936 research outputs found
Hypersonic flow analysis
While the zonal grid system of Transonic Navier-Stokes (TNS) provides excellent modeling of complex geometries, improved shock capturing, and a higher Mach number range will be required if flows about hypersonic aircraft are to be modeled accurately. A computational fluid dynamics (CFD) code, the Compressible Navier-Stokes (CNS), is under development to combine the required high Mach number capability with the existing TNS geometry capability. One of several candidate flow solvers for inclusion in the CNS is that of F3D. This upwinding flow solver promises improved shock capturing, and more accurate hypersonic solutions overall, compared to the solver currently used in TNS
Large-scale Bias and Efficient Generation of Initial Conditions for Non-Local Primordial Non-Gaussianity
We study the scale-dependence of halo bias in generic (non-local) primordial
non-Gaussian (PNG) initial conditions of the type motivated by inflation,
parametrized by an arbitrary quadratic kernel. We first show how to generate
non-local PNG initial conditions with minimal overhead compared to local PNG
models for a general class of primordial bispectra that can be written as
linear combinations of separable templates. We run cosmological simulations for
the local, and non-local equilateral and orthogonal models and present results
on the scale-dependence of halo bias. We also derive a general formula for the
Fourier-space bias using the peak-background split (PBS) in the context of the
excursion set approach to halos and discuss the difference and similarities
with the known corresponding result from local bias models. Our PBS bias
formula generalizes previous results in the literature to include non-Markovian
effects and non-universality of the mass function and are in better agreement
with measurements in numerical simulations than previous results for a variety
of halo masses, redshifts and halo definitions. We also derive for the first
time quadratic bias results for arbitrary non-local PNG, and show that
non-linear bias loops give small corrections at large-scales. The resulting
well-behaved perturbation theory paves the way to constrain non-local PNG from
measurements of the power spectrum and bispectrum in galaxy redshift surveys.Comment: 43 pages, 10 figures. v2: references added. 2LPT parallel code for
generating non-local PNG initial conditions available at
http://cosmo.nyu.edu/roman/2LP
Large-Scale Structure in Brane-Induced Gravity II. Numerical Simulations
We use N-body simulations to study the nonlinear structure formation in
brane-induced gravity, developing a new method that requires alternate use of
Fast Fourier Transforms and relaxation. This enables us to compute the
nonlinear matter power spectrum and bispectrum, the halo mass function, and the
halo bias. From the simulation results, we confirm the expectations based on
analytic arguments that the Vainshtein mechanism does operate as anticipated,
with the density power spectrum approaching that of standard gravity within a
modified background evolution in the nonlinear regime. The transition is very
broad and there is no well defined Vainshtein scale, but roughly this
corresponds to k_*~ 2 at redshift z=1 and k_*~ 1 at z=0. We checked that while
extrinsic curvature fluctuations go nonlinear, and the dynamics of the
brane-bending mode C receives important nonlinear corrections, this mode does
get suppressed compared to density perturbations, effectively decoupling from
the standard gravity sector. At the same time, there is no violation of the
weak field limit for metric perturbations associated with C. We find good
agreement between our measurements and the predictions for the nonlinear power
spectrum presented in paper I, that rely on a renormalization of the linear
spectrum due to nonlinearities in the modified gravity sector. A similar
prediction for the mass function shows the right trends. Our simulations also
confirm the induced change in the bispectrum configuration dependence predicted
in paper I.Comment: 19 pages, 13 figures. v2: corrected typos, added more simulations,
better test of predictions in large mass regime. v3: minor changes, published
versio
Thermo-optic noise in coated mirrors for high-precision optical measurements
Thermal fluctuations in the coatings used to make high-reflectors are
becoming significant noise sources in precision optical measurements and are
particularly relevant to advanced gravitational wave detectors. There are two
recognized sources of coating thermal noise, mechanical loss and thermal
dissipation. Thermal dissipation causes thermal fluctuations in the coating
which produce noise via the thermo-elastic and thermo-refractive mechanisms. We
treat these mechanisms coherently, give a correction for finite coating
thickness, and evaluate the implications for Advanced LIGO
Plasma lipoprotein subfraction concentrations are associated with lipid metabolism and age-related macular degeneration
10.1194/jlr.M073684Journal of Lipid Research5891785-179
Gravity and Large-Scale Non-local Bias
The relationship between galaxy and matter overdensities, bias, is most often
assumed to be local. This is however unstable under time evolution, we provide
proofs under several sets of assumptions. In the simplest model galaxies are
created locally and linearly biased at a single time, and subsequently move
with the matter (no velocity bias) conserving their comoving number density (no
merging). We show that, after this formation time, the bias becomes unavoidably
non-local and non-linear at large scales. We identify the non-local
gravitationally induced fields in which the galaxy overdensity can be expanded,
showing that they can be constructed out of the invariants of the deformation
tensor (Galileons). In addition, we show that this result persists if we
include an arbitrary evolution of the comoving number density of tracers. We
then include velocity bias, and show that new contributions appear, a dipole
field being the signature at second order. We test these predictions by
studying the dependence of halo overdensities in cells of fixed matter density:
measurements in simulations show that departures from the mean bias relation
are strongly correlated with the non-local gravitationally induced fields
identified by our formalism. The effects on non-local bias seen in the
simulations are most important for the most biased halos, as expected from our
predictions. The non-locality seen in the simulations is not fully captured by
assuming local bias in Lagrangian space. Accounting for these effects when
modeling galaxy bias is essential for correctly describing the dependence on
triangle shape of the galaxy bispectrum, and hence constraining cosmological
parameters and primordial non-Gaussianity. We show that using our formalism we
remove an important systematic in the determination of bias parameters from the
galaxy bispectrum, particularly for luminous galaxies. (abridged)Comment: 26 pages, 9 figures. v2: improved appendix
Desperate housewives: An analysis of the characterisations of female gamblers portrayed in gambling movies in Hong Kong
This article examines portrayals of female gamblers in recent Hong Kong movies. The authors report that the depiction of female gamblers is very different from that of male gamblers in the movies made in the same period. Whereas the male gamblers are pitching a lonely and desperate battle against the evil opponent, the female gamblers portrayed in the movies are housewives or small-time players who gamble only for their personal gain. A general negative overtone in portrayals of female gamblers was interpreted as a reflection of the traditional view that discourages women from gambling. The shift of gambling themes in the Hong Kong movies has been identified to reflect the most salient concerns among Hong Kong residents. Such changes are attributed to particular social and cultural changes in the community
Kinetics-based design of a flow platform for highly reproducible on demand synthesis of gold nanoparticles with controlled size between 50 and 150 nm and their application in SERS and PIERS sensing
Seeded-growth synthetic protocols enable precise control of particle size and shape, crucial for many sensing applications. However, scaling-up these syntheses in a reproducible way is challenging, as minimal variation in process parameters such as seed size, concentration or reaction temperature can significantly alter the final product. Flow reactors enable tight control in the process parameters and high reproducibility of the synthesis, representing a potential technology to perform seeded-growth syntheses in large scale. This work reports the design of a flow platform for the controlled synthesis of spherical gold nanoparticles with size up to 150nm through a seeded-growth approach, and their use in Surface Enhanced Raman Scattering (SERS) and Photoinduced Enhanced Raman Spectroscopy (PIERS). The particle growth kinetics were studied via in situ time-resolved UV–Vis spectroscopy. The spectroscopic data were fitted with a kinetic model, which was subsequently used for the design of the reactor. The kinetics-based design approach enabled fast translation of the growth synthesis in flow, eventually allowing the on demand flow synthesis of particles with controllable size, ranging from 50 to 150nm, with high reproducibility and full precursor conversion. The particles were tested for SERS and PIERS for different substrates, including warfare agents and biomolecules, with enhancement factors between 103 and 108 depending on the analyte, demonstrating their potential for detection of various analytes
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