Category Archives: Science
The core of every computer and the bread and butter that will power the entire machine and determine its performance is the CPU. However, going for an expensive one is not always the best choice. A gamer will surely need something powerful with at least four physical cores. An average user that only focuses on productivity tools and web browsing will find that a modest dual core CPU can do the job just right.
Motherboards will host all other components. In order to get it right it is highly important to match the motherboard’s socket to the CPU socket. This will ensure that the parts are compatible and unpleasant situations in which a product must be returned is avoided. In terms of performance, gaming motherboards tend to be more expensive. They usually go from $100 to $500 or more depending on chipset and features. The best ones feature SLI or Crossfire technologies which enables the user to mount two graphics cards to boost the performance of games.
For less resource hungry applications, a going for a motherboard priced at $50 to $90.
Computers store data on Hard Drives or HDDs and the more space the better. Unfortunately, performance is expensive. Traditional HDDs tend to be slower but have a better price per gigabyte. Users interested in photo and video editing, gamers and hardcore coders might want to get an Solid State Drive or SSD for faster loading times. They do not improve the visual performance of games but the can reduce the loading times to 25%. Video and photo editors will notice the same kind of performance boost. Regular users that focus only on browsing and office applications should go for a HDD as it is much cheaper.
The Video Card
Unless the system is designed for a gamer or 3D graphic artist, the onboard Video Card or Graphics Card that is embedded in the CPU is enough. No money needs to be invested in this component. The ones that do want performance to play games should invest some money into one.
The RAM (Random Access Memory)
The only applications that can consume a lot of RAM are games and video/photo editing software. Everything else can work just fine with a single board of 4 GB(gigabytes). From a performance perspective, quantity matters. At least 8 GB are recommended for resource hungry games and programs. Brands are not important and compatibility is not an issue for this computer part.
The CPU Cooler
When purchasing a CPU, a cooler would be required to make sure that it does not overheat. Most vendors offer Box versions of processors that contain a cooler but for overclockers and gamers, an aftermarket cooling solution is highly recommended. For extreme performance tweaks and system stability, liquid cooling is the best option out there. The liquid user is completely safe and even if it is spilled on the components it will not damage them.
Computer cases have no restrictions or compatibility issues. It is all up to the user which case he likes and affords. Internal space might be a selection criteria for some. The bigger the case the more space the user will have for cable management and additional coolers. Users that want something fancy might want to check the ones that have a side window which makes it possible to see inside even when it is closed.
The Power Supply
The Power Supply or the PSU is the most disregarded component. It plays an important role and getting a cheap one can cause the system to be unstable. Users with no aspirations for high performance, multiple hard drives, two or more video cards and additional case coolers should get a 500 Watt PSU. For gaming systems, at least 600 Watts is required to avoid sudden computer power downs at high load.
The Sound Card
Even if it is not a vital component as all motherboards have a sound card embedded by default, some users might want to get a dedicated sound card for a better fidelity. The audio quality difference is notable but sometimes it is not worth spending the money.
Additional Accessories And Tuning
Just like a car, computers can be tuned and customized with various parts such as additional case fans with leds, RAM coolers, HDD coolers, aftermarket cooling solutions, dedicated sound card and so on.
Polymerase chain reaction (PCR) is a revolutionary method used to analyze and amplify short DNA (or RNA) sequences in a sample with small quantities of RNA or DNA. PCR amplifies the selected sequence of DNA segment producing millions of copies within a few hours. Initially, DNA or RNA amplification involved cloning the selected segment using bacteria. This took weeks to amplify. But with PCR, it only takes few hours to produce millions of DNA sequence of interested.
Polymerase chain reaction requires the following components
- Two primers: These are short pieces of single-stranded DNA sequence that are complimentary from beginning to the end of the targeted DNA sequence to be copied.
- Polymerase: This is a type of enzyme that moves along starting from the end of the primers synthesizing new strand of DNA complimentary to the targeted DNA sequence. A polymerase commonly used is Taq DNA polymerase
- DNA template: This is the sample DNA that has the DNA sequence of interest.
- Nucleotides: These are single units of bases C, T, G and A that polymerase needs to make the new DNA strands.
How is PCR done?
Three major steps are involved in polymerase chain reaction. Done in an automated thermal cycler, also called a PCR machine, these three steps are repeated for 30 to 40 cycles with each cycle producing a new strand of DNA. The automated cycler is a device that heats and cools the test tubes contain the sample mixture in a repeated cycle. The cooling and heating process is essential since the three steps takes place at a different temperature.
These three steps are
- Denaturation: A temperature of 94 C (201.2 F) is applied to the original double-stranded DNA molecule so as to open it into two pieces of single-stranded DNA
- Annealing: At a temperature of 54 C (129.2 F), the primers in the reaction mixture anneal or pairs up with the single-stranded DNA template (the sequence to be copied). Starting from the primers, the polymerase attaches and starts copying the template.
- Extension: At a temperature of 72 C (161.6 F), the DNA building blocks or nucleotides which are complimentary to the DNA template of interest are coupled to the primers. This produces a double-stranded DNA molecule.
Within one amplification cycle, a single double-stranded DNA template is copied and amplified resulting into two separate double-stranded DNA segment. The two new DNA segments now will be available for the next amplification cycle and as the cycles continue, more and more copies of double-stranded DNA segment will be generated thus increasing the number of interested template.
How was PCR discovered?
Polymerase chain reaction technique was invented by Kary Mullis in 1985 when he was working in Emeryville, California for a biotechnology company known as Cetus Corporation. The PCR technique allowed scientist to make millions of DNA or RNA copies from a sample that has minute quantities of DNA or RNA.
Since then, the PCR has revolutionized many aspects of scientific research including;
- Criminology where it is used to link specific individuals to samples of hair and blood obtained from a crime scene using DNA comparison.
- Detection of HIV virus in human cells and diagnosis of genetic defects.
- Affects evolutionary studies since small quantities of DNA in fossils can be amplified to large quantities allowing further studies.
- Establishing paternity or biological identity
The widespread and innumerable uses of PCR have made it to become an important tool for use in DNA forensic laboratories among other laboratories that analyze, detect and study genetic materials either in animals or human.
Reverse Transcriptase-Polymerase Chain Reaction
Reverse transcriptase-polymerase chain reaction (RT-PCR) is a technique that is highly sensitive and used to detect and quantify the messenger RNA (mRNA). It consists of two main parts;
- Reverse transcription: Involve Synthesis of complimentary DNA (cDNA) from RNA
- Polymerase chain reaction: Amplification of specific cDNA
This technique is used to measure viral load in HIV patients and to detect other RNA viruses such as mumps and measles.
ATP testing is used for measuring the growing microorganisms by using adenosine triphosphate, or ATP for their detection.
ATP is an energy molecule found in living cells, which gives a direct measure of their health and biological concentration. ATP can be quantified by using a luminometer for measuring the light produced through its reaction with the enzyme luciferase.
ATP tests are useful for:
- Guide biocide dosing programs
- Determine corrosion and deposit process type
- Measure equipment or product sanitation
- Manage fermentation processes
- Determine drinking water cleanliness
- Assess soil activity
- Control biological treatment reactors
The first generation ATP tests were derived from hygiene monitoring applications and therefore the samples were relatively free of interferences. The second generation tests are designed specifically for industrial applications, wastewater, and water. In the second generation ATP tests the samples contain, for the most part, a variety of interfering components.
There are two types of ATP within a water sample containing microorganisms:
- Extracellular ATP, which is located outside of biological cells. The extracellular ATP has been released from stressed or dead organisms.
- Intracellular ATP, which is contained inside the living biological cells.
It is important to perform accurate measurements of these two types of ATP in order to assess biological health and to control water and wastewater processes.
ATP bioluminescence tests have moved mainstream. They are also used in the food industry in order to keep food manufacturing clean. The tests are a reliable, simple, and rapid way to monitor surface contamination in the food industry and to detect contaminants in beverages or drinking water. For surface contamination testing it is used a pen like device which is swabbed over the tested area, then inserted into the handheld reader called relative light unit or RLU, on short. The results are displayed within seconds and can indicate if the sample is clean or unclean. The tests are cheap, as they cost only a few dollars per test. The ATP methods only give a broad indication of the presence of organic substances and not specific microorganisms containing ATP. For this reason they need to be used together with microbial culture tests in order to indicate the type of microorganisms present in the sample.
Using surface ATP bioluminescence testing in the food industry is a proactive tool to assure the processing equipment is clean. It is estimated that 80 percent of the food production facilities in North America and more that 80 percent in Europe are using this ATP testing technology for sanitation monitoring and validation of whether the processing equipment is clean enough to be used for food production.
The widespread adoption of ATP testing resulted from a few important advances in the technology. The instrumentation increased in performance and utility and decreased in size and price. The chemistry improved to the current use of synthetic enzyme that is more temperature tolerant and robust. The ATP testing technology is much easier to use today than it was twenty years ago. The handheld testing devices have a weight of just about a pound. The modern ATP testing devices also include software and in many cases they can be linked to databases in order to help the production managers in the decision making process. It is estimated that the ATP testing will soon spread on new markets such as fast food, hospitals and health services.
Hygiene monitoring is critical when it comes to HACCP compliance. It is common for industries like prepared and processed foods, beverage and dairy to enroll in a HACCP program. Without proper hygiene monitoring by using atp testing kits or other means, there could be many quality issues.
A manufacturing company in any of the aforementioned industries might not only lose its image but end up with a huge loss if there was ever a product recall. With effective hygiene monitoring during food or beverage production, right from the beginning of the process till the end, there is hardly any possibility of product contamination. One of the best methods for contamination testing right now is ATP testing. This method of testing is so simple that anyone, even a person without any scientific background can carry out the test.
In addition, the test results are almost immediate, with some brands of luminometers giving the results in less than 15 seconds without any effect on accuracy at all. ATP or adenosine triphosphate is evident in all living animals and plants including microorganisms like bacteria, mold and yeast. It is actually a molecule which resides within the cell of a living being. So the presence of ATP in water, blood, food or such samples prove the existence of some kind of microorganism in the sample. In other words, there is some level of contamination.
When it comes to an atp testing kit, it normally comprises of cotton swabs and a handheld or portable luminometer. To begin with, the tester should wear a pair of suitable gloves. The type of gloves depends on where he is working. Then he uses a cotton swab to swab the necessary sample, food, water or anything else. The cotton swab is then put into a removable chamber, which is later inserted back into the handheld luminometer.
The reading on the device is usually in RLU or Relative Light Units. Since ATP transfers chemical energy within the cell, the concept of quantified energy presence is used. The reagent in the chamber has an enzyme called luciferase, which reacts with ATP. The ATP energy is then quantified in the form of light and measured in RLU. A higher RLU reading is an indication of more ATP presence, which means a higher level of contamination.
Currently, there are various brands of atp testing kits on the market. They vary in prices but generally, such a kit costs around $1500 on the market. Compared to sending samples for testing somewhere or establishing an internal laboratory to check on product contamination, buying this kind of kit is definitely more cost effective. Moreover, a great deal of time and energy can be saved. The test results are almost immediate and accurate.
Any layman can use this device, even the cleaner. Testing the contamination level of production, testing or surgical equipment surfaces after cleaning is a smart move to reduce the possibility of contamination. If the contamination level is high, then another cleaning can be done. So atp testing kits are useful not only for monitoring contamination of products during manufacturing but also for cleaning purposes at hospitals and such.
PCR stands for Polymerase Chain Reaction, which is often used in biological and chemical labs. A thermal cycler, or PCR machine, has the ability to produce DNA copies of a specific segment that can range from thousands to millions in numbers. (Learn More: What Is The Polymerase Chain Reaction?)
This machine, also called a DNA amplifier, can serve various purposes such as gene analysis, the evolutionary study between organisms or phylogeny and for diagnosing various long term diseases with the help of DNA structure.
Also, it’s used in the field of forensic sciences in arriving at the results based on fingerprints patterns and for testing paternity. Thanks to Kary B. Mullis, who invented PCR technique in 1985!
How PCR Machines Work
The basic function of this machine is copying the sections of DNA and this is performed though a heating cycle. This is performed when the temperature rises to 95 degree Celsius which in turn melts the DNA strands. This melting of DNA strands causes the backbones of sugar phosphate to split apart.
Then as the temperature lowers, the primers bind them 3 inch end of each sequence of target. Primers are able to perform this task as the DNA polymerase taq and free nucleotides aid it in the process.
This process goes on so that there are two strands of double partially stranded molecules of DNA at the end of first cycle. The same process continues to be repeated again and again causing thousands of copies of the particular target sequence.
Features and Uses for a PCR Machine
There are various features of attraction in a DNA amplifier, such as the automated ability, array of thermo cyclers and models, number of manufacturers to choose from, different cooling system designs, variant tubing capacity, heating block in various sizes, multiple heating blocks models and ability to reach to high amplifications within short time.
Though these thermal cyclers are essential tool for all the biologists, they are not very easy to afford. In spite of its price, this DNA amplifier can be found to be extensively used in various laboratories in universal standards, public school facilities, health centers and forensic departments.
There are various advantages of using an automated thermal cycler in comparison to the traditional ones, like the former helps in clinical diagnosis, finds DNA sequencing, medicines, gene manipulation, gene expression study, genomics comparative study and helps in cloning of genes.
Types of PCR Machines
A DNA amplifier is highly versatile in nature and serves great purpose in various fields. It is available in various types to suit the requirements of different sector and other applications. Some of these types are:
Quantitative and Real Time PCR Machine
To quantify and detect DNA sample, this type of machine is widely used for amplification. This thermal cycler uses DNA dyes and fluorescent reporter for its method of probing.
Inverse PCR Machine
This is used to carry out amplification method that helps you identify the flanking sequence of different genomic inserts. This is DND amplification from known sequence to unknown sequence.
Anchored PCR Machine
When small sequence of nucleotides needs to be tagged to a particular DNA of target, the anchor is frequented by poly G by using poly C primer.
Reverse Transcriptase PCR Machine
This is used of RNA molecules amplification. This type of machine is highly used for profiling expression, finding gene expression and identifying RNA sequence in a transcript.
Asymmetric PCR Machine
When there is a requirement for single strand molecules synthesis of DNA, which is essential for DNA sequencing, this PCR machine is widely used. It can perform 20 to 25 cycles of amplification using two primers. When one cycle is completed, one primer gets exhausted and in another 5 to 10 cycles, single strand DNA is produced.
Allele Specific PCR Machine
When there is a need to identify and detect a selective single nucleotide polymorphism, this thermal cycler is widely used. It uses a special design primer, which will match or not match the alleles at the primer end of 3′.
Colony PCR Machine
This machine is used to detect the formation of bacterial colonies after a plasmid transformation.
Conventional PCR Machine
This makes use of standard Polymerase Chain Reaction process that helps you produce billion copies of DNA and RNA strand.
Nested PCR Machine
After the initial 30 to 35 Polymerase Chain Reaction cycles, the new primers are nested along with the old primers to aid in a sensitive process as it reduces the risk involved in it.
You’re wondering – is distilled water safe to drink? The short answer is yes – drinking distilled water is safe. There’s a bit of confusion surrounding this type of water, so let’s go ahead and clear some things up.
Can You Drink Distilled Water Even Though It Has No Minerals?
It seems one of the reasons against drinking distilled water is that it doesn’t have any minerals. This is a ridiculous argument, quite honestly. Most people don’t even drink enough water as it is, and worrying about whether or not you’re getting the proper amount of minerals from the tiny trace amounts of minerals you might be taking in via your water is simply ridiculous.
You get your necessary minerals from food, not water. You get water from water. The only thing you might miss out on is Fluoride. Fluoride is often added to tap water in the United States and some other areas. However, drinking a bottle of distilled water isn’t going to make your teeth fall out of your face from lack of fluoride. There are plenty of people on the planet who get by just fine without this luxury.
Is It OK To Drink Distilled Water Even Though It Tastes Bad?
Well, we’re talking about the safety of drinking distilled water here. People argue that you shouldn’t drink it because it tastes bad. This isn’t really a safety issue at all – you aren’t going to die if you drink water that isn’t up to your flavor standards. You could die if you don’t drink water though, so if your only option is to drink distilled water, you should probably drink up. Water is water, and there are mild flavor differences between any two sources. You could go to a friend’s house and not like their water. You might even find that you prefer the very clean taste of distilled water.
There are no real arguments for or against drinking distilled water as far as health and safety are concerned. There’s no reason to go out of your way avoid it or to specifically drink it, but is it safe to drink distilled water? It sure is.
Final Note: If you’re sitting in your chemistry class, feeling a little thirsty, eye-balling that distilled water bottle, and looking this up on your iPhone because you’re wondering – is distilled water safe to drink? IT’S NOT in this case.
IT’S NEVER SAFE TO DRINK OR EAT ANYTHING IN A CHEMISTRY LAB
As with anything, the density of water is dependent upon temperature. The odd thing about liquid water is that when its temperature is lowered to the point of becoming a solid it actually becomes less dense. You may have heard of this solid substance – it’s called ice. You may have also noticed that ice floats, and this is a result of this interesting water density phenomenon.
What Is The Density of Water?
The density of water at room temperature is 1,000 kg/m³. This means at room temperature 1,000 kg of water will take up approximately 1 cubic meter. It is actually not precisely 1, but rather very close. It does indeed become more dense – approaching closer to 1,000 kg/m³. Water is actually most dense at 4°C, and then the density decreases minimally until it reaches freezing temperature (0°C or 32°F) at which point the density of ice becomes almost 10% less dense than liquid water. This is a result of the molecular structure of ice. Fewer H20 molecules can fit into the same space due to the rigid structure caused by the hydrogen bonds in water, which decreases the density. This relationship between the density of water and ice is a rare one, and few other substances share this property.
A Table of The Density of Water At Different Temperatures
The information for this water density table is from Wikipedia.com.
Amongst the density of water at various temperatures, you can see that freezing temperature is highlighted there. Notice how the density increases up until 4°C, hits freezing, and then rapidly decreases.
The density of salt water is dependent upon the concentration of salt disolved in the water. Sea water with the lowest concentrations of salt are located around the Equator, while those with the highest concentrations are located at the poles.
You should now have a better understanding about how the density of water works.
As for the nerds, we can probably say that their DIY projects are really outstanding most of the time. These people are willing to spend countless of hours just to perfect their craft– whether it’s a self-programmed app or a homebrew computer.
Here are the top 3 DIY computer project ideas for the nerds to try.
1) Lean, Green Gaming Machine
Say goodbye to tablets and smartphones; when it comes to gaming, nothing beats the full-sized gaming computers! In fact, they’re even described as the “true thoroughbreds.” Gaming computers are faster, bigger, and no doubt, more powerful than any type of computer you’d usually find in most homes. However, no matter how awesome they are, there’s still a slight drawback– they’re not that eco-friendly.
If you’re not aware (which we highly doubt), during a serious gaming session, these computers suck down hundreds of watts just to ensure that the CPU, graphic processors, and other high-end components will be running smoothly, no matter what.
Fortunately, there are a number of ways to green your machine.
Select components that consume less wattage. This will be possible if you’ll opt for a custom-built computer with parts that you personally select. Also, due to the fact that most manufacturers are more sensitive to green concerns now, they have produced power-sipping products, such as the AMD and Nvidia. Even ASUS unleashed its Ge-Force GTX 650-E– a high-end graphics card that only consume 60 watts at peak power.
2) A Computer for a Tight Budget
If you’re cheap, or you’re just trying to pinch pennies, then this one is for you– a cheap, yet functional computer. Basically, this computer will have the cheapest components available and you shouldn’t focus much attention for the quality.
The idea here is to get your hands dirty and build your computer without worrying how you can avail a $400 graphic card. Just buy a barebones computer kit and you’re all set. However, if you want to turn this into a hobby or perhaps, a business, there’s no harm in searching for the pieces yourself.
This kind of project will give you the experience you need in matching compatibilities and you’ll also understand the complimentary weaknesses and strengths of the computer parts.
3) DIY Home Theater Computer
Everyone wants to have a home theater, but not all have the budget for that. This DIY idea will turn your computer into the brain of the home theater. Likewise, it will also serve as the storage device for your media, together with the audio and video output. Not just that, you can also use your computer and turn it into a digital recorder.
Though, before you start, keep in mind that there are a lot of things to be considered when building a home theater, such as the need of a remote control and the accompanying software. Though, that’s not all, you’ll also need to look for ways on how to interface the cable with your computer. A TV tuner can be utilized to capture over-the-air television, and you can use HDMI or DVI input to connect your computer to your TV. Don’t worry, most TVs these days have one of these inputs and all you have to do is make your computer compatible for it.
These are just some of the DIY computer project ideas that you can try. There are a lot of options available. Just keep in mind that you have the ability to turn your computer into whatever you want it to be, as long as you have the skills and knowledge needed for it.
Computer desks generally have a top where a keyboard and a mouse sits, and raised area where the monitor sits. Certain desks put the mouse and keyboard on a shelf under the main top. The CPU may sit on top of the computer desk, beside the computer desk, or on some special shelf that’s created for it. The computer desk may be set or designed at any height so as to fit special chairs or stools, or to be utilized while standing. Beyond this, the options are all up to you. Certain users prefer minimal setups, with maybe just a top & the legs; some others prefer a lot of storage area, with drawers and file cabinets.
Most of the planning that’s involved when building the computer desk mainly concerns the placement and the number of peripherals. For instance, a printer is 1 of the peripherals that many users have, & where you actually decide to put it will have a major effect on the design. In case you wish to put it on your desktop, you’ll need to make your desktop larger. You may build a customized shelf for holding it, either above your monitor or below your desktop, or you may build another cabinet that’s entirely separate from your computer desk. Some other peripherals you may need to consider include; power supplies, scanners, graphic pads, external disk drives, and the sound system with speakers.
How To Build a Computer Desk
- 1″ thick wooden plank for the top of your desk
- Plank for the keyboard tray
- 1″ thick wooden plank
- Wood glue
- Sand paper and/or electric sander
- Power drill and a screwdriver
- A pencil
- A ruler
- Wood stain
- Wood varnish
- Brushes for varnish
- L brackets
- Carriage bolts & locking nuts
- Keyboard runners
- Scrap wood for bracing the legs
Instructions for Building A Computer Desk
- Design your desk. Design a top, a good place for your keyboard and your legs. The key thing that usually differs is the actual size of the computer desk.
- Cut the wood planks to a size you need. Legs can be cut from a single plank if angled correctly. Ensure the keyboard desks is wide enough that it can reach both desk ends so the runners can fit properly.
- Sand all the wood pieces until they are smooth.
- Attach the desk legs to the desk top using the L brackets and the carriage bolts & locking nuts. It’s likely that they’ll wobble at this juncture. If they do, measure the spaces diagonally between table top and legs, and then use the scrap pieces of the wood in order to reach across the distance so as to anchor the desk legs much more firmly. Make sure you screw in all the the scrap pieces tightly.
- Use smaller planks of wood & attach your keyboard sliders. Screw the sliders in tightly. If you desire, screw in small pieces of the wood to back of your drawer so the keyboard can’t fall off. You can attach the otherside of sliders to your desk legs. Ensure you attach the drawers at a proper height for comfortable sitting at the table or desk.
- Using a clean damp rag, stain all the wood properly in a smooth circular motion.
- When it dries, apply your varnish with a clean paint brush or a sponge brush. 2 coats may be needed.
- Let it sit for about 24 hours in order to dry, once it has completely dried, you are done.
We take advantage of our access clean drinking water. Most of us go to the faucet and get a glass of clean fresh water several times a day and never give the first thought to the importance of water. We have become so accustomed to having it, we rarely think about what our lives would be like, if we had to struggle to find water that was even halfway safe to drink.
Sadly, in many other countries across the globe, this a problem that is all too real for it’s inhabitants. They are forced to drink water from rivers, streams, watering holes, and other water sources, that are more than likely diseased or polluted. They are forced, often times, to bathe and cook with this same dirty water. Imagine what it would be like if all the water that you had available, was water that you were sure was going to make you sick to drink. What would it feel like to have to give your children this water, knowing that it could endanger their health, or even their life. What a helpless situation this would be. It is heart wrenching too even think that there are people that deal with this every single day of their life.
It does not have to be this way for them. Here in America, and many other countries as well, we have the ability to help these people. There are organizations out there today, that specialize in getting clean water to the people who need it the most. Because of the fact, that most people don’t consider clean water, when thinking of all of the different charities, these organizations struggle. They struggle to accomplish enough, to make a real difference. There are millions of people in need , and only a few hundred who care to help.
You can help by taking charge and stepping up. It’s something we all can, and should do. Start by researching some of the different clean water organizations and seeing what you can do to help. The next step will be to raise awareness to the problem. Start speaking up about this problem in your community. The more people understand and can relate, the more people will be willing to do what they can to help.This is a problem that cannot be fixed overnight. It is going to take a commitment from everyone to even see a little difference. Nevertheless, the more we stand together, the bigger the change can be.
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