40,471 research outputs found
Thermal alteration of organic matter in recent marine sediments. 1: Pigments
Sediment from Tanner Basin, the outer continental shelf off Southern California, was analyzed for photosynthetic pigments and their derivatives, namely carotenes and chlorins. Samples of the sediment were also exposed to raised temperatures (65, 100, 150 C) for various periods of time (1 week, 1 month, 2 months). Analysis of the heat-treated sediment revealed the presence of alpha-ionene and 2,6-dimethylnapthalene, thermal degradation products of Betacarotente. Chlorins were converted to nickel porphyrins of both DPEP and etio series. Possible mechanisms of these transformations are presented
The development of absorptive capacity-based innovation in a construction SME
Traditionally, construction has been a transaction-oriented industry. However, it is changing from the design-bid-build process into a business based on innovation capability and performance management, in which contracts are awarded on the basis of factors such as knowledge, intellectual capital and skills. This change presents a challenge to construction-sector SMEs with scarce resources, which must find ways to innovate based on those attributes to ensure their future competitiveness. This paper explores how dynamic capability, using an absorptive capacity framework in response to these challenges, has been developed in a construction-based SME. The paper also contributes to the literature on absorptive capacity and innovation by showing how the construct can be operationalized within an organization. The company studied formed a Knowledge Transfer Partnership using action research over a two-year period with a local university. The aim was to increase its absorptive capacity and hence its ability to meet the changing market challenges. The findings show that absorptive capacity can be operationalized into a change management approach for improving capability-based competitiveness. Moreover, it is important for absorptive capacity constructs and language to be contextualized within a given organizational setting (as in the case of the construction-based SME in the present study)
Timing the Nearby Isolated Neutron Star RX J1856.5-3754
RX J1856.5-3754 is the X-ray brightest among the nearby isolated neutron
stars. Its X-ray spectrum is thermal, and is reproduced remarkably well by a
black-body, but its interpretation has remained puzzling. One reason is that
the source did not exhibit pulsations, and hence a magnetic field
strength--vital input to atmosphere models--could not be estimated. Recently,
however, very weak pulsations were discovered. Here, we analyze these in
detail, using all available data from the XMM-Newton and Chandra X-ray
observatories. From frequency measurements, we set a 2-sigma upper limit to the
frequency derivative of \dot\nu<1.3e-14 Hz/s. Trying possible phase-connected
timing solutions, we find that one solution is far more likely than the others,
and we infer a most probable value of \dot\nu=(-5.98+/-0.14)e-16 Hz/s. The
inferred magnetic field strength is 1.5e13 G, comparable to what was found for
similar neutron stars. From models, the field seems too strong to be consistent
with the absence of spectral features for non-condensed atmospheres. It is
sufficiently strong, however, that the surface could be condensed, but only if
it is consists of heavy elements like iron. Our measurements imply a
characteristic age of about 4 Myr. This is longer than the cooling and
kinematic ages, as was found for similar objects, but at almost a factor ten,
the discrepancy is more extreme. A puzzle raised by our measurement is that the
implied rotational energy loss rate of about 3e30 erg/s is orders of magnitude
smaller than what was inferred from the H-alpha nebula surrounding the source.Comment: 4 pages, 2 figures, 2 tables; accepted for publication in
Astrophysical Journal (Letters
The continued spectral and temporal evolution of RX J0720.4-3125
RX J0720.4-3125 is the most peculiar object among a group of seven isolated
X-ray pulsars (the so-called "Magnificent Seven"), since it shows long-term
variations of its spectral and temporal properties on time scales of years.
This behaviour was explained by different authors either by free precession
(with a seven or fourteen years period) or possibly a glitch that occurred
around .
We analysed our most recent XMM-Newton and Chandra observations in order to
further monitor the behaviour of this neutron star. With the new data sets, the
timing behaviour of RX J0720.4-3125 suggests a single (sudden) event (e.g. a
glitch) rather than a cyclic pattern as expected by free precession. The
spectral parameters changed significantly around the proposed glitch time, but
more gradual variations occurred already before the (putative) event. Since
the spectra indicate a very slow cooling by
2 eV over 7 years.Comment: seven pages, three figures, three tables; accepted by MNRA
Inequalities for low-energy symmetric nuclear matter
Using effective field theory we prove inequalities for the correlations of
two-nucleon operators in low-energy symmetric nuclear matter. For physical
values of operator coefficients in the effective Lagrangian, the S = 1, I = 0
channel correlations must have the lowest energy and longest correlation length
in the two-nucleon sector. This result is valid at nonzero density and
temperature.Comment: 9 page
New Limits on Radio Emission from X-ray Dim Isolated Neutron Stars
We have carried out a search for radio emission at 820 MHz from six X-ray dim
isolated neutron stars with the Robert C. Byrd Green Bank Radio Telescope. No
transient or pulsed emission was found using fast folding, fast Fourier
transform, and single-pulse searches. The corresponding flux limits are about
0.01 mJy for pulsed emission, depending on the integration time for the
particular source and assuming a duty cycle of 2%, and 20 mJy for single
dispersed pulses. These are the most sensitive limits to date on radio emission
from X-ray dim isolated neutron stars. There is no evidence for isolated radio
pulses, as seen in a class of neutron stars known as rotating radio transients.
Our results imply that either the radio luminosities of these objects are lower
than those of any known radio pulsars, or they could simply be long-period
nearby radio pulsars with high magnetic fields beaming away from the Earth. To
test the latter possibility, we would need around 40 similar sources to provide
a 1 sigma probability of at least one of them beaming toward us. We also give a
detailed description of our implementation of the Fast Folding Algorithm.Comment: 16 pages, 8 figures, 3 tables, accepted to Ap
Brownian Motion Model of Quantization Ambiguity and Universality in Chaotic Systems
We examine spectral equilibration of quantum chaotic spectra to universal
statistics, in the context of the Brownian motion model. Two competing time
scales, proportional and inversely proportional to the classical relaxation
time, jointly govern the equilibration process. Multiplicity of quantum systems
having the same semiclassical limit is not sufficient to obtain equilibration
of any spectral modes in two-dimensional systems, while in three-dimensional
systems equilibration for some spectral modes is possible if the classical
relaxation rate is slow. Connections are made with upper bounds on
semiclassical accuracy and with fidelity decay in the presence of a weak
perturbation.Comment: 13 pages, 6 figures, submitted to Phys Rev
Eigenstate Structure in Graphs and Disordered Lattices
We study wave function structure for quantum graphs in the chaotic and
disordered regime, using measures such as the wave function intensity
distribution and the inverse participation ratio. The result is much less
ergodicity than expected from random matrix theory, even though the spectral
statistics are in agreement with random matrix predictions. Instead, analytical
calculations based on short-time semiclassical behavior correctly describe the
eigenstate structure.Comment: 4 pages, including 2 figure
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