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31.
The aldolase activities of crude rat tissue extracts were separated by starch gel electrophoresis. Aldolase was located on the gel by a specific staining method. Nine bands of different electrophoretic mobility were stainable by this technique. Organ specific isoenzyme patterns could be demonstrated. 相似文献
32.
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34.
M. Christen 《Solid State Communications》1980,36(6):571-573
The anisotropy of the spontaneous resistivity is measured in the ferromagnetic range for PrAl2 and DyAl2 single crystals. For PrAl2 we observed a change of sign in the temperature dependence of θ6 ? θ⊥ which cannot be obtained from existing quadrupole scattering models. 相似文献
35.
A method to enhance sampling of rare events is presented. It makes use of distance or dihedral-angle restraints to overcome an energy barrier separating two metastable states or to stabilize a transition state between the two metastable states. In order not to perturb these metastable end states themselves, a prefactor is introduced into the restraining energy function, which smoothly increases the weight of this function from zero to one at the transition state or on top of the separating energy barrier and then decreases the weight again to zero at the final state. The method is combined with multi-configurational thermodynamic integration and applied to two biomolecular systems, which were difficult to treat using standard thermodynamic integration. As first example the free energy difference of a cyclic alpha-aminoxy-hexapeptide-ion complex upon changing the ion from Cl- to Na+ was calculated. A large conformational rearrangement of the peptide was necessary to accommodate this change. Stabilizing the transition state by (hidden) restraints facilitates that. As a second example, the free energy difference between the 4C1 and the 1C4 conformation of beta-D-glucopyranoside was calculated. In unrestrained simulations the change from the 4C1 into the 1C4 conformation was never observed because of the high energy barrier separating the two states. Using (hidden) restraints, the transition from the 4C1 into the 1C4 state and back could be enforced without perturbing the end states. As comparison, for the same transitions the potential of mean force as obtained by using dihedral-angle constraints is provided. 相似文献
36.
Andrew P. Mendham Brian S. Potter Rex A. Palmer Trevor J. Dines John C. Mitchell Robert Withnall Babur Z. Chowdhry 《Journal of Raman spectroscopy : JRS》2010,41(2):148-159
Experimental Raman and FT‐IR spectra of solid‐state non‐deuterated and N‐deuterated samples of cyclo(L ‐Met‐L ‐Met) are reported and discussed. The Raman and FT‐IR results show characteristic amide I vibrations (Raman: 1649 cm−1, infrared: 1675 cm−1) for molecules exhibiting a cis amide conformation. A Raman band, assigned to the cis amide II vibrational mode, is observed at ∼1493 cm−1 but no IR band is observed in this region. Cyclo(L ‐Met‐L ‐Met) crystallises in the triclinic space group P1 with one molecule per unit cell. The overall shape of the diketopiperazine (DKP) ring displays a (slightly distorted) boat conformation. The crystal packing employs two strong hydrogen bonds, which traverse the entire crystal via translational repeats. B3‐LYP/cc‐pVDZ calculations of the structure of the molecule predict a boat conformation for the DKP ring, in agreement with the experimentally determined X‐ray structure. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
37.
Hermann RP Keppens V Bonville P Nolas GS Grandjean F Long GJ Christen HM Chakoumakos BC Sales BC Mandrus D 《Physical review letters》2006,97(1):017401
M?ssbauer-effect and microwave absorption experimental evidence unambiguously demonstrates the presence of slow, approximately 450 MHz, tunneling of magnetic europium between four equivalent sites in Eu8Ga16Ge30, a stoichiometric clathrate. Remarkably, six of the eight europium atoms, or 11% of the constituents in this solid, tunnel between these four sites separated by 0.55 A. The off centering of the atoms or ions in crystalline clathrates appears to be a promising route for producing Rabi oscillators in solid-state materials. 相似文献
38.
Hans M. Christen Dae Ho Kim Christopher M. Rouleau 《Applied Physics A: Materials Science & Processing》2008,93(3):807-811
Recent advances in film synthesis have made it possible to investigate the properties of well-controlled interfaces in perovskite
metal-oxides. A review of published experimental data and computational results indicate that so far most interfaces that
have been analyzed in ferroelectric materials—while necessary to impose large lattice strain on the polar material—contribute
little to the ferroelectricity and may instead be detrimental to the desired properties. In contrast, a very different situation
arises at interfaces that show changes in the electronic configuration as a consequence of a compositional discontinuity.
Data is shown for LaMnO3/SrTiO3 superlattices as an example of electronic effects that produce enhanced properties, further illustrating the richness of
interfacial properties that can be obtained at interfaces (as shown in numerous published results for different but related
interfaces). 相似文献
39.
Andrew P. Mendham John Spencer Babur Z. Chowdhry Trevor J. Dines Muhammad Mujahid Rex A. Palmer Graham J. Tizzard Simon J. Coles 《Journal of chemical crystallography》2011,41(9):1323-1327
Abstract
The cyclic di-amino acid peptide N,N′-diacetyl-cyclo(Gly-Gly), C8H10N2O4, crystallizes in the triclinic space group P[`1] Pbar{1} with unit cell parameters a = 9.4855(4) ?, b = 10.0250(3) ?, c = 10.0763(4) ?, α = 73.682(2)°, β = 82.816(2)°, γ = 81.733(2)°, V = 906.40(6) ?3, Z = 4 (2 molecules, A and B, per asymmetric unit), Dc = 1.452 g cm−3 and linear absorption coefficient 0.118 mm−1. The crystal structure determination was carried out with MoKα X-ray data measured at 120(2) K. In the final refinement cycle the data/restraints/parameter ratios were 4124/0/258 and goodness-of-fit on F2 = 1.0008. Final R indices for [I > 2σ(I)] were R1 = 0.0501, wR2 = 0.1007 and R indices (all data) R1 = 0.0864, wR2 = 0.11180. The largest electron density difference peak and hole were 0.241 and −0.232 e ?−3, respectively. The DKP rings in both molecules A and B have boat conformations with pseudo mm2 (C2v) symmetry if the N atoms and CH2 groups are considered identical. In each case, the prow and stern of the boat are the α-carbons C(3) and C(6). The overall molecular symmetry of molecules A and B is approximately C2 with the twofold symmetry axis of the DKP boat being maintained through the centre of the DKP ring. Details of the molecular geometry are compared with that of the parent compound cyclo(Gly-Gly) in which the DKP ring is planar with exact symmetry [`1] bar{1} (Ci). 相似文献40.
E. Kapon M. Walther J. Christen M. Grundmann C. Caneau D.M. Hwang E. Colas R. Bhat G.H. Song D. Bimberg 《Superlattices and Microstructures》1992,12(4)
Quantum wire (QWR) heterostructures suitable for optoelectronic applications should meet a number of requirements, including defect free interfaces, large subband separation, long carrier lifetime, efficient carrier capture. The structural and opticl properties of GaAs/AlGaAs and InGaAs/GaAs quantum wire (QWR) heterostructures grown by organometallic chemical vapor deposition on nonplanr substrates, which satisfy many of these criteria, are described. These crescent-shaped QWRs are formed in situ during epitaxial growth resulting in virtually defect free interfaces. Effective wire widths as small as 10nm have been achieved, corresponding to electron subband separations greater than KBT at room temperature. The enhanced density of states at the QWR subbands manifests itself in higher optical absorption and emission as visualized in photoluminescence (PL), PL excitation, amplified spontaneous emission and lasing spectra of these structures. Effective carrier capture into the wires via connected quantum well regions, which is important for enhancing the otherwise extremely small capture cross section of these wires, has also been observed. Room temperature operation of GaAs/AlGaAs and strained InGaAs/GaAs QWR lasers with threshold currents as low as 0.6mA has been demonstrated. 相似文献