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11.
By combining ab initio results for the electronic structure and phonon spectrum with the group theory, we establish the origin of the Verwey transition in Fe3O4. Two primary order parameters with X3 and Delta5 symmetries are identified. They induce the phase transformation from the high-temperature cubic to the low-temperature monoclinic structure. The on-site Coulomb interaction U between 3d electrons at Fe ions plays a crucial role in this transition--it amplifies the coupling of phonons to conduction electrons and thus opens a gap at the Fermi energy. 相似文献
12.
The significance of the electron–phonon interaction for optically stimulated luminescence (OSL) process in quartz is demonstrated. OSL variation with temperature has been investigated for four samples of natural quartz. Changes of the OSL decay rate have been observed for all components of the OSL signal. The scale and tendency of these changes are comparable with outcomes of computer simulations carried out for the model composed of two deep electron traps, one shallow trap and one recombination centre, taking into account the electron–phonon interactions. 相似文献
13.
Krzysztof Bolejko 《General Relativity and Gravitation》2009,41(8):1737-1755
This paper presents the application of the Szekeres Swiss Cheese model to the analysis of observations of the cosmic microwave
background (CMB) radiation. The impact of inhomogeneous matter distribution on the CMB observations is in most cases studied
within the linear perturbations of the Friedmann model. However, since the density contrast and the Weyl curvature within
the cosmic structures are large, this issue is worth studying using another approach. The Szekeres model is an inhomogeneous,
non-symmetrical and exact solution of the Einstein equations. In this model, light propagation and matter evolution can be
exactly calculated, without such approximations as small amplitude of the density contrast. This allows to examine in more
realistic manner the contribution of the light propagation effect to the measured CMB temperature fluctuations. The results
of such analysis show that small-scale, non-linear inhomogeneities induce, via Rees-Sciama effect, temperature fluctuations
of amplitude 10−7–10−5 on angular scale ϑ < 0.24° (ℓ > 750). This is still much smaller than the measured temperature fluctuations on this angular scale. However, local and uncompensated
inhomogeneities can induce temperature fluctuations of amplitude as large as 10−3, and thus can be responsible the low multipoles anomalies observed in the angular CMB power spectrum. 相似文献
14.
We study the size of the set of ergodic directions for the directional billiard flows on the infinite band ${\mathbb{R}\times [0,h]}$ with periodically placed linear barriers of length 0 < λ < h. We prove that the set of ergodic directions is always uncountable. Moreover, if λ/h ∈ (0, 1) is rational, the Hausdorff dimension of the set of ergodic directions is greater than 1/2. In both cases (rational and irrational) we construct explicitly some sets of ergodic directions. 相似文献
15.
The leakage of aqueous contents of neutral (dipalmitoylphosphatidylcholine/cholesterol) liposomes as induced by Rz1, a proline-rich lipoprotein, the bacteriophage Rz1 gene product, was studied. Fluorescence enhancement assay with Tb3+/dipicolinic acid and self-quenching assays with carboxyfluorescein and fluorescein isothiocyanaten-dextran were used to monitor the Rz1-induced leakage from neutral liposomes. The results demonstrated that Rz1 caused local membrane destabilization leading to the leakage of the liposome contents. The extent of the leakage was independent of the molecular mass of the liposome-entrapped solutes in the range of 376–4000 Da. The kinetics of Rz1-liposome leakage was very similar to that obtained with detergent Triton X-100 for all the solutes used. The results suggested that Rz1 can act as a detergent; i.e., by interacting with lipids on both sides of the liposome membranes (inducing perturbation in the lipid packing within the bilayer), it facilitates the transfer of encapsulated molecules into the external liposome environment. The importance of this result for Rz1 physiological function is discussed. 相似文献
16.
Sławomir Prucnal Marcin Turek Andrzej Drozdziel Krzysztof Pyszniak Artur Wójtowicz Sheng-Qiang Zhou Alohe Kanjilal Artem Shalimov Wolfgang Skorupa Jerzy Zuk 《Central European Journal of Physics》2011,9(2):338-343
The InAs quantum structures were formed in silicon by sequential ion implantation and subsequent thermal annealing. Two kinds of crystalline InAs nanostructures were successfully synthesized: nanodots (NDs) and nanopyramids (NPs). The peaks at 215 and 235 cm?1, corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs single-phonon modes, respectively, are clearly visible in the Raman spectra. Moreover, the PL band at around 1.3 µm, due to light emission from InAs NDs with an average diameter 7±2 nm, was observed. The InAs NPs were found only in samples annealed for 20 ms at temperatures ranging from 1000 up to 1200°C. The crystallinity and pyramidal shape of InAs quantum structures were confirmed by HRTEM and XRD techniques. The average size of the NPs is 50 nm base and 50 nm height, and they are oriented parallel to the Si (001) planes. The lattice parameter of the NPs increases from 6.051 to 6.055 Å with the annealing temperature increasing from 1100 to 1200°C, due to lattice relaxation. Energy dispersive spectroscopy (EDS) shows almost stoichiometric composition of the InAs NPs. 相似文献
17.
The influence of alcohol additives on etch rate anisotropy of Si(hkl) planes has been studied. The etching processes were carried out in 3 and 5 M KOH aqueous solutions saturated and non-saturated
with alcohols. Isopropanol, 1-propanol and tert-butanol were examined. It has been showed that the etching process cannot be controlled only by the surface tension of the
solution. Saturation of the etching solution with alcohols modifies etch rate anisotropy, lowering the ratio of the etch rate
of (110) and vicinal planes to the etch rate of (100) plane. The morphology of Si(hkl) planes etched in 3 M KOH solution saturated with tert-butyl alcohol has been studied in detail. Smooth (331) and (221) planes
have been achieved in this solution. The (100) plane turned out to be densely covered by hillocks, opposite to the (100) plane
etched in weak-alkaline solution saturated with isopropanol. To explain this phenomenon, the mechanism of hillocks formation
on Si(100) surface has been proposed. 相似文献
18.
Dobek K 《Journal of fluorescence》2011,21(4):1547-1557
The influence of temperature varied in the range 183 K–323 K on the fluorescence quantum yield, fluorescence lifetime, absorption
and emission transition moments and non-radiative deactivation rate was determined for the well known and largely used dye
Coumarin 153, dissolved in 1-chloropropane. The Kennard-Stepanov relation connecting the absorption and emission spectra was
used to check for the presence of more than one absorbing/emitting species and to investigate whether intramolecular vibrational
redistribution completes in the C153 excited S
1 state before the emission takes place. The emission spectrum corresponding to S
1→S
0 transition, was fitted at each temperature to the model function including the information on the dye vibrational modes coupling.
In this way the displacement in equilibrium distance for the most active vibrational mode was determined for C153 in S
1 and in S
0. Using the temperature dependence of the fluorescence decay time and quantum yield, the non-radiative deactivation rate was
determined. Its temperature dependence was compared to that calculated using the theoretical model with the most active vibrational
mode displacement values taken from steady-state spectra analysis. The somewhat surprising dependence of the fluorescence
decay time and quantum yield on temperature was related to non-trivial coupling between low-frequency vibrational modes of
C153 in the excited and ground states. 相似文献
19.
20.
We present a detailed study of the Schrödinger picture space of states in theSU(2) Chern-Simons topological gauge theory in the simplest geometry. The space coincides with that of the solutions of the chiral Ward identities for the WZW model. We prove that its dimension is given by E. Verlinde's formulae. 相似文献