1,653 research outputs found
Bostonia: The Boston University Alumni Magazine. Volume 32
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
Physics and Technology Research for Liquid-Metal Divertor Development, Focused on a Tin-Capillary Porous System Solution, at the OLMAT High Heat-Flux Facility
The operation of the Optimization of Liquid Metal Advanced Targets (OLMAT) facility began in April 2021 with the scientific objective of exposing liquid-metal plasma facing components (PFCs) to the particle and power fluxes provided by one of the hydrogen neutral beam injectors of the TJ-II stellarator. The system can deliver heat fluxes from 5 to 58 MW mâ2 of high energy hydrogen neutral particles (†33 keV) with fluxes up to 1022m2sâ1 (containing an ion fraction †33% in some instances), pulsed operation of 30â150 ms duration and repetition rates up to 2 minâ1. These characteristics enable OLMAT as a high heat flux (HHF) facility for PFC evaluation in terms of power exhaust capabilities, thermal fatigue and resilience to material damage. Additionally, the facility is equipped with a wide range of diagnostics that includes tools for analyzing the thermal response of the targets as well as for monitoring atomic/plasma physics phenomena. These include spectroscopy, pyrometry, electrical probing and visualization (fast and IR cameras) units. Such particularities make OLMAT a unique installation that can combine pure technological PFC research with the investigation of physical phenomena such as vapor shielding, thermal sputtering, the formation/characterization of plasma plumes with significant content of evaporated metal and the detection of impurities in front of the studied targets. Additionally, a myriad of surface characterization techniques as SEM/EDX for material characterization of the exposed PFC prototypes are available at CIEMAT. In this article, first we provide an overview of the current facility upgrade in which a high-power CW laser, that can be operated in continuous and pulsed modes (0.2â10 ms), dump and electrical (single Langmuir) probe embedded on the target surface have been installed. This laser operation will allow simulating more relevant heat loading scenarios such as nominal steady-state divertor heat fluxes (10â20 MW mâ2 in continuous mode) and transients including ELM loading and disruption-like events (ms time scales and power densities up to GW mâ2 range). The work later focuses on the more recent experimentation (2022 fall campaign) where a 3D printed Tungsten (W) Capillary Porous System (CPS) target, with approximated 30 Όm pore size and a 37% porosity and filled with liquid tin. This porous surface was a mock-up of the PFC investigated in the ASDEX Upgrade divertor manipulator. The target composed with this element was eventually exposed to a sequence of shots with the maximum heat flux that OLMAT provides (58 ± 14 MWmâ2). Key questions as resilience to dry-out and particle ejection of the liquid metal layer, its refilling, the induced damage/modification of the porous W matrix and the global performance of the component are addressed, attempting to shed light on the issues encountered with the PFC at tokamak scale testing.</p
The Sloan Digital Sky Survey Quasar Lens Search. V. Final Catalog from the Seventh Data Release
We present the final statistical sample of lensed quasars from the Sloan
Digital Sky Survey (SDSS) Quasar Lens Search (SQLS). The well-defined
statistical lens sample consists of 26 lensed quasars brighter than i=19.1 and
in the redshift range of 0.6<z<2.2 selected from 50,836 spectroscopically
confirmed quasars in the SDSS Data Release 7 (DR7), where we restrict the image
separation range to 1"<\theta<20" and the i-band magnitude differences in two
image lenses to be smaller than 1.25 mag. The SDSS DR7 quasar catalog also
contains 36 additional lenses identified with various techniques. In addition
to these lensed quasars, we have identified 81 pairs of quasars from follow-up
spectroscopy, 26 of which are physically associated binary quasars. The
statistical lens sample covers a wide range of image separations, redshifts,
and magnitudes, and therefore is suitable for systematic studies of
cosmological parameters and surveys of the structure and evolution of galaxies
and quasars.Comment: 42 pages, 2 figures, 6 tables, accepted for publication in AJ; see
http://www-utap.phys.s.u-tokyo.ac.jp/~sdss/sqls/ for supplemental informatio
Attenuation of polyglutamine-induced toxicity by enhancement of mitochondrial OXPHOS in yeast and fly models of aging
Defects in mitochondrial biogenesis and function are common in many neurodegenerative disorders, including Huntingtonâs disease (HD). We have previously shown that in yeast models of HD, enhancement of mitochondrial biogenesis through overexpression of Hap4, the catalytic subunit of the transcriptional complex that regulates mitochondrial gene expression, alleviates the growth arrest induced by expanded polyglutamine (polyQ) tract peptides in rapidly dividing cells. However, the mechanism through which HAP4 overexpression exerts this protection remains unclear. Furthermore, it remains unexplored whether HAP4 overexpression and increased respiratory function during growth can also protect against polyQ-induced toxicity during yeast chronological lifespan. Here, we show that in yeast, mitochondrial respiration and oxidative phosphorylation (OXPHOS) are essential for protection against the polyQ-induced growth defect by HAP4 overexpression. In addition, we show that not only increased HAP4 levels, but also alternative interventions, including calorie restriction, that result in enhanced mitochondrial biogenesis confer protection against polyQ toxicity during stationary phase. The data obtained in yeast models guided experiments in a fly model of HD, where we show that enhancement of mitochondrial biogenesis can also protect against neurodegeneration and behavioral deficits. Our results suggest that therapeutic interventions aiming at the enhancement of mitochondrial respiration and OXPHOS could reduce polyQ toxicity and delay disease onset
Substructure revealed by RR Lyraes in SDSS Stripe 82
We present an analysis of the substructure revealed by 407 RR Lyraes in Sloan
Digital Sky Survey (SDSS) Stripe 82. Period estimates are determined to high
accuracy using a string-length method. A subset of 178 RR Lyraes with
spectrally derived metallicities are employed to derive
metallicity-period-amplitude relations, which are then used to find
metallicities and distances for the entire sample. The RR Lyraes lie between 5
and 115 kpc from the Galactic center. They are divided into subsets of 316 RRab
types and 91 RRc types based on their period, colour and metallicity. The
density distribution is not smooth, but dominated by clumps and substructure.
Samples of 55 and 237 RR Lyraes associated with the Sagittarius Stream and the
Hercules-Aquila Cloud respectively are identified. Hence, ~ 70 % of the RR
Lyraes in Stripe 82 belong to known substructure. There is a sharp break in the
density distribution at Galactocentric radii of 40 kpc, reflecting the fact
that the dominant substructure in Stripe 82 - the Hercules-Aquila Cloud and the
Sagittarius Stream - lies within 40 kpc. In fact, almost 60 % of all the RR
Lyraes in Stripe 82 are associated with the Hercules-Aquila Cloud alone, which
emphasises its pre-eminence. Additionally, evidence of a new and distant
substructure - the Pisces Overdensity - is found, consisting of 28 faint RR
Lyraes centered on Galactic coordinates (80 deg, -55 deg) and with distances of
~ 80 kpc. The total stellar mass in the Pisces Overdensity is ~10000 solar
masses and its metallicity is [Fe/H] ~ -1.5.Comment: 15 pages, submitted to MNRA
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A simple, biologically plausible feature detector for language acquisition
Language has a complex grammatical system we still have to understand computationally and biologically (Hauser et al., 2002; Yang, 2013). However, some evolutionarily ancient mechanisms have been repurposed for grammar (Dehaene & Cohen, 2007; Endress, Cahill, et al., 2009; Endress, Nespor, et al., 2009; Fitch, 2017) so that we can use insight from other taxa into possible circuit level mechanisms of grammar. Drawing upon recent evidence for the importance of disinhibitory circuits across taxa and brain regions (Chevalier & Deniau, 1990; Letzkus et al., 2015; Hangya et al., 2014; Xu et al., 2013; Goddard et al., 2014; Mysore & Knudsen, 2012; Koyama et al., 2016; Koyama & Pujala, 2018), I suggest a simple circuit that explains the acquisition of core grammatical rules used in 85% of the worldâs languages (Rubino, 2013): grammatical rules based on sameness/difference relations. This circuit acts as a sameness-detector. Different items are suppressed through inhibition, but presenting two identical items leads to inhibition of inhibition. The items are thus propagated for further processing. This sameness-detector thus acts as a feature detector for a grammatical rule. I suggest that having a set of feature detectors for elementary grammatical rules might make language acquisition feasible based on relatively simple computational mechanisms
The Sloan Digital Sky Survey Quasar Lens Search. IV. Statistical Lens Sample from the Fifth Data Release
We present the second report of our systematic search for strongly lensed
quasars from the data of the Sloan Digital Sky Survey (SDSS). From extensive
follow-up observations of 136 candidate objects, we find 36 lenses in the full
sample of 77,429 spectroscopically confirmed quasars in the SDSS Data Release
5. We then define a complete sample of 19 lenses, including 11 from our
previous search in the SDSS Data Release 3, from the sample of 36,287 quasars
with i<19.1 in the redshift range 0.6<z<2.2, where we require the lenses to
have image separations of 1"<\theta<20" and i-band magnitude differences
between the two images smaller than 1.25 mag. Among the 19 lensed quasars, 3
have quadruple-image configurations, while the remaining 16 show double images.
This lens sample constrains the cosmological constant to be
\Omega_\Lambda=0.84^{+0.06}_{-0.08}(stat.)^{+0.09}_{-0.07}(syst.) assuming a
flat universe, which is in good agreement with other cosmological observations.
We also report the discoveries of 7 binary quasars with separations ranging
from 1.1" to 16.6", which are identified in the course of our lens survey. This
study concludes the construction of our statistical lens sample in the full
SDSS-I data set.Comment: 37 pages, 2 figures and 5 tables, accepted to A
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A controlled trial of Partners in Dementia Care: veteran outcomes after six and twelve months
Introduction: âPartners in Dementia Careâ (PDC) tested the effectiveness of a care-coordination program integrating healthcare and community services and supporting veterans with dementia and their caregivers. Delivered via partnerships between Veterans Affairs medical centers and Alzheimerâs Association chapters, PDC targeted both patients and caregivers, distinguishing it from many non-pharmacological interventions. Hypotheses posited PDC would improve five veteran self-reported outcomes: 1) unmet need, 2) embarrassment about memory problems, 3) isolation, 4) relationship strain and 5) depression. Greater impact was expected for more impaired veterans. A unique feature was self-reported research data collected from veterans with dementia. Methods and Findings: Five matched communities were study sites. Two randomly selected sites received PDC for 12 months; comparison sites received usual care. Three structured telephone interviews were completed every 6 months with veterans who could participate. Results: Of 508 consenting veterans, 333 (65.6%) completed baseline interviews. Among those who completed baseline interviews, 263 (79.0%) completed 6-month follow-ups and 194 (58.3%) completed 12-month follow-ups. Regression analyses showed PDC veterans had significantly less adverse outcomes than those receiving usual care, particularly for more impaired veterans after 6 months, including reduced relationship strain (B = â0.09; p = 0.05), depression (B = â0.10; p = 0.03), and unmet need (B = â0.28; p = 0.02; and B = â0.52; p = 0.08). PDC veterans also had less embarrassment about memory problems (B = â0.24; p = 0.08). At 12 months, more impaired veterans had further reductions in unmet need (B = â0.96; p < 0.01) and embarrassment (B = â0.05; p = 0.02). Limitations included use of matched comparison sites rather than within-site randomization and lack of consideration for variation within the PDC group in amounts and types of assistance provided. Conclusions: Partnerships between community and health organizations have the potential to meet the dementia-related needs and improve the psychosocial functioning of persons with dementia. Trial Registry NCT0029116
The Second-Generation Guide Star Catalog: Description and Properties
The GSC-II is an all-sky database of objects derived from the uncompressed
DSS that the STScI has created from the Palomar and UK Schmidt survey plates
and made available to the community. Like its predecessor (GSC-I), the GSC-II
was primarily created to provide guide star information and observation
planning support for HST. This version, however, is already employed at some of
the ground-based new-technology telescopes such as GEMINI, VLT, and TNG, and
will also be used to provide support for the JWST and Gaia space missions as
well as LAMOST, one of the major ongoing scientific projects in China. Two
catalogs have already been extracted from the GSC-II database and released to
the astronomical community. A magnitude-limited (R=18.0) version, GSC2.2, was
distributed soon after its production in 2001, while the GSC2.3 release has
been available for general access since 2007.
The GSC2.3 catalog described in this paper contains astrometry, photometry,
and classification for 945,592,683 objects down to the magnitude limit of the
plates. Positions are tied to the ICRS; for stellar sources, the all-sky
average absolute error per coordinate ranges from 0.2" to 0.28" depending on
magnitude. When dealing with extended objects, astrometric errors are 20% worse
in the case of galaxies and approximately a factor of 2 worse for blended
images. Stellar photometry is determined to 0.13-0.22 mag as a function of
magnitude and photographic passbands (B,R,I). Outside of the galactic plane,
stellar classification is reliable to at least 90% confidence for magnitudes
brighter than R=19.5, and the catalog is complete to R=20.Comment: 52 pages, 33 figures, to be published in AJ August 200
Mass profiles and galaxy orbits in nearby galaxy clusters from the analysis of the projected phase-space
We analyze kinematic data of 41 nearby (z<0.1) relaxed galaxy clusters in
terms of the projected phase-space density using a phenomenological, fully
anisotropic model of the distribution function. We apply the Markov Chain Monte
Carlo approach to place constraints on total mass distribution approximated by
the universal NFW profile and the profile of the anisotropy of galaxy orbits.
We find the normalization of the mean mass-concentration relation is
c=6.9_{-0.7}^{+0.6} at the virial mass M_v=5x10^{14}M_sun. Assuming a
one-to-one correspondence between sigma_8 and the normalization of the
mass-concentration relation in the framework of the concordance model we
estimate the normalization of the linear power spectrum to be
sigma_8=0.91_{-0.08}^{+0.07}. Our constraints on the parameters of the mass
profile are compared with estimates from other methods. We show that galaxy
orbits are isotropic at the cluster centres (with the mean ratio of the
radial-to-tangential velocity dispersions sigma_r/sigma_theta=0.97+/-0.04) and
radially anisotropic at the virial sphere (with the mean ratio
sigma_r/sigma_theta=1.75^{+0.23}_{-0.19}). Although the value of the central
anisotropy appears to be universal, the anisotropy at the virial radius differs
between clusters within the range 1<(sigma_r/sigma_theta)<2. Utilizing the
Bautz-Morgan morphological classification and information on the prominence of
a cool core we select two subsamples of galaxy clusters corresponding to less
and more advanced evolutionary states. It is demonstrated that less evolved
clusters have shallower mass profiles and their galaxy orbits are more radially
biased at the virial sphere. This property is consistent with the expected
evolution of the mass profiles as well as with the observed orbital segregation
of late and early type galaxies.Comment: 16 pages, 12 figures, accepted for publication in MNRA
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