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Energy States (energy + states)
Selected AbstractsInternal-rotation and inversion potential energy surfaces for methylamine and methylphosphineINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2008Hae-Won Kim Abstract Using the HF, MP2, and DFT methods with a 6-311G** basis set, we examine the internal-rotation and inversion of the amino and phosphino groups in methylamine and methylphosphine. The resulting energy surfaces are reported as a function of rotation and inversion descriptors. Both surfaces are characterized by several special points: three minimum energy states, three first-order internal-rotation transition states, six first-order inversion transition states, and six second-order inversion transition states. The MP2 method gave better agreement with experiment. For methylamine, the MP2 energy barrier for internal-rotation is 8.73 kJ/mol; for first-order inversion it is 22.80 kJ/mol and for second-order inversion it is 22.41 kJ/mol. For methylphosphine, the MP2 energy barriers are 7.53, 149.88, and 149.65 kJ/mol, respectively. The energy barriers include ZPE correction contributions. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] An extended dead-end elimination algorithm to determine gap-free lists of low energy statesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2007Edda Kloppmann Abstract Proteins are flexible systems and commonly populate several functionally important states. To understand protein function, these states and their energies have to be identified. We introduce an algorithm that allows the determination of a gap-free list of the low energy states. This algorithm is based on the dead-end elimination (DEE) theorem and is termed X-DEE (extended DEE). X-DEE is applicable to discrete systems whose state energy can be formulated as pairwise interaction between sites and their intrinsic energies. In this article, the computational performance of X-DEE is analyzed and discussed. X-DEE is implemented to determine the lowest energy protonation states of proteins, a problem to which DEE has not been applied so far. We use X-DEE to calculate a list of low energy protonation states for two bacteriorhodopsin structures that represent the first proton transfer step of the bacteriorhodopsin photocycle. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Synthesis of Nanostructured Silicon Carbide through an Integrated Mechanical and Thermal Activation ProcessJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Ruiming Ren Changes of crystal structures and microstructures of SiO2 and graphite powder mixtures induced by high-energy milling, the effect of these changes on the reactivity of reactants, and the mechanism of enhanced SiC formation have been studied using a variety of analytical instruments, including X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, solid-state 29Si nuclear magnetic resonance, and nitrogen adsorption (i.e., the BET method). High-energy milling before carbothermic reduction leads to substantial changes in the structural and energy states of the reactants, which in turn increases the reactivity of the reactants and enhances the formation of nanostructured SiC particles. Furthermore, the structural and energy-state changes contribute to the enhanced SiC formation through the increased reaction kinetics as well as the increased reaction driving force. [source] The star formation efficiency and its relation to variations in the initial mass functionMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Paul C. Clark ABSTRACT We investigate how the dynamical state of a turbulently supported, 1000 M,, molecular cloud affects the properties of the cluster it forms, focusing our discussion on the star formation efficiency (SFE) and the initial mass function (IMF). A variety of initial energy states are examined in this paper, ranging from clouds with |Egrav| = 0.1 Ekin to clouds with |Egrav| = 10 Ekin, and for both isothermal and piece-wise polytropic equations of state (similar to that suggested by Larson). It is found that arbitrary SFEs are possible, with strongly unbound clouds yielding very low SFEs. We suggest that the low SFE in the Maddelena cloud may be a consequence of the relatively unbound state of its internal structure. It is also found that competitive accretion results in the observed IMF when the clouds have initial energy states of |Egrav| ,Ekin. We show that under such conditions the shape of the IMF is independent of time in the calculations. This demonstrates that the global accretion process can be terminated at any stage in the cluster's evolution, while still yielding a distribution of stellar masses that is consistent with the observed IMF. As the clouds become progressively more unbound, competitive accretion is less important and the protostellar mass function flattens. These results predict that molecular clouds should be permeated with a distributed population of stars that follow a flatter than Salpeter IMF. [source] Exciton relaxation in bulk wurtzite GaN: the role of piezoelectric interactionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2003G. Kokolakis Abstract A theoretical study on the relaxation of coupled free carriers and excitons after non-resonant optical excitation in bulk wurtzite GaN is presented. In particular the effect of the acoustic piezoelectric scattering is taken under consideration, and the respective rates have been calculated, including screening effects. Results show that the piezo-acoustic rates are bigger in the wurtzite phase of GaN with respect to the cubic phase, and they are really sensitive to the background doping of the sample. Simulations of the full dynamics of the system are performed by using an Ensemble Monte Carlo method under which all the relevant scattering mechanisms are included. The set of semiclassical Boltzmann equations for electron and hole populations is complemented by an additional equation for the exciton distribution and is coupled by reaction terms describing phonon-mediated exciton binding and dissociation. The temporal evolution is studied in the short range time (100 ps) after photo-excitation. It shows that a high background doping prevents the electrons to relax toward low energy states. [source] The band structure of a layered Hg3TeCl4 crystal formed by energy states of HgCl2 and HgTe crystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2008M. Sznajder Abstract The ab-initio calculated band structure of a not as yet investigated orthorhombic Hg3TeCl4 crystal (Pbca, D152h) was analyzed by means of the elementary energy-bands concept. It was demonstrated that this band structure originates from that of a layered HgCl2 dielectric deformed by the presence of the HgTe structural elements. Further, it was revealed that the valence band of Hg3TeCl4 is composed of the 8-branch elementary energy bands corresponding to the actual Wyckoff position c (x, y, z) of D152h group that indicates the presence of ionic and covalent contributions to the chemical bonding in the crystal. The existence of Davydov splitting in the 8-branch elementary energy band situated in the low-energy range of the valence band was observed, which is typical for layered crystals with a weak interlayer interaction between translationally nonequivalent structural units. It was shown that the anisotropy of the electron and hole effective masses does not correspond to the macroscopic anisotropy of the crystal and an explanation of this behaviour was proposed. The obtained parameters of the crystal (direct energy gap Eg = 2.49 eV as well as values of the estimated electron effective masses) indicate that it could find an application in optoelectronics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fully relativistic analysis of the absorption spectra of Ca3Sc2Ge3O12:Ni2+PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2006M. G. Brik Abstract Systematic analysis of the energy level schemes, ground state absorption (GSA) and covalency effects for the Ni2+ ion in Ca3Sc2Ge3O12 was performed. The recently developed first-principles approach to the analysis of the absorption spectra of impurity ions in crystals based on the discrete variational multi-electron method (DV-ME) [K. Ogasawara et al., Phys. Rev. B 64, 115413 (2001)] was used in the calculations. As a result, complete energy level schemes of Ni2+ and its absorption spectra at both possible crystallographic positions (distorted octahedral Sc3+ and tetrahedral Ge4+ positions) were calculated, assigned and compared with experimental data. Energies of the charge transfer (CT) transitions for both positions are estimated. Numerical contributions of all possible electron configurations into the calculated energy states were determined. By performing analysis of the molecular orbitals (MO) population, it was shown that the covalency of the chemical bonds between the Ni2+ and O2, ions increases in passing from the hexa- to the tetra-coordinated complex. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Self-consistent calculation for energy band profiles and energy levels of cubic quantum dotsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 14 2005Johnson Lee Abstract We have performed a self-consistent calculation for the energy band profiles and energy levels of cubic quantum dots, solving both the Schrödinger and Poisson's equations. In particular, we examined the effect of doping on these levels both in the presence and absence of a positive test charge. We found that the number of levels the cubic dot supported depended on the size of the dot, and that the energy of the levels decreased in the presence of a positive test charge. Moreover, we found that the energy levels of both the singlet and triplet states in the dot increased with the doping density. The quasi-Fermi level was found to be lower in the presence of a positive test charge than in its absence, and the quasi-Fermi level increased sharply with increasing doping density both in the absence and presence of the test charge. With very high doping the Fermi level is located in the barrier while with low doping the Fermi level is located down below the ground state energy which implies that the probability of finding an electron in a dot is very small. We also find that at high doping levels the lowest energy states are no longer confined in the dot. The potential energy profile was found to be dramatically affected by both the doping and the presence of a positive test charge. The profile was found to become asymmetric when the test charge was displaced from the center of the dot. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electronic structure of three-dimensional triangular torus-shaped quantum rings under external magnetic fieldsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2003Yiming Li Abstract In this paper, we calculate the electron,hole energy states and the magnetization for InAs/GaAs triangular torus-shaped (TTS) quantum rings in a magnetic field. Our three-dimensional (3D) model considers (i) the effective one-band Hamiltonian approximation, (ii) the position- and energy-dependent quasi-particle effective mass approximation, (iii) the finite hard wall confinement potential, and (iv) the Ben Daniel-Duke boundary conditions. This model is solved numerically with the nonlinear iterative method to obtain the "self-consistent" solutions. We investigate the electron-hole energy spectra versus magnetic field for two different ring widths: R0 = 20 and 50 nm, and find that they strongly depend on the ring shape and size. Since the magnetic field penetrates into the inside region of the nonsimply connected ring, the electron (hole) transition energy between the lowest states versus magnetic field oscillates nonperiodically and is different from that of quantum dots. We find the magnetization at zero temperature is a negative function, saturates, and oscillates nonperiodically when the magnetic field increases. [source] Dynamics of the Dictyostelium discoideum mitochondrial proteome during vegetative growth, starvation and early stages of developmentPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 1 2010Malgorzata Czarna Abstract In this study, a quantitative comparative proteomics approach has been used to analyze the Dictyostelium discoideum mitochondrial proteome variations during vegetative growth, starvation and the early stages of development. Application of 2-D DIGE technology allowed the detection of around 2000 protein spots on each 2-D gel with 180 proteins exhibiting significant changes in their expression level. In total, 96 proteins (51 unique and 45 redundant) were unambiguously identified. We show that the D. discoideum mitochondrial proteome adaptations mainly affect energy metabolism enzymes (the Krebs cycle, anaplerotic pathways, the oxidative phosphorylation system and energy dissipation), proteins involved in developmental and signaling processes as well as in protein biosynthesis and fate. The most striking observations were the opposite regulation of expression of citrate synthase and aconitase and the very large variation in the expression of the alternative oxidase that highlighted the importance of citrate and alternative oxidase in the physiology of the development of D. discoideum. Mitochondrial energy states measured in vivo with MitoTracker Orange CMÔRos showed an increase in mitochondrial membrane polarization during D. discoideum starvation and starvation-induced development. [source] | |||||||||||||