Computer simulation of proton channelling in silicon

The channelling of 3 MeV protons in the 〈110〉 direction of silicon has been simulated using Vineyard model taking into account thermally vibrating nuclei and energy loss due to ion-electron interactions. A beam made up of constant energy particles but with spatial divergence has been simulated for the purpose. The values of the minimum scattering yield and half width of the channelling dip are shown to be depth sensitive and agree well with the measured values. The dependence of yield on the angle of incidence has been found to give information of all three types of channelling. The critical angles for the three types of channelling and wavelength of planar oscillations are consistent with the previous calculations.     

Protein-enhanced photoreactivity--dye promoted polymerization of acrylates

The photoinduced polymerization of acrylic monomers using dyes in a protein-restricted medium is reported. We studied dyes of different families as potential polymerization catalysts, exploiting the observation that the photophysical properties of some dyes are altered when bound to biopolymers. The light induced polymerization of acrylic monomers in the presence of bovine serum albumin or gelatin using triphenylmethane and azo dyes proceeded smoothly. Using GE Miser 120 W spotlights as a convenient illumination source, we found polymerization could be achieved in some cases within 60 min of irradiation. The polymerization rates were found to be dependent on the concentrations of the dye and the protein. In the absence of protein or dye polymerization was virtually non-existent. When the reaction mixture was blanketed with nitrogen, polymerization was observed to be faster than that that in air equilibrated samples. We believe these photopolymerizations may proceed via a free-radical pathway. Our results suggest the possible role of some of these dyes as polymerization catalysts, though they had previously seemed inert in fluid solutions.     

Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.     

Discussion on a possible neutrino detector located in India

We have identified some important and worthwhile physics opportunities with a possible neutrino detector located in India. Particular emphasis is placed on the geographical advantage with a stress on the complimentary aspects with respect to other neutrino detectors already in operation.     

Contributions of a long side chain to the binding affinity of an anthracene derivative to DNA

Systematic studies on the DNA binding of a new anthracene derivative, carrying a 1,8-octyldiamine side chain, were carried out. Calorimetric, spectroscopic, and helix melting studies show that the side chain, consisting of eight methylene groups, enhances the binding constant by a factor of approximately 35 when compared to the binding of a probe lacking the long side chain. Furthermore, the enthalpy of binding of the long-chain derivative to calf thymus DNA (Delta H = 4.1 +/- 0.1 kcal/mol) is far greater than the sum of the enthalpy changes associated with the binding of the probe lacking the long side chain, and the enthalpy for the binding of 1,8-octyldiamine.2HCl. Strong synergistic effects, therefore, are seen with the long-chain derivative. Spectroscopic data indicate bathochromism, strong hypochromism, and quenching of anthryl fluorescence when the above ligand binds to calf thymus DNA. Fluorescence energy transfer studies and circular dichroism data strongly suggest intercalation of the anthryl ring system. The binding stabilizes the double helix, and the helix melting temperature is increased from 78 degrees C to >90 degrees C. The binding to DNA is reversible, depended on the ionic strength, and the major binding mode was suppressed at high ionic strengths and a new mode begins to dominate binding. Substitution of the anthracene ring with 1,8-octyldiamine chain provided a simple method to enhance the binding constant by nearly a factor of 35.