Sunday, August 7, 2011
Hei we are the rulers of the world..
Hei Im asfak. I born to be awesome. And my aim is to capture this damn world.. Come lets stand together. Hold my hand to create PEACE.. :D :D :D :D :D :D
Saturday, June 18, 2011
Friday, June 3, 2011
chemical formula
Chemical formula
From Wikipedia, the free encyclopedia
| Al2(SO4)3 |
|---|
| chemical formula, aluminium sulfate |
The chemical formula identifies each constituent element by its chemical symbol and indicates the number of atoms of each element found in each discrete molecule of that compound. If a molecule contains more than one atom of a particular element, this quantity is indicated using a subscript after the chemical symbol (although 18th-century books often used superscripts) and also can be combined by more chemical elements. For example, methane, a small molecule consisting of one carbon atom and four hydrogen atoms, has the chemical formula CH4. The sugar molecule glucose has six carbon atoms, twelve hydrogen atoms and six oxygen atoms, so its chemical formula is C6H12O6.
Chemical formulas may be used in chemical equations to describe chemical reactions. For ionic compounds and other non-molecular substances an empirical formula may be used, in which the subscripts indicate the ratio of the elements.
The 19th-century Swedish chemist Jöns Jacob Berzelius worked out this system for writing chemical formulas.
Friday, May 20, 2011
Monday, May 16, 2011
முதலாம் அபின் போர்
முதலாம் அபின் போர்http://tawp.in/r/1gou
கட்டற்ற கலைக்களஞ்சியமான விக்கிப்பீடியாவில் இருந்து.
| முதலாம் அபின் போர் | |||||||||
|---|---|---|---|---|---|---|---|---|---|
 The HEIC Nemesis destroying Chinese war junks in the Second Battle of Chuenpee, 7 January 1841 | |||||||||
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| பிரிவினர் | |||||||||
 ஐக்கிய இராச்சியம் |  சீனக் குவிங் பேரரசு | ||||||||
| தளபதிகள் | |||||||||
| சார்ள்ஸ் எலியட் அண்டனி பிளஸ்லேண்ட் | டாவோகுவாங் பேரரசு லின் சீசு | ||||||||
| Casualties source:[1] | |||||||||
முதலாம் அபின் போர் (First Opium War) என்பது சீனாவுக்குள் பலவந்தமாக அபின் எனும் போதைப்பொருள் வணிகச் சந்தையைசீனாவிற்குள் பலவந்தமாகத் திறப்பதற்கு பிரித்தானியா சீனாவிற்கு எதிராகத் தொடுத்தப் போராகும். இப்போரின் பின்னரே பிரித்தானியப் படைகள் ஹொங்கொங் தீவை கைப்பற்றிக்கொண்டது. இப்போரைமுதலாம் ஆங்கிலோ- சீனப் போர் (First Anglo-Chinese War) என்றும் அழைப்பர். இப்போரின் போது தென்சீனாவின் குவாங்தோவ் மகாணத்தின் கெண்டன் துறைமுகம் மற்றும் அதனை அண்டியப் பகுதிகள் பிரித்தானியப் படைகளால் அழித்தொழிக்கப்பட்டன. அதனைத் தொடர்ந்து பிரித்தானியப் படைகளால் ஹொங்கொங் தீவில் நிலைக்கொண்டன. அதன் பின்னர் நாஞ்சிங் உடன்படிக்கை எனும் உடன்படிக்கையின் படி சீனாவிடம் இருந்து ஹொங்கொங்கை பலவந்தமாக ஒப்புதல் மூலம் பிரித்தானியா பெற்று, பிரித்தானிய முடிக்குரிய குடியேற்றநாடுகளில் ஒன்றாக பிரகடனப் படுத்திக்கொண்டது.
பொருளடக்கம்[மறை] |
[தொகு]முதலாம் அபின் போர் வரலாறு
19 ஆம் நூற்றாண்டின் ஆரம்பக் காலம். பிரித்தானிய வணிக நிறுவனமான பிரித்தானியக் கிழக்கிந்தியக் கம்பனி சீனாவுடனான வணிகத் தொடர்பைக் கொண்டிருந்தது. தென்சீனப்பகுதியான குவாங்தோவ் மகாணத்தில் அமைந்திருந்த கெண்டன் துறைமுகத்தூடாகவே தமது வணிகத்தொடர்பைக் கொண்டிருந்தது. உலகிற்கு தேயிலையை அறிமுகப்படுத்தியவர்கள் சீனர்களாவர். சீனாவிடம் இருந்து தேயிலை கொள்முதல் செய்து ஐரோப்பிய நாடுகளில் விற்பனை செய்வதல் பிரித்தானியாவின் முதன்மை வணகங்களில் ஒன்றாக இருந்தது. குளிர் நாடுகளான ஐரோப்பிய நாடுகளில் தேயிலைக்கு பெரும் செல்வாக்கு இருந்தது. சீனாவில் இருந்து பெருமளவிலான தேயிலை ஏற்றுமதியை செய்துவந்த பிரித்தானியா, அதற்கு ஈடாக கைக்கடிகாரம், மணிக்கூடு போன்ற ஆடம்பரப் பொருட்களை சீனாவிற்குள் இறக்குமதி செய்தது. இந்த வணிகத்தில் சீனாவின் கைமேலோங்கி இருந்தது. சீனாவிடமிருந்து கொள்முதல் செய்யும் தேயிலையின் பெருமதிக்கு ஏற்றவாறு பிரித்தானியாவின் பொருட்களை சீனாவில் இறக்குமதி செய்ய முடியாத நிலை தோன்றியது. எனவே தேயிலையைச் சீனாவிடம் இருந்து கடன் வாங்கும் நிலை பிரித்தானியாவிற்கு தோன்றியது. இதனை ஈடு செய்யும் முகமாக இந்தி்யாவில், வங்காள தேசம் பகுதிகளில்அபின் போதைப்பொருள் உற்பத்தியைப் பெருக்கி அவற்றை சட்டவிரோதமான முறையில் சீனாவில் இறக்குமதி செய்தது. இந்த சட்டவிரோதமான கடத்தல் போதைப்பொருள் வணிகத்தில் பிரித்தானியா அதிக இலாபம் ஈட்டத்தொடங்கியது. அதேவேளை சீனாவில் பொதுமக்கள் இப்போதைப் பொருளுக்கு அடிமையானதுடன் பல சமூக சீர்கேடுகளும் எழத்தொடங்கின. இவ்வாறான அவலங்கள் குறித்தோ, அழிவுகள் குறித்தோ பிரித்தானிய எந்த அக்கறையும் கொள்ளவில்லை. அதன் நோக்கம் எப்படியாயினும் வெள்ளிக்காசுகளை குவிப்பதாகவே இருந்தது. அப்போது சீனாவில் குவிங் வம்ச பேரரசு ஆட்சியில் இருந்தது. சீனாவுக்குள் நடைப்பெற்று வரும் இந்த சட்டவிரோதமானதும் பொது மக்களுக்கும் தீங்கானதுமான போதைப்பொருள் வணிகத்தை குவிங் சீனப்பேரரசு அதிகார பூர்வமாகத் தடைச்செய்தது. இருப்பினும் பிரித்தானியாவால் தொடர்ந்து மேற்கொண்டுவரும் போதைப் பொருள் வணிகத்தை குவிங் பேரரசால் தடுத்து நிறுத்த முடியவில்லை.
[தொகு]குவாங்தோவ் சிறப்பு ஆளுநர்
அப்போது லின் சீசு (Lin Ze-xu) என்பவர் குவிங் பேரரசின், குவங்தோவ் மகாணத்தின் சிறப்பு ஆளுநராகப் (Special Commissioner of Guangzhou) பதவியேற்றார். இவர் சீனாவிற்குள் சட்டவிரோதமாக நடைப்பெற்றுவந்த போதைப்பொருள் வணிகத்தை தடுத்து நிறுத்துவதற்காக கடும் நடவடிக்கைகளை மேற்கொண்டார். அதேவேளை பிரித்தானியா தமது நாட்டிற்குள் அபின் புகைத்தலை தடைச் செய்திருந்தது. பிரித்தானியா தமது நாட்டில் அபின் போதைப்பொருள் பாவனையை தடைச்செய்துக்கொண்டு, அதனையே சீனாவிற்குள் சட்டவிரோதமாக விணியோகித்து அப்பாவி சீன மக்கள் அழிவுக்குள்ளாவதைக் கண்டு ஆத்திரமுற்றார். இந்தச் சட்டவிரோத அபின் வணிகத்தை உடனடியாக நிறுத்தும்படி விக்டோரியா மகாராணிக்கு எழுத்து மூலமாக அறிவித்தார். [2] குவிங் வம்ச சீனப்பேரரசும் மீண்டும் மீண்டும் தடை உத்தரவுகளை பிறப்பித்தவண்ணமே இருந்தது. ஆனால் இவை எதனையும் பிரித்தானியா ஒரு பொருட்டாகக்கொள்ளவில்லை. சீனப்பேரரசின் தடை உத்தரவுகளை மீறி தொடர்ந்து அபினி இறக்குமதியை சீனாவுக்குள் சட்டவிரோதமாக தொடர்ந்த வண்ணமே இருந்தது.
[தொகு]லின் சீசுவின் கடும் நடவடிக்கைகள்
குவாங்தோவ் சிறப்பு ஆளுநரான லின் சீசு இப்போதைப்பொருள் புகைப்போருக்கும், விற்பனைச் செய்வோருக்கும் எதிராக கடுமையான சட்டங்களை உருவாக்கி தண்டித்தார். இப்போதைப்பொருள் ஏற்படுத்தும் பாதிப்புகளையும், பக்கவிளைவுகளையும் மக்களுக்கு எடுத்துக்கூறி விழிப்புணர்வு நடவடிக்கைகளையும் மேற்கொண்டார். இவை எதுவும் நடைமுறைச் சாத்தியமாகவில்லை. பிரித்தானியாவின் போதைப்பொருள் கல்லக்கடத்தல் வணிகம் மேலும் மேலோங்கிக்கொண்டேப் போனது. இதனால் லின் சீசுவின் நடவடிக்கைகளும் கடுமையாகியது. குவாங்தொவ் மகாணத்தில் களஞ்சியப்படுத்திருந்த அபின்களை எல்லாம் தேடி தேடி அழிக்கத் தொடங்கினார். அபின் வணிகத்தில் ஈடுப்பட்டோருக்கு எதிராக கடுமையான நடவடிக்கைகளை எடுத்தார். அபின்கள் ஏற்றி வந்த கப்பல்களும் தாக்கப்பட்டன. அத்துடன் வெளிநாட்டு வணிகம் அனைத்தையும் இடைநிறுத்தினார்.
இதனை எதிர்த்தும் சீனாவிற்குள் பலவந்தமாக அபின் வணிகச் சந்தையை திறப்பதற்கும் பிரித்தானியா, பிரித்தானியக் கிழக்கிந்தியக் கம்பனி படைகளைக் கொண்டு சீனாவுக்கு எதிராகப் போர் தொடுத்தது. இதுவே முதலாம் அபின் போர்என்றழைக்கப்படுகின்றது. உலகில் போதைப்பொருள் வணிகத்திற்காக நடந்த முதல் போரும் இதுவே ஆகும்.
[தொகு]போரின் முடிவு
போரின் முடிவு பிரித்தானியப் துருப்புகள் வெற்றிபெற்றன. அதனைத் தொடர்ந்து பிரித்தானியப் படைகள்ஹொங்கொங் தீவைக் கைப்பற்றிக்கொண்டது. அதன் பின் நாஞ்சிங் உடன்படிக்கை எனும் உடன்படைக்கையில், சீனப்பேரரசை பலவந்தமாகப் பணியவைத்து பலவந்தமாக ஒப்புதல் பெறப்பட்டது. அந்த ஒப்பந்தங்களில் ஒன்றுஹொங்கொங் தீவை சீனப்பேரரசு பிரித்தானியாவிற்கு கையளித்தலாகும்.
[தொகு]
Sunday, March 13, 2011
Saturday, March 12, 2011
algebraic expression
ALGEBRAIC EXPRESSIONS
An algebraic expression is made up of the signs and symbols of algebra. These symbols include the Arabic numerals, literal numbers, the signs of operation, and so forth. Such an expression represents one number or one quantity. Thus, just as the sum of 4 and 2 is one quantity, that is, 6, the sum of c and d is one quantity, that is, c + d. Likewise
, ab, a - b, and so forth, are algebraic expressions each of which represents one quantity or number.
Longer expressions may be formed by combinations of the various signs of operation and the other algebraic symbols, but no matter how complex such expressions are they still represent one number. Thus the algebraic expression
is one number
The arithmetic value of any algebraic expression depends on the values assigned to the literal numbers. For example, in the expression 2x2 - 3ay, if x = -3, a = 5, and y = 1, then we have the following:
2x2 - 3ay = 2(-3)2 -3(5)(1)
= 2(9) - 15 = 18 - 15 = 3
Notice that the exponent is an expression such as 2x2 applies only to the x. If it is desired to indicate the square of 2x, rather than 2 times the square of x, then parentheses are used and the expression becomes (2x)2.
Practice problems. Evaluate the following algebraic expressions when a = 4, b = 2, c = 3, x = 7, and y = 5. Remember, the order of operation is multiplication, division, addition, and subtraction.
Answers:
1. 53
2. -29
3. 19
4. 53
TERMS AND COEFFICIENTS
The terms of an algebraic expression are the parts of the expression that are connected by plus and minus signs. In the expression 3abx + cy - k, for example, 3abx, cy, and k are the terms of the expression.
An expression containing only one term, such as 3ab, is called a monomial (mono means one). A binomial contains two terms; for example, 2r + by. A trinomial consists of three terms. Any expression containing two or more terms may also be called by the general name, polynomial (poly means many). Usually special names are not given to polynomials of more than three times. The expression x3 - 3x2 + 7x + 1 is a polynomial of four terms. The trinomial x2 + 2x + 1 is an example of a polynomial which has a special name.
Practice problems. Identify each of the following expressions as a monomial, binomial, trinomial, or polynomial. (Some expressions may have two names.)
Answers:
1. Monomial
2. Trinomial (also polynomial)
3. Monomial
4. Polynomial
5. Binomial (also polynomial)
6. Binomial (also polynomial)
In general, a COEFFICIENT of a term is any factor or group of factors of a term by which the remainder of the term is to be multiplied. Thus in the term 2axy, 2ax is the coefficient of y, 2a is the coefficient of xy, and 2 is the coefficient of axy. The word "coefficient" is usually used in reference to that factor which is expressed in Arabic numerals. This factor is sometimes called the NUMERICAL COEFFICIENT. The numerical coefficient is customarily written as the first factor of the term. In 4x, 4 is the numerical coefficient, or simply the coefficient, of x. Likewise, in 24xy2, 24 is the coefficient of xy2 and in 16(a + b), 16 is the coefficient of (a + b). When no numerical coefficient is written it is understood to be 1. Thus in the term xy, the coefficient is 1.
COMBINING TERMS
When arithmetic numbers are connected by plus and minus signs, they can always be combined into one number. Thus,
Here three numbers are added algebraically (with due regard for sign) to give one number. The terms have been combined into one term. Terms containing literal numbers can be combined only if their literal parts are the same. Terms containing literal factors in which the same letters are raised to the same power are called like terms. For example, 3y and 2y are like terms since the literal parts are the same. Like terms are added by adding the coefficients of the like parts. Thus, 3y + 2y = 5y just as 3 bolts + 2 bolts = 5 bolts. Also 3a2b and a2b are like; 3a2b + a2b = 4a2b and 3a2b - a2b = 2a2b. The numbers ay and by are like terms with respect to y. Their sum could be indicated in two ways: ay + by or (a + b)y . The latter may be explained by comparing the terms to denominate numbers. For instance, a bolts + b bolts = (a + b) bolts.
Like terms are added or subtracted by adding or subtracting the numerical coefficients and placing the result in front of the literal factor, as in the following examples:
7x2 - 5x2 = (7 - 5)x2 = 2x2
5b2x - 3ay2 - 8b2x + 10ay2 = -3b2x + 7ay2
Dissimilar or unlike terms in an algebraic expression cannot be combined when numerical values have not been assigned to the literal factors. For example, -5x2 + 3xy - 8y2 contains three dissimilar terms. This expression cannot be further simplified by combining terms through addition or subtraction. The expression may be rearranged as x(3y - 5x) - 8y2 or y(3x - 8y) - 5x2, but such a rearrangement is not actually a simplification.
Practice problems. Combine like terms in the following expression:
Answers:
An algebraic expression is made up of the signs and symbols of algebra. These symbols include the Arabic numerals, literal numbers, the signs of operation, and so forth. Such an expression represents one number or one quantity. Thus, just as the sum of 4 and 2 is one quantity, that is, 6, the sum of c and d is one quantity, that is, c + d. Likewise
, ab, a - b, and so forth, are algebraic expressions each of which represents one quantity or number.Longer expressions may be formed by combinations of the various signs of operation and the other algebraic symbols, but no matter how complex such expressions are they still represent one number. Thus the algebraic expression
is one numberThe arithmetic value of any algebraic expression depends on the values assigned to the literal numbers. For example, in the expression 2x2 - 3ay, if x = -3, a = 5, and y = 1, then we have the following:
2x2 - 3ay = 2(-3)2 -3(5)(1)
= 2(9) - 15 = 18 - 15 = 3
Notice that the exponent is an expression such as 2x2 applies only to the x. If it is desired to indicate the square of 2x, rather than 2 times the square of x, then parentheses are used and the expression becomes (2x)2.
Practice problems. Evaluate the following algebraic expressions when a = 4, b = 2, c = 3, x = 7, and y = 5. Remember, the order of operation is multiplication, division, addition, and subtraction.
Answers:
1. 53
2. -29
3. 19
4. 53
TERMS AND COEFFICIENTS
The terms of an algebraic expression are the parts of the expression that are connected by plus and minus signs. In the expression 3abx + cy - k, for example, 3abx, cy, and k are the terms of the expression.
An expression containing only one term, such as 3ab, is called a monomial (mono means one). A binomial contains two terms; for example, 2r + by. A trinomial consists of three terms. Any expression containing two or more terms may also be called by the general name, polynomial (poly means many). Usually special names are not given to polynomials of more than three times. The expression x3 - 3x2 + 7x + 1 is a polynomial of four terms. The trinomial x2 + 2x + 1 is an example of a polynomial which has a special name.
Practice problems. Identify each of the following expressions as a monomial, binomial, trinomial, or polynomial. (Some expressions may have two names.)
Answers:
1. Monomial
2. Trinomial (also polynomial)
3. Monomial
4. Polynomial
5. Binomial (also polynomial)
6. Binomial (also polynomial)
In general, a COEFFICIENT of a term is any factor or group of factors of a term by which the remainder of the term is to be multiplied. Thus in the term 2axy, 2ax is the coefficient of y, 2a is the coefficient of xy, and 2 is the coefficient of axy. The word "coefficient" is usually used in reference to that factor which is expressed in Arabic numerals. This factor is sometimes called the NUMERICAL COEFFICIENT. The numerical coefficient is customarily written as the first factor of the term. In 4x, 4 is the numerical coefficient, or simply the coefficient, of x. Likewise, in 24xy2, 24 is the coefficient of xy2 and in 16(a + b), 16 is the coefficient of (a + b). When no numerical coefficient is written it is understood to be 1. Thus in the term xy, the coefficient is 1.
COMBINING TERMS
When arithmetic numbers are connected by plus and minus signs, they can always be combined into one number. Thus,
Here three numbers are added algebraically (with due regard for sign) to give one number. The terms have been combined into one term. Terms containing literal numbers can be combined only if their literal parts are the same. Terms containing literal factors in which the same letters are raised to the same power are called like terms. For example, 3y and 2y are like terms since the literal parts are the same. Like terms are added by adding the coefficients of the like parts. Thus, 3y + 2y = 5y just as 3 bolts + 2 bolts = 5 bolts. Also 3a2b and a2b are like; 3a2b + a2b = 4a2b and 3a2b - a2b = 2a2b. The numbers ay and by are like terms with respect to y. Their sum could be indicated in two ways: ay + by or (a + b)y . The latter may be explained by comparing the terms to denominate numbers. For instance, a bolts + b bolts = (a + b) bolts.
Like terms are added or subtracted by adding or subtracting the numerical coefficients and placing the result in front of the literal factor, as in the following examples:
7x2 - 5x2 = (7 - 5)x2 = 2x2
5b2x - 3ay2 - 8b2x + 10ay2 = -3b2x + 7ay2
Dissimilar or unlike terms in an algebraic expression cannot be combined when numerical values have not been assigned to the literal factors. For example, -5x2 + 3xy - 8y2 contains three dissimilar terms. This expression cannot be further simplified by combining terms through addition or subtraction. The expression may be rearranged as x(3y - 5x) - 8y2 or y(3x - 8y) - 5x2, but such a rearrangement is not actually a simplification.
Practice problems. Combine like terms in the following expression:
Answers:
logic gates
Logic gates
- The AND gate is an electronic circuit that gives a high output (1) only if all its inputs are high. A dot (.) is used to show the AND operation i.e. A.B. Bear in mind that this dot is sometimes omitted i.e. AB
- The OR gate is an electronic circuit that gives a high output (1) if one or more of its inputs are high. A plus (+) is used to show the OR operation.
- The NOT gate is an electronic circuit that produces an inverted version of the input at its output. It is also known as an inverter. If the input variable is A, the inverted output is known as NOT A. This is also shown as A', or A with a bar over the top, as shown at the outputs. The diagrams below show two ways that the NAND logic gate can be configured to produce a NOT gate. It can also be done using NOR logic gates in the same way.
- This is a NOT-AND gate which is equal to an AND gate followed by a NOT gate. The outputs of all NAND gates are high if any of the inputs are low. The symbol is an AND gate with a small circle on the output. The small circle represents inversion.
- This is a NOT-OR gate which is equal to an OR gate followed by a NOT gate. The outputs of all NOR gates are low if any of the inputs are high.
- The symbol is an OR gate with a small circle on the output. The small circle represents inversion.
- The 'Exclusive-OR' gate is a circuit which will give a high output if either, but not both, of its two inputs are high. An encircled plus sign (
) is used to show the EOR operation.
Digital systems are said to be constructed by using logic gates. These gates are the AND, OR, NOT, NAND, NOR, EXOR and EXNOR gates. The basic operations are described below with the aid of truth tables.
EXNOR gate
The 'Exclusive-NOR' gate circuit does the opposite to the EOR gate. It will give a low output if either, but not both, of its two inputs are high. The symbol is an EXOR gate with a small circle on the output. The small circle represents inversion.
The NAND and NOR gates are called universal functions since with either one the AND and OR functions and NOT can be generated.
Note:
A function in sum of products form can be implemented using NAND gates by replacing all AND and OR gates by NAND gates.
Table 1: Logic gate symbols
- A function in product of sums form can be implemented using NOR gates by replacing all AND and OR gates by NOR gates.
Table 2 is a summary truth table of the input/output combinations for the NOT gate together with all possible input/output combinations for the other gate functions. Also note that a truth table with 'n' inputs has 2n rows. You can compare the outputs of different gates.
Table 2: Logic gates representation using the Truth table
Example
A NAND gate can be used as a NOT gate using either of the following wiring configurations.
(You can check this out using a truth table.)
microscope
The first microscope to be developed was the optical microscope, although the original inventor is not easy to identify. An early microscope was made in 1590 in Middelburg, Netherlands.[1] Two eyeglass makers are variously given credit: Hans Lippershey (who developed an early telescope) and Hans Janssen. Giovanni Faber coined the name microscope for Galileo Galilei's compound microscope in 1625 [2] (Galileo had called it the "occhiolino" or "little eye").
It was not until the 1660s and 1670s that the microscope was used extensively for research in Italy, Holland and England. Marcelo Malpighi in Italy began the analysis of biological structures beginning with the lungs. Robert Hooke's Micrographia had a huge impact, largely because of its impressive illustrations. The greatest contribution came from Antoni van Leeuwenhoek who discovered red blood cells and spermatozoa and helped popularise microscopy as a technique. On 9 October 1676, Leeuwenhoek reported the discovery of micro-organisms.[3]
In 1893 August Köhler developed a key technique for sample illumination, Köhler illumination, which is central to modern light microscopy. This method of sample illumination gives rise to extremely even lighting and overcomes many limitations of older techniques of sample illumination. Further developments in sample illumination came from Fritz Zernike in 1953 and George Nomarski 1955 for their development of phase contrast and differential interference contrast illumination which allow imaging of transparent samples.
A Flea as imaged using an electron microscope
Development of the transmission electron microscope was quickly followed in 1935 by the development of the scanning electron microscope by Max Knoll.[4]
Electron microscopes quickly became popular following the Second World War. Ernst Ruska, working at Siemens developed the first commercial transmission electron microscope and major scientific conferences on electron microscopy started being held in the 1950s. In 1965 the first commercial scanning electron microscope was developed by Professor Sir Charles Oatley and his postgraduate student Gary Stewart and marketed by the Cambridge Instrument Company as the "Stereoscan".
The rise of fluorescence microscopy drove the development of a major modern microscope design, the confocal microscope. The principle was patented in 1957 by Marvin Minsky, although laser technology limited practical application of the technique. It was not until 1978 when Thomas and Christoph Cremer developed the first practical confocal laser scanning microscope and the technique rapidly gained popularity through the 1980s.
Types of microscopesMicroscopes can be separated into several different classes. One grouping is based on what interacts with the sample to generate the image, i.e., light (optical microscopes), electrons (electron microscopes) or a probe (scanning probe microscopes). Alternatively microscopes can be classed on whether they analyse the sample via a scanning point (confocal optical microscopes, scanning electron microscopes and scanning probe microscopes) or analyze the sample all at once (wide field optical microscope and transmission electron microscopes).
The wide field optical microscope and transmission electron microscope use the theory of lenses (optics for light microscopes and electromagnet lenses for electron microscopes) in order to magnify the image generated by the passage of a wave through the sample, or reflected by the sample. The waves used are electromagnetic (in optical microscopes) or electron beams (in electron microscopes). Resolution in these microscopes is limited by the wavelength of the radiation used to image the sample, shorter wavelengths allow a higher resolution.
Scanning optical and electron microscopes, like the confocal microscope and scanning electron microscope, use lenses to focus a spot of light/electrons onto the sample then analyze the reflected and/or transmitted waves. The point is then scanned over the sample to analyze a rectangular region. Magnification of the image is achieved by displaying the data from scanning a small sample area on a large screen. These microscopes have the same resolution limit as wide field optical and electron microscopes.
Scanning probe microscopes also analyze a single point in the sample and then scan the probe over a rectangular sample region to build up an image. As these microscopes do not use electromagnetic or electron radiation for imaging they are not subject to the same resolution limit as the optical and electron microscopes described above.
Sarfus, a recent optical technique increases the sensitivity of standard optical microscope to a point it becomes possible to directly visualize nanometric films (down to 0.3 nanometre) and isolated nano-objects (down to 2 nm-diameter). The technique is based on the use of non-reflecting substrates for cross-polarized reflected light microscopy.
CBP Office of Field Operations agent checking the authenticity of a travel document at an international airport using a stereo microscopeUltraviolet light enables the resolution of microscopic features, as well as to image samples that are transparent to the eye. Near infrared light images circuitry embedded in bonded silicon devices, as silicon is transparent in this region. Many wavelengths of light, ranging from the ultraviolet to the visible are used to excite fluorescence emission from objects for viewing by eye or with sensitive cameras.
Phase contrast microscopy is an optical microscopy illumination technique in which small phase shifts in the light passing through a transparent specimen are converted into amplitude or contrast changes in the image. A phase contrast microscope does not require staining to view the slide. This microscope made it possible to study the cell cycle.
The traditional optical microscope has recently been modified into a digital microscope, where, instead of directly viewing the object, a charge-coupled device (CCD) is used to record the image, which is then displayed on a computer monitor.
[edit] The rise of modern light microscopy
See also: optical microscope
The first detailed account of the interior construction of living tissue based on the use of a microscope did not appear until 1644, in Giambattista Odierna's L'occhio della mosca, or The Fly's Eye.[3]It was not until the 1660s and 1670s that the microscope was used extensively for research in Italy, Holland and England. Marcelo Malpighi in Italy began the analysis of biological structures beginning with the lungs. Robert Hooke's Micrographia had a huge impact, largely because of its impressive illustrations. The greatest contribution came from Antoni van Leeuwenhoek who discovered red blood cells and spermatozoa and helped popularise microscopy as a technique. On 9 October 1676, Leeuwenhoek reported the discovery of micro-organisms.[3]
In 1893 August Köhler developed a key technique for sample illumination, Köhler illumination, which is central to modern light microscopy. This method of sample illumination gives rise to extremely even lighting and overcomes many limitations of older techniques of sample illumination. Further developments in sample illumination came from Fritz Zernike in 1953 and George Nomarski 1955 for their development of phase contrast and differential interference contrast illumination which allow imaging of transparent samples.
[edit] Electron microscopy
See also: electron microscope
In the early 1900s a significant alternative to light microscopy was developed, using electrons rather than light to generate the image. Ernst Ruska started development of the first electron microscope in 1931 which was the transmission electron microscope (TEM). The transmission electron microscope works on the same principle as an optical microscope but uses electrons in the place of light and electromagnets in the place of glass lenses. Use of electrons instead of light allows a much higher resolution.Development of the transmission electron microscope was quickly followed in 1935 by the development of the scanning electron microscope by Max Knoll.[4]
Electron microscopes quickly became popular following the Second World War. Ernst Ruska, working at Siemens developed the first commercial transmission electron microscope and major scientific conferences on electron microscopy started being held in the 1950s. In 1965 the first commercial scanning electron microscope was developed by Professor Sir Charles Oatley and his postgraduate student Gary Stewart and marketed by the Cambridge Instrument Company as the "Stereoscan".
[edit] Scanning probe microscopy
See also: scanning probe microscope
The 1980s saw the development of the first scanning probe microscopes. The first was the scanning tunneling microscope in 1981, developed by Gerd Binnig and Heinrich Rohrer. This was closely followed in 1986 with Gerd Binnig, Quate, and Gerber's invention of the atomic force microscope.[edit] Fluorescence and light microscopy
The most recent developments in light microscope largely centre on the rise of fluorescence microscopy in biology. During the last decades of the 20th century, particularly in the post-genomic era, many techniques for fluorescent labeling of cellular structures were developed. The main groups of techniques are small chemical staining of cellular structures, for example DAPI to label DNA, use of antibodies conjugated to fluorescent reporters, see immunofluorescence, and fluorescent proteins, such as green fluorescent protein. These techniques use these different fluorophores for analysis of cell structure at a molecular level in both live and fixed samples.The rise of fluorescence microscopy drove the development of a major modern microscope design, the confocal microscope. The principle was patented in 1957 by Marvin Minsky, although laser technology limited practical application of the technique. It was not until 1978 when Thomas and Christoph Cremer developed the first practical confocal laser scanning microscope and the technique rapidly gained popularity through the 1980s.
Main article: Microscopy#Sub-diffraction techniques
Much current research (in the early 21st century) on optical microscope techniques is focused on development of superresolution analysis of fluorescently labeled samples. Structured illumination can improve resolution by around two to four times and techniques like stimulated Emission Depletion microscopy are approaching the resolution of electron microscopes.[edit] Types
The wide field optical microscope and transmission electron microscope use the theory of lenses (optics for light microscopes and electromagnet lenses for electron microscopes) in order to magnify the image generated by the passage of a wave through the sample, or reflected by the sample. The waves used are electromagnetic (in optical microscopes) or electron beams (in electron microscopes). Resolution in these microscopes is limited by the wavelength of the radiation used to image the sample, shorter wavelengths allow a higher resolution.
Scanning optical and electron microscopes, like the confocal microscope and scanning electron microscope, use lenses to focus a spot of light/electrons onto the sample then analyze the reflected and/or transmitted waves. The point is then scanned over the sample to analyze a rectangular region. Magnification of the image is achieved by displaying the data from scanning a small sample area on a large screen. These microscopes have the same resolution limit as wide field optical and electron microscopes.
Scanning probe microscopes also analyze a single point in the sample and then scan the probe over a rectangular sample region to build up an image. As these microscopes do not use electromagnetic or electron radiation for imaging they are not subject to the same resolution limit as the optical and electron microscopes described above.
[edit] Optical
Main article: Optical microscope
The most common type of microscope—and the first invented—is the optical microscope. This is an optical instrument containing one or more lenses producing an enlarged image of a sample placed in the focal plane. Optical microscopes have refractive glass and occasionally of plastic or quartz, to focus light into the eye or another light detector. Mirror-based optical microscopes operate in the same manner. Typical magnification of a light microscope, assuming visible range light, is up to 1500x with a theoretical resolution limit of around 0.2 micrometres or 200 nanometres. Specialized techniques (e.g., scanning confocal microscopy, Vertico SMI) may exceed this magnification but the resolution is diffraction limited. The use of shorter wavelengths of light, such as the ultraviolet, is one way to improve the spatial resolution of the optical microscope, as are devices such as the near-field scanning optical microscope.Sarfus, a recent optical technique increases the sensitivity of standard optical microscope to a point it becomes possible to directly visualize nanometric films (down to 0.3 nanometre) and isolated nano-objects (down to 2 nm-diameter). The technique is based on the use of non-reflecting substrates for cross-polarized reflected light microscopy.
Phase contrast microscopy is an optical microscopy illumination technique in which small phase shifts in the light passing through a transparent specimen are converted into amplitude or contrast changes in the image. A phase contrast microscope does not require staining to view the slide. This microscope made it possible to study the cell cycle.
The traditional optical microscope has recently been modified into a digital microscope, where, instead of directly viewing the object, a charge-coupled device (CCD) is used to record the image, which is then displayed on a computer monitor.
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