2,666 research outputs found
Ultra-Low Amplitude Cepheids in the Large Magellanic Cloud
The MACHO variables of LMC Field 77 that lie in the vicinity of the Cepheid
instability strip are reexamined. Among the 144 variables that we identify as
Cepheids we find 14 that have Fourier amplitudes <0.05 mag in the MACHO red
band, of which 7 have an amplitude <0.006 mag : we dub the latter group of
stars ultra-low amplitude (ULA) Cepheids. The variability of these objects is
verified by a comparison of the MACHO red with the MACHO blue lightcurves and
with those of the corresponding OGLE LMC stars. The occurrence of ULA Cepheids
is in agreement with theory. We have also discovered 2 low amplitude variables
whose periods are about a factor of 5--6 smaller than those of F Cepheids of
equal apparent magnitude. We suggest that these objects are Cepheids undergoing
pulsations in a surface mode and that they belong to a novel class of Strange
Cepheids (or Surface Mode Cepheids) whose existence was predicted by Buchler et
al. (1997).Comment: 4 pages, 5 figures, slightly revised, to appear in ApJ Letter
Infrared Spectroscopy of the Diffuse Ionized Halo of NGC 891
We present infrared spectroscopy from the Spitzer Space Telescope at one disk
position and two positions at a height of 1 kpc from the disk in the edge-on
spiral NGC 891, with the primary goal of studying halo ionization. Our main
result is that the [Ne III]/[Ne II] ratio, which provides a measure of the
hardness of the ionizing spectrum free from the major problems plaguing optical
line ratios, is enhanced in the extraplanar pointings relative to the disk
pointing. Using a 2D Monte Carlo-based photo-ionization code which accounts for
the effects of radiation field hardening, we find that this trend cannot be
reproduced by any plausible photo-ionization model, and that a secondary source
of ionization must therefore operate in gaseous halos. We also present the
first spectroscopic detections of extraplanar PAH features in an external
normal galaxy. If they are in an exponential layer, very rough emission
scale-heights of 330-530 pc are implied for the various features. Extinction
may be non-negligible in the midplane and reduce these scale-heights
significantly. There is little significant variation in the relative emission
from the various features between disk and extraplanar environment. Only the
17.4 micron feature is significantly enhanced in the extraplanar gas compared
to the other features, possibly indicating a preference for larger PAHs in the
halo.Comment: 35 pages in ApJ preprint format, 8 figures, accepted for publication
in ApJ. Minor change to Introduction to give appropriate credit to earlier,
related wor
Why do Internet gamblers prefer online versus land-based venues? Some preliminary findings and implications
At a time when land-based gambling opportunities are widely available, why might some people choose or prefer to gamble on the Internet? We investigate this question using qualitative and quantitative data collected from an Internet-based survey of 1,920 Internet gamblers. The primary reasons people gave for preferring Internet gambling were (a) the relative convenience, comfort, and ease of Internet gambling; (b) an aversion to the atmosphere and clientele of land-based venues; (c) a preference for the pace and nature of online game-play; and (d) the potential for higher wins and lower overall expenditures when gambling online. Findings suggest that online venues may offer their clientele a range of experiences and benefits that are perceived to be unavailable at land-based venues. The authors recommend research into whether a competitive edge exists between different aspects of the gambling market, including Internet venues versus land-based gambling establishments. Keywords: gambling, Internet, online, electronic, survey, preference, convenience, expendituresAlberta Gaming Research InstituteYe
Microperimetry hill of vision and volumetric measures of retinal sensitivity
Purpose: Mean retinal sensitivity is the main output measure used in microperimetry. It is, however, of limited use in patients with poor vision because averaging is weighted toward zero in those with significant scotomas creating an artificial floor effect. In contrast, volumetric measures avoid these issues and are displayed graphically as a hill of vision.
Methods: An open-source program was created to manipulate raw sensitivity threshold data files obtained from MAIA microperimetry. Thin plate spline interpolated heat maps and three-dimensional hill of vision plots with an associated volume were generated. Retrospective analyses of microperimetry volumes were undertaken in patients with a range of retinal diseases to assess the qualitative benefits of three-dimensional visualization and volumetric measures. Simulated pathology was applied to radial grid patterns to investigate the performance of volumetric sensitivity in nonuniform grids.
Results: Volumetric analyses from microperimetry in RPGR-related retinitis pigmentosa, choroideremia, Stargardt disease, and age-related macular degeneration were analyzed. In simulated nonuniform testing grids, volumetric sensitivity was able to detect differences in retinal sensitivity where mean sensitivity could not.
Conclusions: Volumetric measures do not suffer from averaging issues and demonstrate superior performance in nonuniform testing grids. Additionally, volume measures enable detection of localized retinal sensitivity changes that might otherwise be undetectable in a mean change.
Translational Relevance: As microperimetry has become an outcome measure in several gene-therapy clinical trials, three-dimensional visualization and volumetric sensitivity enables a complementary analysis of baseline disease characteristics and subsequent response to treatment, both as a signal of safety and efficacy
Robotic Origamis: Self-morphing Modular Robot
Programmable matter is a material that produces
distinctive shapes or patterns according to a given command.
Often they are composed of interconnected modular elements
that are able to make or break the connections or alter
relative orientation. We present programmable matter based
on robotic origami that demonstrates the capability to fold into
3D shapes starting from a nominally 2D sheet. This concept
requires high torque density actuators, flexible electronics and
an integrated substrate. We report on unique robot fabrication
techniques that incorporate torsional shape memory actuators
and stretchable electronics
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Artificial insect wings of diverse morphology for flapping-wing micro air vehicles
The development of flapping-wing micro air vehicles (MAVs) demands a systematic exploration of the available design space to identify ways in which the unsteady mechanisms governing flapping-wing flight can best be utilized for producing optimal thrust or maneuverability. Mimicking the wing kinematics of biological flight requires examining the potential effects of wing morphology on flight performance, as wings may be specially adapted for flapping flight. For example, insect wings passively deform during flight, leading to instantaneous and potentially unpredictable changes in aerodynamic behavior. Previous studies have postulated various explanations for insect wing complexity, but there lacks a systematic approach for experimentally examining the functional significance of components of wing morphology, and for determining whether or not natural design principles can or should be used for MAVs. In this work, a novel fabrication process to create centimeter-scale wings of great complexity is introduced; via this process, a wing can be fabricated with a large range of desired mechanical and geometric characteristics. We demonstrate the versatility of the process through the creation of planar, insect-like wings with biomimetic venation patterns that approximate the mechanical properties of their natural counterparts under static loads. This process will provide a platform for studies investigating the effects of wing morphology on flight dynamics, which may lead to the design of highly maneuverable and efficient MAVs and insight into the functional morphology of natural wings.Organismic and Evolutionary Biolog
Polarimetric Evidence of Non-Spherical Winds
Polarization observations yield otherwise unobtainable information about the
geometrical structure of unresolved objects. In this talk we review the
evidences for non-spherically symmetric structures around Luminous Hot Stars
from polarimetry and what we can learn with this technique. Polarimetry has
added a new dimension to the study of the envelopes of Luminous Blue Variables,
Wolf-Rayet stars and B[e] stars, all of which are discussed in some detail.Comment: 8 pages, 2 encapsulated Postscript figures, uses lamuphys.sty.
Invited review to appear in IAU Coll. 169, Variable and Non-Spherical Stellar
Winds in Luminous Hot Stars, eds. B. Wolf, A.Fullerton and O. Stahl
(Springer
Genetic risk scores associated with baseline lipoprotein subfraction concentrations do not associate with their responses to fenofibrate
Lipoprotein subclass concentrations are modifiable markers of cardiovascular disease risk. Fenofibrate is known to show beneficial effects on lipoprotein subclasses, but little is known about the role of genetics in mediating the responses of lipoprotein subclasses to fenofibrate. A recent genomewide association study (GWAS) associated several single nucleotide polymorphisms (SNPs) with lipoprotein measures, and validated these associations in two independent populations. We used this information to construct genetic risk scores (GRSs) for fasting lipoprotein measures at baseline (pre-fenofibrate), and aimed to examine whether these GRSs also associated with the responses of lipoproteins to fenofibrate. Fourteen lipoprotein subclass measures were assayed in 817 men and women before and after a three week fenofibrate trial. We set significance at a Bonferroni corrected alpha <0.05 (p < 0.004). Twelve subclass measures changed with fenofibrate administration (each p = 0.003 to <0.0001). Mixed linear models which controlled for age, sex, body mass index (BMI), smoking status, pedigree and study-center, revealed that GRSs were associated with eight baseline lipoprotein measures (p < 0.004), however no GRS was associated with fenofibrate response. These results suggest that the mechanisms for changes in lipoprotein subclass concentrations with fenofibrate treatment are not mediated by the genetic risk for fasting levels
Use of Cloud Radar Doppler Spectra to Evaluate Stratocumulus Drizzle Size Distributions in Large-Eddy Simulations with Size-Resolved Microphysics
A case study of persistent stratocumulus over the Azores is simulated using two independent large-eddy simulation (LES) models with bin microphysics, and forward-simulated cloud radar Doppler moments and spectra are compared with observations. Neither model is able to reproduce the monotonic increase of downward mean Doppler velocity with increasing reflectivity that is observed under a variety of conditions, but for differing reasons. To a varying degree, both models also exhibit a tendency to produce too many of the largest droplets, leading to excessive skewness in Doppler velocity distributions, especially below cloud base. Excessive skewness appears to be associated with an insufficiently sharp reduction in droplet number concentration at diameters larger than ~200 ÎĽm, where a pronounced shoulder is found for in situ observations and a sharp reduction in reflectivity size distribution is associated with relatively narrow observed Doppler spectra. Effectively using LES with bin microphysics to study drizzle formation and evolution in cloud Doppler radar data evidently requires reducing numerical diffusivity in the treatment of the stochastic collection equation; if that is accomplished sufficiently to reproduce typical spectra, progress toward understanding drizzle processes is likely
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