Ashland University

 Ashland University is located in the state of Ohio in the mideastern part of the United states, below the Great Lakes system. The small city of Ashland is about an hour's drive from the largest city of Cleveland and Columbus. The 120-acre (49 hectare) campus is one of the most beautiful in the state. The area around Ashland offers summer recreation activities. Four distinct seasons provide a variety of weather. Average temperatures throughout the seasons is from a low of -8 degree celcius to a high of 27 degree celcius.

Education:

Ashland University was founded in 1878, in a small private university that stresses " Accent on the Individual." Its program emphasize the liberal arts, sciences and career-oriented programs. The University offers more than sixty majors, including business, computer science, hotel and restaurant management, environmental science, and communications. The largest number of students are enrolled in business and education. The programs are enhanced by the University Honours Program, the Ashbrook Center (political science/public affairs), and the Gill Center (economics education). The University provides extensive access to the computer facilities for students, including a link to the University computer system in every residence hall room. The academic yeal consists of two semesters. Financial aid of $2000 to $8000 is available for students with a GPA of 2.75 or higher on a 4.0 scale. 

Campus life: 

Ashland's on-campus, undergraduate enrollment numbers 2200 full time students. 700 graduate students are enrolled in evening and weekend programs.  Total enrollment  including all program centers, is 6000. 80% of on-campus students are from Ohio; others come from 25 states and 33 countries. The University offers a variety of housing options in its seven residence halls and senior appartments. All residence hall rooms are wired for Internet access. Residence halls remain open all year, including vacation periods. International students may request to live with American students. The office of student Activities, which won national awards for programming for seven years, coordinates a wide range of activities and organizations, including academic clubs, campus services, special interest organizations, student government, religious life, media/publications and cultural events. The University has extensive sports programme and activities and is a member of the NCCA Division II athletic program. 

For International Students:

The University offers extensive support services for international students, including airport pickup, special advisers, and special orientation sessions. The most popular programs for international students are the international club, the friendship families programand the World Cafe. Health care is provided in campus. Ashland University and the surrounding community have a very low crime rate, which makes this an ideal place to live and learn.

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Health Insurance

Insurance Companies provide various types of health care insurance, including coverage for hospital stays, visits to physicians and surgical procedures. They serve as intermediaries between the health care providers and receipients of health care. Since the cost of health care is so high, individual seek health care insurance as a form of protection against conditions that cause them to incur large health care expenses.

Types of Health Care Plan:

Insurance Companies provide two types of health care plans : managed health care plans and indemnity plans. The primary difference between the two types is that individuals who are insured by a managed care plan may choose only specified health care providers ( hospital  and physicians) who participate in the plan. Individuals who are insured under an indemnity plan can usually choose any provider of health care services. The payment system of two types of plans also distinctly different. The premiums for managed health care plans are generally lower, and payment is typically made directly to the provider. In contrast, indemnity plans reimburse insured individuals for the health care expenses they incur. 

Exposure to Risk:

The major types of risk faced by health insurance companies are:

a. Interest rate risk,

b. Credit risk, 

c. Market risk and

d. Liquidity risk.

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International Education

A wonderful time to be working is now in the field of International higher Education. Government, academia and the private sector never have been more engaged in the vigorous dialogue of how to attract and welcome international students to the United States. New initiatives from the department of State, Education and Commerce and other agencieshave made the U.S even more welcoming. New college programs are becoming more global and adventorous. Even the private sector have become involved, believing that it too may have a role as an engine for change.
Suddenly it seems that every American Campus wants to "internationalize," and many vie for the honour of being recognized as the most internationalized. U.S students as well as international students, look careful for indications that an institution is truely international. The creative energy that comes from the involvement of so many sectors has produced some exciting innovations.
United States has traditionally enrolled many more  of the world's students that any other nation, also it continues to do so today. According to the most recent annual survey, more than 565000 students from other nations are currently studying in the U.S. The diversity, size, prestige and excellence of the higher education system in the United States offer powerful incentives for we like students and other academically gifted young people from around the world who want to have the best educational experience possible.
The U.S higher education system is quite different from most others- largely because the federal government plays a minor role. We have a vast system of community colleges, four-year liberal arts schools, public and private institutions and major Universities granting doctoral degrees. Along with a number of specialized schools at both the undergraduate and graduate levels- all a part of the U.S higher education system. To help us to navigate through the system, the state Department offers an educational advertising network providing unbiased information to all- the EDUCATION USA network. Each year they provide advice and assistance to the hundreds of thousands of prospective students wishing to study in United States. EducationUSA advertising centers are staffed by professional advisers. These centers actively promote U.S higher Education by offering comprehensive, objective, accurate and timely information about educational opportunities in the United States and guidance to the qualified individuals on how best to access those opportunitues. U.S colleges and Universities offer the possibility of educational exellence and we hope you choose to take advantage of this incomparable resource.

Some Recognized Colleges and Universities in United States:

1. Adelphi University (New York)

2. Adrian College (michigan)

3. Boston University (Massachusetts)

4. Bryant University (Rhode Island)

5. Chapman University (California)

6. Colorado State University (Colorado)

7. Florida Gulf Coast University (Florida)

8. Hawai'i Pacific University (Hawaii)

9. Northern Arizona University (Arizona)

10. Johnson and Wales University (Rhode Island)

11. Oklahoma State University (Oklahoma)

12. Marshal University (West Virgina)

13. Fordham University (New York)

14. Hofstra University (New York)

Some Internationally Recognized Universities:

1. Ashford University

2. Northwestern University

3. Harvard University

4. Columbia University

5. Oregon State University

6. Stanford University

7. Strayer University

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Life Insurance Companies

Life Insurance Companies compensate (provide benefits to) the beneficiary of a policy upon the policy holder's death. They charge policyholders a premium that should reflect the probability of making a payment to the beneficiary as well as the size and timing of the payment. Despite the difficulties of forcasting the life expectancy of a given individual, life insurance companies have historically forecasted with reasonable accuracy the benefits they will have to provide beneficiaries. Because they hold a large portfolio of policies, these companies use actuarial tables and mortality figures to forecast the percentage of policies that will require compensation over a given period, based on characteristics such as the age distribution of policy holders.

Life insurance companies also commonly offer employees of a corporation a group life policy. This service has become quite popular and has generated a large volume of business in recent years. Group policies can be provided at a low cost because of the high volume.

Types of Life Insurance:
Some of the more common types of life insurance policies aredescribed here:

Whole Life Insurance:
From the perspective of the insured  policy holders, whole life insurance protects them until death or as long as the premiums are promptly paid. In addition, a whole policy provides a form of savings to the policy holder. It builds a cash value that the policy holders is entitled to even if the policy is cancelled. From the perspective of the life insurance company, whole life policies generate periodic (typically, quarterly and semiannual) premiums that can be invested until the policy holder's death, when benefits are paid to the beneficiary. The amount of benefits are paid to the beneficiary. The amount of benefits is typically fixed.
Present value of benefits on whole life policy= L * mt * PVIFAr,n
where, L= Amount of each policy
             mt= Mortality rate
              n= number of year
              r= cost of money

Term Insurance: 
Term Insurance is temporary, providing insurance only over a specified term and doesnot build a cash value for policy holders. The premiums paid represent only insurance, not savings. Term insurance, however, is signigicantly less expensive than whole life insurance. Policy holders must compare the cash value of whole life insurance to the additional costs to determine whether it is preferable to term insurance. Those who prefer to invest their savings themselves will likely opt for term insurance.
People who need more insurance now than later may choose decreasing term insurance, in which the benefits paid to the beneficiary decrease over time. Families with mortgages commonly select this form of insurance. As time passes, the mortgage balance decreases, and the family is more capable of surviving without the breadwinner's earnings. Thus, less compensation is needed later years.


Universal Life Insurance:
Universal life insurance combines the features of term and whole life insurance. It specifies a period of time over which the policy will exist but also builds a cash value for the policy holder over time. Interest is accumulated from the cash value until the policy holder uses those funds. Universal life insurance allows felexibility on the size and timing of the premiums too. The growth in a policy's cash value is dependent on the place of the premiums. The premium payment is divided into two portions. The first is used to pay the death benefit identified in the policy and to cover any administrative expenses. The second is used for investments and reflects savings for the policy holder.

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Insurance Companies in Nepal

There are altogether 25 insurance companies established under Insurance Act 1992. Among these, 8 offer life insurance services, 16 perform non-life insurance services and one company rendered both life as well as non-life Insurance services.

List of Insurance Companies

Life Insurance Companies:
1. National Life Insurance Company Ltd
2. Nepal Life Insurance Company Ltd
3. Life Insurance Corporation (Nepal) Ltd
4. American Life Insurance Company Ltd
5. Gurans Life Insurance Company Ltd
6. Surya Life Insurance Company Ltd
7. Prime Life Insurance Company Ltd
8. Asian Life Insurance Company Ltd

Non-Life Insurance Companies:
9. Nepal Insurance Company Ltd
10. The Oriental Insurance Company Ltd
11. National Insurance Company Ltd
12. Himalayan General Insurance Company Ltd
13. United Insurance Company (Nepal) Ltd
14. Premier Insurance Company (Nepal) Ltd
15. Everest Insurance Company Ltd
16. Neco Insurance Company Ltd
17. Sagarmatha Insurance Company Ltd
18. Alliance Insurance Company Ltd
19. NB Insurance Company Ltd
20. Prudential Insurance Company Ltd
21. Shikhar Insurance Company Ltd
22. Lumbini General Insurance Company Ltd
23. NLG Insurance Company Ltd
24. Siddhartha Insurance Ltd

Life and Non-life:
25. Rastriya Bima Samsthan

According to the ownership structure, 3 insurance companies are operating under foreign investment and 3 insurance companies are in joint ventures with foreign insurance companies. Likewise, 18 insurance companies are in private sectors whereas one company is under the government ownership. Based on the financial statistics received from the insurance Board, total assets/liabilities of these companies increased by 28.2 percent from last year to Rs. 47.46 billion in mid-july 2010. Total premium collection of these companies is estimated at Rs. 15.40 billion by mid-july 2010. Such collection was Rs. 10.90 billion previous year.

Insurance Companies

Insurance Companies provide various forms of insurance and investment services to individual and charge a fee (called a premium) for this financial service. In general, the insurance provides a payment to the insured (or a named beneficiary) under conditions specified by the insurance policy contract.These conditions typically result in expenses or lost income, so the insurance is a means of financial protection. It reduces the potential financial damage incurred by individuals or firms due to specified conditions.

Common types of insurance offered by insurance companies include:
Life insurance,
Property and Casualty insurance,
Health insurance and
Business insurance.
Many insurance companies offer multiple type of insurance.

An individual's decision to purchase insurance may be influenced by the likelihood of the conditions that would result in receiving an insurance payment. Individuals who are more exposed to specific conditions that cause financial damage will purchase insurance against those conditions. Consequently, the insurance industry faces an adverse selection problem, meaning that those who are most likely to need insurance are most likely to purchase it. Furthermore, insurance can cause the insured to take more risks because they are protected. This is known as the moral hazard problem in the insurance industry.

Insurance companies employ underwriters to calculate the risks of specific insurance policies. The companies decide what types of policies to offer based on the potential level of claims to be paid on those policies and the premiums that they can charge.

Money Market Funds

Money market funds are also known as money market mutual funds in the U.S Money market funds are not in practice in Nepal. These instiutions issue shares that are redeemable at a fixed price (usually 1$) by writing checks. For example, if you buy 5000 shares for $5000, the money market fund uses these funds to invest in short term money market securities (treasury bills, certificates of deposit, commercial paper) that provide you with interest payments. In addition, you are able to write checks up to the $5000 held as shares in the money market fund. Although money market fund shares effectively function as checking account deposits that earn interest, they are not legally deposits and so are not subject to reserve requirements or prohibitions on interest payments.
For this reasons, they can pay higher interest rates than deposit at the banks. The first money market mutual fund was created by two Wall Street mavericks, Bruce Bent and Henry Brown in 1971. In 1977, money market mutual fund has assets under $4 billion; in 1978, their assets climbed to close to $10 billion; in 1979, to over $40 billion. And in 1982, to $230 billion. Currently, their assets are around $2 trillion. To say the least, money market mutual funds have been a successful innovation, which is precisely that we would have anticipated to happen in the late 1970s and early 1980s when investment rates took off past Regulation Q roofs.

Metabolism

All chemical changes occurring in a living cell are called metabolism. Metabolism may be anabolism or catabolism. Anabolism is the process of synthesis of complex chemical molecule from simpler ones. Photosynthesis is an example of anabolism. Catabolism is the process of breaking down of a large and a complex molecule into the simple form. Respiration and digestion are the example of catabolism .

Anabolism and catabolism together are called metabolism . Anabolism is called a constructive process and catabolism is called the destructive process. Metabolism is indicated by the following processes taking places in the body.

a.      Formation of the necessary cells and tissues takes place in the body  as a result of the chemical reaction of various nutritious food.

b.      The blood cells and tissues  become useless  in the body .

Nutrition in the Human body:

Human beings like other animals are unable to prepare their own food so, the nutrition in the human beings is heterotropic. The human being depend on plants directly or indirectly for their food.

Digestive System in Human:

Digestion is a catabolic process or the process of breaking down of complex food materials into simple forms which can  be directly absorbed by the body. The organs concerned with digestion is called digestive system. The digestive system of human body consist of mouth, alimentary canal and the anus.

Mouth:

It is an opening through which food is taken inside the body. The food mixes with saliva inside the mouth and here the mechanical break down food occurs by the help of teeth and tongue. Saliva contains the enzyme ptyalin which helps to break down the carbohydrate partially to the glucose.

Alimentary Canal:

The alimentary canal is basically a long tube extending from the mouth to anus. It is necessary to move the foods in a regulated manner along the digestive tube so that it can be processed properly in each part .  The linings of canal have muscles that contract rhythmically in order to puss the food forward. These peristaltic movements occur all along the gut. Alimentary canal has the following parts:

a.      Food pipe or oesophagus

b.      Stomach

c.       Small intestine

d.      Large intestine

e.      Anus

Food Pipe or Oesophagus:

The food after chewing in the mouth passes to stomach through the food pipe or oesophagus.

Stomach:

The stomach is a large organ which expands when the food enters in it. The muscular walls of stomach helps in mixing the food thoroughly with more digestive juices. The digestive functions are carried out by the gastric glands present in the wall of stomach. The gastric gland release:

a.      Hydrochloric acid

b.      A protein digesting enzyme called protein

c.       Mucus

The hydrochloric acid creates an acidic medium which facilates the action of enzyme pepsin. It also kills the bacteria present in the food.

Life Insurance

Life insurance is intended to bear the insurance against unexpected financial losses caused by the death of his too fast or too long . Here illustrated that in life insurance, the risks faced are :

The risk of death Someone living too long This is, of course, will bring a lot of aspects, if the risks inherent in a person is not insured with insurance companies. For example guarantee for offspring, a father that died prematurely or with a sudden , the child will not be neglected in his life .

It could also happen to a person who has reached the age ketuaannya and not being able to earn a living or pay for their children , then buy life insurance, the risks that may be suffered in terms of lost opportunities to earn a living will be covered by insurance companies . It turns out here that do good life insurance agency with the primary objective is to assume or guarantee the person against financial losses .

Life insurance is a legal contract between two parties, namely the insurance company and the policyholder . This ensures that the recipient receives financial support in the event of the insured 's death or accident . Term insurance policy states that the policyholder agrees to pay a certain premium at regular intervals .

Life insurance depends on a number of factors, including age, income, expenses, loans, number of dependents, health, etc. It is mainly of four different types, universal life insurance, term life insurance, whole life insurance, life insurance and endowment . Described in detail below is offering life insurance benefit . In general, the insurance system offers you a solution where you can guarantee your future financially and Life Insurance offers some kind of solution to the needs of your life in the future. This type of insurance is also available in various types and the choice depends on your needs.

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Auto Insurance

This insurance is something that all drivers must get all day, every day when driving out and on the road. Nowaday, everyone is obliged to have accident protection most in every U.S State. Here are 5 great reasons not to think like "goodness, its alright, i never hit anybody in my life"

1. On the off chance that you don't have your evidence of having collision protection scope when the cop appeal, be arranged to pay for an enormous fine! It totally will be at any rate $500 or more. Regardless of the fact that you have your verification of accident protection, you ought to dependably keep it in your auto all day, every day when you're out and about. Since on the off chance that you don't, be arranged to have your reference closed down by a cop, then bring it to your neighborhood court and pay $10. At the same time recall to verify you accomplish it whenever in the eyes of your court date that is composed on your ticket. I'll let you know a decent motivation behind why! In the event that you miss your first court date, the $10 will be $370 in fine. What's more in the event that you miss your second court date, the $370 will be near to $1000 in fine. Trust me or not, it did befall me.

2. When you get into a pile up with you at flaw and without accident protection, you are going to be in a bad position with the DMV and your fianance when the police come to do the mischance report. First and foremost, you may get your auto towed and permit suspended in the event that you tell the cop that you don't have collision protection scope. On the second, you will likewise need to pay for expense of all harms brought about in the mishap, which are the settling expense for the auto of the individual you hit and the expense of remuneration for his or her damage if created by the mischance. Also believe me on this, 95 percent of the time you will, regardless of the possibility that that individual is not by any stretch of the imagination harming or experiencing the mishap. He or she could at present go to the specialist to have examination or treatment, and the more drawn out the treatment last, the more cash you're going to pay. Taking into account what i evaluated as the normal, one minor mishap without anybody getting damage will at any rate cost you $10,000. Be that as it may in real mishap when somone is truly harmed or injuried that he or she must be hospitalized, i'd say its in the scale of $30,000 - $100,000 that you will need to pay. Also you will go to prison in the event that you don't pay for it.

3. It's generally sheltered to realize that you are protected for yourself as well as for other individuals around you. You could simply feel safe and not stressed realizing that you have accident coverage scope. Accident protection Coverage doesn't generally cost that much in case you're a decent driver with no tickets or any at issue mischances. Espeically for youthful young driversarticle Submission, it could cost generally as low as your telephone bill on the off chance that you know the right accident coverage organizations.

Language of Chemistry

The universe is composed of matter and energy. Matter and energy are inter-convertible to each other. The branch of modern science which deals with the study of composition, transformation and property of matters is known as Chemistry. Chemistry can be classified as:

a.      Physical Chemistry

b.      Iorganic Chemistry and

c.       Organic Chemistry

Element:

An element is defined as pure substance which can neither be decomposed into nor built from simpler substance by any kind of physical or chemical methods. Eg: Hydrogen, Oxygen, Carbon, Sodium etc. The concept of element was first introduced by Robert Boyle.

Atom:

The smallest particle of an element which can take part in chemical change is called an atom. It may or may not be capable of independent existence.

Compound:

A Compound is a substance produced by union of two or more elements in a definite proportion. t can be decomposed into two or more simple substance. Eg:

Water- H2O

Glucose- C6H12O6

Ammonia- NH3 etc.

Molecule:

A molecule is defined as the smallest unit (particle) of any kind of substance, elements or compounds which can exist independently and can possess all properties of substance. Eg: H2, O2, O3, P4, S8, H2O etc.

Homonuclear Molecule: Molecule formed by the combination of similar kinds of atoms are called homonuclear molecule. Eg: O2, O3, P4, S8 etc.

Heteronuclear molecule: Molecule formed by the combination of different kinds of atoms of different elements are called heteronuclear molecule. Eg: CH4, PCl5, H2O etc.

Symbol: Symbol is defined as the abbreviation or shorthand sign for the full name of an element. One or more letter(s) is used to write the symbol of an element.

Eg: Hydrogen        H                                                                                                                                      

      Oxygen            O

      Magnesium     Mg

      Uranium           U

      Vanadium        V

      Antimony         Sb

      Gold                  Au

      Curium             Cm

      Nobelium         No

      Americium       Am

      Plutonium         Pu

Valency:

Valency of an element is the combining capacity of the element which is measured in terms of hydrogen atoms or its equivalent which combine with one atom of that elements. Examples:

Elements       Valency

H                       1

O                      2

N                      3

Al                     3

Ca                    2

Na                    1

Certain elements can have more than one valency that is they exhibit variable valency. Eg:

Fe-  2 and 3

Cu- 1 and 2

Sn- 2 and 4 etc.

The compound in which the metal has lower valency is called an “ ous “ compound while the compound in which the metal has higher valency is called “ ic “ compound.

Eg: Fe= 2 valency FeCl2, Ferrous chloride

      Fe= 3 valency FeCl3, Ferric chloride

Radical:

A radical may be defined as an atom or group of atoms having positive or negative charge and behaves as a single unit in chemical change.  

Some Common Radicals

Monovalent Radicals

1.  Ammonium       NH4

2.  Hydroxide         OH

3.  Cyanide              CN

4.  Nitrite                NO2

5.  Chlorate            ClO3

6.  Amide               NH2 etc.

Divalent Radicals:

1. Carbonate        CO3

2. Oxalate              C2O4

3. Sulphite              SO3

4. Zincate               ZnO2

5. Stannite             SnO2

6. Stannate          SnO3 etc

Trivalent Radicals:

1. Aluminate         AlO3

2. Arsenite            AsO3

3. Arsenate           AsO4

4. Ferricyanide     Fe(CN)6 etc.

Dalton’s Atomic Theory: (John Dalton, In 1808)

Postulate:

1.      All matter consists of extremely small individual particles called atoms.

2.      Atoms of same elements are all alike.

3.      Atoms of different elements are entirely different and have different properties.

4.      Atoms can neither be created nor be destroyed, it can only be transformed to one form to another.

5.      Atoms combines together in simple whole number ratio to give compounds.

6.      The relative number and kinds of atoms are constant in a given compound.

Stoichometry:

Stoichometry is the branch of chemistry which deals with the weight relationship in chemical reaction and weight relationship that prevails in a chemical compound.

Law of Chemical Combination:

1.      Law of conservation of mass

2.      Law of definite proportion

3.      Law of multiple proportions

4.      Law of reciprocal or equivalent proportions

5.      Law of gaseous volume

Internal Commands

        

Time:  This is an internal command. It is used to display current time and also set a new time.
Eg: C:\>time (press enter)

Date:  This is also an internal command. It is used to display current date and also set a new date. The date is shown in the mm-dd-yy format. Eg:  C:\>date (press enter)

Ver: This command is used to display the version number of your computer. Eg:  C:\>ver (press enter)

Vol: This command is used to display the volume serial number of your computer. C:\>vol (press enter)

Cls: (clear logical screen) This command is used to clear the screen. Eg:  C:\>cls  (press enter)

DIR: This command is used to display all the files and directories in your computer. Eg:  C:\>DIR (press enter)

C:\>DIR/P (press enter) : It is used to display files and directories page wise.
C:\>DIR/W (press enter): It is used to display files and directories width wise.
C:\>DIR/AD (press enter): It is used to display only directory.
C:\>DIR/A-D (press enter): It is used to display only files.
C:\>DIR/S (press enter): It is used to display all files and directories of the computer.
Note: Press ctrl+C (key) to stop running files and directories.
(Note: Here, Capital U means space)
C:\>DIR U ??? (press enter): It is used to display those files and directories which have upto 3 characters.
C:\>DIR U* com (press enter): It is used to display those files which have com as an extension only.

File: A collection of information can only be saved in the form of file. Hence, a collection of related information saved in the computer is called a file.

Copy con command: This command is used to make a new file in the computer. Syntax: C:\>copy U con U filename  (press enter)
( Note: Press F6 or ctrl + Z key for save then press enter key )

Type command: The type command is used to display  contents of file. Syntax: C:\>Type U filename (press enter)
Eg:  C:\>Type U Golden (press enter)

DEL (DELETE) or Erase: The DEL command is used to delete (remove) your selected file from the computer. Syntax: C:\>DEL U filename (press enter)
                                  C:\>Erase filename (press enter)

Ren (Rename) command: The Ren command is used to change the filename.
Syntax: C:\>Ren U old filename U new filename (press enter)

Copy command: This command is used to make duplicate file. It is used to combine two or more files. It is also used to copy the file from one disc to another disc.

To make duplicate file:
Syntax: C:\>copy U old filename U new filename (press enter)

To combine the file:
Syntax: C:\>copy U F1 + F2 + F3 U new file name (press enter)

To copy the file from one disk to another disk:
Syntax: C:\>copy U filename U drive name (press enter)

Note: Here, Capital (U) means to give space.

Prompt command: The prompt command is used to change the prompt (C:\>).
C:\>prompt $T  (press enter): It is used to display current time.
C:\>prompt $V (press enter): It is used to display version number of your computer.
C:\>prompt $Q (press enter): It is used to display equal sign.
C:\>prompt $B  (press enter): It is used to display (;) sign.
C:\>prompt $G  (press enter): It is used to display greater than (>) sign.
Type $P $G key then press enter key to display C:\>.

Directory: A table of contents on the disc is called a directory. A directory within a directory is called sub-directory.

MD (Make Directory): The MD command is used to make a new directory.
Syntax: C:\>MD directory name (press enter)

CD (Change Directory): The CD command is used to change the directory.
Syntax: C:\>CD directory name (press enter)

RD (Remove Directory): The RD command is used to remove the directory.
C:\>RD directory name (press enter)
Note: If you want to remove directory then you should remember following points:
Directory must be empty and
Exit from the current directory.

Exit command: This command is used to return the windows screen.
Eg: C:\>exit (press enter)

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Death of a Star

Universe is made up of many different elements. Stars are also one of the element of this Universe. As we know, if the sky is clear then we see many uncountable stars are twinkling at the night time. Have you ever noticed or had a knowledge that stars are born and also they die after certain interval of time. Now in your mind many questions have been raised such as Do the stars are really born? Do they really die? Do these things really happen? After reading this article you will know everything from the born upto death of Stars and afer that also what happens.

When a star is born, its hydrogen goes on being used in fusion. When the hydrogen fuel is exhausted, the outward pressure created by the nuclear reactions ceases and the gravitational force within the star predominates. The star goes on contracting. Due to the contraction, the core temperature rises which causes the expansion of the outer layers of the star. The expansion causes cooling effect. The result is that size of the star grows and the temperature falls. Ultimately, a stage is reached at which the star becomes very large in size and red in color and it is called Red giant. This red giant lasts for millions of years and at its end, the star begins emitting energy at tremendous rate for which the helium becomes the fuel. At the end, a violent explosion called nova/supernova occurs. Due to this explosion, large portion of the stars envelop is thrown into the interstellar space which ends the existence of the star and the star is dead.

 Now, there are three types of dead bodies of stars and they are:
 a. White dwarf
 b. Neutron star and
 c. Black hole

The red giant initially having mass less than 2 Ms (mass of the sun) cools to change its color from white to yellow, yellow to red and finally disappears and its mass becomes equal to that of the earth. This is known as White dwarf.

When the mass of the star is greater than 2 Ms and less than 5 Ms, contraction collide with protons to produce neutrons and eventually the stars becomes full of neutrons. This is known as Neutron star. It does not emit light, but sends out radio waves in the form of pulse. So they are also known as Pulsars. They have a diameter of about 10^-20 km, density 10^17 kg/m^3 and produce intense magnetic field of the order of 10^8 T.

The massive star having mass more than 5 Ms, undergoes uncontrolled contraction because of inward pull of its own gravity. The star becomes so dense that nothing even light can escape from its gravity. This is known as black hole. It is a very large amount of matter packed in a small area. Think of a star 12 times more massive than the sun which is squeezed into a sphere approximately the diameter of Kathmandu city. The result is a gravitational field which is so strong that nothing, even the light cannot escape through it.

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The Laser

The word laser stands for “Light Amplification by Stimulated Emission of Radiation”. The laser is a device that produces an intense beam of coherent monochromatic and unidirectional light as a result of co-operative emission from many atoms. This light beam may be intense enough to vaporize the hardest and most heat-resistant materials.

Principle of Laser:

Consider an assembly of atoms of some kind that have metastable states of excitation energy hv. Suppose we somehow raise a majority of the atoms to the metastable level. If we now shine light of frequency (v) on the assembly, there will be more induced emission from the metastable level than the induced absorption by the lower level. Thus, the result will be an amplification of  the original light. This is the concept that underlies the operation of the laser.

Population Inversion:

Under ordinary conditions of thermal equilibrium, the number of atoms in the higher energy state is considerably smaller than the number in the lower energy state (Since, by the Boltzmann law, N2/N1 = e^{(E2-E1)/kT} i.e., N2<N1. Hence there is very little stimulated emission compared with absorption. Let, by some means, the atoms be initially excited so that there are more atoms in the higher energy state E2 than in the lower energy state E1. Then we have N2>N1. This is known as Population Inversion.

Pumping:

The method of producing population inversion is called pumping. One type of pumping is "optical pumping". Consider a material whose atoms can reside in three different states as shown in figure (a). Atoms in ground state are pumped to state E3 by photons of energy hv' = E3-E1. The excited atoms then undergo non-radiative transitions with a transfer of energy to the lattice thermal motion, to the level E2. They remain in this metastable energy state for a comparatively  long time. Thus there will be more atoms in the higher metastable energy state E2 than in the ground state E1, i.e., we have a "population invertion", atoms in the metastable state E2 are now bombarded by photons of energy hv = E2-E1, resulting in a stimulated emission giving an intense, coherent beam in the direction of the incident photons. This is the method used in the ruby laser.

Mainly, Laser are of three types:

a. Ruby Laser

b. Helium-neon Laser

c. Semiconductor Laser

 

a. Ruby Laser:

It consists of a ruby cylindrical rod whose ends are optically flat and accurately parallel (figure c). One end is fully silvered and the other is only partially silvered. The rod is surrounded by a glass tube. The glass tube is surrounded by a helical xenon flash tube which acts as the optical pumping system.

The energy level diagram of these chromium ions is shown in above figure (c). The Cr ions are excited from level E1 to level E3 by the absorption of light of wavelength 550 nm from the xenon flash tube. The excited ions quickly undergo non-radiative  transitions with a transfer of energy to the lattice thermal motion, to the level E2. The E2 level is a metastable state with a lifetime of about 3 * 10^-3 (usual atomic life times are nearly equal to 10^-8 s). Now, the population of E2 level becomes greater than that of the E1 level. Thus “population inversion” is achieved.
Some photons are produced by spontaneous transition from E2 to E1, and have a wavelength of 694.3 nm (ruby red). The ends of the ruby rod act as reflecting mirror. Therefore, photons that are not moving parallel to the ruby rod escape from the side, but those moving parallel to it are reflected back and forth. These stimulate the emission of similar other photons. The chain reaction quickly develops a beam of photons all moving parallel to the rod, which is monochromatic and is coherent. When the beam develops sufficient intensity, it emerges through the partially silvered end.

Once all the chromium ions in the metastable level have returned to the ground level, the laser action stops. It is necessary to send one more flash of pumping radiation through the rod. Thus the ruby laser operates only in pulses.

b. Helium-neon Laser:

He-ne laser is a type of laser which consists He  and Ne in the ratio of 5:1 and also work with  the principle of laser operation.

Construction of He –Ne laser:

It consists of laser tube of approximately 5 mm in diameter and 0.5m long .It contains a mixture of helium and neon in the ratio of 5:1 at a total pressure of about 1 torr. The tube has parallel mirrors, one of them is partly transparent at both ends. The spacing of the mirrors is equal to an integral number of half wavelengths of laser light. The tube contains two electrodes which are connected to high voltage power supply so that electric field is set up in the tube. The mixture of the gas is ionized by passing electric current through it.

Working:

When the power supply is switched on, the electric field is setup in the tube. Helium atoms are excited very efficiently by electron impact into the 2s level as in the figure while the neon atoms are much readily excited by the electrons. The excited 2s state of helium is relatively long lived. The energy of this level(20.61 eV) is almost the same as the energy of the 5s level in neon (20.61 eV). Hence the energy of the helium atoms is easily transferred to the neon atoms when they collide. This preferential transfer of the neon atoms to the 5s state results in a population inversion between the 5s and 3p states. The purpose of the He atoms is thus to help achieve a population inversion in the Ne atoms. The spontaneous transitions from the 5s state to the 3p state, produce photons of wavelength 632.8 nm, which then trigger stimulated transitions. Photons travelling parallel to the tube are reflected back and forth between the mirrors placed at the ends, and rapidly build up into an intense beam which escapes through the end with the lower reflectivity. The Brewester end windows allow the light of one polarization to pass through without any reflection losses. Because the electron impacts that excite He and Ne atoms occur all the time. Thus, He-Ne laser operates continuously.

c. Semiconductor Laser:

Semiconductor Laser are those laser which are compact, efficient and can be fabricated with ease, however their monochromaticity, coherence and directionality are inferior to those of other lasers.   

Properties of a Laser Beam:

a.    The light is very nearly monochromatic.

b.    A laser beam diverses hardly at all.

c.    The light  is coherent with the waves all exactly in phase with one another.

d.    The beam is extremely intense.

Applications of Laser:

The laser is used in holography, radio communication in outer space, piercing holes in metals, detecting and ranging objects at great distances, welding, surveying  and delicate surgery.