Uniformity of the pseudomagnetic field in strained graphene

We present a study on the uniformity of the pseudomagnetic field in graphene as a function of the relative orientation between the graphene lattice and straining directions. For this, we strained a regular micron-sized graphene hexagon by deforming it symmetrically by displacing three of its edges. By simulations, we found that the pseudomagnetic field is strongest if the strain is applied perpendicular to the armchair direction of graphene. For a hexagon with a side length of 1 ${\rm \mu}$m, the pseudomagnetic field has a maximum of 1.2 T for an applied strain of 3.5% and it is uniform (variance $< 1$%) within a circle with a diameter of $\sim 520$ nm. This diameter is on the order of the typical diameter of the laser spot in a state-of-the-art confocal Raman spectroscopy setup, which suggests that observing the pseudomagnetic field in measurements of shifted magneto-phonon resonance is feasible.Comment: 7 pages, 5 figure

InP homojunction solar cell performance on the LIPS 3 flight experiment

Performance data for the NASA Lewis Research Center indium phosphide n+p homojunction solar cell module on the LIPS 3 Flight Experiment is presented. The objective of the experiment is to measure the performance of InP cells in the natural radiation environment of the 1100 km altitude, 60+ deg inclination orbit. Analysis of flight data indicates that the performance of the four cells throughout the first year is near expected values. No degradation in short-circuit current was seen, as was expected from radiation tolerance studies of similar cells. Details of the cell structure and flight module design are discussed. The results of the temperature dependency and radiation tolerance studies necessary for normalization and analysis of the data are included

Viscous coalescence of droplets: a Lattice Boltzmann study

The coalescence of two resting liquid droplets in a saturated vapor phase is investigated by Lattice Boltzmann simulations in two and three dimensions. We find that, in the viscous regime, the bridge radius obeys a t^{1/2}-scaling law in time with the characteristic time scale given by the viscous time. Our results differ significantly from the predictions of existing analytical theories of viscous coalescence as well as from experimental observations. While the underlying reason for these deviations is presently unknown, a simple scaling argument is given that describes our results well.Comment: 12 pages, 10 figures; as published in Phys. Fluid

Combined proteomic and gene expression analysis to investigate reduced performance in rainbow trout (Oncorhynchus mykiss) caused by environmentally relevant microplastic exposure

The pollution of the environment with microplastics (MPs) is affecting aquatic organisms worldwide, and yet intensive research, has thus far failed to deliver an adequate understanding of the detrimental effects of MP ingestion by fish. Investigations using established health and performance parameters are often insufficient to determine MP toxicity, especially when considering MPs in environmentally relevant concentrations. In the present study, label-free quantitative (LFQ) proteomics of liver tissue was combined with gene expression analysis in order to investigate the long-term effects of MP exposure on rainbow trout (Oncorhynchus mykiss). With the help of a specially designed diet, two groups of fish were exposed for 120 days to environmentally relevant concentrations of MPs (on average 13 particles per fish, every 2 days) and to slightly increased levels representing those expected in the near future (on average 73 MP particles per fish, every 2 days). Both groups were compared to a control. The results provide evidence that long-term exposure to MPs has a dose-dependent negative effect on the performance of rainbow trout. No differences in blood glucose level, hematocrit level or lipid peroxidation were observed between treatments. The proteomic analysis revealed 6071 unique proteins, but no significant change in hepatic protein concentrations compared to their matching controls, although certain proteins appear to have been up- or down-regulated multifold and should be considered in continuing experiments. When comparing highly regulated proteins with the levels of their respective mRNA transcripts, a good correlation was observed just for “differentially regulated trout protein 1”, encoded by drtp1. This may therefore be a suitable biomarker for future studies with trout. Several hypotheses were put forward to explain the observed differences in growth: nutrient dilution, caused by increased amounts of non-digestible material in the diet, and growth effects due to differences in diet quality could be excluded. Physical interference of MPs with the gastrointestinal tract are also unlikely, as fish are regularly exposed to particulate matter in natural environments and previous studies did not find evidence of such interferences. Instead, indirect detrimental effects of MPs, either due to their hydrophobic surface properties or the presence of certain additives, could cause allergic reactions, microbiota dysbiosis or general stress responses. Although no clear cause for the reduced growth was identified, the current study demonstrates the potential utility of omics approaches when dealing with such a complex question. Future studies should extend analyses to the gastrointestinal tract and associated tissues. It should be ensured that the MP exposure is realistic and that the duration of the experiments covers several months. Direct evidence of a significant negative influence of long-term exposure to realistic and near-future MP concentrations on fish highlight the importance of measures to prevent a further increase of MPs in the environment

A Hamiltonian approach for explosive percolation

We introduce a cluster growth process that provides a clear connection between equilibrium statistical mechanics and an explosive percolation model similar to the one recently proposed by Achlioptas et al. [Science 323, 1453 (2009)]. We show that the following two ingredients are essential for obtaining an abrupt (first-order) transition in the fraction of the system occupied by the largest cluster: (i) the size of all growing clusters should be kept approximately the same, and (ii) the inclusion of merging bonds (i.e., bonds connecting vertices in different clusters) should dominate with respect to the redundant bonds (i.e., bonds connecting vertices in the same cluster). Moreover, in the extreme limit where only merging bonds are present, a complete enumeration scheme based on tree-like graphs can be used to obtain an exact solution of our model that displays a first-order transition. Finally, the proposed mechanism can be viewed as a generalization of standard percolation that discloses an entirely new family of models with potential application in growth and fragmentation processes of real network systems.Comment: 4 pages, 4 figure

Peeled film GaAs solar cells for space power

Gallium arsenide (GaAs) peeled film solar cells were fabricated, by Organo-Metallic Vapor Phase Epitaxy (OMVPE), incorporating an aluminum arsenide (AlAs) parting layer between the device structure and the GaAs substrate. This layer was selectively removed by etching in dilute hydrofloric (HF) acid to release the epitaxial film. Test devices exhibit high series resistance due to insufficient back contact area. A new design is presented which uses a coverglass superstrate for structural support and incorporates a coplanar back contact design. Devices based on this design should have a specific power approaching 700 W/Kg

Correlating Josephson supercurrents and Shiba states in quantum spins unconventionally coupled to superconductors

Local spins coupled to superconductors give rise to several emerging phenomena directly linked to the competition between Cooper pair formation and magnetic exchange. These effects are generally scrutinized using a spectroscopic approach which relies on detecting the in-gap bound modes arising from Cooper pair breaking, the so-called Yu-Shiba-Rusinov (YSR) states. However, the impact of local magnetic impurities on the superconducting order parameter remains largely unexplored. Here, we use scanning Josephson spectroscopy to directly visualize the effect of magnetic perturbations on Cooper pair tunneling between superconducting electrodes at the atomic scale. By increasing the magnetic impurity orbital occupation by adding one electron at a time, we reveal the existence of a direct correlation between Josephson supercurrent suppression and YSR states. Moreover, in the metallic regime, we detect zero bias anomalies which break the existing framework based on competing Kondo and Cooper pair singlet formation mechanisms. Based on first-principle calculations, these results are rationalized in terms of unconventional spin-excitations induced by the finite magnetic anisotropy energy. Our findings have far reaching implications for phenomena that rely on the interplay between quantum spins and superconductivity. The impact of local magnetic impurities on superconducting order parameter remains largely unexplored. Here, the authors visualize the effect of different magnetic perturbations on a superconductor, unveiling a rich correlation of the interplay between quantum spins and superconductivity in different spectroscopic regimes

Shrinkage and microstructural development during drying of organically modified silica xerogels

We have studied the different driving forces behind syneresis in MTES/TEOS gels by aging them in different H{sub 2}O/EtOH pore fluids. We show using shrinkage, density, contact angle, and N{sub 2} sorption measurements, the influence of gel/solvent interactions on the microstructural evolution during drying. Competing effects of syneresis (that occurs during aging) and drying shrinkage resulted in the overall linear shrinkage of the organically modified gels to be constant at {approximately}50%. Increasing the hydrophobicity of the gels caused the driving force for syneresis to change from primarily condensation reactions to a combination of condensation and solid/liquid interfacial energy. In addition the condensation driven shrinkage was observed to be irreversible, whereas the interfacial free energy driven shrinkage was observed to be partially reversible. Nitrogen sorption experiments show that xerogels with the same overall extent of shrinkage can have vastly different microstructures due to the effects of microphase separation

Comparison Of Quasi-Phase-Matching Geometries For Second-Harmonic Generation In Poled Polymer Channel Waveguides At 1.5 Mu M

We have investigated three different quasi-phase-matching approaches to second-harmonic generation (SHG) in DANS (4-dimethylamino-4\u27-nitrostilbene) poled polymer channel waveguides at 1.5 mu m. Periodic photobleaching and periodically poled electrodes deposited directly on the film produced unacceptably high propagation losses. However, periodic electrodes on the substrate gave low losses and useful SHG