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851.
S. Sen Y. Xie A. Bansal H. Yang K. Cho L. S. Schadler S. K. Kumar 《The European physical journal. Special topics》2007,141(1):161-165
Recently we established a quantitative equivalence in
thermomechanical properties between polystyrene-silica nanocomposites and
planar freestanding polystyrene thin films. This equivalence was quantified
by drawing a direct analogy between film thickness and an appropriate
experimental particle spacing. Using these findings, here we unequivocally
show that the glass transition process in confined geometries is controlled
by the mean volume fraction of polymer that is affected by the presence of
surfaces. Since separate signatures of the bulk and the surface layers are
never found, we can clearly rule out any simple “two layer” model which
postulates the existence of surfaces which are dynamically decoupled from
the bulk. Rather, we argue that the modification of properties at the
surfaces propagates into the bulk through a spatial gradient: macroscopic
experimental techniques average over these gradients and yield a broadened
signature relative to the bulk polymer. In a second aspect of this paper we
focus on the role of processing conditions on the results obtained. We have
developed a new method of processing the nanocomposites which results in a
better dispersion of the nanoparticles in the matrix. However, these samples
did not show the unique glass transition behavior seen in the first set of
nanocomposites discussed above. This indicates that processing conditions
can profoundly affect the nature of the particle-polymer interface which
controls the macroscopic behavior of these important systems. 相似文献
852.
Coherent control in a single semiconductor quantum dot exhibiting excitonic and biexcitonic features
We have developed a simplified theoretical model to analyze the phenomenon of coherent control in a single semiconductor quantum
dot excited by a pair of optical pulses. The first pulse populates a biexciton state by two-photon absorption while the second
pulse generates population in the exciton state via deexcitation from the biexciton state. We have used density-matrix analysis
for a 3-level system to calculate the time dependent biexciton and exciton state populations. The usual 9×9 matrix has been
reduced to a 6×6 matrix. The time variation of the population in each state and it’s dependence on the pulse delay manifest
coherent control. Numerical estimates made for In0.5Ga0.5As/GaAs single quantum dots qualitatively agree with the recent experimental results.
PACS 78.67.Hc; 42.50.Md; 78.55.Cr 相似文献
853.
Sabyasachi Sen 《Journal of Physics and Chemistry of Solids》2007,68(10):1856-1862
We report on the first direct numerical evidence of doping-induced transformation of Tomonaga-Luttinger liquid to Fermi liquid in quasi-one-dimensional lithium doped trans-polyacetylene chain. Using density functional theoretical calculation, an analysis of density of states near the Fermi energy reveals a power-law scaling factor of Tomonaga-Luttinger liquid at low dopant concentration in the metallic regime. As soon as the doping level reaches 0.0763e/C, normal power-law scaling factor of Fermi liquid has been realized as a special case of Luttinger liquid in one dimension. The variation of density-density correlation is consistent with the present theoretical prediction. 相似文献
854.
ZnO nanoparticles, of average size of 10–15 nm, homogeneously dispersed in a silica matrix were prepared by a two stage citric
acid/sol–gel process and thermal treatments up to 700 °C. The precursors formed at the early stages of the synthesis and their
thermal evolution were investigated by FTIR, 29Si NMR MAS and CPMAS, 13C CPMAS and T1ρ(1H). A unidentate complex was revealed in the gel, together with other complexes in which citrate carboxylate groups are bound
to one Zn2+ ion or act as a bridge between two Zn2+ ions. A comparison of the results from nanocomposite and silica samples prepared by the same method showed that chemical
interactions between amorphous silica and zinc ions are not present either in the precursors or in the final materials. As
a consequence, ZnO particles do not react with silica matrix when they are heated up to 700 °C. This result is ascribed to
a nanophase segregation of zinc citrate complexes from the host matrix. 相似文献
855.
Calik P Ileri N Erdinç BI Aydogan N Argun M 《Langmuir : the ACS journal of surfaces and colloids》2005,21(19):8613-8619
As foaming appears as a problem in chemical and fermentation processes that inhibits reactor performance, the eminence of a novel fluorocarbon-hydrocarbon unsymmetrical bolaform (FHUB: OH(CH2)11N+(C2H4)2(CH2)2(CF2)5CF3 I-) surfactant as an antifoaming agent as well as a foam-reducing agent was investigated and compared with other surfactants and a commercial antifoaming agent. The surface elasticity of FHUB was determined as 4 mN/m, indicating its high potential on thinning of the foam film. The interactions between FHUB and the microoganism were investigated in a model fermentation process related with an enzyme production by recombinant Escherichia coli, in V = 3.0 dm3 bioreactor systems with V(R) = 1.65 dm3 working volume at air inlet rate of Q(o)/V(R) = 0.5 dm3 dm(-3) min(-1) and agitation rate of N = 500 min(-1) oxygen transfer conditions, at T = 37 degrees C, pH(o) = 7.2, and C(FHUB) = 0 and 0.1 mM, in a glucose-based defined medium. As FHUB did not influence the metabolism, specific enzyme activity values obtained with and without FHUB were close to each other; however, because of the slight decrease in oxygen transfer coefficient, slightly lower volumetric enzyme activity and cell concentrations were obtained. However, when FHUB is compared with widely used silicon oil based Antifoam A, with the use of the FHUB, higher physical oxygen transfer coefficient (K(L)a) values are obtained. Moreover, as the amount required for the foam control is very low, minute changes in the working volume of the bioreactor were obtained indicating the high potential of the use of FHUB as an antifoaming agent as well as a foam-reducing agent. 相似文献
856.
Zusammenfassung Zweck dieser Mitteilung ist die Herleitung einer direkten Methode für die Lösung des zweiten Randwertproblems in einer elastischen Scheibe mit kreisförmiger Begrenzung. Zur Veranschaulichung der Methode wird das Problem der unendlichen Scheibe mit einer thermoelastischen Verzerrungsquelle in endlichem Abstand von einem kreisförmigen Loch mit fixiertem Rand gelöst. 相似文献
857.
Most tokamak experimental results [Nucl. Fusion 33, 1205 (1993)]] and basic physics experiments [Phys. Rev. Lett. 89, 095001 (2002)]] in the Columbia Linear Machine indicate dependence of the ion thermal conductivity on the isotopic mass close to chi( perpendicular ) approximately A(-0.5)(i), i.e., inverse gyro-Bohm. This is in stark contradiction to most present theoretical models predicting Bohm (A(0)(i)) or gyro-Bohm (A(0.5)(i)) scaling. A series of experiments designed to explore the physics basis of this scaling appears to lead to a new model for this scaling based on 3-wave coupling of two ion temperature gradient radial harmonics and an ion acoustic wave. 相似文献
858.
B.?MukhopadhyayaEmail author S.?Sen S.?SenGupta S.?Sur 《The European Physical Journal C - Particles and Fields》2004,35(1):129-135
The possibility of parity violation in a gravitational theory with torsion is extensively explored in four and higher dimensions. In the former case, we have listed our conclusions on when and whether parity ceases to be conserved, with both two- and three-index antisymmetry of the torsion field. In the latter, the bulk spacetime is assumed to have torsion, and the survival of parity violating terms in the four dimensional effective action is studied, using the compactification schemes proposed by Arkani-Hamed-Dimopoulos-Dvali and Randall-Sundrum. An interesting conclusion is that the torsion-axion duality arising in a stringy scenario via the second rank antisymmetric Kalb-Ramond field leads to conservation of parity in the gravity sector in any dimension. However, parity violating interactions do appear for spin-1/2 fermions in such theories, which can have crucial phenomenological implications.Received: 17 July 2003, Revised: 12 February 2004, Published online: 23 April 2004 相似文献
859.
We provide a first operational method for checking local indistinguishability of orthogonal states. It originates from that in Ghosh et al. [Phys. Rev. Lett. 87, 5807 (2001)]], though we deal with pure states. Our method shows that probabilistic local distinguishing is possible for a complete multipartite orthogonal basis if and only if all vectors are product. Also, it leads to local indistinguishability of a set of orthogonal pure states of 3 multiply sign in circle 3, which shows that one can have more nonlocality with less entanglement, where "more nonlocality" is in the sense of "increased local indistinguishability of orthogonal states." This is, to our knowledge, the only known example where d orthogonal states in d multiply sign in circle d are locally indistinguishable. 相似文献
860.
NMR methods are widely used to probe the structure and fluid dynamics of porous materials, as they are uniquely suited to these studies since NMR records the correlation of changing local magnetic fields over a time scale of ns to seconds. The local magnetic fields are established by local variations in the bulk magnetic susceptibility of the sample (and so are directly tied to the sample's local structure). The fluctuation in field that a spin sees is due to molecular transport (including molecular diffusion) through these local fields, and so reports on the length scales of structures and impediments to transport. We have developed a new set of methods DIFFUSIVE-MASS to provide a means of systematically varying the effective time scale of the measurement and thus the effective length scale. This new handle permits a detailed, microscopic picture of the structure and dynamics. Diffusive MASS NMR methods will permit a systematic set of methods and analysis for characterizing the chemistry, structure and fluid dynamics of the mobile phase in porous materials. The approach will be applicable to any diamagnetic material. In particular, the industry of oil discovery depends on understanding heterogeneous porous media. 相似文献