8,789 research outputs found
Measurements of Far-UV Emission from Elliptical Galaxies at z=0.375
The ``UV upturn'' is a sharp rise in spectra of elliptical galaxies shortward
of rest-frame 2500 A. It is a ubiquitous phenomenon in nearby giant elliptical
galaxies, and is thought to arise primarily from low-mass evolved stars on the
extreme horizontal branch and beyond. Models suggest that the UV upturn is a
very strong function of age for these old stellar populations, increasing as
the galaxy gets older. In some models the change in UV/optical flux ratio is a
factor of 25 over timescales of less than 3 Gyr. To test the predictions for
rapid evolution of the UV upturn, we have observed a sample of normal
elliptical galaxies in the z=0.375 cluster Abell 370 with the Faint Object
Camera aboard the Hubble Space Telescope. A combination of two long-pass
filters was used to isolate wavelengths shortward of rest-frame 2700 A,
providing a measurement of the UV upturn at a lookback time of approximately 4
Gyr. Surprisingly, the four elliptical galaxies observed show a range of UV
upturn strength that is similar to that seen in nearby elliptical galaxies,
with an equivalent 1550-V color ranging from 2.9-3.4 mag. Our result is
inconsistent with some models for the UV upturn; other models are consistent
only for a high redshift of formation (z_f >= 4).Comment: 4 pages, Latex. 1 figure. To appear in ApJL. Uses emulateapj.sty and
apjfonts.sty. Revision includes minor ApJ edits & fixes typo
A call to action: MTHFR polymorphisms should not be a part of inherited thrombophilia testing
Testing for polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene is still a standard part of thrombophilia testing in many laboratories. However, it is clear that these polymorphisms are not risk factors for arterial or venous thrombosis and therefore should not be part of thrombophilia testing. Eliminating MTHFR from thrombophilia testing will reduce patient concerns and health care costs
Seawater cadmium in the Florida Straits over the Holocene and implications for Upper AMOC variability
Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography and Paleoclimatology 37, (2022): e2021PA004379, https://doi.org/10.1029/2021pa004379.Atlantic Meridional Overturning Circulation (AMOC) plays a central role in the global redistribution of heat and precipitation during both abrupt and longer-term climate shifts. Over the next century, AMOC is projected to weaken due to greenhouse gas warming, though projecting its future behavior is dependent on a better understanding of how AMOC changes are forced. Seeking to resolve an apparent contradiction of AMOC trends from paleorecords of the more recent past, we reconstruct seawater cadmium, a nutrient-like tracer, in the Florida Straits over the last ∼8,000 years, with emphasis on the last millennium. The gradual reduction in seawater Cd over the last 8,000 years could be due to a reduction in AMOC, consistent with cooling Northern Hemisphere temperatures and a southward shift of the Intertropical Convergence Zone. However, it is difficult to reconcile this finding with evidence for an increase in geostrophic flow through the Florida Straits over the same time period. We combine data from intermediate water depth sediment cores to extend this record into the Common Era at sufficient resolution to address the broad scale changes of this time period. There is a small decline in the Cd concentration in the Late Little Ice Age relative to the Medieval Climate Anomaly, but this change was much smaller than the changes observed over the Holocene and on the deglaciation. This suggests that any trend in the strength of AMOC over the last millennium must have been very subtle.This work was funded by the NSF Graduate Research Fellowship DGE-1148903 (SV) and NSF grant OCE-1459563 and OCE-1851900 (JLS)
Variations of Hadron Masses and Matter Properties in Dense Nuclear Matter
Using a self-consistent quark model for nuclear matter we investigate
variations of the masses of the non-strange vector mesons, the hyperons and the
nucleon in dense nuclear matter (up to four times the normal nuclear density).
We find that the changes in the hadron masses can be described in terms of the
value of the scalar mean-field in matter. The model is then used to calculate
the density dependence of the quark condensate in-medium, which turns out to be
well approximated by a linear function of the nuclear density. Some relations
among the hadron properties and the in-medium quark condensate are discussed.Comment: 22 pages, University of Adelaide preperint ADP-94-20/T160, submitted
to Physical Review
The Age Difference between the Globular Cluster Sub-populations in NGC 4472
The age difference between the two main globular cluster sub-populations in
the Virgo giant elliptical galaxy, NGC 4472 (M 49), has been determined using
HST WFPC2 images in the F555W and F814W filters. Accurate photometry has been
obtained for several hundred globular clusters in each of the two main
sub-populations, down to more than one magnitude below the turn-over of their
luminosity functions. This allows precise determinations of both the mean
colors and the turn-over magnitudes of the two main sub-populations. By
comparing the data with various population synthesis models, the
age-metallicity pairs that fit both the observed colors and magnitudes have
been identified. The metal-poor and the metal-rich globular clusters are found
to be coeval within the errors ( Gyr). If one accepts the validity of
our assumptions, these errors are dominated by model uncertainties. A
systematic error of up to 4 Gyr could affect this result if the blue and the
red clusters have significantly different mass distributions. However, that one
sub-population is half as old as the other is excluded at the 99% confidence
level. The different globular cluster populations are assumed to trace the
galaxy's major star-formation episodes. Consequently, the vast majority of
globular clusters, and by implication the majority of stars, in NGC 4472 formed
at high redshifts but by two distinct mechanisms or in two episodes.Comment: 32 pages, including 12 postscript figures, accepted for publication
in the Astronomical Journal, December 1999 issu
Age, Period, and Cohort Trends in Mood Disorder and Suicide-Related Outcomes in a Nationally Representative Dataset, 2005-2017
Drawing from the National Survey on Drug Use and Health (NSDUH; N = 611,880), a nationally representative survey of U.S. adolescents and adults, we assess age, period, and cohort trends in mood disorder and suicide-related outcomes since the mid-2000s. Rates of major depressive episode in the last year among adolescents aged 12 to 17 increased by 52% 2005-2017; major depressive episode in the last year increased 63% between 2009 and 2017 among young adults 18-25. Serious psychological distress in the last month and suicide-related outcomes (suicidal ideation, plans, attempts, and deaths by suicide) in the last year also increased among young adults 18-25 between 2008 and 2017, with less consistent and weaker increases among adults ages 26 and over. Hierarchical linear modeling analyses separating the effects of age, period, and birth cohort suggest the trends among adults are primarily due to cohort, with a steady rise in mood disorder and suicide-related outcomes over birth cohorts from the early 1980s to the late 1990s. Cultural trends contributing to an increase in mood disorders and suicidal thoughts and behaviors since the mid-2000s, including the rise of electronic communication and digital media and declines in sleep duration, may have had a larger impact on younger people, creating a cohort effect
Properties of low-lying states in a diffusive quantum dot and Fock-space localization
Motivated by an experiment by Sivan et al. (Europhys. Lett. 25, 605 (1994))
and by subsequent theoretical work on localization in Fock space, we study
numerically a hierarchical model for a finite many-body system of Fermions
moving in a disordered potential and coupled by a two-body interaction. We
focus attention on the low-lying states close to the Fermi energy. Both the
spreading width and the participation number depend smoothly on excitation
energy. This behavior is in keeping with naive expectations and does not
display Anderson localization. We show that the model reproduces essential
features of the experiment by Sivan et al.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. Let
Haplotype profile comparisons cetween Spodoptera frugiperda (Lepidoptera: Noctuidae) populations from Mexico with those from Puerto Rico, South America, and the United States and their implications to migratory behavior
Fall armyworm [Spodoptera frugiperda (J. E. Smith)] is a major economic pest throughout the Western Hemisphere of maize, cotton, sorghum, and a variety of agricultural grasses and vegetable crops. Previous studies demonstrated extensive annual migrations occurring as far north as Canada from overwintering locations in southern Florida and Texas. In contrast, migratory behavior in the rest of the hemisphere is largely uncharacterized. Understanding the migration patterns of fall armyworm will facilitate efforts to predict the spread of pesticide resistance traits that repeatedly arise in this species and assess the consequences of changing climatic trends on the infestation range. Four independent fall armyworm colonies derived from widely separated populations in Mexico and two field collections were examined for their mitochondrial cytochrome oxidase I (COI) gene haplotypes and compared with other locations. The Mexico populations were most similar in their haplotype profile to those from Texas and South America, but also displayed some distinctive features. The data extend the haplotype distribution map in the Western Hemisphere and confirm that the previously observed regional differences in haplotype frequencies are stable over time. The Mexico collections were associated with haplotypes rarely found elsewhere, suggesting limited migratory interactions with foreign populations, including those in neighboring Texas.Fil: Nagoshi, Rodney N.. United States Department Of Agriculture. Agricultural Research Service; ArgentinaFil: Rosas Garcia, Ninfa M.. Instituto Politécnico Nacional; MéxicoFil: Meagher, Robert L.. United States Department Of Agriculture. Agricultural Research Service; ArgentinaFil: Fleischer, Shelby J.. State University Of Pennsylvania; Estados UnidosFil: Westbrook, John K.. United States Department Of Agriculture. Agricultural Research Service; ArgentinaFil: Sappington, Thomas W.. United States Department Of Agriculture. Agricultural Research Service; ArgentinaFil: Hay Roe, Mirian. United States Department Of Agriculture. Agricultural Research Service; ArgentinaFil: Thomas, Jean M. G.. United States Department Of Agriculture. Agricultural Research Service; ArgentinaFil: Murúa, MarÃa Gabriela. Gobierno de Tucumán. Ministerio de Desarrollo Productivo. Estación Experimental Agroindustrial Obispo Colombres; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentin
NIR-quantum dots in biomedical imaging and their future
Fluorescence imaging has gathered interest over the recent years for its real-time response and high sensitivity. Developing probes for this modality has proven to be a challenge. Quantum dots (QDs) are colloidal nanoparticles that possess unique optical and electronic properties due to quantum confinement effects, whose excellent optical properties make them ideal for fluorescence imaging of biological systems. By selectively controlling the synthetic methodologies it is possible to obtain QDs that emit in the first (650–950 nm) and second (1000–1400 nm) near infra-red (NIR) windows, allowing for superior imaging properties. Despite the excellent optical properties and biocompatibility shown by some NIR QDs, there are still some challenges to overcome to enable there use in clinical applications. In this review, we discuss the latest advances in the application of NIR QDs in preclinical settings, together with the synthetic approaches and material developments that make NIR QDs promising for future biomedical applications
Synthesis, Evaluation and Structural Studies of Antiproliferative Tubulin-targeting Azetidin-2-ones
A series of azetidin-2-ones substituted at positions 2, 3 and 4 of the azetidinone ring scaffold were synthesised and evaluated for antiproliferative, cytotoxic and tubulin binding activity. In these compounds, the cis double bond of the vascular targeting agent combretastatin A-4 is replaced with the azetidinone ring in order to enhance the antiproliferative effects displayed by combretastatin A-4 and prevent the cis/trans isomerization that is associated with inactivation of combretastatin A-4. The series of azetidinones was synthetically accessible via the Staudinger and Reformatsky reactions. Of a diverse range of heterocyclic derivatives, 3-(2-thienyl) analogue 28 and 3-(3-thienyl) analogue 29 displayed the highest potency in human MCF-7 breast cancer cells with IC50 values of 7nM and 10nM respectively, comparable to combretastatin A-4. Compounds from this series also exhibited potent activity in MDA-MB-231 breast cancer cells and in the NCI60 cell line panel. No significant toxicity was observed in normal murine breast epithelial cells. The presence of larger, bulkier groups at the 3-position, for example 3-naphthyl derivative 21 and 3-benzothienyl derivative 26, resulted in relatively lower antiproliferative activity in the micromolar range. Tubulin-binding studies of 28 (IC50=1.37μM) confirmed that the molecular target of this series of compounds is tubulin. These novel 3-(thienyl) β-lactam antiproliferative agents are useful scaffolds for the development of tubulin-targeting drugs
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