Tight Binding method for carbon nanotubes Essay

Tight Binding method for carbon nanotubes - Essay Example Carbon nanotubes are long, thin cylinders of carbon and have a very broad range of electronic, thermal, and structural properties that change depending on the different kinds of nanotube. The chiral vector of the nanotube, B'= nR1 + mR2 where R1 and R2 are unit vectors in the two-dimensional hexagonal lattice, and n and m are integers. Another important parameter is the chiral angle, which is the angle between Band R1. Diameter D = a3 (n2 + nm + m2)/ p ,Where, ac is the distance between neighboring carbon atoms in the flat sheet. The different values of n and m lead to different types of nanotube. They are armchair, zigzag and chiral nanotubes. Armchair nanotubes are formed when n = m and the chiral angle is 30. Zigzag nanotubes are formed when either n =0 or m==0 and the chiral angle is 0. Other nanotubes, with chiral angles between 0 and 30, are known as chiral nanotubes. The properties of nanotubes are determined by their diameter and chiral angle, both of which depend on n and m. The electronic characteristics of the nanotubes have been done by numerical band structure, the structure of the chemical bonds. is given by the local spatial structure of the orbital. The electronic structure of the nanotube fragments are calculated by SCF-MO-LCAOVmethods. In this method, only valence electrons are taken into account and the three- and four-center integrals are omitted and the repulsion of lone electron pairs can be explained. The SCF convergence criterion was 10-8for total-energy changes and 10-5 for charge-density changes between two subsequent cycles. Band structure calculations of [n, 0] (n = 6, 7, 8, 9)tubes were performed using the tight-binding Hamiltonian, with a universal set of first and second nearest-neighbor hopping integrals that reproduce various carbon structures, including graphite. The 2s, 2px, 2py, 2pz, and s* orbital of each carbon atom are used as the basis set for expressing the tight binding model. The Hamiltonian matrix elements and related parameters are obtained by adjusting the model to fit photoemission band-structure data. The (6, 0) carbon tube seems to have the lowest diameter and are thermodynamically unstable. The bonds at the ends of the nanotube fragments get saturated by hydrogen atoms. The structural unit of the tube is the distorted carbon hexagon. All c-c bonds were assumed to be of the same length: 1.4 . Page 3 The distance between third-neighbor carbon atoms along the tube circumference is 2.39 . The point group symmetry of the (6, 0) nanotube fragment is determined by the number N of carbon hexagons along the tube axis. There is a difference between heat of formation of the nanotube fragments, caused by the boundary atoms affect, strongly at the central part of the nanotube fragment. In the above Figure, the dispersion curves of the (n, 0) tubes with n = 6... 11 are shown. This tube family splits into three groups. The (3n, 0) tubes have vanishing energy gaps. The gap increases in (3n + 1, 0) and in (3n + 2, 0) tubes. Consequently, (6, 0) and (9, 0) tubes will likely show metallic conductivity, similar to graph. In graphite, orbital are represented in carbon nanotubes, the radial orbital are analogous to the lone orbital of graphite .This changes the character of the frontier orbital

Warnie orr methodology and its disadvantages Essay Example for Free

Warnie orr methodology and its disadvantages Essay Is a bottom up methodology used to model data and procedures where you identify the output and the processes used to generate them and their inter-relations. Its emphasis is on the output. It is analyzed thoroughly. The logic of the program is built around the structure of its data. That structure is obtained by analysis the output and going backwards to find out what the input could have been. The analysis of the output includes: †¢ Output Oriented Comment The output is the core of this system development methodology. We spend all our energy to capture the true picture of the output requirement. This is done even before we think of the physical design. We use rigorous methods to define the data output through a well designed form known as LOS. We capture details of: †¢ Output definition forms †¢ Output frequencies †¢ Data Elements It is assumed the expert can define these requirements with the help of system users who help him fill the mandatory details of these forms. The system users know what they want, but they have little knowledge of computers and computer terms. The software expert knows little about the area to be computerized and can easily misunderstand some concepts. For example computational requirements, the frequency of data use, frequency of data change. Besides when we collect the data from an existing system which is inefficient, the data is inconsistent and unacceptable. The system owners are unhappy with the output generated and that is why they want to change it in the first place †¢ We must obtain the logical output structure first before we think of its physical outlook. The physical problems of the data remain the headache of and hidden by the implementer. Ours is to give the general guidelines on the data and process requirements. This is easy said than done. We cannot claim to be general when we spend all our time worried about our output and its properties. At that level it is difficult to talk about generalities as well. We have to generate dictionaries with specific data structures. Software compatibility with these structures is mandatory. †¢ The approach is data centered, that is the processes are looked at last Take a critical look at the output before any programming activities are undertaken. We break the program into three parts †¢ The middle mapping. also known as the logical output mapping. It deals with how we produce the output and give details of how calculations are done. It assumes the physical mapping will give it the perfect data and in the correct order it is wanted. †¢ Physical output mapping: Formats the data and sends it to the output device. It is the duty of the physical output to know the details of the data format and how to obtain it from the output device. These details should be hidden from the logical mapping. The physical aspect depends on the operating system platform being used. Which tasks are taken by the operating system and which ones are not and that must be a headache of the programmer †¢ Physical input mapping which knows where and how the data is actually stored. If the data gets reorganized or changed in any way the physical input mapping is updated. When changes occur to any part, it is independent of the other parts and carries no ripple effect. Reusable code modules and design elements can be employed. Generic code can be supported to be used by many programs. Having given a summary of the method let us analyze possible problems with this type of method: Obtaining a complete System design before the physical Design This has always remained elusive in most system development methodologies. System design process continues even after implementation because new facts are discovered during actual implementation. Even when prototypes are used, still more facts and faults come into surface. Separating the logical, physical input, physical output mapping Again we need to combine data and processes together, the reason we call them objects, in objects in object oriented systems. How do obtain inheritance, aggregation and software reuse if we separate them. References 1) Ian Sommerville, Software Engineering 2) Aron, J. D. The Program Development Process 3) Booch G. , Rumbaugh J. : The Unified Modeling

Effect of Temperature on the Rate of Reaction between Sodium Thiosulphate and Hydrochloric Acid :: GCSE Chemistry Coursework Investigation

Effect of Temperature on the Rate of Reaction between Sodium Thiosulphate and Hydrochloric Acid Investigation Chemical reactions are used in our everyday life, they literally keep us alive. They are used in food, respiration and everywhere else in the environment. A chemical reaction mainly occurs when reactants react together to produce a new product. The speed at which this reaction takes place is called the rate of reaction. The product produced has a number of particles in the solution that has formed from the reactants. The concentration is the amount of particles in a certain amount of water. If a cross is placed under the beaker of the solution, the cross will eventually disappear because the high temperature of the water will make the particles move faster because they have more energy and they will move more quicker to give a bigger impact which will cause more frequent and violent collisions and the solution will disappear as the product forms to create a misty solution. The rate of reaction is normally recorded in tables and can then be defined onto graphs to show how the rate curves of different factors affect the speed of the reaction. A rate curve is the curve of a graph that shows how the reaction changes at different intervals. The gradient of the graph tells us whether the different rate curves have the same relation, meaning if they have a similar rate of reaction. Reactions can take place in a variety of customs; they can bee steep or steady. The steeper the slope, the faster the reaction takes place. The steadier the slope, the slower the reaction takes place. Aim: The aim of my investigation is to find out whether the increase of temperature increases the rate of reaction between the two reactants of Sodium Thiosulphate and Hydrochloric acid. I will then find out and evaluate on how temperature affects this particular reaction. Factors There are four main factors, which affect the rate of reaction that are considered as variables for the experiment I will be doing, they are the following: Molecules can only collide when two of them meet together. This meeting between the two particles can only take place on the surface area of the material. If the surface area of the material is increased, the particles gather more space to collide with each other with force. With a large surface area, the particles will have more area to work on so the collision probability will be high. A catalyst is a separate substance to the ones you use in your experiment and is used to speed up the reaction between the reactants.

Reflection paper on date rape for Human Sexuality Essay

There are many sad stories of girls who have been violated by someone that they know. They almost all begin with a wonderful night and eventually get taken advantage of. The woman in the situation may feel as though she asked for it. The male may feel as though she didn’t say no, so if I do this I am doing nothing wrong. It is horrifying to me how many times this has happened to a woman. The number of times it happens to women is the most significant thing about date rape to me, because I didn’t realize that it happened so much. I think knowing this will help me to watch out for things around me a little better and make my trust level go down even further. I think all women need to watch out for themselves in sketchy situations. If she or I feel uncomfortable then she or I should try to avoid the situation before it is too late, if possible. This isn’t always as easy as it sounds though. There have been quite a few times that I was in situations where potentially very bad things could have happened to me and out of pure luck they didn’t. I am usually a very trusting person, but the past couple of years I’ve been having to rethink that and become more of an untrusting person to try to protect myself. Men take their strong, masculine image and use it to their advantage. They may try to use guilt, lies, alcohol, and/or aggressiveness to get a girl to have sex with them. If she declines and he still continues to have sex with her, then he is committing a crime. The worst part is that girls don’t really know who to trust or not to trust. It’s a very scary world in which we live. I wish the world was different and it was ok to trust everyone especially the people you are close to, but since it’s not I have to be really careful when choosing who I will trust.

Social Learning: Psychology

In the beginning of Psychology, an individual would be studied taking into consideration and believing that s/he is acting alone. However, in the rising of Psychology, researchers stated the importance of the social context and that it can have a major effect on the behavior of an individual. The Sociocultural level of Analysis studies the behavior of the individual not based on his biological processes but based on the social context s/he belongs to and how the society has affected the actions of the individual.One of the most important theories under the Sociocultural level of Analysis is the social learning theory which was developed by Albert Bandura. The social learning theory explains that behavior is learnt by observing others. The theory states that people learn behavior through observational learning of social factors in environment. When people observe positive and desirable outcomes from a specific behavior, they are most likely to imitate and adopt that behavior.Bandura s tated that individuals observe behavior of others and see whether they are awarded or punished for that specific behavior. When they are awarded or even when the behaviors aren’t punished, the individual is most likely going to imitate the behavior. There are four different types of modeling, where modeling merans observing and imitating a behavior. The first type of modeling is direct modeling and it’s the simple imitation of a single behavior.The second type of modeling is the synthesized modeling which is the combination of more than one observed acts in order to create new complex behavior. The symbolic modeling is when real life human models are replaced by characters and finally the abstract modeling is the process of inferring the system of rules that underlie complex behaviors. Modeling which is observing and imitating behavior is made of four different steps. The first step is attention which is the process of observing a specific behavior.Afterwards thereâ₠¬â„¢s retention which is the process of creating schemata for the observed behavior. Then, there’s the step of motoric reproduction of the observed behavior and the last step is motivation which is having a reason or a motive to adopt and imitate the same behavior that was observed. The social learning theory is connected with various principles under the sociocultural level of analysis. The first principle to which it is connected is the principle that states that humans are social animals and that they need to belong in a social group.For example when there’s a social group that has a specific characteristic in their behavior that distincts this group from the rest, then in order to belong to this group you need to observe their behavior and imitate it. The second principle to which the social learning theory is connected, is the principle that states that culture affects behavior through norms. Therefore, the individual depending on the culture s/he belongs to obser ves the behavior of the majority which represents the norms of the society and by observing this behavior s/he imitates it since these norms are acceptable in the society.A specific study conducted based on the social learning theory is the research study conducted by Bandura et al. Bandura supported that aggression is learnt from environment through observational learning and imitation and he wanted to conduct the â€Å"Bobo Doll experiment† in order to test this. The aim of the experiment was to see whether children will imitate aggressive behavior when they will have observed it and whether in the imitation the same sex models have any importance.The procedure that he followed was that he made groups of students of 36 girls and 36 boys with an age between 3 and 6. Children were matched based on their aggression as it was reported by their parents and other family members. One group was exposed to adult models who showed aggressive behavior on a bobo doll , another group ob served an adult who showed no aggressive behavior on the bobo doll and that person was assembling the toys for around 10 minutes and then there was a third group which was the control group and they did not see any aggressive behavior.It is important to be stated that some children observed same sex adults and some opposite sex adults. After the observance of the behavior the children went in a room full of toys and they were told that they should not play with the toys since they were for other children and then they were put in a room with a bobo doll. Bandura et al observed that the children who had observed an aggressive behavior behaved more aggressively both physically and verbally.Bandura stated that social learning was demonstrated in the study , since the subjects showed observational learning through the imitation of behavior of the adult and depending on what the subjects observed, an aggressive or non aggressive behavior they simply imitate that behavior when they are in a similar situation with the adult which was having the bobo doll in the room. The experiment conducted by Bandura had various strengths and limitations.One of the strengths is the fact that there was a high control of the variables and it can give a cause and effect relationship. Another strength is the fact that the experiment was replicable and actually showed that those children that observed the aggressive behavior, they imitated it. A limitation is that the experiment was conducted under laboratory conditions and the the study lacks of ecological validity. Another limitation is that it’s not obvious whether the children were showing an aggressive behavior or just a harmless play with the bobo doll.Also many ethical issues arise since the children where not allowed to play with the toys in the beginning which caused frustration of the subjects. The social learning theory has had applications in the every day life of the individuals. Through the social learning theory, p eople can understand the importance of their social background on their own behaviour, since behaviour of human beings is not studied separately anymore, but also taking into consideration the social context, since someone can observe and imitate behaviour within the society.It can also provide with possible explanations for the existence of phobias and eating disorders and that by observing an individual with an eating disorder for example you will probably find out that s/he is the center of attention of others and since the result is quite desirable to a really big number of people, it is most probable that they will imitate the behaviour which led to this outcome. Similarly, the social learning theory can help in the education and the interaction between the teacher and the students.When a student does not have an appropriate behaviour and the teacher always makes remarks of that student and that s/he should stop having that behaviour, if the behaviour is not punished by the tea cher along with being the center of attention because of the continuous remarks of the teacher, it will make other students imitate the observed behaviour which has favourable outcomes to a really big number of them.

Belie and Betray

Belie and Betray Belie and Betray Belie and Betray By Maeve Maddox A reader asks for a discussion of these two words: I get confused when using belie and betray. Sometimes they seem to mean the same thing. Would you please explain when each word should be used, and why. The OED cites two verbs spelled belie that were in use as early as 1000 CE. One belie meant, â€Å"to lie around or encompass.† It was used literally to describe a spatial connection. For example, an army â€Å"belied by the enemy† was surrounded by the enemy. This belie was also a slang word for â€Å"have sex with.† The other belie is the one still used in modern English. Its original meaning was â€Å"to deceive by lying.† Shakespeare plays on the different meanings of the words lie and belie in the scene in which Iago employs innuendo to stoke the Moor’s fears about Michael Cassio: OTHELLO: What hath he said? IAGO: Why, that he did- I know not what he did. OTHELLO: What? what? IAGO: Lie- OTHELLO: With her? IAGO: With her, on her, what you will. OTHELLO: Lie with her? lie on her? We say â€Å"lie on her† when they belie her! Lie with her- that’s fulsome.  - Othello, IV, 1. The belie associated with falsehood expanded to have the following meanings: 1. to tell lies about; especially to calumniate by false statements. 2. to give a false representation or account of, to misrepresent; to present in a false character. 3. to treat a thing as false by speaking or acting at variance with it. 4. to show to be false, prove false or mistaken; to falsify. Belie is often seen in headlines. Here are several examples from the Web: Companies’ Pro-Equality Rhetoric Belied by Their Campaign Donations Image of a Wealthy Gore Is Belied by a Net Worth in Senates Minor League Outsider claims belie political insider past Sometimes belie is used to mean cover up or conceal: Their campaign promises belie a more sinister agenda. Pickfords small stature and cinema sweetness belied a shrewd businesswoman, forming her own production company. Beware of euphemisms that  belie  Ã¢â‚¬Å"hellish†Ã‚  behavior.    A common use of belie is, â€Å"to misrepresent† or â€Å"to reveal as a lie†: Laboratory Tests Belie Promises Of Some GMO-Free Food Labels CO2 emissions belie climate  promises Shattered streets of Homs belie Assads promises of peace Sometimes belie is synonymous with â€Å"call into question†: Marias strength and  intelligence belie  our image of a â€Å"genteel southern lady   Strike, protests  belie  Haitian  governments  free education claims.   Marilyn Monroe and Joanna Lumley belie the dumb blonde image. Monroe was reputed to have an IQ of 170 and Lumley is a member of the Royal Geographical Society. The verb betray also has multiple meanings: to lead into error or sin A Don Juan is a villain who betrays virgins and abandons them. to deliver into the hands of an enemy When he had obtained the confidence of the citizens, he betrayed the town to Darius. to prove faithless or treacherous to a friend How should we react when we find out that a friend  betrayed  us?   to prove faithless to ones country Aaron Burr is often alluded to as the stereotypical traitor: a man who betrayed his country. to reveal A red brick chimney rising up the north side  betrayed the existence of  the small fireplace in the living room. The intended meaning of betray is usually obvious from the context. Because the meaning of belie is not always clear, writers may choose from the following alternatives: contradict be at odds with call into question show to be false disprove debunk discredit negate Want to improve your English in five minutes a day? Get a subscription and start receiving our writing tips and exercises daily! Keep learning! Browse the Vocabulary category, check our popular posts, or choose a related post below:Grammar Test 1What is Dative Case?Plurals of Proper Names

Today We Begin from The End essays

Today We Begin from The End essays Today we begin from the end. To the question of what it was, would be, what it wasnt, could be, what went wrong with the right, and the certainty that the uncertainty will put an end to the beginning. What lets us live, what tells us the past, and that we don't know the future. Time provokes encounters, and it causes mismatches , the tomorrow that was yesterday, and that it is impossible bringing back. The heart that keeps what it was, that time didn't and doesnt erase. The illusion of wanting who doesn't want you, the breathlessness that makes you suffocate for the reason than you don't want to know, because what suffocates you is to know that the air you seek doesn't exist. The surprise of the moment that you had taken as lost, gone, and conformed. The pain of what happened, the pain of what didn't happen, and the pain of not knowing what would have happened. The pain that comes from the desire of a forbidden love. Or the happiness of a love of one day, such day that everything w as as it was supposed to be. The day that rises with the birds, the smile with closed eyes to the light that the sun brought to wake you up to a happy day. The Morning that is already late, of one night that didn't end. The walk holding hands,the sound of a mutual silent song, a ballad that makes you smile to who makes you feel love. The moments of silence and observation, happiness, while starring at the beauty by your side for one long second. The moment that you will keep forever, as a portrait of a smile. The night that falls, the moon that comes out, the breeze that passes by, the cold that gives in, the hug that shelters, the intimacy that surrounds, the safety that is sure, the rain that romanticizes, the eternal moment of one day, that ended yesterday, but comes every day, and everyday to come. The caress of a light touch, a gentle kiss, the soft skin, the warmth of a passion. The glance of fixed eye ...