Folding proteins caught in the Act. biochemists have developed the fastest techniques yet to spy on proteins in the first stages of curling into their final 3D structures - acts that happen in less than a microsecond. /*---------------------------------------------------------------------*/ With Mirrors and Finesse, Labs Domesticate the Xray Laser. Table top xray lasers . First xray lasers were energized by nuclear explosions or jolts of light from giant glass lasers built for fusion experiments - hardly bench top equipment. Substitute electric discharges and lower power optical lasers for brute force pumping techniques of first xray lasers. Boost efficiency by reflecting the xrays back and forth through the laser medium to extract more of its energy. All of which is raising expectations that the intense, coherent, short wavelength pulses from bench top xray lasers will soon be opening windows on the dynamics of chemical reactions or allowing investigators to make holograms of living cells. Xray lasers are no different from lasers at other wavelengths. They extract photons from medium that has been jolted into what is called a population inversion : a state in which many of the atoms have been boosted to energy levels from which they can emit a photon when another photon of the same wavelength brushes past- a process called stimulated emission. The net result, two photons instead of one, both traveling in the same direction, is laser amplification. The shorter the wavelength emitted by the laser, the higher the energy level to which the atoms have to be boosted. And that's the challenge with xray lasers. To get a material - usually a metal such as selenium ,zinc, or ytttrium - to emit xrays, it has to be heated to temperatures as high as millions of degrees centigrade, forming a plasma, or ionized gas. The plasma then has to be excited even further to create the population inversion. Often this is done by heating the plasma so rapidly that the free electrons become much hotter than the positively charged ions and kick the ions into higher energy states. The traditional way of pumping in all this energy - with a single jolt from a powerful infrared laser like the building size Nova laser at LLNL - stands in the way of making xray lasers into tabletop instruments. Lasers like Nova are not only big and costly but also have to cool down after each "shot" limiting the repetition rate of xray pulses to once every 20 minutes at best" The bigger the machine, and the older the technology, the longer it takes to wait for the next shot. But recently scientists have realized that if they create the excite the plasma with several ultrashort pulses, lasting just a few trillionths of second each, rather than a single longer one, they can get away with a smaller pumping laser. Explains Ernst Fill of the Max Planck Institute for quantum Optics in Garching, Germany "A prepulse creates the plasma, and then the main pulse heats it in such a short time that you get an overshoot. a state , far from equilibrium, in which upser heated electrons pummel the cooler ions, efficiently creating the population inversion. At the meeting , Peter Nickles at Max Born Institute in Berlin described how they exploited this multiple pulse approach, which was pioneered at LLNL. With a prepulse of 5joules and the main pulse of 3 joules, nickles ' group was able to spark xray lasing in titanium vapor- a feat requiring a 200joulse pulse at Nova. Although the Berlin group's pumping laser still sprawls across 3 10meter tables, researchers say that transforming it into a tabletop device should be straightforward engineering task. This is a very exciting result, leading the way to table top lasers. Optical lasers reach this state, known as saturation with the aid or mirrors at either end of the lasing medium that reflect the light back and forth through it. This step is key for a practical laser, because it's only a saturation that a laser produces truly coherent radiation - radiation at which the wave motions of all the photons are in step. Coherence, in turn makes the laser light suitable for a host of applications such as holography or interferometry. Saturation has been difficult to achieve for xray lasers, in part because the population inversion often lasts no more than a few tens of picoseconds - time for the xrays to travel only a few centimeters. /*---------------------------------------------------------------------*/ Helical beams Give Particles a Whirl Physicists wanted to pick up and hold particles as small as a single molecule have reached for tweezers optical tweezers. Optical tweezers use the electric field crated at the narrowest point of a tightly focused laser beam to hold onto particles of dielectric, or insulating, materials - which include most biological samples. The particles are electrically attracted to the region where the field and the beam is strongest : right at the center. Miles Paget at St Andrews in Scotland suspected that a laser beam with a different intensity profile,, known as Laguerre-Gaussian might create a more versatile kind of trap.. Such laser beams are doughnut-shaped in cross section, with a dark spot in the middle surrounded by a bright ring of laser power, and are created by shaping the beam with cylindrical lenses or holograms. Like a optical tweezers, a Laguerre-Gaussian beam draws a specimen toward its most intense regions - which are found not at its center but in the bring ring. If the size of the specimen is roughly the same as the ring diameter, it gets pinned by its edges. Both groups managed to trap particles this way. Laguerre-Gaussian beams have a spinning, helical electromagnetic field. Impart angular momentum to a trapped particle, making it spin. /*---------------------------------------------------------------------*/ The World's Fastest Computer University of Tokyo built what they say is now far and away the fastest computer in the world, Able to perform up to 1.08trillion floating point operations per second Tflops. That's 4x as fast as the current record holder for general-purpose supercomputers, a machine made by Fujitsu Ltd. for Japan's national Aerospace Laboratory with a theoretical peak speed of 280gigaflops. The computer GRAPE - 4 (GRAPE stands for Gravity PipE) is a highly specialized beast, designed only to do certain astrophysical calculations. Astrophysicist Junichiro Makino, who developed it with computational physicist Makoto Taiji, says the effort grew out of so-called Nbody simulations, in which large scale astronomical systems such as galaxies and globular clusters are expressed as groups of indivdual bodies interacting through gravity. Astrophysicist Piet Hut of the Institute for Advanced study in Princeton who collaborates with the Tokyo group, explains that in stellar dynamics the heavy work involved in computing gravitational forces makes for a computational bottleneck. while a conventional supercomputer does the work through a series of software operations, Makino and colleagues created a special purpose chip to do the job, hardwiring the equations as circuits on 1692 custom integrated processors. This makes for a qunatum increase in speed: for example, Makino estimates that a simulation of the evolution of a 32000 body globular cluster that took about 3 months on GRAPE 4 would take at least 5 years on a ordinary supercomputer. Of course, the scientists do not plan to stand pat with GRAPE 4 Makino who describes the GRAPE family in july/august issue of journal computers in physics say they are now hoping to harness 20000 of their specialized processors into a $10million petaflop (10^15 operations per second) machine by the turn of the century. /*---------------------------------------------------------------------*/ Drugs to Prevent Alzheimer's Drug : Cognet,Aricept Activity : Acetylcholinesterase inhibitor Mechanism of Action : Compensate loss of cholinergic neurons Drug : Ampakines Activity : Enhance activity of AMPA receptor Mechanism of Action : Improve memory by enhancing long term potentiation Drug : Prednisone, ibuprofen other NSAIDs Activity : Antiinflammatory Mechanism of Action : Prevent inflammatory damage to neurons Drug : Vitamin E Activity : Antioxidant Mechanism of Action : Protects against free radical damage Drug : Premarin Activity : Female hormone Mechanism of Action : Promotes neuronal survival Drug : Nerve growth factor Activity : Maintain cholinergic neurons in brain Mechanism of Action : Promotes neuronal survival Drug : Calcium channel blockers Activity : Inhibit calcium ion entry into neurons Mechanism of Action : Reduce calcium toxicity Drug : Cholesterol lowering drugs Activity : Lower apoE4 concentrations Mechanism of Action : Prevent apoE4 toxicity to neurons Drug : Protease inhibitors Activity : Block B-amyloid production Mechanism of Action : Prevent neuronal loss to b-amyloid toxicity. /*---------------------------------------------------------------------*/ Homogeneous linewidths in the optical spectrum of a single gallium arsenide quantum dot. The homogeneous linewidths in the photoluminescence excitation spectrum of a single, naturally formed gallium arsenide (GaAs) quantum dot have been measured with high spatial and spectral resolution. Th e energies and linewidths of the homogeneous spectrum provide a new perspective on the dephasing dynamics of the exciton in a quantum confined, solid state system. The origins of the linewidths are discussed in terms of the dynamics of the exciton in zero dimensions, in particular, in terms of lifetime broadening through the emission or absorption of phonons and photons. /*---------------------------------------------------------------------*/ Two Calorimetrically Distinct States of Liquid Water Below 150 K. vapor-deposited amorphous solid and hyper quenched glassy water were found to irreversibly transform, on compression at 77kelvin, to a high density amorphous solid. On heating at atmospheric pressure, this solid became viscous water , with a reversible glass-liquid transition onset at 129+/-2 kelvin. A different form of viscous water was formed by heating the uncompressed vapor-deposited amorphous solid and hyper quenched liquid water. On thermal cycling up to 148k , water B remained kinetically and thermodynamically distinct from water A . The occurrence of these two states, which do not interconvert, helps explain both the configurational relaxation of water and stress induced amorphization. /*---------------------------------------------------------------------*/