Satellite antenna construction involves the following equipments: a communication satellite which would send and receive the electromagnetic waves, a parabolic or spherical reflector which would receive the signals sent from the communication satellite and send them to the feedhorn, the front end of the waveguide. The radiowaves or the electromagnetic waves are converted into electrical signals by this device and then transmitted through the coaxial feeder to the sets. The noise levels are also kept in check by this same device.
The reflector is designed in the shape of a parabola because of the property of this geometrical shape. It reflects all the waves coming along the axis to the focal point. Thus the reflector receives the electromagnetic waves from the communication satellites and sends it to the feedhorn at its focus. The reflector is made up of a metal and converted to form a paraboloid of revolution. This forms the diameter of the antenna and this paraboloid has a distinct focal point. The waveguide is placed here.
If lower frequency is used, the designer gets more flexibility to choose its material. The large size dish is typically made out of a metal mesh on a metal framework. Some designs have solid dish with perforations. The feedhorn is a low gain type i.e. it has a broad electromagnetic wave beam width. This is required so that the transmitted signals can overcome even the rough terrain. The very wide beam also helps in reducing the noise and is more reliable. Some of the more complex antennas like Cassegrain antenna have got a secondary reflector which gets illuminated by the energy fed into it and reflects the beam back into the main reflector which then forms the desired beam onto the focus. These sub reflectors are located away from the focal point and helps in the better support of the focal device. The signals are then fed to the radio frequency transmitting devices through coaxial feeders or cable transmission lines.
The directive gain or theoretical gain for a parabolic reflector is given by
G=
Where G is the gain
D is the reflector diameter, units same as wavelength
? is the wavelength of the signal
The above equation shows that as the signal frequency increases (or wavelength decreases) the theoretical gain also increases. Also, the larger the aperture of the reflector, the better the gain achieved. However, due to practical considerations, the actual gain obtained is always less than the theoretical gain. It is roughly 35-55% of the total directive gain.
Practically when the above formula was used to calculate the gain for a 2500 centimeter diameter antennas found in Very Large Array(VLA) and Very Long Baseline Array(VLBA) radio telescopes which are operating at frequency of 1.42 GHz, the gain obtained was of the order of 0.14 million times. The actual gain also depends on other factors like accuracy of shape of reflector, its surface finish and feeedhorn matching.
Tuesday, 5 October 2010
Thyroid cysts
Thyroid cysts are the medical term for inflamed fluid-filled areas of the thyroid gland. These may have a surface area of less than 1 cm but could all of a sudden be rather large or may even happen very unexpectedly. A thyroid nodule can be cystic in character and is hence referred to as a thyroid cyst. A true thyroid cyst refers to a thyroid nodule that has no solid components noticeable inside the fluid. On the other hand, there are thyroid nodules that are rather complex by nature. They contain both fluid and solid components. Thyroid cysts might get bigger and expand unexpectedly at times owing to internal bleeding or bleeding inside a slighter pre-existing nodule.
There are times when quickly expanding thyroid cysts might bring into being warning signs in the neck. This includes pain, difficulty ingesting, and even compression of vocal cords that lead to a alteration in voice quality in some cases.
Thyroid cysts that are completely fluid filled present a much lesser risk of anchoring a miniature thyroid cancer as compared to cysts that contain solid components. Identification of a thyroid cyst growth could be made during the ultrasound, or after a thyroid aspiration biopsy through which fluid is obtained from a thyroid lesion.
Total natural resolution of a thyroid cyst might take place, but is infrequent, i.e., around 15 %. The majority of outsized cysts or difficult cysts ought to be treated with a fine needle. This goes a long way in ruling out the likelihood of malignancy. Ultrasound-guided biopsies of complex cystic nodules could be predominantly helpful in guaranteeing that the biopsy material contains thyroid cells, and not mere cystic fluid.
A thyroid cyst isa fluid-filled areas of the thyroid and could range in size from less than 1/3 inch in diameter to one inch or more. A majority of thyroid cysts are completely filled with fluid, but complex cysts, also have solid components. Fluid-filled cysts are usually benign, but complex cysts are sometimes malignant. Ultrasonography is an imaging method that uses high-frequency sound waves in place of radiation in order to create images. It may be used to differentiate cysts from solid nodules and to assist your doctor in carrying out a FNA biopsy. If you come upon a thyroid cyst, do not be scared as a large number of these are known to be benign cysts. Make sure you carry out tests to determine the effectiveness of a thyroid cyst.
There are times when quickly expanding thyroid cysts might bring into being warning signs in the neck. This includes pain, difficulty ingesting, and even compression of vocal cords that lead to a alteration in voice quality in some cases.
Thyroid cysts that are completely fluid filled present a much lesser risk of anchoring a miniature thyroid cancer as compared to cysts that contain solid components. Identification of a thyroid cyst growth could be made during the ultrasound, or after a thyroid aspiration biopsy through which fluid is obtained from a thyroid lesion.
Total natural resolution of a thyroid cyst might take place, but is infrequent, i.e., around 15 %. The majority of outsized cysts or difficult cysts ought to be treated with a fine needle. This goes a long way in ruling out the likelihood of malignancy. Ultrasound-guided biopsies of complex cystic nodules could be predominantly helpful in guaranteeing that the biopsy material contains thyroid cells, and not mere cystic fluid.
A thyroid cyst isa fluid-filled areas of the thyroid and could range in size from less than 1/3 inch in diameter to one inch or more. A majority of thyroid cysts are completely filled with fluid, but complex cysts, also have solid components. Fluid-filled cysts are usually benign, but complex cysts are sometimes malignant. Ultrasonography is an imaging method that uses high-frequency sound waves in place of radiation in order to create images. It may be used to differentiate cysts from solid nodules and to assist your doctor in carrying out a FNA biopsy. If you come upon a thyroid cyst, do not be scared as a large number of these are known to be benign cysts. Make sure you carry out tests to determine the effectiveness of a thyroid cyst.
How to Wax a Surfboard
Believe it or not, there’s an art to this. Wax is the only thing connecting your feet to your board so it pays to get it right. 1. Score Some Wax. 1 bar basecoat. 1 bar wax. It’s important the temperature rating suits your break or the wax won’t do it’s thing. Get a wax comb too. 2. Remove Old Wax. Leave your deck in the sun for 20 minutes till wax is soft, but not runny. Use the flat scraper on the comb to remove it. You can also use a Wax Pickle or special surf wax solvent to get it all off if you’re keen (now is not the time to get DIY with funky chemicals or you may melt your board). 2. Apply Basecoat. Hold the bar at a 45 degree angle so you rub with the edge. Rub basecoat on lightly in a circular motion - roughly 25cm (10”) circles. If you’re a learner/intermediate then go hard and cover ¾ of the deck from the tail up. Don’t wax the side rails, but do rub a little where your hands grip to pop and duck dive. Use about ¼ of the bar and you should have lot’s of sweet little bumps. Do one final layer rubbing rail to rail, then tip to tail. 3. Apply Wax. Now gently apply wax, again with the bar on an angle rubbing in small-ish circles. You want to end up with nice small round bumps. 4. Future Care. Use a wax comb with diagonal cross-hatching strokes to revitalise traction from time to time. Keep your wax in a plastic snaplock bag so it doesn't get covered in crap and melt all over your pimp ride. Always put your board in your bag the same way up or you’ll get wax on both sides of the bag, which means wax on both sides of your board. That’ll slow you down. When your wax gets flat start again from Step 1. I just wish it tasted as good as it smells. Visit learninghowtosurf.com for more tips to improve your surfing. Retrieved from "http://www.articlesbase.com/extreme-sports-articles/how-to-wax-a-surfboard-276581.html" (ArticlesBase SC #276581) Sebastian Grodd - About the Author:
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Uk music charts
UK Music charts would possibly be the second most popular chart apart from the music chart of the United States of America. Great Britain has produced many musicians of repute such as the Beatles, David Bowie, George Michael, Rod Stewart and the Rolling Stones.
In today's music world there are a lot of British singers who are making waves in United States of America
A list of such singers from the famous songs aired on UK music charts.
Coldplay: Death and All of His Friends - The graceful music that they have produced over the years has held them in good stead - their newest release has been is Viva la Vida and contains some very good music - it would be nice to check this song personally.
Estelle: American Boy featuring Kanye West - This particular number is one of the hottest tracks in the Billboard Music charts in the US. John Legend was responsible for discovering this singer.
Leone Lewis 'Bleeding'- This female singer has a voice which can best be described as husky, sultry and sexy - her music is currently among the top of the music charts which includes the UK Music charts.
Amy Winehouse: Back to Back - She is being described as quite unusual and with a style which is hardly similar to other leading singers - her song "Rehab" was very popular in the US. She certainly has a troubled health record over alcohol and drug abuse - she also has sultry and coarse voice and her message seems to come through powerfully when she sings.
Duffy:' Mercy'- This British female artist is another topper in several music charts including the UK Music charts.
Connie Bailey Rae: Emeraldine - This singer has a pure voice like that of an angel -among her memorable works are "Out Your Records On" and "Like a Star".
Damien Rice: Delicate - His music really stirs your soul - when in full flow it reaches great heights - his music can be found in You Tube and iTunes.
James Elliott: 1973 - One may get fooled by his melancholy lyrics - his music can certainly break hearts. His mixture can best be described as a mixture of pop and rock. One of his most popular songs is, "Wiseman".
KT Tunstall: 'Girl and the Ghost'
Her voice is simple but can move listeners - hers is a type of music that can bring pop and folk together. Among her most famous works are 'Black Horse' and 'the Cherry Tree'.
Paulo Nuitini: New shoes - Check out this cool singer- cool with the type of his songs, his clothes, attitude - appears very laidback about everything he does but deep inside he is very passionate about his work and his music .
In today's music world there are a lot of British singers who are making waves in United States of America
A list of such singers from the famous songs aired on UK music charts.
Coldplay: Death and All of His Friends - The graceful music that they have produced over the years has held them in good stead - their newest release has been is Viva la Vida and contains some very good music - it would be nice to check this song personally.
Estelle: American Boy featuring Kanye West - This particular number is one of the hottest tracks in the Billboard Music charts in the US. John Legend was responsible for discovering this singer.
Leone Lewis 'Bleeding'- This female singer has a voice which can best be described as husky, sultry and sexy - her music is currently among the top of the music charts which includes the UK Music charts.
Amy Winehouse: Back to Back - She is being described as quite unusual and with a style which is hardly similar to other leading singers - her song "Rehab" was very popular in the US. She certainly has a troubled health record over alcohol and drug abuse - she also has sultry and coarse voice and her message seems to come through powerfully when she sings.
Duffy:' Mercy'- This British female artist is another topper in several music charts including the UK Music charts.
Connie Bailey Rae: Emeraldine - This singer has a pure voice like that of an angel -among her memorable works are "Out Your Records On" and "Like a Star".
Damien Rice: Delicate - His music really stirs your soul - when in full flow it reaches great heights - his music can be found in You Tube and iTunes.
James Elliott: 1973 - One may get fooled by his melancholy lyrics - his music can certainly break hearts. His mixture can best be described as a mixture of pop and rock. One of his most popular songs is, "Wiseman".
KT Tunstall: 'Girl and the Ghost'
Her voice is simple but can move listeners - hers is a type of music that can bring pop and folk together. Among her most famous works are 'Black Horse' and 'the Cherry Tree'.
Paulo Nuitini: New shoes - Check out this cool singer- cool with the type of his songs, his clothes, attitude - appears very laidback about everything he does but deep inside he is very passionate about his work and his music .
Global warming impacts
Global warming is the rise in the average temperature of the Earth's atmosphere and the increase of the ocean's sea level. The polar ice caps are slowly melting due to the high temperature of the atmosphere. Global warming has a significant impact on our environments condition. Our everyday life is also greatly affected by this phenomenon. Countries all over the world are taking considerable measures to lessen the global warming impacts.
Global warming is putting animal and plant life under great risks. A couple of animal species have already become extinct due to this drastic change of the Earth's climate. Examples of these extinct species are the golden toad and harlequin frog which used be found in Costa Rica. A lot more species of animals are under threat of extinction because their natural habitats are being wiped out because of the effect of global warming on our environment.
Ecosystems are seriously being affected by global warming. These ecological systems, such as coral reefs, may suffer severe changes that could ultimately be irreversible. One factor of global warming that is affecting the ecosystems is the melting of the glaciers in the Polar Regions. This would be a great loss to our environment. People who want to protect these ecosystems are generally helpless to stop this drastic change. If this changes goes on without proper actions being taken, global extinction will not be impossible in the distant future.
Seasons are also generally affected by global warming, because of the fast change in temperature. The lengths of our seasons may vary, which disrupts the livelihood of man and animals alike. Shorter winters and longer summers may be experienced with extreme temperature levels. Plant life is also disrupted by these unprecedented seasonal changes.
Heat waves across the globe are not uncommon because of the global warming impacts. People are gravely suffering from these conditions. Energy consumptions used for cooling purposes is at an all time high. The already dry places in Earth have become even drier and hotter. These extremes in the temperature has caused outbreaks in heat related sickness or diseases.
Significant research and studies are taken by the world's governments to learn more about global warming. With more knowledge about this phenomenon, proper measures or actions can be taking in lessening or preventing the global warming impacts. People also need to be constantly educated on the facts of global warming and how it can be prevented. They must be aware about the causes of effects of global warming.
Global warming is putting animal and plant life under great risks. A couple of animal species have already become extinct due to this drastic change of the Earth's climate. Examples of these extinct species are the golden toad and harlequin frog which used be found in Costa Rica. A lot more species of animals are under threat of extinction because their natural habitats are being wiped out because of the effect of global warming on our environment.
Ecosystems are seriously being affected by global warming. These ecological systems, such as coral reefs, may suffer severe changes that could ultimately be irreversible. One factor of global warming that is affecting the ecosystems is the melting of the glaciers in the Polar Regions. This would be a great loss to our environment. People who want to protect these ecosystems are generally helpless to stop this drastic change. If this changes goes on without proper actions being taken, global extinction will not be impossible in the distant future.
Seasons are also generally affected by global warming, because of the fast change in temperature. The lengths of our seasons may vary, which disrupts the livelihood of man and animals alike. Shorter winters and longer summers may be experienced with extreme temperature levels. Plant life is also disrupted by these unprecedented seasonal changes.
Heat waves across the globe are not uncommon because of the global warming impacts. People are gravely suffering from these conditions. Energy consumptions used for cooling purposes is at an all time high. The already dry places in Earth have become even drier and hotter. These extremes in the temperature has caused outbreaks in heat related sickness or diseases.
Significant research and studies are taken by the world's governments to learn more about global warming. With more knowledge about this phenomenon, proper measures or actions can be taking in lessening or preventing the global warming impacts. People also need to be constantly educated on the facts of global warming and how it can be prevented. They must be aware about the causes of effects of global warming.
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