1,323 research outputs found
Brorfelde Schmidt CCD Catalog (BSCC)
The Brorfelde Schmidt CCD Catalog (BSCC) contains about 13.7 million stars,
north of +49 deg Declination with precise positions and V, R photometry. The
catalog has been constructed from the reductions of 18,667 CCD frames observed
with the Brorfelde Schmidt Telescope between 2000 and 2007. The Tycho-2 catalog
was used for astrometric and photometric reference stars. Errors of individual
positions are about 20 to 200 mas for stars in the R = 10 to 18 mag range.
External comparisons with 2MASS and SDSS reveal possible small systematic
errors in the BSCC of up to about 30 mas. The catalog is supplemented with J,
H, and K_s magnitudes from the 2MASS catalog. The catalog data file (about 550
MB ASCII, compressed) will be made available at the Strasbourg Data Center
(CDS).Comment: 16 pages, 22 figures, 2 tables, accepted by A
Numerical comparison between a Gyrofluid and Gyrokinetic model investigating collisionless magnetic reconnection
The first detailed comparison between gyrokinetic and gyrofluid simulations
of collisionless magnetic reconnection has been carried out. Both the linear
and nonlinear evolution of the collisionless tearing mode have been analyzed.
In the linear regime, we have found a good agreement between the two approaches
over the whole spectrum of linearly unstable wave numbers, both in the drift
kinetic limit and for finite ion temperature. Nonlinearly, focusing on the
small- regime, with indicating the standard tearing
stability parameter, we have compared relevant observables such as the
evolution and saturation of the island width, as well as the island oscillation
frequency in the saturated phase.The results are basically the same, with small
discrepancies only in the value of the saturated island width for moderately
high values of . Therefore, in the regimes investigated here, the
gyrofluid approach can describe the collisionless reconnection process as well
as the more complete gyrokinetic model.Comment: Accepted for publication on Physics of Plasma
A Double-Mode RR Lyrae Star with a Strong Fundamental Mode Component
NSVS 5222076, a thirteenth magnitude star in the Northern Sky Variability
Survey, was identified by Oaster as a possible new double-mode RR Lyrae star.
We confirm the double-mode nature of NSVS 5222076, supplementing the survey
data with new V band photometry. NSVS 5222076 has a fundamental mode period of
0.4940 day and a first overtone period of 0.3668 day. Its fundamental mode
light curve has an amplitude twice as large as that of the first overtone mode,
a ratio very rarely seen. Data from the literature are used to discuss the
location in the Petersen diagram of double-mode RR Lyrae stars having strong
fundamental mode pulsation. Such stars tend to occur toward the short period
end of the Petersen diagram, and NSVS 5222976 is no exception to this rule.Comment: 14 pages, 4 figures, To be published in the March, 2006, issue of
PAS
Optical-uv spectrum and proper motion of the middle-aged pulsar b1055-52
PSRB1055-52 is a middle-aged (~535 kyr) radio, X-ray, and gamma-ray pulsar
showing X-ray thermal emission from the neutron star (NS) surface. A candidate
optical counterpart to PSRB1055-52 was proposed by Mignani and coworkers based
on Hubble Space Telescope (HST) observations performed in 1996, in one spectral
band only. We report on HST observations of this field carried out in 2008, in
four spectral bands. The astrometric and photometric analyses of these data
confirm the identification of the proposed candidate as the pulsar's optical
counterpart. Similarly to other middle-aged pulsars, its optical-UV spectrum
can be described by the sum of a power-law (PLO) component, presumably emitted
from the pulsar magnetosphere, and a Rayleigh-Jeans (RJ) component emitted from
the NS surface. The spectral index of the PLO component, alpha_O=1.05+/-0.34,
is larger than for other pulsars with optical counterparts. The RJ component,
with the brightness temperature TO=(0.66+/-0.10) d_350**2 R_O,13**-2 MK (where
d_350 and R_O,13 are the distance to the pulsar in units of 350 pc and the
radius of the emitting area in units of 13 km), shows a factor of 4 excess with
respect to the extrapolation of the X-ray thermal component into the
UV-optical. This hints that the RJ component is emitted from a larger, colder
area, and suggests that the distance to the pulsar is smaller than previously
thought. From the absolute astrometry of the HST images we measured the pulsar
coordinates with a position accuracy of 0.15". From the comparison with
previous observations we measured the pulsar proper motion, mu = 42+/-5 mas/yr,
which corresponds to a transverse velocity V_t = (70+/-8) d_350 km/s.Comment: 12 pages, 5 figures, accepted for publication on Astrophysical
Journal, (Fig1a available at http://www.mssl.ucl.ac.uk/~rm2/
The Effect of Sleep Quality and Being Physically Active on Developing Mental Toughness
Mental toughness (MT) has been increasingly associated with successful performance in several stressful and competitive environments (e.g. the military, business, academics, medicine, sports). Being physically active (PA) may compromise sleep quality (SQ). Research has reported conflicting associations regarding PA and MT. Regarding SQ and MT, a bidirectional association has been reported. However, research has not yet focused on the combined effects of PA and SQ on MT. PURPOSE: To characterize the association and the effects of PA and SQ on MT. The authors hypothesized that: (a) PA and SQ are negatively associated; (b) PA and MT are positively associated; (c) SQ and MT are negatively associated; and (d) the interaction effect of PA and SQ on MT will be buffering. METHODS: Sixty-two participants (age 25.4 6.0 SD) completed inventories related to SQ (Pittsburgh Sleep Quality Index) and MT (Mental Toughness Index). PA data were collected according to American College of Sports Medicine guidelines. Main and interaction effects of the responses were analyzed using factorial ANOVA. Significance was set at p \u3c 0.05. All analyses were performed using SPSS. RESULTS: PA was positively correlated with SQ (r = .009, p =.473) and with MT (r = .246, p = .027). SQ was negatively correlated with MT (r = -.470, p = .000). PA (F1,58 = 10.939, p = .002, η2 = .159) and QS (F1,58 = 23.051, p = .000, η2 = .284) had a main effect on MT. The interaction of PA and QS had a buffering moderating effect on MT (F1,58 = 12.394, p = .001, η2 = .176). CONCLUSION: Evidence was found for all but the first hypothesis. PA-participants tending to be mentally tougher than the non-PA ones. Poor sleepers, on average, were mentally tougher than the good sleepers. The buffering effect indicates that the non-PA individuals with poor quality of sleep are the mentally toughest ones, followed by PA individuals with poor quality of sleep. Non-PA individuals with good quality of sleep present the lowest MT levels. In regards to developing mental toughness the authors suggest that: a) PA should be prescribed to good quality of sleepers and b) in poor quality sleepers focus should be placed on sleep before PA. Such findings may be useful to exercise and health-related practitioners when prescribing PA in a wide variety of individuals that report sleep quality issues in relation to MT capacities
Application of mineralogical, petrological and geochemical tools for evaluating the palaeohdrogeological evolution of the PADAMOT study sites
The role of Work Package (WP) 2 of the PADAMOT project – ‘Palaeohydrogeological Data
Measurements’ - has been to study late-stage fracture mineral and water samples from
groundwater systems in Spain, Sweden, United Kingdom and the Czech Republic, with the aim
of understanding the recent palaeohydrogeological evolution of these groundwater systems. In
particular, the project sought to develop and evaluate methods for obtaining information about
past groundwater evolution during the Quaternary (about the last 2 million years) by examining
how the late-stage mineralization might record mineralogical, petrographical and geochemical
evidence of how the groundwater system may have responded to past geological and
climatological changes.
Fracture-flow groundwater systems at six European sites were studied:
• Melechov Hill, in the Bohemian Massif of the Czech Republic: a shallow (0-100 m)
dilute groundwater flow system within the near-surface weathering zone in fractured
granitic rocks;
• Cloud Hill, in the English Midlands: a (~100 m) shallow dilute groundwater flow system
in fractured and dolomitized Carboniferous limestone;
• Los Ratones, in southwest Spain: an intermediate depth (0-500 m) dilute groundwater
flow system in fractured granitic rocks;
• Laxemar, in southeast Sweden: a deep (0-1000 m) groundwater flow system in fractured
granitic rocks. This is a complex groundwater system with potential recharge and
flushing by glacial, marine, lacustrine and freshwater during the Quaternary;
• Sellafield, northwest England: a deep (0-2000 m) groundwater flow system in fractured
Ordovician low-grade metamorphosed volcaniclastic rocks and discontinuous
Carboniferous Limestone, overlain by a Permo-Triassic sedimentary sequence with
fracture and matrix porosity. This is a complex coastal groundwater system with deep
hypersaline sedimentary basinal brines, and deep saline groundwaters in crystalline
basement rocks, overlain by a shallow freshwater aquifer system. The site was glaciated
several times during the Quaternary and may have been affected by recharge from glacial
meltwater;
• Dounreay, northeast Scotland: a deep (0-1400 m) groundwater flow system in fractured
Precambrian crystalline basement overlain by fractured Devonian sedimentary rocks.
This is within the coastal discharge area of a complex groundwater system, comprising
deep saline groundwater hosted in crystalline basement, overlain by a fracture-controlled
freshwater sedimentary aquifer system. Like Sellafield, this area experienced glaciation
and may potentially record the impact of glacial meltwater recharge.
In addition, a study has been made of two Quaternary sedimentary sequences in Andalusia in
southeastern Spain to provide a basis of estimating the palaeoclimatic history of the region that
could be used in any reconstruction of the palaeoclimatic history at the Los Ratones site:
• The Cúllar-Baza lacustrine sequence records information about precipitation and
palaeotemperature regimes, derived largely from the analysis of the stable isotope (δ18O
and δ13C) signatures from biogenic calcite (ostracod shells).
• The Padul Peat Bog sequence provided information on past vegetation cover and
palaeogroundwater inputs based on the study of fossil pollen and biomarkers as proxies
for past climate change.
Following on from the earlier EC 4th Framework EQUIP project, the focus of the PADAMOT
studies has been on calcite mineralization. Calcite has been identified as a late stage mineral, closely associated with hydraulically-conductive fractures in the present-day groundwater
systems at the Äspö-Laxemar, Sellafield, Dounreay and Cloud Hill sites. At Los Ratones and
Melechov sites late-stage mineralization is either absent or extremely scarce, and both the
quantity and fine crystal size of any late-stage fracture mineralization relevant to Quaternary
palaeohydrogeological investigations is difficult to work with. The results from the material
investigated during the PADAMOT studies indicate that the fracture fillings at these sites are
related to hydrothermal activity, and so do not have direct relevance as Quaternary indicators.
Neoformed calcite has not been found at these two sites at the present depth of the investigations.
Furthermore, the HCO3
- concentration in all the Los Ratones groundwaters is mainly controlled
by complex carbonate dissolution. The carbonate mineral saturation indices do not indicate
precipitation conditions, and this is consistent with the fact that neoformed calcite, ankerite or
dolomite have not been observed petrographically
Optical properties of structurally-relaxed Si/SiO superlattices: the role of bonding at interfaces
We have constructed microscopic, structurally-relaxed atomistic models of
Si/SiO superlattices. The structural distortion and oxidation-state
characteristics of the interface Si atoms are examined in detail. The role
played by the interface Si suboxides in raising the band gap and producing
dispersionless energy bands is established. The suboxide atoms are shown to
generate an abrupt interface layer about 1.60 \AA thick. Bandstructure and
optical-absorption calculations at the Fermi Golden rule level are used to
demonstrate that increasing confinement leads to (a) direct bandgaps (b) a blue
shift in the spectrum, and (c) an enhancement of the absorption intensity in
the threshold-energy region. Some aspects of this behaviour appear not only in
the symmetry direction associated with the superlattice axis, but also in the
orthogonal plane directions. We conclude that, in contrast to Si/Ge, Si/SiO
superlattices show clear optical enhancement and a shift of the optical
spectrum into the region useful for many opto-electronic applications.Comment: 11 pages, 10 figures (submitted to Phys. Rev. B
Modulation of the electroluminescence emission from ZnO/Si NCs/p-Si light-emitting devices via pulsed excitation
In this work, the electroluminescence (EL) emission of zinc oxide (ZnO)/Si nanocrystals (NCs)-based light-emitting devices was studied under pulsed electrical excitation. Both Si NCs and deep-level ZnO defects were found to contribute to the observed EL. Symmetric square voltage pulses (50-μs period) were found to notably enhance EL emission by about one order of magnitude. In addition, the control of the pulse parameters (accumulation and inversion times) was found to modify the emission lineshape, long inversion times (i.e., short accumulation times) suppressing ZnO defects contribution. The EL results were discussed in terms of the recombination dynamics taking place within the ZnO/Si NCs heterostructure, suggesting the excitation mechanism of the luminescent centers via a combination of electron impact, bipolar injection, and sequential carrier injection within their respective conduction regimes
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