102 research outputs found
A Look at Veterinary Technicians
Veterinary technicians should actually be termed animal technicians, although the paraprofessional vocation is most generally associated with the veterinary profession. Other situations where animal technicians are employed include biological research at various laboratories, drug and feed companies, animal production facilities, and others. It should be emphasized that the animal technician serves primarily as an assistant to senior biological workers, technologists, and other scientists as well as to veterinarians
GRB 071028B, a burst behind large amounts of dust in an unabsorbed galaxy
We report on the discovery and properties of the fading afterglow and
underlying host galaxy of GRB 071028B, thereby facilitating a detailed
comparison between these two. Observations were performed with the Gamma-ray
Burst Optical and Near-infrared Detector at the 2.2 m telescope on the La Silla
Paranal Observatory in Chile. We conducted five observations from 1.9 d to
227.2 d after the trigger and obtained deep images in the g'r'i'z' and JHKs
bands. Based on accurate seven-channel photometry covering the optical to
near-infrared wavelength range, we derive a photometric redshift of z = 0.94
+0.05 -0.10 for the unabsorbed host galaxy of GRB 071028B. In contrast, we show
that the afterglow with an intrinsic extinction of AV(SB) = (0.70 +/- 0.11) mag
is moderately absorbed and requires a relatively flat extinction curve.
According to the reported Swift/BAT observations, the energetics yield an
isotropic energy release of E(gamma,iso.,rest) = (1.4 +2.4 -0.7) x 10^51 erg.Comment: 8 pages, 5 figures, accepted for publication in A&
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Breaking into the blackbox: Trend following, stop losses and the frequency of trading - The case of the S&P500
In this article, we compare a variety of technical trading rules in the context of investing in the S&P500 index. These rules are increasingly popular, both among retail investors and CTAs and similar investment funds. We find that a range of fairly simple rules, including the popular 200-day moving average (MA) trading rule, dominate the long-only, passive investment in the index. In particular, using the latter rule we find that popular stop-loss rules do not add value and that monthly end-of-month investment decision rules are superior to those which trade more frequently: this adds to the growing view that trading can damage your wealth. Finally, we compare the MA rule with a variety of simple fundamental metrics and find the latter far inferior to the technical rules over the last 60 years of investing
On Measuring Chemical Abundances in Distant Galaxies Using Global Emission Line Spectra
The advent of 8--10 meter class telescopes enables direct measurement of the
chemical properties in the ionized gas of cosmologically--distant galaxies with
the same nebular analysis techniques used in local H II regions. We show that
spatially unresolved (i.e., global) emission line spectra can reliably indicate
the chemical properties of distant star-forming galaxies. However, standard
nebular chemical abundance measurement methods (those with a measured electron
temperature from [O III] lambda4363) may be subject to small systematic errors
when the observed volume includes a mixture of gas with diverse temperatures,
ionization parameters, and metallicities. To characterize these systematic
effects, we compare physical conditions derived from spectroscopy of individual
H II regions with results from global galaxy spectroscopy. We consider both
low-mass, metal poor galaxies with uniform abundances and larger galaxies with
internal chemical gradients. Well-established empirical calibrations using
strong-line ratios can serve as reliable (~0.2 dex) indicators of the overall
systemic oxygen abundance even when the signal-to-noise of the Hbeta and [O
III] emission lines is as low as 8:1. We present prescriptions, directed toward
high-redshift observers, for using global emission line spectra to trace the
chemical properties of star-forming galaxies in the distant universe.
[abridged]Comment: Accepted for Publication in the Astrophysical Journal; 34 pages, 10
figures, uses AASTeX and psfi
Efficient intravenous tumor targeting using the αvβ6 integrin-selective precision virotherapy Ad5NULL-A20
We previously developed a refined, tumor-selective adenovirus, Ad5NULL-A20, harboring tropism ablating mutations in each major capsid protein, to ablate all native means of infection. We incorporated a 20-mer peptide (A20) in the fiber knob for selective infection via αvβ6 integrin, a marker of aggressive epithelial cancers. Methods: To ascertain the selectivity of Ad5NULL-A20 for αvβ6-positive tumor cell lines of pancreatic and breast cancer origin, we performed reporter gene and cell viability assays. Biodistribution of viral vectors in mice harboring xenografts with low, medium, and high αvβ6 levels was quantified by qPCR for viral genomes 48 h post intravenous administration. Results: Ad5NULL-A20 vector transduced cells in an αvβ6-selective manner, whilst cell killing mediated by oncolytic Ad5NULL-A20 was αvβ6-selective. Biodistribution analysis following intravenous administration into mice bearing breast cancer xenografts demonstrated that Ad5NULL-A20 resulted in significantly reduced liver accumulation coupled with increased tumor accumulation compared to Ad5 in all three models, with tumor-to-liver ratios improved as a function of αvβ6 expression. Conclusions: Ad5NULL-A20-based virotherapies efficiently target αvβ6-integrin-positive tumors following intravenous administration, validating the potential of Ad5NULL-A20 for systemic applications, enabling tumor-selective overexpression of virally encoded therapeutic transgenes
Small Platforms, High Return: The Need to Enhance Investment in Small Satellites for Focused Science, Career Development, and Improved Equity
In the next decade, there is an opportunity for very high return on
investment of relatively small budgets by elevating the priority of smallsat
funding in heliophysics. We've learned in the past decade that these missions
perform exceptionally well by traditional metrics, e.g., papers/year/\$M
(Spence et al. 2022 -- arXiv:2206.02968). It is also well established that
there is a "leaky pipeline" resulting in too little diversity in leadership
positions (see the National Academies Report at
https://www.nationalacademies.org/our-work/increasing-diversity-in-the-leadership-of-competed-space-missions).
Prioritizing smallsat funding would significantly increase the number of
opportunities for new leaders to learn -- a crucial patch for the pipeline and
an essential phase of career development. At present, however, there are far
more proposers than the available funding can support, leading to selection
ratios that can be as low as 6% -- in the bottom 0.5th percentile of selection
ratios across the history of ROSES. Prioritizing SmallSat funding and
substantially increasing that selection ratio are the fundamental
recommendations being made by this white paper.Comment: White paper submitted to the Decadal Survey for Solar and Space
Physics (Heliophysics) 2024-2033; 6 pages, 1 figur
Active Galactic Nuclei in the Sloan Digital Sky Survey: II. Emission-Line Luminosity Function
The emission line luminosity function of active galactic nuclei (AGN) is
measured from about 3000 AGN included in the main galaxy sample of the Sloan
Digital Sky Survey within a redshift range of . The \Ha and
[OIII] luminosity functions for Seyferts cover luminosity range
of in H and the shapes are well fit by broken power
laws, without a turnover at fainter nuclear luminosities. Assuming a universal
conversion from emission line strength to continuum luminosity, the inferred B
band magnitude luminosity function is comparable both to the AGN luminosity
function of previous studies and to the low redshift quasar luminosity function
derived from the 2dF redshift survey. The inferred AGN number density is
approximately 1/5 of all galaxies and about of the total
light of galaxies in the -band comes from the nuclear activity. The numbers
of Seyfert 1s and Seyfert 2s are comparable at low luminosity, while at high
luminosity, Seyfert 1s outnumber Seyfert 2s by a factor of 2-4. In making the
luminosity function measurements, we assumed that the nuclear luminosity is
independent of the host galaxy luminosity, an assumption we test {\it a
posteriori}, and show to be consistent with the data. Given the relationship
between black hole mass and host galaxy bulge luminosity, the lack of
correlation between nuclear and host luminosity suggests that the main variable
that determines the AGN luminosity is the Eddington ratio, not the black hole
mass. This appears to be different from luminous quasars, which are most likely
to be shining near the Eddington limit.Comment: AASTeX v5.02 preprint; 35 pages, including 2 table and 12 figures. To
appear in the April 2005 issue of AJ. See astro-ph/0501059 for Paper
Defining the Middle Corona
International audienceAbstract The middle corona, the region roughly spanning heliocentric distances from 1.5 to 6 solar radii, encompasses almost all of the influential physical transitions and processes that govern the behavior of coronal outflow into the heliosphere. The solar wind, eruptions, and flows pass through the region, and they are shaped by it. Importantly, the region also modulates inflow from above that can drive dynamic changes at lower heights in the inner corona. Consequently, the middle corona is essential for comprehensively connecting the corona to the heliosphere and for developing corresponding global models. Nonetheless, because it is challenging to observe, the region has been poorly studied by both major solar remote-sensing and in-situ missions and instruments, extending back to the Solar and Heliospheric Observatory (SOHO) era. Thanks to recent advances in instrumentation, observational processing techniques, and a realization of the importance of the region, interest in the middle corona has increased. Although the region cannot be intrinsically separated from other regions of the solar atmosphere, there has emerged a need to define the region in terms of its location and extension in the solar atmosphere, its composition, the physical transitions that it covers, and the underlying physics believed to shape the region. This article aims to define the middle corona, its physical characteristics, and give an overview of the processes that occur there
Historical Reconstruction Reveals Recovery in Hawaiian Coral Reefs
Coral reef ecosystems are declining worldwide, yet regional differences in the trajectories, timing and extent of degradation highlight the need for in-depth regional case studies to understand the factors that contribute to either ecosystem sustainability or decline. We reconstructed social-ecological interactions in Hawaiian coral reef environments over 700 years using detailed datasets on ecological conditions, proximate anthropogenic stressor regimes and social change. Here we report previously undetected recovery periods in Hawaiian coral reefs, including a historical recovery in the MHI (∼AD 1400–1820) and an ongoing recovery in the NWHI (∼AD 1950–2009+). These recovery periods appear to be attributed to a complex set of changes in underlying social systems, which served to release reefs from direct anthropogenic stressor regimes. Recovery at the ecosystem level is associated with reductions in stressors over long time periods (decades+) and large spatial scales (>103 km2). Our results challenge conventional assumptions and reported findings that human impacts to ecosystems are cumulative and lead only to long-term trajectories of environmental decline. In contrast, recovery periods reveal that human societies have interacted sustainably with coral reef environments over long time periods, and that degraded ecosystems may still retain the adaptive capacity and resilience to recover from human impacts
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