5,453 research outputs found
Tunable superconducting critical temperature in ballistic hybrid structures with strong spin-orbit coupling
We present a theoretical description and numerical simulations of the
superconducting transition in hybrid structures including strong spin-orbit
interactions. The spin-orbit coupling is taken to be of Rashba type for
concreteness, and we allow for an arbitrary magnitude of the spin-orbit
strength as well as an arbitrary thickness of the spin-orbit coupled layer.
This allows us to make contact with the experimentally relevant case of
enhanced interfacial spin-orbit coupling via atomically thin heavy metal
layers. We consider both interfacial spin-orbit coupling induced by inversion
asymmetry in an S/F-junction, as well as in-plane spin-orbit coupling in the
ferromagnetic region of an S/F/S- and an S/F-structure. Both the pair
amplitudes, local density of states and critical temperature show dependency on
the Rashba strength and, importantly, the orientation of the exchange field. In
general, spin-orbit coupling increases the critical temperature of a proximity
system where a magnetic field is present, and enhances the superconducting gap
in the density of states. We perform a theoretical derivation which explains
these results by the appearance of long-ranged singlet correlations. Our
results suggest that in ballistic spin-orbit coupled superconducting
structures may be tuned by using only a single ferromagnetic layer.Comment: 14 pages, 14 figures. Published in PR
Uniqueness of Current Cosmic Acceleration
One of the strongest arguments against the cosmological constant as an
explanation of the current epoch of accelerated cosmic expansion is the
existence of an earlier, dynamical acceleration, i.e. inflation. We examine the
likelihood that acceleration is an occasional phenomenon, putting stringent
limits on the length of any accelerating epoch between recombination and the
recent acceleration; such an epoch must last less than 0.05 e-fold (at z>2) or
the matter power spectrum is modified by more than 20%.Comment: 6 pages, 5 figures; v2 corrected typo in Eq.
Measuring dark energy properties with 3D cosmic shear
We present parameter estimation forecasts for present and future 3D cosmic
shear surveys. We demonstrate that, in conjunction with results from cosmic
microwave background (CMB) experiments, the properties of dark energy can be
estimated with very high precision with large-scale, fully 3D weak lensing
surveys. In particular, a 5-band, 10,000 square degree ground-based survey to a
median redshift of zm=0.7 could achieve 1- marginal statistical errors,
in combination with the constraints expected from the CMB Planck Surveyor, of
w0=0.108 and wa=0.099 where we parameterize w by
w(a)=w0+wa(1-a) where a is the scale factor. Such a survey is achievable with a
wide-field camera on a 4 metre class telescope. The error on the value of w at
an intermediate pivot redshift of z=0.368 is constrained to
w(z=0.368)=0.0175. We compare and combine the 3D weak lensing
constraints with the cosmological and dark energy parameters measured from
planned Baryon Acoustic Oscillation (BAO) and supernova Type Ia experiments,
and find that 3D weak lensing significantly improves the marginalized errors. A
combination of 3D weak lensing, CMB and BAO experiments could achieve
w0=0.037 and wa=0.099. Fully 3D weak shear analysis avoids the
loss of information inherent in tomographic binning, and we show that the
sensitivity to systematic errors is much less. In conjunction with the fact
that the physics of lensing is very soundly based, this analysis demonstrates
that deep, wide-angle 3D weak lensing surveys are extremely promising for
measuring dark energy properties.Comment: 18 pages, 16 figures. Accepted to MNRAS. Figures now in grayscale.
Further discussions on non-Gaussianity and photometric redshift errors. Some
references adde
Maskierte Mastoiditis beim Säugling
Zusammenfassung: Wir berichten über den seltenen Fall einer okkulten Mastoiditis bei einem 5Monate alten, voll gestillten Säugling, welcher außer einer retroaurikulären, progredienten Schwellung keinerlei Krankheitssymptome zeigte. Ungewöhnlich sind der frühe Beginn der Erkrankung, da die Pneumatisation des Mastoids erst nach der Geburt einsetzt und der Umstand, dass der maternale Schutz über die Muttermilch offenbar nicht ausreichend war. Die Diagnose erfolgte klinisch durch die abstehende Ohrmuschel und radiologisch mittels Computertomographie. Die operative Drainage bestätigte eine ausgedehnte Abszedierung durch einen Pneumokokkeninfek
Modified Gravity Away from a CDM Background
Within the effective field theory approach to cosmic acceleration, the
background expansion can be specified separately from the gravitational
modifications. We explore the impact of modified gravity in a background
different from a cosmological constant plus cold dark matter (CDM) on
the stability and cosmological observables, including covariance between
gravity and expansion parameters. In No Slip Gravity the more general
background allows more gravitational freedom, including both positive and
negative Planck mass running. We examine the effects on cosmic structure
growth, as well as showing that a viable positive integrated Sachs-Wolfe effect
crosscorrelation easily arises from this modified gravity theory. Using current
data we constrain parameters with a Monte Carlo analysis, finding a maximum
running . We provide the modified {\tt hi\_class} code
publicly on GitHub, now enabling computation and inclusion of the redshift
space distortion observable as well as the No Slip Gravity
modifications.Comment: 14 pages, 13 figures. Matches published version in JCAP, LCDM
discussion adde
Fingerprinting dark energy
Dark energy perturbations are normally either neglected or else included in a
purely numerical way, obscuring their dependence on underlying parameters like
the equation of state or the sound speed. However, while many different
explanations for the dark energy can have the same equation of state, they
usually differ in their perturbations so that these provide a fingerprint for
distinguishing between different models with the same equation of state. In
this paper we derive simple yet accurate approximations that are able to
characterize a specific class of models (encompassing most scalar-field models)
which is often generically called "dark energy". We then use the approximate
solutions to look at the impact of the dark energy perturbations on the dark
matter power spectrum and on the integrated Sachs-Wolfe effect in the cosmic
microwave background radiation.Comment: 11 pages, 5 figures, minor changes to match published versio
Probabilistic modeling of one dimensional water movement and leaching from highway embankments containing secondary materials
Predictive methods for contaminant release from virgin and secondary road construction materials are important for evaluating potential long-term soil and groundwater contamination from highways. The objective of this research was to describe the field hydrology in a highway embankment and to investigate leaching under unsaturated conditions by use of a contaminant fate and transport model. The HYDRUS2D code was used to solve the Richards equation and the advection–dispersion equation with retardation. Water flow in a Minnesota highway embankment was successfully modeled in one dimension for several rain events after Bayesian calibration of the hydraulic parameters against water content data at a point 0.32 m from the surface of the embankment. The hypothetical leaching of Cadmium from coal fly ash was probabilistically simulated in a scenario where the top 0.50 m of the embankment was replaced by coal fly ash. Simulation results were compared to the percolation equation method where the solubility is multiplied by the liquid-to-solid ratio to estimate total release. If a low solubility value is used for Cadmium, the release estimates obtained using the percolation/equilibrium model are close to those predicted from HYDRUS2D simulations (10–4–10–2 mg Cd/kg ash). If high solubility is used, the percolation equation over predicts the actual release (0.1–1.0 mg Cd/kg ash). At the 90th percentile of uncertainty, the 10-year liquid-to-solid ratio for the coal fly ash embankment was 9.48 L/kg, and the fraction of precipitation that infiltrated the coal fly ash embankment was 92%. Probabilistic modeling with HYDRUS2D appears to be a promising realistic approach to predicting field hydrology and subsequent leaching in embankments
Spin-Transfer Torque and Magnetoresistance in Superconducting Spin-Valves
We study the spin-transfer torque and magnetoresistance of a
ferromagnetsuperconductorferromagnet spin-valve, allowing for an
arbitrary magnetization misorientation and treating both s-wave and d-wave
symmetries of the superconductor. We take fully into account Andreev reflection
and also the spin-triplet correlations that are generated when the
magnetizations are non-collinear. It is found that the torque and
magnetoresistance are both strongly enhanced when topological zero-energy
states are present at the interfaces, which is the case for d-wave
superconductors with a crystallographic orientation of [110] relative to the
interface (-wave symmetry). Moreover, we find that the
magnetoresistance displays a strong oscillatory and non-monotonous behavior as
a function of where and are the interlayer width of the
superconducting region and the superconducting coherence length, respectively.
This feature is also attributed to the crossover from layers of size to layers of size , where the contribution to transport from
zero-energy states gradually vanishes.Comment: 10 pages, 7 figures. Accepted for publication in Phys. Rev.
Cosmic Growth History and Expansion History
The cosmic expansion history tests the dynamics of the global evolution of
the universe and its energy density contents, while the cosmic growth history
tests the evolution of the inhomogeneous part of the energy density. Precision
comparison of the two histories can distinguish the nature of the physics
responsible for the accelerating cosmic expansion: an additional smooth
component - dark energy - or a modification of the gravitational field
equations. With the aid of a new fitting formula for linear perturbation growth
accurate to 0.05-0.2%, we separate out the growth dependence on the expansion
history and introduce a new growth index parameter \gamma that quantifies the
gravitational modification.Comment: 8 pages, 3 figures; minor changes to match version accepted to PR
A forgotten facial nerve tumour: granular cell tumour of the parotid and its implications for treatment
We present a rare case of a facial nerve granular cell tumour in the right parotid gland, in a 10-year-old boy. A parotid or neurogenic tumour was suspected, based on magnetic resonance imaging. Intra-operatively, strong adhesions to surrounding structures were found, and a midfacial nerve branch had to be sacrificed for complete tumour removal. Recent reports verify that granular cell tumours arise from Schwann cells of peripheral nerve branches. The rarity of this tumour within the parotid gland, its origin from peripheral nerves, its sometimes misleading imaging characteristics, and its rare presentation with facial weakness and pain all have considerable implications on the surgical strategy and pre-operative counselling. Fine needle aspiration cytology may confirm the neurogenic origin of this lesion. When resecting the tumour, the surgeon must anticipate strong adherence to the facial nerve and be prepared to graft, or sacrifice, certain branches of this nerv
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