Ab-initio investigation of phonon dispersion and anomalies in palladium

In recent years, palladium has proven to be a crucial component for devices ranging from nanotube field effect transistors to advanced hydrogen storage devices. In this work, I examine the phonon dispersion of fcc Pd using first principle calculations based on density functional perturbation theory. While several groups in the past have studied the acoustic properties of palladium, this is the first study to reproduce the phonon dispersion and associated anomaly with high accuracy and no adjustable parameters. In particular, I focus on the Kohn anomaly in the [110] direction.Comment: 19 pages, preprint format, 7 figures, added new figures and discussio

Constraints on Galaxy Density Profiles from Strong Gravitational Lensing: The Case of B 1933+503

We consider a wide range of parametric mass models for B 1933+503, a ten-image radio lens, and identify shared properties of the models with the best fits. The approximate rotation curves varies by less than 8.5% from the average value between the innermost and the outermost image (1.5h^{-1} kpc to 4.1h^{-1} kpc) for models within 1 \sigma of the best fit, and the radial dependence of the shear strength and angle also have common behavior for the best models. The time delay between images 1 and 6, the longest delay between the radio cores, is \Delta t = (10.6^{+2.4}_{-1.1})h^{-1} days (\Omega_0=0.3, \lambda_0=0.7) including all the modeling uncertainties. Deeper infrared observations, to more precisely register the lens galaxy with the radio images and to measure the properties of the Einstein ring image of the radio source's host galaxy, would significantly improve the model constraints and further reduce the uncertainties in the mass distribution and time delay.Comment: 24 pages, 10 figures, final version to appear in ApJ. Some minor corrections (e.g. constraint on central unseen image was stronger than intended earlier, now agrees with text, conventions on angles fixed in text/plots). Resulting model fits have some change in chi squareds and best parameters (e.g. cores, flatness of rotation curve) have some changes. Properties of model families and trends for best fitting models very close to earlier results; general conclusions the sam

Investigation of scaling effect on power factor of permanent magnet Vernier machines for wind power application

This study investigates the scaling effect on power factor of surface mounted permanent magnet Vernier (SPM-V) machines with power ratings ranging from 3 kW, 500 kW, 3 MW to 10 MW. For each power rating, different slot/pole number combinations have been considered to study the influence of key parameters including inter-pole magnet leakage and stator slot leakage on power factor. A detailed analytical modelling, incorporating these key parameters, is presented and validated with two-dimensional finite-element analysis for different power ratings and slot/pole number combinations. The study has revealed that with scaling (increasing power level), significant increase in electrical loading combined with the increased leakage fluxes, i.e. (i) magnet leakage flux due to large coil pitch to rotor pole pitch ratio, (ii) magnet inter-pole leakage flux and (iii) stator slot leakage flux, reduces the ratio of armature flux linkage to permanent magnet flux linkage and thereby has a detrimental effect on the power factor. Therefore, unlike conventional SPM machines, the power factor of SPM-V machines is found to be significantly reduced at high power ratings

Limits on a Stochastic Background of Gravitational Waves from Gravitational Lensing

We compute the effects of a stochastic background of gravitational waves on multiply imaged systems or on weak lensing. There are two possible observable effects, a static relative deflection of images or shear, and an induced time dependent shift or proper motion. We evaluate the rms magnitude of these effects for a COBE normalized, scale-invariant spectrum, which is an upper limit on spectra produced by inflation. Previous work has shown that large-scale structure may cause a relative deflection large enough to affect observations, but we find that the corresponding effect of gravity waves is smaller by $\sim 10^4$ and so cannot be observed. This results from the oscillation in time as well as the redshifting of the amplitude of gravity waves. We estimate the magnitude of the proper motion induced by deflection of light due to large-scale structure, and find it to be $\sim 10^{-8}$ arcsec per year. This corresponds to $\sim 50$ km/s at cosmological distances, which is quite small compared to typical peculiar velocities. The COBE normalized gravity wave spectrum produces motions smaller still by $\sim 10^2$. We conclude that light deflection due to these cosmological perturbations cannot produce observable proper motions of lensed images. On the other hand, there are only a few known observational limits on a stochastic background of gravity waves at shorter, astrophysical wavelengths. We calculate the expected magnitudes of the effects of lensing by gravity waves of such wavelengths, and find that they are too small to yield interesting limits on the energy density of gravity waves.Comment: 14 pages, LaTex + 1 PS Figure, accepted version to be published in Phys. Rev. D15, Dec. 1996. An incorrect assumption was removed, also various other minor change

Determination of Inflationary Observables by Cosmic Microwave Background Anisotropy Experiments

Inflation produces nearly Harrison-Zel'dovich scalar and tensor perturbation spectra which lead to anisotropy in the cosmic microwave background (CMB). The amplitudes and shapes of these spectra can be parametrized by $Q_S^2$, $r\equiv Q_T^2/Q_S^2$, $n_S$ and $n_T$ where $Q_S^2$ and $Q_T^2$ are the scalar and tensor contributions to the square of the CMB quadrupole and $n_S$ and $n_T$ are the power-lawspectral indices. Even if we restrict ourselves to information from angles greater than one third of a degree, three of these observables can be measured with some precision. The combination $130^{1-n_S}Q_S^2$ can be known to better than $\pm 0.3\%$. The scalar index $n_S$ can be determined to better than $\pm 0.02$. The ratio $r$ can be known to about $\pm 0.1$ for $n_S \simeq 1$ and slightly better for smaller $n_S$. The precision with which $n_T$ can be measured depends weakly on $n_S$ and strongly on $r$. For $n_S \simeq 1$ $n_T$ can be determined with a precision of about $\pm 0.056(1.5+r)/r$. A full-sky experiment with a $20'$beam using technology available today, similar to those being planned by several groups, can achieve the above precision. Good angular resolution is more important than high signal-to-noise ratio; for a given detector sensitivity and observing time a smaller beam provides significantly more information than a larger beam. The uncertainties in $n_S$ and $r$ are roughly proportional to the beam size. We briefly discuss the effects of uncertainty in the Hubble constant, baryon density, cosmological constant and ionization history.Comment: 28 pages of uuencoded postscript with 8 included figures. A postscript version is also available by anonymous ftp at ftp://astro.uchicago.edu/pub/astro/knox/fullsim.p

4D Imaging and Diffraction Dynamics of Single-Particle Phase Transition in Heterogeneous Ensembles

In this Letter, we introduce conical-scanning dark-field imaging in four-dimensional (4D) ultrafast electron microscopy to visualize single-particle dynamics of a polycrystalline ensemble undergoing phase transitions. Specifically, the ultrafast metal–insulator phase transition of vanadium dioxide is induced using laser excitation and followed by taking electron-pulsed, time-resolved images and diffraction patterns. The single-particle selectivity is achieved by identifying the origin of all constituent Bragg spots on Debye–Scherrer rings from the ensemble. Orientation mapping and dynamic scattering simulation of the electron diffraction patterns in the monoclinic and tetragonal phase during the transition confirm the observed behavior of Bragg spots change with time. We found that the threshold temperature for phase recovery increases with increasing particle sizes and we quantified the observation through a theoretical model developed for single-particle phase transitions. The reported methodology of conical scanning, orientation mapping in 4D imaging promises to be powerful for heterogeneous ensemble, as it enables imaging and diffraction at a given time with a full archive of structural information for each particle, for example, size, morphology, and orientation while minimizing radiation damage to the specimen

Metagenomic assessment of nitrate-contaminated mine wastewaters and optimization of complete denitrification by indigenous enriched bacteria

Nitrate contamination in water remains to be on the rise globally due to continuous anthropogenic activities, such as mining and farming, which utilize high amounts of ammonium nitrate explosives and chemical-NPK-fertilizers, respectively. This study presents insights into the development of a bioremediation strategy to remove nitrates (NO3−) using consortia enriched from wastewater collected from a diamond mine in Lesotho and a platinum mine in South Africa. A biogeochemical analysis was conducted on the water samples which aided in comparing and elucidating their unique physicochemical parameters. The chemical analysis uncovered that both wastewater samples contained over 120 mg/L of NO3− and over 250 mg/L of sulfates (SO42-), which were both beyond the acceptable limit of the environmental surface water standards of South Africa. The samples were atypical of mine wastewaters as they had low concentrations of dissolved heavy metals and a pH of over 5. A metagenomic analysis applied to study microbial diversities revealed that both samples were dominated by the phyla Proteobacteria and Bacteroidetes, which accounted for over 40% and 15%, respectively. Three consortia were enriched to target denitrifying bacteria using selective media and then subjected to complete denitrification experiments. Denitrification dynamics and denitrifying capacities of the consortia were determined by monitoring dissolved and gaseous nitrogen species over time. Denitrification optimization was carried out by changing environmental conditions, including supplementing the cultures with metal enzyme co-factors (iron and copper) that were observed to promote different stages of denitrification. Copper supplemented at 50 mg/L was observed to be promoting complete denitrification of over 500 mg/L of NO3−, evidenced by the emission of nitrogen gas (N2) that was more than nitrous oxide gas (N2O) emitted as the terminal by-product. Modification and manipulation of growth conditions based on the microbial diversity enriched proved that it is possible to optimize a bioremediation system that can reduce high concentrations of NO3−, while emitting an environmentally-friendly N2 instead of N2O, that is, a greenhouse gas. Data collected and discussed in this research study can be used to model an upscale NO3− bioremediation system aimed to remove nitrogenous and other contaminants without secondary contamination

Cell-wall synthesis and ribosome maturation are co-regulated by an RNA switch in Mycobacterium tuberculosis

The success of Mycobacterium tuberculosis relies on the ability to switch between active growth and non-replicating persistence, associated with latent TB infection. Resuscitation promoting factors (Rpfs) are essential for the transition between these states. Rpf expression is tightly regulated as these enzymes are able to degrade the cell wall, and hence potentially lethal to the bacterium itself. We have identified a regulatory element in the 5' untranslated region (UTR) of rpfB. We demonstrate that this element is a transcriptionally regulated RNA switch/riboswitch candidate, which appears to be restricted to pathogenic mycobacteria, suggesting a role in virulence. We have used translation start site mapping to re-annotate the RpfB start codon and identified and validated a ribosome binding site that is likely to be targeted by an rpfB antisense RNA. Finally, we show that rpfB is co-transcribed with ksgA and ispE downstream. ksgA encodes a universally conserved methyltransferase involved in ribosome maturation and ispE encodes an essential kinase involved in cell wall synthesis. This arrangement implies co-regulation of resuscitation, cell wall synthesis and ribosome maturation via the RNA switch

Brief Report: Inhibitory Control of Socially Relevant Stimuli in Children with High Functioning Autism

The current study explored whether inhibitory control deficits in high functioning autism (HFA) emerged when socially relevant stimuli were used and whether arousal level affected the performance. A Go/NoGo paradigm, with socially relevant stimuli and varying presentation rates, was applied in 18 children with HFA (including children with autism or Asperger syndrome) and 22 typically developing children (aged 8–13 years). Children with HFA did not show inhibitory control deficits compared to the control group, but their performance deteriorated in the slow presentation rate condition. Findings were unrelated to children’s abilities to recognize emotions. Hence, rather than a core deficit in inhibitory control, low arousal level in response to social stimuli might influence the responses given by children with HFA