Physics News off the Web No 1
Compiled by John O’Connor, Past Federal President of AIP
THE PROTON HAS A DIFFERENT SIZE IN DIFFERENT NUCLEI. The electron, which is mostly impervious to the nuclear forces, can penetrate deep inside a nucleus. Therefore, scattering high energy electrons from a nucleus is an excellent way of exploring the electric and magnetic properties of the nucleus as a whole and of its constituent protons and neutrons, especially when the electron transfers some of its spin to a proton in a telltale way. For example, recent results from such an experiment, conducted at the Jefferson Lab, gave evidence that the proton is not necessarily spherical. Now a new experiment at JLab, comparing electrons scattering from single protons (a hydrogen nucleus) with electron scattering from helium nuclei, suggests that each nucleus "kneads" its protons in a different way (see figure at ). The kneading allows the constituent quarks inside the proton to spread out a bit at time, perhaps into a peanut shape, even though its average shape is round. (Strauch et al., Physical Review
Stars make an early entrance (Jul 23)
Astronomers have found evidence for star formation in the earliest known object in the universe. Fabian Walter of the National Radio Astronomy Observatory in the US and colleagues in France, Germany and the US detected the tell-tale signature of carbon monoxide in the infrared emissions of quasar J1148+5251. The discovery suggests that star formation was already underway just 800 million years after the big bang (F Walter et al 2003 Nature 424 406).
Why is the tropopause getting higher? (Jul 24)
Scientists have shown that human activity is having an impact on the height of the tropopause - the boundary between the troposphere (the lowest layer of the atmosphere) and the stratosphere. The height of the tropopause increased by about 200 metres between 1979 and 1999, and Benjamin Santer of the Lawrence Livermore National Laboratory in the US and colleagues in Germany, the UK and the US have used computer models to show that about 80% of this increase was directly caused by human activity (B Santer et al. 2003 Science 301 479).
Nanoscale sensor approaches the quantum regime (Jul 16)
Two physicists in the US have made a motion sensor that can detect movements as small as a thousandth of a nanometre. The sensor combines a nanoelectromechanical bridge and a single-electron transistor, and could be used in applications where ultrahigh precision is essential, such as magnetic resonance microscopy. And if the sensitivity of the device could be improved by a factor of 100 it would be possible to detect quantum effects in a macroscopic system (R Knobel and A Cleland 2003 Nature 424 291) .
PICOSECOND X-RAY CRYSTALLOGRAPHY of a protein has been demonstrated for the first time, by a multinational collaboration (Philip Anfinrud, NIH, ), enabling atom-scale movies of an important biomolecule as it performs a speedy function. This accomplishment will be presented at the upcoming American Crystallographic Association meeting from July 26-31 in Cincinnati ( ; see also Schotte et al., Science, 20 June 2003). While crystallographers have previously obtained frozen snapshots of thousands of proteins, they have yet to capture the full range of motion in even a single protein. Previous x-ray movies of proteins have been on the nanosecond time scale, which is too slow for capturing the steps of many protein processes. Recently, however, at the European Synchrotron and Radiation Facility (ESRF) inFrance, researchers made picosecond-scale movies of a mutant myoglobin molecule getting rid of a toxic carbon monoxide (CO) molecule. Myoglobin is the protein that stores oxygen in muscle tissue. The researchers chose to study a mutant version of the protein because the highly strained atomic structure in part of the protein causes it to get rid of a CO molecule much more quickly than does ordinary myoglobin. To capture this process, they first sent a 1-ps pulse of laser light to the protein to eject the CO. Immediately afterward, they illuminated the protein with intense, 150-ps x-ray pulses from the ESRF synchrotron. Crucial to this process was the ability to isolate single x-ray pulses from the synchrotron. A CCD camera recorded the patterns from the successive x-ray pulses as they passed through the protein. The resulting movie showed the CO migrating to various sites in the protein, with the myoglobin rearranging its shape to accommodate the expulsion of the CO. In addition to enabling researchers to study many important transitions in proteins, the picosecond time-scale of these movies is commensurate with the timescale of many molecular dynamics simulations, allowing for closer comparison between theory and experiment.
Fast and slow light made easy (Jul 10)
Physicists have created "slow" and "fast" light in a crystal at room temperature for the first time. The team at the University of Rochester in the US used an `alexandrite' crystal to reduce the speed of light to just 91 metres per second, and also to make a laser pulse travel faster than the speed of light. Previously these effects - which are not in conflict with special relativity - had only been observed at cryogenic temperatures or in complicated experimental set-ups. The new technique could be used for applications such as optical data storage, optical memories and quantum information devices (M Bigelow et al. 2003 Science 301 200).
HIGH-T SQUIDS PRODUCE MAGNETOCARDIOGRAMS that are clinically practical. SQUIDs (superconducting quantum interference devices) can detect incredibly small magnetic fields, even those produced by nerve signals in the brain or heart. Arrays of SQUIDs have been used to make magnetic maps of the heart in the past but only with models using the lower-critical-temperature superconductors that must be chilled in liquid helium, and operated in a room-sized enclosure needed to shield against extraneous magnetic fields. Now, for the first time, a group of scientists at Hitachi in Japan has produced a magnetocardiograph machine based on high-temperature superconductors which can be chilled with much more tractable liquid nitrogen, and magnetically shielded by a much smaller cylindrical enclosure. The Hitachi device employs a 4 x 4 SQUID array to map the heart's magnetism at field strengths as small as 50 pico-tesla, a million times weaker than Earth's field. One of the authors, Koichi Yokosawa (, 81-423-23-111-39), suggests that magnetocardiography will prove to be one of the forefront applications of high-Tc superconductor technology. (Yokosawa et al., Applied Physics Letters, 30 June 2003)
STAR OUT OF ROUND. The Very Large Telescope Interferometer (VLTI), an array of 2 telescopes which combine their light signals to achieve a higher angular resolution than is possible with any one scope, has determined that the star Achernar is the flattest star ever studied. The VLTI, which does not provide an actual image of the star but can provide an accurate estimate of the star's profile, has determined that Achernar's equatorial radius is 50% larger than its polar radius. This is quite oblate compared to most other celestial bodies, such as our Earth, whose equatorial radius is only 0.3% larger than its polar radius.Theorists do not yet know how to explain how a star like this could turn fast enough to adopt with such a shape without flying apart. Achernar is about 145 light years away from Earth in the southern sky and has a mass of about 6 solar masses. The telescopes used to make the interference map were not the giant 8.2-m VLT telescopes, but more modest 40-cm reflectors set at various configurations with separations as large as 140 m. (European Southern Observatory press release, 11 June, )
Where did the Moon come from? (Jul 3)
Astronomers believe that the Moon was formed when a Mars-sized body smashed into the Earth, ejecting matter into orbit and lengthening our day to its present value of 24 hours. Until recently, however, estimates of much of the Moon is "impactor material" that came from this impactor object, as opposed to the Earth, have varied wildly - from 1 to 90%. Now, by comparing the compositions of lunar and terrestrial rock samples, astronomers in Germany have calculated that no more than two-thirds of the Moon is impactor material. Moreover, they estimate that the Moon must be at least 4.5 billion years old (C Münker et al 2003 Science 301 84).
>Nuclear physicists confirm element 110 discovery (Jul 4)
The production of an element that has already been seen in three different laboratories would not normally be newsworthy. However, confirmation that element 110 can be made in collisions between lead and nickel nuclei is noteworthy given the recent scandal over element 118. Last year the Lawrence Berkeley National Laboratory in the US sacked physicist Victor Ninov after an internal review committee found that he had fabricated data purporting to show the existence of a new element containing 118 protons. Now an international team of nuclear physicists led by Ken Gregorich from Berkeley - and containing many of Ninov's former co-workers - has provided the first confirmation of the discovery of element 110 at the GSI laboratory in Darmstadt, Germany (T Ginter et al. 2003 Phys. Rev. C 67 064609).
Room-temperature single-electron devices made easier (Jun 24)
Physicists at Cambridge University in the UK and the Japan Science Technology Corporation in Tokyo have exploited a "natural" system of tunnel barriers in nanocrystalline silicon to make a single-electron transistor that operates at room temperature. The researchers say that the technique used to fabricate the transistor is compatible with existing silicon technology and has "considerable processing advantages" over the techniques previously used to make similar devices (Y T Tan et al. 2003 J. Appl. Phys. 94 633).