HIGH-G CENTRIFUGE TRAINING TO GIVE MILITARY PILOTS AN EDGE

Section:

Simulation & Training

The next advance in training for strike and fighter pilots will be a combined flight simulator and centrifuge, adding the feel of realistic highg-forces to the cues from a wide-field-of-view visual system, as the pilot maneuvers his aircraft. 

The benefits for training pilots in air combat maneuvers, missile avoidance, recovery of aircraft that have ``departed'' from controlled flight, and for tactics innovation could be huge--increasing pilots' tactical capability and survivability. The new device also could help close the gap between the growing g-capability of modern fighter aircraft and that of the pilot. 

ENVIRONMENTAL TECTONICS Corp. (ETC) of Southampton, Pa., developed the top-of-the-line G-FET II dynamic flight simulator. The pilot's cockpit and visual system is inside a gondola on the end of a 25-ft. rotating arm. Gimbals allow the gondola to actively move in roll and pitch. Accurate control of the direction of the g-vector (g-pointing) and the ability to create rapid g-onset and sustained gs distinguish it from earlier centrifuge systems. 

The G-FET II can accelerate very quickly, with rates up to 15g per sec.--more than a pilot can withstand without becoming incapacitated from g-induced loss of consciousness (g-loc)--and can maintain 25g. Modern fighters can sustain more than 9g at onset rates of more than 9g/sec. during air combat maneuvering, which exceeds pilots' capability. Learning to fly and operate systems under sustained g-forces is vital to getting the most out of aircraft weapon systems. 

Accurately reproducing the ``g feel'' of a maneuvering aircraft stems from 30 years of development at ETC's Aeromedical Training Center and a cooperative effort with the Air Force Institute of Technology. Acceleration in the X, Y and Z axes has to be highly synchronized with the pilot's flight control inputs and the wide-field-of-view visual system. The ETC system continuously orients the gondola through the multi-axis gimbals to respond to pilot input. 

If the pilot can perceive any delay or ``artifacts''--responses that don't ``feel'' right--realism suffers. The gondola is designed so the pilot's ear is at the center of rotation to minimize extraneous vestibular sensory artifacts. A software model called the Inverse Dynamic Controller blends the inputs to give the high-fidelity response that makes G-FET II feel like a real aircraft, according to ETC. 

A training facility could buy a number of different aircraft cockpits that can be installed in the gondola in just 60 min., according to the company. Each cockpit has its own 120 X 50-deg. wide-field-of-view vision system. In one of ETC's concepts, an uninstalled cockpit could function as a stationary trainer, either linked to others or operating independently. For installation into the gondola, a cockpit would be lifted by an overhead hoist and lowered into place. A pilot enters the cockpit via stairs that drop down from the bottom of the gondola. 

ALTHOUGH FLIGHT physiologists have used centrifuges for years, their value for pilot training has been well established only since the 1970s, according to ETC. The real impetus for high-g training was the advent of modern nimble aircraft that place pilots more at risk of g-loc.

Sustained gs were not a problem with earlier aircraft. The Vietnam era A-7 could pull 7g, but only for a short time, because the airspeed bled off, and the g-forces came off before the pilots had a large g-loc problem. But USAF's F-15 and F-16 and the Navy's F/A-18 can hold 6g in a turn until they run out of fuel, according to Al Hall. He is the lead engineer for the training system division at the Navy Air Warfare Center at Lemoore, Calif. 

The Navy has an earlier version of ETC's dynamic flight simulator, called a centrifuge flight environment trainer, at Lemoore. Hall said it is being used to teach F/A-18 and F-14 pilots straining and breathing techniques to resist the effects of high-g. 

Following 2 hr. of classroom time, where pilots learn and practice the g-tolerance techniques, they put theory into practice by going through a series of increasing and decreasing g-profiles during a 15-min. simulator ride. ``Pilots are reluctant to get in, but they walk out with a different attitude,'' Hall said. At the moment, training is slated for only once in a career. The Air Force has a similar ETC simulator, but with a little shorter arm, for pilot training at Holloman AFB, N.M. 

The two main hazards for pilots are rapid g-onset and sustained g. Older centrifuges could sustain high g-forces but accelerated slowly. At Lemoore, as one part of their training, pilots are exposed to an onset of 6g in 1 sec., ``which gives them a real kick in the pants,'' Hall said. 

At the moment, the devices at Lemoore and Holloman are the only multi-axis trainers that the U.S. owns. Singapore and Japan currently each have an ETC high-end centrifuge capable of g-pointing, but do not have the modular cockpit or tactical flight simulator. As a result, the full training capability envisioned by ETC is still ``around the corner.'' That device, called the TFS-400, will sell for about $35 million.

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The human centrifuge

Section:

Histories

"His countenance attached to saturnine blackness, the eyes, suffused with bile, were immovably fixed on the ground, the limbs seemed deprived of their locomotive powers, the action of the lungs, and the circulation retarded, the tongue parched and silent, and the whole man resembled an automaton." In Dr Cox's opinion, his patient was in the grip of a "melancholy stupor". As the director of one of the largest private asylums in Georgian England, Joseph Mason Cox was mad-doctor to the better off and bad just the thing to rouse this poor soul from the depths of his depression. Cox, one of the first qualified doctors in England to specialise in mental disorders, had invented a new sort of treatment: a human centrifuge. A spin in Cox's "circulating swing" was said to shock the madness from a man.

GOOD wine, a relaxing massage and soothing music: for Asclepiades, a Greek doctor practising in 1st century Rome, these were the best remedies for insanity. Kind and gentle treatment was far better than chains and beatings. And the best therapy of all was sleep -- preferably natural, wholesome slumber rather than that induced by poppy juice or other mind-altering preparations. To encourage a better sort of sleep, Asclepiades invented one of the most enlightened pieces of medical technology: a swinging bed.

If gentle swinging was effective, then, how much more might be achieved by rapid rotation? At the start of the 19th century, a radical variation on the swinging bed began to appear in asylums across Europe. However, patients treated in Joseph Cox's circulating chair found the experience anything but relaxing. Tied down and spun round at speed, they turned pale, threw up and passed out. It was a far cry from Asclepiades's soothing swing, but it got results. Even the most disturbed patients became calm and easy to control. Cox believed any fear or discomfort was all to the good, helping to distract a patient's mind from mad thoughts. Best of all, it encouraged deep and therapeutic sleep.

Down the centuries ideas about how to deal with the insane veered from one extreme to another: some advocated kindness, others believed that physical restraint and intimidation were more effective. Most asylums had been little more than places to lock up the mad, but by the late 18th century attitudes were changing. Cox was one of a new breed of mad-doctor. He was not a jailer or a manager of maniacs, but a medical professional who had studied mental disorders and was prepared to devote his life to investigating better ways to treat them.

The concept of swinging as therapy had gone in and out of fashion ever since Asclepiades. Towards the end of the 18th century, James Carmichael Smith, a Commissioner for Madhouses and physician to Britain's most illustrious madman --King George III -- revived the notion. He suggested swinging could be used to subdue "the nervous influence" and "the principle of irritability" in many sorts of madness.

The idea of the human centrifuge sprang from the fertile mind of Erasmus Darwin, physician, poet and inventor, Darwin was interested in the nature of disease and how to cure bodies rather than minds. He was a great believer in the healing power of sleep. But how best to induce it? Darwin's friend James Brindley provided inspiration, Although famous as a canal engineer, Brindley started out as a millwright: he'd heard that if a man lay on a millstone as it turned, he soon fell asleep. "The centrifugal motion of the head and feet must accumulate the blood in both those extremities of the body, and thus compress the brain," Darwin reasoned.

The same effect, he suggested, could be achieved more comfortably in a bed suspended "so as to whirl the patient round with his head most distant from the centre of rotation". Darwin enlisted another friend, steam pioneer lames Watt, to draw up designs for a "rotative couch", a bed attached to an arm that revolved around a vertical shaft fixed to the floor and ceiling. Darwin never built his revolving bed. It was more suited to a hospital than the parlour of a man in private practice, he said. When Cox took over his family's asylum in 1788, he was ideally placed to test it.

Cox was soon singing the praises of rapid rotation. By the time he published his Practical Observations on Insanity in 1804 he had considerable experience of it. Whirling his patients round at speed worked wonders, he wrote. Like Darwin, Cox believed in the restorative powers of sleep. He also believed that if you provoked some sort of physical crisis in the body, it would shock the mind back to normality, at least temporarily. Spinning certainly had a drastic effect on the body. At first the motion made patients feel nauseous; up the speed and they vomited then lost control of bladder and bowels. Some bled from the nose and ears; some had convulsions. Many passed out.

It was a sizeable shock to the system and invariably had a calming effect. According to Cox, even the most demented, violent patients would be left quiet and easy to control without resort to drugs. "The slumbers thus procured differ as much from those induced by opiates as the rest of the hardy sons of labour from that of the pampered, intemperate debauchee."

The simplest version of Cox's device consisted of a Windsor chair suspended from a hook in the ceiling and rotated with the help of ropes around the chair legs. The patient, Cox advised, should be secured in a straitjacket and "prevented from falling out of the chair by a broad leather strap, passed round the waist and buckled to the spars, while another strap to each leg may fasten it to the front ones of the chair." A more sophisticated version was a bed or chair attached to an arm that revolved around a vertical shaft, much like Darwin's concept. "The necessary motion may be given by the hand of an attendant pushing or pulling the extremity of the projecting arm, with greater or lesser force, each time it circulates, but by a little simple additional machinery any degree of velocity might be given, and the motion communicated with the utmost facility."

By 1813 Cox was promoting spinning as a safe and effective treatment for most kinds of madness. "No remedy is capable of effecting so much with so little hazard. In almost every case it will produce perfect quiescence, allay all irritation, silence the most vociferous and loquacious." It was, he confessed, harder to make a madman giddy than a sane one, "but there are very few of them who can resist the action of a continued whirling with increased velocity, especially if suddenly stopped. The shock this gives to the system and the alarm it excites is not easily conceived by those who have never witnessed it."

Cox's chair became hugely popular in asylums in both the UK and elsewhere. In Ireland, William Hallaran, who ran the Cork Lunatic Asylum, was a great enthusiast, so much so he built a version that could take four patients at a time and spun at 100 revolutions a minute. The effect was much as Cox described: patients felt sick, threw up and later fell into a deep sleep, from which, Hallaran maintained, they awoke with their mad ideas "totally altered". The device, he wrote, rendered his asylum "remarkable for its tranquillity…regularity and order".

After a few decades Cox's chairs began to fall out of favour. Some doctors suspected they did little more than exhaust patients into submission. The treatment was dangerous -- some patients died. By the end of the century the chairs had been consigned to museums. in the meantime the human centrifuge emerged in a new guise. When Austrian physiologist Robert Bárány carried out his ground breaking research into the role of the inner ear in our sense of balance, he used a piece of equipment that differed from Cox's spinning chair in just one respect: it was called the Bárány chair. In 1914, his research won him a Nobel prize.

Further reading: "Cox's chair: 'a moral and a medical mean in the treatment of maniacs'" by Nicholas Wade and others, History of Psychiatry, vol 16, p 73

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The gas centrifuge and nuclear weapons proliferation

Section:

feature article

Uranium enrichment by centrifugation is the basis for the quick and efficient production of nuclear fuel-or nuclear weapons.

The most difficult step in building a nuclear weapon is the production of fissile material. One can either make plutonium-239 in a nuclear reactor or enrich uranium to increase the abundance of its fissile isotope uranium-235. Historically, enrichment has been the more obscure of the two routes, but the recent spread of one technology--the gas centrifuge-from the Netherlands to Pakistan and on to Libya, Iran, and North Korea has brought enrichment to the forefront of proliferation. That development is challenging old ideas about how to ensure the peaceful use of nuclear technology and prevent the further spread of nuclear weapons.

The gas centrifuge is particularly well suited for acquiring a first nuclear weapon. It is also the most economically efficient way to enrich uranium for peaceful power-reactor fuel, and therefore essentially impossible to abandon and difficult to control by political means. Combined, those aspects lead to a new kind of control problem that has not been experienced with other technologies. This article outlines the problem, showing how technical aspects affect policy options, and discusses some of the solutions currently under consideration.

The gas centrifuge

The gas centrifuge works much like a classic centrifuge: It is a hollow cylindrical tube that is spun at very high speeds about its axis.( n1) The centrifugal force is able to separate chemically identical isotopes because of the variation in isotopic weight. For the separation of uranium isotopes, the gas fed into the centrifuge is uranium hexafluoride. Figure 1a shows the feed stream and two withdrawal streams: the product stream enriched in the desired isotope, ²³⁵U, and the tails or waste stream depleted in ²³⁵U. Technical details are presented in box 1.

Centrifuges have been fabricated from a variety of materials, with varying lengths, diameters, and operating speeds. Figure 1b shows the relative lengths of a number of centrifuges. The first and second Pakistani centrifuges were based on early designs by Urenco Ltd, a consortium involving the UK, Germany, and the Netherlands. Also shown are the more modem Urenco centrifuges. The largest centrifuge was developed in the US and is now called the American Centrifuge. Centrifuges of that design will be used by USEC Inc at a plant in Ohio.

Figure 1. (a) Schematic of the flows into and out of a gas centrifuge plus the countercurrent flow in the separation chamber. (Adapted from Sci. Am., August 1978, p. 39.)(b) Comparison of lengths of the first two Pakistani centrifuges P1 and P2, the range of modern Urenco centrifuges, and the current US centrifuge design. (c) Arrangement of gas centrifuges in a 15-stage ideal cascade.

A single centrifuge cannot simultaneously produce useful enrichment levels and product flow rates. To achieve those, centrifuges are connected in cascades. By connecting the centrifuges in series, the enrichment level is increased, and by connecting in parallel, the product flow rate is increased. A cascade schematic is presented in figure 1c. Each row represents a stage, and the number of stages in the cascade is determined by the performance of each centrifuge and by the desired enrichment level.

From Charlottesville to Natanz

The separation of isotopes by gas centrifugation was first suggested by Frederick Lindemann and Francis Aston in 1919, immediately after the existence of isotopes had been experimentally confirmed.( n2) Robert Mulliken in the US, William Harkins in Germany, and Sydney Chapman in the UK tried unsuccessful experiments for more than a decade. It wasn't until 1934 that Jesse Beams of the University of Virginia first reported the successful separation by centrifuge with the isotopes of chlorine. His insight was to place the centrifuge rotor in a vacuum to thermally isolate it from the environment and thereby minimize the convective mixing that had foiled earlier attempts. Figure 2 shows a timeline of the centrifuge's history.

 

Figure 2. Timeline of centrifuge-related events.

During World War II, Beams and others at the University of Virginia became involved with the Manhattan Project with the goal of producing enriched uranium for a nuclear weapon. However, the technology was not successful during that time because mechanically reliable ultrahigh-speed bearings had not been perfected. Nonetheless, development of the gas centrifuge continued after the war, especially in the USSR, where Austrian prisoner of war Gernot Zippe introduced a reliable pivot-magnetic bearing combination. In the summer of 1956, Zippe was released and intercepted by US intelligence agents. Ultimately, he was persuaded to come to the University of Virginia and repeat what he had done in the USSR. That work led to a new generation of advanced centrifuges in the US and the Urenco states. Over time, gas-centrifuge enrichment plants were built in each of those countries, and eventually the process became the workhorse of the international enrichment industry. Today, centrifuges are the primary method of uranium enrichment, and they will soon replace the two surviving plants based on the older gaseous-diffusion technology, located in the US and France.

In 1974 India exploded a nuclear device, which it called a peaceful explosion. That event spurred the development of Pakistan's nuclear weapons program. It also incited Pakistani metallurgist Abdul Qadeer Khan, who was working for Urenco in the Netherlands, to assist Pakistan by making copies of blueprints for centrifuge designs. He later returned to Pakistan, where he used the design information and his contacts in Europe to build an enrichment plant to produce the fuel for Pakistan's first nuclear bomb.

Once Pakistan had demonstrated that a developing country could make fissile material for nuclear weapons with centrifuges, others followed. In the summer of 1987, Iraq initiated its own covert centrifuge program. It floundered at first, but with the help of several disaffected German engineers, Iraq managed to build a modified version of an old Urenco design and test it in the days just prior to the invasion in January 1991.

In parallel to Iraq's effort, Khan began to sell old Pakistani centrifuge parts and blueprints on the black market. Fearing a sting operation, Iraq declined Khan's offer, but Iran and Libya decided to buy. In 2002 there were reports that North Korea had also been in contact with Khan and was developing a gas centrifuge of its own. As of July 2008, traces of highly enriched uranium were reportedly found on North Korean documents, but no evidence of an enrichment plant has emerged. The UK and US were successful in convincing Muammar Qaddafi to dismantle Libya's program, and most of the equipment was shipped to the US. Iran, however, has continued with its centrifuge program, including the recent installation of machines in an underground facility at Natanz. Iran insists that its program is peaceful and has defied international appeals to suspend the program and fully open it to inspection.

The Iran story

The controversy sparked by Iran's nuclear program has done more than any other event in the 60-year history of nuclear nonproliferation to underscore the challenges related to centrifuge proliferation. Iran's program was first revealed by non-government sources in August 2002, and Iran confirmed in February 2003 that it was constructing two centrifuge plants. By that time the program had been secretly under way for more than 15 years, according to information provided by Iran to the International Atomic Energy Agency, with the first centrifuge blueprints and components received from a foreign source in 1987.( n3) Eventually, investigations revealed that source to be Khan and his network of suppliers. (The IAEA Board of Governors has released more than 20 reports on the status of the Iranian nuclear program since June 2003).

In the months following the revelation of the Natanz site, the IAEA carried out several inspections there and made some surprising discoveries. Iran had not declared past enrichment experiments--activities that they were required to report to the IAEA. The agency also found documents related to the production of nuclear weapons and traces of highly enriched uranium, which suggested a foreign origin for some of the equipment.

Initially, a resolution looked workable. In November 2003 Iran suspended its enrichment program after it acknowledged that it had indeed carried out "a limited number of tests, using small amounts of UF₆" in the years 1999 and 2002. Shortly thereafter, Iran also signed (but did not ratify) the Additional Protocol and voluntarily complied with its terms, which give the IAEA broader access to Iran's facilities.

Diplomatic efforts pursued during the suspension period included attempts to persuade Iran to abandon its program in return for an incentive package that included fuel supply assurances and reactor technology. Eventually, all those efforts collapsed. Iran resumed centrifuge production in June 2004 and enrichment activities in January 2006. In the meantime, Mahmoud Ahmadinejad was elected president, and the centrifuge program became a platform for winning domestic political support. In April 2006 Iran began testing the first complete 164-machine cascade, shown in figure 3, and reported the successful production of minute quantities of low-enriched uranium.

Figure 3. The first publicly released picture of the 164-machine cascade installed at Iran's aboveground Pilot Fuel Enrichment Plant. The photo was used in a presentation by Mohammad Saeidi of the Atomic Energy Organization of Iran in September 2005.

By then, the IAEA board of governors had referred Iran's case to the United Nations Security Council, which passed Resolution 1696 in July 2006, demanding "that Iran shall suspend all enrichment-related … activities, including research and development" to build confidence in the exclusively peaceful purpose of its nuclear program. Iran continues to defy those resolutions, and it appears increasingly unlikely that the country will roll back its enrichment project any time soon, given the project's broad domestic support. Various international efforts are being made to accommodate the Iranian technology in a multinational enrichment plant, supplemented by arrangements and features that would make military use of such a facility more difficult. See box 2 for more about Iran's program.

A new kind of challenge

Since early in the nuclear age, the IAEA has been charged with safeguarding nuclear technology to ensure that it is not used for the production of nuclear weapons. The operating premise of those safeguards is deterrence through timely detection. Thus it is not the role of safeguards to prevent proliferation. Rather, safeguards are meant to detect nonpeaceful activities sufficiently early that they can be stopped by political intervention. The centrifuge, however, has properties that make timely detection difficult. One of those properties is the speed with which any peaceful-use plant can be converted to nonpeaceful purposes. That so-called rapid breakout enables the proliferating country to produce nuclear weapons before there is time for a political response and thus renders safeguards largely ineffective. A second problem is the potential for clandestine plants. Compared with nuclear reactors and large gaseous-diffusion plants, a centrifuge plant uses little electricity and produces little detectable signal, so it is much easier to hide the plant and evade safeguards altogether.

The rapid-breakout problem. The inventory of UF₆ in a centrifuge is limited by the condensation pressure at the wall; the UF₆ must remain in gas form, or the rotor will become unbalanced and crash. For normal operating temperatures, the maximum pressure is on the order of 0.001 atmosphere, and the corresponding gas inventory is only a few grams. Typical throughput is on the order of milligrams per second, so an individual machine (or cascade stage) can be flushed of its UF₆ inventory in less than an hour.

In addition, centrifuges typically achieve separation factors (defined in box 1) of 1.2 to 1.5. That is high compared with the earlier gaseous-diffusion process, which is characterized by a separation factor of no more than 1.004. Because of the larger separation factor, a plant based on centrifuges requires fewer total stages to achieve a given level of enrichment. Even for a first-generation centrifuge, the gas needs only to pass through a series of 30-40 stages to reach the high enrichment levels used in nuclear weapons. The combination of few total, stages with the short equilibrium time per stage means the overall cascade equilibrium time is also small. Thus a cascade designed to produce low-enriched uranium for fuel can be re-fed its low-enriched product and begin converting it to highly enriched uranium suitable for weapons use in a matter of days--a procedure called batch recycling. Alternatively, the machines can be reconfigured into a narrower but longer cascade with more stages, a process that requires additional time before production of highly enriched uranium can begin but is more efficient than batch recycling. If the available enrichment capacity is sufficient, the options give a country the ability to produce weapon quantities of material before there is time to respond politically. For an example of a breakout scenario based on Iran's current technology, see box 3.

The clandestine problem. A country could try to build a clandestine plant in the hope of escaping detection altogether. A clandestine centrifuge plant could be difficult to detect. Centrifuges can be placed in buildings indistinguishable in appearance from other industrial facilities. A typical plant uses about 160 W/m², comparable to an average food services facility; that low consumption makes the centrifuge plant impossible to detect by IR imaging. (In contrast, the older gaseous-diffusion plants, which use hundreds or thousands of large compressors, require 10 000 W/m².) Furthermore, most of the pipes in a centrifuge plant operate below atmospheric pressure, so little of the process gas leaks into the atmosphere. Those effluents provide a method of detecting centrifuge plants, but their exceedingly low level makes detection impossible at distances of more than a few kilometers, so it is impractical to detect a covert plant whose location is not already known.

Problems of control

The inability of safeguards to adequately deal with centrifuge plants went largely unnoticed when the technology was held exclusively by states that already possessed nuclear weapons and by their close allies. Today, increasing numbers of states possess centrifuges, including states that are not supporters of the nonproliferation regime and might willingly transfer the technology to like-minded nations. In addition to concerns about state-to-state transfer, residual black-market elements are left over from the Khan network, and qualified technical people are available for hire. UN Resolution 1540 has been important in addressing some of those latter problems by requiring states to put in place stringent export controls and to criminalize private-party proliferation, but the solutions are neither perfect nor easily implemented, especially in resource-starved nations.

Some have argued that if controlling the technology per se is not possible, then it might be possible to set rules on who can own centrifuges and when. The problems with that strategy are twofold. First, peaceful-use nuclear energy provides a legitimate reason to possess centrifuges. States with reactors, or even plans for reactors, can argue that they need to build a national centrifuge enrichment plant to ensure the uninterrupted supply of nuclear fuel for those facilities. Yet a centrifuge plant built to fuel just one commercial-sized reactor is adequate to produce highly enriched uranium for dozens of nuclear weapons per year.

Efforts have been made to counter the energy-security argument by pointing out that it is often cheaper to purchase enrichment services on the international market than to build a national plant at home. Although that is technically true, the economic penalty is not severe. Even if the cost of national enrichment were triple the market price, it results in less than a 10% increase in the final cost of nuclear power--a small insurance premium for energy security. Others have argued that existing market mechanisms have yet to fail. However, the past shows mainly that the market works when the enriching and client states are friends; we have yet to see a state supplying nuclear fuel to one of its enemies. Still others have proposed various kinds of internationalized fuel-supply assurances. Paradoxically, those proposals have not received much traction, because most countries are satisfied with their existing arrangements--and it is difficult to create a new international system without their support.

The second major problem with attempts to set rules limiting the acquisition of centrifuge plants is that many states have grown weary of giving up sovereign rights in the name of nonproliferation. The current nonproliferation regime was based on a bargain between the nuclear haves and have-nots: Those without weapons would forgo the right to possess them and subject themselves to perpetual inspections in exchange for assistance with peaceful-use nuclear technology and eventual disarmament by the nuclear weapons states. So far, none of the original nuclear weapons states has disarmed, "cooperative assistance has been less than forthcoming, and nuclear energy has not been the panacea it was once thought to be. As a result, many states oppose nuclear weapons but also oppose what they see as an inherently unfair nuclear control regime. Some states have even cast their acquisition of centrifuge technology as a political protest against efforts to cement a permanent state of inequity among nations.

Other incentives to acquire centrifuge technology are also increasing. Because of the Iranian nuclear program and the international attention it attracted, centrifuges are now seen as a mark of power and prestige in the Middle East. Although in reality it may be more technically impressive to build any number of other peaceful-use technologies, the connection to nuclear weapons, combined with the efforts to prevent the acquisition of the technology, has rendered the centrifuge a symbol of power. Governments like those of Pakistan and Iran have successfully parlayed that symbolism into widespread domestic support for their centrifuge programs and brought considerable resistance to international efforts to place those programs into abeyance. What is more worrisome is that their enthusiasm might be contagious. It is perhaps not mere coincidence that many Persian Gulf states announced their interest in nuclear power shortly after Iran's centrifuge program became popular.

Looking ahead

As we have seen, safeguards cannot prevent proliferation, especially in the case of centrifuges. However, safeguards can be extended to nuclear materials so as to make the breakout and clandestine loopholes less attractive. In a breakout scenario, speed is the critical factor, and breakout can be made about three times faster if the state uses preenriched UF₆ instead of natural uranium to feed its cascades. Thus it would be sensible to require that all enriched uranium be stored offsite and in a chemical form, such as uranium oxide, that is not suitable for direct reenrichment. That requirement would minimize the amount of low-enriched uranium that can be readily fed back into the centrifuge cascade, extend the breakout timeline, and allow more time for political intervention. However, the solution works only for small-scale facilities; large facilities could enrich uranium fast enough to break out using unenriched uranium feed.

Safeguards might also address the covert-facility problem by safeguarding flows of unenriched UF₆, starting at the facilities where the UF₆ is produced. Traditionally, that material has received relatively little attention. Monitoring unenriched UF₆ more carefully can make its diversion to a covert plant more difficult. Thus, although direct detection 'of covert plants may not be possible, safeguards can make it more difficult to operate those plants with undeclared feed.

With material controls helping to close the loopholes, the application of safeguards to the overall centrifuge complex becomes important again, with a focus especially on uranium flows in the plant. Existing safeguards do not adequately address many of the strategies for centrifuge misuse. Upgrades directed toward better monitoring of enrichment levels and flows are needed both in and around the plant. New technologies, such as RF identification tags, can automate and facilitate the tracking of UF₆ containers. Online monitors can report throughput and enrichment levels in real time. It is important that any new measures be put in place quickly because several large-scale facilities are under construction or planned for Iran, Brazil, France, Russia, and the US; it will be far more difficult to retrofit those plants later, given the delicate nature of centrifuges and their propensity for failure during spin-up and spin-down. Those facilities are likely to set a de facto standard for new plants in other countries, so there is now a unique opportunity to define a new baseline for best practices and safeguards by design.

Safeguards will not, however, be a complete solution. Breakout is still possible with a plant of sufficient size, and covert plants are possible, especially when combined with covert UF₆ production. Owing to the lack of good technical solutions, the centrifuge challenge might be better addressed in the political domain, with arrangements to limit the number of states owning centrifuges or to raise the barriers to using them for weapons purposes.

One proposal now receiving increasing support is the criteria-based approach, which aims to set minimally politicized criteria for the acquisition of a national enrichment capability. Proposed criteria have included the acceptance of certain voluntary safeguard measures, a minimum infrastructure requirement to justify domestic enrichment, and a requirement that the installation of the centrifuge plant not be regionally destabilizing. There may yet be hope for the international fuel-supply assurances discussed earlier, including multinational ownership of facilities, but that depends on whether nations can develop a fair fuel-supply framework that is robust enough to persuade existing nuclear states to give up their right to operate national enrichment plants.

Barring solutions, the problem is likely to grow, especially if there is an expansion in the total number of countries using nuclear energy, which might--or might not--happen in the coming decades. And even if proposed technological and institutional fixes are put in place, they cannot entirely solve the problem; incentives to acquire centrifuge enrichment as a nuclear weapons hedge will remain. Solutions to those problems must involve a country's national security-not just its energy security.

Box 1. How the gas centrifuge works

The gas in the Centrifuge settles into a dynamic equilibrium, balancing the centrifugal force that presses the gas against the wall of the rotor and the diffusive force that seeks to distribute the gas equally throughout the volume of the rotor. For a binary mixture and no internal flow, the resulting distribution holds independently for each species. An equilibrium separation factor α₀ representing the difference in the concentrations of the species at the wall of the rotor is given by

( 1) α₀ = exp[(M₂- M₁)v_{a, sup 2[/2RT},

where V_a is the peripheral speed of the rotor, M₁ and M₂ are the molecular weights of the two species, R is the universal gas constant, and T is the gas temperature. Normally, a c0untercurrent flow is established as depicted in figure 1, and that convective flow carries the lighter isotope to the top of the centrifuge and the heavier isotope to the bottom. That results in an axial separation factor that tends to be much larger than the radial separation factor given by equation 1. The overall separation factor for the centrifuge is defined as

( 2) α = X]sub p]/1 - X_p/ x_W/1 - x_W,

where x_p and x_w are the concentrations of uranium-235 in the product and waste streams, respectively.

The performance of a gas centrifuge is measured in separative work units per Unit time, which has units of kgU/yr. The separative work ΔU is not a measure of energy, but it is nonetheless a measure of the effort expended by the centrifuge. A function of flows into and out of the centrifuge and the concentrations of the streams, it is calculated by the formula

( 3) ΔU = PV(x_p) + WV(x_W) - FV(x_F),

where P, W, and F are product, waste, and feed mass flows, respectively, x_F is the concentration of ²³⁵U in the feed, and V(x) is the value function derived by Paul Dirac and is given by

( 4) V(x) = (2x- 1)In[x/( 1-x)].

The expression for the maximum theoretical performance of a gas centrifuge was also derived by Dirac and given by

( 5) ΔU(max) = π/2 L ρD (ΔM v_{a, sup 2}/2RT)².

Dirac's work was published as part of a book by Karl Cohen.( n4)

In equation 5, L is the length of the centrifuge, ρD is the binary diffusion coefficient, and ΔM is the difference in molecular weights. The actual, or achievable, performance has some efficiency factors related to the shape of the flow profile and the strength of the countercurrent flow. Equation 5 shows that the performance has a fourth-power dependence on the peripheral speed of the rotor V_a and is directly proportional to the length. In practice, the dependence on speed is closer to V_{a, sup 2}, but that is still a strong dependence and emphasizes the importance of rotor speed.

Controlling the countercurrent flow optimizes both the flow profile efficiency and the separative work produced by a single gas centrifuge. Solving the fluid-dynamics equations of motion allows the flow pattern to be optimized, That has been done by directly solving the equations numerically and by obtaining exact solutions. In the US program, a theory group led by Lars Onsager addressed the problem in the 1960s. Onsager used a minimum principle to obtain a single sixth-order partial differential equation, which he solved by eigen-function methods. An analysis of the mathematical details can be found in reference 5.

Making long centrifuges spin at high speeds requires consideration of the materials of construction and dynamics of the rotor. To first order, the maximum peripheral speed is given by V_a = √ σ/ρ where σ is the tensile strength and ρ is the density of the rotor. There is thus a need for strong, lightweight materials.

Long rotors spinning at high speeds have natural bending frequencies, which should not coincide with the operating frequency. A centrifuge operating above the lowest bending frequency is called a supercritical centrifuge, otherwise subcritical. One way to traverse the resonant speeds is to connect a number of shorter rotor segments together with flexible bellows, which provide damping to help the rotor accelerate past the resonances.

Box 2. Is Iran pursuing a nuclear weapon?

Many questions relating to the scope and nature of Iran's nuclear program have been addressed over the past few years. However, as of May 2008, the International Atomic Energy Agency remains unable to certify that Iran's program is for entirely peaceful purposes. From other states, the IAEA obtained evidence that points to weaponization efforts: alleged studies on converting uranium to UF₄ (a precursor of uranium metal), testing of special firing equipment and detonators used in nuclear weapons, and the design of a special missile reentry vehicle suitable for nuclear warheads. Iran maintains that those allegations are baseless and all related documents fabricated.

In addition, early in the investigation, a 15-page document, was found in Iran describing the process of converting uranium into metal form and machining it into hemispheres, a step related to the production of weapons. Iran has reiterated that it obtained the document through the Abdul Qadeer Khan network in 1987 along with centrifuge documentation, but that it had not requested that information. To date, the IAEA still seeks to confirm with contacts in Pakistan the circumstances of the delivery of that document.

All the documents suggesting weapons-related activities date to before the year 2004. That is consistent with the November 2007 US National Intelligence Estimate, which judged with high confidence that in fall 2003, Teheran halted its nuclear weapons program," primarily in response to international pressure. Iran maintains that it never pursued a nuclear weapons option or program.

Even if Iran has terminated specific weapons-related activities for the time being, the remaining centrifuge plant represents the most significant step in acquiring weapons; it can be readily converted to weapons purposes and the other details worked out quickly. It is that fact, combined with the lack of transparency, past infractions, and the possible sublimated interest in nuclear weapons, that continues to fuel tensions between the West and Iran.

Box 3. How credible and fast is a breakout scenario?

Represented in the figure are two plants, one with 12 and one with 36 164-machine cascades (1968 and 5904 machines, respectively), all based on P1-type centrifuges (see figure l b). Two different strategies can be pursued for breakout: simple batch recycling, in which product material is fed back into the original cascades, and cascade interconnection, which involves reconfiguration of the cascades. In each scenario, the material to be used for breakout may be either natural uranium (0.72% ²³⁵U) or a stock of low-enriched uranium (3.5% ²³⁵U). The objective is the production of weapons-grade highly enriched uranium (90% ²³⁵U or more).( n6)

Breakout using natural uranium feed is less credible because most of the required separative work goes into enriching the uranium to LEU levels-an activity that could plausibly be carried out under safeguards prior to breakout. However, if it were done using the full 36-cascade plant, about 40 kg of HEU could be produced in one year by batch recycling; the process is much more efficient if about 12 of the 36 cascades, or about 2000 P1 centrifuges, are reconfigured as dedicated LEU-to-HEU cascades. More than 90 kg/yr of HEU can be obtained that way, but the reconfiguration requires replacement of the complex cascade pipework, which could add several weeks or months up front.

Breakout becomes more credible when preenriched feedstock is available. Then the 12-cascade plant can produce 90 kg of HEU per year, and the 36'cascade plant can yield three times that amount. One concern is that the cascades designed for LEU-to-HEU production may be located at an undeclared site, which would avoid the need to reconfigure the safeguarded centrifuge plant. The covert plant could be contained in a building as small as 500 m² and would be impossible to detect using satellite imagery alone. With a second covert plant, LEU from the declared facility, still in the form of uranium hexafluoride, could be transferred to the undeclared site, and HEU production could commence without further delay. There is still a risk of detection if the diverted LEU is subject to safeguards. However, existing safeguards might be unable to detect the production of excess LEU via certain covert arrangements, and that excess could serve as an unsafeguarded source of LEU for an undeclared facility.

Twelve 164-machine cascades can produce 90 kg/yr or more of HEU when supplied with low-enriched feed by the remaining 24-cascasdes

References

(n1.) S. Villani, ed., Uranium Enrichment, Springer, New York (1979).

(n2.) R. S. Kemp, Sci. Global Sec. (in press).

(n3.) International Atomic Energy Agency Director General, Implementation of the NPT Safeguards Agreement in the Islamic Republic of Iran, GOV/2004/83, IAEA Board of Governors, Vienna, Austria (15 November 2004).

(n4.) K. Cohen, The Theory of Isotope Separation as Applied to the LargeScale Production of U²³⁵, McGraw-Hill, New York (1951).

(n5.) H. G. Wood, J. B. Morton, J. Fluid Mech. 101, 1 (1980).

(n6.) A. Glaser, Sci. Global Sec. (in press).

~~~~~~~~

By Houston G. Wood; Alexander Glaser and R. Scott Kemp

Houston Wood is a professor of mechanical and aerospace engineering at the University of Virginia in Charlottesville. Alexander Glaser is an associate research scholar and Scott Kemp is a PhD candidate in the program on science and global security at, Princeton University in Princeton, New Jersey.

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Perkembangan Alam Pikiran Manusia

hmmm.. oke disini saya mau memberikan pendapat tentang perkembangan alam pikiran manusia. menurut saya perkembangan alam pikiran manusia itu sama seperti perkembangan pemikiran manusia dahulu dengan pemikiran manusia modern. pemikiran manusia sekarang bisa dibilang sepeti pemikiran maju. pemikiran maju menurut saya itu adalah hasil pemikiran seseorang yang berfikiran secara dinamis yang dipengaruhi oleh lingkungan sekitarnya, agar seseorang tersebut tidak berjalan ditempat dan dapat melakukan hal-hal baru dari hasil pemikirannya yang dapat memajukan kehidupan seseorang tesebut.

menurut artikel yang pernah saya baca , "manusia mempunyai hasrat / rasa ingin tahu yang sangat besar. dan banyak diantaranya akan mencoba menjawab dengan menggunakan pengamatan dan penggunaan pengalaman, tetapi sering upaya itu tidak terjawab secara memuaskan".

dan pada dasarnya manusia memang mempunyai hasrat untuk memuaskan hasrat berfikirnya tersebut, bisa dilakukan dengan cara bertanya atau mencari sebuah informasi untuk menjawab semua hal yang ada pada pikiran manusia tersebut. perkembangan pemikiran manusia sendiri berlangsung sangat cepat. bisa dilihat dari kemajuan-kemajuan teknologi sekarang ini. semua ini berawal dari pemikiran kecil seseorang untuk melakukan hal untuk membuat sebuah sesuatu yang akan membantu memudahkan dirinya untuk melakukan aktifitas kesehariannuya tersebut.

 banyak pendapat yang mengatakan bahwa kita sebagai manusia memang harus selalu mengembangkan pemikiran kita. menurut dosen pancasila saya mah " kalo hidup itu harus berinovasi ". memang jika kita tidak untuk berinovasi dalam berfikir , kita bisa dibilang menjadi manusia yang tertinggal dalam hal pemikiran tersebut. karena banyak hal-hal baru yang muncul atas pemikiran manusia itu sendiri. contoh nya banyak filsuf atau ilmuan yang mengutarakan hasil pemikirannya tentang alam dunia ini.

dampak-dampak dari terlalu pesatnya perkembangan pemikiran seseorang pada zaman modern meliputi: 

• dampak positifnya adalah banyaknya pemikiran-pemikiran maju yang membuat manusia tersebut untuk melakukan sesuatu / hal baru yang dapat juga meningkatkan perekonomian dirinya atau di lingkungannya.
• dampak negatifnya adalah banyaknya pemikiran maju seseorang yang menjurus ke hal negatif , yang dapat merugikan semua orang.

sekian yang dapat saya bagikan menurut pendapat saya, kurang lebinhnya bisa diutarakan menurut pendapat kalian sendiri. thks.



Nb: bukan plagiat kan.. cantumin sumber ya kalo mau copas.

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Konversi Ukuran ( m, cm, kaki, inci )

Untuk konversi ukuran meter (m) atau centimeter (cm), ke atau dari feet (kaki) dan inch (inci) bisa dilakukan. Meskipun feet tersebut biasa disebut dengan kaki. Misalnya tingginya 6 kaki atau tingginya 6 feet. Jadi feet itu sebuah ukuran baku dan jangan beranggapan bahwa feet itu adalah sebuah ukuran kaki, yang panjangnya tidak tentu dan berdasarkan perkiraan saja. Ukuran feet ini sering dipakai di negara Inggris atau Amerika. Sementara itu di Indonesia, jarang sekali ditemukan pengukuran dengan menggunakan feet, rata-rata yang digunakan adalah meter atau centimeter. Sehingga telinga kita tidak familiar dengan ukura feet ini.

Misalnya saja, begitu kita mendengar seseorang dengan tinggi 160 cm, maka kita akan segera bisa memperkirakan tinggi orang itu, karena kita familiar dengan ukuran menggunakan centimeter. Sedangkan jika kita mendengar tinggi orang 5 feet, atau 5 kaki, tentu banyak orang Indonesia yang kebingungan memperkirakan tinggi orang tersebut.

Inilah rumus konversi feet dan inci dari atau ke meter:
1 feet = 0,3048 meter, atau
1 meter = 3,2808 feet
1 feet = 12 inch
1 inch = 0,0833 feet
1 meter = 39,3696 inch
1 inch = 0,2734 meter

Sedangkan untuk ukuran centimeter (cm), caranya adalah meter dibagi seratus, karena 1 m = 100 cm.

Feet biasanya ditulis dengan tanda ( ' ), sedangkan untuk inch biasa diberikan tanda ( " ). Contohnya adalah angka 8'35", artinya adalah 8 feet 35 inch. Perhitungan lain adalah misalnya kita menghitung tinggi seseorang 178 cm, ke dalam perhitungan feet dan inch. Langkah perhitungannya adalah sebagi berikut:

178 cm = 1,78 m
1,78 m = 5,839824 feet (hasil dari 1,78 x 3,2808)

Kemudian untuk desimal yang dibelakang (0,839824) harus dijadikan inci, karena satuannya masih feet. Caranya adalah sebagi berikut.

0,839824 feet = 10,077888 inch (hasil dari 0,839824 x 12)
Dibulatkan menjadi 10 inch.

Jadi penulisan tinggi orang tersebut dalam feet dan inch adalah 5'10" (5 kaki 10 inci), tinggi itu sama dengan 178 cm. Begitulah cara perhitungannya, anda bisa mencoba dan melatih sendiri perhitungan tersebut.

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