2,362 research outputs found
Estimating Infection Risks and the Global Burden of Diarrheal Disease Attributable to Intermittent Water Supply Using QMRA.
: Intermittent water supply (IWS) is prevalent throughout low and middle-income countries. IWS is associated with increased microbial contamination and potentially elevated risk of waterborne illness. We used existing data sets to estimate the population exposed to IWS, assess the probability of infection using quantitative microbial risk assessment, and calculate the subsequent burden of diarrheal disease attributable to consuming fecally contaminated tap water from an IWS. We used reference pathogens Campylobacter, Cryptosporidium, and rotavirus as conservative risk proxies for infections via bacteria, protozoa, and viruses, respectively. Results indicate that the median daily risk of infection is an estimated 1 in 23 500 for Campylobacter, 1 in 5 050 000 for Cryptosporidium, and 1 in 118 000 for rotavirus. Based on these risks, IWS may account for 17.2 million infections causing 4.52 million cases of diarrhea, 109 000 diarrheal DALYs, and 1560 deaths each year. The burden of diarrheal disease associated with IWS likely exceeds the WHO health-based normative guideline for drinking water of 10-6 DALYs per person per year. Our results underscore the importance water safety management in water supplies and the potential benefits of point-of-use treatment to mitigate risks.<br/
Models of Type I X-Ray Bursts in 4U 1820-30
I present ignition models for Type I X-ray bursts and superbursts from the
ultracompact binary 4U 1820-30. A pure helium secondary is usually assumed for
this system, although some evolutionary models predict a small amount of
hydrogen (around 10% by mass). I show that even this small amount of hydrogen
significantly affects the expected Type I burst properties. Using the 2-4 hour
recurrence times observed during periods of regular bursting, I determine the
accretion rate onto the star for different compositions, a new constraint on
evolutionary models. I show that models with hydrogen predict 10% variations in
burst fluence with recurrence time, which should in future allow the accreted
composition to be determined. For superbursts, I show that the expected
recurrence times are 1-2 years for pure He accretion, and 5-10 years if
hydrogen is present. These results emphasise that a combined analysis of normal
Type I X-ray bursts and superbursts is a promising way to probe the thermal
structure and composition of the neutron star's outer layers.Comment: To appear in the Astrophysical Journal (13 pages; 4 figures
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New Investor Categories, Agility and HRM: The Case of Sovereign Wealth Funds
This article reviews the existing literature on SWFs and the firm, focusing particular attention on the implications of the rise of SWFs strategic agility and HRM. This paper outlines three main channels through which sovereign wealth fund (SWF) investment has implications for employees. First, SWFs influence macroeconomic environments, and hence affect labor conditions. Second, institutional conditions in different countries shape the behavior of SWFs around the world, which in turn has implications for HR strategy and practice. Fourth, SWFs can have a direct effect on the corporate governance and hence HR strategies and employees of organizations in which they invest. We review and discuss these three channels and outline avenues for future research
Terahertz oscillations in an In<sub>0.53</sub>Ga<sub>0.47</sub>As submicron planar gunn diode
The length of the transit region of a Gunn diode determines the natural frequency at which it operates in fundamental mode – the shorter the device, the higher the frequency of operation. The long-held view on Gunn diode design is that for a functioning device the minimum length of the transit region is about 1.5μm, limiting the devices to fundamental mode operation at frequencies of roughly 60 GHz. Study of these devices by more advanced Monte Carlo techniques that simulate the ballistic transport and electron-phonon interactions that govern device behaviour, offers a new lower bound of 0.5μm, which is already being approached by the experimental evidence that has shown planar and vertical devices exhibiting Gunn operation at 600nm and 700nm, respectively. The paper presents results of the first ever THz submicron planar Gunn diode fabricated in In<sub>0.53</sub>Ga<sub>0.47</sub>A on an InP substrate, operating at a fundamental frequency above 300 GHz. Experimentally measured rf power of 28 µW was obtained from a 600 nm long ×120 µm wide device. At this new length, operation in fundamental mode at much higher frequencies becomes possible – the Monte Carlo model used predicts power output at frequencies over 300 GHz
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Mitigation of Moral Hazard and Adverse Selection in Venture Capital Financing: The Influence of the Country’s Institutional Setting
A venture capitalist (VC) needs to trade off benefits and costs when attempting to mitigate agency problems in their investor-investee relationship. We argue that signals of ventures complement the VC’s capacity to screen and conduct a due diligence during the pre-investment phase, but its attractiveness may diminish in institutional settings supporting greater transparency. Similarly, whereas a VC may opt for contractual covenants to curb potential opportunism by ventures in the post-investment phase, this may only be effective in settings supportive of shareholder rights enforcement. Using an international sample of VC contracts, our study finds broad support for these conjectures. It delineates theoretical and practical implications for how investors can best deploy their capital in different institutional settings whilst nurturing their relationships with entrepreneurs
Invited Article: CO_2 laser production of fused silica fibers for use in interferometric gravitational wave detector mirror suspensions
In 2000 the first mirror suspensions to use a quasi-monolithic final stage were installed at the GEO600 detector site outside Hannover, pioneering the use of fused silica suspension fibers in long baseline interferometric detectors to reduce suspension thermal noise. Since that time, development of the production methods of fused silica fibers has continued. We present here a review of a novel CO_2 laser-based fiber pulling machine developed for the production of fused silica suspensions for the next generation of interferometric gravitational wave detectors and for use in experiments requiring low thermal noise suspensions. We discuss tolerances, strengths, and thermal noise performance requirements for the next generation of gravitational wave detectors. Measurements made on fibers produced using this machine show a 0.8% variation in vertical stiffness and 0.05% tolerance on length, with average strengths exceeding 4 GPa, and mechanical dissipation which meets the requirements for Advanced LIGO thermal noise performance
Investigation of mechanical losses of thin silicon flexures at low temperatures
The investigation of the mechanical loss of different silicon flexures in a
temperature region from 5 to 300 K is presented. The flexures have been
prepared by different fabrication techniques. A lowest mechanical loss of
was observed for a 130 m thick flexure at around 10 K.
While the mechanical loss follows the thermoelastic predictions down to 50 K a
difference can be observed at lower temperatures for different surface
treatments. This surface loss will be limiting for all applications using
silicon based oscillators at low temperatures. The extraction of a surface loss
parameter using different results from our measurements and other references is
presented. We focused on structures that are relevant for gravitational wave
detectors. The surface loss parameter = 0.5 pm was obtained. This
reveals that the surface loss of silicon is significantly lower than the
surface loss of fused silica.Comment: 16 pages, 7 figure
Circumstellar Na I and Ca II lines of type Ia supernovae in symbiotic scenario
Formation of circumstellar lines of Na I and Ca II in type Ia supernovae is
studied for the case, when supernova explodes in a binary system with a red
giant. The model suggests a spherically-symmetric wind and takes into account
ionization and heating of the wind by X-rays from the shock wave and by
gamma-quanta of ^{56}Ni radioactive decay. For the wind density typical of the
red giant the expected optical depth of the wind in Na I lines turnes out too
low (\tau<0.001}) to detect the absorption. For the same wind densities the
predicted optical depth of Ca II 3934 \AA is sufficient for the detection
(\tau>0.1). I conclude that the absorption lines detected in SN 2006X cannot
form in the red giant wind; they are rather related to clouds at distances
larger than the dust evaporation radius (r>10^{17} cm). From the absence in SN
2006X of Ca II absorption lines not related with the similar Na I components I
derive the upper limit of the mass loss rate by the wind with velocity u:
\dot{M}<10^{-8}(u/10 km/s) M_{\odot} yr^{-1}.Comment: 10 pages, 6 figures, Astronomy Letters (accepted
Precise radial velocities of giant stars. IV. A correlation between surface gravity and radial velocity variation and a statistical investigation of companion properties
Since 1999, we have been conducting a radial velocity survey of 179 K giants
using the CAT at UCO/Lick observatory. At present ~20-100 measurements have
been collected per star with a precision of 5 to 8 m/s. Of the stars monitored,
145 (80%) show radial velocity (RV) variations at a level >20 m/s, of which 43
exhibit significant periodicities. Our aim is to investigate possible
mechanism(s) that cause these observed RV variations. We intend to test whether
these variations are intrinsic in nature, or possibly induced by companions, or
both. In addition, we aim to characterise the parameters of these companions. A
relation between log g and the amplitude of the RV variations is investigated
for all stars in the sample. Furthermore, the hypothesis that all periodic RV
variations are caused by companions is investigated by comparing their inferred
orbital statistics with the statistics of companions around main sequence
stars. A strong relation is found between the amplitude of the RV variations
and log g in K giant stars, as suggested earlier by Hatzes & Cochran (1998).
However, most of the stars exhibiting periodic variations are located above
this relation. These RV variations can be split in a periodic component which
is not correlated with log g and a random residual part which does correlate
with log g. Compared to main-sequence stars, K giants frequently exhibit
periodic RV variations. Interpreting these RV variations as being caused by
companions, the orbital param eters are different from the companions orbiting
dwarfs. Intrinsic mechanisms play an important role in producing RV variations
in K giants stars, as suggested by their dependence on log g. However, it
appears that periodic RV variations are additional to these intrinsic
variations, consistent with them being caused by companions.Comment: 10 pages, accepted by A&
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