Spin dynamics in high-mobility two-dimensional electron systems

Understanding the spin dynamics in semiconductor heterostructures is highly important for future semiconductor spintronic devices. In high-mobility two-dimensional electron systems (2DES), the spin lifetime strongly depends on the initial degree of spin polarization due to the electron-electron interaction. The Hartree-Fock (HF) term of the Coulomb interaction acts like an effective out-of-plane magnetic field and thus reduces the spin-flip rate. By time-resolved Faraday rotation (TRFR) techniques, we demonstrate that the spin lifetime is increased by an order of magnitude as the initial spin polarization degree is raised from the low-polarization limit to several percent. We perform control experiments to decouple the excitation density in the sample from the spin polarization degree and investigate the interplay of the internal HF field and an external perpendicular magnetic field. The lifetime of spins oriented in the plane of a [001]-grown 2DES is strongly anisotropic if the Rashba and Dresselhaus spin-orbit fields are of the same order of magnitude. This anisotropy, which stems from the interference of the Rashba and the Dresselhaus spin-orbit fields, is highly density-dependent: as the electron density is increased, the kubic Dresselhaus term becomes dominant and reduces the anisotropy.Comment: 13 pages, 6 figure

Body weight, body mass index, overweight and obesity in consecutive cohorts of children at school entry in a community in Lower Bavaria 1997-2002

Objective: To study time trends of weight, body mass index, overweight and obesity of children at school entry and to analyze potential effects of changes in the structure of consecutive cohorts of children at school entry over time on these weight-related measures. Design: We studied height, weight and body mass index (BMI) in 6 consecutive cohorts (1997-2002) of children at school entry (N=6,420). Overweight and obesity were defined by internationally valid sex and age specific cut-off points. In addition to descriptive statistics for time trends we applied an analysis of covariance to estimate the impact of covariates on weight and BMI and logistic regression models for the impact of covariates on overweight and obesity. Results: Although we found an overall decrease of mean body weight (minus 9%), BMI (minus 9.5%), overweight (minus 7.4%) and obesity (minus 6.8%) between 1997 and 2002, there was a considerable variation in these measures between single years. The analysis of covariance showed significant impact of age, gender and year of examination on weight and BMI. Whereas there were significant differences in the proportion of overweight children between different age groups, the effect of age was not significant for the proportion of obesity. Multiple logistic regression models showed that age (OR, 2.8; 95% CI, 2.3-3.5) and female gender (OR, 1.3; 95% CI, 1.2-1.5) were significantly associated with overweight and significantly with obesity (age: OR, 1.8; 95% CI, 1.2-2.9; female gender: OR, 1.4; 95% CI, 1.0-1.99), respectively. In these models the years of examination of 1998 (OR, 1.9; 95 %CI, 1.5-2.5) and 1999 (OR, 2.5; 95% CI, 1.97-3.3) were significantly associated with overweight, and the year 1999 (OR, 2.9; 95% CI, 1.6-5.2) with obesity. Conclusions: Our study showed that changes in age and gender distribution have to be taken into account when time trends of weight, BMI, overweight and obesity are derived from investigations of children at school entry.Bernard Theodor Baune, Rafael Thomas Mikolajczyk, Heribert Stich, Alexander Kräme

Dynamic Structure Factor of Liquid and Amorphous Ge From Ab Initio Simulations

We calculate the dynamic structure factor S(k,omega) of liquid Ge (l-Ge) at temperature T = 1250 K, and of amorphous Ge (a-Ge) at T = 300 K, using ab initio molecular dynamics. The electronic energy is computed using density-functional theory, primarily in the generalized gradient approximation, together with a plane wave representation of the wave functions and ultra-soft pseudopotentials. We use a 64-atom cell with periodic boundary conditions, and calculate averages over runs of up to 16 ps. The calculated liquid S(k,omega) agrees qualitatively with that obtained by Hosokawa et al, using inelastic X-ray scattering. In a-Ge, we find that the calculated S(k,omega) is in qualitative agreement with that obtained experimentally by Maley et al. Our results suggest that the ab initio approach is sufficient to allow approximate calculations of S(k,omega) in both liquid and amorphous materials.Comment: 31 pages and 8 figures. Accepted for Phys. Rev.

Thermodynamic Behavior of a Model Covalent Material Described by the Environment-Dependent Interatomic Potential

Using molecular dynamics simulations we study the thermodynamic behavior of a single-component covalent material described by the recently proposed Environment-Dependent Interatomic Potential (EDIP). The parameterization of EDIP for silicon exhibits a range of unusual properties typically found in more complex materials, such as the existence of two structurally distinct disordered phases, a density decrease upon melting of the low-temperature amorphous phase, and negative thermal expansion coefficients for both the crystal (at high temperatures) and the amorphous phase (at all temperatures). Structural differences between the two disordered phases also lead to a first-order transition between them, which suggests the existence of a second critical point, as is believed to exist for amorphous forms of frozen water. For EDIP-Si, however, the unusual behavior is associated not only with the open nature of tetrahedral bonding but also with a competition between four-fold (covalent) and five-fold (metallic) coordination. The unusual behavior of the model and its unique ability to simulation the liquid/amorphous transition on molecular-dynamics time scales make it a suitable prototype for fundamental studies of anomalous thermodynamics in disordeered systems.Comment: 48 pages (double-spaced), 13 figure

Self-organized stable pacemakers near the onset of birhythmicity

General amplitude equations for reaction-diffusion systems near to the soft onset of birhythmicity described by a supercritical pitchfork-Hopf bifurcation are derived. Using these equations and applying singular perturbation theory, we show that stable autonomous pacemakers represent a generic kind of spatiotemporal patterns in such systems. This is verified by numerical simulations, which also show the existence of breathing and swinging pacemaker solutions. The drift of self-organized pacemakers in media with spatial parameter gradients is analytically and numerically investigated.Comment: 4 pages, 4 figure

Genetic diversity and linkage disequilibrium of two homologous genes to maize D8: sorghum SbD8 and pearl millet PgD8

Yield and yield stability of sorghum [Sorghum bicolor (L.) Moench.] and pearl millet [Pennisetum glaucum (L.) R.Br.] are highly influenced by flowering time and photoperiodic sensitivity in the arid to semi-arid regions of West and Central Africa. Photoperiodic sensitivity is the key adaptation trait of local landraces because it assures flowering at the end of the rainy season, independent of variable dates of planting. Flowering time genes are mainly integrated into four pathways with close interaction among each other: Vernalization, autonomous, GA (gibberellic acid) and photoperiod. In the GA pathway, maize D8, wheat RHT1 and rice SLR have been identified as homologous genes to the Arabidopsis GAI, which is a negative regulator of GA response. We have identified two homologous genes to D8: Sorghum SbD8 and pearl millet PgD8. These genes were expressed in the root and leaves of sorghum and pearl millet as revealed by EST database search and reverse transcription PCR, respectively. The genetic diversity of SbD8 was considerably lower than that of PgD8. The extent of linkage disequilibrium in PgD8 is lower than that of maize D8. SbD8 and PgD8 polymorphisms might be appropriate for dissection of photoperiod sensitivity using association mapping approaches

The Relationship Between Belief and Credence

Sometimes epistemologists theorize about belief, a tripartite attitude on which one can believe, withhold belief, or disbelieve a proposition. In other cases, epistemologists theorize about credence, a fine-grained attitude that represents one’s subjective probability or confidence level toward a proposition. How do these two attitudes relate to each other? This article explores the relationship between belief and credence in two categories: descriptive and normative. It then explains the broader significance of the belief-credence connection and concludes with general lessons from the debate thus far

A learning robot for cognitive camera control in minimally invasive surgery

Background!#!We demonstrate the first self-learning, context-sensitive, autonomous camera-guiding robot applicable to minimally invasive surgery. The majority of surgical robots nowadays are telemanipulators without autonomous capabilities. Autonomous systems have been developed for laparoscopic camera guidance, however following simple rules and not adapting their behavior to specific tasks, procedures, or surgeons.!##!Methods!#!The herein presented methodology allows different robot kinematics to perceive their environment, interpret it according to a knowledge base and perform context-aware actions. For training, twenty operations were conducted with human camera guidance by a single surgeon. Subsequently, we experimentally evaluated the cognitive robotic camera control. A VIKY EP system and a KUKA LWR 4 robot were trained on data from manual camera guidance after completion of the surgeon's learning curve. Second, only data from VIKY EP were used to train the LWR and finally data from training with the LWR were used to re-train the LWR.!##!Results!#!The duration of each operation decreased with the robot's increasing experience from 1704 s ± 244 s to 1406 s ± 112 s, and 1197 s. Camera guidance quality (good/neutral/poor) improved from 38.6/53.4/7.9 to 49.4/46.3/4.1% and 56.2/41.0/2.8%.!##!Conclusions!#!The cognitive camera robot improved its performance with experience, laying the foundation for a new generation of cognitive surgical robots that adapt to a surgeon's needs