Self-organizing nanodot structures on InP surfaces evolving under low-energy ion irradiation: analysis of morphology and composition

Surfaces of InP were bombarded by 1.9 keV Ar(+) ions under normal incidence. The total accumulated ion fluence Φ the samples were exposed to was varied from 1 × 10(17) cm(−2) to 3 × 10(18) cm(−2), and ion fluxes f of (0.4 − 2) × 10(14) cm(−2) s(−1) were used. The surface morphology resulting from these ion irradiations was examined by atomic force microscopy (AFM). Generally, nanodot structures are formed on the surface; their dimensions (diameter, height and separation), however, were found to depend critically on the specific bombardment conditions. As a function of ion fluence, the mean radius r, height h, and spacing l of the dots can be fitted by power-law dependences: r ∝ Φ(0.40), h ∝ Φ(0.48), and l ∝ Φ(0.19). In terms of ion flux, there appears to exist a distinct threshold: below f ~ (1.3 ± 0.2) × 10(14) cm(−2) s(−1), no ordering of the dots exists and their size is comparatively small; above that value of f, the height and radius of the dots becomes substantially larger (h ~ 40 nm and r ~ 50 nm). This finding possibly indicates that surface diffusion processes could be important. In order to determine possible local compositional changes in these nanostructures induced by ion impact, selected samples were prepared for atom probe tomography (APT). The results indicate that APT can provide analytical information on the composition of individual InP nanodots. By means of 3D APT data, the surface region of such nanodots evolving under ion bombardment could be examined with atomic spatial resolution. At the InP surface, the values of the In/P concentration ratio are distinctly higher over a distance of approximately 1 nm and amount to 1.3 to 1.7

Determinanten und Einkommenseffekte beruflicher Weiterbildung - Eine Analyse mit Daten des Mikrozensus 1993, 1998 und 2003

Berufliche Fort- und Weiterbildung hat in den letzten Jahren erheblich an Bedeutung gewonnen. Die Gründe hierfür liegen im ständigen, immer schnelleren, technischen und organisatorischen Wandel der Arbeitswelt und in der zunehmenden Alterung der Bevölkerung. In diesem Aufsatz werden anhand von Daten der Mikrozensen 1993, 1998 und 2003 verschiedene Faktoren untersucht, die einen Einfluss darauf haben, welche Personen sich besonders an beruflicher Weiterbildung beteiligen. Ein Ziel ist es dabei, ein möglichst breites Spektrum an möglichen Einflussgrößen zu berücksichtigen. So werden individuelle, sozio-ökonomische Faktoren einerseits und strukturelle, berufsbezogene Faktoren andererseits miteinbezogen. Neben den Determinanten wird auch untersucht, ob berufliche Weiterbildung sich tatsächlich positiv im Einkommen niederschlägt. Bei der Bearbeitung dieser Fragen werden außerdem einige Spezifika des Mikrozensus als Datensatz für Weiterbildungsanalysen dargestellt. Den theoretischen Rahmen für die Analysen bildet dabei die Humankapitaltheorie. Die aus ihr abgeleiteten Hypothesen finden sich größtenteils auch in den empirischen Ergebnissen bestätigt. So verfügen Teilnehmer an beruflicher Weiterbildung über ein höheres Einkommen als Nichtteilnehmer. Insbesondere Bildung und das berufliche Umfeld haben einen starken Einfluss auf die Beteiligung an beruflicher Weiterbildung. Sozial benachteiligte Gruppen wie Geringqualifizierte oder Ausländer sind in Weiterbildungsmaßnahmen weniger stark vertreten als Hochqualifizierte oder Deutsche. Diese Ergebnisse finden sich zu allen drei Zeitpunkten bestätigt. Veränderungen im Zeitverlauf fallen zumeist eher gering aus. Ein wichtiges Ergebnis ist also, dass berufliche Weiterbildung zwar positiv mit dem Einkommen korreliert, aber andererseits soziale Ungleichheit noch verstärkt anstatt dieser entgegenzuwirken.Weiterbildung; Mikrozensus; Einkommenseffekte

Neural Simulations on Multi-Core Architectures

Neuroscience is witnessing increasing knowledge about the anatomy and electrophysiological properties of neurons and their connectivity, leading to an ever increasing computational complexity of neural simulations. At the same time, a rather radical change in personal computer technology emerges with the establishment of multi-cores: high-density, explicitly parallel processor architectures for both high performance as well as standard desktop computers. This work introduces strategies for the parallelization of biophysically realistic neural simulations based on the compartmental modeling technique and results of such an implementation, with a strong focus on multi-core architectures and automation, i.e. user-transparent load balancing

Differential effects of synchronous and asynchronous multifinger coactivation on human tactile performance

<p>Abstract</p> <p>Background</p> <p>Repeated execution of a tactile task enhances task performance. In the present study we sought to improve tactile performance with unattended activation-based learning processes (i.e., focused stimulation of dermal receptors evoking neural coactivation (CA)). Previous studies show that the application of CA to a single finger reduced the stationary two-point discrimination threshold and significantly increased tactile acuity. These changes were accompanied by an expansion of the cortical finger representation in primary somatosensory cortex (SI). Here we investigated the effect of different types of multifinger CA on the tactile performance of each finger of the right hand.</p> <p>Results</p> <p>Synchronous and asynchronous CA was applied to all fingers of a subject's dominant hand. We evaluated changes in absolute touch thresholds, static two-point discrimination thresholds, and mislocalization of tactile stimuli to the fingertips. After synchronous CA, tactile acuity improved (i.e., discrimination thresholds decreased) and the frequency of mislocalization of tactile stimuli changed from directly neighboring fingers to more distant fingers. On the other hand, asynchronous CA did not significant improve tactile acuity. In fact, there was evidence of impaired tactile acuity. Multifinger CA with synchronous or asynchronous stimulation did not significantly alter absolute touch thresholds.</p> <p>Conclusion</p> <p>Our results demonstrate that it is possible to extend tactile CA to all fingers of a hand. The observed changes in mislocalization of tactile stimuli after synchronous CA indicate changes in the topography of the cortical hand representation. Although single-finger CA has been shown to improve tactile acuity, asynchronous CA of all fingers of the hand had the opposite effect, suggesting the need for synchrony in multifinger CA for improving tactile acuity.</p

Repetitive Electric Stimulation Elicits Enduring Improvement of Sensorimotor Performance in Seniors

Age-related changes occur on all stages of the human somatosensory pathway, thereby deteriorating tactile, haptic, and sensorimotor performance. However, recent studies show that age-related changes are not irreversible but treatable through peripheral stimulation paradigms based on neuroplasticity mechanisms. We here applied repetitive electric stimulation (rES) to the fingers on a bi-weekly basis for 4 weeks to induce enduring amelioration of age-related changes in healthy individuals aged 60–85 years. Tactile, haptic, and motor performance gradually improved over time of intervention. After termination of rES, tactile acuity recovered to baseline within 2 weeks, while the gains in haptic and motor performance were preserved for 2 weeks. Sham stimulation showed no comparable changes. Our data indicate that age-related decline of sensorimotor performance can be ameliorated by rES and can be stabilized by the repeated application. Thus, long-term application of rES appears as a prime candidate for maintaining sensorimotor functions in elderly individuals

Improvement of sensorimotor functions in old age by passive sensory stimulation

Sensorimotor functions decrease in old age. The well-documented loss of tactile acuity in elderly is accompanied by deterioration of haptic performance and fine manipulative movements. Physical training and exercise can maintain sensorimotor fitness into high age. However, regular schedules of training require discipline and physical fitness. We here present an alternative interventional paradigm to enhance tactile, haptic, and fine motor performance based on passive, sensory stimulation by means of tactile coactivation. This approach is based on patterned, synchronous tactile stimulation applied to the fingertips for 3 hours. The stimulation drives plastic reorganizational changes in somatosensory cortex that affect perception and behavior: We demonstrate that following 3 hours of coactivation tactile acuity as well as haptic object exploration and fine motor performance are improved for at least 96 hours. Because this kind of intervention does not require active participation or attention of the subjects, we anticipate that coactivation is a prime candidate for future therapeutic interventions in patients with impaired sensorimotor abilities. It can be assumed that the maintenance and restoration of sensorimotor functions can ensure and preserve independence of daily living. Further optimizing of the stimulation protocol can be assumed to strengthen both the range and durability of its efficacy