1,821 research outputs found
Sparse sampling, galaxy bias, and voids
To study the impact of sparsity and galaxy bias on void statistics, we use a
single large-volume, high-resolution N-body simulation to compare voids in
multiple levels of subsampled dark matter, halo populations, and mock galaxies
from a Halo Occupation Distribution model tuned to different galaxy survey
densities. We focus our comparison on three key observational statistics:
number functions, ellipticity distributions, and radial density profiles. We
use the hierarchical tree structure of voids to interpret the impacts of
sampling density and galaxy bias, and theoretical and empirical functions to
describe the statistics in all our sample populations. We are able to make
simple adjustments to theoretical expectations to offer prescriptions for
translating from analytics to the void properties measured in realistic
observations. We find that sampling density has a much larger effect on void
sizes than galaxy bias. At lower tracer density, small voids disappear and the
remaining voids are larger, more spherical, and have slightly steeper profiles.
When a proper lower mass threshold is chosen, voids in halo distributions
largely mimic those found in galaxy populations, except for ellipticities,
where galaxy bias leads to higher values. We use the void density profile of
Hamaus et al. (2014) to show that voids follow a self-similar and universal
trend, allowing simple translations between voids studied in dark matter and
voids identified in galaxy surveys. We have added the mock void catalogs used
in this work to the Public Cosmic Void Catalog at http://www.cosmicvoids.net.Comment: 11 pages, 7 figures, MNRAS accepted. Minor changes from previous
version. Public catalog available at http://www.cosmicvoids.ne
Conduction spectroscopy of a proximity induced superconducting topological insulator
The combination of superconductivity and the helical spin-momentum locking at
the surface state of a topological insulator (TI) has been predicted to give
rise to p-wave superconductivity and Majorana bound states. The
superconductivity can be induced by the proximity effect of a an s-wave
superconductor (S) into the TI. To probe the superconducting correlations
inside the TI, dI/dV spectroscopy has been performed across such S-TI
interfaces. Both the alloyed BiSbTeSe and the
stoichiometric BiSbTeSe have been used as three dimensional TI. In the case
of BiSbTeSe, the presence of disorder induced
electron-electron interactions can give rise to an additional zero-bias
resistance peak. For the stoichiometric BiSbTeSe with less disorder, tunnel
barriers were employed in order to enhance the signal from the interface. The
general observations in the spectra of a large variety of samples are
conductance dips at the induced gap voltage, combined with an increased sub-gap
conductance, consistent with p-wave predictions. The induced gap voltage is
typically smaller than the gap of the Nb superconducting electrode, especially
in the presence of an intentional tunnel barrier. Additional uncovered
spectroscopic features are oscillations that are linearly spaced in energy, as
well as a possible second order parameter component.Comment: Semiconductor Science and Technology; Special Issue on Hybrid Quantum
Materials and Device
Surface Enhanced Raman Spectroscopy of Organic Molecules on Magnetite (Fe_3O_4) Nanoparticles
Surface-enhanced Raman spectroscopy (SERS) of species bound to environmentally relevant oxide nanoparticles is largely limited to organic molecules structurally related to catechol that facilitate a chemical enhancement of the Raman signal. Here, we report that magnetite (Fe_3O_4) nanoparticles provide a SERS signal from oxalic acid and cysteine via an electric field enhancement. Magnetite thus likely provides an oxide substrate for SERS study of any adsorbed organic molecule. This substrate combines benefits from both metal-based and chemical SERS by providing an oxide surface for studies of environmentally and catalytically relevant detailed chemical bonding information with fewer restrictions of molecular structure or binding mechanisms. Therefore, the magnetite-based SERS demonstrated here provides a new approach to establishing the surface interactions of environmentally relevant organic ligands and mineral surfaces
Linear optical elements based on cooperative subwavelength emitter arrays
We describe applications of two-dimensional subwavelength quantum emitter
arrays as efficient optical elements in the linear regime. For normally
incident light, the cooperative optical response, stemming from emitter-emitter
dipole exchanges, allows the control of the array's transmission, its resonance
frequency, and bandwidth. Operations on fully polarized incident light, such as
generic linear and circular polarizers as well as phase retarders can be
engineered and described in terms of Jones matrices. Our analytical approach
and accompanying numerical simulations identify optimal regimes for such
operations and reveal the importance of adjusting the array geometry and of the
careful tuning of the external magnetic fields amplitude and direction.Comment: 12 pages main text + 4 Appendix, 8 figure
InSAR Meteorology: High-Resolution Geodetic Data Can Increase Atmospheric Predictability
AbstractThe present study assesses the added value of high‐resolution maps of precipitable water vapor, computed from synthetic aperture radar interferograms , in short‐range atmospheric predictability. A large set of images, in different weather conditions, produced by Sentinel‐1A in a very well monitored region near the Appalachian Mountains, are assimilated by the Weather Research and Forecast (WRF) model. Results covering more than 2 years of operation indicate a consistent improvement of the water vapor predictability up to a range comparable with the transit time of the air mass in the synthetic aperture radar interferograms footprint, an overall improvement in the forecast of different precipitation events, and better representation of the spatial distribution of precipitation. This result highlights the significant potential for increasing short‐range atmospheric predictability from improved high‐resolution precipitable water vapor initial data, which can be obtained from new high‐resolution all‐weather microwave sensors
Classification of Benthic Habitat Based on Object with Support Vector Machines and Decision Tree Algorithm Using Spot-7 Multispectral Imagery in Harapan and Kelapa Island
The research of object based image classification (OBIA) with machine learning algorithm for high resolution image in Indonesia is still limited especially for coral reef mapping, therefore further research needed for comparison in method and application of algorithms as alternative of classification. This research aims to map benthic habitat based on multiscale classification using OBIA method with support vector machine and decision tree algorithm in Harapan Island and Kelapa Island, Kepulauan Seribu. Segmentation was performed using a multiresolution segmentation algorithm with a scale factor of 15. The OBIA method is applied to atmospheric corrected images with a predefined benthic habitat classification scheme. The overall accuracy of SVM and DT algorithm implementations are 76.68% and 60.62%, respectively. The Z statistic value analysis obtained from the application of two algorithms used is 2.23, where this value indicates that the classification with SVM algorithm is significantly different from the DT algorithm. This research suggest that the OBIA technique could be a promise approach for mapping benthic habitats
Metasurface-based hybrid optical cavities for chiral sensing
Quantum metasurfaces, i.e., two-dimensional subwavelength arrays of quantum
emitters, can be employed as mirrors towards the design of hybrid cavities,
where the optical response is given by the interplay of a cavity-confined field
and the surface modes supported by the arrays. We show that, under external
magnetic field control, stacked layers of quantum metasurfaces can serve as
helicity-preserving cavities. These structures exhibit ultranarrow resonances
and can enhance the intensity of the incoming field by orders of magnitude,
while simultaneously preserving the handedness of the field circulating inside
the resonator, as opposed to conventional cavities. The rapid phase shift in
the cavity transmission around the resonance can be exploited for the sensitive
detection of chiral scatterers passing through the cavity. We discuss possible
applications of these resonators as sensors for the discrimination of chiral
molecules.Comment: 6+11 pages, 2+3 figure
αV-Integrins Are Required for Mechanotransduction in MDCK Epithelial Cells
The properties of epithelial cells within tissues are regulated by their immediate microenvironment, which consists of neighboring cells and the extracellular matrix (ECM). Integrin heterodimers orchestrate dynamic assembly and disassembly of cell-ECM connections and thereby convey biochemical and mechanical information from the ECM into cells. However, the specific contributions and functional hierarchy between different integrin heterodimers in the regulation of focal adhesion dynamics in epithelial cells are incompletely understood. Here, we have studied the functions of RGD-binding αV-integrins in a Madin Darby Canine Kidney (MDCK) cell model and found that αV-integrins regulate the maturation of focal adhesions (FAs) and cell spreading. αV-integrin-deficient MDCK cells bound collagen I (Col I) substrate via α2β1-integrins but failed to efficiently recruit FA components such as talin, focal adhesion kinase (FAK), vinculin and integrin-linked kinase (ILK). The apparent inability to mature α2β1-integrin-mediated FAs and link them to cellular actin cytoskeleton led to disrupted mechanotransduction in αV-integrin deficient cells seeded onto Col I substrate
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