Difference between revisions of "Team:Peking/test"

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                         <h2 class="lead">Safety</h2>
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                         <h2 class="lead">Sequential logic vs. combinational logic</h2>
 
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                         <h3>GENERAL</h3>
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                         <h3>Introduction</h3>
 
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                             Working in the lab means that  we have  safety guidelines! First of all, lab coat and gloves are mandatory along with safety glasses where needed. We start every experiment cleaning  our workbench with ethanol and end that same experiment doing exactly the same, preventing growth of contaminants. Furthermore, we separated the benches used for E. coli and Yeast to avoid contamination. When working near the flames we avoided using gloves. All bacterial and yeast cultures were neutralized with bleach before disposal and put in the biowaste. Posttreatment of the waste was done by the home institute facility and according to the legislation in our country.
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                             Combinational logic circuits implement Boolean functions, which always depend on input. Boolean functions are mappings of input to output. They are functions of input only. It means that if you feed in an input to a circuit, the output will always be the same for that circuit. If that value were not the same every single time, then the output must not completely depend on input. Something else must be affecting the output.  
 
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                         <h3>GENERAL</h3>
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                         <h3>Example-Buy coffee</h3>
 
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                             Working in the lab means that  we have  safety guidelines! First of all, lab coat and gloves are mandatory along with safety glasses where needed. We start every experiment cleaning  our workbench with ethanol and end that same experiment doing exactly the same, preventing growth of contaminants. Furthermore, we separated the benches used for E. coli and Yeast to avoid contamination. When working near the flames we avoided using gloves. All bacterial and yeast cultures were neutralized with bleach before disposal and put in the biowaste. Posttreatment of the waste was done by the home institute facility and according to the legislation in our country.
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                             Let's consider a vending machine. We want to see if its output is solely dependent on the input.
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Imagine this vending machine only sells coffee, and that the price of a coffee is 75 cents. The machine can only take quarters. Once 75 cents are deposited, a coffee is dispensed without any button being pressed. (What a stupid machine!)
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One day, when you want to drink coffee, you see this machine, and you happen to be holding several quarters. You place the first quarter in the machine, and out comes...nothing! Undaunted, you put another quarter in, and out comes.... nothing! Frustrated, you decide to put in yet another quarter, and out comes a coffee! Delicious, savory and mellow Coke! You drink, and are content.
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Then, invigorated by caffeine, you begin to think "Is this machine a function?"
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You gave the same input, three times in a row, but it did not produce the same output.
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A mathematical function maps inputs to outputs. Thus, once you know what the input maps to, that should be it. In this case, the input (a quarter) mapped to nothing. So, clearly, this does not behave like a function.
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What's happening? Clearly, the machine is storing some information. In particular, it's records how much money you have entered so far. The output is determined not only by the input, but also by this stored information.
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                         <h3>Sequential logicS</h3>
 
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                            We are working with dCas9, a catalytically dead version of CRISPR-Cas9, which unlike its active form isn’t able to cut DNA sequences but it only binds to them depending on the guide RNA (gRNA). Therefore the danger from off-targets is already much lower. That did not stop us from checking for any binding sequences for gRNAs in the yeast and human genome (even though we do not intend to use our gates in humans) to add another layer of security. The risk in this could be unwanted inhibition/activation of some of the genes in our own genome! Luckily, we were able to design and obtain gRNAs with no such human-binding capabilities!
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Key things to notice:
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 Like combinational logic circuits, a sequential logic circuit has inputs and outputs.
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 Unlike combinational logic circuits, a sequential logic circuit is related to time.
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 Also, there is a box inside the circuit called State. This box contains flip flops. Assume it has k flip flops. The flip flops basically store a k-bit number representing the current state. The state can be updated.
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 The output is computed based on the inputs and the state coming out of the state box.
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The information needed to update to the state (called the next state) comes from the current state (the current value of q) and the input, which is fed through combinational logic, and fed back into the state box, telling the state box how to update itself.
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The main difference between sequential circuits and combinational circuits is that sequential circuits compute their output based on input and state, and that the state is updated. Combinational logic circuits implement Boolean functions, so they are functions only of their inputs, and are not based on clocks.
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Revision as of 04:55, 15 October 2017

iGEM EPFL 2016

Sequential logic vs. combinational logic

Introduction

Combinational logic circuits implement Boolean functions, which always depend on input. Boolean functions are mappings of input to output. They are functions of input only. It means that if you feed in an input to a circuit, the output will always be the same for that circuit. If that value were not the same every single time, then the output must not completely depend on input. Something else must be affecting the output.

Example-Buy coffee

Let's consider a vending machine. We want to see if its output is solely dependent on the input. Imagine this vending machine only sells coffee, and that the price of a coffee is 75 cents. The machine can only take quarters. Once 75 cents are deposited, a coffee is dispensed without any button being pressed. (What a stupid machine!) One day, when you want to drink coffee, you see this machine, and you happen to be holding several quarters. You place the first quarter in the machine, and out comes...nothing! Undaunted, you put another quarter in, and out comes.... nothing! Frustrated, you decide to put in yet another quarter, and out comes a coffee! Delicious, savory and mellow Coke! You drink, and are content. Then, invigorated by caffeine, you begin to think "Is this machine a function?" You gave the same input, three times in a row, but it did not produce the same output. A mathematical function maps inputs to outputs. Thus, once you know what the input maps to, that should be it. In this case, the input (a quarter) mapped to nothing. So, clearly, this does not behave like a function. What's happening? Clearly, the machine is storing some information. In particular, it's records how much money you have entered so far. The output is determined not only by the input, but also by this stored information.

Sequential logicS

Key things to notice:  Like combinational logic circuits, a sequential logic circuit has inputs and outputs.  Unlike combinational logic circuits, a sequential logic circuit is related to time.  Also, there is a box inside the circuit called State. This box contains flip flops. Assume it has k flip flops. The flip flops basically store a k-bit number representing the current state. The state can be updated.  The output is computed based on the inputs and the state coming out of the state box.  The information needed to update to the state (called the next state) comes from the current state (the current value of q) and the input, which is fed through combinational logic, and fed back into the state box, telling the state box how to update itself.

Summary

The main difference between sequential circuits and combinational circuits is that sequential circuits compute their output based on input and state, and that the state is updated. Combinational logic circuits implement Boolean functions, so they are functions only of their inputs, and are not based on clocks.