Persistent currents in n-fold twisted Moebius strips

We investigate the influence of the topology on generic features of the persistent current in n-fold twisted Moebius strips formed of quasi one--dimensional mesoscopic rings, both for free electrons and in the weakly disordered regime. We find that there is no generic difference between the persistent current for untwisted rings and for Moebius strips with an arbitrary number of twists.Comment: 7 pages, 2 figure

Dynamic transitions between metastable states in a superconducting ring

Applying the time-dependent Ginzburg-Landau equations, transitions between metastable states of a superconducting ring are investigated in the presence of an external magnetic field. It is shown that if the ring exhibits several metastable states at a particular magnetic field, the transition from one metastable state to another one is governed by both the relaxation time of the absolute value of the order parameter tau_{|psi|} and the relaxation time of the phase of the order parameter tau_{phi}. We found that the larger the ratio tau_{|psi|}tau_{phi} the closer the final state will be to the absolute minimum of the free energy, i.e. the thermodynamic equilibrium. The transition to the final state occurs through a subsequent set of single phase slips at a particular point along the ring.Comment: 7 pages, 6 figures, Revtex 4.0 styl

Transverse depinning in strongly driven vortex lattices with disorder

Using numerical simulations we investigate the transverse depinning of moving vortex lattices interacting with random disorder. We observe a finite transverse depinning barrier for vortex lattices that are driven with high longitudinal drives, when the vortex lattice is defect free and moving in correlated 1D channels. The transverse barrier is reduced as the longitudinal drive is decreased and defects appear in the vortex lattice, and the barrier disappears in the plastic flow regime. At the transverse depinning transition, the vortex lattice moves in a staircase pattern with a clear transverse narrow-band voltage noise signature.Comment: 4 pages, 4 figure

Local growth of CuInSe2 micro solar cells for concentrator application

A procedure to fabricate CuInSe2 CISe micro absorbers and solar cells for concentrator applications is presented. The micro absorbers are developed from indium precursor islands, which are deposited on a molybdenum coated glass substrate back contact , followed by deposition of copper on top and subsequent selenization as well as selective etching of copper selenides. In order to compare the properties of the locally grown absorbers to those of conventional large area CISe films, we systematically examine the compositional and morphological homogeneity of the micro absorbers and carry out photoluminescence measurements. Preliminary devices for micro concentrator solar cell applications are fabricated by optimizing the copper to indium ratio and the size of the indium precursor islands. The resulting micro solar cells provide a characteristic I V curve under standard illumination conditions 1 su

Dynamic ordering and frustration of confined vortex rows studied by mode-locking experiments

The flow properties of confined vortex matter driven through disordered mesoscopic channels are investigated by mode locking (ML) experiments. The observed ML effects allow to trace the evolution of both the structure and the number of confined rows and their match to the channel width as function of magnetic field. From a detailed analysis of the ML behavior for the case of 3-rows we obtain ({\it i}) the pinning frequency $f_p$, ({\it ii}) the onset frequency $f_c$ for ML ($\propto$ ordering velocity) and ({\it iii}) the fraction $L_{ML}/L$ of coherently moving 3-row regions in the channel. The field dependence of these quantities shows that, at matching, where $L_{ML}$ is maximum, the pinning strength is small and the ordering velocity is low, while at mismatch, where $L_{ML}$ is small, both the pinning force and the ordering velocity are enhanced. Further, we find that $f_c \propto f_p^2$, consistent with the dynamic ordering theory of Koshelev and Vinokur. The microscopic nature of the flow and the ordering phenomena will also be discussed.Comment: 10 pages, 7 figure, submitted to PRB. Discussion has been improved and a figure has been adde

Nature of the quantum phase transitions in the two-dimensional hardcore boson model

We use two Quantum Monte Carlo algorithms to map out the phase diagram of the two-dimensional hardcore boson Hubbard model with near ($V_1$) and next near ($V_2$) neighbor repulsion. At half filling we find three phases: Superfluid (SF), checkerboard solid and striped solid depending on the relative values of $V_1$, $V_2$ and the kinetic energy. Doping away from half filling, the checkerboard solid undergoes phase separation: The superfluid and solid phases co-exist but not as a single thermodynamic phase. As a function of doping, the transition from the checkerboard solid is therefore first order. In contrast, doping the striped solid away from half filling instead produces a striped supersolid phase: Co-existence of density order with superfluidity as a single phase. One surprising result is that the entire line of transitions between the SF and checkerboard solid phases at half filling appears to exhibit dynamical O(3) symmetry restoration. The transitions appear to be in the same universality class as the special Heisenberg point even though this symmetry is explicitly broken by the $V_2$ interaction.Comment: 10 pages, 14 eps figures, include

Phase I, open-label study of pasireotide in patients with <i>BRAF-</i>wild type and <i>NRAS</i>-wild type, unresectable and/or metastatic melanoma.

Somatostatin analogues exert antitumour activity via direct and indirect mechanisms. The present study was designed to assess the safety and efficacy of pasireotide in patients with &lt;i&gt;BRAF&lt;/i&gt; -wild type (WT) and &lt;i&gt;NRAS&lt;/i&gt; -WT metastatic melanoma. Patients with unresectable and/or metastatic melanoma or Merkel cell carcinoma were eligible. Pasireotide was administered at different doses for ≤8 weeks in dose-escalation phase, followed by long-acting pasireotide 80 mg or lower dose in case of toxicity in follow-up phase up to six additional months. Primary endpoint was safety in the first 8 weeks of dose-escalation phase. The study was terminated early due to slow recruitment. Of the 10 patients with metastatic melanoma enrolled, only four reached the high dose level: two patients reached 3600 µg in dose-escalation and follow-up phases and two patients reached 3600 µg in dose-escalation and long-acting pasireotide 80 mg in follow-up phases and were stable for &gt;5 months. Most common adverse events (AEs) during dose-escalation phase in ≥2 patients (20%) were: diarrhoea (50%), nausea (50%), fatigue (20%), hyperglycaemia (20%), hypophosphatemia (20%), chills (20%) and tumour pain (20%). Grade 3 or 4 study drug-related AEs were diarrhoea and nausea, reported in one patient. Partial response was documented in one patient and stable disease in another. Pasireotide was well tolerated, and safety results were similar to those previously reported in other indications. Further studies are needed to evaluate its antitumour activity alone and in combination with other drugs in melanoma

Velocity-force characteristics of an interface driven through a periodic potential

We study the creep dynamics of a two-dimensional interface driven through a periodic potential using dynamical renormalization group methods. We find that the nature of weak-drive transport depends qualitatively on whether the temperature $T$ is above or below the equilibrium roughening transition temperature $T_c$. Above $T_c$, the velocity-force characteristics is Ohmic, with linear mobility exhibiting a jump discontinuity across the transition. For $T \le T_c$, the transport is highly nonlinear, exhibiting an interesting crossover in temperature and weak external force $F$. For intermediate drive, $F>F_*$, we find near $T_c^{-}$ a power-law velocity-force characteristics $v(F)\sim F^\sigma$, with $\sigma-1\propto \tilde{t}$, and well-below $T_c$, $v(F)\sim e^{-(F_*/F)^{2\tilde{t}}}$, with $\tilde{t}=(1-T/T_c)$. In the limit of vanishing drive ($F\ll F_*$) the velocity-force characteristics crosses over to $v(F)\sim e^{-(F_0/F)}$, and is controlled by soliton nucleation.Comment: 18 pages, submitted to Phys. Rev.

A Quantitative and Dynamic Model of the Arabidopsis Flowering Time Gene Regulatory Network

Various environmental signals integrate into a network of floral regulatory genes leading to the final decision on when to flower. Although a wealth of qualitative knowledge is available on how flowering time genes regulate each other, only a few studies incorporated this knowledge into predictive models. Such models are invaluable as they enable to investigate how various types of inputs are combined to give a quantitative readout. To investigate the effect of gene expression disturbances on flowering time, we developed a dynamic model for the regulation of flowering time in Arabidopsis thaliana. Model parameters were estimated based on expression time-courses for relevant genes, and a consistent set of flowering times for plants of various genetic backgrounds. Validation was performed by predicting changes in expression level in mutant backgrounds and comparing these predictions with independent expression data, and by comparison of predicted and experimental flowering times for several double mutants. Remarkably, the model predicts that a disturbance in a particular gene has not necessarily the largest impact on directly connected genes. For example, the model predicts that SUPPRESSOR OF OVEREXPRESSION OF CONSTANS (SOC1) mutation has a larger impact on APETALA1 (AP1), which is not directly regulated by SOC1, compared to its effect on LEAFY (LFY) which is under direct control of SOC1. This was confirmed by expression data. Another model prediction involves the importance of cooperativity in the regulation of APETALA1 (AP1) by LFY, a prediction supported by experimental evidence. Concluding, our model for flowering time gene regulation enables to address how different quantitative inputs are combined into one quantitative output, flowering time