Visualizing hybridized quantum plasmons in coupled nanowires:From classical to tunneling regime

We present full quantum mechanical calculations of the hybridized plasmon modes of two nanowires at small separation, providing real space visualization of the modes in the transition from the classical to the quantum tunneling regime. The plasmon modes are obtained as certain eigenfunctions of the dynamical dielectric function which is computed using time dependent density functional theory (TDDFT). For freestanding wires, the energy of both surface and bulk plasmon modes deviate from the classical result for low wire radii and high momentum transfer due to effects of electron spill-out, non-local response, and coupling to single-particle transitions. For the wire dimer the shape of the hybridized plasmon modes are continuously altered with decreasing separation, and below 6 {\AA} the energy dispersion of the modes deviate from classical results due to the onset of weak tunneling. Below 2-3 {\AA} separation this mode is replaced by a charge-transfer plasmon which blue shifts with decreasing separation in agreement with experiment, and marks the onset of the strong tunneling regime.Comment: To appear in PR

Exploring effort–reward imbalance and professional quality of life among health workers in Cape Town, South Africa: a mixed-methods study

Background In the context of a growing appreciation for the wellbeing of the health workforce as the foundation of high-quality, sustainable health systems, this paper presents findings from two complementary studies to explore occupational stress and professional quality of life among health workers that were conducted in preparation for a task-shifting intervention to improve antenatal mental health services in Cape Town. Methods This mixed-methods, cross-sectional study was conducted in public sector Midwife Obstetric Units and associated Non-Profit Organisations in Cape Town. Semi-structured interviews and a quantitative survey were conducted among facility-and community-based professional and lay health workers. The survey included demographic as well as effort–reward imbalance (ERI) and professional quality of life (PROQOL) questionnaires to examine overall levels of work-related psychosocial stress and professional quality of life, as well as differences between lay and professional health workers. Qualitative data was analysed using a thematic content analysis approach. Quantitative data was analysed using STATA 12. Results Findings from 37 qualitative interviews highlighted the difficult working conditions and often limited reward and support structures experienced by health workers. Corroborating these findings, our quantitative survey of 165 professional and lay health workers revealed that most health workers experienced a mismatch between efforts spent and rewards gained at work (61.1% of professional and 70.2% of lay health workers; p = 0.302). There were few statistically significant differences in ERI and PROQOL scores between professional and lay health workers. Although Compassion Satisfaction was high for all health worker groups, lay health workers also showed elevated levels of burnout and compassion fatigue, with community-based health workers particularly affected. Conclusions Findings of this study add to the existing evidence base on adverse working conditions faced by South African public-sector health workers that should be taken into consideration as national and local governments seek to ‘re-engineer’ South Africa’s Primary Health Care system. Furthermore, they also highlight the importance of taking into consideration the wellbeing of health workers themselves to develop interventions that can sustainably foster resilient and high-quality health systems

The development of gaseous detectors with solid photocathodes for low temperature

There are several applications and fundamental research areas which require the detection of VUV light at cryogenic temperatures. For these applications we have developed and successfully tested special designs of gaseous detectors with solid photocathodes able to operate at low temperatures: sealed gaseous detectors with MgF2 windows and windowless detectors. We have experimentally demonstrated, that both primary and secondary (due to the avalanche multiplication inside liquids) scintillation lights could be recorded by photosensitive gaseous detectors. The results of this work may allow one to significantly improve the operation of some noble liquid gas TPCs.Comment: Presented at the X Vienna Conference on Instumentation, Vienna, February 200

The Architecture of the GW Ori Young Triple Star System and Its Disk: Dynamical Masses, Mutual Inclinations, and Recurrent Eclipses

We present spatially and spectrally resolved Atacama Large Millimeter/submillimeter Array (ALMA) observations of gas and dust orbiting the pre-main sequence hierarchical triple star system GW Ori. A forward-modeling of the ${}^{13}$CO and C${}^{18}$O $J$=2-1 transitions permits a measurement of the total stellar mass in this system, $5.29 \pm 0.09\,M_\odot$, and the circum-triple disk inclination, $137.6 \pm 2.0^\circ$. Optical spectra spanning a 35 year period were used to derive new radial velocities and, coupled with a spectroscopic disentangling technique, revealed that the A and B components of GW Ori form a double-lined spectroscopic binary with a $241.50\pm0.05$ day period; a tertiary companion orbits that inner pair with a $4218\pm50$ day period. Combining the results from the ALMA data and the optical spectra with three epochs of astrometry in the literature, we constrain the individual stellar masses in the system ($M_\mathrm{A} \approx 2.7\,M_\odot$, $M_\mathrm{B} \approx 1.7\,M_\odot$, $M_\mathrm{C} \approx 0.9\,M_\odot$) and find strong evidence that at least one (and likely both) stellar orbital planes are misaligned with the disk plane by as much as $45^\circ$. A $V$-band light curve spanning 30 years reveals several new $\sim$30 day eclipse events 0.1-0.7~mag in depth and a 0.2 mag sinusoidal oscillation that is clearly phased with the AB-C orbital period. Taken together, these features suggest that the A-B pair may be partially obscured by material in the inner disk as the pair approaches apoastron in the hierarchical orbit. Lastly, we conclude that stellar evolutionary models are consistent with our measurements of the masses and basic photospheric properties if the GW Ori system is $\sim$1 Myr old.Comment: 26 pages, 15 figures, accepted to Ap

Enhanced erodibility of fine-grained marine sediments by Hydrobia ulvae

Abstract The common mud snail Hydrobia ulvae is a widespread and dominant deposit feeder on fine-grained substrata along the European Atlantic coastline. Previous studies have shown that mud snail activities such as grazing, faecal pellet production and mucous production may influence physical properties of the surface sediment layer and thus depositional and erosional processes. To quantify the influence of Hydrobia density on key parameters such as erosion threshold and erosion rate, a shortterm laboratory experiment was conducted. Snails were placed on fine-grained sediment at densities of 10 000 and 50 000 ind m À 2 and erosion experiments were carried out one, three and five days after establishment of the sediment beds. Controls without H. ulvae were treated the same way. The presence of H. ulvae significantly increased the erosion rate and decreased the erosion threshold compared to snail-free control plots. The erosion rate was increased by a factor of 2 to 4 when H. ulvae were present and showed stronger influence by the snail than the erosion threshold. Snail density did not affect the erosion threshold, but the erosion rate doubled with an increase in density from 10 000 to 50 000 ind m À 2 . The erosion rate was only marginally different after one day but the difference increased over time and the erosion rate was significantly different for all treatments after five days. No significant time dependence was observed for the erosion threshold. The results generally confirm results obtained in situ and differences can be related to different hydrodynamic conditions under field and laboratory conditions.

The optical/near-IR spectral energy distribution of the GRB 000210 host galaxy

We report on UBVRIZJsHKs-band photometry of the dark GRB 000210 host galaxy. Fitting a grid of spectral templates to its Spectral Energy Distribution (SED), we derived a photometric redshift (z=0.842\+0.0540.042) which is in excellent agreement with the spectroscopic one (z=0.8463+/-0.0002; Piro et al. 2002). The best fit to the SED is obtained with a blue starburst template with an age of 0.181\+0.0370.026 Gyr. We discuss the implications of the inferred low value of Av and the age of the dominant stellar population for the non detection of the GRB 000210 optical afterglow.Comment: 4 pages, 1 figure, contribution to the Rome 2002 GRB worksho

Constraints on the optical afterglow emission of the short/hard burst GRB 010119

We report optical observations of the short/hard burst GRB 010119 error box, one of the smallest error boxes reported to date for short/hard GRBs. Limits of R > 22.3 and I > 21.2 are imposed by observations carried out 20.31 and 20.58 hours after the gamma-ray event, respectively. They represent the most constraining limits imposed to date on the optical emission from a short/hard gamma-ray burst afterglow.Comment: 6 pages, 7 figures, submitted to A&