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121.
Vladislav Chernysh 《Proceedings of the American Mathematical Society》2006,134(9):2771-2777
In this paper we show that for Riemannian manifolds with boundary the natural restriction map is a quasifibration between spaces of metrics of positive scalar curvature. We apply this result to study homotopy properties of spaces of such metrics on manifolds with boundary.
122.
123.
NAD+ is degraded by horse liver alcohol dehydrogenase in a reaction with p-methylbenzyl hydroperoxide, which acts as a pseudo-substrate. An unstable intermediate product (called compound I) is formed, and this is converted into the final product NADX. The reaction can be monitored by capillary electrophoresis. NADX migrates as two well resolved peaks (NADX1 and NADX2), which belong probably to the tautomers of the same substance. The intermediate product, compound I, has the same effective mobility as the conformer NADX2 and it was impossible to separate compound I from NADX2. The spectra taken during the separation show clearly that the “9-min” peak contains different compounds during the course of the reaction and the NADX2 is not identical with compound I. 相似文献
124.
A comparison between two models of proton transfer in the symmetric H-bond interacting in a thermal reservoir is made. It is shown that in a more general model (including both previous ones as special cases) a new qualitative feature in proton damping appears. 相似文献
125.
126.
Vladislav Čápek 《Czechoslovak Journal of Physics》1996,46(11):1001-1009
We apply a previous analysis of the dependence of the dynamic time-convolution equations and their solution on the degree of the initial strength of the polaron cloud to the usual zero-bias spin-boson model and standard second order (i.e. Born) approximation (in tunneling, i.e. the standard dilute blip approximation at =1). At temperatureT=0 and for the usual Ohmic type spin-boson coupling, the asymptotic-time-symmetry-breaking phenomenon as a function of the coupling strentghg can be analyzed, in the above Born approximation, in the wholeg- plane. A hardly interpretable conclusion is found that the symmetry breaking in the above approximation appears just at discrete lines in the plane. This implies instability of the phenomenon in the second-order theory with respect to arbitrarily small perturbations of the initial state and complies with exact proofs of absence of the partial symmetry-breaking phenomenon in analogous symmetric models.The author has pleasure in acknowledging fruitful discussions with Dr. P. Chvosta and Prof. M. Wagner. Supports of grants 292/1994 from the Grant agency of Charles University and 202/93/2428 from the Czech Grant Agency are also gratefully acknowledged. 相似文献
127.
Adam R. Hill Pablo Cubillas James T. Gebbie-Rayet Mollie Trueman Nathan de Bruyn Zulaikha al Harthi Rachel J. S. Pooley Martin P. Attfield Vladislav A. Blatov Davide M. Proserpio Julian D. Gale Duncan Akporiaye Bjrnar Arstad Michael W. Anderson 《Chemical science》2021,12(3):1126
A Monte Carlo crystal growth simulation tool, CrystalGrower, is described which is able to simultaneously model both the crystal habit and nanoscopic surface topography of any crystal structure under conditions of variable supersaturation or at equilibrium. This tool has been developed in order to permit the rapid simulation of crystal surface maps generated by scanning probe microscopies in combination with overall crystal habit. As the simulation is based upon a coarse graining at the nanoscopic level features such as crystal rounding at low supersaturation or undersaturation conditions are also faithfully reproduced. CrystalGrower permits the incorporation of screw dislocations with arbitrary Burgers vectors and also the investigation of internal point defects in crystals. The effect of growth modifiers can be addressed by selective poisoning of specific growth sites. The tool is designed for those interested in understanding and controlling the outcome of crystal growth through a deeper comprehension of the key controlling experimental parameters.Generic in silico methodology – CrystalGrower – for simulating crystal habit and nanoscopic surface topology to determine crystallisation free energies. 相似文献
128.
The [Fe(II)(Cys)(4)](2-) site of rubredoxin from Clostridium pasteurianum (Rd(red)) has been studied by M?ssbauer spectroscopy in both purified protein and whole cells of Escherichia coli overproducing it. Excellent fits were obtained to an S = 2 spin Hamiltonian for D = 5.7(3) cm(-1), E/D = 0.25(2), delta = 0.70(3) mm/s, DeltaE(Q) = -3.25(2) mm/s, eta = 0.75(5), A(x) = -20.1(7) MHz, A(y) = -11.3(2) MHz, and A(z) = -33.4(14) MHz. These parameters were analyzed with crystal-field theory for the (5)D manifold of iron(II), revealing a d(z(2)) orbital ground state that is admixed by approximately 0.21 d(x(2) - y(2)). The spin-Hamiltonian parameters are consistent within the (5)D theory, apart from the zero-field splitting parameter, D. This problem was solved by extending the crystal-field treatment with spin-orbit coupling to spin-triplet d-d excited states of the iron. Theoretical estimates are given for the spin-triplet (D(T)) and spin-quintet contributions (D(Q)) to D based on excitation energies derived from time-dependent density functional theory, TD-DFT. The computational results were interpreted in terms of crystal-field theory, yielding the Racah parameters B = 682 cm(-1) and C = 2583 cm(-1). The theoretical analysis gives the relative magnitudes D(Q):D(T):D(ss) = 51%: 42%:7% (D(ss) originates from spin-spin interaction). The DFT analysis corroborates the pivotal role of the torsion angles (omega(i)) of the C-S(i) bonds in shaping the electronic structure of the iron(II) site. Rd(red) in overexpressing whole cells accounts for 60% of the M?ssbauer absorption. The Rd(red) spectra from whole cells are virtually identical to those of the purified protein. By using the theoretical omega dependence of the spin Hamiltonian parameters, the torsions for Rd(red) in whole cells and purified protein samples are estimated to be the same within 2 degrees. These findings establish M?ssbauer spectroscopy as a structural tool for investigating iron sites in whole cells. 相似文献
129.
Andrew G. Ogienko Elissa A. Ukraintseva Tatyana A. Chingina Vladislav Yu. Komarov Andrey Yu. Manakov 《Journal of inclusion phenomena and macrocyclic chemistry》2005,53(3-4):231-236
The phase diagram of the pyridine–iron(III) chloride system has been studied for the 223–423 K temperature and 0–56 mass-% concentration ranges using differential thermal analysis (DTA) and solubility techniques. A solid with the highest pyridine content formed in the system was found to be an already known clathrate compound, [FePy3Cl3]·Py. The clathrate melts incongruently at 346.9 ± 0.3 K with the destruction of the host complex: [FePy3Cl3]·Py(solid)=[FePy2Cl3](solid) + liquor. The thermal dissociation of the clathrate with the release of pyridine into the gaseous phase (TGA) occurs in a similar way: [FePy3Cl3]·Py(solid)=[FePy2Cl3](solid) + 2 Py(gas). Thermodynamic parameters of the clathrate dissociation have been determined from the dependence of the pyridine vapour pressure over the clathrate samples versus temperature (tensimetric method). The dependence experiences a change at 327 K indicating a polymorphous transformation occurring at this temperature. For the process ${1 \over 2}[\hbox{FePy}_{3}\hbox{Cl}_{3}]\cdot \hbox{Py}_{\rm (solid)} = {1 \over 2}[\hbox{FePy}_{2}\hbox{Cl}_{3}]_{\rm (solid)} + \hbox{Py}_{\rm (gas)}$ in the range 292–327 K, ΔH $^{0}_{298}$ =70.8 ± 0.8 kJ/mol, ΔS $^{0}_{298}$ =197 ± 3 J/(mol K), ΔG $^{0}_{298}$ =12.2 ± 0.1 kJ/mol; in the range 327–368 K, ΔH $^{0}_{298}$ =44.4 ± 1.3 kJ/mol, ΔS $^{0}_{298}$ =116 ± 4 J/(mol K), ΔG $^{0}_{298}$ =9.9 ± 0.3 kJ/mol. 相似文献
130.
Holba Vladislav Benko Ján Grančičová Ol'ga Vollárová Ol'ga 《Transition Metal Chemistry》1985,10(3):84-89
Summary The kinetics of oxidation of [Co(NH3)5(NCS)]2+ by peroxodisulphate and periodate were investigated at different ionic strengths, and at different temperatures and concentrations
of perchloric acid. Rate constants and activation parameters are also reported in mixed water-organic solvents. It was shown
that the acid-base equilibria involving S2O
8
−2
, and IO
4
−
ions are important in the reactions studied. Solvent effects on the oxidation are interpreted in terms of the solvation of
both the initial state and the activated complex. 相似文献