2,299 research outputs found
Ultrafast circular polarization oscillations in spin-polarized vertical-cavity surface-emitting laser devices
Spin-polarized lasers offer new encouraging possibilities for future devices. We investigate the polarization dynamics of electrically pumped vertical-cavity surface-emitting lasers after additional spin injection at room temperature. We find that the circular polarization degree exhibits faster dynamics than the emitted light. Moreover the experimental results demonstrate a strongly damped ultrafast circular polarization oscillation due to spin injection with an oscillation frequency of approximately 11GHz depending on the birefringence in the VCSEL device. We compare our experimental results with theoretical calculations based on rate-equations. This allows us to predict undamped long persisting ultrafast polarization oscillations, which reveal the potential of spin-VCSELs for ultrafast modulation applications
Birefringence controlled room-temperature picosecond spin dynamics close to the threshold of vertical-cavity surface-emitting laser devices
We analyze the spin-induced circular polarization dynamics at the threshold of vertical-cavity surface-emitting lasers at room-temperature using a hybrid excitation combining electrically pumping without spin preference and spin-polarized optical injection. After a short pulse of spin-polarized excitation, fast oscillations of the circular polarization degree (CPD) are observed within the relaxation oscillations. A theoretical investigation of this behavior on the basis of a rate equation model shows that these fast oscillations of CPD could be suppressed by means of a reduction of the birefringence of the laser cavity
Fabrication, Characterisation and Tribological Investigation of Artificial Skin Surface Lipid Films
This article deals with the tribology of lipid coatings that resemble those found on human skin. In order to simulate the lipidic surface chemistry of human skin, an artificial sebum formulation that closely resembles human sebum was spray-coated onto mechanical skin models in physiologically relevant concentrations (5-100μg/cm2). Water contact angles and surface free energies (SFEs) showed that model surfaces with ≤25μg/cm2 lipids appropriately mimic the physico-chemical properties of dry, sebum-poor skin regions. In friction experiments with a steel ball, lipid-coated model surfaces demonstrated lubrication effects over a wide range of sliding velocities and normal loads. In friction measurements on model surfaces as a function of lipid-film thickness, a clear minimum in the friction coefficient (COF) was observed in the case of hydrophilic, high-SFE materials (steel, glass), with the lowest COF (≈0.5) against skin model surfaces being found at 25μg/cm2 lipids. For hydrophobic, low-SFE polymers, the COF was considerably lower (0.4 for PP, 0.16 for PTFE) and relatively independent of the lipid amount, indicating that both the mechanical and surface-chemical properties of the sliders strongly influence the friction behaviour of the skin-model surfaces. Lipid-coated skin models might be a valuable tool not only for tribologists but also for cosmetic chemists, in that they allow the objective study of friction, adhesion and wetting behaviour of liquids and emulsions on simulated skin-surface condition
Brane Formation and Cosmological Constraint on the Number of Extra Dimensions
Special relativity is generalized to extra dimensions and quantized energy
levels of particles are obtained. By calculating the probability of particles'
motion in extra dimensions at high temperature of the early universe, it is
proposed that the branes may have not existed since the very beginning of the
universe, but formed later. Meanwhile, before the formation, particles of the
universe may have filled in the whole bulk, not just on the branes. This
scenario differs from that in the standard big bang cosmology in which all
particles are assumed to be in the 4D spacetime. So, in brane models, whether
our universe began from a 4D big bang singularity is questionable. A
cosmological constraint on the number of extra dimensions is also given which
favors .Comment: 11 pages, no figures. To appear in IJT
Simulated dynamics of optically pumped dilute nitride 1300 nm spin vertical-cavity surface-emitting lasers
The authors report a theoretical analysis of optically pumped 1300 nm dilute nitride spin-polarised vertical-cavity surface-emitting lasers (VCSELs) using the spin-flip model to determine the regions of stability and instability. The dependence of the output polarisation ellipticity on that of the pump is investigated, and the results are presented in twodimensional contour maps of the pump polarisation against the magnitude of the optical pump. Rich dynamics and various forms of oscillatory behaviour causing self-sustained oscillations in the polarisation of the spin-VCSEL subject to continuouswave pumping have been found because of the competition of the spin-flip processes and birefringence. The authors also reveal the importance of considering both the birefringence rate and the linewidth enhancement factor when engineering a device for high-frequency applications. A very good agreement is found with the experimental results reported by the authors' group. © The Institution of Engineering and Technology 2014
Music-evoked incidental happiness modulates probability weighting during risky lottery choices
We often make decisions with uncertain consequences. The outcomes of the choices we make are usually not perfectly predictable but probabilistic, and the probabilities can be known or unknown. Probability judgments, i.e., the assessment of unknown probabilities, can be influenced by evoked emotional states. This suggests that also the weighting of known probabilities in decision making under risk might be influenced by incidental emotions, i.e., emotions unrelated to the judgments and decisions at issue. Probability weighting describes the transformation of probabilities into subjective decision weights for outcomes and is one of the central components of cumulative prospect theory (CPT) that determine risk attitudes. We hypothesized that music-evoked emotions would modulate risk attitudes in the gain domain and in particular probability weighting. Our experiment featured a within-subject design consisting of four conditions in separate sessions. In each condition, the 41 participants listened to a different kind of music-happy, sad, or no music, or sequences of random tones-and performed a repeated pairwise lottery choice task. We found that participants chose the riskier lotteries significantly more often in the "happy" than in the "sad" and "random tones" conditions. Via structural regressions based on CPT, we found that the observed changes in participants' choices can be attributed to changes in the elevation parameter of the probability weighting function: in the "happy" condition, participants showed significantly higher decision weights associated with the larger payoffs than in the "sad" and "random tones" conditions. Moreover, elevation correlated positively with self-reported music-evoked happiness. Thus, our experimental results provide evidence in favor of a causal effect of incidental happiness on risk attitudes that can be explained by changes in probability weighting
A numerical method for detecting incommensurate correlations in the Heisenberg zigzag ladder
We study two Heisenberg spin-1/2 chains coupled by a frustrating ``zigzag''
interaction. We are particularly interested in the regime of weak interchain
coupling, which is difficult to analyse by either numerical or analytical
methods. Previous density matrix renormalisation group (DMRG) studies of the
isotropic model with open boundary conditions and sizeable interchain coupling
have established the presence of incommensurate correlations and of a spectral
gap. By using twisted boundary conditions with arbitrary twist angle, we are
able to determine the incommensurabilities both in the isotropic case and in
the presence of an exchange anisotropy by means of exact diagonalisation of
relatively short finite chains of up to 24 sites. Using twisted boundary
conditions results in a very smooth dependence of the incommensurabilities on
system size, which makes the extrapolation to infinite systems significantly
easier than for open or periodic chains.Comment: 6 pages, including 7 figure
Two problems related to prescribed curvature measures
Existence of convex body with prescribed generalized curvature measures is
discussed, this result is obtained by making use of Guan-Li-Li's innovative
techniques. In surprise, that methods has also brought us to promote
Ivochkina's estimates for prescribed curvature equation in \cite{I1, I}.Comment: 12 pages, Corrected typo
Using Enzyme-Based Biosensors to Measure Tonic and Phasic Glutamate in Alzheimer\u27s Mouse Models
Neurotransmitter disruption is often a key component of diseases of the central nervous system (CNS), playing a role in the pathology underlying Alzheimer\u27s disease, Parkinson\u27s disease, depression, and anxiety. Traditionally, microdialysis has been the most common (lauded) technique to examine neurotransmitter changes that occur in these disorders. But because microdialysis has the ability to measure slow 1-20 minute changes across large areas of tissue, it has the disadvantage of invasiveness, potentially destroying intrinsic connections within the brain and a slow sampling capability. A relatively newer technique, the microelectrode array (MEA), has numerous advantages for measuring specific neurotransmitter changes within discrete brain regions as they occur, making for a spatially and temporally precise approach. In addition, using MEAs is minimally invasive, allowing for measurement of neurotransmitter alterations in vivo. In our laboratory, we have been specifically interested in changes in the neurotransmitter, glutamate, related to Alzheimer\u27s disease pathology. As such, the method described here has been used to assess potential hippocampal disruptions in glutamate in a transgenic mouse model of Alzheimer\u27s disease. Briefly, the method used involves coating a multi-site microelectrode with an enzyme very selective for the neurotransmitter of interest and using self-referencing sites to subtract out background noise and interferents. After plating and calibration, the MEA can be constructed with a micropipette and lowered into the brain region of interest using a stereotaxic device. Here, the method described involves anesthetizing rTg(TauP301L)4510 mice and using a stereotaxic device to precisely target sub-regions (DG, CA1, and CA3) of the hippocampus
Magnetization jump in the XXZ chain with next-nearest-neighbor exchange
We study the dependence of the magnetization M with magnetic field B at zero
temperature in the spin-1/2 XXZ chain with nearest-neighbor (NN) J1 and next-NN
J2 exchange interactions, with anisotropies Delta1 and Delta2 respectively. The
region of parameters for which a jump in M(B) exists is studied using numerical
diagonalization, and analytical results for two magnons on a ferromagnetic
background in the thermodynamic limit. We find a line in the parameter space
(J2/J1, Delta1/J1, Delta2/J2) (determined by two simple equations) at which the
ground state is highly degenerate. M(B) has a jump near this line, and at or
near the isotropic case with ferromagnetic J1 and antiferromagnetic J2, with
|J2/J1| near 1/4. These results are relevant for some systems containing CuO
chains with edge-sharing CuO4 units.Comment: 9 pages, 8 figures, submitted to Phys. Rev.
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