6,476 research outputs found
Bayesian Model Comparison and Analysis of the Galactic Disk Population of Gamma-Ray Millisecond Pulsars
Pulsed emission from almost one hundred millisecond pulsars (MSPs) has been
detected in -rays by the Fermi Large-Area Telescope. The global
properties of this population remain relatively unconstrained despite many
attempts to model their spatial and luminosity distributions. We perform here a
self-consistent Bayesian analysis of both the spatial distribution and
luminosity function simultaneously. Distance uncertainties, arising from errors
in the parallax measurement or Galactic electron-density model, are
marginalized over. We provide a public Python package for calculating distance
uncertainties to pulsars derived using the dispersion measure by accounting for
the uncertainties in Galactic electron-density model YMW16. Finally, we use
multiple parameterizations for the MSP population and perform Bayesian model
comparison, finding that a broken power law luminosity function with Lorimer
spatial profile are preferred over multiple other parameterizations used in the
past. The best-fit spatial distribution and number of -ray MSPs is
consistent with results for the radio population of MSPs.Comment: 13 pages, 8 figures, 3 tables + Appendix. Public code and source list
available from http://github.com/tedwards2412/MSPDis
First Report of the Alfalfa Blotch Leafminer (Diptera: Agromyzidae), and Selected Parasites (Hymenoptera: Eulophidae) in Minnesota and Wisconsin, USA
Alfalfa blotch leafminer, Agromyza frontella, has been a serious pest of alfalfa, Medicago sativa, in the northeastern U.S. and in eastern Ontario, Canada. Until recently, the western edge of the A. frontella distribution in the U.S. was limited to eastern Ohio. We document for the first time, the occurrence of A. frontella in Minnesota and Wisconsin. Alfalfa stems damaged by A. frontella, based on adult feeding punctures, obvious blotched leafmining or the presence of larvae, were first found in 3 northern Minnesota counties during October, 1994. Infested counties included Lake of the Woods, Cook and Lake, all bordering western Ontario, Canada. In 1995, A. frontella was again found in Cook and Lake counties, where 99-100% of the stems, and 18-35% of the trifoliates/stem, contained larvae or exhibited obvious feeding damage. In 1996, following a more expanded survey, a total of 11 and 5 counties, in Minnesota and Wisconsin, respectively, showed some level of A. frontella feeding damage (stem samples ranged from \u3c5 to 100% infested). Based on additional counties surveyed 11 October, 1996, where A. frontella was not found, we now have a reasonable estimate of the southern edge of the distribution in Minnesota and Wisconsin. A total of 2 and 6 A. frontella adults were identified from sweep-net samples taken from fields with obvious feeding damage during 1995 (Lake Co.) and 1996 (Cook Co,), respectively. Three eulophid (Hymenoptera) parasites were reared from A. frontella-infested alfalfa stems collected during October, 1994 in Cook Co., Minn., including: Diglyphus begini, D. pulchripes, and Diglyphus sp., prob. isaea, all of which are new records. Our hypothesis is that A. frontella moved into Minnesota from Ontario Canada, via alfalfa hay purchased by northern Minnesota growers
Geometric Scaling in Inclusive Charm Production
We show that the cross section for inclusive charm production exhibits
geometric scaling in a large range of photon virtualities. In the HERA
kinematic domain the saturation momentum stays below the hard
scale , implying charm production probing mostly the color
transparency regime and unitarization effects being almost negligible. We
derive our results considering two saturation models which are able to describe
the DESY ep collider HERA data for the proton structure function at small
values of the Bjorken variable . A striking feature is the scaling on
above saturation limit, corroborating recent
theoretical studies.Comment: 4 pages, 2 figures. Version to be published in Physical Review
Letter
Observation and absolute frequency measurements of the 1S0 - 3P0 optical clock transition in ytterbium
We report the direct excitation of the highly forbidden (6s^2) 1S0 - (6s6p)
3P0 optical transition in two odd isotopes of ytterbium. As the excitation
laser frequency is scanned, absorption is detected by monitoring the depletion
from an atomic cloud at ~70 uK in a magneto-optical trap. The measured
frequency in 171Yb (F=1/2) is 518,295,836,593.2 +/- 4.4 kHz. The measured
frequency in 173Yb (F=5/2) is 518,294,576,850.0 +/- 4.4 kHz. Measurements are
made with a femtosecond-laser frequency comb calibrated by the NIST cesium
fountain clock and represent nearly a million-fold reduction in uncertainty.
The natural linewidth of these J=0 to J=0 transitions is calculated to be ~10
mHz, making them well-suited to support a new generation of optical atomic
clocks based on confinement in an optical lattice.Comment: 4 pages, 3 figure
Attosecond time-scale intra-atomic phase matching of high harmonic generation
Includes bibliographical references (page 5461).Using a model of high-harmonic generation that couples a fully quantum calculation with a semi-classical electron trajectory picture, we show that a new type of phase matching is possible when an atom is driven by an optimal optical waveform. For an optimized laser pulse shape, strong constructive interference is obtained in the frequency domain between emissions from different electron trajectories, thereby selectively enhancing a particular harmonic order. This work demonstrates that coherent control in the strong-field regime is possible by adjusting the peaks of a laser field on an attosecond time scale
Исторические аспекты общества знания на Западе и в СССР
Рецензія на монографію: Осипов Г.В., Кара-Мурза С.Г. Общество знания: История модернизации на Западе и в СССР. — М.: Книжный дом «ЛИБРОКОМ», 2013. — 368 с
- …