131,957 research outputs found
Effect of distributed energy systems on the electricity grid
A feasibility study is being carried out at Ecotricity into a distributed
energy storage system comprising Energy stores (batteries) placed at
consumer level (in customer’s homes). The aim is to flatten consumer
demand and make better use of home-based generation. The Study
Group considered the mechanism of connecting batteries to the local
distribution system, the ability to meet engineering requirements for the
standard of the connection, and the potential impact of large numbers of
such connections on stability of the local distribution network. Network
and (DC-AC) invertor models were used to examine network connection
transients. A statistical model was proposed to estimate the distribution
of key electrical parameters to determine the likelihood of engineering
standards being exceeded. The Study Group also considered stochastic
methods of modelling wind speed, to better understand the requirements
for battery energy storage as a complement to wind power
An Examination of Student Performance in Pre-Requisite Coursework and Upper Division Nursing Coursework
Admission and retention of qualified nursing students are essential in meeting the demands of a rapidly changing health care environment and nursing shortage. The purpose of this exploratory correlational study was to determine the relationship between student performance in quantitative pre-requisite coursework and student performance in upper division nursing coursework in order to identify students at-risk for attrition. A series of descriptive and correlational analyses were conducted using pre-existing institutional data. A moderate relationship existed among the chemistry II and first-year upper division nursing courses (r = .21 to r = .40). These results suggest that prerequisite chemistry course performance could be a reliable predictor of academic success
Detection of methane on Kuiper Belt Object (50000) Quaoar
The near-infrared spectrum of (50000) Quaoar obtained at the Keck Observatory
shows distinct absorption features of crystalline water ice, solid methane and
ethane, and possibly other higher order hydrocarbons. Quaoar is only the fifth
Kuiper belt object on which volatile ices have been detected. The small amount
of methane on an otherwise water ice dominated surface suggests that Quaoar is
a transition object between the dominant volatile-poor small Kuiper belt
objects (KBOs) and the few volatile-rich large KBOs such as Pluto and Eris.Comment: 8 pages, 2 figures, accepted for publication in ApJ
Solving the electrical control of magnetic coercive field paradox
The ability to tune magnetic properties of solids via electric voltages instead of external magnetic fields is a physics curiosity of great scientific and technological importance. Today, there is strong published experimental evidence of electrical control of magnetic coercive fields in composite multiferroic solids. Unfortunately, the literature indicates highly contradictory results. In some studies, an applied voltage increases the magnetic coercive field and in other studies the applied voltage decreases the coercive field of composite multiferroics. Here, we provide an elegant explanation to this paradox and we demonstrate why all reported results are in fact correct. It is shown that for a given polarity of the applied voltage, the magnetic coercive field depends on the sign of two tensor components of the multiferroic solid: magnetostrictive and piezoelectric coefficient. For a negative applied voltage, the magnetic coercive field decreases when the two material parameters have the same sign and increases when they have opposite signs, respectively. The effect of the material parameters is reversed when the same multiferroic solid is subjected to a positive applied voltage
Evidence for an Io plasma torus influence on high-latitude Jovian radio emission
We report the discovery with the Ulysses unified radio and plasma wave (URAP) instrument of features in the Jovian hectometer (HOM) wavelength radio emission spectrum which recur with a period about 2–4% longer than the Jovian System III rotation period. We conclude that the auroral HOM emissions are periodically blocked from “view” by regions in the torus of higher than average density and that these regions rotate more slowly than System III and persist for considerable intervals of time. We have reexamined the Voyager planetary radio astronomy (PRA) data taken during the flybys in 1979 and have found similar features in the HOM spectrum. Contemporaneous observations by Brown (1994) show an [SII] emission line enhancement in the Io plasma torus that rotates more slowly than System III by the same amount as the HOM feature
Flight investigation to evaluate the roll-rate stabilization system of the Naval Ordnance Test Station Sidewinder missile at Mach numbers from 0.9 to 2.3
Foreground removal requirements for measuring large-scale CMB B-modes in light of BICEP2
The most convincing confirmation that the B-mode polarization signal detected
at degree scales by BICEP2 is due to the Cosmic Microwave Background (CMB)
would be the measurement of its large-scale counterpart. We assess the
requirements for diffuse component separation accuracy over large portions of
the sky in order to measure the large-scale B-mode signal corresponding to a
tensor to scalar ratio of r=0.1-0.2.
We use the method proposed by Bonaldi & Ricciardi (2011) to forecast the
performances of different simulated experiments taking into account noise and
foreground removal issues. We do not consider instrumental systematics, and we
implicitly assume that they are not the dominant source of error. If this is
the case, the confirmation of an r=0.1-0.2 signal is achievable by Planck even
for conservative assumptions regarding the accuracy of foreground cleaning. Our
forecasts suggest that the combination of this experiment with BICEP2 will lead
to an improvement of 25-45% in the constraint on r.
A next-generation CMB polarization satellite, represented in this work by the
COrE experiment, can reduce dramatically (by almost another order of magnitude)
the uncertainty on r. In this case, however, the accuracy of foreground removal
becomes critical to fully benefit from the increase in sensitivity.Comment: 8 pages, 3 figures, 1 table. Accepted by MNRA
Near-infrared (NIR) spectra of Centaurs and Kuiper belt objects
We present here an extensive survey of near-infrared (NIR) spectra of Kuiper belt objects (KBOs) and Centaurs taken with the Keck I Telescope. We find that most spectra in our sample are well characterized by a combination of water ice and a featureless continuum. A comparative analysis reveals that the NIR spectral properties have little correlation to the visible colors or albedo, with the exception of the fragment KBOs produced from the giant impact on 2003 EL61. The results suggest that the surface composition of KBOs is heterogeneous, though the exposure of water ice may be controlled by geophysical processes. The Centaurs also display diverse spectral properties, but the source of the variability remains unclear. The results for both the KBOs and the Centaurs point to inherent heterogeneity in either the processes acting on these objects or materials from which they formed
Photon Bunching at TeV Energies
Harwit, Protheroe, and Biermann (1999) recently proposed that Bose-Einstein
photon bunching might significantly affect the interpretation of Cerenkov
counts of TeV gamma photons. Here, we show that a combination of two recent
results of Aharonian et al. (2000) and Aharonian et al. (2001) permits us to
set new, more stringent upper limits of on the fractional amount
of photon bunching in the 7-10 TeV radiation from Markarian 501. Potential
bunching at even higher energies should nevertheless continue to be
investigated for this and other TeV sources, since a clear understanding of TeV
energy spectra is required to unambiguously determine the spectral energy
density of the mid-infrared extragalactic background
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