Merkle root of the transaction and a random nonce value that miners get to choose. Now this has been used in an altcoin called Primecoin and it's actually paid off in some sense. Many of the largest known Cunningham chains have come from miners in the Primecoin network. Now this is interesting because there have been distributed computing projects such as PrimeGrid which have also tried to find prime number chains of this sort. This also adds some confidence that this is truly a hard problem because a lot of other people are also interested in finding solutions to this sort of problem. So is this actually useful? Well possibly. There is at least one known use of Cunningham prime number chains but the kind of Cunningham chains that are found by Primecoin miners are actually entirely overkill for this application. Now there's another approach towards having a proof of useful work which is rather than focusing on the amount of power or work output of the network we might instead focus on the effect of investment in Bitcoin mining infrastructure. Now just as an estimate a lot more than a hundred million dollars have been spent on customized Bitcoin mining hardware overall. This includes designing new Bitcoin mining equipment as well as actually manufacturing it. Now this Bitcoin mining equipment is very good at computing SHA-2 hashes but this improvement in technology is only useful for the Bitcoin network. It has no other use otherwise. So the idea is what if we could design a puzzle where the investment in newer and better Bitcoin mining hardware would itself be useful even if the work that's done in the power output of the network is still wasted. Now here's one example of a proposal that has this quality. It's called Permacoin and the idea is to replace Bitcoin mining rigs which compute SHA-2 hash functions with storage devices such as hard drives and memory. Now the side effect of Bitcoin miners investing in better mining equipment would be a side effect of having a massively distributed replicated backup storage system. Now the way that Permacoin works begins by assuming that we have a large file F which everyone knows about and the goal of the network is going to be to store this file. Now for simplicity imagine that F is chosen globally by a trusted dealer at the beginning. Each user is going to store a random subset of this file. Now Permacoin is based on an alternative puzzle that uses storage. Now assume that you have the file F broken up into several blocks. The first part of Permacoin involves building a Merkle hash tree over each of the blocks of the file. Now every user is going to generate a key pair in order to mine which is going to include a public key pk. They're going to use their public pk to pseudo randomly select a subset of these file segments F that they're now responsible for storing. Now for each mining attempt the miner is going to select a random nonce value and they're going to compute a hash function h1 that includes the previous block hash the Merkle root of transactions their public key pk and the nonce value that they chose. Now rather than checking if this is a puzzle solution immediately they first have to fetch k pseudo randomly chosen file segments from the subset that they're storing which is determined from that hash value h1. Now they compute a second hash value h2 which includes all of the data used to compute the first hash as well as the actual contents of the file blocks F. Now from the second hash value h2 it's compared to a target in order to see if the puzzle solution is actually a valid solution. So the idea here is that the only way to make attempts at finding a puzzle solution and determine if an attempt is a valid puzzle solution requires you to store the random subset of file blocks that you were supposed to based on your public key. Here's one application of the permacoin storage puzzle. This involves a kind of subtle point about bitcoins incentives. There's a cost to being an honest miner in bitcoin. Remember that honest miners are supposed to validate every bitcoin transaction that's included in a block. However validating a transaction requires storing the unspent transaction outputs database which at the current time requires about 200 megabytes of storage. Now maintaining this unspent transaction output database doesn't help you find puzzle solutions any faster. It's a little bit like unpaid overtime. So the idea would be to use the permacoin storage base puzzle in order to reward miners for actually storing copies of the unspent transaction output database. This would reduce the marginal cost of being honest versus just mining for the sake of getting all of the rewards. So to summarize this section having a proof of useful work is a very natural goal but the challenge is to have this secondary side effect while still maintaining the essential security requirements. There's an argument that any benefit would have to be a pure public good because if there were a way for an individual miner to get the benefit of the useful work they were doing then this benefit would also benefit an attacker. So it would make attacks on the network subsidized to the same amount that it would add any secondary improvement to society. Now potentially viable approaches to this include storage and finding large trains of prime numbers but other potential approaches could be possible as well. So even though some of these useful proofs of work have been implemented in practice arguably the benefit to society so far from these is pretty minimal. Now we're going to talk about another topic for alternate puzzles which are puzzles that discourage consolidation of mining power. Now bitcoin miners mostly participate by joining mining pools rather than participating as independent individuals. Now this means that very large mining pools that are directed by a central pool administrator become a very large potential consolidation of power. Now bitcoin's core value is decentralization so this consolidation of power poses a big threat to bitcoin's core values. Now if the power is consolidated in a few large centrally managed pools then the large pool operators become a juicy target for attacks like coercion or hacking. So a point could be made that we might want to discourage the very large pools from forming. There's even an analogy to voting here. It's illegal in the United States for example to sell your vote to someone for money. Arguably by participating in a pool controlled by someone else it's akin to selling your vote in the bitcoin network. Now recently this has become a popular problem because the very largest bitcoin mining pool, gigahash.io has reached larger than 50% of the network's overall hash power. This has led to a bunch of public outcries explaining that this is a very big threat to bitcoin and spells doom or something to that effect and demanding technical solutions to this problem. Now the observation behind one technical approach to this problem is the observation that members in a bitcoin mining pool don't inherently trust each other. Actually pools can only form and become very large because members of the pool are able to prove to the pool operator that they're towing the line in doing mining work that can only benefit the pool as a whole. This works by using the shares protocol that was described in earlier lectures. Now recall that in a bitcoin mining pool there's typically a pool operator who has a well-known public key. Now each of the miners sends their near misses or their mining shares to the pool operator to show that they're mining on a puzzle that directs the reward to the pool operator's public key. When a solution is found the pool operator then distributes the rewards among the pool participants who have contributed to finding the solution. Now there's an interesting attack on bitcoin mining pools which we're going to call the vigilante attack. Suppose that there's a pool member who's very upset with a large mining pool. He can participate in the pool by mining and submitting his near miss share values to the pool operator just like normal. But in the event that he actually finds a bitcoin puzzle solution that would reward the pool he just throws that away and doesn't tell the pool operator about it. Now the effect of this attack is that the overall effective mining output of the mining pool is reduced. However the vigilante only loses a little bit. He still gets rewards for other puzzle solutions that are found. He gets a proportional reward due to the shares that he submits. Now one problem with this attack is that a vigilante still has to lose something and doesn't gain anything. And so it seems unwise to rely on vigilantes like this monitoring the network and rightfully choosing when to do this to only attack large pools. Here's an illustration of what the vigilante attack looks like. The vigilante still submits shares to the pool operator and if he finds a solution discards it. So the approach of a non outsourceable puzzle is to encourage the vigilante to perform this attack in the following way. We'd like to make it so that whoever actually finds the bitcoin puzzle solution is able to take the reward for themselves. Now the vigilante would have an incentive, a direct personal incentive to perform the same attack and harm the pool. Now the approach to having a puzzle that works this way is to have a puzzle where each puzzle attempt requires signing the puzzle solution value using a private public key pair. In particular each attempt at a puzzle solution requires knowledge of the private key and that same private key would then be used to spend the reward later. Now as an illustration of this, instead of the pool operator just having a key any of the mining pool participants who are contributing mining resources also have to have knowledge of the private key in order for their mining to be effective. If any one of them does find a solution then they would be able to take the money. A secondary goal is that we'd like to even provide the ability for mining pool members in this case to evade detection. Now I'm going to describe how a particular instance of a non outsourceable puzzle would work. Now a solution to this puzzle contains the same information as an ordinary bitcoin puzzle including the previous block hash, a merkle route which is a commitment to all of the transactions to be included in this block and an arbitrarily chosen nonce value. Now this also includes a public key pk which the miner would have to know the corresponding private key in order to find puzzle solutions. It's also going to include two signatures made using this key pair S1 and S2. Now the first step to determining whether a particular nonce value as a puzzle solution is to create a signature S1 using the key pair. Now this has to be a valid signature over the previous block hash as well as the nonce value that's been chosen. Now in order to tell if this nonce was a valid solution you have to compute the hash h over the string containing the previous block hash, the public key, the nonce and the signature S1 then you compare this hash value to a target just like in bitcoin's puzzle. Now only after you find out whether or not this nonce was a valid puzzle solution you then compute a second signature S2 using the same key pair and only in this signature do you include the merkle route of the transactions. So the idea here is that you need to be able to compute the signature value S1 using the private key in order to find out whether or not you found a puzzle solution and only if you found a puzzle solution do you then compute the second signature S2 in order to choose which transactions are going to be included. This means that to find a puzzle solution you have to know the private key and if you know the private key you get to choose transactions that will direct the reward to yourself. There are several potential concerns with this nonoutsourceable puzzle. One problem is that it basically throws the baby out with the bathwater. This nonoutsourceable puzzle would discourage all pools from forming not only the decentralized ones which were the original motivation for this but also the harmless decentralized mining pools like P2Pool which were discussed in previous lectures as well. Now the effect of this could be that if miners are discouraged from participating in any mining pool they might find themselves steered towards other forms of outsourcing which are even more harmful such as hiring hosted mining services to do their mining for them. Hosted mining services are potentially an even larger threat to the decentralization of Bitcoin's mining power because the hosted mining administrator is actually in physical possession of all of the Bitcoin mining rigs. Now there are potential approaches to addressing these concerns but that's an ongoing research project and I won't get into the details here. In this section we're going to talk about a technique called proof of stake mining puzzles and a variety of related techniques which all together I'll call virtual mining because they don't involve any computational work at all. Now the motivation for this is that Bitcoin mining seems to have an unnecessary step. If you look at the ecosystem of Bitcoin mining economics Bitcoin miners earn monetary rewards in the form of Bitcoins. They have to spend money buying power and equipment in order to operate their mining rigs and they use those mining rigs to find puzzle solutions which in turn give them reward. So what would happen if we removed the step of spending money on power and equipment? In this case you would have something that looks like the following which is what I mean by virtual mining. Instead of mining with computational hardware like Bitcoin mining rigs you could mine just by using the money that you would have spent on mining rigs directly within the system. Think of this as using your money and sending it to a special address and then a winner is chosen in order to have a mining reward based on the amount of money that miners have contributed by sending it to this special address. Now it would be possible in a virtual mining scheme like this to essentially recreate the same dynamics and reward structure as in current Bitcoin mining. The only thing that's removed is the external step of having to use real power and real hardware.  One is that it definitely would lower the overall cost of the Bitcoin mining system. Virtual mining since it doesn't involve using any power or manufacturing any special hardware would have no impact on the environment. Now you can think of the savings that would result from this as being distributed to all of the holders of coins in this system. There's another argument which is that holders of the Bitcoin currency are stakeholders in the currency. They have an incentive to do things that would benefit the Bitcoin currency system as a whole because it increases the value of the coins that they hold. So this argument is that the very people who are stakeholders in the currency have incentives aligned to be good stewards of the system. Now because there's no ASICs involved there would be no concern about an ASIC advantage so any virtual mining puzzle is also an ASIC resistant puzzle. And there's finally an argument that this approach would reduce the hazard of 51% attacks whereby the network is dominated by very large miners with extremely powerful equipment. Now let me describe this argument in a little more detail. The way the argument works is basically that the Bitcoin economy is smaller than the overall world economy. It's possible for an attacker who has a lot of wealth outside the Bitcoin network to be able to acquire very large mining rigs that they might not be able to acquire if they could only use their wealth inside the Bitcoin network. So to illustrate this imagine that there's a wealthy attacker like a nation state or just some very wealthy attacker on the network who's able to purchase very large mining equipment that's very powerful. Now all of their wealth is outside the system and they're able to acquire this mining resources and then they can use it to attack the Bitcoin economy. Now if mining were based on the coins that were inside the network then a wealthy attacker wouldn't be able to go outside the network and find more mining power. The only way they could acquire the amount of virtual mining power they would need to attack the network would be to buy up 51% of all of the coins in existence. This would require them to go to Bitcoin exchanges and exchange whatever form of wealth they already had for wealth measured in the tokens inside the system. This would likely raise the price of the coins within the system while they were doing so. It's arguably much more expensive to acquire half of the value of the bitcoins than it would be to acquire mining power that's larger than half the existing Bitcoin network. Now this provides an extra disincentive against conducting such a large scale attack.  The original one is called proof of stake which assigns to each coin in the system a stake value and the idea is that the stake value grows over time for every coin as long as the coin isn't used. Every time you spend a coin or make a transaction including a coin or enter a coin in a mining puzzle by using the coin to mine the stake value for that coin gets reset. Another alternative is called proof of burn and in this scenario when you decide to mine using a coin you actually have to send it to an unspendable address and the coin essentially is deleted or gone forever. On the other hand you do have a chance of winning a mining reward and then that would replace the coins that you put in. Another variation is called proof of deposit and this involves mining with your coins by depositing them in something like a time locked account where they aren't burned forever you'll be able to get them back eventually but only after some amount of time has passed. Effectively by choosing to mine with your coin in this scheme you're losing the opportunity cost of whatever else you could have done with your coin instead at that time. The last variation is proof of activity. In this variation everyone with a coin is automatically entered into the mining lottery. If one of your coins is chosen then you're responsible for choosing the next block and you have to respond by creating a signed message about the block that you choose within a certain amount of time. Now virtual mining puzzles like these are an active area of ongoing research and there's a large open problem which we don't know the answer to yet which goes like this Is there any form of security that you can only get by having a proof of work system that involves really burning real resources requiring real computational hardware and expending real electrical power in order to find puzzle solutions? If so, if there is some kind of security that you can only get by having a proof of work puzzle and not with virtual mining then the apparent waste of the proof of work system is actually just the cost of the security that you get. On the other hand, if it does turn out that virtual mining can provide exactly the same security or more that you can get by having a proof of work system then it seems likely that eventually proof of work systems because they're so much more expensive will eventually give way in favor of cheaper alternatives based on virtual mining. This question is as of yet unanswered. Let's conclude this lecture by summarizing some of the things we've just talked about. We've discussed a variety of approaches towards designing alternate Bitcoin mining puzzles that achieve a variety of different goals. These include preventing ASIC miners from becoming a consolidated source of power in the Bitcoin ecosystem. We've discussed puzzles that prevent large mining pools from becoming consolidations of power. We've also discussed puzzles that have some intrinsic usefulness that can help society and reduce waste. And we've looked at the option of a mining puzzle that doesn't require any computational hardware at all. Now for now the best trade-off between these puzzles is unclear. And our speculation about the future is that for the near future there will be many alternatives co-existing and it will continue to be unclear exactly which alternative is the best. Now in the next lecture we're going to talk about Bitcoin as a platform. This is going to include applications beyond just the currency that we've seen so far. This includes applications like use, prediction markets, smart contracts, financial derivatives, and many more.


So, when we talk about naturally occurring soils and there have been lot of questions regarding this, these are basically from disintegration of rocks which we discussed sometime back. There are 3 types of rocks you must have studied very good sedimentary then why I have written like this metamorphic or metamorphic. So, this is basically rock cycle is it not. So sedimentary to metamorphosed or metamorphic and further action of pressure and temperature and all the agency which we have discussed you know the carriers mostly this is P and T pressure and temperature condition. So sedimentary is the one which is you know remember Amalia's a lot of weathering process going on, big boulders getting formed, they keep on hitting each other, they get fragmented because of the flow of water. Each fraction further keeps on becoming smaller and smaller by the time it comes to the gangetic plane and then something happens from gangetic plane up to the Calcutta, Hoogli all these areas what happens even the small particles become much more finer alright. So, conversion from very big size to medium size to the finest size and this is the journey with the material is following in geological terms scale time scales. So sedimentary is something please understand this concept carefully, this is going to be useful forever. You have seen deltas, alluviums, pan formation, Sundarban is a beautiful example of the delta which has got created you know at the junction of the Bengal and Hoogli river. So, what has happened? Suppose if you do the mechanics of this problem, so the river is bringing sediments, what are the sediments? These sediments are the disintegrated form of the rocks which are coming all the way from Himalayas, mountains clear and they have been travelling so long in terms of time, in terms of distance and they got fragmented, they got super fine, weathering process somebody was asking what is weathering? So, these rivers have lot of suspended loads, we call them as sediments mostly this is freshwater, try to capture the attributes. So, for an engineer the attributes are very important, so the keywords which I use know, what did I do? I said river and then I said suspended load from where suspended load is coming from all that weathering process, agreed? And then suddenly I brought in the concept of fresh water, what fresh water has to do with in this context? Density of the fluid, clear? So, the fresh water let us say because I am sure all of you know that from the stretch of the Himalayas up to the southern portion where the Ganga comes, water can be just drunk without filtering it and then the human activity start and the water become polluted, clear? But then there was a time when people used to drink it up to Varanasi or Allahabad or Gaya and Prayag and what not, clear? So, this is the fresh water, density is going to be less and this suddenly comes and meets the Bay of Bengal. I am sure many of you would be taking it up as a research project in your career, in whatever form, I do not know. So, it is very deceptive, you right now you think I will never do this, ultimately you end up doing this, even if you become a CEO of a company, you will realize that most of the development is going on now in these areas in the country, clear? Most of the companies are establishing themselves over here. Now, what I am going to tell you is this is typical seawater, what is the emphasis, why I am saying this seawater? So, it is fine, density, correct? Density contrast. So, if this was row 1, this has become row 2 where row 2 is greater than row 1, clear? What is going to happen? A lighter fluid entering into a denser phase what is going to happen? Sorry, say it loudly. No, yes, someone else, what are the attributes of the system? This system is fresh water having lot of suspended loads, imagine you, you must have, all of you must have realized the turbulence in the aircraft when you travel, why do you face turbulence jittery it becomes, why? So, you are going from a lighter phase of the air into a denser phase, clear? Particularly when you land then most of the problems come and when you take off, imagine close your eyes, what you are doing? You are going or you are moving into a denser liquid and again coming out into the lighter liquid, is this correct? So, the same thing is happening over here, the reverse carrying suspended load and these suspended sediments are entering into a dense surface, what is going to happen? Velocity reduction, number 1, the moment velocity reduction occurs, all these sediments will have a tendency to settle, correct? Sedimentation process, is this part clear? The rocks which are formed because of the sedimentation process, now what are the major players in the formation of the sedimentary rocks? Simple process like this, loads of sediments which are present in the fresh water, they are entering into a system which is denser, sediments have a tendency to settle down, now look at the micro mechanism what is going to happen? So, if this is the river bed or ocean bed or whatever it is, I will say water body bed, so this is the bed of the water body, clear? And imagine this is the fresh water, normally water we depict like you make a triangle and draw something like this, this becomes a water level, clear? Connotation is like this, for soils we show a horizontal line and this, this is the ground level, is this okay? So, all these sediments mostly coarse grained materials, they keep on settling, initial process, next load of sediment comes, it gets deposited like this, the whole process is happening under gravity, clear? Nothing else, in the process somebody was asking about bacterial action might be a situation where the bacteria starts secreting something and they all become a co-haste material, co-haste means cohesion, individual grain is now getting glued because of either microbial activity or it could be because of physical activity also, suppose if I take two particles, take two balls and press them hard, cold welding, what happens? There is a contact which you have created, very high pressure, clear? And low temperatures, alright? Otherwise everything is going on with self-rate, later on I will use this concept to define the state of the material and engineering aspects, that how you are going to make buildings on this type of formations, clear? Now, this system gets metamorphosed because of several things, pressure, temperature conditions, chemical conditions, temperature, fire, whatever, becomes metamorphic, under extreme temperatures and pressure this becomes igneous, it becomes magma, you know, it becomes highly uniform system, so these are the igneous rocks. I hope you are aware of some of the examples you can write, what are the examples of sedimentary rocks? Sandstones, clay stones, limestones, mudstones, shale, conglomerate, fine? I will repeat sandstone, limestone, mudstone, shale and conglomerate, should I write or it is okay? What are the examples of metamorphic system? Yeah, so we were talking about this metamorphosed or metamorphic rocks, so when the temperatures are very high, you know, the type of rocks which you are going to get formed is marble and quartzite and when pressures are very high, what will happen? Then you have slate and schist, slate, see if pressures are very high, I write normally like this, if pressures are very high, then you have marble and quartzite and when temperatures are very high, what is going to happen? Shale and schist and I think sedimentary rocks I have given several examples, all sorts of limestone, sandstone, claystone, you know, they form this category. Ignious rocks, under acute pressure and temperature conditions, any examples of igneous rocks, basalt, granite, alright, they form the category of igneous rocks. Now, shale could be formed because of the processes which we have already discussed out of any of the three, so A, that is use S, M, I, so you have a triangle, sedimentary to metamorphic to igneous and further disintegration of igneous might get resulted into the sedimentary also, clear? And at any stage of this, you might find soil getting generated, only thing is that this is the functions of pressure and temperature, the conditions, is this ok? Now, what this has to do with the definition of the soils? You remember, we were talking about the attributes profession, then we were talking about, you know, uses, then we were talking about what is the origin and now we have to talk about the transporting agencies, is this fine? One question which comes automatically is, what is the difference between rocks and soils? Again, this has to be profession dependent, again it has to be process dependent. By thumb rule, if I need to cut anything or if I need to blast anything, you were talking about declension, is this correct? So, if I have to cut something or if I have to blast something, that means a hard system, normally rocks are cut and blasted, there are different type of cutters, right now metro work is going on in the entire bombacity, you can go and visit what is happening there, how they are cutting the entire rock mass, what are the tools which they use to cut the, you know, we call them as tunnel boring machines, TBMs, they are very good videos which are available on the websites, YouTube and all, you should be, you can watch them. I would not advise you to go inside because sometimes back when I took some of the students there, one of them printed at 80 meter depth, most of you are not physically very fit, is it not?  So, it is not a very advisable thing to carry everybody there and ultimately inviting a lot of problems for yourself. It requires a lot of mental strength, I would say, you know. Anyway, so coming back to the point, rocks are the ones which need blasting and cutting, normally soils are not of that type, they are mostly excavated. So, this is one of the difference as far as a very layman's language is concerned that rocks need cutting and blasting soils normally do not, but it may so happen that soils also might require some cutting by the way, but definitely not the blasting operations. You must have studied the most scale of the hardness of these materials and so on. I can say that these are the parent material, these are the offsprings and hence the matrix, you understand the matrix? Matrix means texture, texture is okay. I mean this texture is very fine as compared to the one which you are wearing. So, the physical appearance, alright? So, the texture is different, rocks are mostly, I cannot use the word very smooth because sedimentary rocks are not going to be smooth, clear? So, they are basically made up of stiff matrix as compared to the soils, alright? This is another way of defining or maybe differentiating, but it so happens that the mineralogy is going to be same, that is DNA. The linkage is going to be between the parents and the kids, genetics, clear? So, the mineralogy of the system is going to be same as the mineralogy of the system. Somebody was asking here about that the mineralogy may also get altered. I do not remember, somebody had hinted on this, you know? So, it may so happen that chances are that whatever minerals are present in this form in a very intact form, dense form, clear? Would be present over here with or without abnormalities, agreed? But not in that much dense matrix, is this okay? Now, this is what you are asking is a research idea. So, I remember long, long back when India was initiating this Mars mission. Israel had some, send some samples of the Mars, Mars and soils to my laboratory. I was a part of that mission. You are testing those samples, alright? So, I was trying to understand myself that what would be the relationship between the two. You got it? That is what NASA does. They will take out the samples of the rocks and they will send some rock rovers, land rovers and what do they do? They will detect by using some X-ray or some non-destructive way to find out the mineralogy, clear? And that mineralogy if I can relate to this, my job is done. I have created a linkage between the two. Carbon dating is one of the ways to find out whether the origin of these type of soils is what. You got the answer to your question? Read more and more about this. It is a very interesting topic of research and many people are working in these areas. Particularly the guys who are into offshore engineering, those who are into hydrates, is it not? The origin of soils in which the hydrocarbons are present or a particular type of mineral which you are looking for. So, as I said, you have to take care of this and your intentions. Put these two together to deal with the material. Got it? This becomes more of a intuitive task. Now, let us enter into the classification schemes of the soils. When we said types of rocks, alright? And I linked it with the naturally occurring soils which is the origin. Let me talk about the, this is the classification scheme for the rock. Now, let us talk about the classification schemes which are used for soils. If you remember in the beginning of the lecture I said, creation is one thing. Transporting agency is another thing which attributes lot of knowledge into the system and ultimate thing is how it gets deposited. You remember three stages, origin, transportation and then deposition. And there I tried to give you some hints, somebody goes outside, gets exposed to the environment, society more and more as compared to the one who remains confined to one place, residual systems, clear? We will talk about this now. These are naturally occurring processes. You can contain, you can slow down, you can retard the process. That is an engineering. That is a technology. So, if you go to Middle East, if you get a chance to work over there, Middle East is famous for having big, big cavities in the formations. You know, subsurface, strata which I was talking about. So, a million dollar question there is, check it on net. Why it is difficult to lay foundations in Middle East? Most of the regions in Middle East. So, suppose if I lay a foundation over here, you never know there will be a big cavity over here. What is this cavity? Look at this, another example of, you know, the chemical process. Okay. So, you see, coming back to your question and the one which you asked, these type of subsurfaces of the deposits are very notorious. Actually they are limestone, alright and they are sitting on the, in the coastal areas, clear? What sea water has to do with this? Now, this sea water ingresses into the foundations or the strata has a tendency to eat up the limestone and create cavities under a very specific condition of pressure and temperature and humidity. Now, this is what is known as lime dissolution. I was a consultant to Bandaroli sea link. I do not know whether you are aware or not. So, all the foundations have been designed and verified by me in 1998-99. A big problem was this. You might be laying a foundation over here and you never know there is a big cavity waiting for you. Hope you understand what is going to happen, coming in. So, the moment traffic goes on the system, the entire pair of the bridge or the foundation might sink into the cavity. So, UAE, Sharjah, Middle East, Oman, all these places, the big problem is lime dissolution because of the sea water under very specific conditions of pressure, temperature, humidity, clear? And salinity, chemical process and your question was, repeat your question now and link it with this. My question was that whether the conversion of rock to soil is a desirable progress. So, here I have given you a phenomena where what has happened to the limestone, it has got dissolved. Another extreme, clear? Now, whether it is, so the discussion was that nothing is in your control. You remember, this is what we were discussing. It is a natural phenomenon. I cannot stop it. There is no way I can put a containment like this. It can be done only on the blackboard. In real life, you cannot do it. Why? Water will come from down. All right? Is this okay? So, you cannot control it. You have to live with it. Now where is the engineering? Engineering is fully knowing the facts that this is going to happen. I should be having a strategy in my mind to counter it so that if the entire system is going to sustain itself for 20 years, I will add another X years to this. That is my engineering and technology. You got this point. That is it. So, what technologies are doing? They are providing techniques like surgeons. What do they do? They do colon surgery. Clear?  What I have done? This is the seawater. Have not I done the same thing? I have cut the axis of the seawater from the structure by providing some bypass. Are you getting this point? No? We will discuss this in details. All right? Yes. Sir, another thing. Can you tell something about what is happening in runoff touch? I mean they also have the entire thing covered up with salt. So, is there something like the soil is somehow, man, change in somewhere by the sea? Rejuvenation of deserts. Read this topic. Write it down. Rejuvenation of desert areas. All right? And second is when you come down towards Bhavnagar and all these areas which are runoff touch type what you are talking about, ingress of salt water into the soils. Clear? So, how would you stop this? How would you rejuvenate the entire land? Have you been to these areas? Why from all the way from eastern part of the country to the extreme west of the country? I had recently been to runoff touch and so. What did you saw there? What did you see there? The festival. So, means the grand festival which happens in the winters. So, I had been there to the. Government of India's atomic energy program depends largely on the bentonite which comes from that area. You know this and I think I told you today about 1.5 hour back. A bentonite is not there. You cannot run your atomic reactors.  So, runoff touch is very famous for minerals and nowadays you must have realized if you have gone towards the Pakistan border, Dakshineshwar temple is there. Google pay you can check. So, from there the border is hardly 35 kilometers. Now, this is the area where most of the mining activities are happening and most of the industries are being set up. So, I am consulting at 2 of the places there. Extra deep mines, somebody was talking about the mining in this sector. You know, somebody was talking about the mines. So, extra deep mines when you do what is going to happen, saltwater intrusion, saltwater getting flooded into the pits and you do not know what to do, how to survive is corrosive water, clear? So, then you have to do something. Okay, so let us talk about the geological characterization of soils. Mainly this whole thing is including genetics into it, the heritage, family tree, heritage. Is it not? We call it as a genetics, genomics, whatever you may call it. So, most of the time geological classification is carrying a connotation of the geomorphological features of the soils. Geo is earth, clear? Geo, geotechnical. Techniques which are going to be used to understand the materials which are lying inside the earth or on the earth, geotechnical, clear? And engineering with those materials. So, when we talk about this, the first thing which comes to the mind is these are two broad characteristics. The first one is transported and I think you are all aware now what transported soils are and the second one is the residual soils. Transported soils after weathering is over, they get transported from one place to another place by a transporting agency, clear? And we discussed about two, three things. So, the transporting agency is, say it again, what are the transporting agencies you are talking about? Water, wind, not air, wind. There is a difference, use right language. Water, wind, gravity, sorry, human activity, oh very nice. The one which you have forgotten is ice, clear? This is another form of water but ice is also a transporting agency. Why? Avalanche, how many of you have seen Avalanche? Not only in Hindi movies and Hollywood, Bollywood movies but in real life. How many of you have been to Manali, Prothang and all these places? You must have seen Avalanche, Snow Avalanche. What are the properties of Snow Avalanche? These are also geomaterials. Why? Anything which is resting on earth. Even we are also geomaterials. Agreed?  Perfect example of geomaterials. And in the process what not we do? All chaos we create. You agree? Is this fine? So, Avalanche is also a sort of a geomaterial. Water vapors getting deposited in the form of the snow and settling down over the upper reaches of hillocks or hills. And under extreme low temperatures and high pressure from regular pressure is coming. The first layer, I was talking about sedimentation process that was the river induced. Now what happens? The first layer of snow comes, the second layer, third layer and self-weight compaction, consolidation, clear? We will discuss about this quite in detail later. And ultimately this whole thing becomes so hard. So, the moment temperature changes, climatic conditions change, it breaks and it slides, it hits something, causes a disaster. So, transporting agencies are as you are rightly saying, water, wind, ice, this could be any other human activity, gravity and so on. Fine?  Agreed? So, why ice becomes a very important carrier or transporting agency?  The countries where most of the time, the entire thing remains no bound. There is no free water on the surface, clear? So, it is not possible that the rivers are going to carry anything from one place to another place, clear? So, this is totally because of the ice effects, the transportation could occur. There is another logic, come as another my suggestion would be the soil mechanics which you are studying should not be confined to only Indian context. Ultimately what you want to become, you want to become an international guy.  I have not talked about geography, I will talk about that also. Is this okay? Now, if you look at the attributes of these materials which have been transported, attribute means let us say color and shape, how many have been to Gangetic plain? Brahmaputra river or say Ganges or Yamuna and all those. So, why I am asking like this, transported soils depending upon the transportation agencies, they will have peculiar attributes in terms of their shape, particles, texture, color, why? So, if water is the carrier agency, what is going to happen? All these particles will be getting washed, I do not know for how many times in their entire life. What will happen? Shining particles, you know, and the more and more abrasion takes place because of the rolling effects, I hope you understand rolling is taking place because they are coming from higher reaches. So, what is going to happen? The water acts as a abrasive, it gives the abrasive effect. So, the particles are going to be mostly perfect, spherical in layman's language, not microscopically. Typical sands, sands are one of the varieties of soils. Somebody who was sitting here said mud last time. Oh, yes. So, mud is a layman's language, clear? So, technically when we say soils, one of the variety of the soils would be sands, clear? Round particles, why? When they got broken because of the physical, chemical, biological, weathering, they were all distorted. But look at this, the moment they started travelling from A to B, you remember? There were so many rolling which are occurring, water is washing them, ultimately what happens? They all become minimum surface area or maximum surface area. The sphere has a minimum surface area or maximum surface area? Minimum, sure. Why not maximum? Because that is the law of entropy. So, that means these particles are going to have the minimum possible surface area inert in nature. Anyway, coming back to the point, this transporting agency is also going to shape up the whole morphology of the particle. What is morphology? Shape, size, roundness, irregularity, you know, this is a perfect sphere. I could have drawn a sphere like this. The particles are like this also, irregular shaped, clear? There could be a particle like this, clicks. So, it all depends upon which transportation agency is acting to transport the weathered material which is coming out of the rocks. It is expected that the water is going to create a system of the particle which is near spherical, shining, very good looking, fresh quarts, pinkish color, peculiar properties of gangetic sands, alright? Mostly aerobic process is controlling the whole process. I hope you understand what is aerobic process. Now, I have interlinked environment engineering with the geotechnical engineering. So, this answers your questions of bioactivity and you know what is happening and why and all those things, clear? So, the texture, the shape and the color gets guided by the transportation agency. So, be it water? Now, tell me, if I replace water with wind, what is going to happen? What do you expect? Fine particles. Good, fine particles. The most important attribute would be wind associated with the wind, very good, light, excellent. So, weight of the particle, clear? We call it as a specific gravity. So, when wind is playing an important role, what is going to happen? Particles will not be so smooth, why? Wind is not so abrasive in nature as compared to water, you agree? Is that correct? That means, here the chances are that the particles are going to be more irregular but lighter in nature. So, what is the problem associated with pollution in NCR, which you are reading in newspaper and what soil mechanics guys can do? What role they can play? This can be a good question. What could be the role of a geotechnical engineer in stopping the pollution of NCR?  What are your views on this? This answers your point also. So, when wind is playing a role, particles are going to be mostly not very rounded, number one, they are going to be lighter so that they may become airborne. Otherwise, they will not get lifted up, all right? So, these particles are going to be lighter as compared to the particles which are being carried or transported by water. Difference is clear? They form dunes. Jaisalmer, go to the places called sum, you must have been several times or you are studying all the time. Barnmer, all right, Ruzali and all these Hindi movies you must have seen. They show big, big dunes and they keep on migrating from one place to another place, clear? What are the challenges associated with this?  So, these particles are going to be lighter, the structure is like that. So, if you take a particle and put it beneath the microscope, SEM, scanning electron microscope, you will see that they are very furry.  They will have a lot of protrusion. Why? They want to, they have to become airborne. They have to be get airlifted, clear? And they form aerosols. So, half of the problem of NCR is because of, in summers, dust storm, in winters, these particles which remain in the air, they form aerosols, agreed? And that is the problem. How do you solve this rejuvenation of what? Deserts, clear? How? It is a big question. But we are talking about some process by which I can convert soil into a rock. I can use this over here also to get rid of this problem. Try this at a global level, not in the laboratory. In laboratory, enough experiments have been done. Read about that, clear? These are the answers to the question which you are asking. So, mostly these type of soils are known as Aeolin. I will talk about all those things. Do not worry. Just you understand the concepts right now. Okay? How about the, how about the, how about the size? When they are getting airlifted, airborne, particle size has to be extremely small, clear?  Why? Irregular shape, these are very sharp edges. So, they are so irregular shaped, very sharp cutting edges. So, the moment you touch them, rub them on your palm, the chances are you may bleed. What about the color? There is no washing going on with water. So, color is going to be muddy, not so sparkling, shining, you know, pure form of the colors. These are going to be mostly brownish and dirty looking colors. All right? How about the ice? We will talk about this, very special category. So, water, wind and gravity is again a sort of a, you know, combination of rockfall, but normally we do not consider gravity as a transporting agency. And then manmade, what we were talking about. The second category is residual. So, again, I will repeat. Geological classification of soil says like soils get formed because of weathering and then a transportation agency comes in the picture. It transports the material from its original place or the formation place to the another formation which is deposition. I am using the word formation two times. One is the process formation, another one is a deposition of and the formation which is because of the deposition. Is this okay? Fine? In residual, it is a different story altogether. Incidentally, these are very good building materials, lot of pozzolonic activity. You need my paper on desert sands of India. I do not remember the exact title, but this is written I think long back. This is a classification of desert soils from just check it on my back. All right? But there is a paper on this in engineering geology. And that paper is required in demand because most of the guys who are producing cement, they want to use this technology for using directly the sands into making concrete. We are negotiating. All right? Now the residual ones are the ones. As I said, they were formed, very unfortunate. Nobody allowed them to move out. They got created there, clear? They formed there and they got disintegrated also there. But in the process, these are the best soils where as far as the economy of the nation is concerned. Any guess? Another guess? Economy is always what? Hydrocarbons, oil and gas. Nothing can beat that. You agree? It is okay? So these are the soils which are the best deposits of what? Best deposits of what? Hydrocarbons, oils and gas. Why? They got formed. They could not get transported. They remained deposited there and they got disintegrated because of microbial biological activity. So these are the ones who are storing maximum reservoirs of hydrocarbons. Now tell me which one is good or bad? No one. I think this is what we were discussing during the break. Agree? Intentionally I gave you this example. So my job is whether this is with me or whether this is with me, what I am supposed to do? I can always change, switch over my Dharma. Here I will be a beautiful geotechnical engineer and here what I will do? I will try to help the guys who are into hydrocarbon exploration because without my help they cannot do any exploration, remember. So I can earn both ways. That is the art of practicing geotechnical engineering. Is this part clear? I use the word art of practicing geotechnical engineering. That means the concepts remain the same. What I have to do? I have to just use this material the way I can and here my strategy will be changing. So I will use different strategy. So residual soils are the ones who remain deposited after getting generated at that place. So there is a typical way of showing this. I mean the upper layer is known as upper zone and then it is followed by the intermediate zone. This is the schematic diagram for depicting the residual soils followed by partially weathered zone and this is followed by the parent rock. So this is how the depth varies. This is the extent and this becomes a strata for me. So most of the regions of Bombay coastal areas where we are right now, if you have to learn geotechnical engineering the best places are coastal areas not the gangetic plains. So this is a subject which flourishes in coastal areas. Why? Any questions? So here we will have size, shape, texture, angularity which petroleum geotechnologists have to learn from you. He is amazed to see the role which civil engineers and geotechnical engineers have to play. All right. So let me give you now a few examples of classification of transported soils now. So different types of transportation soils, transported soils. The first one is depending upon the transportation agency all these groups have been created. You know what is alluvial soils? Sometimes you may say that these are the deposits as well. What is an alluvium? What is alluvium? The soils which have something to do with the water clear alluvium. Check the dictionary meaning of the word alluvium. Check the meaning of all these words which I am going to write clear and try to remember them. Yes Manan, what is the meaning of word alluvial? That means the soils or the deposits which have been created by running water. Running water is important. You see each and every word is important. You know why? Suppose if it becomes stationary water, class changes immediately. So as far as stationary things are concerned, it becomes a different class altogether. So running water is very, very important. Why? Because running water will give that abrasive effect, cleaning effect. All right? The particle will be very strong because it has undergone all that hydraulic pressure is padding from Himalaya to that point. Imagine how much robust the particle would be. Especially gravity is going to be good. Clear? Heavy particle, then only it is going to get suspended. I hope now you are getting a feel of how the attributes are interlinking with each other. What lawyers do? Legal advisors. What do they do? They catch the words. No? Do you agree or not? In crime series and all these series, what do they show? The whole thing will start with the word and then will end with the analysis of that word. So in our subject, the terminology and the words are very, very important. Immediately I objected that it is because of the running water, not because of the stagnant and stationary water. Clear? So whatever is getting formed in the Poway lake is different. Though this is also water, but this is stagnant water. And I am sure with your knowledge of environmental engineering, now you can interlink very easily that this process is going to be linked with aerobic and anaerobic. Is this okay? The second one is, this is my S, Laker strain. Laker strain deposits, check it on the next dictionary. What is Laker strain? Basically the term lack has come from lake. So all these deposits are in the freshwater lakes. So a Laker strain deposit of the soil is freshwater lakes. Is this okay? The third one is marine deposits. It so happens that the marine deposits could fall in both the categories. They could be transported as well as they could be residual. You know, particularly in this Deccan trap, I hope you understand the word Deccan trap, the Deccan peninsula of the country starting from let us say, Nakur onwards up to the Cape of Cameron. This is your triangular portion, we call it as a Deccan trap. All along this Deccan trap, the soils which you get in the coastal regions are marine deposits. It could be because of delta formation we were discussing, suspended particles coming and because of density contrast of the flit, they get deposited and they get formed over there. We will talk about the marine clays again when we talk about the residual soils. Granite gets decomposed, fine. Somebody was talking about black cotton soil in this sector. I am now hinting on that. Granite getting decomposed because of temperature, pressure, salinity of the water, the way the dissolution of limestone was taking place. Agreed? There is no agency which could have transported it because sea waves cannot really transport sediments, though people study sediment transportation. So, please do not misunderstand what I am saying. Those of you who will be taking course in the offshore engineering will realize this very soon that these residual soils are the ones which got created because of the weathering of the granite or basalt, clear? And they remain there. They had lot of organic matter in that themselves. They got disintegrated because of bacterial activity and they got converted into clays. Clays is another variety of soils, what you were referring to mud or slush. Slush and mud are not technical words, clear? So, we have introduced two words today. One is sands, another one clays, fine? So, the residual soils are also one of the types of residual soil would be marine clays and in marine deposits also we can have transported marine deposits. Mostly, these are the suspensions in seawater. Then we have fourth category as aeoline. We call them as aeoline soils. What are aeoline soils? Aeoline, A E O L I A N aeoline. Aeoline has something to do with the air, clear? Arrow. These are the soils which have been lifted up by wind activity and verifying particles, they got deposited and hence aeoline. So, most of the transported soils which you have in the Jaisalmer, Bardmer, Bikaner, the western part of the India, these are all aeoline deposits, clear? I do not know how many of you are aware of or not, there was a time when Bombay High used to produce most of the oil for the country when I was a student. Now, what is the scenario? I have hinted everything, 90% hint I have given to you. So, check it on the net. The western part of the country, particularly the deserts are the places where now most of the oil companies have started their production. Why? What were deserts earlier? Geologically. Answer this question to yourself. So, most of the oil companies are now concentrating on the western part, the bordering area of Pakistan and India. At least there are new nine fields, oil fields which have been identified and the work is already going on in a big way. Imagine, when you see in Hindi movies, these dunes migrating from one place to other place, what is the biggest challenge? Sorry? Direction of what? No, direction is not a problem, okay. Technical issue. Yeah, they are rolling dunes, is it not? They keep on shifting. How to make a structure stand on this? I said oil production is being done. How to create the facility? Infrastructure, storage tanks. You will produce something, you have to store it somewhere, no? Have you ever seen an oil tank? You go to Oren side, there are big, big tank farms, Bore V, all over the country, the entire coastal area where you have marine deposits, there are, these are the places where the oil is stored. Anybody here from Visakhapatnam? Nice. Why Visakhapatnam is famous? As far as petrochemicals are concerned, what is that? I am talking about something different. I am talking about, see connect with the context of the discussion. Yes, I was talking about the oil industries being operational in that region. And then suddenly I ask you a question, how many of you are from Visakhapatnam? What is the meaning of that? I think I was discussing about where to store the oil. That means naturally I am trying to hint you at what is happening near Visakhapatnam. Oil extraction cannot be done onshore. This is a place where big, big caverns have been created inside the ground where the oil from the entire country crude is deposited and from there again it is shunted to refineries. So, it has become a big money chest for the country. You know what is money chest? You know what is money chest? Check on the website of RBI. What is money chest? Where they keep the money safe, clear? A lot of siblings are involved in that. So, these are the places where most of the oil is deposited. Why? Big question. So, whatever you are producing, what I was saying is that these deposits are very good in hydrocarbon. Even these deposits are very good in hydrocarbon. Why? And then I ask you a question, what is the similarity between coastal areas and the deserts? Geologically. So, try to understand this question and try to get the answer to this. Next one, the common linkage is hydrocarbon and the question is if these deposits are not very stable how I am going to create infrastructure on the top of it. So, it so happened that after you have created a oil tank which is normally 60 meter in diameter, 60 meter diameter is minimum, 45 meter is the height. This is the height of a typical crude oil storage tank. Fine. Now, you measure it and realize how big this size would be. You can play cricket inside easily. Now, these systems are going to sit on these deposits because just now I said that there are 9 fields of hydrocarbon very actively people are working on them to expect the hydrocarbons. Now, how would you make them stable is a technology. It is not engineering because people do not have much idea about how to do this type of work. So, most of my clients are from BPCL, IOCL, Indian oil, Shell, Burma and all this. So, I design most of the foundations for the tanks for them. And right now in India is a big movement, you know, everywhere, every city the major issue is India should be self-reliant as far as the energy is concerned because our need for the energy has gone up so much. You must be a kid when there was a big discussion in the parliament on whether India should go nuclear or not. Dr. Manmohan Singh was the prime minister at that time. Try to find out what geotechnical engineers have to do in this context. That will be another role which will realize what geotechnical engineers have to play. Then comes the glacial deposits. I think I have given you another enough idea about glacial deposits, anything which is formed due to ice. The sixth one is volcanic. You can say volcanic deposits, why not? Be from a volcano when it erupts, what is going to happen? Under very high pressure and temperature, you know, the rocks, they get molded. This thing starts flowing. So this is your molten lava. And what happens? This molten lava comes and settles somewhere over here and forms the igneous rocks. And many times because lot of air or the gases get trapped in it, there are vesicules.  This is the process of formation. If you get a chance to go to Japan or the countries which are quite heavily affected by volcanic activities, what comes to your mind would be a big challenge to a geotechnical engineer in this context. You will be having lot of settlements over here, is it not? Lot of buildings and so on. So I was talking about the management of the lava. All right. So what happens is, I hope you can realize a big task would be how to safeguard these settlements against the lava which is going to come out. Imagine what will be the temperature. So most of the guys are doing river training work. If you check it on net, what is meant by river training work? You know, they may train the river entirely. One of the examples of the river training work would be in Germany they have done beautiful work. Just check it. What are the cases where they have bypassed the entire village and they have done a colon, colon surgery. I have in fact answered your, answered the question. Very close to colon. What they have done is they have trained the river in such a manner that village used to get flooded every now and then. So the whole river has been shifted. Check it on net and that has been made as a now canal which is being used for commercial purposes. So let us talk about quickly the residual soils. But I have already discussed most of these soils are you know upper zonal, intermediate zonal, partially weathered soils. They might be having lot of organic matter in them. A good example of this is musket. I do not know where these deposits are in India. Check it. Why this is important just to sum up what we have done today before we go. See, I have given you a complete philosophy of what this material is. In geotechnical engineering, we are talking about the materials which are either soils or rocks and I have given you complete philosophy and overall picture of how they are getting formed. What are their attributes? What causes them to resettle somewhere clear and how to utilize them. In other words, I have talked about three states of the material, past, present and future. So future is all about the engineering. The whole idea of this discussion is to give you enough background about the material so that tomorrow you can use it the way you want to use it.