960 research outputs found
Compton Echoes from Gamma-ray Bursts
Recent observations of gamma-ray bursts (GRBs) have provided growing evidence
for collimated outflows and emission, and strengthened the connection between
GRBs and supernovae. If massive stars are the progenitors of GRBs, the hard
photon pulse will propagate in the pre-burst, dense environment. Circumstellar
material will Compton scatter the prompt GRB radiation and give rise to a
reflection echo. We calculate luminosities, spectra, and light curves of such
Compton echoes in a variety of emission geometries and ambient gas
distributions, and show that the delayed hard X-ray flash from a pulse
propagating into a red supergiant wind could be detectable by Swift out to
z~0.2. Independently of the gamma-ray spectrum of the prompt burst, reflection
echoes will typically show a high-energy cutoff between m_ec^2/2 and m_ec^2
because of Compton downscattering. At fixed burst energy per steradian, the
luminosity of the reflected echo is proportional to the beaming solid angle,
Omega_b, of the prompt pulse, while the number of bright echoes detectable in
the sky above a fixed limiting flux increases as Omega_b^{1/2}, i.e. it is
smaller in the case of more collimated jets. The lack of an X-ray echo at one
month delay from the explosion poses severe constraints on the possible
existence of a lateral GRB jet in SN 1987A. The late r-band afterglow observed
in GRB990123 is fainter than the optical echo expected in a dense red
supergiant environment from a isotropic prompt optical flash. Significant MeV
delayed emission may be produced through the bulk Compton (or Compton drag)
effect resulting from the interaction of the decelerating fireball with the
scattered X-ray radiation.Comment: LaTeX, 18 pages, 4 figures, revised version accepted for publication
in the Ap
OSSE spectral analysis techniques
Analysis of the spectra from the Oriented Scintillation Spectrometer Experiment (OSSE) is complicated because of the typically low signal to noise (approx. 0.1 percent) and the large background variability. The OSSE instrument was designed to address these difficulties by periodically offset-pointing the detectors from the source to perform background measurements. These background measurements are used to estimate the background during each of the source observations. The resulting background-subtracted spectra can then be accumulated and fitted for spectral lines and/or continua. Data selection based on various environmental parameters can be performed at various stages during the analysis procedure. In order to achieve the instrument's statistical sensitivity, however, it will be necessary for investigators to develop a detailed understanding of the instrument operation, data collection, and the background spectrum and its variability. A brief description of the major steps in the OSSE spectral analysis process is described, including a discussion of the OSSE background spectrum and examples of several observational strategies
Mutual Zonated Interactions of Wnt and Hh Signaling Are Orchestrating the Metabolism of the Adult Liver in Mice and Human
The Hedgehog (Hh) and Wnt/β-Catenin (Wnt) cascades are morphogen pathways whose pronounced influence on adult liver metabolism has been identified in recent years. How both pathways communicate and control liver metabolic functions are largely unknown. Detecting core components of Wnt and Hh signaling and mathematical modeling showed that both pathways in healthy liver act largely complementary to each other in the pericentral (Wnt) and the periportal zone (Hh) and communicate mainly by mutual repression. The Wnt/Hh module inversely controls the spatiotemporal operation of various liver metabolic pathways, as revealed by transcriptome, proteome, and metabolome analyses. Shifting the balance to Wnt (activation) or Hh (inhibition) causes pericentralization and periportalization of liver functions, respectively. Thus, homeostasis of the Wnt/Hh module is essential for maintaining proper liver metabolism and to avoid the development of certain metabolic diseases. With caution due to minor species-specific differences, these conclusions may hold for human liver as well
Observations of GRB 990123 by the Compton Gamma-Ray Observatory
GRB 990123 was the first burst from which simultaneous optical, X-ray and
gamma-ray emission was detected; its afterglow has been followed by an
extensive set of radio, optical and X-ray observations. We have studied the
gamma-ray burst itself as observed by the CGRO detectors. We find that
gamma-ray fluxes are not correlated with the simultaneous optical observations,
and the gamma-ray spectra cannot be extrapolated simply to the optical fluxes.
The burst is well fit by the standard four-parameter GRB function, with the
exception that excess emission compared to this function is observed below ~15
keV during some time intervals. The burst is characterized by the typical
hard-to-soft and hardness-intensity correlation spectral evolution patterns.
The energy of the peak of the nu f_nu spectrum, E_p, reaches an unusually high
value during the first intensity spike, 1470 +/- 110 keV, and then falls to
\~300 keV during the tail of the burst. The high-energy spectrum above ~MeV is
consistent with a power law with a photon index of about -3. By fluence, GRB
990123 is brighter than all but 0.4% of the GRBs observed with BATSE, clearly
placing it on the -3/2 power-law portion of the intensity distribution.
However, the redshift measured for the afterglow is inconsistent with the
Euclidean interpretation of the -3/2 power-law. Using the redshift value of >=
1.61 and assuming isotropic emission, the gamma-ray fluence exceeds 10E54 ergs.Comment: Submitted to The Astrophysical Journal. 16 pages including 4 figure
Total prostatectomy as a treatment for prostatic carcinoma in 25 dogs
Objective: To describe the complications and outcome after total prostatectomy in dogs with histologically confirmed prostatic carcinoma. Study Design: Multi-institutional retrospective case series. Animals: 25 client-owned dogs. Methods: Medical records of dogs undergoing total prostatectomy were reviewed from 2004 to 2016. Data retrieved included signalment, presenting signs, preoperative clinical findings, laboratory data, diagnostic imaging, surgical technique, histologic diagnosis, postoperative complications, occurrence of postoperative metastasis, and survival. Results: Twenty-five dogs underwent total prostatectomy for prostatic carcinoma. Urinary anastomotic techniques included urethrourethral anastomosis in 14 dogs, cystourethral anastomosis in 9 dogs, ureterocolonic anastomosis in 1 dog, and anastomosis between the bladder neck and penile urethra in 1 dog. All dogs survived to discharge. Fifteen dogs were diagnosed with transitional cell carcinoma, 8 dogs with prostatic adenocarcinoma, 1 with prostatic cystadenocarcinoma, and 1 with an undifferentiated carcinoma. Permanent postoperative urinary incontinence was present in 8 of 23 dogs. The median survival time was shorter in dogs with extracapsular tumor extension compared with those with intracapsular tumors. The overall median survival time was 231 days (range, 24-1255), with 1- and 2-year survival rates equal to 32% and 12%, respectively. Conclusion and Clinical Significance: Total prostatectomy, combined with adjunct therapies, prolongs survival and lowers complication rates compared to previous reports of dogs with prostatic carcinoma. It should be noted, however, that case selection likely played a significant role in postoperative outcome
Influence of Exercise Modality on Cerebral-Ocular Hemodynamics and Pressures
Background: Moderate and high intensity aerobic or resistance exercise has clearly identified benefits for cardiac, muscle, and bone health. However, the impact of such exercise - either as a mitigating or an exacerbating factor - on the development of the visual impairment and intracranial pressure syndrome (VIIP) is unknown. Accordingly, our aim was to characterize the effect of an acute bout of resistance (RE), moderate-intensity continuous (CE), and high-intensity interval exercise (IE) during a cephalad fluid shift on cerebral-ocular hemodynamics and pressures. Methods: 10 male subjects (36 plus or minus 9 years) completed 4 testing days in a 15 degree head-down tilt (HDT): (1) assessment of maximum volume of O (sub 2), (2) RE session (4 sets of 12 repetition maximum leg press exercise), (3) CE session (30 minutes of cycling at 60 percent maximum volume of O (sub 2)), and (4) IE session (4 by 4-minute intervals of exercise at 85 percent maximum volume of O (sub 2) with 3-minute active rest periods). During each session, blood flow (Vivid-e, GE Healthcare) in extracranial arteries (common carotid artery, CCA; internal carotid artery, ICA; external carotid artery, ECA and vertebral artery, VA), and mean blood flow velocity in middle cerebral artery (MCA), internal jugular pressure (IJP; VeinPress), and intraocular pressure (IOP; Icare PRO) were measured at rest, at the end of each resistance or interval set, and every 5 minutes during continuous exercise. Translaminar pressure gradient (TLPG) was estimated by subtracting IJP from IOP. Results: There were no differences across days in pre-exercise resting blood flows or pressures. IOP decreased slightly from HDT rest (20.2 plus or minus 2.3 millimeters of mercury) to exercise (RE: 19.2 plus or minus 2.8 millimeters of mercury; CE: 18.9 plus or minus 3.2 millimeters of mercury; IE: 20.1 plus or minus 2.8 millimeters of mercury), while IJP decreased during CE (31.6 plus or minus 9.5 millimeters of mercury) and RE (32.0 plus or minus 8.1 millimeters of mercury), and increased during IE (35.1 plus or minus 9.5 millimeters of mercury) from HDT rest (33.3 plus or minus 6.5 millimeters of mercury). Estimated TLPG was increased during IE only. Compared to RE and CE, IE resulted in the greatest increase in MCA blood flow velocity and extracranial artery blood flow. Conclusions: These preliminary results suggest that high-intensity IE acutely increases cerebral blood flow, IJP, and TLPG. Alterations in TLPG is one mechanism that may contribute to optic nerve sheath edema in astronauts. Accordingly, acutely raising IOP and/or orbital pressure during exercise could optimize cerebral-ocular pressures during spaceflight
Characterizing College Science Assessments: The Three-Dimensional Learning Assessment Protocol
Citation: Laverty, J. T., Underwood, S. M., Matz, R. L., Posey, L. A., Carmel, J. H., Caballero, M. D., . . . Cooper, M. M. (2016). Characterizing College Science Assessments: The Three-Dimensional Learning Assessment Protocol. Plos One, 11(9), 21. doi:10.1371/journal.pone.0162333Many calls to improve science education in college and university settings have focused on improving instructor pedagogy. Meanwhile, science education at the K-12 level is undergoing significant changes as a result of the emphasis on scientific and engineering practices, crosscutting concepts, and disciplinary core ideas. This framework of "three-dimensional learning" is based on the literature about how people learn science and how we can help students put their knowledge to use. Recently, similar changes are underway in higher education by incorporating three-dimensional learning into college science courses. As these transformations move forward, it will become important to assess three-dimensional learning both to align assessments with the learning environment, and to assess the extent of the transformations. In this paper we introduce the Three-Dimensional Learning Assessment Protocol (3D-LAP), which is designed to characterize and support the development of assessment tasks in biology, chemistry, and physics that align with transformation efforts. We describe the development process used by our interdisciplinary team, discuss the validity and reliability of the protocol, and provide evidence that the protocol can distinguish between assessments that have the potential to elicit evidence of three-dimensional learning and those that do not
Netrin-3 Signals Through Serine Phosphorylation in Tetrahymena thermophila
The netrin family of proteins are structurally related to laminin and, while first discovered in the nematode Caenorhabditis elegans, are now known to be present in species throughout the animal kingdom, including humans. These proteins also have a wide variety of roles that include inhibition of apoptosis, chemorepulsion, and axonal guidance. Due to the results of previous studies involving netrin-1 in vertebrate systems, the current prevailing assumption is that netrins, when acting as chemorepellents, signal using tyrosine kinases. However, data that we gathered through phosphoserine-targeting ELISA assays and immunofluorescence microscopy demonstrates that the netrin-3 peptides signal Tetrahymena thermophila through serine phosphorylation instead, causing the ciliate protists to avoid netrin-3 peptides in response. Treatment with netrin-3 peptides also seems to cause mitotic inhibition in Tetrahymena, which can be reversed by addition of a serine kinase inhibitor. This new information suggests that netrin-3 may have physiological roles that have previously been unexplored
Gamma Radiation from PSR B1055-52
The telescopes on the Compton Gamma Ray Observatory (CGRO) have observed PSR
B1055-52 a number of times between 1991 and 1998. From these data, a more
detailed picture of the gamma radiation from this source has been developed,
showing several characteristics which distinguish this pulsar: the light curve
is complex; there is no detectable unpulsed emission; the energy spectrum is
flat, with no evidence of a sharp high-energy cutoff up to >4 GeV. Comparisons
of the gamma-ray data with observations at longer wavelengths show that no two
of the known gamma-ray pulsars have quite the same characteristics; this
diversity make s interpretation in terms of theoretical models difficult.Comment: 31 pages, 5 figures and 1 separate table, accepted for publication in
Ap
Pseudomonas aeruginosa Adaptation to Lungs of Cystic Fibrosis Patients Leads to Lowered Resistance to Phage and Protist Enemies
Pathogenic life styles can lead to highly specialized interactions with host species, potentially resulting in fitness trade-offs in other ecological contexts. Here we studied how adaptation of the environmentally transmitted bacterial pathogen, Pseudomonas aeruginosa, to cystic fibrosis (CF) patients affects its survival in the presence of natural phage (14/1, ΦKZ, PNM and PT7) and protist (Tetrahymena thermophila and Acanthamoebae polyphaga) enemies. We found that most of the bacteria isolated from relatively recently intermittently colonised patients (1-25 months), were innately phage-resistant and highly toxic for protists. In contrast, bacteria isolated from long time chronically infected patients (2-23 years), were less efficient in both resisting phages and killing protists. Moreover, chronic isolates showed reduced killing of wax moth larvae (Galleria mellonella) probably due to weaker in vitro growth and protease expression. These results suggest that P. aeruginosa long-term adaptation to CF-lungs could trade off with its survival in aquatic environmental reservoirs in the presence of microbial enemies, while lowered virulence could reduce pathogen opportunities to infect insect vectors; factors that are both likely to result in poorer environmental transmission. From an applied perspective, phage therapy could be useful against chronic P. aeruginosa lung infections that are often characterized by multidrug resistance: chronic isolates were least resistant to phages and their poor growth will likely slow down the emergence of beneficial resistance mutations
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