Fusion AGM Weekend 2005

As we go to press, final preparations are underway for our AGM Weekend at the University of Sussex in Brighton on 21-23 January 2005. See page 8 for the full details.

Annual General Meeting

On 22nd January at the Society's AGM a new Fusion Committee will be elected. Some members of the existing committee will submit themselves for re-election while others will retire. All full members of the society are eligible to stand for committee posts. In particular we need a new treasurer, merchandise member and events coordinator although all posts are open for election. An active committee is essential for a healthy society and we hope that all full members will consider putting their names forward. If you would like to know more about any particular post then please get in touch with any Committee member or with the existing post holder through the email links on our Committee Page. If you feel unprepared to take on a particular role at present you could consider standing for a "without portfolio" position with a view to standing for a particular post in a year's time.

Newsletter available on-line!

We are pleased to announce that every past Fusion Newsletter is now available on-line in the Newsletters Section of this web site. A lot of cool stuff has been published over the past three years, so now you can take a walk down memory lane and see how good it really was! Newer members can see what they have missed and why joining Fusion was such a good idea. And you can view all the photos in colour!

Institute of Physics Recognition

For the last 10 years the Institute of Physics has operated a scheme for recognising OU degrees that fulfil the education requirements for Chartered Physicist (CPhys) status. CPhys indicates that a person is a 'professional physicist' and in addition to the degree requirement it requires three years in appropriate employment.

The IoP reviews accreditation of all university physics degrees about every 5 years, and the OU has recently been reviewed, with very positive results. The visiting panel was very impressed with the quality of our courses and thought that the teaching material was outstanding. They were also impressed by the operation of the residential school that they visited (Electromagnetism at Sussex). They expressed some concerns about variability in tutor support (presumably based on feedback from students at the residential school).

The panel will be recommending to the Accreditation Committee of the IoP that an accredited degree must include compulsory courses: S207, MST207/MST209, SM355, SXP390; plus either SMT356 or S357; plus 2 residential school courses, one from SMXR355 or SMXR356 and one from SXR207, SXR208, MSXR209.

This adds to 230 points and the other points can come from any other OU course. The proposed scheme allows much more free choice than the current scheme, but has more compulsory courses and is much more physics focussed. If students omit courses because they have studied equivalent material elsewhere, they will have their accreditation considered on an individual basis by the IoP.

There will be a transition period when the existing and proposed schemes will both be available, so that students who are part way through their degree are not unduly disadvantaged by the change.

The new scheme is not 'official' until the IoP Council formally approves it (sometime in late autumn), but it is unusual for the visiting panel's recommendations to be revised. I think that this is a very good outcome for OU Physics and physics students - it provides students with a clear route to a degree that meets the requirements for professional recognition, and though the new scheme contains less choice within the compulsory courses it does focus on the core physics and skills needed by a professional physicist.

I anticipate that most of the students whose degrees are accredited in the future will have been awarded BSc Physical Science, but clearly many students with this degree won't get IoP recognition (for example, because they have concentrated on the astronomy strand). However, since accreditation is based on courses not the degree title, it will still be possible to get accreditation for an unnamed degree, or BSc Natural Sciences (with Physics).

Stuart Freake - Physical Science Programme Director

QUANTA AND CONTINUUM

Null Hypothesis

Mark Steer and a couple of colleagues from the University of Bristol have started producing a new satirical science journal called Null Hypothesis. It's been described as a cross between Private Eye and New Scientist, publishing spoof articles, fascinating real research and nuggets of the bizarre. Full details and the first issue are available at www.null-hypothesis.co.uk.

One of the things they are particularly interested in promoting is the chance for budding science-writers to have articles published in a national magazine. Articles can be fiction or fact, silly or straight - they don't mind as long as they are well-written.

OUSEDS Founded!

Karen Hurren tells us that OUSEDS - a branch of the United Kingdom Students for the Exploration and Development of Space (UK-SEDS) - has been formed at the OU. UK-SEDS is part of an international organization founded by, and for, students who share a common interest in human space activities. The first UK-SEDS branches were formed in 1989, but interested Fusion members can now join the newly founded UK-SEDS branch within the Open University.

UK-SEDS Branch activities will include regular talks, films and discussions on past, present and future activities in space exploration and development. Trips to space facilities and science centres will be planned, as well as exchange trips and participation in the summer school - Student Undergraduate Research Fellowship Programme at NASA-JPL in California, through the national UK-SEDS organization.

You do not have to be a "science" person to be involved in UK-SEDS. Members of this group come from all academic backgrounds, as it is becoming clear that space will be a more and more important part of all our lives in the future. The founding meeting of OUSEDS took place on the 9th January 2005 at the National Space Centre in Leicester.

The web site address is www.uk.seds.org and if you are interested in joining please email karen@hurren.fslife.co.uk.

Now Something Really Silly

"How I need a drink, alcoholic of course, after the heavy lectures involving quantum mechanics."
What's that all about? Well, actually it's a way of remembering π to 14 decimal places! Look at the lengths of the words... they make up the number 3.14159265358979. We got that from Simon Singh's new book "Big Bang".

Crackpots

If you're not sure how to recognise one, this web article will improve your detection rate! http://math.ucr.edu/ home/baez/crackpot.html.

Shaking Hands with an Alien?

Imagine that an alien has contacted you, and you have communicated by radio, and described one another's worlds, and then you arrange to meet up. But you are concerned in case he's made of antimatter and annihilates you when you shake hands. (This begs the question of what are you both standing on, but never mind!) The thing to do apparently is to watch which hand he puts out to shake yours with, as you have of course explained to him that the tradition on Earth is to shake hands with the hand that corresponds, in its relationship to your body, to the "handedness" of the electrons arising from beta decay. If CP symmetry is observed, a reversal in "C" (matter to antimatter) will be accompanied by a reversal in "P" (parity) so that an anti-alien will try to shake with his left hand, and you should get the hell out of there!
Based on a talk given by Richard Feynman in 1962 at MIT, entitled "Symmetry in Physical Laws" (ch 52 vol 1 The Feynman Lectures on Physics).

Membership Update

To be sure of receiving the Fusion newsletter and details of Fusion events please keep the society up to date about any changes to your postal address, email address and telephone numbers. This will ensure uninterrupted delivery of your Fusion newsletters as well as email notices of Fusion activities. Email is our preferred tool for advising members about last minutes changes to events as it minimises administration costs as well as guaranteeing swift delivery; however, for every mailing a large number of messages are returned as "undeliverable" meaning that the members concerned are not receiving the latest information. Fusion is registered with the Data Protection Registrar and this information will not be used for any other purpose unless you have opted- in to the members' contact list. If your contact details need updating please email membership@oufusion.org.uk or write to Fusion Membership,
142 Kingsley Road,
Northampton NN2 7BY.

International Association of Physics Students

IAPS is an international student-run association seeking to promote peaceful relations among physics students around the world. Through exposing physics students to the international community and helping them to build professional relations, they are fostering a collaborative attitude among young physicists across the globe. Their biggest event is the International Conference of Physics Students (ICPS) where more than 300 physics students get together every year to share scientific results, as well as having a fantastic time making new friends from all over the world. The latest issue of their journal (JIAPS) is out now and available for download in PDF format at www.iaps.info/publications/jiaps/.

ASK-A-BOFFIN

OU Student Ian Robinson asked the following question recently on the "Physical Science Student Chat" conference on First Class:

"Does anyone know if it is possible to measure the time it takes for a transition between allowed energy levels in a quantised system? For example, the time it takes for an electron to transition from the ground state level in a hydrogen atom to a higher energy level when it absorbs a suitable photon."

There have been nearly 40 responses, but no-one has provided a definitive answer. So - does anyone know? Is it instantaneous, or finite?

Revision Weekend Success

by Digby Tarvin

Last October saw the presentation of the first Science Revision Weekend organized as a joint effort by Fusion and the OU Chemistry Society (OUCS).

The revision weekend was held from the 1st to the 3rd of October at the University of York, and by all accounts was a resounding success. The weekend was attended by 23 staff and 301 students (of which 280 of the students were resident). The weekend covered all Open University chemistry, physics and biology 'S' courses for which there was sufficient student demand.

In earlier years many of the physics subjects were catered for by the revision weekend at Aston University run by the OU's M500 Maths Society. However the facilities at Aston were beginning to strain, and in order to allow new subjects to be added to the list, it was decided in negotiations between Fusion and M500 that Fusion would shepherd the transfer of the physics related subjects from Aston to the York weekend, allowing M500 to concentrate on those subjects which are primarily mathematics.

Those that attended the new weekend will know that it was certainly no picnic. The Classes started at 20:30 on the Friday night, and on the Saturday, after breakfast, ran from 8:45 in the morning to 20:30 in the evening, with breaks just long enough for a hearty lunch and dinner, as well as a very welcome morning and afternoon tea. On the Sunday classes started at the same ungodly hour, and the weekend drew to a close at 15:30. Those of us that were used to the Saturday night guest lecture and social events of the Aston weekend no doubt found it a punishing schedule, but hopefully felt the benefit at exam time. We certainly got our "pound of flesh" from the tutors.

Attentive students at Roger O'Brian's S357 Revision Weekend class on Sunday afternoon.

The accommodation was comfortable, although a bit of a maze to navigate initially, spread as it was between three colleges (Langwith, Vanbrugh and Derwent), and the food was plentiful. The courses covered by the weekend this year, and the number of students attending for each are listed below. Where one tutor was involved with more than one course, they contribute an appropriate fraction to the tutor count for each course listed, assuming an equal contribution to each. A complete listing of tutors and the courses to which they contributed is also displayed below.

Next year the Science Revision Weekend is scheduled to take place at York University from 30 September to 2 October 2005. If you are interested, keep an eye on the revision weekend web site at www.sciencerevision.org.uk for announcements.

Second Level Courses
Course	ST240	S204	S205	S207	S216	S269	S282	S283
Tutors	2.75	2	2.25	2	1.75	2	1	2
Students	13	22	27	19	29	29	22	6

Third Level Courses
Course	SD329	S343	S344	S357	SMT356	S381
Tutors	2	1	1	1	1	1
Students	29	48	30	22	30	16

The tutors and subjects to which they contributed were as follows.

Tutor	Subjects
Keith Adkins	SMT356
Carole Arnold	ST240
Stuart Bennett	ST240, S205, S216, S343
Eric Bowers	S204
Alan Cayless	S282
Ken Clarke	SD329
Ian Coleman	S381
Michael Czajkowski	S283
Michael Gagan	ST240, S216
Richard Howell	SD329
Rob Janes	S205, S343
Joe Jennings	S269
David Keen	S207
Heather Kelly	S204
Mike Mortimer	S205, S343
Gordon Nicholas	ST240, S205
Roger O'Brian	S357
Hara Papathanassiou	S283
Ian Saunders	S207
Tony Skinner	S344
Peter Taylor	ST240, S205, S344
Jane Tubb	S269
Adeline Wong	S216

OUCSTSS - A History

by Elsie Denham, OUCSTSS Secretary

As Fusion welcomes over 80 new members from OUCSTSS, Elsie Denham explains a little of the history of the Open University Computer, Sci-Tech and Space Society.

The OU Computer Society (OUCS) started sometime in the 1970s, but it then went through four years of inactivity before it restarted in 1982 with 45 members and £50. What really boosted membership was Sharpey Schafer taking over the running of the Society and the publication of a 50 page £2 booklet Self Help with Home Micros for OU courses, containing programs in Universal Basic for conversion to all home computers. This came at a time when home computers were just being welcomed in the OU and there were few books available. It doubled OUCS membership in a month. To quote Sharpey:

"At study centre terminals a student's mental efficiency drops by 50% due to: no table to spread out numerous books and papers; a pokey room or position; a faint printer ribbon; poor lighting; hit the wrong key foul-ups and starting again from the beginning; the mental pressure of limited one hour slots causing more errors; up to four travel-visits to iron out program bugs. How did we ever put up with it for so long? By contrast one's micro as a terminal at home is a boon and a joy forever."

Meanwhile other societies were going through difficulties and OUCS offered their members a refuge. So by 1988 OUCS was producing a joint journal with the OU Science and Technology Society (OUSTS) - the same journal, but with different covers - whilst the OU Space Society (OUSS) had been absorbed as a special interest area. At this stage the state of the Societies was:

Society	Number of Members
OUSS	88	Group within OUCS
OUSTS	43	Subsidised by OUCS
OUCS	851	Turnover £3000+ p.a.

The next AGM ratified the proposal to formally merge the Societies and thus the OU Computer, Sci-Tech and Space Society was born (OUCSTSS).

In the 1990s new societies grew up which covered some of the individual areas OUCSTSS had absorbed: Fusion covering physics; Chemistry Society; Astronomy and Planetary Society; Development and Environment Society; and for a time, VOUS. So our membership started to decline (not least because no one can work out what the initials stand for!)

Our President, J. M. Sharpey Schafer, had given a large donation to funds in the 1980s which had been invested and grown substantially over the years. Therefore, the Society decided that it would be sensible to spread some of these funds to others and it was agreed that we should approach OU societies with overlapping interests and purchase block membership for OUCSTSS members. These societies would gain additional members and funds; our members would gain new interests and ideas.

So here we are - and I hope we will all benefit from this association!

Diving Physics and Liquid Ventilation

by Anikó Udvarhelyi

Each year there are more and more new certified divers, and this sport is about to become more popular. Parallel to this, it is essential that divers are confident with the physical laws concerning this subject, concerning the problems of pressure and the human body, but this topic can be interesting for non-divers as well. The main questions are: what is happening with our body while it is exposed to pressure, how is it possible to dive 100 or even 300 metres deep?

In the first part I would like to go through the basic physical laws. Firstly, with every 10 metres of depth the ambient pressure increases by an additional 1 atm. This means that the snorkel, the long tube going to the surface for breathing, has got a maximal length: since the muscles to expand and contract the lungs during breathing are not strong enough the maximal snorkel-height was set at 60 cm. But since the difference of the ambient pressure 60 cm deep and the atmospheric pressure coming through the snorkel is 0.06 bar which is already a figure that could tear the lungs, it is forbidden even to use 60 cm long snorkels.

Concerning the compressibility of gases and fluids the simple formula

ΔV/V = - κΔp    describes the behaviour,

where κ is κ_water = 5 x 10^-5 at^-1 for water and κ_idealgas = 1 at^-1 for an ideal gas.

To compare: in the case of water the volume shrinks by only 0.5% at 100 bar pressure-difference, so we could easily dive even 1000 metres deep if we didn't have any gas-filled organs. The huge difference between the compressibility-features of gases and fluids is the key to the diving problem. There are two main possible ways of getting under water: the first is the atmospheric pressure diving where e.g. a submersible protects the diver's body from the ambient pressure. The second is the ambient pressure diving where the body is directly exposed to the ambient pressure and the dive is only possible by choosing a suitable gas-mixture to inhale.

Our task now is to find a proper gas-mixture for a given depth we want to reach. We have to take into consideration Dalton's Law:

p = p_i

which states that the total pressure exerted by a mixture of gases is the sum of the partial pressures that would be exerted by each gas as if it alone occupied the total volume. And secondly Henry's law:

c_i = p_i /H

which means that in a fluid at a given temperature the amount of dissolved gas (c, concentration) is directly proportional (constant H) to the partial pressure of the gas. Hence, the higher the partial pressure, the higher the dissolved concentration of the gas in the blood.

The most important gas to deal with is probably nitrogen. It is an inert gas but it dissolves in the blood according to Henry's Law. Dissolved nitrogen's effect on the human body can be roughly compared with drinking Martini; every 15 m depths is equivalent to drinking one glass of Martini. This is called nitrogen- narcosis; the more and more dissolved amount of nitrogen in the blood affects the brain. However, it isn't this disease which causes the most problems. While ascending too rapidly, the biologically inert dissolved gas, nitrogen, comes out of solution as bubbles due to the reduction of the ambient pressure. These bubbles can be very harmful. If bubble-formation occurs in the vascular system because of the rupture of the alveoli, then it is the cause of arterial gas embolism. Air is being forced trough ruptured alveoli and air bubbles block arteries in the brain and the heart. Both illnesses are treated by recompression with oxygen in a chamber. To avoid decompression illness divers should ascend slowly in order to give the dissolved nitrogen time to come out of the body and secondly the bottom time and the amount of dissolved nitrogen should be strictly calculated in each case.

The only essential gas that has to be mixed to every gas-mixture is of course oxygen. But even with oxygen there are certain limitations (see figure below). Too high oxygen partial pressure is toxic, the 1.5-1.6 bar limit is reached 60-70 metres deep in case of compressed-air diving. This means that with compressed air it is impossible to dive deeper than 60 metres!

To conclude, if we want to dive longer and deeper both the oxygen and the nitrogen percentage of the gas-mixture have to be reduced.

Longer but not very deep dives (maximum 40 metres) can be realised with the gas-mixture "Nitrox" which has a reduced percentage of nitrogen to allow longer bottom times with the same risks of decompression illness. The name Enriched Air Nitrox also indicates that the rest of the gas mixture is oxygen. The following table compares two types of Nitrox, one with 32%, the other with 36% oxygen. We can see that especially for shallow dives these mixtures allow very long dives (15 metres deep 251 minutes with EAN36 in contrast to only 72 minutes with compressed air).

Depth	Bottomtime (minutes)
(metres)	Air	Nitrox	Nitrox
		32% O2	36% O2
15	72	167	251
21	31	57	76
27	18	30	38
33	12	19	24
39	9	14

One solution for deeper dives is helium which is an inert gas as well but doesn't cause narcosis like nitrogen. The other advantage of He is that it is less dense at 90 metres than N₂ is at sea level. On the other hand it has also serious disadvantages. As He is a small molecule it dissolves into blood and tissues much faster than nitrogen does. Therefore, the decompression-times are much longer.

Depth	Mixture (%)
(metres)	O2	He	N2
50	23	33	44
60	20	43	37
70	17	50	33
80	15	56	29
90	14	60	26
100	13	64	23
110	12	67	21
120	11	69	20
130	10	71	19
140	9	73	17

So how is it possible to reach a hundred metres depth? The gas-mixture called "Trimix" is made out of oxygen, nitrogen and of a high percentage of helium. As the table above shows, it is possible with the suitable mixing of these three gases. One can even reach 600 metres and not exceed the 1.4 bar partial oxygen pressure if a mixture containing only 2% of oxygen is used!

No matter what kind of special gas mixtures we use, much greater depths are impossible to achieve. However, liquid-ventilation could be a solution since there wouldn't be any compressibility-problems; in the film Abyss there were divers who applied this technique. Liquid-ventilation, however, is not anymore present only in films, it has become reality. What we need is a special fluid, perfluorocarbon (PFC) which is colourless, and insoluble in water and lipids. An essential requirement is that it has to be able to dissolve enough oxygen. The perfluorocarbons are similar to hydrocarbons with the hydrogen replaced by fluorine. There are already perfluorocarbons in which there can be 20 times more O₂ and 3 times more CO₂ dissolved than in water. Liquid-ventilation experiments have started in the 1960s on mice and today Liquid-ventilation is also performed in humans. There are two main forms of it: during Total Liquid Ventilation (TLV) the lungs are filled with the substance and a liquid ventilator makes the patient breathe PFC. During Partial Liquid Ventilation (PLV) one performs gas ventilation of the PFC-filled lungs using a gas mechanical ventilator. PLV-experiments on patients with severe respiratory failure show that there have been improvements in gas exchange. The adverse effects were self-limited, transient and manageable.

Could even divers profit from this technique one day? At the moment it seems unlikely, since the muscles are not strong enough to breathe a dense substance like a fluid without any ventilator. If scuba divers obey the rules and are aware of the risks of compressed gas diving, diving is easily enjoyable between the limits. But who knows what the future will bring?

Anikó Udvarhelyi is a 2nd year student at the Budapest University of Technology and Economics studying engineering-physics. She is interested in biophysics and medical physics, and has been a diver for eight years. This article is based on a talk given at ICPS 2004.

Safety in Bungee Jumping

A physicist's perspective by Andy Higginbotham

Several years ago, I arrived at Oxford as an enthusiastic young undergraduate. One of the first events in freshers' week was the infamous Freshers' Fair: a chance for university clubs to recruit new blood. One club in particular caught my eye - the Oxford Stunt Factory. This group of "twisted stunt mongers" (to quote Loaded magazine) offered a range of activities from abseiling to zorbing. However, the real gem in the club's crown is Bungee Jumping, a sport that many of its members pioneered.

I soon got to thinking about the physics involved in such sports and one jump in particular caught my eye, the Napalm Touchdown. This stunt involves the jumper leaping from 180 ft, falling towards the ground at breakneck speed and finally touching down on the ground as the bungee rope's tension slows them to a halt. At this serene moment, a 5 kg napalm simulation charge is detonated at their feet engulfing them in a huge ball of flame. How is it possible to engineer a bungee jump so accurately without severely injuring the jumper?

The first ports of call in producing a model of the jump were Hooke's law and a classic conservation of energy calculation. It was immediately obvious that such a crude calculation could never replicate the behaviour of the system but it seemed as good a starting point as any. My first worry was that rubber (out of which most cords are made) doesn't actually obey Hooke's law but displays hysteresis. This results in a force-extension graph that looks distinctly non- linear (see top graph below). A good approximation to this however is to consider the graph as two linear sections joining at a point corresponding to an extension of x₀. This change of behaviour relates to the reordering of the underlying polymeric structure during elongation. The energy stored by the cord is then easily found to be

F dx = k₁x₀² + k₁x₀(x - x₀) + k₂(x - x₀)²

by calculating the area under the graph. I expected this to be only a small improvement on the original Hooke's law approach, but with a few extra corrections pertaining to the lost gravitational potential energy, I found that the model was already accurate to about 3%. This is clearly not enough to model a successful touchdown but it made me consider a far more fundamental question. If I can model to within 3% in a couple of hours, how do so many jumpers get it so wrong?

Every year new stories reach us of people dying during bungee jumping. Is the sport as predictable as my model leads me to believe? The key difference between calculations for a touchdown and those for safety is not of course the model, but the data extracted from it. My model gave 97% accuracy in the mass of jumper needed to touch down safely, but this does not prove that they will make it through the jump without catastrophic equipment failure. What kind of forces are involved?

The model predicts a maximum dynamic force of around 3000 N for a jumper of the maximum mass allowed on our rig. This is the amount our bungee cord itself must be capable of withstanding. Add to this the 7000 N static weight of the rig itself, and a total force of 10 kN must be supported by structural components of the rig.

Maximum Working Loads
Karabiners	~ 20 kN
Harnesses	~ 20-30 kN
Rope	~ 15 kN
Chain	~ 15 kN
Crane Cable	~ 400 kN

A brief investigation of the maximum working loads of the common equipment used in the sport reveals that it is more than adequate to support the loads it experiences during a jump. So we return to our original problem, why do accidents happen when the physics is on our side?

There are two parts to the answer of this question, one of which is based in physics and the other of which is more an exercise in sociology. A small fraction of the accidents that occur are classed as unpredictable. They result from the chaotic nature of the system as a whole. The model above is restricted to one dimension for simplicity and although this captures the essence of the kinetics, it completely underestimates the dynamical side of the jump. The jumper can swing, somersault and even tangle in the rope on the rebound, a phenomenon called wraparound. Wraparound accounts for a small number of incidents in the history of the sport and its results can be horrific (broken limbs, ripping out of hair and unconsciousness all occurring in one recent accident). However, physics again comes to our aid and helps to minimise the probability of serious wraparound injuries. The first contributing factor is the torsional stiffness of the cord. This means that it is very difficult to wrap the cord around yourself as it doesn't like to bend in such a tight loop. Other factors such as the pendulum motion of the jumper prevent the cord coming close to them on the rebound, further minimising the risk. Even when wraparound does occur it tends to unravel harmlessly on the way back down.

The real cause of injury in the sport is, more often than not, negligence on behalf of the site crew. Failure to fully check the equipment can lead to faulty components being used. This has led to a number of jumpers being injured due to catastrophic equipment failure during jumps. Another more sinister cause of injury is bungee companies using inferior methods and equipment in order to cut costs or increase turnaround time for jumpers. This drive to maximise profits led the first commercial operations to use ankle harnessing as opposed to the much safer full body harnesses, purely because they are cheaper and quicker to apply and remove from jumpers.

This lack of attention to safety was the driving force behind the formation of BERSA (the British Elastic Rope Sports Association), the regulatory body of bungee jumping in the UK. BERSA (many of whose members have been involved in the sport since its creation by Oxford's Dangerous Sports Club in 1979), were the first to set out a code of safe practice which, if followed, can help to minimise the risks of the sport by ensuring that safety is always put first. It should come as no surprise to find out that the Oxford Stunt Factory is a founder member of the association.

Hopefully you will feel a little more convinced of the safety of the sport after reading this. One unconfirmed statistic suggests that the risk of serious injury during a jump is the same as the risk during a 100 mile car journey, around one in 500,000 (and significantly lower than this if you jump with a BERSA registered club!) Even the medical profession are now admitting that the effects of bungee jumping on the body are not as severe as was once thought¹.

So go out there and try it. I guarantee that the physics of the jump will be far from your mind as you fall for what seems like the longest and most thrilling few seconds of your life.

Andy Higginbotham is an undergraduate student at Oxford University. His talk on the Physics of Bungee Jumping won the Nexus Undergraduate Lecture Competition at the Young Physicists' Conference in 2003.

¹ After the Fall: Symptoms in Bungee Jumpers - The Physician and Sports Medicine - Vol 26 - No. 5 - May 98.

Occulted

by Fiona Vincent at the University of St. Andrews

This CCD frame was taken from St. Andrews, Scotland. It is centred on RA=04h53m51s, Dec=9d46m58s (2000.0). It is about 17 arc-minutes square, and north is (roughly!) at the top. The exposure was deliberately trailed in declination for 50 seconds, starting at 23:06:23 on 2003 December 11th. The two central trails belong to the stars GSC 688:836 on the left (magnitude 11) and GSC 688:862 on the right (magnitude 12). The gap in the right-hand trail shows where this star was occulted by the 13th- magniude asteroid (585)Bilkis, for about 3.5 seconds starting at 23:06:30.

If an event like this is recorded by several different observers, it is possible to map out the shadow of the asteroid on the Earth, and so to measure accurately its shape and size. Unfortunately, this particular occultation was not reported by anyone else. So all we can deduce is that (585)Bilkis is at least 40km across. I still find it impressive that I could measure something that small, at a distance of 1.3 Astronomical Units (194,500,000 km).

COURSE REVIEW

SXR208 - Observing the Universe

by Karen Hurren

The textbook is subtitled A Guide to Observational Astronomy and Planetary Science, and the course guide introduces the course as being "designed to allow you to exploit the fascination that emerges from observing the breathtaking wonders in the Universe and beyond". And this is exactly what the course does. It gives you the chance to get hands-on experience with setting- up and using a telescope and associated equipment, such as spectrometers and CCD cameras, as well as analyzing the data obtained.

Although it is held at the Observatori Astronomic De Mallorca (OAM), on the lovely island of Mallorca, this course is definitely not a holiday. It is a 15 point course and involves quite a lot of work, with two TMAs to be sent in for assessment.

Accommodation is provided at a hotel in the resort of Cala Millor. However, once there you are basically in a night-shift routine, leaving the hotel each afternoon for the OAM, and returning about 5am the following morning. There is one afternoon for sightseeing - we had a choice of visiting a nearby monastery or the local caves. Apart from that if you want to sightsee it means getting up 'early' and looking around in the morning. Some of us got up around 9am for the first couple of mornings but this became progressively later as the week wore on!

There is a choice of four out of seven projects to be undertaken during the week, with either an astronomy or planetary science flavour. There are also teaching sessions in the planetarium and a number of very good planetarium shows - although the seats are so comfortable it can be very difficult to stop nodding off to sleep, especially the first night following the journey to Mallorca! Previous experience in using a telescope is not necessary so don't be put off if you've never used one before. I hadn't and it really wasn't a problem.

A residential school such as this has been badly needed for a long time. Both tutors and OAM staff worked very hard to make it an unqualified success. As students of the first ever presentation of the course we were all impressed at how smoothly everything went - I don't think anyone wanted to go home at the end of the week.

In conclusion, a fantastic course. Anyone with an interest in astronomy or planetary science should not miss it!