272 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
The Nonvariability of the Progenitor of Supernova 1993J in M81
An archive of images taken in the early 1980s exists for a field which includes the progenitor of supernova 1993J in M81. Fifty-four CCD frames in V, and several in other colors from this set taken in 1984 are analyzed to demonstrate that the progenitor of supernova 1993J was not variable to within a limit of 0.2 mag. The frames analyzed cover a time span of 150 days. The colors of the M81 SN progenitor are consistent with those of a late G supergiant
SN~1991T: Reflections of Past Glory
We have obtained photometry and spectra of SN~1991T which extend more than
1000 days past maximum light, by far the longest a SN~Ia has been followed.
Although SN~1991T exhibited nearly normal photometric behavior in the first 400
days following maximum, by 600 days its decline had slowed, and by 950~days the
supernova brightness was consistent with a constant apparent magnitude of
. Spectra near maximum showed minor variations on the SN~Ia theme
which grew less conspicuous during the exponential decline. At 270 days the
nebular spectrum was composed of Fe and Co lines common to SNe~Ia. However, by
750 days past maximum light, these lines had shifted in wavelength, and were
superimposed on a strong blue continuum. The luminosity of SN~1991T at 950 days
is more than ~ergs~s with a rate of
decline of less than mags/100~days. We show that this emission is likely
to be light that was emitted by SN~1991T near maximum light which has reflected
from foreground dust, much like the light echos observed around SN~1987A.Comment: 15 pages (includes figures and tables) uuencoded compressed
postscript, CfA Preprint - To Appear in ApJ
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]
The Nonvariability of the Progenitor of Supernova 1993J in M81
An archive of images taken in the early 1980s exists for a field which includes the progenitor of supernova 1993J in M81. Fifty-four CCD frames in V, and several in other colors from this set taken in 1984 are analyzed to demonstrate that the progenitor of supernova 1993J was not variable to within a limit of 0.2 mag. The frames analyzed cover a time span of 150 days. The colors of the M81 SN progenitor are consistent with those of a late G supergiant
Effect of Tuned Parameters on a LSA MCQ Answering Model
This paper presents the current state of a work in progress, whose objective
is to better understand the effects of factors that significantly influence the
performance of Latent Semantic Analysis (LSA). A difficult task, which consists
in answering (French) biology Multiple Choice Questions, is used to test the
semantic properties of the truncated singular space and to study the relative
influence of main parameters. A dedicated software has been designed to fine
tune the LSA semantic space for the Multiple Choice Questions task. With
optimal parameters, the performances of our simple model are quite surprisingly
equal or superior to those of 7th and 8th grades students. This indicates that
semantic spaces were quite good despite their low dimensions and the small
sizes of training data sets. Besides, we present an original entropy global
weighting of answers' terms of each question of the Multiple Choice Questions
which was necessary to achieve the model's success.Comment: 9 page
mTORC1 signalling and eIF4E/4E-BP1 translation initiation factor stoichiometry influence recombinant protein productivity from GS-CHOK1 cells
Many protein-based biotherapeutics are produced in cultured Chinese hamster ovary (CHO) cell lines. Recent reports have demonstrated that translation of recombinant mRNAs and global control of the translation machinery via mammalian target of rapamycin (mTOR) signalling are important determinants of the amount and quality of recombinant protein such cells can produce. mTOR complex 1 (mTORC1) is a master regulator of cell growth/division, ribosome biogenesis and protein synthesis, but the relationship between mTORC1 signalling, cell growth and proliferation and recombinant protein yields from mammalian cells, and whether this master regulating signalling pathway can be manipulated to enhance cell biomass and recombinant protein production (rPP) are not well explored. We have investigated mTORC1 signalling and activity throughout batch culture of a panel of sister recombinant glutamine synthetase-CHO cell lines expressing different amounts of a model monoclonal IgG4, to evaluate the links between mTORC1 signalling and cell proliferation, autophagy, recombinant protein expression, global protein synthesis and mRNA translation initiation. We find that the expression of the mTORC1 substrate 4E-binding protein 1 (4E-BP1) fluctuates throughout the course of cell culture and, as expected, that the 4E-BP1 phosphorylation profiles change across the culture. Importantly, we find that the eIF4E/4E-BP1 stoichiometry positively correlates with cell productivity. Furthermore, eIF4E amounts appear to be co-regulated with 4E-BP1 amounts. This may reflect a sensing of either change at the mRNA level as opposed to the protein level or the fact that the phosphorylation status, as well as the amount of 4E-BP1 present, is important in the co-regulation of eIF4E and 4E-BP1
Application of an NMR/Crystallography Fragment Screening Platform for the Assessment and Rapid Discovery of New HIV-CA Binding Fragments
Identification and assessment of novel targets is essential to combat drug resistance in the treatment of HIV/AIDS. HIV Capsid (HIV-CA), the protein playing a major role in both the early and late stages of the viral life cycle, has emerged as an important target. We have applied an NMR fragment screening platform and identified molecules that bind to the N-terminal domain (NTD) of HIV-CA at a site close to the interface with the C-terminal domain (CTD). Using X-ray crystallography, we have been able to obtain crystal structures to identify the binding mode of these compounds. This allowed for rapid progression of the initial, weak binding, fragment starting points to compounds 37 and 38, which have 19F-pKi values of 5.3 and 5.4 respectively.</p
Therapeutic administration of broadly neutralizing FI6 antibody reveals lack of interaction between human IgG1 and pig Fc receptors
Influenza virus infection is a significant global health threat. Because of the lack of cross-protective universal vaccines, short time window during which antivirals are effective and drug resistance, new therapeutic anti-influenza strategies are required. Broadly, cross-protective antibodies that target conserved sites in the hemagglutinin (HA) stem region have been proposed as therapeutic agents. FI6 is the first proven such monoclonal antibody to bind to H1–H16 and is protective in mice and ferrets. Multiple studies have shown that Fc-dependent mechanisms are essential for FI6 in vivo efficacy. Here, we show that therapeutic administration of FI6 either intravenously or by aerosol to pigs did not reduce viral load in nasal swabs or broncho-alveolar lavage, but aerosol delivery of FI6 reduced gross pathology significantly. We demonstrate that pig Fc receptors do not bind human IgG1 and that FI6 did not mediate antibody-dependent cytotoxicity (ADCC) with pig PBMC, confirming that ADCC is an important mechanism of protection by anti-stem antibodies in vivo. Enhanced respiratory disease, which has been associated with pigs with cross-reactive non-neutralizing anti-HA antibodies, did not occur after FI6 administration. Our results also show that in vitro neutralizing antibody responses are not a robust correlate of protection for the control of influenza infection and pathology in a natural host model
Mapping main, epistatic and sex-specific QTL for body composition in a chicken population divergently selected for low or high growth rate
<p>Abstract</p> <p>Background</p> <p>Delineating the genetic basis of body composition is important to agriculture and medicine. In addition, the incorporation of gene-gene interactions in the statistical model provides further insight into the genetic factors that underlie body composition traits. We used Bayesian model selection to comprehensively map main, epistatic and sex-specific QTL in an F<sub>2 </sub>reciprocal intercross between two chicken lines divergently selected for high or low growth rate.</p> <p>Results</p> <p>We identified 17 QTL with main effects across 13 chromosomes and several sex-specific and sex-antagonistic QTL for breast meat yield, thigh + drumstick yield and abdominal fatness. Different sets of QTL were found for both breast muscles [<it>Pectoralis (P) major </it>and <it>P. minor</it>], which suggests that they could be controlled by different regulatory mechanisms. Significant interactions of QTL by sex allowed detection of sex-specific and sex-antagonistic QTL for body composition and abdominal fat. We found several female-specific <it>P. major </it>QTL and sex-antagonistic <it>P. minor </it>and abdominal fatness QTL. Also, several QTL on different chromosomes interact with each other to affect body composition and abdominal fatness.</p> <p>Conclusions</p> <p>The detection of main effects, epistasis and sex-dimorphic QTL suggest complex genetic regulation of somatic growth. An understanding of such regulatory mechanisms is key to mapping specific genes that underlie QTL controlling somatic growth in an avian model.</p
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