652 research outputs found
A Deep Multicolor Survey I. Imaging Observations and Catalog of Stellar Objects
We have used the KPNO 4-meter Mayall telescope to image 0.83 square degrees
of sky in six fields at high galactic latitude in six filters spanning
3000-10000\AA\ to magnitude limits ranging from 22.1 to 23.8. We have assembled
a catalog of 21,375 stellar objects detected in the fields for use primarily in
conducting a multicolor search for quasars. This paper describes the data
reduction techniques used on the CCD data, the methods used to construct the
stellar object catalog, and the simulations performed to understand its
completeness and contamination.Comment: To Appear in ApJ Supplement, 1996. 168k uuencoded gunzipped tarred
tex file (requires aas2pp4.sty and tighten.sty) and 4 PostScript figures.
Also available at http://astro.as.arizona.edu/~pathall/astro.html#preprint
Air/Sea Transfer of Highly Soluble Gases Over Coastal Waters
The deposition of soluble trace gases to the sea surface is not well studied due to a lack of flux measurements over the ocean. Here we report simultaneous air/sea eddy covariance flux measurements of water vapor, sulfur dioxide (SO2), and momentum from a coastal North Atlantic pier. Gas transfer velocities were on average about 20% lower for SO2 than for H2O. This difference is attributed to the difference in molecular diffusivity between the two molecules (D SO 2/D H 2O = 0.5), in reasonable agreement with bulk parameterizations in air/sea gas models. This study demonstrates that it is possible to observe the effect of molecular diffusivity on airâside resistance to gas transfer. The slope of observed relationship between gas transfer velocity and friction velocity is slightly smaller than predicted by gas transfer models, possibly due to wind/wave interactions that are unaccounted for in current models
Prelamin A Accumulation Attenuates Rac1 Activity and Increases the Intrinsic Migrational Persistence of Aged Vascular Smooth Muscle Cells
Vascular smooth muscle cell (VSMC) motility is essential during both physiological and pathological vessel remodeling. Although ageing has emerged as a major risk factor in the development of cardiovascular disease, our understanding of the impact of ageing on VSMC motility remains limited. Prelamin A accumulation is known to drive VSMC ageing and we show that presenescent VSMCs, that have accumulated prelamin A, display increased focal adhesion dynamics, augmented migrational velocity/persistence and attenuated Rac1 activity. Importantly, prelamin A accumulation in proliferative VSMCs, induced by depletion of the prelamin A processing enzyme FACE1, recapitulated the focal adhesion, migrational persistence and Rac1 phenotypes observed in presenescent VSMCs. Moreover, lamin A/C-depleted VSMCs also display reduced Rac1 activity, suggesting that prelamin A influences Rac1 activity by interfering with lamin A/C function at the nuclear envelope. Taken together, these data demonstrate that lamin A/C maintains Rac1 activity in VSMCs and prelamin A disrupts lamin A/C function to reduce Rac1 activity and induce migrational persistence during VSMC ageing
Pulmonary effects of inhalation of spark-generated silver nanoparticles in Brown-Norway and Sprague-Dawley rats
The increasing use of silver nanoparticles (AgNPs) in consumer products is concerning. We examined the potential toxic effects when inhaled in Brown-Norway (BN) rats with a pre-inflammatory state compared to Sprague-Dawley (SD) rats.We determined the effect of AgNPs generated from a spark generator (mass concentration: 600-800Â ÎŒg/mm(3); mean diameter: 13-16Â nm; total lung doses: 8 [Low] and 26-28 [High] ÎŒg) inhaled by the nasal route in both rat strains. Rats were sacrificed at day 1 and day 7 after exposure and measurement of lung function.In both strains, there was an increase in neutrophils in bronchoalveolar lavage (BAL) fluid at 24Â h at the high dose, with concomitant eosinophilia in BN rats. While BAL inflammatory cells were mostly normalised by Day 7, lung inflammation scores remained increased although not the tissue eosinophil scores. Total protein levels were elevated at both lung doses in both strains. There was an increase in BAL IL-1ÎČ, KC, IL-17, CCL2 and CCL3 levels in both strains at Day 1, mostly at high dose. Phospholipid levels were increased at the high dose in SD rats at Day 1 and 7, while in BN rats, this was only seen at Day 1; surfactant protein D levels decreased at day 7 at the high dose in SD rats, but was increased at Day 1 at the low dose in BN rats. There was a transient increase in central airway resistance and in tissue elastance in BN rats at Day 1 but not in SD rats. Positive silver-staining was seen particularly in lung tissue macrophages in a dose and time-dependent response in both strains, maximal by day 7. Lung silver levels were relatively higher in BN rat and present at day 7 in both strains.Presence of cellular inflammation and increasing silver-positive macrophages in lungs at day 7, associated with significant levels of lung silver indicate that lung toxicity is persistent even with the absence of airway luminal inflammation at that time-point. The higher levels and persistence of lung silver in BN rats may be due to the pre-existing inflammatory state of the lungs
A Deep Multicolor Survey II. Initial Spectroscopy and Comparison With Expected Quasar Number Counts
We have used the KPNO 4-meter Mayall telescope to image 0.83 square degrees
of sky in six fields at high galactic latitude in six filters spanning
3000-10000\AA\ to magnitude limits ranging from 22.1 to 23.8. As a first use of
this database, we have conducted a multicolor survey for quasars. We discuss
various methods of selecting outliers in different color-color diagrams and
multicolor space that have been used to identify quasars at all redshifts from
their colors alone. We discuss the initial results of our program of
spectroscopic identification which has so far resulted in the identification of
over forty faint quasars, including one at z4, a similar number of compact
narrow-emission-line galaxies, and a number of unusual and potentially
interesting stars. We use these spectroscopic results, along with extensive
simulations of quasar spectra, to study the efficiency of our candidate
selection procedures. Finally, we compare the number counts of our quasars and
quasar candidates to the expected numbers based on previous studies of the
quasar luminosity function. The agreement of our observations with these
expectations is good in most cases. However, we do estimate that our survey
contains more quasars with B21 and z2.3 than expected from the results of
Koo \& Kron (1988) and more z3 quasars than expected from the results of
Warren, Hewett, \& Osmer (1994), both at the 3\ level. Additional
spectroscopic observations will be required to confirm or refute these
excesses.Comment: To appear in ApJ Vol. 462, May 20, 1996. 87k gunzipped uuencoded
PostScript file. Figures (2750k) available from
http://astro.as.arizona.edu/~pathall/astro.html#preprints or via anonymous
ftp to ftp://gemini.tuc.noao.edu/pub/phall/ or by email to
[email protected]
Bergmann\u27s Clines in Ectotherms: Illustrating a Life-History Perspective with Sceloporine Lizards
The generality and causes of Bergmann\u27s rule have been debated vigorously in the last few years, but Bergmann\u27s clines are rarely explained in the context of life-history theory. We used both traditional and phylogenetic comparative analyses to explore the causes of latitudinal and thermal clines in the body size of the eastern fence lizard (Sceloporus undulatus). The proximate mechanism for larger body sizes in colder environments is delayed maturation, which results in a greater fecundity but a lower survival to maturity. Life-history theory predicts that a higher survivorship of juveniles in colder environments can favor the evolution of a Bergmann\u27s cline. Consistent with this theory, lizards in colder environments survive better as juveniles and delay maturation until reaching a larger body size than that of lizards in warmer environments. We expect similar relationships among temperature, survivorship, and age/size at maturity exist in other ectotherms that exhibit Bergmann\u27s clines. However, life-history traits of S. undulatus were more strongly related to latitude than they were to temperature, indicating that both abiotic and biotic factors should be considered as causes of Bergmann\u27s clines. Nonetheless, analyses of the costs and benefits of particular body sizes in different thermal environments will enhance our understanding of geographic variation
Nesprin-2-dependent ERK1/2 compartmentalisation regulates the DNA damage response in vascular smooth muscle cell ageing
Prelamin A accumulation and persistent DNA damage response (DDR) are hallmarks of vascular smooth muscle cell (VSMC) ageing and dysfunction. Although prelamin A is proposed to interfere with DNA repair, our understanding of the crosstalk between prelamin A and the repair process remains limited. The extracellular signal-regulated kinases 1 and 2 (ERK1/2) have emerged as key players in the DDR and are known to enhance ataxia telangiectasia-mutated protein (ATM)activity at DNA lesions, and in this study, we identified a novel relationship between prelamin A accumulation and ERK1/2 nuclear compartmentalisation during VSMC ageing. We show both prelamin A accumulation and increased DNA damage occur concomitantly, before VSMC replicative senescence, and induce the localisation of ERK1/2 to promyelocytic leukaemia protein nuclear bodies (PML NBs) at the sites of DNA damage via nesprin-2 and lamin A interactions. Importantly, VSMCs treated with DNA damaging agents also displayed prelamin A accumulation and ERK compartmentalisation at PML NBs, suggesting that prelamin A and nesprin-2 are novel components of the DDR. In support of this, disruption of ERK compartmentalisation at PML NBs, by either depletion of nesprin-2 or lamins A/C, resulted in the loss of ATM from DNA lesions. However, ATM signalling and DNA repair remained intact after lamins A/C depletion, whereas nesprin-2 disruptionablated downstream Chk2 activation and induced genomic instability. We conclude that lamins A/C and PML act as scaffolds to organise DNA-repair foci and compartmentalise nesprin-2/ERK signalling. However, nesprin-2/ERK signalling fidelity, but not their compartmentalisation at PML NBs, is essential for efficient DDR in VSMCs
Bostonia: The Boston University Alumni Magazine. Volume 12
Founded in 1900, Bostonia magazine is Boston Universityâs main alumni publication
A comparison of precipitation and filtration-based SARS-CoV-2 recovery methods and the influence of temperature, turbidity, and surfactant load in urban wastewater
Wastewater-based epidemiology (WBE) has become a complimentary surveillance tool during the SARS-CoV-2 pandemic. Viral concentration methods from wastewater are still being optimised and compared, whilst viral recovery under different wastewater characteristics and storage temperatures remains poorly understood. Using urban wastewater samples, we tested three viral concentration methods; polyethylene glycol precipitation (PEG), ammonium sulphate precipitation (AS), and CP selectâą InnovaPrepÂź (IP) ultrafiltration. We found no major difference in SARS-CoV-2 and faecal indicator virus (crAssphage) recovery from wastewater samples (nâŻ=âŻ46) using these methods, PEG slightly (albeit non-significantly), outperformed AS and IP for SARS-CoV-2 detection, as a higher genome copies per litre (gc/l) was recorded for a larger proportion of samples. Next generation sequencing of 8 paired samples revealed non-significant differences in the quality of data between AS and IP, though IP data quality was slightly better and less variable. A controlled experiment assessed the impact of wastewater suspended solids (turbidity; 0â400âŻNTU), surfactant load (0â200âŻmg/l), and storage temperature (5â20âŻÂ°C) on viral recovery using the AS and IP methods. SARS-CoV-2 recoveries were >20% with AS and âŻ0.05), whilst surfactant and storage temperature combined were significant negative correlates (pâŻ<âŻ0.001 and pâŻ<âŻ0.05, respectively). In conclusion, our results show that choice of methodology had small effect on viral recovery of SARS-CoV-2 and crAssphage in wastewater samples within this study. In contrast, sample turbidity, storage temperature, and surfactant load did affect viral recovery, highlighting the need for careful consideration of the viral concentration methodology used when working with wastewater samples
Core-collapse model of broadband emission from SNR RX J1713.7-3946 with thermal X-rays and Gamma-rays from escaping cosmic rays
We present a spherically symmetric, core-collapse model of SNR RX
J1713.7-3946 that includes a hydrodynamic simulation of the remnant evolution
coupled to the efficient production of cosmic rays (CRs) by nonlinear diffusive
shock acceleration (DSA). High-energy CRs that escape from the forward shock
(FS) are propagated in surrounding dense material that simulates either a
swept-up, pre-supernova shell or a nearby molecular cloud. The continuum
emission from trapped and escaping CRs, along with the thermal X-ray emission
from the shocked heated ISM behind the FS, integrated over the remnant, is
compared against broadband observations. Our results show conclusively that,
overall, the GeV-TeV emission is dominated by inverse-Compton from CR electrons
if the supernova is isolated regardless of its type, i.e., not interacting with
a >>100 Msun shell or cloud. If the SNR is interacting with a much larger mass
>10^4 Msun, pion-decay from the escaping CRs may dominate the TeV emission,
although a precise fit at high energy will depend on the still uncertain
details of how the highest energy CRs are accelerated by, and escape from, the
FS. Based on morphological and other constraints, we consider the 10^4 Msun
pion-decay scenario highly unlikely for SNR RX J1713.7-3946 regardless of the
details of CR escape. Importantly, even though CR electrons dominate the
GeV-TeV emission, the efficient production of CR ions is an essential part of
our leptonic model.Comment: 11 pages with 7 figures. Submitted to Ap
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