3,903 research outputs found
Quantitative evaluation of polymer gel dosimeters by broadband ultrasound attenuation
Ultrasound has been examined previously as an alternative readout method for irradiated polymer gel dosimeters, with authors reporting varying dose response to ultrasound transmission measurements. In this current work we extend previous work to measure the broadband ultrasound attenuation (BUA) response of irradiated PAGAT gel dosimeters, using a novel ultrasound computed tomography system
Amygdala functional connectivity with medial prefrontal cortex at rest predicts the positivity effect in older adultsâ memory
As people get older, they tend to remember more positive than negative information. This age-by-valence interaction has been called âpositivity effect.â The current study addressed the hypotheses that baseline functional connectivity at rest is predictive of older adults' brain activity when learning emotional information and their positivity effect in memory. Using fMRI, we examined the relationship among resting-state functional connectivity, subsequent brain activity when learning emotional faces, and individual differences in the positivity effect (the relative tendency to remember faces expressing positive vs. negative emotions). Consistent with our hypothesis, older adults with a stronger positivity effect had increased functional coupling between amygdala and medial PFC (MPFC) during rest. In contrast, younger adults did not show the association between resting connectivity and memory positivity. A similar age-by-memory positivity interaction was also found when learning emotional faces. That is, memory positivity in older adults was associated with (a) enhanced MPFC activity when learning emotional faces and (b) increased negative functional coupling between amygdala and MPFC when learning negative faces. In contrast, memory positivity in younger adults was related to neither enhanced MPFC activity to emotional faces, nor MPFCâamygdala connectivity to negative faces. Furthermore, stronger MPFCâamygdala connectivity during rest was predictive of subsequent greater MPFC activity when learning emotional faces. Thus, emotionâmemory interaction in older adults depends not only on the task-related brain activity but also on the baseline functional connectivity
New measurements of the cosmic infrared background fluctuations in deep Spitzer/IRAC survey data and their cosmological implications
We extend previous measurements of cosmic infrared background (CIB)
fluctuations to ~ 1 deg using new data from the Spitzer Extended Deep Survey.
Two fields, with depths of ~12 hr/pixel over 3 epochs, are analyzed at 3.6 and
4.5 mic. Maps of the fields were assembled using a self-calibration method
uniquely suitable for probing faint diffuse backgrounds. Resolved sources were
removed from the maps to a magnitude limit of AB mag ~ 25, as indicated by the
level of the remaining shot noise. The maps were then Fourier-transformed and
their power spectra were evaluated. Instrumental noise was estimated from the
time-differenced data, and subtracting this isolates the spatial fluctuations
of the actual sky. The power spectra of the source-subtracted fields remain
identical (within the observational uncertainties) for the three epochs
indicating that zodiacal light contributes negligibly to the fluctuations.
Comparing to 8 mic power spectra shows that Galactic cirrus cannot account for
the fluctuations. The signal appears isotropically distributed on the sky as
required for an extragalactic origin. The CIB fluctuations continue to diverge
to > 10 times those of known galaxy populations on angular scales out to < 1
deg. The low shot noise levels remaining in the diffuse maps indicate that the
large scale fluctuations arise from the spatial clustering of faint sources
well below the confusion noise. The spatial spectrum of these fluctuations is
in reasonable agreement with an origin in populations clustered according to
the standard cosmological model (LCDM) at epochs coinciding with the first
stars era.Comment: ApJ, to be publishe
A crossâfaculty simulation model for authentic learning
This paper proposes a crossâfaculty simulation model for authentic learning that bridges the gap between short groupâbased simulations within the classroom and longer individual placements in professional working contexts. Dissemination of the model is expected to widen the use of authentic learning approaches in higher education (HE). The model is based on a crossâfaculty project in which UK HE students acted as professional developers to produce prototype educational games for academic clients from other subject areas. Perceptions about the project were obtained from interviews with project participants. The stakeholders believed the crossâfaculty simulation to be a motivating learning experience, whilst identifying possible improvements. To evaluate whether the authenticity of the studentâclient relationship could be improved, the interview data were compared to four themes for authentic learning described by Rule in 2006. The data supported Ruleâs themes, whilst highlighting the added value gained from metaâawareness of the simulation as a learning opportunity
The Expected Rate of Gamma-Ray Burst Afterglows In Supernova Searches
We predict the rate at which Gamma-Ray Burst (GRB) afterglows should be
detected in supernova searches as a function of limiting flux. Although GRB
afterglows are rarer than supernovae, they are detectable at greater distances
because of their higher intrinsic luminosity. Assuming that GRBs trace the
cosmic star formation history and that every GRB gives rise to a bright
afterglow, we find that the average detection rate of supernovae and afterglows
should be comparable at limiting magnitudes brighter than K=18. The actual rate
of afterglows is expected to be somewhat lower since only a fraction of all
gamma-ray selected GRBs were observed to have associated afterglows. However,
the rate could also be higher if the initial gamma-ray emission from GRB
sources is more beamed than their late afterglow emission. Hence, current and
future supernova searches can place strong constraints on the afterglow
appearance fraction and the initial beaming angle of GRB sources.Comment: 13 pages, submitted to ApJ
On the number of Mather measures of Lagrangian systems
In 1996, Ricardo Ricardo Ma\~n\'e discovered that Mather measures are in fact
the minimizers of a "universal" infinite dimensional linear programming
problem. This fundamental result has many applications, one of the most
important is to the estimates of the generic number of Mather measures.
Ma\~n\'e obtained the first estimation of that sort by using finite dimensional
approximations. Recently, we were able with Gonzalo Contreras to use this
method of finite dimensional approximation in order to solve a conjecture of
John Mather concerning the generic number of Mather measures for families of
Lagrangian systems. In the present paper we obtain finer results in that
direction by applying directly some classical tools of convex analysis to the
infinite dimensional problem. We use a notion of countably rectifiable sets of
finite codimension in Banach (and Frechet) spaces which may deserve independent
interest
Submillimeter wavelength survey of the galactic plane from l = -5 deg to l = +62 deg: Structure and energetics of the inner disk
Results from a large scale survey of the first quadrant of the Milky Way galactic plane at wavelengths of 150, 250, and 300 microns with a 10x10 arcmin beam are presented. The emission detected in the survey arises from compact sources, most of which are identified with known peaks of 5 GHz and/or CO emission, and from an underlying diffuse background with a typical angular width of approximately 0.9 deg (FWHM) which accounts for most of the emission. A total of 80 prominent discrete sources were identified and characterized, of which about half were not previously reported at far infrared wavelengths. The total infrared luminosity within the solar circle is approximately 1 to 2x10 to the 10th power L sub 0, and is probably emitted by dust that resides in molecular clouds
Management Issues and Their Relative Priority within State Fisheries Agencies
For researchers and managers to work together for greatest mutual benefit, researchers must understand
what issues fisheries managers consider most important. To assess management priorities, we conducted a
mail survey asking U.S. state fisheries agencies to identify the priority, based on personnel time, they place
on 12 fisheries management issues. Based on an 88% response rate, we determined relative emphases across (1) management issues, (2) geographic regions, and (3) freshwater or marine orientations. Issues
directly linked to sport and commercial fishers, i.e., stocking, harvest regulations, fishing pressure, and
exploring recruitment, were of paramount importance in all agency time budgets. The issue that included
conflict, policy, and human dimensions concerns also was identified as "high priority." Six other issueshabitat
restoration, hydropower licensing, instream flow, contaminants, introduced species, and nongame
species-were of "moderate priority" nationwide. Approximately 50% of the issues varied in emphases
across geographic region, and five issues were differentially emphasized in agencies with freshwater and
marine responsibilities. To solve persistent problems that plague fisheries management, agencies must
clearly identify high-priority management concerns and communicate their specific problem-solving
needs to researchers. Results of this survey should provide a first step in identifying these management
priorities and research needs
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