1,250 research outputs found
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Quantifying the increasing sensitivity of power systems to climate variability
Large quantities of weather-dependent renewable energy generation are expected in power systems under climate change mitigation policies, yet little attention has been given to the impact of long term climate variability. By combining state-ofthe-art multi-decadal meteorological records with a parsimonious representation of a power system, this study characterises the impact of year-to-year climate variability on multiple aspects of the power system of Great Britain (including coal, gas and
nuclear generation), demonstrating why multi-decadal approaches are necessary. All aspects of the example system are impacted by inter-annual climate variability, with the impacts being most pronounced for baseload generation. The impacts of inter-annual climate variability increase in a 2025 wind-power scenario, with a 4-fold increase in
the inter-annual range of operating hours for baseload such as nuclear. The impacts on peak load and peaking-plant are comparably small. Less than 10 years of power supply and demand data are shown to be insuffcient for providing robust power system planning guidance. This suggests renewable integration studies - widely used in policy, investment and system design - should adopt a more robust approach to climate characterisation
Transport properties of pristine few-layer black phosphorus by van der Waals passivation in an inert atmosphere
Ultrathin black phosphorus is a two-dimensional semiconductor with a sizeable band gap. Its excellent electronic properties make it attractive for applications in transistor, logic and optoelectronic devices. However, it is also the first widely investigated two-dimensional material to undergo degradation upon exposure to ambient air. Therefore a passivation method is required to study the intrinsic material properties, understand how oxidation affects the physical properties and enable applications of phosphorene. Here we demonstrate that atomically thin graphene and hexagonal boron nitride can be used for passivation of ultrathin black phosphorus. We report that few-layer pristine black phosphorus channels passivated in an inert gas environment, without any prior exposure to air, exhibit greatly improved n-type charge transport resulting in symmetric electron and hole transconductance characteristics.B.O. acknowledges support by the National Research Foundation, Prime Minister's Office, Singapore under its Competitive Research Programme (CRP Award No. NRF-CRP9-2011-3) and the SMF-NUS Research Horizons Award 2009-Phase II. A.H.C.N. acknowledges the NRF-CRP award 'Novel 2D materials with tailored properties: beyond graphene'. The calculations were performed at the GRC computing facilities. A.Z. and D.F.C. acknowledge the NSF grant CHE-1301157. (NRF-CRP9-2011-3 - National Research Foundation, Prime Minister's Office, Singapore under its Competitive Research Programme (CRP); SMF-NUS Research Horizons Award-Phase II; NRF-CRP award 'Novel 2D materials with tailored properties: beyond graphene'; CHE-1301157 - NSF)Published versio
Social Support Protects against the Negative Effects of Partner Violence on Mental Health
Objectives: Social support for abused women may reduce the impact of abuse on mental health, yet few studies have addressed this issue. We wish to determine associations between intimate partner violence (IPV) and mental health outcomes and to assess the protective role of abuse disclosure and support on mental health among abused women.
Methods: A cross-sectional survey was conducted of 1152 women, ages 18–65, recruited from family practice clinics from 1997 through 1999. They were screened for IPV during a brief in-clinic interview, and physical and mental health status was assessed in a follow-up interview.
Results: IPV, defined as sexual, physical, or psychological abuse, was associated with poor perceived mental and physical health, substance abuse, symptoms of posttraumatic stress disorder (PTSD), current depression, anxiety, and suicide ideation/actions. Among women experiencing IPV and controlling for IPV frequency, higher social support scores were associated with a significantly reduced risk of poor perceived mental health (adjusted relative risk [aRR] 0.5, 95% confidence interval [CI] 0.3, 0.6) and physical health (aRR 0.6, 95% CI 0.5, 0.8), anxiety (aRR 0.3, 95% CI 0.2, 0.4), current depression (aRR 0.6, 95% CI 0.5, 0.8), PTSD symptoms (aRR 0.5, 95% CI 0.4, 0.8), and suicide attempts (aRR 0.6, 95% CI 0.4, 0.9).
Conclusions: Healthcare providers can be instrumental in identifying IPV and helping women develop skills, resources, and support networks to address IPV. Physicians, family, or friends may provide needed social support
The Role of Magnetic Field Dissipation in the Black Hole Candidate Sgr A*
The compact, nonthermal radio source Sgr A* at the Galactic Center appears to
be coincident with a 2.6 million solar mass point-like object. Its energy
source may be the release of gravitational energy as gas from the interstellar
medium descends into its potential well. Simple attempts at calculating the
spectrum and flux based on this picture have come close to the observations,
yet have had difficulty in accounting for the low efficiency in this source.
There now appear to be two reasons for this low conversion rate: (1) the plasma
separates into two temperatures, with the protons attaining a significantly
higher temperature than that of the radiating electrons, and (2) the magnetic
field, B, is sub-equipartition, which reduces the magnetic bremsstrahlung
emissivity, and therefore the overall power of Sgr A*. We investigate the
latter with improvement over what has been attempted before: rather than
calculating B based on a presumed model, we instead infer its distribution with
radius empirically with the requirement that the resulting spectrum matches the
observations. Our ansatz for B(r) is motivated in part by earlier calculations
of the expected magnetic dissipation rate due to reconnection in a compressed
flow. We find reasonable agreement with the observed spectrum of Sgr A* as long
as its distribution consists of 3 primary components: an outer equipartition
field, a roughly constant field at intermediate radii (~1000 Schwarzschild
radii), and an inner dynamo (more or less within the last stable orbit for a
non-rotating black hole) which increases B to about 100 Gauss. The latter
component accounts for the observed sub-millimiter hump in this source.Comment: 33 pages including 2 figures; submitted to Ap
Determination of the characteristic directions of lossless linear optical elements
We show that the problem of finding the primary and secondary characteristic
directions of a linear lossless optical element can be reformulated in terms of
an eigenvalue problem related to the unimodular factor of the transfer matrix
of the optical device. This formulation makes any actual computation of the
characteristic directions amenable to pre-implemented numerical routines,
thereby facilitating the decomposition of the transfer matrix into equivalent
linear retarders and rotators according to the related Poincare equivalence
theorem. The method is expected to be useful whenever the inverse problem of
reconstruction of the internal state of a transparent medium from optical data
obtained by tomographical methods is an issue.Comment: Replaced with extended version as published in JM
Laboratory Experiments, Numerical Simulations, and Astronomical Observations of Deflected Supersonic Jets: Application to HH 110
Collimated supersonic flows in laboratory experiments behave in a similar
manner to astrophysical jets provided that radiation, viscosity, and thermal
conductivity are unimportant in the laboratory jets, and that the experimental
and astrophysical jets share similar dimensionless parameters such as the Mach
number and the ratio of the density between the jet and the ambient medium.
Laboratory jets can be studied for a variety of initial conditions, arbitrary
viewing angles, and different times, attributes especially helpful for
interpreting astronomical images where the viewing angle and initial conditions
are fixed and the time domain is limited. Experiments are also a powerful way
to test numerical fluid codes in a parameter range where the codes must perform
well. In this paper we combine images from a series of laboratory experiments
of deflected supersonic jets with numerical simulations and new spectral
observations of an astrophysical example, the young stellar jet HH 110. The
experiments provide key insights into how deflected jets evolve in 3-D,
particularly within working surfaces where multiple subsonic shells and
filaments form, and along the interface where shocked jet material penetrates
into and destroys the obstacle along its path. The experiments also underscore
the importance of the viewing angle in determining what an observer will see.
The simulations match the experiments so well that we can use the simulated
velocity maps to compare the dynamics in the experiment with those implied by
the astronomical spectra. The experiments support a model where the observed
shock structures in HH 110 form as a result of a pulsed driving source rather
than from weak shocks that may arise in the supersonic shear layer between the
Mach disk and bow shock of the jet's working surface.Comment: Full resolution figures available at
http://sparky.rice.edu/~hartigan/pub.html To appear in Ap
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The changing sensitivity of power systems to meteorological drivers: a case study of Great Britain
The increasing use of intermittent renewable generation (such as wind) is increasing the exposure of national power systems to meteorological variability. This study identifies how the integration of wind power in one particular country (Great Britain, GB) is affecting the overall sensitivity of the power system to weather using three key metrics: total annual energy requirement and peak residual load (from sources other than wind) and wind power curtailment.
The present-day level of wind power capacity (approximately 15GW) is shown to have already changed the power system's overall sensitivity to weather in terms of the total annual energy requirement, from a temperature- to a wind-dominated regime (which occurred with 6GW of installed wind power capacity). Peak residual load from sources other than wind also shows a similar shift. The associated changes in the synoptic- and large-scale meteorological drivers associated with each metric are identified and discussed. In a period where power systems are changing rapidly, it is therefore argued that past experience of the weather impacts on the GB power system may not be a good guide for the impact on the present or near-future power system
Low angular momentum flow model of Sgr A* activity
Sgr A* is the closest massive black hole and can be observed with the highest
angular resolution. Nevertheless, our current understanding of the accretion
process in this source is very poor. The inflow is almost certainly of low
radiative efficiency and it is accompanied by a strong outflow and the flow is
strongly variable but the details of the dynamics are unknown. Even the amount
of angular momentum in the flow is an open question. Here we argue that low
angular momentum scenario is better suited to explain the flow variability. We
present a new hybrid model which describes such a flow and consists of an outer
spherically symmetric Bondi flow and an inner axially symmetric flow described
through MHD simulations. The assumed angular momentum of the matter is low,
i.e. the corresponding circularization radius in the equatorial plane of the
flow is just above the innermost stable circular orbit in pseudo-Newtonian
potential. We compare the radiation spectrum from such a flow to the broad band
observational data for Sgr A*.Comment: Proceedings of the AHAR 2008 Conference: The Universe under the
Microscope; Astrophysics at High Angular Resolution, Bad Honef
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