The Range of Validity for the Kelvin Force

In a recent Letter, Luo, Du and Huang reported a novel convective instability driven by a force rarely studied before -- that exerted by an external magnetic field on a strongly magnetizable liquid. The associated physics is surprisingly rich and promises many more interesting results for the future. Unfortunately, the analysis starts from a misconception and employs the Kelvin force outside its range of validity. Since few would recognize this as a mistake, and since its consequence in the given experiment is particularly direct and critical, this is a point well worth being clarified, and clearly understood.Comment: 1 pag

Scenarios for Gluino Coannihilation

We study supersymmetric scenarios in which the gluino is the next-to-lightest supersymmetric particle (NLSP), with a mass sufficiently close to that of the lightest supersymmetric particle (LSP) that gluino coannihilation becomes important. One of these scenarios is the MSSM with soft supersymmetry-breaking squark and slepton masses that are universal at an input GUT renormalization scale, but with non-universal gaugino masses. The other scenario is an extension of the MSSM to include vector-like supermultiplets. In both scenarios, we identify the regions of parameter space where gluino coannihilation is important, and discuss their relations to other regions of parameter space where other mechanisms bring the dark matter density into the range allowed by cosmology. In the case of the non-universal MSSM scenario, we find that the allowed range of parameter space is constrained by the requirement of electroweak symmetry breaking, the avoidance of a charged LSP and the measured mass of the Higgs boson, in particular, as well as the appearance of other dark matter (co)annihilation processes. Nevertheless, LSP masses $m_\chi \lesssim 8$~TeV with the correct dark matter density are quite possible. In the case of pure gravity mediation with additional vector-like supermultiplets, changes to the anomaly-mediated gluino mass and the threshold effects associated with these states can make the gluino almost degenerate with the LSP, and we find a similar upper bound.Comment: 25 pages, 22 figure

Superconductivity in sputtered CuMO6S8

Samples were prepared by melting the metals, followed by annealing to various temperatures. The result was a structurally weak material. Sputtered films on sapphire substrates were prepared and studied. The substrates give the films mechanical strength and permit easy attachment of electrical leads. Materials were characterized by X-ray diffraction, electron microscopy, electrical resistance vs. temperature, and critical current measurements. Some of the results on CuMo6S8 are presented

Engineering the Kondo and Fano effects in double quantum dots

We demonstrate delicate control over the Kondo effect and its interplay with quantum interference in an Aharonov-Bohm interferometer containing one Kondo dot and one noninteracting dot. It is shown that the Kondo resonance undergoes a dramatic evolution as the interdot tunnel coupling progressively increases. A novel triple Kondo splitting occurs from the interference between constant and Lorentzian conduction bands that cooperate in forming the Kondo singlet. The device also manifests a highly controllable Fano-Kondo effect in coherent electronic transport, and can be tuned to a regime where the coupled dots behave as decoupled dots.Comment: 5 pages, 4 figure

Tracers of chromospheric structure. I. CaII H&\&K emission distribution of 13000 F, G and K stars in SDSS DR7 spectroscopic sample

We present chromospheric activity index $S\rm_{HK}$ measurements for over 13,000 F, G and K disk stars with high signal-to-noise ratio ($>$ 60) spectra in the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) spectroscopic sample. A parameter $\delta$S is defined as the difference between $S\rm_{HK}$ and a `zero' emission line fitted by several of the most inactive stars. The $S\rm_{HK}$ indices of subgiant stars tend to be much lower than dwarfs, which provide a way to distinguish dwarfs and giants with relatively low resolution spectra. Cooler stars are generally more active and display a larger scatter than hotter stars. Stars associated with the thick disk are in general less active than those of the thin disk. The fraction of K dwarfs that are active drops with vertical distance from the Galactic plane. Metallicity affects $S\rm_{HK}$ measurements differently among F, G and K dwarfs in this sample. Using the open clusters NGC 2420, M67 and NGC6791 as calibrations, ages of most field stars in this SDSS sample range from 3-8 Gyr.Comment: 9 pages, 11 figures, AJ, 2013, 145, 14

Beyond the CMSSM without an Accelerator: Proton Decay and Direct Dark Matter Detection

We consider two potential non-accelerator signatures of generalizations of the well-studied constrained minimal supersymmetric standard model (CMSSM). In one generalization, the universality constraints on soft supersymmetry-breaking parameters are applied at some input scale $M_{in}$ below the grand unification (GUT) scale $M_{GUT}$, a scenario referred to as `sub-GUT'. The other generalization we consider is to retain GUT-scale universality for the squark and slepton masses, but to relax universality for the soft supersymmetry-breaking contributions to the masses of the Higgs doublets. As with other CMSSM-like models, the measured Higgs mass requires supersymmetric particle masses near or beyond the TeV scale. Because of these rather heavy sparticle masses, the embedding of these CMSSM-like models in a minimal SU(5) model of grand unification can yield a proton lifetime consistent with current experimental limits, and may be accessible in existing and future proton decay experiments. Another possible signature of these CMSSM-like models is direct detection of supersymmetric dark matter. The direct dark matter scattering rate is typically below the reach of the LUX-ZEPLIN (LZ) experiment if $M_{in}$ is close to $M_{GUT}$, but may lie within its reach if $M_{in} \lesssim 10^{11}$ GeV. Likewise, generalizing the CMSSM to allow non-universal supersymmetry-breaking contributions to the Higgs offers extensive possibilities for models within reach of the LZ experiment that have long proton lifetimes.Comment: 42 pages, 15 figure

Microscopy of glazed layers formed during high temperature sliding wear at 750C

The evolution of microstructures in the glazed layer formed during high temperature sliding wear of Nimonic 80A against Stellite 6 at 750 ◦C using a speed of 0.314ms−1 under a load of 7N has been investigated using scanning electron microscopy (SEM), energy dispersive analysis by X-ray (EDX), X-ray diffraction (XRD) analysis, scanning tunnelling microscopy (STM) and transmission electron microscopy (TEM). The results indicate the formation of a wear resistant nano-structured glazed layer. The mechanisms responsible for the formation of the nano-polycrystalline glazed layer are discussed

Efficient photosynthesis of carbon monoxide from CO2 using perovskite photovoltaics

Artificial photosynthesis, mimicking nature in its efforts to store solar energy, has received considerable attention from the research community. Most of these attempts target the production of H2 as a fuel and our group recently demonstrated solar-to-hydrogen conversion at 12.3% efficiency. Here, in an effort to take this approach closer to real photosynthesis, which is based on the conversion of CO2, we demonstrate the efficient reduction of CO2 to carbon monoxide driven solely by simulated sunlight using water as the electron source. Employing series-connected perovskite photovoltaics and high-performance catalyst electrodes, we reach a solar-to-CO efficiency exceeding 6.5%, which represents a new benchmark in sunlight-driven CO2 conversion. Considering hydrogen as a secondary product, an efficiency exceeding 7% is observed. Furthermore, this study represents one of the first demonstrations of extended, stable operation of perovskite photovoltaics, whose large open-circuit voltage is shown to be particularly suited for this process