433 research outputs found
Long-Wavelength Anomalies in the Asymptotic Behavior of Mode-Coupling Theory
We discuss the dynamic behavior of a tagged particle close to a classical
localization transition in the framework of the mode-coupling theory of the
glass transition. Asymptotic results are derived for the order parameter as
well as the dynamic correlation functions and the mean-squared displacement
close to the transition. The influence of an infrared cutoff is discussed.Comment: 15 pages, 8 figures, to appear in J Phys Condens Matte
Enhanced wavelength-dependent surface tension of liquid-vapour interfaces
Due to the simultaneous presence of bulk-like and interfacial fluctuations
the understanding of the structure of liquid-vapour interfaces poses a
long-lasting and ongoing challenge for experiments, theory, and simulations. We
provide a new analysis of this topic by combining high-quality simulation data
for Lennard-Jones fluids with an unambiguous definition of the
wavenumber-dependent surface tension based on the two-point
correlation function of the fluid. Upon raising the temperature,
develops a maximum at short wavelengths. We compare these results with
predictions from density functional theory. Our analysis has repercussions for
the interpretation of grazing-incidence small-angle X-ray scattering (GISAXS)
at liquid interfaces
Entangled Dynamics of a Stiff Polymer
Entangled networks of stiff biopolymers exhibit complex dynamic response,
emerging from the topological constraints that neighboring filaments impose
upon each other. We propose a class of reference models for entanglement
dynamics of stiff polymers and provide a quantitative foundation of the tube
concept for stiff polymers. For an infinitely thin needle exploring a planar
course of point obstacles, we have performed large-scale computer simulations
proving the conjectured scaling relations from the fast transverse
equilibration to the slowest process of orientational relaxation. We determine
the rotational diffusion coefficient of the tracer, its angular confinement,
the tube diameter and the orientational correlation functions
Cluster-resolved dynamic scaling theory and universal corrections for transport on percolating systems
For percolating systems, we propose a universal exponent relation connecting
the leading corrections to scaling of the cluster size distribution with the
dynamic corrections to the asymptotic transport behaviour at criticality. Our
derivation is based on a cluster-resolved scaling theory unifying the scaling
of both the cluster size distribution and the dynamics of a random walker. We
corroborate our theoretical approach by extensive simulations for a site
percolating square lattice and numerically determine both the static and
dynamic correction exponents.Comment: 6 pages, 5 figures, 1 tabl
Electromechanical tuning of vertically-coupled photonic crystal nanobeams
We present the design, the fabrication and the characterization of a tunable
one-dimensional (1D) photonic crystal cavity (PCC) etched on two
vertically-coupled GaAs nanobeams. A novel fabrication method which prevents
their adhesion under capillary forces is introduced. We discuss a design to
increase the flexibility of the structure and we demonstrate a large reversible
and controllable electromechanical wavelength tuning (> 15 nm) of the cavity
modes.Comment: 11 pages, 4 figure
Verification of band offsets and electron effective masses in GaAsN/GaAs quantum wells : Spectroscopic experiment versus 10-band k.p modeling
Optical transitions in GaAs1-xNx/GaAs quantum wells (QWs) have been probed by two complementary techniques, modulation spectroscopy in a form of photoreflectance and surface photovoltage spectroscopy. Transition energies in QWs of various widths and N contents have been compared with the results of band structure calculations based on the 10-band k.p Hamiltonian. Due to the observation of higher order transitions in the measured spectra, the band gap discontinuities at the GaAsN/GaAs interface and the electron effective masses could be determined, both treated as semi-free parameters to get the best matching between the theoretical and experimental energies. We have obtained the chemical conduction band offset values of 86% for x = 1.2% and 83% for x = 2.2%, respectively. For these determined band offsets, the electron effective masses equal to about 0.09 m(o) in QWs with 1.2% N and 0.15 m(o) for the case of larger N content of 2.2%.Publisher PDFPeer reviewe
Memristive operation mode of a site-controlled quantum dot floating gate transistor
The authors gratefully acknowledge financial support from the European Union (FPVII (2007-2013) under Grant Agreement No. 318287 Landauer) as well as the state of Bavaria.We have realized a floating gate transistor based on a GaAs/AlGaAs heterostructure with site-controlled InAs quantum dots. By short-circuiting the source contact with the lateral gates and performing closed voltage sweep cycles, we observe a memristive operation mode with pinched hysteresis loops and two clearly distinguishable conductive states. The conductance depends on the quantum dot charge which can be altered in a controllable manner by the voltage value and time interval spent in the charging region. The quantum dot memristor has the potential to realize artificial synapses in a state-of-the-art opto-electronic semiconductor platform by charge localization and Coulomb coupling.Publisher PDFPeer reviewe
Coherence dynamics and quantum-to-classical crossover in an exciton-cavity system in the quantum strong coupling regime
Interaction between light and matter generates optical nonlinearities, which are particularly pronounced in the quantum strong coupling regime. When a single bosonic mode couples to a single fermionic mode, a Jaynes-Cummings (JC) ladder is formed, which we realize here using cavity photons and quantum dot excitons. We measure and model the coherent anharmonic response of this strongly coupled exciton-cavity system at resonance. Injecting two photons into the cavity, we demonstrate a root 2 larger polariton splitting with respect to the vacuum Rabi splitting. This is achieved using coherent nonlinear spectroscopy, specifically four-wave mixing, where the coherence between the ground state and the first (second) rung of the JC ladder can be interrogated for positive (negative) delays. With increasing excitation intensity and thus rising average number of injected photons, we observe spectral signatures of the quantum-to-classical crossover of the strong coupling regime.Peer reviewe
Mudanças morfológicas nas células de Sertoli durante o ciclo reprodutivo de machos do teleósteo Piaractus mesopotamicus (Holmberg, 1887)
An investigation of the histological and ultrastructural changes of Sertoli cells during the male reproductive cycle in Piaractus mesopotamicus was made. The results showed that the Sertoli cell development is closely related with germ cell maturation. Therefore, these cells may have some role in germ cell maturation during the reproductive cycle of this species, whether in forming a tissue framework for the developing spermatogenic cysts, aiding in testes reorganization for a new reproductive cycle, in addition to other possible functions discussed in the text.Realizou-se uma investigação das mudanças histolĂłgicas e ultra-estruturais das cĂ©lulas de Sertoli durante o ciclo reprodutivo de machos de Piaractus mesopotamicus. Os resultados mostraram que o desenvolvimento das cĂ©lulas de Sertoli está estritamente relacionado Ă maturação das cĂ©lulas gamĂ©ticas. Portanto, as cĂ©lulas de Sertoli tĂŞm algum papel na maturação das cĂ©lulas germinativas durante o ciclo reprodutivo dessa espĂ©cie, talvez formando um tecido de sustentação para os cistos espermatogĂŞnicos em desenvolvimento, ajudando a reorganização testicular para um novo ciclo reprodutivo, alĂ©m de outras possĂveis funções discutidas no texto.24124
The Localization Transition of the Two-Dimensional Lorentz Model
We investigate the dynamics of a single tracer particle performing Brownian
motion in a two-dimensional course of randomly distributed hard obstacles. At a
certain critical obstacle density, the motion of the tracer becomes anomalous
over many decades in time, which is rationalized in terms of an underlying
percolation transition of the void space. In the vicinity of this critical
density the dynamics follows the anomalous one up to a crossover time scale
where the motion becomes either diffusive or localized. We analyze the scaling
behavior of the time-dependent diffusion coefficient D(t) including corrections
to scaling. Away from the critical density, D(t) exhibits universal
hydrodynamic long-time tails both in the diffusive as well as in the localized
phase.Comment: 13 pages, 7 figures
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