But we have a fun talk this afternoon. I don't know about you all, but I love a good Rick Roll. And our next speaker, Rick Roll, is entire high school, which is pretty awesome. So please welcome Mindenk for his first time up here at DEF CON speaking, telling us about how he Rick rolled his whole high school. Thank you. Hi, everyone. Thanks for coming to my talk. My name is Min. I'm 19 years old. And I'm starting my second year as an undergraduate at the University of Illinois at Urbana-Champaign next week. This is my first time at DEF CON, and my second time ever attending a security conference. So it's extremely humbling to be up here on stage as a noob. Before we proceed, first on the disclaimers, if you came to this talk expecting anything other than a scripted story, then you didn't read the abstract carefully. This presentation is for educational purposes only. I do not condone hijacking and Rick rolling other high schools. Also, please don't hack my own high school district. They are very cool people, and they don't deserve that. So let's start from the beginning. Here's a picture of my high school, which has about 2,000 students and is part of a larger school district in suburban Chicago, which has six high schools in total. My school offers some IC classes. They essentially had a career pathway that you can follow from freshman to senior year. Obviously, I was going into computers, so of course I signed up in my freshman year. Those classes were held in this room. It's pretty amazing. It's where I developed my cybersecurity skills thanks to my awesome teacher, Mr. Drenth.  Now, one of the coolest things about this room was this closet. Inside this closet were two desktop PCs that were each running Windows 7. I inherited this space from the upperclassmen, and it was here that I really started developing my script kitty face. I never owned my own computer before, so this was the next best thing since I basically had both these computers to myself. And like any hacker want to be, I started running scans against my school network. I was quite ambitious and decided to scan the entire 10 dot subnet. I had some help from my upperclassmen friends, and we took turns running Angry IP scanner, and we had to split the scans into parts because if we tried to open one big scan, it would crash notepad. We learned quite a bit from the scans. The first being that our school district has its own metropolitan area network. So all the high schools are connected to the same network, and they each have their own subnets. We also found a ton of different things. Printers, voice over IP phones, switches. One of the coolest things we found was the security cameras. The top left is me when I first found them, and the bottom right is my friend giving me the middle finger after I showed him. Now, one of the most important things we found in the network that forms the basis for this entire talk is the IPTV system. The system is manufactured by Xterity and consists of three main products. The first is the video player, which are receivers attached to projectors. They send serial commands to the projector to control its current state and also what content is displayed. Here is the web interface for the video player. You can change the input source and volume, and you can also change the current channel to a specific RTP or UDP stream. Next up is the Vadia stream, which is attached to the device that displays video output. The encoder then takes that video output and broadcasts it as a network stream, which receivers can connect to and display. Here is an example of the Carousel live stream for my high school, which is displayed on all the hallway TVs. The stream is broadcasted by the encoder to the Vadia players. It's just a slideshow showing special events to time, weather, et cetera, but it was also used to show morning announcements. And finally, we have the Vadia server, which provides an easy to use interface to manage all the devices at once. Here is the projector control from the Vadia server, where we can drag and drop receivers onto the control buttons at the top, like PowerOn and HDMI. Now, each of the six schools has its own Vadia server, which controls the Xterity devices in a respective subnet. And in this case, I am viewing the projectors for my specific high school. So that was pretty much the bulk of my freshman year. I was just scanning the district network, finding random devices to screw around with and figuring out how things worked. All right, we're gonna skip a few years to my senior year. And the time skip is because nothing notable happened in my sophomore year. And my junior year is when the COVID-19 pandemic hit. And the first semester of my senior year was hybrid learning, so not much happened then either. Then the district decided in March of my senior year that everyone would be required to come back in person in April. It's at this point that I remember, oh hey, I still have access to all those devices from freshman year, and I should probably tell the district about it.  And finally, I conclude, oh hey, I should recall my high school district. So I asked a few friends for help. So I asked a few friends for help and we officially began working on Operation Big Rick. One of the first things we needed to do was establish access to the district network from home. Now, I already had a working solution for this because I installed Chrome RDP on every PC in the classroom dimension earlier. On the screen right now is a list of all those PCs. They're grayed out because they reform at the machines every year, so I can't access them anymore. Now, while we did have network access through those PCs, it's not going to be very hard for district tech to pinpoint me if any scan or exploitation traffic is coming from those machines. So, we need a way to pivot to different machines that are not associated with us so we don't get found out. So now, I will introduce Land School. Who here knows what Land School is? Okay, not a lot. For those who don't know, Land School is a program that gives teacher control over the devices in their classroom. There are two applications. One is Land School Student, which is installed as a background process on all the student devices. And the other application is Land School Teacher, which a teacher uses on their computer to control all the student devices. So, what can you do with Land School Teacher? You can freeze a student computer to make it unusable. This is the one that every student hates. You can remotely view and control a student. You can upload arbitrary files. You can execute arbitrary files. And you can view keystroke history, which I think is absolutely insane because it opens up a massive door for abuse. Imagine what would happen if a threat actor got access to all this control. Turns out it's pretty easy to obtain a copy of Land School Teacher if you know where to look. And if you're an IT guide provisioning hundreds of student computers, well, you're not exactly going to prioritize adding passwords to the classrooms. And here I'm viewing a student's keystroke history. It looks like they're doing some 3D modeling based on district history. Now, it also turns out Land School Student was not only installed on the student computers, but also on some staff computers as well. Here's a desktop of one of the security guards. So, using our district network access and Land School Teacher, we were able to pivot to a different high school. So that way, when we'd run our scans from there, the district wouldn't be able to track us. I now had a better knowledge of what to scan for, so we found a few new things. It turns out all exterior devices run SSH. And they let you open a shell, like direct user access to this system. This makes things way easier, though, because instead of sending a bunch of web requests to control each of the receivers, we can create a payload that runs the serial commands locally on device. Now, this payload is really just a batch script that makes requests to the web interface locally, but it's pretty simple and it boils down to this logic. The first thing we do is set the receiver to play the Ripple Stream. So it's at address 2025, 2525, 255000. The next thing we do is set the input to HDMI, since this is the input where the video stream is playing. Then we disable infrared capabilities. This way, the teacher cannot use her remote to turn off the receiver. Although, they still can technically power off the projector off manually by pressing the power button, but we'll get on to how to fix that later. And the final step in our initial process is to actually turn it on. Then we enter the first loop for three minutes. It's during this loop that the countdown is displayed, not the actual rickroll yet. The loop basically sets the volume to the max and then ascends the power on command every 10 seconds. And this fixes the issue I mentioned earlier where the teacher could just manually turn off the projector, but that doesn't work because it just turns on again. Close to the end of the countdown, we switch the input back to HDMI to make sure that the projector is still showing a rickroll. Then we run the main loop a second time, but this time for nine minutes, and this covers the entire rickroll stream, and also allows people to read the final message as displayed after the rickroll. Finally, we restore the channel that the receiver was broadcasting previously using a backup we made, and then re-enable the infrared remote so everything goes back to normal. At old times, we maintained a pivot of at least three Avedia players before connecting to the Avedia server. This way, the district would not be able to trace us back even to the land school computers without significant effort. And then our plan was to slowly distribute the script from the Avedia server to all of the Avedia players that we identified. In my research, I also found a privilege escalation in the Avedia player and the Avedia stream. Here's a shell where I'm logging in as root. The way that the exploit works is that you can export a backup of the device configuration to an FTP server, which will be the attacker machine. The backup also includes a shadow file, so you can just change the root hash to something you know, import that backup back onto the device, and then login as root via SSH.  So you can just create a service file that executes a command as root and call system control on it. Do the root hashes by the way, in case anyone's interested in tracking them. I haven't tried anything beyond rocky.txt at all, so don't shame me if you do manage to get it. All right, let's go time now. We picked a date April 30th because that was a Friday before AP exam started. We've had plenty of times to test and get things working. We're ready. But at the last minute, we found something new. First, let me introduce the Epic system. Epic stands for education, paging, and intercom communications. It's exactly what it sounds like. It consists of speakers, which can be installed on the ceilings of hallways and classrooms. Similar to the IPTV system, these speakers also have a central server called the Epic server. Here's an example of one of the projectors I mentioned earlier. You use the Epic server to control various alarms, and you can create and manage bell schedules for when class starts and when class is dismissed. And more importantly, you can upload custom money over bells. So April 27th, it's exactly three days before the Big Rick. When we discovered the IP ranges for network speakers, the reason we didn't find them in my freshman year is because the Epic system was installed in my junior year. This looks exciting for us. If we can get access, then we can change the bells to use a Rick roll. Unfortunately, the default passwords don't work. Today's pass, it's one pass midnight on April 29th. One of my partner's shapes is sad because he was the one trying to push us into getting the Epic system. Five minutes later, he finds the password. So it turns out that the district did change the default password, but they used the example password from the manual. When we checked the settings, we found the IP address of the server that I was bound to, which brought us to this login page when we connected. We found out that this was a login page for the Epic server. So we quickly found the default credentials in the manual, which weren't changed. And boom, we now have control of the bell system for one of the schools. However, there's a slight problem. The Epic system at the other schools had their default password changed. We can't log in, but all hope is not lost. In the settings, I found an SMB server that was configured for backups with the same default credentials. And then I thought one of the backup servers for the other school still have default credentials. I was right. He already extracted contents of one of the backup archives for another Epic server, which we did not have initial access to. And in each archive is a SQL dump of the entire configuration, including user entries. Now, most of these entries were just teacher accounts connected to LDAP, so no password hashes there. But there are a few local manufacturer-created accounts, which you can see in the top left corner. So it makes sense that I would try to correct the password for one of these accounts, right? The problem is that the hashes for these accounts were different across each school. And unfortunately, it didn't work for any of them. However, I discovered something strange. It was a local account with the username district. And what stood out was that this account is at the bottom of the table. It was also created in 2017, which matches the date of the other local accounts, which means that this is an account created by the manufacturer, not one installed by the district. I couldn't find any information online about this account, and it doesn't show up in the user's list on the actual webinar face. So I concluded it's a backdoor account. And even better, the password was password. So now, using the backdoor control account, we control the bell systems for all the schools in the district. And that's how we epically pwned all the Epic servers. All done in less than a day and a day before the Big Rick. And now we upload the Rickroll audio file as a bell. Can you guess which one is a Rickroll? I'll give you a hint. One of the lowercase L's in musical scale is a capital I. Also, it's the one that's streaming as long. Then the final step is to modify the schedule to replace the bell with our newly added bell. And we're done. The final task is to set up our stream with the countdown timer here and when it hits zero, the Rickroll begins. It was a massive success and both the IPTV systems and bell system Rickrolls worked. Here are some gifts across the district showing the result. This is one of my favorite ones. It's a student experiencing the Rickroll from their Zoom meeting and the teacher is showing it to them. And this is the final message that I just played when the Rickrolls finished. I was very tame and careful about the wording because I did not want to provoke teachers more than I already did. So you might be wondering what happened afterwards. Well, we compiled all the things we did into a 26 penetration test report, 26 page, sorry. And then we sent that to all the technical supervisors in the district after the Rickrolls were done. And of course we did this anonymously. A few days later, we got a response. It was from the director of technology for the district. And because of our documentation and ethics, he said that the administration would not be pursuing discipline and actually asked us to hold a debrief. So you can imagine our reaction. It was a pretty big relief for all of us. I'm sure many of you have heard stories where students report vulnerabilities through school and it does not end well for them. So we were extremely fortunate that the district was studying with us and in fact, listening to our advice. Here's a screenshot from the debrief we had over Zoom. I was the only one who revealed my full identity since my other peers thought it was a sting operation. It clearly wasn't or I wouldn't be here. In our debrief presentation, we referenced each other as a caller. So we thought it would be funny to identify as crewmates from the hate game among us. Overall, the meeting went in streaming well and we managed to resolve the issues in the district. So lessons I learned from the big Rick always maintain a pivot since doing that threw off district tech and they could not figure out who did the big Rick until I came forward. Check your scans carefully or you might miss a server that controls all the speakers and waste two out of three days before the deadline for an attack. Try to keep things as tame as possible so you don't end up in too much trouble. I could have been a horrible person and displayed anything else that would have not been school appropriate. Document everything to protect yourself at least if what you're doing is ethical. It really helped me in this case at least. I'd like to thank my accomplices, Shapes, Jimmy and Green because I wouldn't have been able to do this without you guys. I also want to give a shout out to Mr. Drenth for being the best IT teacher ever. I'd also like to thank Sigpony and friends for encouraging and helping me prepare for this talk. And finally, I want to thank my school district for letting me graduate and not pressing charges. Here's my website, follow me on Twitter and thank you for coming to my talk.


Principles of planning. Evaluation. Welcome. By the end of this presentation you will be able to define evaluation and describe the role, process and timing of an evaluation. Step 6 is the evaluation phase of a project plan. It is the end stage of the planning cycle. Step 6 activities must also be planned at the beginning of the project. Evaluation is defined as a scientifically rigorous critical assessment of the degree to which health services fulfil stated objectives. In other words, evaluation is a scientific approach that measures the change between, before and after a programme or project is carried out. It also takes into account any unexpected consequences of the programme. An evaluation helps us to discover both the intended and the unintended consequences of a plan. This helps planners to fully understand all of a programme's outputs and outcomes, not just those included in the plan. Ideally, evaluations are planned at the very start of a programme and resources for it are allocated and ring fenced. When should planners and managers evaluate? Ongoing, during the programme, at the end of a pre-agreed time period, often midway through a programme. Terminal, this is 6 to 12 months after a programme has been completed. And X post evaluation, this is several years after the end of a programme when full impact should have been realised. Who does an evaluation? Evaluation is an activity that must be unbiased, so it is best to recruit an external consultant or team to carry it out. Stakeholders, that includes the community, eye care professionals and funders, may also be involved as support and source of direction or information for the evaluation. How is an evaluation carried out? Terms of reference, or the scope, are agreed between the district and national coordinators and the external evaluators. Data from all monitoring activities is made available to the evaluators who carry out what is known as a desk evaluation. The evaluator will also collect data from community and outreach if needed. A report is then compiled and shared with all the stakeholders. And the next action plan takes the report's recommendations on board. In conclusion, an evaluation is needed to find out if a programme has been a success. It is also important for identifying scale-up opportunities and necessary changes. It must be done externally so that it is unbiased and it must be shared with all partners. Evaluation timings have to be planned for at the onset of the programme.


after they were married and began talking about children. The ideal picture was children of their own, but problems with that route arose. Aaron felt guilty that he couldn't give his new wife the child that she so desperately wanted. Putting on a brave face, he sat her down and started talking about something that he never thought he'd have to. The couple felt like their lives were on track. They both had found the love of their life and married them. But it was painfully clear that they were missing something. Aaron didn't mind adoption, but Rachel wasn't so sure. He prayed for a miracle, and that's when he saw an opportunity arise. The couple was met with the opportunity to adopt two beautiful children. Rachel had to give up on having a child of her own and help these children in need of a home. They adopted the two children. Rachel soon found that she felt like the children were her own.  They knew the chances of conception were low but they had to keep it up while they looked after their two adopted children. They went to the best doctors for help but the news was always the same. Rachel confided in some of her friends from her hometown in Mississippi. Then, suddenly, Rachel had something she had to tell her husband. She just didn't really know how to break the news to him. It truly was a miracle. Rachel had the best possible news for her husband. She was carrying a child. Aaron couldn't believe it. He was so happy. He already loved his adopted kids so he couldn't imagine how much he'd love his own flesh and blood. But after getting a checkup, the doctor said something that Aaron couldn't believe. The doctor told them they were pregnant from an artificial insemination process from a few weeks earlier. Like their adopted children before, they had chosen ethnic minority embryos since they are the least picked. Aaron's parents were missionaries in Honduras. He was a blue-eyed white boy and stuck out a lot there. So the family he wanted just felt right to him. But the doctor wasn't done yet. Rachel decided to be inseminated with two embryos to strengthen the likelihood of falling pregnant. Now they were told that she wasn't just pregnant with one, but two children. Their two children grew to four overnight and fate had one more surprise for them that they didn't expect. After nine months, the family was in Honduras and had to rush Rachel to the hospital after she told Aaron that she felt contractions.  Rachel said that the doctors were fantastic and the labor went as smoothly as it could have. Aaron was by his wife's side the entire time. But the doctors noticed the surprise on his face when he saw his children. It wasn't what he was expecting. The doctors told them that when a mother undergoes a pregnancy with multiple babies, there's a good chance the full-term pregnancy isn't completed. Once she was going to give birth to twins her husband had to keep a watchful eye on her and make sure nothing happened. The doctors ultimately chose to perform a C-section for the safeties of the babies and the mother. But the doctor found something that made him gasp. He couldn't believe this. Seeing the look on the doctor's face, Aaron began to panic. Was something wrong? Were the babies okay? Then, the doctor looked up and said two words that sent a chill down his spine. And when Aaron finally saw the babies with his own eyes, he took a closer look and couldn't stop crying. Aaron will remember the day in the hospital for the rest of his life. And he certainly hadn't planned for this. He looked over at Rachel to monitor her reaction to the doctor's news. Rachel and Aaron were expecting twins. They were thinking about the names of their would-be children. However, it became clear that they would need to think of another name. Aaron was already expecting two African American babies when his wife went into labor, but he certainly wasn't expecting three. The doctor cried, it's triplets. But how had this even happened? The doctor questioned the couple, asking them if they were sure that Rachel had only been implanted with two embryos. Aaron's mouth dropped open. That couldn't be right, could it? Although Aaron already considered himself a fully-fledged father to Ford and Catherine, something prepared him for the feeling he had inside the operating room. But when the doctor pulled him aside and began to question him about the embryos they had adopted, he just didn't know what to think. Something wasn't adding up. They had adopted two embryos, not three. It turned out that, unbeknownst to the couple, one of the embryos had split again, making triplets. When the babies were ready, Aaron excitedly held them in his arms. He couldn't believe how beautiful his three new children were in that finally, they have the family they'd always dreamed of. But life still had more surprises in store. Rachel gave birth to Anne, Whitley, and Riley in 2016. Even though it was not exactly what they had in mind, it turned out to be even better. As soon as the triplets were born, Rachel and Aaron felt that their family was finally complete. The couple was full of happiness. But they never expected the heartache that soon followed. Although they didn't share the same DNA or ethnicity with their five kids, the Halberts was proud to be their parents. They appreciated the beauty of their interracial family. In our minds, we are just living out our dream. A dream that may not look like the average family, but one that we are thankful could come true in light of our country's history, Aaron continued. But did their family support them? The beauty of a multi-ethnic family is found there, in the fact that the differences are the very thing that makes ours richer and fuller. It pushes you to think in a new way about how you think, speak, act, and live.  But what did others think? It's been heartening to see virtually all of our friends and family express overwhelming support for our family and the unusual ways we built it, Aaron said. However, the new parents were surprised when they discovered that not everyone around them would be as supportive as their family and friends. While Aaron and Rachel couldn't have been prouder of their multi-ethnic family, some people had made a point of showing them what they thought.  And an elderly white woman looked at us with disgust. But it would take more than that to get the Halbert family down. There will always be the older white woman in Walmart who stared at us with sheer disgust or the African-American mother who looked at us and just shook her head, Aaron said in an interview with the Washington Post. But, thankfully, they also had good experiences. The Halberts were aware that not everyone would agree with their diversity. However, they were not seeking anyone's approval. The family will more than likely have to deal with spectators who don't agree with their life choices. The Halberts are aware that not all people are in favor of diversity. But they don't care about other people's opinions. Aaron said, one of the central themes of Christianity is, after all, that God, through His Son, is calling people from every tongue, tribe, and nation. Grasping diversity will make the world stronger as we marvel at God's creative genius on display through His people's varying pigments, personalities, and proficiencies, Aaron explained. Our differences are cause for celebration, not scorn. Besides standing for diversity, the couple also had something to say about embryo adoption. The couple believes that adopting an embryo is just as important as adopting a child. After they did their own research, they discovered that there are still millions of embryos waiting to be adopted. The embryos that Rachel received had been frozen for 12 years. Rachel said, we were not saying that those lives are any more important than the lives of the babies and children waiting to be adopted all across the world. No, they are not any more important, but they are no less important either. All of our children's lives are valued. Although the couple was happy with their decision to proceed with embryo adoption, they warned that it's not a decision to be taken lightly. They also agree that it's not for everyone. Embryo adoption can also be very difficult for the donor family. I know the decision to donate your frozen embryos for adoption is probably the hardest you'll ever make. It can be so painful to know that someone else is raising your biological children, explained Rachel. Even though embryo adoption is not for everyone, it was the perfect choice for Aaron and Rachel. The couple got triplets as well as the priceless experience of pregnancy. Rachel describes the experience as beautiful and unique. She also demonstrated her gratitude to the brave and selfless biological parents who donate the embryos. The Halberts were completely open-minded about the idea of adoption and went into the process with an open heart and they received fantastic blessings in return. Rachel had hoped she would have four or five kids, but she never thought it would happen so fast. The children are happy and healthy. They have two great parents who teach them good values and impart good morals.  But how does Rachel cope with five kids? Anyone who has a child will agree that that one child is enough to keep a mom busy. Now, imagine having five.  But there's another question on everyone's mind. You may be wondering if Aaron and Rachel will adopt more children after their experience. We'll see what the future holds. For now, we're enjoying this phase of life right now, explained Rachel in an interview. As we can imagine, five kids are sure to keep them fully occupied. But Aaron and Rachel have not given up on their other life goals. After the triplets were born, they decided to relocate to Tegucigalpa. Aaron and Rachel work in the capital and give back to the less fortunate. The special duo also has equal responsibility in taking care of their five children. Nevertheless, Rachel is now a full-time mom. But the Halberts remain in the city to share the gospel in every way possible. All five children enjoy growing up in America and in Honduras. The Halbert family portraits are definitely not traditional, but their variety and love for one another shines through. The Halberts have displayed their humanity through their remarkable family story, and the children look happier than ever. Moreover, people around the world thank them for adopting children in need. Since the first day of their incredible journey, Rachel and Aaron recognized the people who fully understand their missions and dreams in life. They both know that they can't have it all. However, they have enough to make their lives worth living. Rachel and Aaron shared that while many people look down on their family for having African-American children, none of them can ruin their happiness.


When you travel through Yellowstone National Park, you expect to see grizzly bears in the wild. Did you know that the population has grown from just 136 bears in 1975 to over 700 today? This spring, the U.S. Vision Wildlife Service released a proposed decision to remove the greater Yellowstone population of grizzly bears from the federal list of threatened and endangered species. Central to the proposed decision is the ability of bears to adapt and vary their foraging behavior. Whitebark pine has been documented as a valuable food source for bears and its decrease in range across the western United States led many scientists to question how the bear would respond. A study conducted by the interagency grizzly bear study team showed that Yellowstone's grizzlies were able to vary their diet and some spent no time in whitebark pine habitats at all. In addition, bears appeared able to maintain body condition and reproductive rates regardless of the specific foods they ingested. Keep an eye on policy and emerging science as management options for this iconic omnivore are developed. From the University of Wyoming Extension, I'm Mae Smith, Exploring the Nature of Wyoming.


Welcome to this material characterization course. In the last class, we looked at the effect of crystallite size on the peak intensity of X-ray diffraction. Similarly, we also looked at the effect of stream on the X-ray intensity peak after diffraction. And before we get into the details, further details, I would like to show you a little bit about the intensity peak details, because we always say that whether it is the effect of crystal size as well as strain or instrumental broadening, everything we account for the breadth of the peak. So, how to understand this and how to correct this peak for the required intensity from which you either calculate the crystallite size or characterize the strain in the material. So, look at this slide. This is a typical X-ray diffraction peak where you have a peak intensity as well as the integrated intensity which is under area under the peak. And then you have the, typically we always measure the full width at half maximum and then this is the background, you have to subtract I background. And you have the intensity at full width of maximum is equal to I, that means intensity peak minus intensity background divided by 2. And we also discuss about this peak broadening is due to sample as well as the instrumentation reasons. So, that can be represented by this w square sample is equal to w square full width at half maximum minus w square instrumentation. So, this is a typical peak representation of X-ray diffraction. So, from there how to I mean separate all these effects that is exactly we want to see. Before that we would like to see some of the models, typical models for X-ray diffraction. It is very clear that if you want to quantify some of these effects you need to model them first. And then some of the models which are represented in this table for an X-ray diffraction you see that the first column is a function, second column is the intensity. So, you see the first the Gaussian, if your peak can be fitted into the Gaussian this model based upon this expression, then we can do certain type of calculations. And then secondly if your peak can be modeled with the Laurentian function like this, then that has got some advantage we will see. And then you also have a pseudo void model which is represented by this equation. I will not get into the details of this, but you should know the basic idea of the fitting the X-ray diffraction then how it can be utilized. So, let us look at the meaning of the details of the terms which is given in this equation. I2 theta i is the intensity at ith point on the peak. That means any point on the peak, Ip is the peak intensity, 2 theta i is the position along the profile, 2 theta p is the peak position, w fw hm is the full width half maximum of the peak and eta is the mixing fraction having a value between 0 to 1 and 1. So, if you have this kind of an expression then we have some advantage of using this mathematical model to separate some of the effects namely instrumentation or a crystal size effect or the strain in the lattice and so on. So, we will have a look at those aspects today and before we really look into the separation of these effects from an X-ray diffraction, I would like to go back to little more fundamental aspects of X-ray diffraction itself. And I would like to draw some of the typical X-ray diffraction pattern for a crystalline material as well as for a liquid and an amorphous material and then you will have a gases, how the X-ray diffraction peak will look like and then how do we understand them.  So, what I have drawn is a typical X-ray diffraction pattern from three different kind of material. One is crystal, the other is for the lipids and amorphous solid and then you have a monatomic gas. So, what do we understand from this? This is now well known to us. The intensity is 0, almost 0 except at particular 2 theta value typically known as a Bragg angle. So, one thing you have to understand from this very important you see you take a single atom then you assume that X-rays are interacting with this atom that atom scatters the X-rays in all directions. And in a periodic lattice you just assume that you get only with certain 2 theta angle this intensity is seen. That means rest of the all directions the intensity is cancelled by the destructive interference. So, which is also very important aspects of a diffraction as much as the constructive interference you have to appreciate that. So, the destructive interference plays a crucial role in appreciating this the constructive interference that happens only at particular angle of I mean Bragg law that is Bragg angle. Rest all the other directions is completely cancelled by the all the atoms which is arranged in a three dimensional periodic lattice. So, that is point number one. If you look at the intensity versus 2 theta peak for a lipids and an amorphous solid it is quite interesting to note that you do not have a very sharp peak for a given 2 theta. So, it is quite random you say it is something called you know it is a lack of order you see that there is no a concrete order or a three dimensional periodicity. What you see the peak is one or two peak statistically chosen by the system and then what you really observe is a very broad peak. So, you can so it is only a statistical preference of particular inter atomic distance which will give a two preferential angle peak and then eventually you see only a broad peak which is true for an amorphous solid and liquids which really lacks the order the crystal order orderliness. And if you look at the monotomic gas it is much more interesting you do not even see that any kind of a peak broadening because of the a complete randomness. So, you can write that the features no periodicity at all I would say no structural periodicity no structural periodicity and the curve is this is point number 1 point number 2 is it is featureless horizontal it is since it does not have any structural periodicity you will have the a featureless a curve or a peak like this you will obtain for a monotomic type of a gas. So, now let us look at the let us come back to the X-ray diffraction peak where you have the contribution from a crystal size as well as the strain effect of the lattice. So, how to separate them that we will see now. So, the first point to note down here is when you talk about the crystal size which you obtain from the X-ray diffraction experiments if you are the crystal sizes obtained from a peak width measures give volume average sizes whereas, from the peak shape analysis give the number averages. So, these two subtle things you have to appreciate whether it is peak shape analysis or from the peak width analysis. So, now let us look at the contribution from. So, the contributions from crystal size micro strain and an instrumental effects can be separated if the peaks are Laurentian or Gaussian shaped. So, just like just before we have seen in the slides where we have how this peaks are modeled and if your peak is close to this models then separating this effects are straight forward. So, we will see how suppose your B experiment is the experimentally measured B experiment that is full width half maximum B size. So, you have different contribution to the peak width B experiment is the experimentally measured full width half maximum B size is the FWHM due to the crystallite size B strain is the FWHM due to micro strain and B instrument is the FWHM due to the instrument effect. Now if it is for Laurentian peaks B experiments equal to B size plus B strain plus B instrument and for Gaussian peaks. So, for a Gaussian peaks it is a square of these terms that is B square experiments equal to B square size plus B square strain plus B square instrument. So, now correction for the instrument is done you can write that also as a point. So, how to get this instrumental width contribution the correction for the instrumental width in either case that is both these cases can be obtained by recording a diffraction pattern under identical conditions of the same substance, but in a well unhealed large grained condition.  So, now let us write so what I have drawn here is a plot of B cos theta by lambda versus sin theta by lambda that is B cos theta versus sin theta that is what I have written here separation of size and strain can be done by plotting B cos theta as a function of sin theta. So, let us write so this type of plot that is B cos theta versus sin theta is known as Williams and Hall plot Williams and Hall plot and implicitly assumes that the peak shape are Lorentzian. So, let us now try to understand this how this separates the size and strain terms of what is the crystallite size equation I am saying here rearranging the terms of earlier equation for crystallite size that is Schroer formula we can write B cos theta is equal to 0.9 lambda divided by t and this one equation we know and we also then the other equation that is strain equation minus 2 delta d by d. So, these two equations are quite familiar to us this one is a Schroer formula I have just rearranged and this one is again rearranged if you differentiate the Bragg's law with respect to theta and d you get this expression that we have seen in the last class. So, combine these two we can now explain this plot how this separates the first remark is if so let us look at what is that details of this using these two equations if the size broadening is the only significant contribution to the peak width then B cos theta is the constant for all peaks that means its Williams and Hall plot is a horizontal line. So, like this you have a straight line and if the strain broadening is the important contribution then B cos theta is a linear function of sin theta. So, like this. So, what you have the data points here plotted for magnesium oxide as well as aluminum oxide, magnesium and then this is for alumina. So, now we can see that this portion here is this. So, now let us complete that discussion this plot as I mentioned belong to two materials magnesium and alumina after two conditions after ball milling and ball milling followed by an annealing at 1350 degree centigrade for two hours. So, you have the when you say ball milling that means you are basically trying to make the powders more fine that means you are straining the system or straining the lattice. So, you have the strain accumulation is there then after this annealing the complete strain is relieved. So, you have only the size contribution not the strain contribution and that is how this two effects are separated in these two examples. So, if you look at the complete procedure it is first you have to measure the instrumental broadening, subtract them and then use these two equations one for strain one for sorry one for size and one for strain and then plot this because theta versus sin theta then you will be able to separate these two effects. So, this is one typical examples of application of x-ray diffraction where we have demonstrated how this size effect as well as strain effect can be measured and then other typical applications of x-ray diffraction is a crystal structure determination which everybody commonly use this technique and also the x-ray diffraction is primarily used for the phase identification. Suppose if you have a mixture of two or three phases in a substance and then how to identify each phase that is again a primary application of this technique and then finally people use this technique quite often for a stress measurements that is residual stress measurements of all the engineering compounds that is one of the vital industrial application and also x-ray diffraction is used for crystal orientation determination namely a texture analysis. So, we will touch upon all this application part with small case studies in the coming classes. Thank you.