289 research outputs found
Numerical wave optics and the lensing of gravitational waves by globular clusters
We consider the possible effects of gravitational lensing by globular
clusters on gravitational waves from asymmetric neutron stars in our galaxy. In
the lensing of gravitational waves, the long wavelength, compared with the
usual case of optical lensing, can lead to the geometrical optics approximation
being invalid, in which case a wave optical solution is necessary. In general,
wave optical solutions can only be obtained numerically. We describe a
computational method that is particularly well suited to numerical wave optics.
This method enables us to compare the properties of several lens models for
globular clusters without ever calling upon the geometrical optics
approximation, though that approximation would sometimes have been valid.
Finally, we estimate the probability that lensing by a globular cluster will
significantly affect the detection, by ground-based laser interferometer
detectors such as LIGO, of gravitational waves from an asymmetric neutron star
in our galaxy, finding that the probability is insignificantly small.Comment: To appear in: Proceedings of the Eleventh Marcel Grossmann Meetin
Narrow-line magneto-optical cooling and trapping of strongly magnetic atoms
Laser cooling on weak transitions is a useful technique for reaching
ultracold temperatures in atoms with multiple valence electrons. However, for
strongly magnetic atoms a conventional narrow-line magneto-optical trap (MOT)
is destabilized by competition between optical and magnetic forces. We overcome
this difficulty in Er by developing an unusual narrow-line MOT that balances
optical and magnetic forces using laser light tuned to the blue side of a
narrow (8 kHz) transition. The trap population is spin-polarized with
temperatures reaching below 2 microkelvin. Our results constitute an
alternative method for laser cooling on weak transitions, applicable to
rare-earth-metal and metastable alkaline earth elements.Comment: To appear in Phys. Rev. Lett. 4 pages, 5 figure
Out-of-Distribution Generalization in Algorithmic Reasoning Through Curriculum Learning
Out-of-distribution generalization (OODG) is a longstanding challenge for
neural networks, and is quite apparent in tasks with well-defined variables and
rules, where explicit use of the rules can solve problems independently of the
particular values of the variables. Large transformer-based language models
have pushed the boundaries on how well neural networks can generalize to novel
inputs, but their complexity obfuscates they achieve such robustness. As a step
toward understanding how transformer-based systems generalize, we explore the
question of OODG in smaller scale transformers. Using a reasoning task based on
the puzzle Sudoku, we show that OODG can occur on complex problems if the
training set includes examples sampled from the whole distribution of simpler
component tasks
Bod1, a novel kinetochore protein required for chromosome biorientation
We have combined the proteomic analysis of Xenopus laevis in vitroâassembled chromosomes with RNA interference and live cell imaging in HeLa cells to identify novel factors required for proper chromosome segregation. The first of these is Bod1, a protein conserved throughout metazoans that associates with a large macromolecular complex and localizes with kinetochores and spindle poles during mitosis. Small interfering RNA depletion of Bod1 in HeLa cells produces elongated mitotic spindles with severe biorientation defects. Bod1-depleted cells form syntelic attachments that can oscillate and generate enough force to separate sister kinetochores, suggesting that microtubuleâkinetochore interactions were intact. Releasing Bod1-depleted cells from a monastrol block increases the frequency of syntelic attachments and the number of cells displaying biorientation defects. Bod1 depletion does not affect the activity or localization of Aurora B but does cause mislocalization of the microtubule depolymerase mitotic centromere- associated kinesin and prevents its efficient phosphorylation by Aurora B. Therefore, Bod1 is a novel kinetochore protein that is required for the detection or resolution of syntelic attachments in mitotic spindles
Squeezed light in a frontal-phase-modulated signal-recycled interferometer
The application of squeezed Light to a frontal-phase-modulated signal-recycled interferometer is considered. We present a simple model to understand the required spectrum of squeezing so as to make the interferometer more sensitive. In particular we analyze the broad-and narrow-band cases for signal recycling and fmd that the sensitivity of the detector can be enhanced provided an appropriate input squeezed spectrum is used. We also discuss the effect of using squeezed light on the bandwidth of the detector
Over 50 years of fish community monitoring in Illinoisâ large rivers: The evolution of methods used by the Illinois Natural History Surveyâs Long-term Survey and Assessment of Large-River Fishes in Illinois
Federal Aid in Sport Fish Restoration Act (F-101-R), administered by the U.S. Fish and Wildlife Service and Illinois Department of Natural Resourcesis peer reviewedOpe
Troubling Places: Walking the âtroubling remnantsâ of postâconflict space
This paper explores the productive potential of walking methods in postâconflict space, with particular emphasis on Northern Ireland. We argue that walking methods are especially well suited to studying postâconflict spatial arrangements, yet remain underutilised for a variety of reasons. Specifically, we argue that walking methods can âtroubleâ dominant productions of postâconflict space, revealing its storied depth, multiâtemporality, and the alternative narratives of the past that frequently remain hidden in places touched by violence. Critically, employing such placeâsensitive approaches challenges âbad scriptsâ that reify polarised narratives of conflicted places, thereby enabling the writing of new spatial stories that are potentially generative of new research questions and scholarly insights rooted in overlooked, marginalised, or takenâforâgranted people, places, and landscapes. Informed by both authors' ongoing research journeys, we argue that walking in troubled places can help scholars dig into the reservoirs of emotion, affect, vitality, and multiâtemporality people experience in postâconflict landscapes, thus opening up new research vistas in places scholars might not have sought to look using only sedentary methods.</jats:p
Optical design of the Off-plane Grating Rocket Experiment
The Off-plane Grating Rocket Experiment (OGRE) is a soft X-ray spectroscopy suborbital rocket payload scheduled for launch in Q3 2020 from Wallops Flight Facility. The payload will serve as a testbed for several key technologies which can help achieve the desired performance increases for the next generation of X-ray spectrographs and other space-based missions: monocrystalline silicon X-ray mirrors developed at NASA Goddard Space Flight Center, reflection gratings manufactured at The Pennsylvania State University, and electron-multiplying CCDs developed by the Open University and XCAM Ltd. With these three technologies, OGRE hopes to obtain the highest-resolution on-sky soft X-ray spectrum to date. We discuss the optical design of the OGRE payload
The Off-plane Grating Rocket Experiment (OGRE) system overview
The Off-plane Grating Rocket Experiment (OGRE) is a sub-orbital rocket payload that will make the highest spectral resolution astronomical observation of the soft X-ray Universe to date. Capella, OGREâs science target, has a well-defined line emission spectrum and is frequently used as a calibration source for X-ray observatories such as Chandra. This makes Capella an excellent target to test the technologies on OGRE, many of which have not previously flown. Through the use of state-of-the-art X-ray optics, co-aligned arrays of off-plane reflection gratings, and an X-ray camera based around four Electron Multiplying CCDs, OGRE will act as a proving ground for next generation X-ray spectrometers
The state of the Martian climate
60°N was +2.0°C, relative to the 1981â2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes
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