1,263 research outputs found
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Phd-kurs ved NTNU-bibliotekene – en utviklingshistorieVi vil se nærmere på ide/opplegg, organisering, gjennomføring og erfaringer fra forskjellige kurs for phd-kandidater ved NTNU-biblioteket: Kurs for humanister og samfunnsvitere, kurs for medisinere og kurs for kandidater innen teknologi og naturvitenskap (mest sivilingeniører), avholdt på forskjellige campuser og av forskjellige undervisere. Å mestre avansert søking og databehandling blir bare mer og mer sentralt for forskning, selv om det varierer fra disiplin til disiplin. Vi vil gjennomgå egen erfaring, fagmiljøenes behov og hva forskning viser om behovet for informasjonskompetanse-undervisning av PhD-kandidater, med fokus på forskjellige vitenskapers informasjonskompetanse. Krav om at forskning skal være original, bygge på tidligere forskning og de muligheter som vi har fått til å behandle mye større mengder data enn før (e-science) innebærer at kursholderne må være svært oppdatert og ha spisskompetanse i de enkelte baser og verktøy. Dessuten er plagiering og kildevurdering viktige og aktuelle tema. Kursene krever høy kompetanse hos kursholderne og det beste er å utnytte de forskjellige kompetansene som finnes i biblioteket slik at kursene blir et resultat av team-arbeid. I tillegg trekkes andre fagfolk inn (forskningsetikk, akademisk skriving m.m). De organisatoriske utfordringene og markedsføring av kursene blir også viktige når vi arrangerer slike kurs. Undervisningstilbudet blir evaluert fortløpende, og vi ønsker å sette fokus på erfaringsutveksling og praktisk gjennomføring i tillegg til å se på innholdet i våre kurs
The relationship between galaxy and dark matter halo size from z ∼ 3 to the present
We explore empirical constraints on the statistical relationship between the radial size of galaxies and the radius of their host dark matter haloes from z similar to 0.1-3 using the Galaxy And Mass Assembly (GAMA) and Cosmic Assembly Near Infrared Deep Extragalactic Legacy Survey (CANDELS) surveys. We map dark matter halo mass to galaxy stellar mass using relationships from abundance matching, applied to the Bolshoi-Planck dissipationless N-body simulation. We define SRHR equivalent to r(e)/R-h as the ratio of galaxy radius to halo virial radius, and SRHR lambda equivalent to r(e)/(lambda R-h) as the ratio of galaxy radius to halo spin parameter times halo radius. At z similar to 0.1, we find an average value of SRHR similar or equal to 0.018 and SRHR. similar or equal to 0.5 with very little dependence on stellar mass. Stellar radius-halo radius (SRHR) and SRHR lambda have a weak dependence on cosmic time since z similar to 3. SRHR shows a mild decrease over cosmic time for low-mass galaxies, but increases slightly or does not evolve formoremassive galaxies. We find hints that at high redshift (z similar to 2-3), SRHR. is lower for more massive galaxies, while it shows no significant dependence on stellar mass at z less than or similar to 0.5. We find that for both the GAMA and CANDELS samples, at all redshifts from z similar to 0.1-3, the observed conditional size distribution in stellar mass bins is remarkably similar to the conditional distribution of lambda R-h. We discuss the physical interpretation and implications of these results
Merger of binary neutron stars of unequal mass in full general relativity
We present results of three dimensional numerical simulations of the merger
of unequal-mass binary neutron stars in full general relativity. A -law
equation of state is adopted, where , ,
\varep, and are the pressure, rest mass density, specific internal
energy, and the adiabatic constant, respectively. We take and the
baryon rest-mass ratio to be in the range 0.85--1. The typical grid size
is for . We improve several implementations since the
latest work. In the present code, the radiation reaction of gravitational waves
is taken into account with a good accuracy. This fact enables us to follow the
coalescence all the way from the late inspiral phase through the merger phase
for which the transition is triggered by the radiation reaction. It is found
that if the total rest-mass of the system is more than times of the
maximum allowed rest-mass of spherical neutron stars, a black hole is formed
after the merger irrespective of the mass ratios. The gravitational waveforms
and outcomes in the merger of unequal-mass binaries are compared with those in
equal-mass binaries. It is found that the disk mass around the so formed black
holes increases with decreasing rest-mass ratios and decreases with increasing
compactness of neutron stars. The merger process and the gravitational
waveforms also depend strongly on the rest-mass ratios even for the range --1.Comment: 32 pages, PRD68 to be publishe
Tidal decay and orbital circularization in close-in two-planet systems
The motion of two planets around a Sun-like star under the combined effects
of mutual interaction and tidal dissipation is investigated. The secular
behaviour of the system is analyzed using two different approaches. First, we
solve the exact equations of motion through the numerical simulation of the
system evolution. In addition to the orbital decay and circularization, we show
that the final configuration of the system is affected by the shrink of the
inner orbit. Our second approach consist in the analysis of the stationary
solutions of mean equations of motion based on a Hamiltonian formalism. We
consider the case of a hot super-Earth planet with a more massive outer
companion. As a real example, the CoRoT-7 system is analyzed solving the exact
and mean equations of motion. The star-planet tidal interaction produces
orbital decay and circularization of the orbit of CoRoT-7b. In addition, the
long-term tidal evolution is such that the eccentricity of CoRoT-7c is also
circularized and a pair of final circular orbits is obtained. A curve in the
space of eccentricities can be constructed through the computation of
stationary solutions of mean equations including dissipation. The application
to CoRoT-7 system shows that the stationary curve agrees with the result of
numerical simulations of exact equations. A similar investigation performed in
a super-Earth-Jupiter two-planet system shows that the doubly circular state is
accelerated when there is a significant orbital migration of the inner planet,
in comparison with previous results were migration is neglected.Comment: Accepted for publication in MNRAS; 10 pages, 13 figure
Hypoxia induces a glycolytic complex in intestinal epithelial cells independent of HIF-1-driven glycolytic gene expression
The metabolic adaptation of eukaryotic cells to hypoxia involves increasing dependence upon glycolytic adenosine triphosphate (ATP) production, an event with consequences for cellular bioenergetics and cell fate. This response is regulated at the transcriptional level by the hypoxia-inducible factor-1(HIF-1)-dependent transcriptional upregulation of glycolytic enzymes (GEs) and glucose transporters. However, this transcriptional upregulation alone is unlikely to account fully for the levels of glycolytic ATP produced during hypoxia. Here, we investigated additional mechanisms regulating glycolysis in hypoxia. We observed that intestinal epithelial cells treated with inhibitors of transcription or translation and human platelets (which lack nuclei and the capacity for canonical transcriptional activity) maintained the capacity for hypoxia-induced glycolysis, a finding which suggests the involvement of a nontranscriptional component to the hypoxia-induced metabolic switch to a highly glycolytic phenotype. In our investigations into potential nontranscriptional mechanisms for glycolytic induction, we identified a hypoxia-sensitive formation of complexes comprising GEs and glucose transporters in intestinal epithelial cells. Surprisingly, the formation of such glycolytic complexes occurs independent of HIF-1-driven transcription. Finally, we provide evidence for the presence of HIF-1α in cytosolic fractions of hypoxic cells which physically interacts with the glucose transporter GLUT1 and the GEs in a hypoxia-sensitive manner. In conclusion, we provide insights into the nontranscriptional regulation of hypoxia-induced glycolysis in intestinal epithelial cells.</p
Histidine modification and mutagenesis point to the involvement of a large conformational change in the mechanism of action of phage lambda lysozyme
Phage lambda lysozyme is structurally related to other known lysozymes but its mechanism of action is different from the classical lysozyme mechanism, acting as a transglycosidase rather than a hydrolase. As two conformations have been revealed by the crystal structure, we investigated the effect of mutating and modifying a histidine located near to or far from the active site in the respective closed and open conformations. Whereas its asparagine mutation has little or no effect on activity, its N-carbethoxylation inactivates the enzyme. This provide further evidence for the involvement of the closed conformation and for the need of conformational mobility in lambda lysozyme function
Active Galactic Nuclei and the Truncation of Star Formation in K+A Galaxies
We have searched for active galactic nuclei (AGNs) in K+A galaxies, using
multiwavelength imaging and spectroscopy in the Bootes field of the NOAO Deep
Wide-Field Survey. The K+A galaxies, which have had their star formation
rapidly truncated, are selected via their strong Balmer absorption lines and
weak H-alpha emission. Our sample consists of 24 K+A galaxies selected from
6594 0.10<z<0.35 galaxies brighter than I=20 with optical spectroscopy from the
AGN and Galaxy Evolution Survey. Two thirds of the K+A galaxies are likely
ongoing galaxy mergers, with nearby companion galaxies or tidal tails. Galaxy
mergers may be responsible for the truncation of star formation, or we are
observing the aftermath of merger triggered starbursts. As expected, the
optical colors of K+A galaxies largely fall between blue galaxies with ongoing
star formation and red passive galaxies. However, only 1% of the galaxies with
colors between the red and blue populations are K+A galaxies, and we conclude
that the truncation of star formation in K+A galaxies must have been unusually
abrupt (<100 Myr). We examined the AGN content of K+A galaxies with both
optical emission-line ratios (BPT diagrams) and Chandra X-ray imaging. At least
half of all K+A galaxies display the optical emission-line ratios of AGNs, and
a third of M_R<-22 K+A galaxies host AGNs with X-ray luminosities of 10^{42}
erg/s. The faintest K+A galaxies do not show clear evidence for hosting AGNs,
having emission-line ratios consistent with photoionization by massive stars
and few X-ray detections. We speculate that two mechanisms may be responsible
for the truncation of star formation in K+A galaxies, with AGN feedback only
playing a role in M_R<-20.5 galaxies.Comment: Accepted for publication in the Astrophysical Journal. 13 pages, 8
figure
The central image of a gravitationally lensed quasar
A galaxy can act as a gravitational lens, producing multiple images of a
background object. Theory predicts there should be an odd number of images but,
paradoxically, almost all observed lenses have 2 or 4 images. The missing image
should be faint and appear near the galaxy's center. These ``central images''
have long been sought as probes of galactic cores too distant to resolve with
ordinary observations. There are five candidates, but in one case the third
image is not necessarily a central image, and in the others, the central
component might be a foreground source rather than a lensed image. Here we
report the most secure identification of a central image, based on radio
observations of PMN J1632-0033, one of the latter candidates. Lens models
incorporating the central image show that the mass of the lens galaxy's central
black hole is less than 2 x 10^8 M_sun, and the galaxy's surface density at the
location of the central image is more than 20,000 M_sun per square parsec, in
agreement with expectations based on observations of galaxies hundreds of times
closer to the Earth.Comment: Nature, in press [7 pp, 2 figs]. Standard media embargo applies
before publicatio
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