The only problem with the chain reaction is the fact that each stage of the reaction instigates more than twice as many fissions as the next stage (almost three times as many!).This results in the amount of energy produced at each stage more than doubling if the reaction is left unchecked. Each stage occurs in less than a millionth of a second therefore the heat energy produced can be phenomenal.The reaction is said to escalate. If we requirea steady energy output of energy only one neutron from each fission should be allowed to go on to make another fission reaction. The reaction needs to be controlled - see control rods.

The diagram below summarises what happens in a chain reaction. You are often asked to sketch a diagram to show chain reactions in exams - make sure you label them properly.

The Earth's atmosphere is a layer of gases surrounding the planet Earth that is held in place by the pull of Earth's gravity.

The Earth's atmosphere contains a mixture of gases is commonly known as air:

• 78% nitrogen,
• 21% oxygen,
• 0.93% argon,
• 0.04% carbon dioxide - although this is increasing
• water vapour (average of 1% - but that varies).
• trace amounts of other gases

The atmosphere protects life on Earth .

• It is deep enough to absorb X-rays and gamma rays from outer space, preventing them from reaching ground level at all.
• The ozone layer absorbs ultraviolet solar radiation.
• The atmosphere acts like a blanket over the Earth, reducing temperature extremes between day and night - making it easier for life forms to survive.

The atmosphere absorbs and reflects some of the heat radiation from the Sun.

This prevents the Earth’s surface from getting too hot during the day. It retains some of that energy so that all of the energy collected from the Sun is not lost during the night (as would be the case if there was no atmosphere). Only some of it is radiated back out into space. This stops the temperature of the Earth from dropping too low during the night. It is able to do this because some of the molecules of gas in the atmosphere are ‘greenhouse gases’.

There is no definite boundary between the atmosphere and outer space. It slowly becomes thinner and fades into space. Three quarters of the atmosphere's mass is within 11 km of the planetary surface.

• People who travel above an altitude of 80.5 km (50 miles) are called astronauts.
• An altitude of 120 km (75 miles) marks the boundary where atmospheric effects become noticeable during re-entry.
• The Kármán line, at 100 km (62 miles), is also frequently regarded as the boundary between atmosphere and outer space.

The temperature of the Earth's atmosphere varies with altitude (how high up you are!); the mathematical relationship between temperature and altitude varies among five different atmospheric layers.

The troposphere is the layer closest to the earth, and it is the layer in which we live. It is about ten miles deep. Seventy five percent of the mass of all our atmospheric molecules is in the troposphere, and this is where we find water vapour, dust, pollen, and soot particles. Weather happens in the troposphere. This layer is turbulent, with storms and atmospheric mixing.

In the troposphere, the air cools gradually as it gets further from the earth. At the very top of this layer the air temperature is about -60 ^oC. Water vapour is therefore in the form of ice. This forms what we call the cold trap - a temperature region where water vapour rises no further (because it has solidified). If we had no cold trap, water molecules could rise higher and higher in the atmosphere are they would eventually break down into oxygen and hydrogen at the outermost layers - the small, light hydrogen molecules could then escape into space. Earth would lose its water if we had no cold trap!

Mitochondria are the cell's power producers. They convert energy into forms that are usable by the cell. They are the sites of cellular respiration which ultimately generates fuel for the cell's activities.

What are their distinguishing characteristics?

Mitochondria are bounded by a double membrane. Each of these membranes is a phospholipid bilayer with embedded proteins. The outermost membrane is smooth while the inner membrane has many folds. These folds are called cristae. The folds enhance the "productivity" of cellular respiration by increasing the available surface area.

Muscle Cell Mitochondria, Copyright Dennis Kunkel.

The double membranes divide the mitochondrion into two distinct parts: the intermembrane space and the mitochondrial matrix. The intermembrane space is the narrow part between the two membranes while the mitochondrial matrix is the part enclosed by the innermost membrane. Several of the steps in cellular respiration occur in the matrix due to its high concentration of enzymes.

Mitochondrion with matrix, Image courtesy of The Virtual Cell.

Mitochondria are semiautonomous (semi- auto-) in that they can divide and grow to make more of themselves. They also have their own DNA and ribosomes.

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Distinguishing Characteristics:

The Nucleolus:

In Journey into the Cell, we looked at the structure of the two major types of cells: prokaryotic and eukaryotic cells.

Now we turn our attention to the "movers" of a eukaryotic cell, cilia and flagella.

What are cilia and flagella?

What are some distinguishing characteristics?

Where can cilia and flagella be found?

• If the salt water solution is hypertonic it would contain a higher concentration of solute and a lower concentration of water than the blood cells. Fluid would flow from the area of low solute concentration (the blood cells) to an area of high solute concentration (water solution). As a result the blood cells will shrink.
  
  
• If the salt water solution is isotonic it would contain the same concentration of solute as the blood cells. Fluid would flow equally between the blood cells and the water solution. As a result the blood cells will remain the same size.
  
  
• If the salt water solution is hypotonic it would contain a lower concentration of solute and a higher concentration of water than the blood cells. Fluid would flow from the area of low solute concentration (water solution) to an area of high solute concentration (the blood cells). As a result the blood cells will swell and even burst.

Diffusion

Passive Transport

What is the aorta?

Function of the Aorta

Structure of the Aortic Walls

Branches of the Aorta

• Ascending Aorta - Extends from the left ventricle of the heart.
  
  
  Coronary Arteries

• Aortic Arch
  
  
  Brachiocephalic Artery
  
  
  • Right Common Carotid Artery
    
    
  • Right Subclavian Artery
  
  Left Common Carotid Artery
  
  Left Subclavian Artery

• Descending Aorta
  
  Chest Region:
  
  
  • Visceral Branches - Supply blood to the lungs, pericardium, lymph nodes, and esophagus.
    
    
  • Parietal Branches - Supply blood to the chest muscles, diaphragm, and spinal cord.
  
  Abdominal Region:
  
  
  Celiac Artery
  
  
  • Left Gastric Artery - Supplies blood to the esophagus and portions of the stomach.
    
    
  • Hepatic Artery - Supplies blood to the liver.
    
    
  • Splenic Artery - Supplies blood to the stomach, spleen, and pancreas.
  
  Superior Mesenteric Artery - Supplies blood to the intestines.
  
  Inferior Mesenteric Artery - Supplies blood to the colon.
  
  
  • Renal Arteries - Supplies blood to the kidneys.
    
    
  • Ovarian Arteries - Supplies blood to the female reproductive organs.
    
    
  • Testicular Arteries - Supplies blood to the male reproductive organs.
  
  Common Iliac Artery
  
  
  • Femoral Arteries - Supply blood to the lower legs and feet.

What Is a Capillary?

Capillary Size

Capillary Microcirculation

Ventricles of the Heart

Function of the Ventricles

• Right ventricle: Receives blood from the right atrium and pumps it to the main pulmonary artery. The main pulmonary artery extends from the right ventricle and branches into left and right pulmonary arteries, which extend to the lungs. Here oxygen-poor blood picks up oxygen and is returned to the heart via the pulmonary veins.
  
  
• Left ventricle: Receives blood from the left atrium and pumps it to the aorta. The aorta carries and distributes oxygen-rich blood to the rest of the body.

COURTS and legal scholars love quoting legal maxims in Latin. One of the most famous is fiat justitia ruat caelum. The phrase is a resolute affirmation of the rule of law. It means "Let justice be done though the heavens fall".

It was intended as hyperbole. But, ironically, courts may now have to confront these words on literal terms. In various countries, plaintiffs have sought court orders to halt the operation of the Large Hadron Collider at CERN near Geneva, Switzerland, with the most extraordinary of allegations: that the experiment may create a black hole that will devour the Earth.

Up until now, the various lawsuits filed against the LHC have faltered. But if the right kind of claim is filed in the proper court, a judge may soon have to face the question of whether an injunction might be needed to save the world.

Injunctions are court orders that command persons to do or refrain from doing something. They are relatively routine, for example when a building of historic significance is threatened with demolition. But wading into the world of particle physics to shut down the LHC would be a forbidding proposition for anyone in judges' robes.

In deciding whether or not to issue an injunction, courts engage in what lawyers refer to as a "balancing test". The idea is that the court weighs the hardships that would be endured by both parties if the injunction were or were not issued, taking into account the likelihood and severity of the alleged consequences. The test closely resembles what is portrayed by courthouse statues around the world - Lady Justice holding up scales to measure the relative weight of the plaintiff's and defendant's cases.

So let's do the balancing test for the LHC case. The hardship CERN would suffer from an injunction is enormous - idling thousands of workers and equipment worth billions of euros, and upending a great scientific adventure. That weighs on the scales heavily. But on the other side is an Earth-mass black hole. That not only tips the scales, it eats them up.

The remaining task is to determine whether the questions raised are sufficiently serious. For that, a court must take a careful look at the scientific controversy. Yet the physics involved is difficult terrain even for physicists. A judge with maybe just a few days to ponder has scant chance of learning the science well enough to confidently decide who is right and who is wrong.

Usually when complex scientific issues are involved, courts turn to expert witnesses. But there is a problem with using experts in this case: none would seem to be without bias. CERN employs half of the world's particle physicists; the other half are their friends. All of them are anxiously awaiting data from the LHC to advance their field. The LHC is not just a particle physics experiment, it is the particle physics experiment. So what is a court to do?

Courts can maintain the rule of law in a fair and principled way by looking at the human context surrounding the scientific debate. While the physics may be largely impenetrable to the court, the human factors are not.

One question a court can investigate is how likely it is that the theoretical underpinnings of the scientific work are defective. Those seeking an injunction could, for example, ask a court to consider the history of shifting arguments for why the LHC is safe.

In 1999, physicists said no particle accelerator for the foreseeable future would have the power to create a black hole. But theoretical work published in 2001 showed that if hidden extra dimensions in space-time did exist, the LHC might create black holes after all. Thereafter, the argument for safety was changed. In 2003, it said that any black holes created would instantly evaporate. But when subsequent theoretical work suggested otherwise, the argument changed again. In 2008, CERN issued a report arguing a safety case based, ultimately, on astrophysical arguments and observations of eight white dwarf stars. These flip-flops on safety might cause a court to find current assurances less persuasive than they would otherwise be.

In addition, a court could look at the sociological and psychological context in which the disputed scientific work was carried out. Social scientists have identified a number of phenomena that can skew attempts to reach objective assessments of risk. For instance, cognitive dissonance describes the tendency of people to seek information that is consistent with their beliefs and to avoid information that is inconsistent. "Groupthink" describes a process by which intelligent individuals, working in a group, can reach a worry-free outlook that is not justified by the facts. And the phenomenon of confirmation bias - the tendency to filter information so as to confirm working hypotheses - was cited by the Columbia Accident Investigation Board as one explanation for why space shuttle programme managers ignored sure signs of trouble.

A court charged with deciding whether an injunction should be issued could consider whether these sorts of social effects plausibly undermine the conclusion that the LHC is safe.

These lines of inquiry might strike physicists as unfair. Many will argue that scientific work should be debated on its scientific merits alone. That objection is well put in a purely academic dispute, but the question of whether the LHC is safe is not academic - it is a real-world question with the highest possible stakes. Evaluating the science from a real-world perspective, and understanding scientific work to be a fallible human enterprise, is not merely fair - where justice is concerned, it is essential.

Los Angeles police are getting tip-offs from unlikely informants: mathematicians.

Using crime data from southern California, Jeffrey Brantingham of the University of California, Los Angeles, and his colleagues set out to calculate how the movements of criminals and victims create opportunities for crime, and how police can reduce it. They came up with a pair of equations that could explain how local crime hotspots form – which turned out to be similar to those that describe molecular reactions and diffusion.

The equations suggested that there are two kinds of hotspot. The first, called "supercritical", arises when small spikes in crime pass a certain threshold and create a local crime wave. The second, "subcritical", happens when a particular factor – the presence of a drug den, for instance – causes a large spike in crime. The equations also indicated that rigorous policing could completely eliminate the subcritical hotspots, but would simply displace the supercritical variety.

The approach "presents a novel hypothesis of how hotspots form", says John Eck, a criminologist at the University of Cincinnati, Ohio. Brantingham hopes eventually to be able to predict where subcritical hotspots are forming, so police can step in to nip problems in the bud. His team is already collaborating with Los Angeles police.

An intrepid subatomic particle has travelled through the bedrock of Japan and triggered a detector on the other side of the country, heralding a new attempt to probe the mystery of neutrino oscillations. The result could take us closer to answering one very big question – why is the universe full of matter?

In the "T2K" (Tokai-to-Kamioka) experiment, an intense beam of neutrinos is being generated in a particle accelerator near Tokai village north of Tokyo, and aimed at the Super-Kamiokande neutrino detector 300 kilometres away.

Neutrinos interact only reluctantly with matter, but from time to time one of the trillions in the beam will be lucky enough to hit an atomic nucleus inside Super-Kamiokande, and so create a distinctive flash of light.

The goal is to understand a strange kind of subatomic metamorphosis. These particles come in three types or flavours: electron, muon and tau neutrinos. From earlier experiments, physicists know that neutrinos spontaneously change their flavour, oscillating back and forth from one kind to another. But the details are still hazy.

Extremely sensitive

With T2K they are hoping to fill in some of the blanks. "We will be able to look for the appearance of electron neutrinos in a muon neutrino beam much more sensitively than has been done before," says David Wark of Imperial College, London. "It is ten times as sensitive as previous experiments."

This could shed some light on why we exist. "The known laws of physics should lead to roughly the same quantity of matter and antimatter in the universe," says Wark.

But because matter and antimatter destroy one another, that would have led to a cosmos full of radiation and almost no solid stuff. Instead matter somehow predominated. "That tells us there must be a law of physics that is different for matter and antimatter," Wark told New Scientist. "We don't know what it is, but neutrino oscillations are someplace where it might show up."

To test the idea, researchers will first measure what fraction of muon neutrinos in the T2K beam turn into electron neutrinos. Then T2K and other experiments could compare neutrinos and antineutrinos, to finally find out why the cosmos is so biased against antimatter.

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Menteri Negara Lingkungan Hidup Gusti Muhammad Hatta menargetkan dapat menurunkan jumlah vila yang berada di kawasan puncak, Bogor, Jawa Barat.

"Kita harapkan setiap tahun ada penurunan jumlah vila," kata MenLH pada acara penanaman pohon di area Situ Cibeureum, Bojong Gede, Bogor, Jawa Barat, Jumat (8/1/2010).

Dia mengatakan, pihaknya membantu Pemkab Bogor sebagai ujung tombak pemilik daerah puncak untuk menata kembali kawasan itu sebagai daerah resapan air.

"Kita mencoba melakukan berbagai pendekatan, termasuk pendekatan persuasif. Kita tidak ingin mempermalukan orang," katanya.

MenLH tidak menyebutkan jumlah vila yang sekarang ada dan jumlah vila yang akan ditertibkan di daerah itu.

Sebelumnya, Satuan Polisi Pamong Praja (Satpol PP) mulai Selasa secara bertahap membongkar 87 vila liar di kawasan Cisarua, Kabupaten Bogor, Jawa Barat.

Pada kesempatan tersebut, MenLH beserta jajaran eselon I KLH dan Bupati Bogor Rahmat Yasin menyerahkan secara simbolis 250 bibit pohon trembesi, mahoni dan belimbing, serta 3000 ikan nila dan mujair di Situ Cibeureum.

Ada sekitar 850 bibit pohon yang bakal ditanam di kawasan Situ Cibeureum yang berasal dari sumbangan Yayasan Kehati, Solidaritas Istri Kabinet Indonesia Bersatu-2 dan KLH, yang selanjutnya akan dipelihara oleh masyarakat sekitar.

Kesadaran masyarakat terhadap konservasi lingkungan masih tetap rendah. Vera, misalnya, bayi orangutan (Pongo pygmaeus) berumur dua tahun ini akan diselundupkan ke Arab Saudi, tetapi digagalkan Balai Karantina Bandar Udara Soekarno-Hatta, Tangerang, dan diserahkan kepada Departemen Kehutanan,

Pusat Penelitian Hutan Tropis Universitas Mulawarman, Samarinda, menyelamatkan seekor anak orangutan (Pongo pygmaeus) yang ditemukan di sebuah perkebunan kelapa sawit. Orangutan yang berusia sekitar satu tahun tersebut sempat telantar karena tidak ada pihak yang bersedia menampung.

Setelah telantar selama lebih dari 10 hari, anak orangutan jantan itu akhirnya dititipkan di Kebun Raya Universitas Mulawarman, Samarinda, Sabtu (16/1/2010). Kepala Pusat Penelitian Hutan Tropis Universitas Mulawarman Chandra Dewana Boer mengatakan, anak orangutan tersebut awalnya ditemukan oleh pegawai PT Agro Urea Sakti pada 5 Januari lalu.

Ketika itu, anak orangutan terlihat bersama induknya sedang mencari makan di lahan perkebunan yang masuk wilayah Kecamatan Sebulu, Kabupaten Kutai Kartanegara. Keduanya lalu diusir dari lahan perkebunan karena dikhawatirkan akan merusak tanaman sawit. Namun, induk orangutan kabur, sedangkan anaknya tertinggal di lokasi perkebunan.

Anak orangutan itu lalu dibawa ke perusahaan. Pada 10 Januari, anak orangutan itu diserahkan ke hutan pendidikan Penelitian dan Pengembangan Kehutanan Kementerian Kehutanan di Sebulu. ”Salah seorang peneliti Jepang dari Sumitomo Forestry yang ada di sana, Rio Soda, merekomendasikan supaya orangutan itu diselamatkan, jangan dilepaskan lagi di sekitar perkebunan itu karena di sekitar perkebunan sudah tidak ada hutan lagi,” kata Boer.

Selain tak ada jaminan dapat bertahan hidup, orangutan juga bisa ditangkap lagi oleh warga. ”Saya lalu menghubungi Yayasan Penyelamatan Orang Utan Borneo (Borneo Orang Utan Survival Foundation), tetapi di sana sudah penuh sehingga tidak bisa menampung orangutan baru,” kata Boer.

Pusat Penelitian Hutan Tropis Universitas Mulawarman lalu menghubungi Balai Konservasi Sumber Daya Alam Kalimantan Timur untuk meminta masukan. ”Karena belum ada solusi, lalu saya minta izin BKSDA untuk mengambil orangutan itu dari hutan penelitian Dephut. Sementara ini orangutan akan dititipkan di Kebun Raya Universitas Mulawarman dengan menggunakan berita acara,” kata Boer.

Sebelum dititipkan di Kebun Raya Universitas Mulawarman, orangutan itu sempat berada di kantor Pusat Penelitian Hutan Tropis Samarinda selama dua hari.