Extracts from the Internet

Electron orbitals

Standard x-ray diffraction methods yield only the averaged distribution of atoms in a crystal lattice. By combining electron diffraction and electron microscopy, J. M. Zuo and colleagues of Arizona State University were able to visualize the shape of individual electron orbitals (electron density distribution around atoms). The 3D map so obtained shows that Cu-Cu bonds in Cu2O are of covalent character and formed by d-orbital electrons and by holes. The study is likely to provide further insight into high-temperature superconductivity and to speed up the development of new superconductors. Source: Nature 401 49 1999

Optical parametric amplifier

In their experiments on infrared image amplification, Kumar and his colleagues at Northwestern University in Evanston, IL, used a potassium titanyl phosphate (KTP) crystal to avoid noise problems that typically plague the work of conventional amplifiers. Green laser photons produce IR photon pairs when passing through a crystal, and if the image of an object is simultaneously projected onto the crystal, the IR beam will stimulate the production of additional IR photon pairs, which will join forces with the initial ones to amplify the image. This `optical parametric amplification' technique may find useful applications according to its authors, despite the challenge of synchronizing laser light and IR photons to obtain the stimulated emission. Source: Phys.Rev.Let. 83 1938 1999

Fermi degenerate atomic gas

In the past few years researchers have succeeded in producing the Bose degenerate gas (Bose-Einstein condensate) of alkali metals and hydrogen atoms by descending to low enough temperatures for the average distance between atoms to be comparable to their de Broglie wavelength. As compared to bosons, fermions are much harder to cool, however, because the Pauli exclusion principle makes atoms in identical states effectively repel one another thus disabling the evaporative cooling method. Researchers at the National Institute of Standars and Technology in Colorado, USA, were able, for the first time, to overcome this difficulty and prepare a degenerate gas of Fermi atoms. In their experiment, 40K atoms with opposite spins were first accumulated in a magneto- optical trap and then subject to an alternating electromagnetic field; as a result, atoms of one spin orientation left the trap thus carrying away energy and cooling to superlow temperatures the opposite-spin atoms still in the trap. With this technique, a degenerate gas of 700,000 atoms at about 300 nK was prepared. Source: Physics News Update, Number 443; Science 285 1703 1999

Chandra X-ray Observatory

The Chandra X-ray Space Observatory, so named in honor of the Nobel laureate S Chandrasekhar, has yielded important data while still at its testing and tuning stage following the 23 July, 1999 launch. Chandra's two instruments, each a two-in-one device consisting of an imager and a spectrometer, far exceed all previous instruments in sensitivity and resolution power. Directed at the remnants of Cassiopea A supernova (which exploded about 300 years ago and strangely enough remained undetected by astronomers of the time), Chandra discovered a previously unobserved neutron star left behind by the explosion. Among other findings, a jet from the core of a faraway quasar and a hot crown of a star are noteworthy. As work goes on, many other interesting observations are likely to be done. Source: http://wwwssl.msfc.nasa.gov/default.htm

The Hubble constant

The Hubble images of Cepheid variable stars in faraway galaxies have lead to an improved extragalactic distance scale and a more accurate value of the Hubble constant H0. From the known period- luminosity dependence of long-period Chepeids, their absolute stellar magnitudes and hence photometric distances can be determined. Data on 25 Cepheids within 25 Mpc of the Earth have allowed a number of secondary distance determination methods using the Tully-Fisher relation, Type Ia supernovae, etc. to be more accurately calibrated. In adding the velocities of a local galaxy group relative to close clusters and a local supercluster, a linear model was employed. The least-mean-squares fitted result is H0=71±6km/sec/Mpc, the largest contributor to its uncertainty being the distance to the Large Magellanic Cloud, with more than 1000 known Cepheids. Source: http://xxx.lanl.gov/abs/astro-ph/9909260

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The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) — the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.

Permanent editor is Yu.N. Eroshenko.

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