Dipole trap model for the metallic state in gated silicon-inversion layers

In order to investigate the metallic state in high-mobility Si-MOS structures, we have further developed and precised the dipole trap model which was originally proposed by B.L. Altshuler and D.L. Maslov [Phys. Rev. Lett.\ 82, 145 (1999)]. Our additional numerical treatment enables us to drop several approximations and to introduce a limited spatial depth of the trap states inside the oxide as well as to include a distribution of trap energies. It turns out that a pronounced metallic state can be caused by such trap states at appropriate energies whose behavior is in good agreement with experimental observations.Comment: 16 pages, 10 figures, submitte

Contralateral manual compensation for velocity-dependent force perturbations

It is not yet clear how the temporal structure of a voluntary action is coded allowing coordinated bimanual responses. This study focuses on the adaptation to and compensation for a force profile presented to one stationary arm which is proportional to the velocity of the other moving arm. We hypothesised that subjects would exhibit predictive coordinative responses which would co-vary with the state of the moving arm. Our null hypothesis is that they develop a time-dependent template of forces appropriate to compensate for the imposed perturbation. Subjects were trained to make 500 ms duration reaching movements with their dominant right arm to a visual target. A force generated with a robotic arm that was proportional to the velocity of the moving arm and perpendicular to movement direction acted on their stationary left hand, either at the same time as the movement or delayed by 250 or 500 ms. Subjects rapidly learnt to minimise the final end-point error. In the delay conditions, the left hand moved in advance of the onset of the perturbing force. In test conditions with faster or slower movement of the right hand, the predictive actions of the left hand co-varied with movement speed. Compensation for movement-related forces appeared to be predictive but not based on an accurate force profile that was equal and opposite to the imposed perturbatio

Narrating psychological distress: Associations between cross-clausal integration and mental health difficulties

Psychological research has emphasized the importance of narrative for a person’s sense of self. Building a coherent narrative of past events is one objective of psychotherapy. However, in guided self-help therapy the patient has to develop this narrative autonomously. Identifying patients’ narrative skills in relation to psychological distress could provide useful information about their suitability for self-help. The aim of this study was to explore whether the syntactic integration of clauses into narrative in texts written by prospective psychotherapy patients was related to mild to moderate psychological distress. Cross-clausal syntax of texts by 97 people who had contacted a primary care mental health service was analyzed. Severity of symptoms associated with mental health difficulties was assessed by a standardized scale (Clinical Outcomes in Routine Evaluation outcome measure). Cross-clausal syntactic integration was negatively correlated with the severity of symptoms. A multiple regression analysis confirmed that the use of simple sentences, finite complement clauses, and coordinated clauses was associated with symptoms (R2 = .26). The results suggest that the analysis of cross-clausal syntax can provide information on patients’ narrative skills in relation to distressing events and can therefore provide additional information to support treatment decisions

Relation among concentrations of incorporated Mn atoms, ionized Mn acceptors, and holes in p-(Ga,Mn)As epilayers

The amount of ionized Mn acceptors in various p-type Mn-doped GaAs epilayers has been evaluated by electrochemical capacitance-voltage measurements, and has been compared systematically with concentrations of incorporated Mn atoms and holes for wide range of Mn concentration (10^17 ~ 10^21 cm^-3). Quantitative assessment of anomalous Hall effect at room temperature is also carried out for the first time.Comment: 8 pages, 4 figures, tabl

A comparison of tourist evaluation of beaches in Malta, Romania and Turkey

The characteristics, perceptions, attitudes and behaviour of beach users at three locations: St George's Bay, Malta, Mamaia, Romania and Olu Deniz, Turkey, were determined from questionnaire surveys. Respondents comprised locals, domestic and foreign tourists. Results for these parameters had substantial agreement both across the three beaches and with previous studies. The amounts beach users were willing to pay (WTP), via the contingent valuation method and their consumer surpluses (CS), via the travel cost method were determined. The average amount beach users were willing to pay per visit, was £0.64 on St George's bay, £0.32 on Mamaia and £0.94 on Olu Deniz. The willingness to pay varied with social class, earnings, amount of beach use and between local, domestic and foreign user groups. The consumer surplus also varied for these groups as British tourists had a CS of £0.62 per visit, with domestic Turkish and Romanian users having values of £0.46 and £0.69, respectively. Diminishing marginal utility, as measured by WTP, with beach use was found in all three surveys. Charging for actual use would be acceptable for the majority of beach users. Coastal zone managers could realise significant revenues from beach users if they charge adults on a per visit basis (the favoured mode of payment) and spend the revenue on the maintenance and improvements identified by the users. Only one of the beaches (Olu Deniz, Turkey) currently has restricted access, which would facilitate such a payment method.peer-reviewe

Magnetic irreversibility and Verwey transition in nano-crystalline bacterial magnetite

The magnetic properties of biologically-produced magnetite nanocrystals biomineralized by four different magnetotactic bacteria were compared to those of synthetic magnetite nanocrystals and large, high quality single crystals. The magnetic feature at the Verwey temperature, $T_{V}$, was clearly seen in all nanocrystals, although its sharpness depended on the shape of individual nanoparticles and whether or not the particles were arranged in magnetosome chains. The transition was broader in the individual superparamagnetic nanoparticles for which $T_{B}<T_{V}$, where $T_{B}$ is the superparamagnetic blocking temperature. For the nanocrystals organized in chains, the effective blocking temperature $T_{B}>T_{V}$ and the Verwey transition is sharply defined. No correlation between the particle size and $T_{V}$ was found. Furthermore, measurements of $M(H,T,time)$ suggest that magnetosome chains behave as long magnetic dipoles where the local magnetic field is directed along the chain and this result confirms that time-logarithmic magnetic relaxation is due to the collective (dipolar) nature of the barrier for magnetic moment reorientation

Self-Motion Holds a Special Status in Visual Processing

Agency plays an important role in self-recognition from motion. Here, we investigated whether our own movements benefit from preferential processing even when the task is unrelated to self-recognition, and does not involve agency judgments. Participants searched for a moving target defined by its known shape among moving distractors, while continuously moving the computer mouse with one hand. They thereby controlled the motion of one item, which was randomly either the target or any of the distractors, while the other items followed pre-recorded motion pathways. Performance was more accurate and less prone to degradation as set size increased when the target was the self-controlled item. An additional experiment confirmed that participant-controlled motion was not physically more salient than motion recorded offline. We found no evidence that self-controlled items captured attention. Taken together, these results suggest that visual events are perceived more accurately when they are the consequences of our actions, even when self-motion is task irrelevant

Shot-noise suppression by Fermi and Coulomb correlations in ballistic conductors

We investigate the injection of degenerate Fermi-Dirac electrons into a multimode ballistic conductor under the space-charge limited regime. The nonequilibrium current fluctuations were found to be suppressed by both Coulomb and Fermi correlations. We show that the Fermi shot-noise suppression factor is limited below by the value 2kT/epsilon_F, where T is the temperature and epsilon_F the Fermi energy of the injected electrons. The Coulomb noise suppression factor may attain much lower values epsilon_F/2qU, because of its dependence on the applied bias U >> kT/q. The asymptotic behaviour of the overall shot-noise suppression factor in a high degenerate limit was found to be kT/qU, independently of the material parameters.Comment: 8 pages, 4 figures, minor changes, published versio

Combined approach of density functional theory and quantum Monte Carlo method to electron correlation in dilute magnetic semiconductors

We present a realistic study for electronic and magnetic properties in dilute magnetic semiconductor (Ga,Mn)As. A multi-orbital Haldane-Anderson model parameterized by density-functional calculations is presented and solved with the Hirsch-Fye quantum Monte Carlo algorithm. Results well reproduce experimental results in the dilute limit. When the chemical potential is located between the top of the valence band and an impurity bound state, a long-range ferromagnetic correlations between the impurities, mediated by antiferromagnetic impurity-host couplings, are drastically developed. We observe an anisotropic character in local density of states at the impurity-bound-state energy, which is consistent with the STM measurements. The presented combined approach thus offers a firm starting point for realistic calculations of the various family of dilute magnetic semiconductors.Comment: 5 pages, 4 figure