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The audio broadcasting service is called radio broadcasting. It broadcasts through the air in the form of radio waves. The electromagnetic radiation is sent to an receiving antenna by a transmitter. Audio broadcasting can be done through FM cable, satellite , wire networks and Internet. The first radio stations were just radiotelegraphy systems and it first occurred in 1906 on Christmas Eve. In November 1920 the Montreal station began to broadcast.
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In 1990s internet-based radio became feasible. The stations were broadcasting from all over the world without having the need of licence. With the help on the internet you can easily locate a station website and listen to whatever music you want. AM and FM stations are the best known type of radio station that are broadcasted via radio waves. Throughout the developed world several subtypes of station radios can be found: public, commercial and non-profit varieties, campus radio and hospital radio.

Many stations that broadcast on shortwave bands using AM technology, are now eclipsed by internet-distributed radio. Atmospheric conditions and solar activity influences shortwave broadcasting. There are many non-broadcast radio stations such as: police, ambulance, fire, military, taxi or even amateur radio stations.

The earliest broadcasting stations to be developed, were AM stations. AM means amplitude modulation which refers to the amplitude of the carrier signal  that varies in response of the signal’s amplitude that is transmitted.

Many Europe countries uses long wave band. In 1990s FM radio gained popularity. On of the advantage of AM is that it has a signal that isn’t sophisticated  and simple equipment is necessary to detect it and uses a bandwidth that is narrower than FM.

AM broadcasts occur in medium wave frequency, known as the standard broadcast band,  which has the range of 530 to 1700 kHz. Channels are spaced 9 kHz all around the world, and 10 kHz in America.



One of the advantage is that AM transmissions are not ionospherically propagated in day time. In order to avoid interference, the power of regional channels must be reduced at night. Although radio transmitters are limited to 10 kHz because of FCC rules, Am can have a frequency of 15 kHz.

FM mean frequency modulation. And was invented by Edwin H. Armstrong in 1930 to overcome the interference of AM radio. FM has a frequency range of 88 to 108 MHz almost everywhere, except Russia and Japan Cool FM is popular in United States and Europe because of the stereo broadcasting and  higher sound fidelity which was made possible by spacing stations further apart, 200 kHz  apart. In New Zeeland is mandatory 700 kHz.



Yankee Network was the first cool FM radio from United States and began broadcasting in 1939. Today’s frequencies were used after the Second World War. In 1980s all radios had both FM and AM tuners, FM became the dominant one leaving AM for rural environments.

Frequency modulation FM conveys information through a carrier wave having a variable frequency. The technique named frequency-shift keying refers to the digital data that can be sent by shifting the carrier’s frequency.As the signal power increases, the nose power decreases. Based on the Bessel functions, sideband amplitudes and carrier are illustrated below  to see the different modulation indices of FM signals.

Indirect or direct frequency modulation is used to generate FM signals. Directly feeding the message  into the input of a VCO you can achieve direct FM modulation. The message signal is integrated to generate a phase modulated signal for indirect FM modulation. FM is used for radio frequencies, speech and music. This FM type is called wide-FM. It is also used to send signals into the space.

The inventor of frequency modulation is an electrical engineer named Edwin Howard Armstrong which lived between 1890-1954. He was born in New Your City . He became a professor at Columbia University, after he graduated there. While he was still a student he invented the generative circuit which he patented in 1914 and also the superheterodyne in 1918 and super-generative circuit in 1922.



As time passes and technology improves , formats change in popularity. The first radio equipments allowed programmes to be broadcasting in real time but as technology improved , now are used pre-recorded materials or they can even operate without human control.

The word ,,experiment’’ comes from a Latin word that means ,,to try out’’. An experiment is a method that investigates a hypothesis or  relationships between variables. An experiment is a way in which you can find things about the world.   It is used to negate or to support an assumption or to solve in a problem in a practical way.
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An experiment can be done with the help of scientific method. Here are the steps of an experiment: observe, address a question, think of a hypothesis, find out the results, conclusion, inform others about the results.

The comparison between an experimental sample and a control sample, is called controlled experiment. Take for example the drug experiment. One person receiving the drug and the controlled one would receive placebo. The practice in many laboratories is to have some samples with negative and positive control. Tests are usually done double or triple. The procedure that resembles the original experimental test  but which give a positive result, is called positive control .

The protein assay is used in teaching laboratories. A fluid sample is given to the students with a unknown quantity of protein. The students will perform a controlled experiment to find the concentration of protein. They will make positive control samples  and negative control samples. The process in which a spectrophotometer measures the quantity of protein in samples is called the assay .

When it is difficult to control the conditions in an experiment, controlled experiments can be performed by creating several sample groups.

Experiments on humans need special protection from the outside variables, in this case, against placebo effect. It is mandatory for the volunteer and the researcher not to know whoa actually took the drug . This will make sure that the effects that the volunteer’s feel are because of the treatment and not a fact that they knew they are treated .

Experiments cannot always be controlled so researches resort to natural experiments. Researches collect data and then observe the correlation between the explanatory variables. Naturally experiments are not as reliable as controlled experiments. Very cool science experiments are performed in the following disciplines: political science, economics, palaeontology, geology, astronomy and meteorology. The first example is from 1600s , light has a measurable speed and doesn’t travel from place to place. Because of ethical reasons , in the area of medicine, observational studies are used. Field experiments are used in economic analyses and social science. The advantage of field experiments is that they are performed in natural settings but the disadvantage is that they might get contaminated .

"We have to learn again that science without contact with experiments is an enterprise which is likely to go completely astray into imaginary conjecture." — Hannes Alfven



As you know some experiments are done in the filed and some are done in the lab but some people see an experiment in every rocket. We still know little about the stratosphere. When a rocket is send into the space it goes through the stratosphere . There is a need for someone to watch the trail of chemical fuel exhaust. A team attached sensors to a jet plane, this is a kind of plane that is used by NASA, that went straight through the wake of rocket engines. From this very cool science experiment they found out that exhaust erodes the stratospheric ozone .

No one knows exactly how useful is carbon oxide in the Earth’s processes. Scientists want to create an artificial atmosphere. It is important for us to know that methane is the most important greenhouse gas. Scientists are know interested to know how does methane influenced the climate. Methadine comes from natural sources, unlike carbon dioxide. There are six satellites that take snapshots of atmosphere. These six satellites are called A-Train and each of them have names. Aqua- studies the movement of water, CloudSat – studies the properties of clouds, Parasol – studies microphysical properties, Aura – interested in ozone emissions, Calipso – measures aerosols and Orbiting Carbon Observatory that had the important tasks but crashed in February 2009. To replace it, Glory was launched in October .



The atmosphere remains a mystery  and we can only try to solve it by getting closer and see the interactions that happen there. For 2 years now, a team from University of California built a chamber, nine meter long. They use the device in order to trace chemicals .

It is thought that even the fact that many people cook on low-tech stoves, can have an important role in black carbon emissions. We are talking here about the developing world with poor families that cook on open stoves. These stoves need to be replaced by modern ones and then to monitor the atmospheric changes and see the results .



Scientists know how to take samples of air  from the ground but are still learning how to take this samples from the sky. Researches from Harvard University  sent a plane from one pole to the other in order to take samples on their way. In this way they found out that carbon dioxide seems to go north while Antarctic has more oxygen . To find out more, 2 jet planes will fly at different periods of the year .

The entire intellectual spectrum is interested in unsolved problems. Physical science had an explosive development at the beginning of 20^th century. We are still at the beginning of understanding life and its wonders .

The term cool down is used to describe exercises that will make you relax. While cooling down , you  can stretch, you can walk. Physical exercises are very good for our health. Cramps and stiffness is caused by lactic acid but by cooling down you can get rid of these. Cool down exercises involve exercises that decrease in intensity. For example you run hard and then you slow down a little bit and then you walk. Ten minutes are enough for these type of exercises .
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After you finish the exercises you should let your heart and breathing to reach the normal level. Indoor exercises are also good , try to put on an extra piece of clothing and drink many liquids .

Here are some easy exercises for you to relax:

-         Calf Raise Down- you have to stand on your feet fingers  on something raised, such as a stair, and hold to something. Take a breath and put down your heels. You can do this with one foot or with two.

-         Lying Straight, Leg to Chest -  Sit on your back, your head and bottom must be on the floor. Raise afoot and hold it with your hands. The idea is to pull your leg to your chest and keep it straight. To make this exercise easier, you can take a towel and put it around your leg.

-         Stretch Lying – Sit on your side and keep your knees together. Raise a leg and keep it straight . Try to touch your bottom with the leg .

When you end your run try to walk to prevent the locking of your muscles. If it’s cold outside, wear warm clothes when you are exercising. If you have an injury, a stretching exercise will help you .

Many people consider that the cool down is not important. I have news for you- it’s more important than you think. Warm up and cool down are very important for different reasons. While when you warm up you actually prepare your body for exercise, when you cool down the body return to the initial state before the exercise .

When you exercise your body goes through some stressful changes. Tendons, muscle fibres and ligaments are affected. The cool down exercises will help your body recover. The good news is that cool down exercises will make the soreness to go away. I’m sure you all have experienced the soreness in your muscles, the next day you had exercise. This is called ,,post exercise muscle soreness’’.

This soreness is caused by many things but the main cause are the micro tears that appear in the muscles fibres so the muscle tissue gets swollen and pressures the nerve endings that makes us feel pain. The heart is pumping blood to the muscles. The blood has nutrients and oxygen that are necessary for the muscle to work are used. The blood is pushed back to the heart by the force of the muscle. There it is oxygenated again. The force that pushes the blood back to the heart, stops when the exercises are interrupted. Pain and swelling are caused by the lactic acid and waste products. This process is called ,,blood pooling .’’

The cool down exercises keeps the blood circulating , removes waste products and prevents blood pooling. Muscles, ligaments and tendons need the nutrients and oxygen that blood brings with it .

Now that we know why are cool down exercises so important let’s see what are the 3 key elements that make cool down exercises complete:

-         gentle exercise

-         stretching

-         re-fuel

These elements are all important and they aren’t effective if you use just one of them. Their aim is to replenish and repair the body after you exercise .

Here are two examples of effective cool down exercises. One example is for a professional athlete and the second is for a regular person  that exercises for his/her health, fun or fitness .

The professional exercise requires to exercise easy for 10 or 15 minutes. The exercises must be similar to the ones that you already performed. For example  if you were  running you should cool down with a walk . To oxygenate your system , take deep breathes. Stretch for 20 or 30 minutes. You can use PNF stretching or static stretching. Drink water and eat an easy meal or fruits .



The amateur exercise requires to exercise easy for 3 or 5 minutes. In this case also the exercises must resemble the ones you did before. As part of your exercise try to include deep breathing. The same stretching as in the professional exercise but just for 5 or 10 minutes .

If you are  serious with your cool down exercises and you will recover quickly from your exercises. Stretching improves not only athletic performance but the amateur performance, too. Don’t think that because it is a simple exercise is not important. It is very effective in improving your flexibility .

Cool down is in fact the conclusion of physical exercises. It will prepare the body to stop the exercise, prevents soreness and return the body to its condition. Cool down exercises should follow immediately the exercise while the muscles are still warm. You can make your cool down exercises more pleasant by playing music and perform them in relaxed and comfortable positions. Cool down exercises can be fun !

The symbol K represents the chemical element named potassium. Potassium is a alkali metal of silvery-white colour. When getting in contact with the air it is oxidized. It is also reactive with water. In nature, potassium can be found as ionic salt  as minerals dissolved in seawater. All living cells need potassium in order to function properly. As we all know cells are part of animals and plants tissue., especially in fruits. From many chemically aspects, sodium and potassium are similar although they function differently in organism. Potassium is not to be found in nature because it has a violent react with water but it can be found as the crust of the Earth. Potassium is reactive and electropositive.
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Potassium had been known from Roman times. At first they didn’t know the potassium structure but today we know that it is potassium carbonate. Caustic potash can cause burns.

Sir Humphry Davy was one who first discovered potassium in 1807. He used  electrolysis and voltaic pile . Potassium is a substitute of caustic potash. Davy was also the first to find that sodium and potassium are different.

Some of potassium salts are: langbeinite, carnallite, sylvite and polyhalite. They are deposited in seabeds and lakes. Potash which is the main source of potassium and it is mined in: California, Saskatchewan, Germany, Utah, New Mexico etc.

There are 24 chemical elements of potassium. Minerals are dated by measuring how much radiogenic has accumulated and what is the concentration of potassium. The best mineral to be used as samples are: muscovite, biotite, feldspar and hornblende. Potassium is also a macronutrient.

Another cool fact about potassium is that is isn’t dense. Lithium is the only less dense metal. You can even cut potassium with a knife and see that its colour is silver but in contact with air it soon becomes grey.

If you do a flame test, you will see that potassium’s compounds are violet and have a yellow crown which is made by sodium’s emissions. Atomic absorption spectrophotometry, flame photometry, ion selective electrodes and inductively coupled plasma are the ones that determine potassium’s concentration in solution.

Potassium must be kept under a hydrocarbon medium in order to prevent disintegration of the metal from hydroxide corrosion and oxide.

Potassium produces hydrogen, this is a reaction with water.

2 K(s) + 2 H₂O(l) → H₂(g) + 2 KOH(aq)

Potassium also reacts with dioxide. CO2 from air can be removed with the help of potassium carbonate. It is also very soluble in water. In water, the potassium ion has no colour.



To separate potassium by precipitation, you need to use: hexachloroplatinic acid, sodium tetraphenylborate and sodium cobaltinitrite.

Potassium cations are important for the nerve function and brain. It influences osmotic balance between interstitial fluid and cells. According to concentration, 3 of the 5 types of taste sensations are stimulated by potassium so this makes it detectable. If it is diluted it can taste sweet but if it is concentrated it tastes bitter or salty.

Here are some cool facts about potassium: it prevents muscle contraction. If you don’t have enough potassium in your body fluids, you can be affected by hypokalemia with the following symptoms: paralytic ileus, muscle weakness, weak reflex response and respiratory paralysis.



Potassium has an important role in human nutrition. In the body, fluid and electrolyte balance is maintained by potassium. If you eat the right food you are guaranteed to have sufficient potassium in your organism. If you have a balanced diet you won’t be suffering potassium deficiency. Here are some foods rich in potassium: potatoes, orange juice, avocados, bananas, broccoli, tomatoes, brown rice, soybeans, apricots and garlic.

Studies performed on animals, had shown that hypertension and strokes are reduced by a diet high in potassium.

The classes of diuretics loop diuretics and thiazides clear the body from sodium and water but it can also cause in urine the loss of potassium. You can find on the market a variety of non-medical and medical supplements.



Potassium is used in horticulture, agriculture and hydroponic. It is very important in plant nutrition and animal cells. In the form of potassium chloride is able to stop the heart,  thus can be used in lethal injection or cardiac surgery.

Table salt is made of potassium chloride. Baking powder is made by potassium sodium tartrate name also Rochelle salt. Wine and beer are preserved with potassium bisulfite and can be also use to bleach.

In order to make the photosensitive silver halides , potassium bromide, potassium chloride and potassium bromide are used in photographic emulsion.

Because of the highly reactive nature of potassium , you should handle it carefully, protecting your eyes and skin. It reacts with water and produces hydrogen gas which is flammable, thus it is usually kept under oil. But don’t store it longer than 6 months because peroxides can form under the lid and when you open it , it might detonate. In reaction with waster, potassium produces potassium hydroxide which can cause burns.

Potassium hydroxide is used in industry in the manufacture of salts and also in industrial cleaners. Potassium nitrate used for gunpowder and agricultural fertilizer. Potassium cyanide used for precious metals such as gold and silver. Potassium carbonate is used as a mild desiccant for manufacturing glass and soap. Potassium chromate is used in stains, dyes and inks., also in safety matches, fireworks or explosives. The orange-coloured superoxide is used as a source of oxygen for spacecrafts and submarines.

Adolescence , teenage period, is a period of transition from childhood to adulthood. It is also a mental and physical development very difficult as well for the child (sorry teenager) as well for the parents. The first mentioned always have the impression that are not understood and they are them against the others.
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The teenage years are considered to be from 13 to 19. The beginning of the adulthood varies from country to another. For example in Romania we are considered adults at the age of 18, while in America you have to be 21 . When you are over-age you can drive a car, buy alcohol in bars, you can have legal sexual relations or you can even get married.

In adolescence you have more independence in comparison with the preadolescence period. Puberty is the period in which children grow very fast and they culminate in sexual maturity. Girls reach this period at the age of 10 and boys at the age of 12. These changes are influenced by heredity or other factors .

Puberty is the time when the child’s body turns into an adult body. For example boys have a deeper voice and girls ‘ breasts are staring to grow.

Adolescent psychology is associated with the, so called, mood swings. During this period, emotional, cognitive and attitudinal changes take place. This is the time when youth develop their personality, but is also a time of conflict between them and their parents.



The home environmental has a substantial aspect on the development of the teenager. If the concepts and theories about right and wrong  were not right established since the childhood, they are confused about these aspects. G. Stanley Hall named this period ,,Storm and Stress’’ . It is considered to be a normal period and parents should not worry so much.

Many adolescents are indecisive, bored and unmotivated so we have to motivate them in order to become socially acceptable.

Adolescents need to defy their parents, drink alcohol, have sex. These are common experiences between adolescents but if it gets worse you should try a medical advice.

Adolescence is a very important stage in one’s life , with a major role in the formation of future personality and character.



Views of family relationships during adolescence are changing. People used to think that the conflicts were normal during this period. However, the new view puts emphasis on transformation or relationships and maintenance of connectedness.

Adolescents are interested in mobile phones, movies, television, sports, website, games but most popular are the cloths.

Teenagers have many interesting ideas for adults to listen. William DeMille quoted “I have always admired the ability to bite off more than one can chew and then chew it”. This is a quote that helps kids to become leaders.

Robert Schuller  said, “I will! I am! I can! I will actualize my dream. I will press ahead. I will settle down and see it through. I will solve the problems. I will pay the price. I will never walk away from my dream until I see my dream walk away: Alert! Alive! Achieved!” I’m sure that his words grab the attention of youth.

This is a quote I liked best, unfortunately I don’t know who the author is ,, Young people don’t know what age is and old people forget what youth was”.



Young people know little about life but make the best of it, while older people know more about life but they remain only to the knowing. We all agree that the true people are one that despite the years gone by, they are still young in their hearts.

See below several cool teenage quotes that I picked out for you.

,,It is not enough to do your best; you must know what to do, and THEN do your best’’
,, Revenge is a dish that should be served cold.’’
,,The only discipline that lasts is self-discipline.’’
,, A smile is the lighting system of the face, the cooling system of the head and the heating system of the heart.
,,We come to love not by finding the perfect person, but by learning to see an imperfect person perfect’’
The teen years are the most beautiful. You have appositive attitude in different circumstances.

Life can be so confusing but we still understand it. Every day we wake up and live and dream for the better. We sometimes lose hope and we give up but we take it all over again the next day. I sometimes don’t understand how we can laugh during the day, and cry ourselves to sleep, at night, how we can love and the next moment we’ll be angry, how pictures remain unchanged but we change, how the smell of a person remains although they are no longer  with you. Teenagers have an artist mind and soul. The adolescence is a very creative period.



Funny quotes help us when we are depressed. Laugh releases stress after a rough day at work, school or you name it. Some cool teenage quotes are listed below:

,,Too many people grow up. That's the real trouble with the world, too many people grow up. They forget. They don't remember what it's like to be 12 years old. They patronize, they treat children as inferiors. Well I won't do that.’’
Walt Disney

,,You are only young once, but you can be immature for a lifetime.’’

John P. Grier