872 research outputs found
Interpretation of UV Absorption Lines in SN1006
We present a theoretical interpretation of the broad silicon and iron UV
absorption features observed with the Hubble Space Telescope in the spectrum of
the Schweizer-Middleditch star behind the remnant of Supernova 1006. These
features are caused by supernova ejecta in SN1006. We propose that the
redshifted SiII2 1260 A feature consists of both unshocked and shocked SiII.
The sharp red edge of the line at 7070 km/s indicates the position of the
reverse shock, while its Gaussian blue edge reveals shocked Si with a mean
velocity of 5050 km/s and a dispersion of 1240 km/s, implying a reverse shock
velocity of 2860 km/s. The measured velocities satisfy the energy jump
condition for a strong shock, provided that all the shock energy goes into
ions, with little or no collisionless heating of electrons. The line profiles
of the SiIII and SiIV absorption features indicate that they arise mostly from
shocked Si. The total mass of shocked and unshocked Si inferred from the SiII,
SiIII and SiIV profiles is M_Si = 0.25 \pm 0.01 Msun on the assumption of
spherical symmetry. Unshocked Si extends upwards from 5600 km/s. Although there
appears to be some Fe mixed with the Si at lower velocities < 7070 km/s, the
absence of FeII absorption with the same profile as the shocked SiII suggests
little Fe mixed with Si at higher (before being shocked) velocities. The column
density of shocked SiII is close to that expected for SiII undergoing steady
state collisional ionization behind the reverse shock, provided that the
electron to SiII ratio is low, from which we infer that most of the shocked Si
is likely to be of a fairly high degree of purity, unmixed with other elements.
We propose that the ambient interstellar density on the far side of SN1006 is
anomalously low compared to the density around the rest of the remnant. ThisComment: 24 pages, with 8 figures included. Accepted for publication in the
Astrophysical Journa
GPS water level measurements for Indonesia's Tsunami Early Warning System
On Boxing Day 2004, a severe tsunami was generated by a strong earthquake in Northern Sumatra causing a large number of casualties. At this time, neither an offshore buoy network was in place to measure tsunami waves, nor a system to disseminate tsunami warnings to local governmental entities. Since then, buoys have been developed by Indonesia and Germany, complemented by NOAA's Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys, and have been moored offshore Sumatra and Java. The suite of sensors for offshore tsunami detection in Indonesia has been advanced by adding GPS technology for water level measurements. <br><br> The usage of GPS buoys in tsunami warning systems is a relatively new approach. The concept of the German Indonesian Tsunami Early Warning System (GITEWS) (Rudloff et al., 2009) combines GPS technology and ocean bottom pressure (OBP) measurements. Especially for near-field installations where the seismic noise may deteriorate the OBP data, GPS-derived sea level heights provide additional information. <br><br> The GPS buoy technology is precise enough to detect medium to large tsunamis of amplitudes larger than 10 cm. The analysis presented here suggests that for about 68% of the time, tsunamis larger than 5 cm may be detectable
Chronically stressed or stress-preconditioned neurons fail to maintain stress granule assembly
Dysregulation of stress granules (SGs) and their resident proteins contributes to pathogenesis of a number of (neuro)degenerative diseases. Phosphorylation of eIF2α is an event integrating different types of cellular stress and it is required for SG assembly. Phosphorylated eIF2α (p-eIF2α) is upregulated in the nervous system in some neurodegenerative conditions. We found that increasing p-eIF2α level by proteasomal inhibition in cultured cells, including mouse and human neurons, prior to a SG-inducing stress (âstress preconditioningâ), limits their ability to maintain SG assembly. This is due to upregulation of PP1 phosphatase regulatory subunits GADD34 and/or CReP in preconditioned cells and early decline of p-eIF2α levels during subsequent acute stress. In two model systems with constitutively upregulated p-eIF2α, mouse embryonic fibroblasts lacking CReP and brain neurons of tau transgenic mice, SG formation was also impaired. Thus neurons enduring chronic stress or primed by a transient mild stress fail to maintain p-eIF2α levels following subsequent acute stress, which would compromise protective function of SGs. Our findings provide experimental evidence on possible loss of function for SGs in certain neurodegenerative diseases
Bubbles and denaturation in DNA
The local opening of DNA is an intriguing phenomenon from a statistical
physics point of view, but is also essential for its biological function. For
instance, the transcription and replication of our genetic code can not take
place without the unwinding of the DNA double helix. Although these biological
processes are driven by proteins, there might well be a relation between these
biological openings and the spontaneous bubble formation due to thermal
fluctuations. Mesoscopic models, like the Peyrard-Bishop-Dauxois model, have
fairly accurately reproduced some experimental denaturation curves and the
sharp phase transition in the thermodynamic limit. It is, hence, tempting to
see whether these models could be used to predict the biological activity of
DNA. In a previous study, we introduced a method that allows to obtain very
accurate results on this subject, which showed that some previous claims in
this direction, based on molecular dynamics studies, were premature. This could
either imply that the present PBD should be improved or that biological
activity can only be predicted in a more complex frame work that involves
interactions with proteins and super helical stresses. In this article, we give
detailed description of the statistical method introduced before. Moreover, for
several DNA sequences, we give a thorough analysis of the bubble-statistics as
function of position and bubble size and the so-called -denaturation curves
that can be measured experimentally. These show that some important
experimental observations are missing in the present model. We discuss how the
present model could be improved.Comment: 15 pages, 5 figures, published as Eur. Phys. J. E 20 : 421-434 AUG
200
SRM targeted proteomics in search for biomarkers of HCV âinduced progression of fibrosis to cirrhosis in HALT â C patients
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92042/1/pmic7038.pd
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