Badai Matahari Lenyapkan Elektron Dalam Sabuk Radiasi Bumi

Ketika matahari mendekati solar maximun pada 2013, cahaya baru telah muntahkan efek dari peristiwa tersebut pada magnetosfer planet kita, menurut sebuah penelitian yang dipublikasikan pada Nature Physics (29/1).

Para astronom di Universitas California-Los Angeles (UCLA) telah menemukan bahwa sebagian dari elektron pada sabuk radiasi luar Bumi lenyap pada awal terjadinya badai geomagnetik, dan hanya muncul kembali dalam beberapa jam kemudian. Wilayah berbentuk donat ini penuh dengan energik elektron yang bergerak mendekati kecepatan cahaya.

 “Ini efek membingungkan,” ujar penulis Vassilis Angelopoulos dalam siaran persnya. “Sejumlah samudera di Bumi tidak dengan tiba-tiba kehilangan sebagian besar air, namun sabuk radiasi diisi dengan elektron-elektron yang dapat dengan cepat mendepopulasi.”

Awalnya yang tercatat oleh para ilmuwan pada 1960, tim ini menjelaskan misteri ini dengan menggunakan data yang dikumpulkan dari armada pengorbit, termasuk pesawat ruang angkasa NASA THEMIS (Times History of Events and Macroscale Interactions during Substorms).

 “Apa yang kami teliti adalah penemuan pertama di era antariksa,” ujar Yuri Shprits. “Orang-orang menyadari bahwa peluncuran pesawat antariksa bukan hanya membuat berita, namun mereka juga dapat membuat penemuan ilmiah yang benar-benar tak terduga.”

Sebuah studi 2006 menunjukkan bahwa elektron dapat lenyap ke media antarplanet. Namun, penelitian baru menunjukkan bahwa sejumlah elektron jatuh ke dalam atmosfir kita, akan tetapi sebagian besar menjauh dari Bumi sebagai partikel angin matahari dari badai geomagnetik yang memborbardir sabuk radiasi.

 “Ini merupakan tonggak penting dalam pemahaman lingkungan ruang Bumi,” ujar penulis utama, Drew Turner. “Kami mulai salah satu langkah menuju pemahaman dan memprediksi fenomena cuaca ruang angkasa.”

Ketika matahari mengalami peristiwa seperti ejections coronal mass, partikel dengan beban tinggi akan menghantam medan magnet Bumi, mengakibatkan badai geomagnetik yang dapat merusak satelit pemantau cuaca, komunikasi dan ancangan global. Pemahaman tentang efek aktivitas matahari pada sabuk radiasi Bumi dapat membantu melindungi satelit-satelit dan perjalanan para astronot yang melewati sabuk dengan resiko radiasi sangat tinggi.

 “Kini sebagian besar satelit dirancang dengan beberapa tingkat proteksi radiasi, para enginer pesawat antariksa harus bersandar pada perkiraan dan statistik karena mereka tidak memiliki data yang dibutuhkan untuk memprediksi perilaku elektron energi tinggi di luar sabuk radiasi,” ujar Turner.

 “Sebagai masyarakat, kita telah sangat tergantung pada tekhnologi yang berbasis ruang angkasa,” pungkasnya. Pemahaman populasi elektron energik dan variasi ekstrem akan dapat membantu menciptakan model-model yang lebih akurat untuk memprediksi efek dari badai geomagnetik pada sabuk radiasi.”

Para peneliti UCLA ini, kini bekerja sama dengan para ilmuwan Moscow State University Rusia, untuk mengukur elektron energi tinggi dengan akurasi yang lebih besar dengan menggunakan wahana antariksa Lomonosov, yang rencananya diluncurkan musim semi mendatang.

sumber: http://erabaru.net/

Natural Gas

Natural gas, the first cousin to crude oil, is a combustible fossil fuel often found in underground reservoirs and comprised of methane and other hydrocarbon compounds.

A century ago, natural gas was considered a waste product in oil fields and flared or vented off. But after a giant gas field was found in the Panhandle in 1918, it was used to manufacture carbon black, which is used to make car tires. Eventually, Americans began using gas to heat their homes and, later, to fire power plants. But it never became as important a fuel as coal, oil or even nuclear power.

A combination of circumstances have drawn new attention to natural gas.

The crisis at a nuclear plant that followed the earthquake and tsunami in Japan in March 2011 raised questions about the safety of nuclear energy. New exploration has yet to resume in the Gulf of Mexico after the blowout of a  BP oil well in 2010. And coal plants have been under a shadow because of their contribution to global warming.

Meanwhile, natural gas has overcome two of its biggest hurdles — volatile prices and questionable supplies. In large part because of new discoveries in the United States and abroad that have significantly increased known reserves, natural gas prices have been relatively low in the last two years.

Turbine

Introduction

Whe­n you go to an airport and see the commercial jets there, you can't help but notice the huge ­engines that power them. Most commercial jets are powered by turbofan engines, and turbofans are one example of a general class of engines called gas turbine engines.

You may have never heard of gas turbine engines, but they are used in all kinds of un­expected places. For example, many of the helicopters you see, a lot of s­maller power plants and even the M-1 Tank use gas turbines.

Type of Turbine

There are many different kinds of turbines:

• You have probably heard of a steam turbine. Most power plants use coal, natural gas, oil or a nuclear reactor to create steam. The steam runs through a huge and very carefully designed multi-stage turbine to spin an output shaft that drives the plant's generator.
• Hydroelectric dams use water turbines in the same way to generate power. The turbines used in a hydroelectric plant look completely different from a steam turbine because water is so much denser (and slower moving) than steam, but it is the same principle.
• Wind turbines, also known as wind mills, use the wind as their motive force. A wind turbine looks nothing like a steam turbine or a water turbine because wind is slow moving and very light, but again, the principle is the same.

A gas turbine is an extension of the same concept. In a gas turbine, a pressurized gas spins the turbine. In all modern gas turbine engines, the engine produces its own pressurized gas, and it does this by burning something like propane, natural gas, kerosene or jet fuel. The heat that comes from burning the fuel expands air, and the high-speed rush of this hot air spins the turbine.

The Gas Turbine Process

Gas turbine engines are, theoretically, extremely simple. They have three parts:

• Compressor - Compresses the incoming air to high pressure
• Combustion area - Burns the fuel and produces high-pressure, high-velocity gas
• Turbine - Extracts the energy from the high-pressure, high-velocity gas flowing from the combustion chamber

The following figure shows the general layout of an axial-flow gas turbine -- the sort of engine you would find driving the rotor of a helicopter, for example:

In this engine, air is sucked in from the right by the compressor. The compressor is basically a cone-shaped cylinder with small fan blades attached in rows (eight rows of blades are represented here). Assuming the light blue represents air at normal air pressure, then as the air is forced through the compression stage its pressure rises significantly. In some engines, the pressure of the air can rise by a factor of 30. The high-pressure air produced by the compressor is shown in dark blue.

Combustion Area

This high-pressure air then enters the combustion area, where a ring of fuel injectors injects a steady stream of fuel. The fuel is generally kerosene, jet fuel, propane or n­atural gas. If you think about how easy it is to blow a candle out, then you can see the design problem in the combustion area -- entering this area is high-pressure air moving at hundreds of miles per hour. You want to keep a flame burning continuously in that environment. The piece that solves this problem is called a "flame holder," or sometimes a "can." Thecan is a hollow, perforated piece of heavy metal. Half of the can in cross-section is shown below:

The injectors are at the right. Compressed air enters through the perforations. Exhaust gases exit at the left. You can see in the previous figure that a second set of cylinders wraps around the inside and the outside of this perforated can, guiding the compressed intake air into the perforations.

The Turbine

At the left of the engine is the turbine section. In this figure there are two sets of turbines. The first set directly drives the compressor. The turbines, the shaft and the compressor all turn as a single unit:

At the far left is a final turbine stage, shown here with a single set of vanes. It drives the output shaft. This final turbine stage and the output shaft are a completely stand-alone, freewheeling unit. They spin freely without any connection to the rest of the engine. And that is the amazing part about a gas turbine engine -- there is enough energy in the hot gases blowing through the blades of that final output turbine to generate 1,500 horsepower and drive a 63-ton M-1 Tank! A gas turbine engine really is that simple.

In the case of the turbine used in a tank or a power plant, there really is nothing to do with the exhaust gases but vent them through an exhaust pipe, as shown. Sometimes the exhaust will run through some sort of heat exchanger either to extract the heat for some other purpose or to preheat air before it enters the combustion chamber.

The discussion here is obviously simplified a bit. For example, we have not discussed the areas of bearings, oiling systems, internal support structures of the engine, stator vanes and so on. All of these areas become major engineering problems because of the tremendous temperatures, pressures and spin rates inside the engine. But the basic principles described here govern all gas turbine engines and help you to understand the basic layout and operation of the engine.