Magnetoresistance oscillations in GaAs/AlGaAs superlattices subject to in-plane magnetic fields

The MBE-grown GaAs/AlGaAs superlattice with Si-doped barriers has been used to study a 3D-2D transition under the influence of the in-plane component of applied magnetic field. The longitudinal magnetoresistance data measured in tilted magnetic fields have been interpreted in terms of a simple tight-binding model. The data provide values of basic parameters of the model and make it possible to reconstruct the superlattice Fermi surface and to calculate the density of states for the lowest Landau subbands. Positions of van Hove singularities in the DOS agree excellently with magnetoresistance oscillations, confirming that the model describes adequately the magnetoresistance of strongly coupled semiconductor superlattices.Comment: 4 pages, 3 figures, elsart/PHYEAUTH macros; presented on the EP2DS-16 Conference in Albuquerque, New Mexico USA. To be published in Physica

Best scale for detecting the effects of stratospheric sulphate aerosol geoengineering on surface temperature

Stratospheric sulfate aerosol injection (SAI) has been proposed as a way to geo-engineer climate. Whilst swift global-mean surface cooling is generally expected from tropical SAI, the regional impacts of such perturbation on near-surface air temperature (SAT) are projected to be spatially inhomogeneous. By using existing simulations from the Geoengineering Model Intercomparison Project (GeoMIP) G4 scenario, where 5 Tg yr-1 of sulfur dioxide (SO2) is injected into the tropical stratosphere to offset some of the warming in a mid-range representative greenhouse gas concentration pathway (RCP4.5) between 2020 and 2070, we examine the regional detectability of the SAI surface cooling effect, and attempt to find the best spatial scale for potential SAI monitoring. We use optimal fingerprint detection and attribution techniques to estimate the time horizon over which the SAI surface cooling effect would be detected after implementation in 2020 on sub-global scales, ranging from the near-global in situ observational coverage down to sub-continental regions. We show that using the spatio-temporal SAT pattern across the Northern and Southern extra-tropics and the Tropics, and across the Northern and Southern Hemispheres, as well as averaging SATs over the whole globe robustly result in successful SAI detection within 10 years of geoengineering implementation in a majority of the included plausible geoengineering realizations. However, detecting the SAI effect on SAT within the first decade of implementation would be more challenging on sub-continental scales

Das BonaRes Datenzentrum: Unterstützung für Wissenschaftler bei der Bereitstellung ihrer Forschungsdaten

In Deutschland wurden und werden viele hervorragende Forschungsdaten erhoben. Leider kommt es allzu oft vor, dass diese Daten nicht von weiteren Wissenschaftlern nachgenutzt werden können. Im besten Fall wird damit der Mehrwert, der mit erheblichem Aufwand erhobenen, Forschungsdaten nicht ausgenutzt. Im schlimmsten Fall kommt es zu doppelten Beprobungen des gleichen Gebietes oder sogar zum Verlust von Daten. Auch leidet die Überprüfbarkeit und Transparenz der Forschung. Die Gründe hierfür sind vielfältig und reichen von persönlichen Vorbehalten gegenüber der Nachnutzung über ungeklärte Rechte bis hin zu mangelnden technischen Möglichkeiten der Wissenschaftler und Institutionen. Große, auch internationale, Institutionen haben die freie Nachnutzung von Forschungsdaten auf ihre Agenda geschrieben: Berliner Erklärung (2003), OECD (2007), Deutsche Forschungsallianz (2010). Bei den Förderinstitutionen (z.B. DFG, BMBF und EU) hat ebenfalls ein Umdenken eingesetzt. Oft wird schon bei der Antragstellung ein Konzept gefordert, Daten, die mit öffentlichen Mitteln gefördert werden, zeitnah zur freien Nachnutzung bereitzustellen und langfristig sicher zu speichern. Im BonaRes Datenzentrum werden Forschungsdaten, insbesondere aus den BonaRes Verbundprojekten, zusammengeführt und in standardisierter Form zur freien Nachnutzung als Teil einer vernetzten Dateninfrastruktur bereitgestellt. Besonderes Interesse gilt den Dauerfeldversuchen, die für die Untersuchung langfristiger Bodenveränderungen einen unverzichtbaren Beitrag leisten. Das Erstverwertungsrecht wird durch die Vergabe von angemessenen Embargozeiten gewährleistet. Der rechtliche Rahmen wird vor der Veröffentlichung der Daten durch die Vergabe einer international anerkannten Lizenz (Creative Commons) und einen Haftungsausschluss geregelt. Das BonaRes Metadatenschema vereint international anerkannte Standards für Geodaten (INSPIRE) und Forschungsdaten (DataCite) und ergänzt diese um Informationen, die die Möglichkeiten der wissenschaftlichen Nachnutzung weiter erhöhen. Daten, die im Datenzentrum gespeichert sind, können durch die Vergabe eines DOI registriert und damit zitierfähig gemacht werden. Diskutiert werden die Vor- und Nachteile einer zeitnahen freien Nachnutzung von Forschungsdaten

Structural plasticity underlies experience-dependent functional plasticity of cortical circuits

The stabilization of new spines in the barrel cortex is enhanced after whisker trimming, but its relationship to experience-dependent plasticity is unclear. Here we show that in wild-type mice, whisker potentiation and spine stabilization are most pronounced for layer 5 neurons at the border between spared and deprived barrel columns. In homozygote alphaCaMKII-T286A mice, which lack experience-dependent potentiation of responses to spared whiskers, there is no increase in new spine stabilization at the border between barrel columns after whisker trimming. Our data provide a causal link between new spine synapses and plasticity of adult cortical circuits and suggest that alphaCaMKII autophosphorylation plays a role in the stabilization but not formation of new spines

Motoneuron axon pathfinding errors in zebrafish: Differential effects related to concentration and timing of nicotine exposure

© 2015 Elsevier Inc. Nicotine exposure during embryonic stages of development can affect many neurodevelopmental processes. In the developing zebrafish, exposure to nicotine was reported to cause axonal pathfinding errors in the later born secondary motoneurons (SMNs). These alterations in SMN axon morphology coincided with muscle degeneration at high nicotine concentrations (15-30. μM). Previous work showed that the paralytic mutant zebrafish known as sofa potato exhibited nicotine-induced effects onto SMN axons at these high concentrations but in the absence of any muscle deficits, indicating that pathfinding errors could occur independent of muscle effects.In this study, we used varying concentrations of nicotine at different developmental windows of exposure to specifically isolate its effects onto subpopulations of motoneuron axons. We found that nicotine exposure can affect SMN axon morphology in a dose-dependent manner. At low concentrations of nicotine, SMN axons exhibited pathfinding errors, in the absence of any nicotine-induced muscle abnormalities. Moreover, the nicotine exposure paradigms used affected the 3 subpopulations of SMN axons differently, but the dorsal projecting SMN axons were primarily affected. We then identified morphologically distinct pathfinding errors that best described the nicotine-induced effects on dorsal projecting SMN axons. To test whether SMN pathfinding was potentially influenced by alterations in the early born primary motoneuron (PMN), we performed dual labeling studies, where both PMN and SMN axons were simultaneously labeled with antibodies. We show that only a subset of the SMN axon pathfinding errors coincided with abnormal PMN axonal targeting in nicotine-exposed zebrafish. We conclude that nicotine exposure can exert differential effects depending on the levels of nicotine and developmental exposure window

Statistical Theory of Force Induced Unzipping of DNA

The unzipping transition under the influence of external force of a dsDNA molecule has been studied using the Peyrard-Bishop Hamiltonian. The critical force $F_c(T)$ is found to depend on the potential parameters $k$, represents the stiffness of single strand of DNA and the potential depth $D$. We used constant extension ensemble to calculate the average force needed to stretch a base pair $y$ distance apart. A very large peak around $y = 1 {\rm \AA}$ is found. The value of $F(y)$ needed to stretch a base pair located far away from the ends of a dsDNA molecule is found twice the value of the force needed to stretch a base pair located at one of the ends to the same distance. The effect of mismatching in the base pairs on the peak height and position is investigated. The formation and behaviour of a loop of Y shape when one of the ends base pair is stretched and a bubble of ssDNA with the shape of "an eye" when a base pair far from ends is stretched are investigated.Comment: Minor changes in figures, published versio