Steady-state thermally annealed GaAs with room-temperature-implanted Si

Semi-insulating Cr-doped single-crystal GaAs samples were implanted at room temperature with 300-keV Si ions in the dose range of (0.17–2.0)×1015 cm–2 and were subsequently steady-state annealed at 900 and 950°C for 30 min in a H2 ambient with a Si3N4 coating. Differential Hall measurements showed that an upper threshold of about 2×1018/cm3 exists for the free-electron concentration. The as-implanted atomic-Si profile measured by SIMS follows the theoretical prediction, but is altered during annealing. The Cr distribution also changes, and a band of dislocation loops ~2–3 kÅ wide is revealed by cross-sectional TEM at a mean depth of Rp~3 kÅ. Incomplete electrical activation of the Si is shown to be the primary cause for the effect

Pulsed electron beam induced recrystallization and damage in GaAs

Single-pulse electron-beam irradiations of 300-keV 10^(15)Kr+/cm^2 or 300-keV 3×10^(12)Se+/cm^2 implanted layers in unencapsulated GaAs are studied as a function of the electron beam fluence. The electron beam pulse had a mean electron energy of ~-20 keV and a time duration of ~-10^(–7) s. Analyses by means of MeV He + channeling and TEM show the existence of narrow fluence window (0.4–0.7 J/cm^2) within which amorphous layers can be sucessfully recrystallized, presumably in the liquid phase regime. Too high a fluence produces extensive deep damage and loss of As

Bay of Bengal: From monsoons to mixing

The Bay of Bengal has a surprisingly large influence on the world. It nurtures the South Asian summer monsoon, a tremendous ocean-atmosphere-land phenomenon that delivers freshwater to more than a third of the human population on this planet. During summer, southwesterly winds gather moisture from the ocean and carry it deep inland over the Indian subcontinent, bringing welcome rains to a parched land. During winter, the winds reverse to northeasterly, and the ocean circulation responds by dispersing the terrestrial freshwater run off concentrated in the northern part of the bay

Biochemical study of certain enzymes and metabolites of the carbohydrate metabolism in the skeletal muscle of the dengue virus-infected mice

Changes in enzymes and metabolites of the carbohydrate metabolism in skeletal muscles were studied in mice after intracerebral inoculation of dengue type 2 virus. It was noted that lactic dehydrogenase, aldolase, phosphogluco-isomerase, phosphoglucomutase, GO-T and GP-T activity were enhanced initially by two- to three-fold, reaching a peak on day 5. As the illness appeared in mice, all the enzyme activities were lowered and were about three times less in the paralytic stage on the 8th day as compared to controls. Fructose-1,6-diphosphatase activity was increased on the 4th and 5th days but decreased later. Acid phosphatase increased abruptly from the 6th day while alkaline phosphatase activity was irregular. Creatine increased on the 4th and 5th days but diminished later. Glycogen decreased from the beginning and was lowest on the 5th day, but the levels increased later and were maximum in paralysed muscles. On the other hand, lactic acid began accumulating in the muscles and was maximum on the 5th day, then declined. Dengue virus was detected in the muscles from the 2nd day but higher titres were seen from the 6th day. Changes similar to the preparalytic stage of mice may occur in human beings, causing myalgia

The effect of hydrophobic glassy organic material on the cloud condensation nuclei activity of particles with different morphologies

Particles composed of organic and inorganic components can assume core-shell morphologies. The kinetic limitation of water uptake due to the presence of a hydrophobic viscous outer shell may increase the critical supersaturation required to activate such particles into cloud droplets. Here we test this hypothesis through laboratory experiments. Results show that the viscosity of polyethylene particles is 5×106&thinsp;Pa&thinsp;s at 60&thinsp;∘C. Extrapolation of temperature dependent viscosity measurements suggests that the particles are glassy at room temperature. Cloud condensation nuclei (CCN) activity measurements demonstrate that pure polyethylene particles are CCN inactive at diameters less than 741&thinsp;nm and 2.5&thinsp;% water supersaturation. Thus, polyethylene is used as proxy for hydrophobic glassy organic material. Ammonium sulfate is used as proxy for hygroscopic CCN active inorganic material. Mixed particles were generated using coagulation of oppositely charged particles; charge-neutral polyethylene–ammonium sulfate dimer particles were then isolated for online observation. Morphology of these dimer particles was varied by heating, such that liquefied polyethylene partially or completely engulfed the ammonium sulfate. Critical supersaturation was measured as a function of dry particle volume, particle morphology, and organic volume fraction. The data show that kinetic limitations do not change the critical supersaturation of 50&thinsp;nm ammonium sulfate cores coated with polyethylene and polyethylene volume fractions up to 97&thinsp;%. Based on these results, and a synthesis of literature data, it is suggested that mass transfer limitations by glassy organic shells are unlikely to affect cloud droplet activation near laboratory temperatures.</p

Effects of magnetic field induced chiral-spin interactions on quasi-one-dimensional spin systems

It is known that in certain non-bipartite quasi-one dimensional spin systems in a magnetic field, in addition to the usual Pauli coupling of the spins to the field, new parity breaking three spin interactions, i.e. chiral spin interactions, are induced at higher order due to virtual processes involving the intrinsic electronic nature of the underlying spins. The strenght of these interactions depend strongly on the orientation of the field, a feature which can be exploited to detect chiral effects experimentally. In many spin systems, these chiral interactions are generated and should be taken into account before any comparison with experiments can be made. We study the effect of the chiral interactions on certain quasi-one-dimensional gapped spin half systems and show that they can potentially alter the physics expected from the Pauli coupling alone. In particular, we demonstrate that these terms alter the universality class of the C-IC transition in spin-tubes. More interestingly, in weakly coupled XX zig-zag ladders, we find that the field induced chiral term can close the singlet gap and drive a second order transition in the non-magnetic singlet sector, which manifests itself as a two component Luttinger liquid-like behaviour in the spin correlation functions. Finally, we discuss the relevance of our results to experiments.Comment: RevTex, 11 pages, 3 figure

GASP XVIII: Star formation quenching due to AGN feedback in the central region of a jellyfish galaxy

We report evidence for star formation quenching in the central 8.6 kpc region of the jellyfish galaxy JO201 which hosts an active galactic nucleus, while undergoing strong ram pressure stripping. The ultraviolet imaging data of the galaxy disk reveal a region with reduced flux around the center of the galaxy and a horse shoe shaped region with enhanced flux in the outer disk. The characterization of the ionization regions based on emission line diagnostic diagrams shows that the region of reduced flux seen in the ultraviolet is within the AGN-dominated area. The CO J$_{2-1}$ map of the galaxy disk reveals a cavity in the central region. The image of the galaxy disk at redder wavelengths (9050-9250 \overset{\lower.5em\circ}{\mathrm{A}}) reveals the presence of a stellar bar. The star formation rate map of the galaxy disk shows that the star formation suppression in the cavity occurred in the last few 10$^8$ yr. We present several lines of evidence supporting the scenario that suppression of star formation in the central region of the disk is most likely due to the feedback from the AGN. The observations reported here make JO201 a unique case of AGN feedback and environmental effects suppressing star formation in a spiral galaxy.Comment: Author's accepted manuscrip

A Strong-Coupling Approach to the Magnetization Process of Polymerized Quantum Spin Chains

Polymerized quantum spin chains (i.e. spin chains with a periodic modulation of the coupling constants) exhibit plateaux in their magnetization curves when subjected to homogeneous external magnetic fields. We argue that the strong-coupling limit yields a simple but general explanation for the appearance of plateaux as well as of the associated quantization condition on the magnetization. We then proceed to explicitly compute series for the plateau boundaries of trimerized and quadrumerized spin-1/2 chains. The picture is completed by a discussion how the universality classes associated to the transitions at the boundaries of magnetization plateaux arise in many cases from a first order strong-coupling effective Hamiltonian.Comment: 5 pages REVTeX, three PostScript figures included using psfig.st

Frustrated trimer chain model and Cu3Cl6(H2O)2 2H8C4SO2 in a magnetic field

Recent magnetization and susceptibility measurements on Cu3Cl6(H2O)2 2H8C4SO2 by Ishii et.al. [J. Phys. Soc. Jpn. 69, 340 (2000)] have demonstrated the existence of a spin gap. In order to explain the opening of a spin gap in this copper-trimer system, Ishii et.al. have proposed a frustrated trimer chain model. Since the exchange constants for this model have not yet been determined, we develop a twelfth-order high-temperature series for the magnetic susceptibility and fit it to the experimentally measured one. We find that some of the coupling constants are likely to be ferromagnetic. The combination of several arguments does not provide any evidence for a spin gap in the parameter region with ferromagnetic coupling constants, but further results e.g. for the magnetization process are in qualitative agreement with the experimental observations.Comment: 9 pages REVTeX, 4 PostScript figures included using psfig.sty; for series and supplementary material see http://www.tu-bs.de/~honecker/3mer/ or http://www.itp.phys.ethz.ch/staff/laeuchli/3mer ; substantial reorganization including shifting part of the discussion to WWW pages with "supplementary material"; new appendix shows that antiferromagnetic J_i > 0 are not compatible with the experimental data for the magnetic susceptibilit

Far Infrared Observations of the Galactic Star Forming Regions associated with IRAS 00338+6312 and RAFGL 5111

Two Galactic star forming regions, one in a very early phase of evolution and another evolved one, associated with the IRAS sources 00338+6312 and 03595+5110 (RAFGL 5111) respectively have been studied in detail. These sources have been mapped simultaneously in two far infrared bands at 143 & 185 \micron), with about 1.5 arcmin angular resolution, using the TIFR 100 cm balloon borne telescope. The HIRES processed IRAS maps at 12, 25, 60 & 100 \micron, have been used for comparison. Whereas IRAS 00338+6312 is resolved only in the TIFR bands, RAFGL 5111 is very well resolved in both the TIFR bands, as well as in at least 3 IRAS bands. The neighbouring fainter source IRAS 04004+5114 has also been resolved in the TIFR bands. Taking advantage of the identical beams in the two TIFR bands at 143 & 185 \micron, dust colour temperature, $T(143/185)$, and optical depth, $\tau_{150}$, maps have been generated for RAFGL 5111. These maps show interesting structural details. Radiative transfer modelling in spherical geometry has been carried out for individual sources. The best fit models are in good agreement with the observed spectral energy distribution (SED), radio continuum data etc. Another scheme of radiative transfer through the interstellar dust-gas cloud including the heavier elements has been used to predict ionic nebular line emission, which are in reasonable agreement with the measurements for RAFGL 5111. An important conclusion from the present study is that, for all the three sources (IRAS 00338+6312; 03595+5110; and 04004+5114, a faint source in the neighbourhood of RAFGL 5111), the best fit to the observed SED is obtained for a uniform density ($n(r) \sim r^0$) cloud