Edge Dynamics in a Quantum Spin Hall State: Effects from Rashba Spin-Orbit Interaction

We analyze the dynamics of the helical edge modes of a quantum spin Hall state in the presence of a spatially non-uniform Rashba spin-orbit (SO) interaction. A randomly fluctuating Rashba SO coupling is found to open a scattering channel which causes localization of the edge modes for a weakly screened electron-electron (e-e) interaction. A periodic modulation of the SO coupling, with a wave number commensurate with the Fermi momentum, makes the edge insulating already at intermediate strengths of the e-e interaction. We discuss implications for experiments on edge state transport in a HgTe quantum well.Comment: 4 pages, 2 figures; published versio

Robust adaptive beamforming for MIMO monopulse radar

Researchers have recently proposed a widely separated multiple-input multiple-output (MIMO) radar using monopulse angle estimation techniques for target tracking. The widely separated antennas provide improved tracking performance by mitigating complex target radar cross-section fades and angle scintillation. An adaptive array is necessary in this paradigm because the direct path from any transmitter could act as a jammer at a receiver. When the target-free covariance matrix is not available, it is critical to include robustness into the adaptive beamformer weights. This work explores methods of robust adaptive monopulse beamforming techniques for MIMO tracking radar

Explicit simulation of aerosol physics in a cloud-resolving model

International audienceThe role of convection in introducing aerosols and promoting the formation of new particles to the upper troposphere has been examined using a cloud-resolving model coupled with an interactive explicit aerosol module. A baseline simulation suggests good agreement in the upper troposphere between modeled and observed results including concentrations of aerosols in different size ranges, mole fractions of key chemical species, and concentrations of ice particles. In addition, a set of 34 sensitivity simulations has been carried out to investigate the sensitivity of modeled results to the treatment of various aerosol physical and chemical processes in the model. The size distribution of aerosols is proved to be an important factor in determining the aerosols' fate within the convective cloud. Nucleation mode aerosols (02SO4. Accumulation mode aerosols (d>?31.0 nm) are almost completely removed by nucleation (activation of cloud droplets) and impact scavenging. However, a substantial part (up to 10% of the boundary layer concentration) of the Aitken mode aerosol population (5.84 nm<?d<?31.0 nm) reaches the top of the cloud and the free troposphere. These particles may continually survive in the upper troposphere, or over time form ice crystals, both that could impact the atmospheric radiative budget. The sensitivity simulations performed indicate that critical processes in the model causing a substantial change in the upper tropospheric Aitken mode number concentration are coagulation, condensation, nucleation scavenging, nucleation of aerosols and the transfer of aerosol mass and number between different aerosol bins. In particular, for aerosols in the Aitken mode to grow to CCN size, coagulation appears to be more important than condensation. Less important processes are dry deposition, impact scavenging and the initial vertical distribution and concentration of aerosols. It is interesting to note that in order to sustain a vigorous storm cloud, the supply of CCN must be continuous over a considerably long time period of the simulation. Hence, the treatment of the growth of particles is in general much more important than the initial aerosol concentration itself

Seasonal variation of aerosol water uptake and its impact on the direct radiative effect at Ny-Ålesund, Svalbard

© Author(s) 2014. This work is distributed under the Creative Commons Attribution 3.0 LicenseIn this study we investigated the impact of water uptake by aerosol particles in ambient atmosphere on their optical properties and their direct radiative effect (ADRE, W m-2) in the Arctic at Ny-Ålesund, Svalbard, during 2008. To achieve this, we combined three models, a hygroscopic growth model, a Mie model and a radiative transfer model, with an extensive set of observational data. We found that the seasonal variation of dry aerosol scattering coefficients showed minimum values during the summer season and the beginning of fall (July-August-September), when small particles (< 100 nm in diameter) dominate the aerosol number size distribution. The maximum scattering by dry particles was observed during the Arctic haze period (March-April-May) when the average size of the particles was larger. Considering the hygroscopic growth of aerosol particles in the ambient atmosphere had a significant impact on the aerosol scattering coefficients: the aerosol scattering coefficients were enhanced by on average a factor of 4.30 ± 2.26 (mean ± standard deviation), with lower values during the haze period (March-April-May) as compared to summer and fall. Hygroscopic growth of aerosol particles was found to cause 1.6 to 3.7 times more negative ADRE at the surface, with the smallest effect during the haze period (March-April-May) and the highest during late summer and beginning of fall (July-August-September).Peer reviewe

A Linguistic Analysis of the Content, Context, and Demographic Variables Related to Clinician Professional Misconduct

The professions of counseling, marriage and family therapy, and social work are highly controlled with regulators frequently issuing findings of professional misconduct against clinicians. Although much research has been conducted with regard to clinician professional misconduct in general, there is a scarcity of research investigating the relationship between gender and types of professional misconduct, and no research to date has been conducted to investigate the content of final findings of professional misconduct as determined by state regulators. What remains unknown, therefore, is to what degree specific clinician gender correlates with sanctions for acts of professional misconduct and the linguistic content and context of these sanctions. This research consists of two studies investigating the content and context of professional misconduct findings against licensed counselors, marriage and family therapists, and social workers. The first study is titled “The Relationship of Clinician Demographic Variables to Discipline Board Misconduct Content.” The second study is titled “Clinician Discipline Board Misconduct Decisions: A Study of Linguistic Differences.” These studies were designed around a retrospective cross-sectional analysis of a linguistic corpus created from a randomized convenience sample of final determinations of disciplinary actions across eight states. This linguistic corpus was created from the findings of fact of 509 final determinations of misconduct against clinicians. For the first study, word counts from the contents of the findings of misconduct for the following linguistic categories: (a) family words, (b) substance words, (c) finance words, (d) sex words, (e) friend words, and (f) recordkeeping words were compared to the criterion variables consisting of (a) gender, (b) years of experience, (c) geographical region, and (d) type of license. Frequency rates and rankings of the variables were calculated and the relationships between variables were evaluated through a multiple linear regression analysis. For the second study, raw word counts and a normalized frequency were reported for each linguistic category of professional misconduct and a GraphColl of the collocates of the most frequent word in each category was produced. The results of the first study demonstrate a wide variation of prevalence rates across the control variables and suggest some significant relationships between these demographic variables and the linguistic categories. Three meaningful findings emerged from the second study. The first finding is the sexual or intimate nature of the term “relationship.” The second finding was the nuclear family context of the term “mother” in relation to the family word list. The third finding was the relatively high frequency of the term “alcohol” among the substance terms. The findings from both studies provide empirical data regarding the linguistic content and context of professional misconduct and identify relationships between clinicians’ professional misconduct and their personal and professional demographics. This data is necessary to better understand types and contexts of professional misconduct to effectively and efficiently educate, develop, and supervise clinicians

Electromagnetic properties of non-Dirac particles with rest spin 1/2

We resolve a number of questions related to an analytic description of electromagnetic form factors of non-Dirac particles with the rest spin 1/2. We find the general structure of a matrix antisymmetric tensor operator. We obtain two recurrence relations for matrix elements of finite transformations of the proper Lorentz group and explicit formulas for a certain set of such elements. Within the theory of fields with double symmetry, we discuss writing the components of wave vectors of particles in the form of infinite continued fractions. We show that for $Q^{2} \leq 0.5$ (GeV/c)$^{2}$, where $Q^{2}$ is the transferred momentum squared, electromagnetic form factors that decrease as $Q^{2}$ increases and are close to those experimentally observed in the proton can be obtained without explicitly introducing an internal particle structure.Comment: 18 pages, 2 figure

Electrical control of the Kondo effect in a helical edge liquid

Magnetic impurities affect the transport properties of the helical edge states of quantum spin Hall insulators by causing single-electron backscattering. We study such a system in the presence of a Rashba spin-orbit interaction induced by an external electric field, showing that this can be used to control the Kondo temperature, as well as the correction to the conductance due to the impurity. Surprisingly, for a strongly anisotropic electron-impurity spin exchange, Kondo screening may get obstructed by the presence of a non-collinear spin interaction mediated by the Rashba coupling. This challenges the expectation that the Kondo effect is stable against time-reversal invariant perturbations.Comment: 7 pages, 2 figures. Expression for the current operator corrected. (Conclusions unaffected.) Erratum to be publishe

Wintertime Arctic Ocean sea water properties and primary marine aerosol concentrations

Sea spray aerosols are an important part of the climate system through their direct and indirect effects. Due to the diminishing sea ice, the Arctic Ocean is one of the most rapidly changing sea spray aerosol source areas. However, the influence of these changes on primary particle production is not known. &lt;br&gt;&lt;br&gt; In laboratory experiments we examined the influence of Arctic Ocean water temperature, salinity, and oxygen saturation on primary particle concentration characteristics. Sea water temperature was identified as the most important of these parameters. A strong decrease in sea spray aerosol production with increasing water temperature was observed for water temperatures between &amp;minus;1&amp;deg;C and 9&amp;deg;C. Aerosol number concentrations decreased from at least 1400 cm&lt;sup&gt;&amp;minus;3&lt;/sup&gt; to 350 cm&lt;sup&gt;&amp;minus;3&lt;/sup&gt;. In general, the aerosol number size distribution exhibited a robust shape with one mode close to dry diameter &lt;i&gt;D&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt; 0.2 &amp;mu;m with approximately 45% of particles at smaller sizes. Changes in sea water temperature did not result in pronounced change of the shape of the aerosol size distribution, only in the magnitude of the concentrations. Our experiments indicate that changes in aerosol emissions are most likely linked to changes of the physical properties of sea water at low temperatures. The observed strong dependence of sea spray aerosol concentrations on sea water temperature, with a large fraction of the emitted particles in the typical cloud condensation nuclei size range, provide strong arguments for a more careful consideration of this effect in climate models