Structure, stability and dissociation of silanitriles RSiN (R = H2B, H2N, H2P)

Structure, stability, and dissociation of H₂BSiN, H₂NSiN, H₂PSiN and their isomers H₂BNSi, H₂NNSi, H₂PNSi have been studied in detail using ab initio MP2 and CCSD(T) methods. After dissociation of H₂BNSi, H₂NNSi, H₂PNSi and their isomers, the fragmented atoms have been considered to be either in their ground state or in their valence excited state in various dissociation channels. Only allowed dissociations of these molecules are considered. Various dissociation channels of H₂BNSi, H₂NNSi, H₂PNSi and their isomers have been explored and interesting trends are observed for the dissociation of stable isomers H₂BNSi, H₂NNSi, H₂PNSi and less stable isomers H₂BSiN, H₂NSiN, H₂PSiN. The effect of substituents on their structural properties has been discussed. The potential energy surfaces for the RSiN ? RNSi isomerization reactions have been analyzed. The structural properties of these molecules agree well with the theoretical values wherever available.     

Modulation of residual stress in diamond like carbon films with incorporation of nanocrystalline gold

Residual stress modulation in the diamond-like carbon coatings with incorporation of gold nanoparticles was studied critically. The films were deposited on glass and Si (1 0 0) substrates by using capacitatively coupled plasma chemical vapor deposition. Stresses in the films were determined from the broadening of the optical absorption tail and were found to decrease from 2.3 GPa to 0.48 GPa with increasing gold content (2-7 at.% Au) in the DLC matrix. Gold incorporation also made the films harder than the corresponding DLC coatings. Modulation of stress with nanocrystalline gold content in the DLC matrix was related to the relative amount of sp²/sp³ content in the DLC films.     

A possible connection between neutrino mass generation and the lightness of a NMSSM pseudoscalar

One of the interesting properties of the NMSSM is that it can accommodate a light pseudoscalar of order 10 GeV. However, such scenarios are challenged by several experimental constraints, especially those related to the fermionic decays of the pseudoscalar. In this Letter, we extend the NMSSM field content by two gauge singlets, with lepton numbers +1 and −1. This serves the twin purpose of generating neutrino masses via the inverse seesaw mechanism and keeping the option of a very light pseudoscalar experimentally viable by opening dominant invisible decay channels of the pseudoscalar which help it evade the existing bounds.     

Coexistence of competing predators in a coral reef ecosystem

An analysis is made using a four-dimensional mathematical model where there is a constant rate of flow of input nutrient. An organism is introduced in the model which is growing by taking in that nutrient. Two other predators on that organism are also introduced. The predators at the second and third trophic levels belong to the same species, though of different age groups. The predator at the third trophic level exhibits a distinct cannibalistic attitude to the predator of the second trophic level. Our analysis leads to different thresholds in terms of the model parameters acting as conditions under which the species associated with the system cannot thrive even in the absence of competition. Local stability of the system is obtained when one or more of the predators go extinct. Under appropriate circumstances a positive rest point of the system is obtained. Computer simulations have been carried out to illustrate different analytical results.     

Aqueous-phase synthesis of PAA in PVDF membrane pores for nanoparticle synthesis and dichlorobiphenyl degradation

This paper deals with bimetallic (Fe/Pd) nanoparticle synthesis inside the membrane pores and application for catalytic dechlorination of toxic organic compounds form aqueous streams. Membranes have been used as platforms for nanoparticle synthesis in order to reduce the agglomeration, encountered in solution phase synthesis which leads to a dramatic loss of reactivity. The membrane support, polyvinylidene fluoride (PVDF) was modified by in situ polymerization of acrylic acid in aqueous phase. Subsequent steps included ion exchange with Fe²⁺, reduction to Fe⁰ with sodium borohydride and Pd deposition. Various techniques, such as STEM, EDX, FTIR and permeability measurements, were used for membrane characterization and showed that bimetallic (Fe/Pd) nanoparticles with an average size of 20–30 nm have been incorporated inside of the PAA-coated membrane pores. The Fe/Pd-modified membranes showed a high reactivity toward a model compound, 2,2′-dichlorobiphenyl and a strong dependence of degradation on Pd (hydrogenation catalyst) content. The use of convective flow substantially reduces the degradation time: 43% conversion of dichlorobiphenyl to biphenyl can be achieved in less than 40 s residence time. Another important aspect is the ability to regenerate and reuse the Fe/Pd bimetallic systems by washing with a solution of sodium borohydride, because the iron becomes inactivated (corroded) as the dechlorination reaction proceeds.     

On the calculation of second order properties: An equation of motion approach

In the light of the equation of motion method a general expression for polarisability calculation has been derived. From this general expression, different approximation methods can be deduced for different choices of ground state and excitation manifold. Among these the coupled Hartree-Fock theory is the most extensively used one for polarisability calculations. It has also been shown that this theory has a simple relationship with random phase approximation.     

Simultaneous determinations of a monofluorinated imidazo[1, 5-a] [1, 4] benzodiazepine and the corresponding benzophenone as a function of pH and in aqueous formulations by 19F nuclear magnetic resonance spectrometry

8-Chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazo[1, 5-a] [1, 4 ]benzodiazepine (called “midazolam”) exists in equilibrium with the corresponding benzophenone (the“open-Mng form”). The two compounds were determined simultaneously as a function of pH with ¹⁹F-n.m.r. spectrometry. In a unique application of ¹⁹F-n.m.r. spectrometry, the compounds are determined simultaneously in aqueous dosage forms without the need for sample preparation. The optimum signal-to-noise ratio for the major compound for the lowest concentration of sample used (≈ 1 mg ml^-1) was 200:1 for 3000 scans. This was obtained by partial proton decoupling and exponential multiplication of the free induction decay with a line-broadening parameter of 12 Hz. Quantitative results are presented with a standard deviation of < 2.0% in the mean ratio of the two compounds. The results are also compared with those obtained by the spectrophotometric fluorescamine method. Advantages of the ¹⁹F-n.m.r. technique in this determination are discussed.     

Robust Hurwitz stability via sign-definite decomposition

In this paper, we first consider the problem of determining the robust positivity of a real function f(x) as the real vector x varies over a box X∈R^l. We show that, it is sufficient to check a finite number of specially constructed points. This is accomplished by using some results on sign-definite decomposition. We then apply this result to determine the robust Hurwitz stability of a family of complex polynomials whose coefficients are polynomial functions of the parameters of interest. We develop an eight polynomial vertex stability test that is a sufficient condition of Hurwitz stability of the family. This test reduces to Kharitonov’s well known result for the special case where the parameters are just the polynomial coefficients. In this case, the result is tight. This test can be recursively and modularly used to construct an approximation of arbitrary accuracy to the actual stabilizing set. The result is illustrated by examples.     

Beyond the standard model: Working group report

This report summarises the work done in the ‘Beyond the Standard Model’ working group of the Sixth Workshop on High Energy Physics Phenomenology (WHEPP-6) held at the Institute of Mathematical Sciences, Chennai, Jan 3–15, 2000. The participants in this working group were: R Adhikari, B Ananthanarayan, K P S Balaji, Gour Bhattacharya, Gautam Bhattacharyya, Chao-Hsi Chang (Zhang). D Choudhury, Amitava Datta, Anindya Datta, Asesh K Datta, A Dighe, N Gaur, D Ghosh, A Goyal, K Kar, S F King, Anirban Kundu, U Mahanta, R N Mohapatra, B Mukhopadhyaya, S Pakvasa, P N Pandita, M K Parida, P Poulose, G Raffelt, G Rajasekaran, S Rakshit, Asim K Ray, A Raychaudhuri, S Raychaudhuri, D P Roy, P Roy, S Roy, K Sridhar and S Vempati.