230 research outputs found
Void Scaling and Void Profiles in CDM Models
An analysis of voids using cosmological N-body simulations of cold dark
matter models is presented. It employs a robust statistics of voids, that was
recently applied to discriminate between data from the Las Campanas Redshift
Survey and different cosmological models. Here we extend the analysis to 3D and
show that typical void sizes D in the simulated galaxy samples obey a linear
scaling relation with the mean galaxy separation lambda: D=D_0+nu*lambda. It
has the same slope nu as in 2D, but with lower absolute void sizes. The scaling
relation is able to discriminate between different cosmologies. For the best
standard LCDM model, the slope of the scaling relation for voids in the dark
matter halos is too steep as compared to the LCRS, with too small void sizes
for well sampled data sets. The scaling relation of voids for dark matter halos
with increasing mass thresholds is even steeper than that for samples of
galaxy-mass halos where we sparse sample the data. This shows the stronger
clustering of more massive halos. Further, we find a correlation of the void
size to its central and environmental average density. While there is little
sign of an evolution in samples of small DM halos with v_{circ} ~ 90 km/s,
voids in halos with circular velocity over 200 km/s are larger at redshift z =
3 due to the smaller halo number density. The flow of dark matter from the
underdense to overdense regions in an early established network of large scale
structure is also imprinted in the evolution of the density profiles with a
relative density decrease in void centers by 0.18 per redshift unit between z=3
and z=0.Comment: 12 pages, 9 eps figures, submitted to MNRA
Voids in the LCRS versus CDM Models
We have analyzed the distribution of void sizes in the two-dimensional slices
of the Las Campanas Redshift Survey (LCRS). Fourteen volume-limited subsamples
were extracted from the six slices to cover a large part of the survey and to
test the robustness of the results against cosmic variance. Thirteen samples
were randomly culled to produce homogeneously selected samples. We then studied
the relationship between the cumulative area covered by voids and the void size
as a property of the void hierarchy. We find that the distribution of void
sizes scales with the mean galaxy separation, . In particular, we find
that the size of voids covering half of the area is given by D_{med} \approx
\lambda + (12\pm3) \h^{-2}Mpc. Next, by employing an environmental density
threshold criterion to identify mock galaxies, we were able to extend this
analysis to mock samples from dynamical -body simulations of Cold Dark
Matter (CDM) models. To reproduce the observed void statistics, overdensity
thresholds of are necessary. We have compared
standard (SCDM), open (OCDM), vacuum energy dominated (CDM), and
broken scale invariant CDM models (BCDM): we find that both the void coverage
distribution and the two-point correlation function provide important and
complementary information on the large-scale matter distribution. The
dependence of the void statistics on the threshold criterion for the mock
galaxy indentification shows that the galaxy biasing is more crucial for the
void size distribution than are differences between the cosmological models.Comment: 10 pages, 8 eps figures, submitted to MNRA
Fracture in Three-Dimensional Fuse Networks
We report on large scale numerical simulations of fracture surfaces using
random fuse networks for two very different disorders. There are some
properties and exponents that are different for the two distributions, but
others, notably the roughness exponents, seem universal. For the universal
roughness exponent we found a value of zeta = 0.62 +/- 0.05. In contrast to
what is observed in two dimensions, this value is lower than that reported in
experimental studies of brittle fractures, and rules out the minimal energy
surface exponent, 0.41 +/- 0.01.Comment: 4 pages, RevTeX, 5 figures, Postscrip
Elasticity of Gaussian and nearly-Gaussian phantom networks
We study the elastic properties of phantom networks of Gaussian and
nearly-Gaussian springs. We show that the stress tensor of a Gaussian network
coincides with the conductivity tensor of an equivalent resistor network, while
its elastic constants vanish. We use a perturbation theory to analyze the
elastic behavior of networks of slightly non-Gaussian springs. We show that the
elastic constants of phantom percolation networks of nearly-Gaussian springs
have a power low dependence on the distance of the system from the percolation
threshold, and derive bounds on the exponents.Comment: submitted to Phys. Rev. E, 10 pages, 1 figur
Removing orientation-induced localization biases in single-molecule microscopy using a broadband metasurface mask
Nanoscale localization of single molecules is a crucial function in several advanced microscopy techniques, including single-molecule tracking and wide-field super-resolution imaging. Until now, a central consideration of such techniques is how to optimize the precision of molecular localization. However, as these methods continue to push towards the nanometre size scale, an increasingly important concern is the localization accuracy. In particular, single fluorescent molecules emit with an anisotropic radiation pattern of an oscillating electric dipole, which can cause significant localization biases using common estimators. Here we present the theory and experimental demonstration of a solution to this problem based on azimuthal filtering in the Fourier plane of the microscope. We do so using a high-efficiency dielectric metasurface polarization/phase device composed of nanoposts with subwavelength spacing. The method is demonstrated both on fluorophores embedded in a polymer matrix and in dL5 protein complexes that bind malachite green
Wavefront shaping with disorder-engineered metasurfaces
Recently, wavefront shaping with disordered media has demonstrated optical manipulation capabilities beyond those of conventional optics, including extended volume, aberration-free focusing and subwavelength focusing. However, translating these capabilities to useful applications has remained challenging as the inputâoutput characteristics of the disordered media (P variables) need to be exhaustively determined via O(P) measurements. Here, we propose a paradigm shift where the disorder is specifically designed so its exact inputâoutput characteristics are known a priori and can be used with only a few alignment steps. We implement this concept with a disorder-engineered metasurface, which exhibits additional unique features for wavefront shaping such as a large optical memory effect range in combination with a wide angular scattering range, excellent stability, and a tailorable angular scattering profile. Using this designed metasurface with wavefront shaping, we demonstrate high numerical aperture (NAâ>â0.5) focusing and fluorescence imaging with an estimated ~2.2âĂâ10^8 addressable points in an ~8âmm field of view
Fracture of disordered solids in compression as a critical phenomenon: I. Statistical mechanics formalism
This is the first of a series of three articles that treats fracture
localization as a critical phenomenon. This first article establishes a
statistical mechanics based on ensemble averages when fluctuations through time
play no role in defining the ensemble. Ensembles are obtained by dividing a
huge rock sample into many mesoscopic volumes. Because rocks are a disordered
collection of grains in cohesive contact, we expect that once shear strain is
applied and cracks begin to arrive in the system, the mesoscopic volumes will
have a wide distribution of different crack states. These mesoscopic volumes
are the members of our ensembles. We determine the probability of observing a
mesoscopic volume to be in a given crack state by maximizing Shannon's measure
of the emergent crack disorder subject to constraints coming from the
energy-balance of brittle fracture. The laws of thermodynamics, the partition
function, and the quantification of temperature are obtained for such cracking
systems.Comment: 11 pages, 2 figure
Visible Wavelength Color Filters using Dielectric Subwavelength Gratings for Backside-illuminated CMOS Image Sensor Technologies
We report transmissive color filters based on subwavelength dielectric gratings that can replace conventional dye-based color filters used in backside-illuminated CMOS image sensor (BSI CIS) technologies. The filters are patterned in an 80-nm-thick poly-silicon film on a 115-nm-thick SiO_2 spacer layer. They are optimized for operating at the primary RGB colors, exhibit peak transmittance of 60-80%, and an almost insensitive response over a ±20° angular range. This technology enables shrinking of the pixel sizes down to near a micrometer
An essential role for complement C5a in the pathogenesis of septic cardiac dysfunction
Defective cardiac function during sepsis has been referred to as âcardiomyopathy of sepsis.â It is known that sepsis leads to intensive activation of the complement system. In the current study, cardiac function and cardiomyocyte contractility have been evaluated in rats after cecal ligation and puncture (CLP). Significant reductions in left ventricular pressures occurred in vivo and in cardiomyocyte contractility in vitro. These defects were prevented in CLP rats given blocking antibody to C5a. Both mRNA and protein for the C5a receptor (C5aR) were constitutively expressed on cardiomyocytes; both increased as a function of time after CLP. In vitro addition of recombinant rat C5a induced dramatic contractile dysfunction in both sham and CLP cardiomyocytes, but to a consistently greater degree in cells from CLP animals. These data suggest that CLP induces C5aR on cardiomyocytes and that in vivo generation of C5a causes C5aâC5aR interaction, causing dysfunction of cardiomyocytes, resulting in compromise of cardiac performance
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