Exciton binding energy in CdMnTe crystals

We report some results of magnetoabsorption and magnetoreflectivity measurements performed on CdMnTe crystals in magnetic field up to 30 T. The exciton energy at low fields in materials containing magnetic ions is calculated on the basis of the Altarelli-Lipari model and compared with the experimental results. It is shown that spin mixing in degenerate bands strongly affects magnetoabsorption.     

Synthesis of long-chain monosaccharides via the coupling of three ‘normal’ sugar units via Wittig type methodology: unusual removal of the benzyl group under basic conditions

The reaction of diacetonogalactose phosphonate 6 with 2,3:4,5-di-O-isopropylidene-d-arabinose (7) afforded C₁₂-higher sugar enone with an E-geometry across the double bond, which was converted into the fully protected C₁₁-aldehyde 16. This compound was very unreactive and resistant toward the Wittig type and Tebbe reagents, but under PTC conditions, underwent a reaction with stabilized sugar phosphonate to afford C₁₈-enone 17. Very surprisingly unusual removal of the benzyl blocks under these conditions was observed.     

Thermal unfolding of proteins

Thermal unfolding of proteins is compared to folding and mechanical stretching in a simple topology-based dynamical model. We define the unfolding time and demonstrate its low-temperature divergence. Below a characteristic temperature, contacts break at separate time scales and unfolding proceeds approximately in a way reverse to folding. Features in these scenarios agree with experiments and atomic simulations on titin.     

Denaturation of proteins near polar surfaces

All-atom molecular dynamics simulations for proteins placed near a model mica surface indicate existence of two types of evolution. One type leads to the surface-induced unfolding and the other just to a deformation. The two behaviors are characterized by distinct properties of the radius of gyration and of a novel distortion parameter that distinguishes between elongated, globular, and planar shapes. They also differ in the nature of their single site diffusion and two-site distance fluctuations. The four proteins chosen for the studies, the tryptophan cage, protein G, hydrophobin and lyzozyme, are small to allow for a fair determination of the forces generated by the surface as the effects of finite cutoffs in the Coulombic interactions are thus minimized. When the net charge on the surface is set to zero artificially, infliction of deformation is seen to persists but no unfolding takes place. Unfolding may also be prevented by a cluster of disulfide bonds, as we observe in simulations of hydrophobin.     

Microlensing of Kepler stars as a method of detecting primordial black hole dark matter

If the dark matter consists of primordial black holes (PBHs), we show that gravitational lensing of stars being monitored by NASA's Kepler search for extrasolar planets can cause significant numbers of detectable microlensing events. A search through the roughly 150,000 light curves would result in large numbers of detectable events for PBHs in the mass range 5×10(-10) M(⊙) to 10(-4) M(⊙). Nondetection of these events would close almost 2 orders of magnitude of the mass window for PBH dark matter. The microlensing rate is higher than previously noticed due to a combination of the exceptional photometric precision of the Kepler mission and the increase in cross section due to the large angular sizes of the relatively nearby Kepler field stars. We also present a new formalism for calculating optical depth and microlensing rates in the presence of large finite-source effects.     

Working group report: Heavy-ion physics and quark-gluon plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported.     

Isolation of NO(3)(-)-N as 1-phenylazo-2-naphthol (Sudan-1) for measurement of delta(15)N

The conversion of nitrate (NO(3)(-)) to 1-phenylazo-2-naphthol (Sudan-1) has been examined as a method for natural abundance measurement of delta(15)N of NO(3)(-). The reaction results in dilution of NO(3)(-)-N with only one reagent-derived N and the product is readily concentrated from dilute samples by reverse phase chromatography. There is systematic isotopic fractionation during the reaction, but this can be allowed for by analysing known NO(3)(-) standards along with each sample set. Sudan-1 prepared from surface water samples containing approximately 50 &mgr;g NO(3)(-)-N can be analysed by automated continuous flow isotope ratio mass spectrometry with a precision of 0.2 per thousand (one standard deviation) and the accuracy is not affected by interference from other nitrogenous species in the sample or reagents. Copyright 1999 John Wiley & Sons, Ltd.