24,990 research outputs found
The Short-period Drag Perturbations of the Orbits of Artificial Satellites
Short-period perturbation computation of artificial satellite orbits caused by atmospheric dra
Neutron die-away experiment for remote analysis of the surface of the moon and the planets, phase 3
Continuing work on the two die-away measurements proposed to be made in the combined pulsed neutron experiment (CPNE) for analysis of lunar and planetary surfaces is described. This report documents research done during Phase 3. A general exposition of data analysis by the least-squares method and the related problem of the prediction of variance is given. A data analysis procedure for epithermal die-away data has been formulated. In order to facilitate the analysis, the number of independent material variables has been reduced to two: the hydrogen density and an effective oxygen density, the latter being determined uniquely from the nonhydrogeneous elemental composition. Justification for this reduction in the number of variables is based on a set of 27 new theoretical calculations. Work is described related to experimental calibration of the epithermal die-away measurement. An interim data analysis technique based solely on theoretical calculations seems to be adequate and will be used for future CPNE field tests
Theory of Local Dynamical Magnetic Susceptibilities from the Korringa-Kohn-Rostoker Green Function Method
Within the framework of time-dependent density functional theory combined
with the Korringa-Kohn-Rostoker Green function formalism, we present a real
space methodology to investigate dynamical magnetic excitations from
first-principles. We set forth a scheme which enables one to deduce the correct
effective Coulomb potential needed to preserve the spin-invariance signature in
the dynamical susceptibilities, i.e. the Goldstone mode. We use our approach to
explore the spin dynamics of 3d adatoms and different dimers deposited on a
Cu(001) with emphasis on their decay to particle-hole pairs.Comment: 32 pages (preprint), 6 figures, one tabl
In silico estimates of the free energy rates in growing tumor spheroids
The physics of solid tumor growth can be considered at three distinct size
scales: the tumor scale, the cell-extracellular matrix (ECM) scale and the
sub-cellular scale. In this paper we consider the tumor scale in the interest
of eventually developing a system-level understanding of the progression of
cancer. At this scale, cell populations and chemical species are best treated
as concentration fields that vary with time and space. The cells have
chemo-mechanical interactions with each other and with the ECM, consume glucose
and oxygen that are transported through the tumor, and create chemical
byproducts. We present a continuum mathematical model for the biochemical
dynamics and mechanics that govern tumor growth. The biochemical dynamics and
mechanics also engender free energy changes that serve as universal measures
for comparison of these processes. Within our mathematical framework we
therefore consider the free energy inequality, which arises from the first and
second laws of thermodynamics. With the model we compute preliminary estimates
of the free energy rates of a growing tumor in its pre-vascular stage by using
currently available data from single cells and multicellular tumor spheroids.Comment: 27 pages with 5 figures and 2 tables. Figures and tables appear at
the end of the pape
Causal vs. Noncausal Description of Nonlinear Wave Mixing; Resolving the Damping-Sign Controversy
Frequency-domain nonlinear wave mixing processes may be described either
using response functions whereby the signal is generated after all interactions
with the incoming fields, or in terms of scattering amplitudes where all fields
are treated symetrically with no specific time ordering. Closed Green's
function expressions derived for the two types of signals have different
analytical properties. The recent controversy regarding the sign of radiative
damping in the linear (Kramers Heisenberg) formula is put in a broader context
Spin Orbit Coupling and Spin Waves in Ultrathin Ferromagnets: The Spin Wave Rashba Effect
We present theoretical studies of the influence of spin orbit coupling on the
spin wave excitations of the Fe monolayer and bilayer on the W(110) surface.
The Dzyaloshinskii-Moriya interaction is active in such films, by virtue of the
absence of reflection symmetry in the plane of the film. When the magnetization
is in plane, this leads to a linear term in the spin wave dispersion relation
for propagation across the magnetization. The dispersion relation thus assumes
a form similar to that of an energy band of an electron trapped on a
semiconductor surfaces with Rashba coupling active. We also show SPEELS
response functions that illustrate the role of spin orbit coupling in such
measurements. In addition to the modifications of the dispersion relations for
spin waves, the presence of spin orbit coupling in the W substrate leads to a
substantial increase in the linewidth of the spin wave modes. The formalism we
have developed applies to a wide range of systems, and the particular system
explored in the numerical calculations provides us with an illustration of
phenomena which will be present in other ultrathin ferromagnet/substrate
combinations
Evaluation of diffusive gradients in thin-films using a Diphonix® resin for monitoring dissolved uranium in natural waters
Commercially available Diphonix® resin (TrisKem International) was evaluated as a receiving phase for use with the diffusive gradients in thin-films (DGT) passive sampler for measuring uranium. This resin has a high partition coefficient for actinides and is used in the nuclear industry. Other resins used as receiving phases with DGT for measuring uranium have been prone to saturation and significant chemical interferences. The performance of the device was evaluated in the laboratory and in field trials. In laboratory experiments uptake of uranium (all 100% efficiency) by the resin was unaffected by varying pH (4–9), ionic strength (0.01–1.00 M, as NaNO3) and varying aqueous concentrations of Ca2+ (100–500 mg L−1) and HCO3− (100–500 mg L−1). Due to the high partition coefficient of Diphonex®, several elution techniques for uranium were evaluated. The optimal eluent mixture was 1 M NaOH/1 M H2O2, eluting 90% of the uranium from the resin. Uptake of uranium was linear (R2 = 0.99) over time (5 days) in laboratory experiments using artificial freshwater showing no saturation effects of the resin. In field deployments (River Lambourn, UK) the devices quantitatively accumulated uranium for up to 7 days. In both studies uptake of uranium matched that theoretically predicted for the DGT. Similar experiments in seawater did not follow the DGT theoretical uptake and the Diphonix® appeared to be capacity limited and also affected by matrix interferences. Isotopes of uranium (U235/U238) were measured in both environments with a precision and accuracy of 1.6–2.2% and 1.2–1.4%, respectively. This initial study shows the potential of using Diphonix®-DGT for monitoring of uranium in the aquatic environment
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Bump start needed: linking guidelines, policy and practice in promoting physical activity during and beyond pregnancy
First paragraph: There is compelling evidence that regular physical activity (PA) during pregnancy benefits both mother and baby.1 2 Notably, physical and psychological benefits are evident in the literature, such as marked reductions in the development of gestational diabetes and hypertensive disorders, alongside improvements in depressive symptoms and cardiorespiratory fitness.1 2 The evidence base has been reflected by recent policy initiatives, for example, in 2017 (relaunched in 2019), the UK‘s chief medical officers (CMOs) published PA guidelines for pregnant women, which made substantial strides in unifying and translating the evidence into recommendations.1 The CMO guidelines are aimed at supporting health professionals to provide consistent, evidence-based PA messages to women throughout pregnancy.1 Recently, the Chartered Institute for the Management of Sport and Physical Activity have updated their professional standards for working with antenatal and postnatal clients to align with these CMO guidelines.3 However, not all women have access to professionals with this level of expertise and training, potentially limiting the impact of the CMO guidelines
Is there a link between treatments with exogenous corticosteroids and dog behaviour problems?
Possible side effects of exogenous corticosteroids have been described in both humans and laboratory animals, with recent studies highlighting this issue in dogs. In this paper the behaviour of 345 dogs drawn from the caseload of a behaviour clinic based in the north of Italy between February 2012 and November 2014 were analysed. Possible relationships between dogs that received treatment with corticosteroids versus dogs that received treatment with drugs other than corticosteroids and positive or negative affective states, aggression towards people, other behaviour problems apart from aggression, occurrence of severe bites, and prescription of psychoactive drugs were initially assessed using a Pearson's chi-squared test. Regression analysis was then performed in order to evaluate the best predictors of the investigated items. The goal of this retrospective survey was to investigate possible relationships between the affective states associated with the behavioural complaint of dogs and their previous history of treatment with corticosteroids. Results showed that a history of corticosteroid treatment was a significant predictor of a range of behaviour problems associated with negative affective state, but this result may be confounded by age-related effects
Carbon nanotube: a low-loss spin-current waveguide
We demonstrate with a quantum-mechanical approach that carbon nanotubes are
excellent spin-current waveguides and are able to carry information stored in a
precessing magnetic moment for long distances with very little dispersion and
with tunable degrees of attenuation. Pulsed magnetic excitations are predicted
to travel with the nanotube Fermi velocity and are able to induce similar
excitations in remote locations. Such an efficient way of transporting magnetic
information suggests that nanotubes are promising candidates for memory devices
with fast magnetization switchings
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