Aging effect in the BESIII drift chamber

As the main tracking detector of BESIII, the drift chamber provides accurate measurements of the position and the momentum of the charged particles produced in e+e-collisions at BEPCII. After six years of operation, the drift chamber is suffering from aging problems due to huge beam-related background. The gains of the cells in the first ten layers show an obvious decrease, reaching a maximum decrease of about 29% for the first layer cells. Two calculation methods for the gain change(Bhabha events and accumulated charges with 0.3% aging ratio for inner chamber cells) give almost the same results. For the Malter effect encountered by the inner drift chamber in January 2012, about 0.2% water vapor was added to the MDC gas mixture to solve this cathode aging problem.These results provide an important reference for MDC operating high voltage settings and the upgrade of the inner drift chamber.     

Crystal structure and solid state computational (DFT/Hirshfeld surface) study for probing a new efficient and recyclable oxidation reagent, 1,2-ethandiylbis(triphenylphosphonium) peroxodisulfate dihydrate

A new, efficient and recyclable reagent, 1,2-Ethandiylbis(triphenylphosphonium) peroxodisulfate dihydrate, for the oxidation of benzylic alcohols has been synthesized and characterized by IR, NMR spectroscopy, and single crystal X-ray crystallography. Using the title compound, the results indicate that the oxidation reactions are rapid, take place under mild reaction conditions, easily to work-up and high yielding. The Hirshfeld surface and associated finger print plots were derived from the X-ray structure to visualize the significant nonclassical C-H ??? O/π interactions in the crystal packing. The geometry, vibrational spectroscopy and electronic properties of the bis(triphenylphosphonium) dication have also been investigated by various DFT computational methods.     

Effect of Ga and As vacancies on electronic properties of Ga0.9375Al0.0625As

Electronic properties of Ga_0.9375Al_0.0625As with Ga and As monovacancies are investigated with the density functional theory. A perfect GaAlAs, which specifically produces a radiation wavelength of ～825.6 nm, has been determined in terms of size and number of atoms of substances. We have introduced eight types of vacancies depending on the distance from the Al atom to the vacancy to obtain the changes in charges, band structures, density of states, and optical conductivity. We found that the Fermi level enters into the valence band due to the formations of the Ga or As vacancies so that the vacant materials may show the characteristics of the p-type semiconductor. Interestingly, Ga-vacancy systems make direct band gaps, which are still good for the use in a semiconductor laser. But, As-vacancy systems, where the indirect gaps appear, are not feasible for the same application. It has been found that the latter phenomenon is induced by a newly formed density of state, which comes from the overlapping of hybridised 4s and 4p orbitals of Ga atoms around As vacancy.     

Synthesis,crystal structure and Hirshfeld surface analysis of a new 0D nanostructured [{Ar-Cl)tetra-azo-S}2Hg] coordination supramolecular compound derived from phenyl isothiocyanate ligand

Abstract

Nanoparticles of a new mercury(II) coordination supramolecular compound (CSC), [{(Ar-Cl)tetra-azo-S}₂Hg] (1), were synthesized using a sonochemical process and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and elemental analyses (EA). The single crystal X-ray data of 1 revealed that the Hg ion was two-coordinate. Also, Hirshfeld surface analysis of 1 showed the effective role of interactions related to nitrogen atoms in stabilization of the supramolecular structure. The role of ultrasonic power, sonicating time and temperature on the size and morphology of the nano-structured compound obtained from 1 were investigated. The results indicated that increasing temperature and sonication power and decreasing sonication time led to reducing the particle size.     

Synthesis,characterization, and solid state electrical conductivity of coordination polymers with copper and zinc

Heterobimetallic complexes [Cu _x Zn_{1? x} (dadb)?·?yH₂O] _n {where dadb?=?2,5-diamino-3,6-dichloro-1,4-benzoquinone (1); x?=?1 (2), 0.5 (4), 0.25 (5), 0.125 (6), 0.0625 (7), and 0 (3); y?=?2; n?=?degree of polymerization} were synthesized and characterized. All metal complexes are stable at room temperature but weakly absorb moisture on exposure to air. Monometallic 2 exhibits subnormal magnetic moment whereas 3 exhibits diamagnetism. Heterobimetallic complexes exhibit normal magnetic moments. Heterobimetallic complexes are characterized from powder X-ray diffraction, thermal analysis, and electron spin resonance (ESR) spectral studies. Delocalization of unpaired electron from metal to ligand has been inferred from ESR and natural bond orbital (NBO) analysis. Greater delocalization of unpaired electron of Cu(II) on ligand of 4 as compared to that of 2 is reflected from NBO analysis. Heterobimetallic complexes show higher conductivity than monometallic complexes; all the complexes exhibit semiconductor behavior.     

Quantum mechanically derived AMBER-compatible heme parameters for various states of the cytochrome P450 catalytic cycle

Molecular mechanics (MM) methods are computationally affordable tools for screening chemical libraries of novel compounds for sites of P450 metabolism. One challenge for MM methods has been the absence of a consistent and transferable set of parameters for the heme within the P450 active site. Experimental data indicate that mammalian P450 enzymes vary greatly in the size, architecture, and plasticity of their active sites. Thus, obtaining X-ray-based geometries for the development of accurate MM parameters for the major classes of hepatic P450 remains a daunting task. Our previous work with preliminary gas-phase quantum mechanics (QM)-derived atomic partial charges greatly improved the accuracy of docking studies of raloxifene to CYP3A4. We have therefore developed and tested a consistent set of transferable MM parameters based on gas-phase QM calculations of two model systems of the heme-a truncated (T-HM) and a full (F-HM) for four states of the P450 catalytic cycle. Our results indicate that the use of the atomic partial charges from the F-HM further improves the accuracy of docked predictions for raloxifene to CYP3A4. Different patterns for substrate docking are also observed depending on the choice of heme model and state. Newly parameterized heme models are tested in implicit and explicitly solvated MD simulations in the absence and presence of enzyme structures, for CYP3A4, and appear to be stable on the nanosecond simulation timescale. The new force field for the various heme states may aid the community for simulations of P450 enzymes and other heme-containing enzymes.     

Improvement on the breakdown voltage for silicon-on-insulator devices based on epitaxy-separation by implantation oxygen by a partial buried n~+-layer

A novel silicon-on-insulator (SOI) high-voltage device based on epitaxy-separation by implantation oxygen (SIMOX) with a partial buried n +-layer silicon-on-insulator (PBN SOI) is proposed in this paper.Based on the proposed expressions of the vertical interface electric field,the high concentration interface charges which are accumulated on the interface between top silicon layer and buried oxide layer (BOX) effectively enhance the electric field of the BOX (E_I),resulting in a high breakdown voltage (BV) for the device.For the same thicknesses of top silicon layer (10 μm) and BOX (0.375 μm),the E I and BV of PBN SOI are improved by 186.5% and 45.4% in comparison with those of the conventional SOI,respectively.     

Lattice Dynamics at Zone-Center of Sulphide and Selenide Spinels

A rigid-ion model is used to calculate the force constants and effective dynamical charges of sulphide and selenide spinels. The Raman and infrared phonon modes of normal cubic sulphide spinels MCr₂Se₄ (M = Mn, Co, Fe, Hg, Zn, and Cd) and selenide spinels MCr₂Se₄ (M = Hg, Zn, and Cd) are calculated at the first Brillouin zone-centre using above model. The significant outcome of the present work is (i) the interatomic interaction between Cr-S (Se) dominates over the Cr-S(Se) and S-S(Se-Se) type of interatomic interactions, (ii) the effective dynamical charges of the bivalent metal ions are nearly zero, and (iii) the selenide spinels are less ionic than the sulphide spinels and the ionicity decreases as MnCr₂S₄ > FeCr₂S₄ > CoCr₂S₄ > and CdCr₂C₄ > ZnCr₂C₄ > HgCr₂C₄ (C = S and Se). The zone-center phonon frequencies, calculated using these parameters, are found to be in very good agreement with the observed results.     

A minimal design of order 11 on the 3-sphere

We prove that the 120 vertices of the regular four-dimensional polyhedron with the Schläfli symbol {3, 3, 5} form a minimal spheric design of order 11 onS ³. It is shown that the system of equal charges at these vertices provides the minimal potential energy among all systems of 120 equal charges onS ³.     

Atomic charges for molecular dynamics calculations

Atomic charges obtained with the fit of the ab initio electrostatic potential suffers of several defects, for instance, chemical meaning is not insured. We have employed a method recently put forward for deriving atomic charges which addresses the issue of chemical meaning and conformational transferability to N,N-dibutylacetamide and ethylenediaminetetraacetate. The charges have been used in molecular dynamics calculations where the interaction with a metallic cation is considered. We found structural parameters for the complexes in good agreement with the available experimental results.