4,021 research outputs found
GRAPE: a balloon-borne gamma-ray polarimeter
The Gamma-RAy Polarimeter Experiment (GRAPE) is a concept for an astronomical hard X-ray Compton polarimeter operating in the 50 - 500 keV energy band. The instrument has been optimized for wide-field polarization measurements of transient outbursts from energetic astrophysical objects such as gamma-ray bursts and solar flares. The GRAPE instrument is composed of identical modules, each of which consists of an array of scintillator elements read out by a multi-anode photomultiplier tube (MAPMT). Incident photons Compton scatter in plastic scintillator elements and are subsequently absorbed in inorganic scintillator elements; a net polarization signal is revealed by a characteristic asymmetry in the azimuthal scattering angles. We have constructed a prototype GRAPE module that has been calibrated at a polarized hard X-ray beam and flown on an engineering balloon test flight. A full-scale scientific balloon payload, consisting of up to 36 modules, is currently under development. The first flight, a one-day flight scheduled for 2011, will verify the expected scientific performance with a pointed observation of the Crab Nebula. We will then propose long-duration balloon flights to observe gamma-ray bursts and solar flares
Plans for the first balloon flight of the gamma-ray polarimeter experiment (GRAPE)
We have developed a design for a hard X-ray polarimeter operating in the energy range from 50 to 500 keV. This modular design, known as GRAPE (Gamma-Ray Polarimeter Experiment), has been successfully demonstrated in the lab using partially polarized gamma-ray sources and using fully polarized photon beams at Argonne National Laboratory. In June of 2007, a GRAPE engineering model, consisting of a single detector module, was flown on a high altitude balloon flight to further demonstrate the design and to collect background data. We are currently preparing a much larger balloon payload for a flight in the fall of 2011. Using a large (16-element) array of detector modules, this payload is being designed to search for polarization from known point sources of radiation, namely the Crab and Cygnus X-1. This first flight will not only provide a scientific demonstration of the GRAPE design (by measuring polarization from the Crab nebula), it will also lay the foundation for subsequent long duration balloon flights that will be designed for studying polarization from gamma-ray bursts and solar flares. Here we shall present data from calibration of the first flight module detectors, review the latest payload design and update the predicted polarization sensitivity for both the initial continental US balloon flight and the subsequent long-duration balloon flights
It\u27s Not Where You Start, It\u27s How You Finish: Predicting Law School and Bar Success
In this study, we examine the extent to which academic and student engagement factors explain law school grades and first-time bar exam performance. Applying fixed effects linear and logit modeling, our analysis leverages law student transcript data and responses to the Law School Survey of Student Engagement (LSSSE) among students from a diverse group of 20 law schools to estimate academic performance and odds of bar passage. Most notably, we find that GPA improvement during law school is associated with greater odds of passing the bar exam, particularly among students who struggle the most during the first semester. Furthermore, while we find that LSAT scores and undergraduate GPA are predictive (p \u3c 0.05) of both law school performance and bar success (as in previous research), these effects are quite modest. Based on these findings, we propose and discuss several recommendations. These should be helpful to higher education scholars and practitioners, particularly law school deans, administrators, faculty, and academic support staff
Simulations of a monolithic lanthanum bromide gamma-ray detector
We have been working on the development of a detector design for a large area coded aperture imaging system operating in the 10-600 keV energy range. The detector design is based on an array of Lanthanum Bromide (LaBr3) scintillators, each directly coupled to a Hamamatsu 64-channel multi-anode photomultiplier tube (MAPMT). This paper focuses on the development of the GEANT4-based simulations as an aid in the optimization of the detector design. The simulations have been validated by comparisons with various laboratory data sets. We will summarize the current status and latest findings from this study
The Impact on the Ohio River Watershed by the United States Federal Government
poster abstractThis interactive timeline, which currently covers 1775 through the first quarter of 2014, takes accounts of water-related actions of the federal government and places them alongside water-related environmental events. Research drew together water use information within Acts of Congress, legal cases argued before the Supreme Court, actions undertaken by agencies within the Executive Department, and reports of pollution or flood incidents. This data was then charted using Tiki-Toki software into separate bands along the timeline with descriptions, images, and links to add depth of explanation. This juxtaposition reveals a story tracing human interaction along the Ohio River watershed since the American Revolution. In addition, the Tiki-Toki software makes the information available in multiple views through which different patterns emerge allowing future researchers to manipulate the timeline to more easily see connections with their own projects. Because of the data’s inclusiveness and ease of use, this timeline can provide a platform for comparison with the companion site of the Rivers of the Anthropocene study, the River Tyne. However, since the primary region of study in the United States is the Ohio River and its tributaries, only data applicable to this region specifically or all water in the United States generally was utilized. Because of the exclusiveness of the data, frequent gaps in events may risk being misinterpreted as a period of inactivity on the part of the federal government, though this is likely not the case; even apparent inactivity along the Ohio reveals much about human impact on the waterway systems
Recommended from our members
Life History and Secondary Production of Caenis latipennis Banks (Ephemeroptera: Caenidae) in Honey Creek, Oklahoma
A study of the life history and secondary production of Caenis latipennis, a caenid mayfly, was conducted on Honey Creek, OK. from August 1999 through September 2000. The first instar nymph was described. Nymphs were separated into five development classes. Laboratory egg and nymph development rates, emergence, fecundity, voltinism, and secondary production were analyzed. C. latipennis eggs and nymphs take 132 and 1709 degree days to develop. C. latipennis had an extended emergence with five peaks. Females emerged, molted, mated, and oviposited in an estimated 37 minutes. Mean fecundity was 888.4 ± 291.9 eggs per individual (range 239 -1576). C. latipennis exhibited a multivoltine life cycle with four overlapping generations. Secondary production was 6,052.57 mg/m2/yr
It’s Not Where You Start, It’s How You Finish: Predicting Law School and Bar Success
In this study, we examine the extent to which academic and student engagement factors explain law school grades and first-time bar exam performance. Applying fixed effects linear and logit modeling, our analysis leverages law student transcript data and responses to the Law School Survey of Student Engagement (LSSSE) among students from a diverse group of 20 law schools to estimate academic performance and odds of bar passage. Most notably, we find that GPA improvement during law school is associated with greater odds of passing the bar exam, particularly among students who struggle the most during the first semester. Furthermore, while we find that LSAT scores and undergraduate GPA are predictive (p < 0.05) of both law school performance and bar success (as in previous research), these effects are quite modest. Based on these findings, we propose and discuss several recommendations. These should be helpful to higher education scholars and practitioners, particularly law school deans, administrators, faculty, and academic support staff
Room-temperature exciton-polaritons with two-dimensional WS2
Two-dimensional transition metal dichalcogenides exhibit strong optical
transitions with significant potential for optoelectronic devices. In
particular they are suited for cavity quantum electrodynamics in which strong
coupling leads to polariton formation as a root to realisation of inversionless
lasing, polariton condensationand superfluidity. Demonstrations of such
strongly correlated phenomena to date have often relied on cryogenic
temperatures, high excitation densities and were frequently impaired by strong
material disorder. At room-temperature, experiments approaching the strong
coupling regime with transition metal dichalcogenides have been reported, but
well resolved exciton-polaritons have yet to be achieved. Here we report a
study of monolayer WS coupled to an open Fabry-Perot cavity at
room-temperature, in which polariton eigenstates are unambiguously displayed.
In-situ tunability of the cavity length results in a maximal Rabi splitting of
meV, exceeding the exciton linewidth. Our data
are well described by a transfer matrix model appropriate for the large
linewidth regime. This work provides a platform towards observing strongly
correlated polariton phenomena in compact photonic devices for ambient
temperature applications.Comment: 12 pages, 6 figure
Strong exciton-photon coupling with colloidal nanoplatelets in an open microcavity
Colloidal semiconductor nanoplatelets exhibit quantum size effects due to
their thickness of only few monolayers, together with strong optical band-edge
transitions facilitated by large lateral extensions. In this article we
demonstrate room temperature strong coupling of the light and heavy hole
exciton transitions of CdSe nanoplatelets with the photonic modes of an open
planar microcavity. Vacuum Rabi splittings of meV and meV
are observed for the heavy and light hole excitons respectively, together with
a polariton-mediated hybridisation of both transitions. By measuring the
concentration of platelets in the film we compute the transition dipole moment
of a nanoplatelet exciton to be D. The large oscillator
strength and fluorescence quantum yield of semiconductor nanoplatelets provide
a perspective towards novel photonic devices, combining polaritonic and
spinoptronic effects.Comment: 9 pages, 4 figure
High fidelity simulations of ion trajectories in miniature ion traps using the boundary-element method
In this paper we present numerical modeling results for endcap and linear ion
traps, used for experiments at the National Physical Laboratory in the UK and
Innsbruck University respectively. The secular frequencies for Strontium-88 and
Calcium-40 ions were calculated from ion trajectories, simulated using
boundary-element and finite-difference numerical methods. The results were
compared against experimental measurements. Both numerical methods showed high
accuracy with boundary-element method being more accurate. Such simulations can
be useful tools for designing new traps and trap arrays. They can also be used
for obtaining precise trapping parameters for desired ion control when no
analytical approach is possible as well as for investigating the ion heating
rates due to thermal electronic noise.Comment: 6 pages, 5 figures, changes made to the text according to the
editor's and referee's comment
- …