On the Nature of Velocity Fields in High z Galaxies

We analyze the gas kinematics of damped Lya systems (DLAs) hosting high z gamma-ray bursts (GRBs) and those toward quasars (QSO-DLAs) focusing on threestatistics: (1) dv, the velocity interval encompassing 90% of the totaloptical depth, (2,3) Wsi and Wciv, the rest equivalent widths of the SiII1526 and CIV1548 transitions. The dv distributions of the GRB-DLAs and QSO-DLAs are similar, each has median dv~80km/s and a significant tail to several hundred km/s. This suggests comparable galaxy masses for the parent populations of GRB-DLAs and QSO-DLAs and we infer the average dark matter halo mass of GRB galaxies is <~10^{12} Msol. The unique configuration of GRB-DLA sightlines and the presence (and absence) of fine-structure absorption together give special insight into the nature of high z, protogalactic velocity fields. The data support a scenario where the dv statistic reflects dynamics in the interstellar medium (ISM) and Wsi traces motions outside the ISM (e.g. halo gas, galactic-scale winds). The Wsi statistic and gas metallicity [M/H] are tightly correlated, especially for the QSO-DLAs: [M/H]=a + b log(Wsi/1A) with a=-0.92+/-0.05 and b=-1.41+/-0.10. We argue that the Wsi statistic primarily tracks dynamical motions in the halos of high z galaxies and interpret this correlation as a mass-metallicity relation with very similar slope to the trend observed in local, low-metallicity galaxies. Finally, the GRB-DLAs exhibit systematically larger Wsi values (>0.5A) than the QSO-DLAs (~ 0.5A) which may suggest galactic-scale outflows contribute to the largest observed velocity fields.Comment: 14 pages, 9 figures. Submitted to Ap

Transport of a colloidal particle driven across a temporally oscillating optical potential energy landscape

A colloidal particle is driven across a temporally oscillating one-dimensional optical potential energy landscape and its particle motion is analysed. Different modes of dynamic mode locking are observed and are confirmed with the use of phase portraits. The effect of the oscillation frequency on the mode locked step width is addressed and the results are discussed in light of a high-frequency theory and compared to simulations. Furthermore, the influence of the coupling between the particle and the optical landscape on mode locking is probed by increasing the maximum depth of the optical landscape. Stronger coupling is seen to increase the width of mode locked steps. Finally, transport across the temporally oscillating landscape is studied by measuring the effective diffusion coefficient of a mobile particle, which is seen to be highly sensitive to the driving velocity and mode locking

Probing energy barriers and quantum confined states of buried semiconductor heterostructures with ballistic carrier injection: An experimental study

A three-terminal spectroscopy that probes both subsurface energy barriers and interband optical transitions in a semiconductor heterostructure is demonstrated. A metal-base transistor with a unipolar p-type semiconductor collector embedding InAs/GaAs quantum dots (QDs) is studied. Using minority/majority carrier injection, ballistic electron emission spectroscopy and its related hot-carrier scattering spectroscopy measures barrier heights of a buried AlxGa1-xAs layer in conduction band and valence band respectively, the band gap of Al0.4Ga0.6As is therefore determined as 2.037 +/- 0.009 eV at 9 K. Under forward collector bias, interband electroluminescence is induced by the injection of minority carriers with sub-bandgap kinetic energies. Three emission peaks from InAs QDs, InAs wetting layer, and GaAs are observed in concert with minority carrier injection.Comment: 11 pages, 4 figures, submitted to Physical Review

TEM Cell Testing of Cable Noise Reduction Techniques From 2 MHz to 200 MHz - Part 1

This paper presents empirical results of cable noise reduction techniques as demonstrated in a TEM cell operating with radiated fields from 2 - 200 MHz. It is the first part of a two-paper series. This first paper discusses cable types and shield connections. In the second paper, the effects of load and source resistances and chassis connections are examined. For each topic, well established theories are compared to data from a real-world physical system. Finally, recommendations for minimizing cable susceptibility (and thus cable emissions) are presented. There are numerous papers and textbooks that present theoretical analyses of cable noise reduction techniques. However, empirical data is often targeted to low frequencies (e.g. 100 MHz). Additionally, a comprehensive study showing the relative effects of various noise reduction techniques is needed. These include the use of dedicated return wires, twisted wiring, cable shielding, shield connections, changing load or source impedances, and implementing load- or source-to-chassis isolation. We have created an experimental setup that emulates a real-world electrical system, while still allowing us to independently vary a host of parameters. The goal of the experiment was to determine the relative effectiveness of various noise reduction techniques when the cable is in the presence of radiated emissions from 2 MHz to 200 MHz. The electronic system (Fig. 1) consisted of two Hammond shielded electrical enclosures, one containing the source resistance, and the other containing the load resistance. The boxes were mounted on a large aluminium plate acting as the chassis. Cables connecting the two boxes measured 81 cm in length and were attached to the boxes using standard D38999 military-style connectors. The test setup is shown in Fig. 2. Electromagnetic fields were created using an HP8657B signal generator, MiniCircuits ZHL-42W-SMA amplifier, and an EMCO 5103 TEM cell. Measurements were taken using an Agilent E4401B spectrum analyzer and HP1141a differential probes

The applicability of three-dimensional aromaticity in BiSnn- Zintl analogues

Three-dimensional aromaticity is shown to play a role in the stability of deltahedral Zintl clusters and here we examine the connection between aromaticity and stability. In order to gain further insight, we have studied Zintl analogs comprised of bismuthdopedtin clusters with photoelectron spectroscopy and theoretical methods. To assign aromaticity, we examine the ring currents induced around the cage by using the nucleus independent chemical shift. In the current study, BiSn4− is a stable cluster and fits aromatic criteria, while BiSn5− is found to fit antiaromatic criteria and has reduced stability. The more stable clusters exhibit an aromatic character which originates from weakly interacting s-states and bonding orbitals parallel to the surface of the cluster, while nonbonding lone pairs perpendicular to the surface of the cluster account for antiaromaticity and reduced stability. The effect of three-dimensional aromaticity on the electronic structure does not result in degeneracies, so the resulting variations in stability are smaller than those seen in conventional aromaticity

High growth rate 4H-SiC epitaxial growth using dichlorosilane in a hot-wall CVD reactor

Thick, high quality 4H-SiC epilayers have been grown in a vertical hot-wall chemical vapor deposition system at a high growth rate on (0001) 80 off-axis substrates. We discuss the use of dichlorosilane as the Si-precursor for 4H-SiC epitaxial growth as it provides the most direct decomposition route into SiCl2, which is the predominant growth species in chlorinated chemistries. A specular surface morphology was attained by limiting the hydrogen etch rate until the system was equilibrated at the desired growth temperature. The RMS roughness of the grown films ranged from 0.5-2.0 nm with very few morphological defects (carrots, triangular defects, etc.) being introduced, while enabling growth rates of 30-100 \mum/hr, 5-15 times higher than most conventional growths. Site-competition epitaxy was observed over a wide range of C/Si ratios, with doping concentrations < 1x1014 cm-3 being recorded. X-ray rocking curves indicated that the epilayers were of high crystallinity, with linewidths as narrow as 7.8 arcsec being observed, while microwave photoconductive decay (\muPCD) measurements indicated that these films had high injection (ambipolar) carrier lifetimes in the range of 2 \mus

The Hepatitis C Cascade of Care: Identifying Priorities to Improve Clinical Outcomes

Background: As highly effective hepatitis C virus (HCV) therapies emerge, data are needed to inform the development of interventions to improve HCV treatment rates. We used simulation modeling to estimate the impact of loss to follow-up on HCV treatment outcomes and to identify intervention strategies likely to provide good value for the resources invested in them. Methods: We used a Monte Carlo state-transition model to simulate a hypothetical cohort of chronically HCV-infected individuals recently screened positive for serum HCV antibody. We simulated four hypothetical intervention strategies (linkage to care; treatment initiation; integrated case management; peer navigator) to improve HCV treatment rates, varying efficacies and costs, and identified strategies that would most likely result in the best value for the resources required for implementation. Main measures Sustained virologic responses (SVRs), life expectancy, quality-adjusted life expectancy (QALE), costs from health system and program implementation perspectives, and incremental cost-effectiveness ratios (ICERs). Results: We estimate that imperfect follow-up reduces the real-world effectiveness of HCV therapies by approximately 75%. In the base case, a modestly effective hypothetical peer navigator program maximized the number of SVRs and QALE, with an ICER compared to the next best intervention of $48,700/quality-adjusted life year. Hypothetical interventions that simultaneously addressed multiple points along the cascade provided better outcomes and more value for money than less costly interventions targeting single steps. The 5-year program cost of the hypothetical peer navigator intervention was$14.5 million per 10,000 newly diagnosed individuals. Conclusions: We estimate that imperfect follow-up during the HCV cascade of care greatly reduces the real-world effectiveness of HCV therapy. Our mathematical model shows that modestly effective interventions to improve follow-up would likely be cost-effective. Priority should be given to developing and evaluating interventions addressing multiple points along the cascade rather than options focusing solely on single points