One can examine and observe the internal structure of a material at various levels of observation.The degree of magnification required to study a material by various methods is called a measure of the levels of observation.
Depending on the level, we can classify the structure of materials as:
1. Macro structure
2. Micro structure
3. Sub structure
4. Crystal structure
5. Electronic structure
6. Nuclear structure
1. Macro structure:
Macrostructure of a material is examined by low- power magnification or with naked eye. It deals with the shape, size and atomic arrangement in a crystalline material. The internal symmetry of the atoms in a crystalline material may reflect in the external form of a crystal such as quartz.
Macrostructure may be observed directly on a fracture surface or on a forging specimen. Macrostructure can reveal flaws,segregation; cracks etc., by using proper techniques. Large individual crystals of a crystalline material may be visible to the naked eye.
2. Micro structure:
This generally refers to the structure of the material observed under the optical microscope. Optical microscopes can magnify structures about 1500 to 3000 times linear, without loss of resolution of details of the material structure. The optical microscope can resolve two lines separately when their difference of separation is about 0.1 %u03BCm (10-7 m). Cracks, porosity, non-metallic insulations within materials can be revealed by examining them under powerful optical microscope.
3. Sub structure:
When crystal imperfections such as dislocation in a structure are to be examined, a special microscope having higher magnification and resolution than the optical microscope is used.Electron microscope with magnification 10 powerof 5 is used for this purpose.Another important modern
microscope is field ion microscope, which can produce images of individual atoms as well as defects in individual atomic arrangement.
4. Crystal structure:
It tells us the details of the atomic arrangement within a crystal. It is usually sufficient to study the arrangement of atoms within a unit cell. The crystal is formed by a very large number of unit cells forming regularly repeating patterns in space. The main technique employed for determining the
crystal structure is the X- ray diffraction and electron diffraction method. (Assemblies of atoms,geometries determined by bonding).
5. Electronic structure:
This usually refers to the electrons in the outermost shells of individual atoms that constitute the solid. Spectroscopic techniques are commonly used for determining the electronic structure.
6. Nuclear structure:
It is studied by nuclear spectroscopic techniques such as nuclear magnetic resonance (NMR) and mossbauer studies.
CHARISTOPHER ALEXANDER Says that each pattern describes a problem which occurs over and over again in our environment and that describes the core of the solution to that problem in such a way that you can use these solutions a million times without ever doing it.A design pattern is a general repeatable solution to a commonly occurring problem in software design. A design pattern isn't a finished design that can be transformed directly into code. It is a description or template for how to solve a problem that can be used in many different situations.
Uses of design pattern:
- Design patterns are the best solution for the recording problem in the application programming environment.
- It is responsible for design pattern analysis in another arms including GUI (graphical user interface)
- It is mainly used in object oriented programming
Design pattern elements:
In general a pattern has four essential elements they are
PATTERN NAME: The pattern name is a handle we can use to describe a design problem, its solutions, and consequences in a word or two. Naming a pattern immediately increases our design vocabulary. It lets us design at a higher level of abstraction. Having a vocabulary for patterns lets us talk about them with our colleagues, in our documentation, and even to ourselves. It makes it easier to think about designs and to communicate them and their trade-offs to others. Finding good names has been one of the hardest parts of developing our catalog.
PROBLEMS: The problem describes when to apply the pattern. It explains the problem and its context. It might describe specific design problems such as how to represent algorithms as objects. It might describe class or object structures that are symptomatic of an inflexible design. Sometimes the problem will include a list of conditions that must be met before it makes sense to apply the pattern.
SOLUTIONS:The solution describes the elements that make of the design there relationships responsibilities and collaborations.
CONSEQUENCES: The consequences are the result and trade of applying the pattern The consequence of a pattern includes its impact on a system i.e;Every problem will be having some consequences
In modulation process two signals are used low frequency signal and high frequency signal
The process of combining low frequency signal with high frequency signal in order transfer it through a large distances is known as modulation
The advantages of modulation are:
1.Reduces the height of antenna
2.Avoid mixing of signals
3.Increase the range of communication
4.Improves the quality of reception
8051 has the following features they are:
1.4096 bytes of on-chip program memory
2.128 bytes on-chip data memory
3.Four register banks
4.128 user defined software software flags
5.32 bidirectional I/O lines organised as four 8-bit ports
6.Two multiple modes ,16-bit timers/counters
7.Two level prioritized interrupt structure
8.Binary or decimal arthematic
8086 has powerful set of registers .It includes general purpose registers,segment registers,pointers and index registers and flag registers
GENERAL PURPOSE REGISTERS:8086 has four 16-bit general purpose registers.They are labeled as AX,BX,CX,DX.Each 16-bit register can be split into 28bit registers.For example BX can be split into BH and BL.The general purpose registers are either used for holding data,variables and intermediate results temporarily.
- AX-used as accumulator
- BX-used as offset storage for generating physical address
- CX-used as a default counter in case of string and loop instruction.
SEGMENT REGISTER: the physical address of 8086 is 20-bit wdide to access 1 mbyte memory locations .8086 uses memory segmentation.It treats the 1mbyte of memory as divided into segments with a max size of 64kbyte.There are 4 active segments.They are code segment,data segment,stack segment and extra segment.
- cs register holds the upper 16-bit of starting address of the segment from which the BIU is currently fetching code byte
- ss register holds for the upper 16-bit of the starting address for the program stack
- es and ds registers are used to hold the upper 16-bits of starting address of the two memory segments which are used for data
POINTERS AND INDEXED REGISTERS: To get 20-bit physical address one or more pointer or indexed registers are associated with each segment registers.The pointer rgister IP,BP,and SP are associated with code,data and stack segments .The index registers DI and SI are used as a general purpose registers as well as for offset storage in case of indexed,base indexed and relative based indexed addressing modes.
FLAG REGISTER: flag register contains the following active flags
carry flag(CF),parity flag(PF),auxiliary flag(AF),zero flag(ZF),sign flag(SF),overflow flag(OF),trap flag(TF),interrupt flag(IF),direction flag(DF).
THE TYPES OF THE ANTENNA ARE
1. Yagi uda antenna.
2. Folded dipole antenna.
3. Helical antenna.
4. Horn antenna.
1.YAGI UDA ANTENNA:
A yagi uda antenna consists of the one driven element , one reflector & one or more directors.
· The input is supplied to the driven element so it is known as the active element.
· For reflectors and directors we are not applying any input .so the reflectors and directors are called as parasitic elements.
· Driven element and parasitic elements are placed parallel to each other and close to each other.
· The reflector is placed back side of the driven element which is longer than driven element and compare to the all element . The element infront of the driven element is director which is smaller than all elements.
2.FOLDED DIPOLE ANTENNA:
Two half wave dipoles folded and joint each other then the folded dipole is formed . One dipole is in continuous and another is break at the centre to feed the input.
· The advantage of the folded dipole antenna is it will provide high resistance in compared to normal dipole.
· The length of the dipole is lambda/2 and the spacing between the two dipole is very small.
· Due to applied voltage %u201CV%u201D the current %u201CI/2%u201D is flowing through each dipole.
Helical antenna is broadband vhf & uhf antenna . It provides CIRCULAR POLARIZATION.
· Consider a thick copper wire or tube is wounded in the form of helix.
· The input to the helix is given to the coaxial cable the inner conductor of coaxial cable is connected to helix and outer is connected to the ground.
HELICAL ANTENNA IS OPERATED IN TWO MODES
1. NORMAL MODE:
In the normal mode the maximum radiation is perpendicular to the axis of the helix . So it is called %u201CNORMAL MODE OR PERPENDICULAR MODE%u201D.
· The normal mode is obtained when the values of helix are very small in compared to wavelength i.e., N,S<<LAMBDA.
2. AXIAL MODE:
In axial mode the maximum radiation occurs parallel to the axis of the helix.
· The axial mode is occurs when the diameter of helix are approximately equal to the wave length.
· The circumference of helix is around one wave length and spacing between the turns around PI/4.
4.HORN ANTENNA :
Horn antenna is a wave guide of different cross section which flared (or) tampered into large opening is called as the horn antenna . One end is exicted and another end is opened.When a wave guide is used as a antenna it cannot radiates due to the mismatch of impedance wit free space . By flaring the one end we are getting the impedance matching as well as high directivity.
TYPES OF HORN ANTENNA :
Basically we have two types of horn antenna they are
· RECTANGULAR HORN ANTENNA.
· CIRCULAR HORN ANTENNA.
1.RECTANGULAR HORN ANTENNA:
Based on the direction of the flaring angle again the rectangular horn antenna classified into SECTORIAL and PYRAMIDAL HORN ANTENNA.
· Again sectorial horn antenna is divided into two parts they are E-PLANE and H-PLANE based on the direction of the E & H PLANE.
2.CIRCULAR HORN ANTENNA:
Based on the direction of the flaring angle again the circular horn antenna classified into CONICAL HORN ANTENNA and BIDIRECTIONAL HORN ANTENNA.