13,761 research outputs found
Frequency of Solar-like Systems and of Ice and Gas Giants Beyond the Snow Line from High-magnification Microlensing Events in 2005-2008
We present the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval –4.5 200) microlensing events during 2005-2008. The sampled host stars have a typical mass M_(host) ~ 0.5 M_⊙, and detection is sensitive to planets over a range of planet-star-projected separations (s ^(–1)_(max)R_E, s_(max)R_E), where R_E ~ 3.5 AU(M_(host)/M_⊙)^(1/2) is the Einstein radius and s_(max) ~ (q/10^(–4.3))^(1/3). This corresponds to deprojected separations roughly three times the "snow line." We show that the observations of these events have the properties of a "controlled experiment," which is what permits measurement of absolute planet frequency. High-magnification events are rare, but the survey-plus-follow-up high-magnification channel is very efficient: half of all high-mag events were successfully monitored and half of these yielded planet detections. The extremely high sensitivity of high-mag events leads to a policy of monitoring them as intensively as possible, independent of whether they show evidence of planets. This is what allows us to construct an unbiased sample. The planet frequency derived from microlensing is a factor 8 larger than the one derived from Doppler studies at factor ~25 smaller star-planet separations (i.e., periods 2-2000 days). However, this difference is basically consistent with the gradient derived from Doppler studies (when extrapolated well beyond the separations from which it is measured). This suggests a universal separation distribution across 2 dex in planet-star separation, 2 dex in mass ratio, and 0.3 dex in host mass. Finally, if all planetary systems were "analogs" of the solar system, our sample would have yielded 18.2 planets (11.4 "Jupiters," 6.4 "Saturns," 0.3 "Uranuses," 0.2 "Neptunes") including 6.1 systems with two or more planet detections. This compares to six planets including one two-planet system in the actual sample, implying a first estimate of 1/6 for the frequency of solar-like systems
Short period eclipsing binary candidates identified using SuperWASP
We present light curves and periods of 53 candidates for short period eclipsing binary stars identified by SuperWASP. These include 48 newly identified objects with periods <2 × 10^4 s (~0.23 d), as well as the shortest period binary known with main sequence components (GSC2314–0530 = 1SWASP J022050.85 + 332047.6) and four other previously known W UMa stars (although the previously reported periods for two of these four are shown to be incorrect). The period distribution of main sequence contact binaries shows a sharp cut-off at a lower limit of around 0.22 d, but until now, very few systems were known close to this limit. These new candidates will therefore be important for understanding the evolution of low mass stars and to allow investigation of the cause of the period cut-off
Probing Neutral Majorana Fermion Edge Modes with Charge Transport
We propose two experiments to probe the Majorana fermion edge states that
occur at a junction between a superconductor and a magnet deposited on the
surface of a topological insulator. Combining two Majorana fermions into a
single Dirac fermion on a magnetic domain wall allows the neutral Majorana
fermions to be probed with charge transport. We will discuss a novel
interferometer for Majorana fermions, which probes their Z_2 phase. This setup
also allows the transmission of neutral Majorana fermions through a point
contact to be measured. We introduce a point contact formed by a
superconducting junction and show that its transmission can be controlled by
the phase difference across the junction. We discuss the feasibility of these
experiments using the recently discovered topological insulator Bi_2 Se_3.Comment: 4 page
InN dielectric function from the midinfrared to the visible range
The dispersion of the dielectric function for wurtzite InN is analytically
evaluated in the region near the fundamental energy gap. The real part of the
dielectric function has a logarithmic singularity at the absorption edge. This
results in the large contribution into the optical dielectric constant. For
samples with degenerate carriers, the real part of the dielectric function is
divergent at the absorption edge. The divergence is smeared with temperatures
or relaxation rate. The imaginary part of the dielectric function has a plateau
far away from the absorption onset.Comment: 5 pages, 2 figure
Superpartners at LHC and Future Colliders: Predictions from Constrained Compactified M-Theory
We study a realistic top-down M-theory compactification with low-scale
effective Supersymmetry, consistent with phenomenological constraints. A
combination of top-down and generic phenomenological constraints fix the
spectrum. The gluino mass is predicted to be about 1.5 TeV. Three and only
three superpartner channels, , and
(where are Wino-like), are expected
to be observable at LHC-14. We also investigate the prospects of finding heavy
squarks and Higgsinos at future colliders. Gluino-stop-top,
gluino-sbottom-bottom associated production and first generation squark
associated production should be observable at a 100 TeV collider, along with
direct production of heavy Higgsinos. Within this framework the discovery of a
single sparticle is sufficient to determine uniquely the SUSY spectrum,
yielding a number of concrete testable predictions for LHC-14 and future
colliders, and determination of and thereby other fundamental
quantities.Comment: 19 pages, 4 figure
Description of data plots from the University of Minnesota ion chamber and electron spectrometer on OGO-1 and OGO-3
Data plots obtained from ion chamber and electron spectrometer experiments aboard OGO A and OGO C satellite
Dispersal Dynamics of the Bivalve Gemma Gemma in a Patchy Environment
The purpose of this study was to analyze the dispersal dynamics of the ovoviviparous bivalve Gemma gemma (hereafter referred to as Gemma) in an environment disturbed by the pit-digging activities of horseshoe crabs, Limulus polyphemus. Gemma broods its young and has no planktonic larval stage, so all dispersal is the result of juvenile and adult movement. Animal movement was measured using natural crab pits, hand-dug simulated crab pits, and cylindrical bottom traps in the intertidal zone at Tom\u27s Cove, Virginia, USA.
This study demonstrated that horseshoe crabs create localized patches with reduced densities of Gemma, that all sizes and ages of Gemma quickly disperse into these low density patches, and that the mechanism of dispersal is passive bedload and suspended load transport. Freshly excavated natural pits had significantly lower Gemma densities than did undisturbed background sediment, but there were no significant differences in total density of other species, number of species, and species diversity (H\u27). Equitability (J\u27) was greater in pits than in controls because of the reduced abundance of Gemma, the numerically dominant species. Newly dug simulated crab pits also had significantly lower Gemma densities than controls and returned to control levels by the next day. Density recovery trajectories for individually marked pits showed consistent responses in summer and fall, but not in winter when low Gemma abundance resulted in greater variability among pits.
Significant positive correlations between the volume of sediment and the number of Gemma collected per bottom trap support the hypothesis that Gemma dispersal is a passive transport phenomenon. Assuming no active, density-dependent movement, the product of the Gemma density frequency distribution in undisturbed background sediment and the frequency distribution of sediment volume collected per trap created a predicted Gemma frequency distribution in traps that matched the actual distribution. Absolute dispersal rates and relative dispersal rates (absolute dispersal rate divided by background density in undisturbed sediment) into pits and traps were greater in summer than winter. Dispersal rate results suggest that increased horseshoe crab disturbance in summer may cause an increase in Gemma transport. Because Gemma individuals are dispersed by hydrodynamic action, it was expected that small, young individuals would be most easily transported in the bedload. There was, however, little evidence that movement into pits and traps was size- or age-selective.
Most recent benthic dispersal research has focused on the large-scale movement and settlement patterns of invertebrate larvae. The results from this study illustrate that dispersal of bottom-dwelling juveniles and adults plays an important role in regulating the local distribution and abundance of Gemma. Previous workers have shown that young Gemma live in dense aggregations and that growth and fecundity are reduced at such high densities, leading to population crashes. This study demonstrated a mechanism by which Gemma disperses into low-density patches where intraspecific competition may be mitigated, possibly resulting in enhanced individual reproductive success and population fitness
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