Relaxation of hole spins in quantum dots via two-phonon processes

We investigate theoretically spin relaxation in heavy hole quantum dots in low external magnetic fields. We demonstrate that two-phonon processes and spin-orbit interaction are experimentally relevant and provide an explanation for the recently observed saturation of the spin relaxation rate in heavy hole quantum dots with vanishing magnetic fields. We propose further experiments to identify the relevant spin relaxation mechanisms in low magnetic fields.Comment: 5 pages, 2 figure

Academic Development of First-Year Living-Learning Program Students before and after Hurricanes Katrina and Rita of 2005

Previous research suggests that the far-reaching impacts of hurricanes include the academic performance of students. In an examination of such impacts, we found a trend toward self-perceived decline in some performance indicators relative to students at peer universities. However, few longitudinal impacts were found, perhaps because of the sense of community offered by the living-learning program. These results may inform administrators and faculty of areas for emphasis in mitigating future impacts. Robert V. Rohli is a Professor of Geography and Faculty Director of the Residential Colleges Program at Louisiana State University in Baton Rouge, LA. Kurt J. Keppler is Vice Chancellor for Student Life & Enrollment at Louisiana State University. Daniel L. Winkler is a Graduate Assistant at Louisiana State University

Dynamic spin-Hall effect and driven spin helix for linear spin-orbit interactions

We derive boundary conditions for the electrically induced spin accumulation in a finite, disordered 2D semiconductor channel. While for DC electric fields these boundary conditions select spatially constant spin profiles equivalent to a vanishing spin-Hall effect, we show that an in-plane ac electric field results in a non-zero ac spin-Hall effect, i.e., it generates a spatially non-uniform out-of-plane polarization even for linear intrinsic spin-orbit interactions. Analyzing different geometries in [001] and [110]-grown quantum wells, we find that although this out-of-plane polarization is typically confined to within a few spin-orbit lengths from the channel edges, it is also possible to generate spatially oscillating spin profiles which extend over the whole channel. The latter is due to the excitation of a driven spin-helix mode in the transverse direction of the channel. We show that while finite frequencies suppress this mode, it can be amplified by a magnetic field tuned to resonance with the frequency of the electric field. In this case, finite size effects at equal strengths of Rashba- and Dresselhaus SOI lead to an enhancement of the magnitude of this helix mode. We comment on the relation between spin currents and boundary conditions.Comment: 10 pages, 5 figures, added references, corrected typos, extended section V, VI

Strong Spin-Orbit Interaction and Helical Hole States in Ge/Si Nanowires

We study theoretically the low-energy hole states of Ge/Si core/shell nanowires. The low-energy valence band is quasidegenerate, formed by two doublets of different orbital angular momenta, and can be controlled via the relative shell thickness and via external fields. We find that direct (dipolar) coupling to a moderate electric field leads to an unusually large spin-orbit interaction of Rashba type on the order of meV which gives rise to pronounced helical states enabling electrical spin control. The system allows for quantum dots and spin qubits with energy levels that can vary from nearly zero to several meV, depending on the relative shell thickness.Comment: 8 pages, 6 figure

High-Flow Vascular Malformations in Children.

Children can have a variety of intracranial vascular anomalies ranging from small and incidental with no clinical consequences to complex lesions that can cause substantial neurologic deficits, heart failure, or profoundly affect development. In contrast to high-flow lesions with direct arterial-to-venous shunts, low-flow lesions such as cavernous malformations are associated with a lower likelihood of substantial hemorrhage, and a more benign course. Management of vascular anomalies in children has to incorporate an understanding of how treatment strategies may affect the normal development of the central nervous system. In this review, we discuss the etiologies, epidemiology, natural history, and genetic risk factors of three high-flow vascular malformations seen in children: brain arteriovenous malformations, intracranial dural arteriovenous fistulas, and vein of Galen malformations

Insulator-to-metal transition in sulfur-doped silicon

We observe an insulator-to-metal (I-M) transition in crystalline silicon doped with sulfur to non- equilibrium concentrations using ion implantation followed by pulsed laser melting and rapid resolidification. This I-M transition is due to a dopant known to produce only deep levels at equilibrium concentrations. Temperature-dependent conductivity and Hall effect measurements for temperatures T > 1.7 K both indicate that a transition from insulating to metallic conduction occurs at a sulfur concentration between 1.8 and 4.3 x 10^20 cm-3. Conduction in insulating samples is consistent with variable range hopping with a Coulomb gap. The capacity for deep states to effect metallic conduction by delocalization is the only known route to bulk intermediate band photovoltaics in silicon.Comment: Submission formatting; 4 journal pages equivalen

Infant behavioral reactivity predicts change in amygdala volume 12 years later

The current study examined the link between temperamental reactivity in infancy and amygdala development in middle childhood. A sample (n = 291) of four-month-old infants was assessed for infant temperament, and two groups were identified: those exhibiting negative reactivity (n = 116) and those exhibiting positive reactivity (n = 106). At 10 and 12 years of age structural imaging was completed on a subset of these participants (n = 75). Results indicate that, between 10 and 12 years of age, left amygdala volume increased more slowly in those with negative compared to positive reactive temperament. These results provide novel evidence linking early temperament to distinct patterns of brain development over middle childhood

Modelling and prediction of bacterial attachment to polymers

Infection by pathogenic bacteria on implanted and indwelling medical devices during surgery causes large morbidity and mortality worldwide. Attempts to ameliorate this important medical issue have included development of antimicrobial surfaces on materials, ‘no touch’ surgical procedures, and development of materials with inherent low pathogen attachment. The search for new materials is increasingly being carried out by high throughput methods. Efficient methods for extracting knowledge from these large data sets are essential. We used data from a large polymer microarray exposed to three clinical pathogens to derive robust and predictive machine-learning models of pathogen attachment. The models could predict pathogen attachment for the polymer library quantitatively. The models also successfully predicted pathogen attachment for a second-generation library, and identified polymer surface chemistries that enhance or diminish pathogen attachment

Attenuation and modification of the ballast water microbial community during voyages into the Canadian Arctic

Aim: Ballast water is a major vector of non-indigenous species introductions world-wide. Our understanding of population dynamics of organisms entrained in ballast is largely limited to studies of zooplankton and phytoplankton. Bacteria are more numerous and diverse than zooplankton or phytoplankton, yet remain comparatively understudied. We apply a metagenomics approach to characterize changes in the microbial ballast water community over the course of three voyages on one ship, and assess the effects of ballast water exchange (BWE), spring/summer sampling month and time since voyage start. Location: Quebec City and Deception Bay, Quebec, and the coastal marine region offshore of eastern Canada. Methods: We used universal primers to Ion Torrent sequence a fragment of the bacterial 16S ribosomal DNA for samples collected over three voyages of one ship between Quebec City and Deception Bay in June, July and August 2015. We compared richness (total number of species in the community) and diversity (accounts for both species abundance and evenness) using linear mixed-effects analysis and compared community composition using non-metric multidimensional scaling and permutational multivariate analysis of variance. Initial comparisons were between months. Subsequent analyses focused on each month separately. Results: Ion Torrent sequencing returned c. 2.9 million reads and revealed monthly differences in diversity and richness, and in community structure in ballast water. June had higher richness and diversity than either July or August, and showed most clearly the effect of BWE on the microbial community. Main conclusions: Our results suggest that environmental conditions associated with different spring/summer sampling months drive differences in microbial diversity in ballast water. This study showed that BWE removes some components of the freshwater starting microbial community and replaces them with other taxa. BWE also changed proportional representation of some microbes without removing them completely. It appears that some taxa are resident in ballast tanks and are not removed by BWE. © 2017 John Wiley & Sons Lt

Intersubband-induced spin-orbit interaction in quantum wells

Recently, we have found an additional spin-orbit (SO) interaction in quantum wells with two subbands [Phys. Rev. Lett. 99, 076603 (2007)]. This new SO term is non-zero even in symmetric geometries, as it arises from the intersubband coupling between confined states of distinct parities, and its strength is comparable to that of the ordinary Rashba. Starting from the $8 \times 8$ Kane model, here we present a detailed derivation of this new SO Hamiltonian and the corresponding SO coupling. In addition, within the self-consistent Hartree approximation, we calculate the strength of this new SO coupling for realistic symmetric modulation-doped wells with two subbands. We consider gated structures with either a constant areal electron density or a constant chemical potential. In the parameter range studied, both models give similar results. By considering the effects of an external applied bias, which breaks the structural inversion symmetry of the wells, we also calculate the strength of the resulting induced Rashba couplings within each subband. Interestingly, we find that for double wells the Rashba couplings for the first and second subbands interchange signs abruptly across the zero bias, while the intersubband SO coupling exhibits a resonant behavior near this symmetric configuration. For completeness we also determine the strength of the Dresselhaus couplings and find them essentially constant as function of the applied bias.Comment: 16 pages, 12 figure