http://www.physmathcentral.com/pmcphysb/ The most accessed research articles published by PMC Physics B 2009-12-18T00:00:00Z This is an RSS newsfeed from BioMed Central It is intended to be used with an RSS reader. For more information about RSS newsfeeds from BioMed Central, visit http://www.biomedcentral.com/info/about/rss/ Absolute angle-differential cross-section data are presented for excitation of the 3p54s manifold in argon by electron impact. The investigation focuses on the near-threshold region, where previous studies have revealed persistent disparities between measurements and theoretical predictions. For the present experiment, the time-of-flight (TOF) technique is employed. This method allows for scattered electrons to be measured over a broad range of energies with a constant transmission, thereby eliminating a potential major source of error in relating relative intensities of elastic and inelastic transitions inherent to other experimental techniques. The present experimental data are compared to theoretical results obtained in relativistic distorted-wave and various R-matrix (close-coupling) approaches, as well as to other recently published experimental data.PACS Codes: 34.80.Dp http://www.physmathcentral.com/1754-0429/2/3 Subhendu Mondal Julian Lower Stephen Buckman Robert McEachran Gustavo Garcia Oleg Zatsarinny Klaus Bartschat PMC Physics B 2009, 2:3 2009-12-18T00:00:00Z doi:10.1186/1754-0429-2-3 PMC Physics B 1754-0429 2 3 2009-12-18T00:00:00Z XML Formation of complex polyaniline (PANI) films with diamagnetic TCNQ and paramagnetic metal ion impurities cast under applied magnetic field was studied. It has been found that the applied magnetic field affects interaction of PANI chains with the impurities and induces formation of magnetically ordered regions in the complex film doped by paramagnetic metal ions in contrast to the reference film of the same composition but prepared under ambient conditions. The magnetically ordered regions have been observed directly by scanning magnetic force microscopy. It was found a correlation in distribution of the magnetically ordered regions and peculiarities of the surface relief of a film. Electronic absorption spectra and conductivity measurements showed that an applied stationary magnetic field can suppress the interaction of PANI chains and paramagnetic metal ions and lowers conductivity of the resulting complex film up to one order of magnitude as compared with the reference film. An alternating magnetic field was found to improve interaction of PANI and diamagnetic TCNQ molecules. The mechanisms of the magnetic field influence on the complex film formation are discussed.PACS: 75.70.-i; 72.80. Le; 78.40. Me http://www.physmathcentral.com/1754-0429/1/15 Oleg Dimitriev Petro Lytvyn Alla Dimitriyeva Ostap Getsko PMC Physics B 2008, 1:15 2008-10-21T00:00:00Z doi:10.1186/1754-0429-1-15 PMC Physics B 1754-0429 1 15 2008-10-21T00:00:00Z XML The compound Cr1.4Fe0.6O3 has been synthesized through mechanical alloying of Cr2O3 and α-Fe2O3 powders and subsequent thermal annealing. The XRD spectrum, SEM picture and microanalysis of EDAX spectrum have been used to understand the structural evolution during alloy formation. The alloyed samples have been matched to rhombohedral structure with R3C space group. The observation of a modulated magnetic order confirmed the systematic diffusion of Fe atoms into the Cr sites of lattice structure. A field induced magnetic behaviour has been noted in the field dependence of magnetization data of the annealed samples. This feature is significantly different from that of the mechanical alloyed samples. The experimental results also provided the indications of considering the present material as a potential candidate for opto-electronic applications.PACS Codes: 75.30.-m, 75.20.En, 81.40.Rs http://www.physmathcentral.com/1754-0429/1/20 R n Bhowmik Nrisimha Murty Sekhar Srinadhu PMC Physics B 2008, 1:20 2008-12-29T00:00:00Z doi:10.1186/1754-0429-1-20 PMC Physics B 1754-0429 1 20 2008-12-29T00:00:00Z XML Evolution of structure of spherical SiO2 nanoparticles upon cooling from the melt has been investigated via molecular-dynamics (MD) simulations under non-periodic boundary conditions (NPBC). We use the pair interatomic potentials which have weak Coulomb interaction and Morse type short-range interaction. The change in structure of SiO2 nanoparticles upon cooling process has been studied through the partial radial distribution functions (PRDFs), coordination number and bond-angle distributions at different temperatures. The core and surface structures of nanoparticles have been studied in details. Our results show significant temperature dependence of structure of nanoparticles. Moreover, temperature dependence of concentration of structural defects in nanoparticles upon cooling from the melt toward glassy state has been found and discussed.PACS Codes: 61.43.Bn; 78.55.Qr; 78.67.Bf http://www.physmathcentral.com/content/1/1/16 Huynh Nguyen Hoang Vo Zung Hoang PMC Physics B 2008, 1:16 2008-10-30T00:00:00Z doi:10.1186/1754-0429-1-16 PMC Physics B 1754-0429 1 16 2008-10-30T00:00:00Z XML Recent measurements of the cross sections for electronic state excitations in H2O have made it possible to calculate rates applicable to these excitation processes. We thus present here calculations of electron energy transfer rates for electronic and vibrational state excitations in H2O, as well as rates for excitation of some of these states by atmospheric thermal and auroral secondary electrons. The calculation of these latter rates is an important first step towards our aim of including water into a statistical equilibrium model of the atmosphere under auroral conditions.PACS Codes: 34.50.Gb 34.50.Ez http://www.physmathcentral.com/1754-0429/2/1 Penny Thorn Laurence Campbell Michael Brunger PMC Physics B 2009, 2:1 2009-01-02T00:00:00Z doi:10.1186/1754-0429-2-1 PMC Physics B 1754-0429 2 1 2009-01-02T00:00:00Z XML A comparative study of two earlier three-state and fifteen-state [Chaudhuri et al., Pramana- J. Phys., 43, 175 (1994); ibid., Phys. Rev. A, 52, 1137 (1995)] close-coupled treatments of He2+-He single and double charge transfer collisions is made in this paper with a larger, 27-state close-coupled calculation. The calculations have been done using the diabatic molecular basis set used in the earlier work extended by adding excited orbitals leading to higher excitation channels up to 3s and 3p. For such molecular basis functions that go to the correct separated-atom limits used in this work, the present results show that without the inclusion of the electron translation factors (ETFs) the quantitative cross-section calculations up to velocity ~1.1 a.u. (~30 keV/amu) are in good agreement with both experiment and other calculations. This suggests that if ETFs are properly incorporated into the charge transfer collision studies at low energies this diabatic molecular basis can be used for benchmark calculations. With the aid of the Wannier's picture of the ground state correlations, a combined detailed analysis and comparison has been carried out to find a connection with the dynamic two-electron correlation picture in charge transfer collision processes which involve sequential/simultaneous two-electron exchange. If ETFs are included, the model approach of the present work may open up opportunities to investigate dynamic two-electron correlation effect in charge transfer ion-atom collision processes with benchmark accuracy.PACS codes: 34.70.+e, 34.20.-b http://www.physmathcentral.com/1754-0429/2/2 Chanchal Chaudhuri PMC Physics B 2009, 2:2 2009-06-09T00:00:00Z doi:10.1186/1754-0429-2-2 PMC Physics B 1754-0429 2 2 2009-06-09T00:00:00Z XML The Schlegel-Frisch ab initio molecular dynamics (ADMP) (DFT:B3LYP), T = 310 K, is used to study complexation between adenosinetriphosphate (ATP), ATP subsystem, and magnesium cofactor [Mg(H2O)6]2+, Mg subsystem, in a water pool, modeled with 78 water molecules, in singlet (S) and triplet (T) states. The computations prove that the way of ATP cleavage is governed by the electron spin of Mg. In the S state Mg prefers chelation of γ-β-phosphate oxygens (O1-O2), whereas in the T state it chelates β-α-phosphate oxygens (O2-O3) or produces a single-bonded intermediate. Unlike the chelates, which initiate ionic reaction paths, the single-bonded intermediate starts off a free-radical path of ATP cleavage, yielding a highly reactive adenosinemonophosphate ion-radical, •AMP-, earlier observed in the CIDNP (Chemically Induced Dynamic Nuclear Polarization) experiment (A.A. Tulub, 2006). The free-radical path is highly sensitive to Mg nuclear spin, which through a hyperfine interaction favors the production of unpaired electron spins. The unique role of Mg in ATP cleavage comes through its ability to serve as a unique redox center, initially accepting an electron from ATP and then giving it back to products. Redox activity of Mg differs for T and S states and affects the number of coordinated water molecules. The findings give a new insight into the NTP (N = nucleoside) energetics and assembly of NTP-operating molecules, including proteins.PACS codes: 87.15.-v http://www.physmathcentral.com/1754-0429/1/18 Alexander Tulub PMC Physics B 2008, 1:18 2008-12-04T00:00:00Z doi:10.1186/1754-0429-1-18 PMC Physics B 1754-0429 1 18 2008-12-04T00:00:00Z XML The electronic structure, linear and nonlinear optical properties have been calculated for CuInX2 (X = S, Se, Te) chalcopyrite-structure single crystals using the state-of-the-art full potential linear augmented plane wave (FP-LAPW) method. We present results for band structure, density of states, and imaginary part of the frequency-dependent linear and nonlinear optical susceptibilities. We find that these crystals are semiconductors with direct band gaps. We have calculated the birefringence of these crystals. The birefringence is negative for CuInS2 and CuInSe2 while it is positive for CuInTe2 in agreement with the experimental data. Calculations are reported for the frequency-dependent complex second-order non-linear optical susceptibilities χ123(2)(ω) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIXaqmcqaIYaGmcqaIZaWmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B5@. The intra-band and inter-band contributions to the second harmonic generation increase when we replace S by Se and decrease when we replace Se by Te. We find that smaller energy band gap compounds have larger values of χ123(2)(0) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIXaqmcqaIYaGmcqaIZaWmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabicdaWaGaayjkaiaawMcaaaaa@34D6@ in agreement with the experimental data and previous theoretical calculations.PACS Codes: 71.15.-m, 31.15.-p http://www.physmathcentral.com/1754-0429/1/12 Ali Reshak S Auluck PMC Physics B 2008, 1:12 2008-05-19T00:00:00Z doi:10.1186/1754-0429-1-12 PMC Physics B 1754-0429 1 12 2008-05-19T00:00:00Z XML Experimental measurements of the second order susceptibilities for the second harmonic generation are reported for YAl3(BO3)4 (YAB) single crystals for the two principal tensor components xyz and yyy. First principle's calculation of the linear and nonlinear optical susceptibilities for Yttrium Aluminum Borate YAl3(BO3)4 (YAB) crystal have been carried out within a framework of the full-potential linear augmented plane wave (FP-LAPW) method. Our calculations show a large anisotropy of the linear and nonlinear optical susceptibilities. The observed dependences of the second order susceptibilities for the static frequency limit and for the frequency may be a consequence of different contribution of electron-phonon interactions. The imaginary parts of the second order SHG susceptibility χ123(2)(ω) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIXaqmcqaIYaGmcqaIZaWmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B5@, χ112(2)(ω) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIXaqmcqaIXaqmcqaIYaGmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B1@, χ222(2)(ω) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIYaGmcqaIYaGmcqaIYaGmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B5@, and χ213(2)(ω) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacqaIYaGmcqaIXaqmcqaIZaWmaeaacqGGOaakcqaIYaGmcqGGPaqkaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@35B5@ are evaluated. We find that the 2ω inter-band and intra-band contributions to the real and imaginary parts of χijk(2)(ω) MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbwvMCKfMBHbqedmvETj2BSbqee0evGueE0jxyaibaieYdOi=BI8qipeYdI8qiW7rqqrFfpeea0xe9LqFf0xc9q8qqaqFn0dXdHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabeE8aJnaaDaaaleaacaWGPbGaamOAaiaadUgaaeaacaGGOaGaaGOmaiaacMcaaaGcdaqadaqaaiabeM8a3bGaayjkaiaawMcaaaaa@3752@ show opposite signs. The calculated second order susceptibilities are in reasonable good agreement with the experimental measurements.PACS Codes: 71.15. Mb; 71.15.-m http://www.physmathcentral.com/1754-0429/1/8 Ali Reshak S Auluck A Majchrowski I Kityk PMC Physics B 2008, 1:8 2008-03-17T00:00:00Z doi:10.1186/1754-0429-1-8 PMC Physics B 1754-0429 1 8 2008-03-17T00:00:00Z XML Recently, two-dimensional (2D) periodically L and C loaded transmission-line (TL) networks have been applied to represent metamaterials. The commercial Agilent's Advanced Design System (ADS) is a commonly-used tool to simulate the TL metamaterials. However, it takes a lot of time to set up the TL network and perform numerical simulations using ADS, making the metamaterial analysis inefficient, especially for large-scale TL networks. In this paper, we propose transmission-matrix method (TMM) to simulate and analyze the TL-network metamaterials efficiently. Compared to the ADS commercial software, TMM provides nearly the same simulation results for the same networks. However, the model-process and simulation time has been greatly reduced. The proposed TMM can serve as an efficient tool to study the TL-network metamaterials.PACS Codes: 41.20.Jb http://www.physmathcentral.com/1754-0429/1/10 Hui Feng Ma Tie Jun Cui Jessie Yao Chin Qiang Cheng PMC Physics B 2008, 1:10 2008-04-08T00:00:00Z doi:10.1186/1754-0429-1-10 PMC Physics B 1754-0429 1 10 2008-04-08T00:00:00Z XML