3,555 research outputs found
Discrete gauge symmetries and proton stability in the U(1)'-extended MSSM
The Minimal Supersymmetric Standard Model (MSSM) with conserved R-parity
suffers from several fine-tuning problems, e.g. the mu-problem and the problem
of proton decay through higher dimension operators. Both of these problems can
be avoided by replacing R-parity with a non-anomalous U(1)' gauge symmetry
which is broken at the TeV scale. The new gauge symmetry does not necessarily
forbid all renormalizable R-parity violating interactions among the MSSM
fields, and may allow for either lepton number or baryon number violation at
the renormalizable level. However, the proton decay problem resurfaces with the
introduction of new TeV-scale exotic fields which are required for gauge
anomaly cancellations. In this paper we investigate the issue of proton
stability in the presence of TeV-scale exotics. We show that there are large
classes of models in which TeV exotics do not destabilize the proton. We
classify the viable models according to the residual discrete symmetries after
U(1)' and electroweak symmetry breaking. In some of our examples the residual
U(1)' discrete gauge symmetry within the MSSM sector alone ensures that the
proton is absolutely stable, for any exotic representations. In other cases the
proton can be sufficiently long-lived, depending on the U(1)' and hypercharge
discrete charge assignments for the exotic fields. Our analysis outlines a
general scheme for ensuring proton stability in the presence of light exotics
with baryon and lepton number violating interactions.Comment: Version to appear in JHE
Dark Matter Halo Properties vs. Local Density and Cosmic Web Location
We study the effects of the local environmental density and the cosmic web
environment (filaments, walls, and voids) on key properties of dark matter
halos using the Bolshoi-Planck LCDM cosmological simulation. The z = 0
simulation is analysed into filaments, walls, and voids using the SpineWeb
method and also the VIDE package of tools, both of which use the watershed
transform. The key halo properties that we study are the specific mass
accretion rate, spin parameter, concentration, prolateness, scale factor of the
last major merger, and scale factor when the halo had half of its z = 0 mass.
For all these properties, we find that there is no discernible difference
between the halo properties in filaments, walls, or voids when compared at the
same environmental density. As a result, we conclude that environmental density
is the core attribute that affects these properties. This conclusion is in line
with recent findings that properties of galaxies in redshift surveys are
independent of their cosmic web environment at the same environmental density
at z ~ 0. We also find that the local web environment of the Milky Way and the
Andromeda galaxies near the centre of a cosmic wall does not appear to have any
effect on the properties of these galaxies' dark matter halos except for their
orientation, although we find that it is rather rare to have such massive halos
near the centre of a relatively small cosmic wall.Comment: 23 page
, Nuclear quadrupole moment of 139La from relativistic electronic structure calculations of the electric field gradients in LaF, LaCl, LaBr and LaI
Relativistic coupled cluster theory is used to determine accurate electric field gradients in order to provide a theoretical value for the nuclear quadrupole moment of La139. Here we used the diatomic lanthanum monohalides LaF, LaCl, LaBr, and LaI as accurate nuclear quadrupole coupling constants are available from rotational spectroscopy by Rubinoff [J. Mol. Spectrosc. 218, 169 (2003)]. The resulting nuclear quadrupole moment for La139 (0.200±0.006 barn) is in excellent agreement with earlier work using atomic hyperfine spectroscopy [0.20 (1) barn]. © 2007 American Institute of Physics
Identification of the protein kinases Pyk3 and Phg2 as regulators of the STATc-mediated response to hyperosmolarity
Cellular adaptation to changes in environmental osmolarity is crucial for cell survival. In Dictyostelium, STATc is a key regulator of the transcriptional response to hyperosmotic stress. Its phosphorylation and consequent activation is controlled by two signaling branches, one cGMP- and the other Ca(2+)-dependent, of which many signaling components have yet to be identified. The STATc stress signalling pathway feeds back on itself by upregulating the expression of STATc and STATc-regulated genes. Based on microarray studies we chose two tyrosine-kinase like proteins, Pyk3 and Phg2, as possible modulators of STATc phosphorylation and generated single and double knock-out mutants to them. Transcriptional regulation of STATc and STATc dependent genes was disturbed in pyk3(-), phg2(-), and pyk3(-)/phg2(-) cells. The absence of Pyk3 and/or Phg2 resulted in diminished or completely abolished increased transcription of STATc dependent genes in response to sorbitol, 8-Br-cGMP and the Ca(2+) liberator BHQ. Also, phospho-STATc levels were significantly reduced in pyk3(-) and phg2(-) cells and even further decreased in pyk3(-)/phg2(-) cells. The reduced phosphorylation was mirrored by a significant delay in nuclear translocation of GFP-STATc. The protein tyrosine phosphatase 3 (PTP3), which dephosphorylates and inhibits STATc, is inhibited by stress-induced phosphorylation on S448 and S747. Use of phosphoserine specific antibodies showed that Phg2 but not Pyk3 is involved in the phosphorylation of PTP3 on S747. In pull-down assays Phg2 and PTP3 interact directly, suggesting that Phg2 phosphorylates PTP3 on S747 in vivo. Phosphorylation of S448 was unchanged in phg2(-) cells. We show that Phg2 and an, as yet unknown, S448 protein kinase are responsible for PTP3 phosphorylation and hence its inhibition, and that Pyk3 is involved in the regulation of STATc by either directly or indirectly activating it. Our results add further complexities to the regulation of STATc, which presumably ensure its optimal activation in response to different environmental cues
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Postoperative Pain Management in DIEP Flap Breast Reconstruction: Identification of Patients With Poor Pain Control
Objective: Adequate control of postoperative pain directly improves patient satisfaction and outcomes, and timely identification of patients with poorly controlled pain is essential. Pain management protocols are best studied in patients recovering from the same operation. In our institution, the postoperative pain regimen for patients undergoing deep inferior epigastric perforator (DIEP) flap breast reconstruction is standardized using patient-controlled analgesia (PCA) followed by conversion to oral narcotics. From this uniform population, we were able to identify a subgroup of patients with poor pain control. Methods: Over a 44-month period, 179 consecutive patients underwent DIEP flap breast reconstruction with 242 flaps performed. A retrospective chart review recorded PCA usage, visual analog scale pain scores, and length of stay. Results: Pain management with PCA after DIEP flap breast reconstruction was uniformly controlled. Most patients (74.9%) required PCA usage in the first 2 days with conversion to oral analgesics. A subgroup of patients (25.1%) continued to require PCA usage on the third postoperative day. These “nonresponder” patients had a higher visual analog scale score on the first postoperative day, higher total intravenous morphine use, and a longer length of stay (all, P < .05). A multivariate analysis revealed more nonresponders among patients undergoing immediate breast reconstruction (P < .05); however, all other factors analyzed had no correlation. Conclusion: We report a subgroup of patients with poor pain control after DIEP flap breast reconstruction. This group of patients required a longer course of pain management and subsequently a longer hospital stay. Pain management protocols that identify these patients promptly can allow for appropriate modifications
Pure point diffraction and cut and project schemes for measures: The smooth case
We present cut and project formalism based on measures and continuous weight
functions of sufficiently fast decay. The emerging measures are strongly almost
periodic. The corresponding dynamical systems are compact groups and
homomorphic images of the underlying torus. In particular, they are strictly
ergodic with pure point spectrum and continuous eigenfunctions. Their
diffraction can be calculated explicitly. Our results cover and extend
corresponding earlier results on dense Dirac combs and continuous weight
functions with compact support. They also mark a clear difference in terms of
factor maps between the case of continuous and non-continuous weight functions.Comment: 30 page
Radioactive 26Al and massive stars in the Galaxy
Gamma-rays from radioactive 26Al (half life ~7.2 10^5 yr) provide a
'snapshot' view of ongoing nucleosynthesis in the Galaxy. The Galaxy is
relatively transparent to such gamma-rays, and emission has been found
concentrated along the plane of the Galaxy. This led to the conclusion1 that
massive stars throughout the Galaxy dominate the production of 26Al. On the
other hand, meteoritic data show locally-produced 26Al, perhaps from spallation
reactions in the protosolar disk. Furthermore, prominent gamma-ray emission
from the Cygnus region suggests that a substantial fraction of Galactic 26Al
could originate in localized star-forming regions. Here we report high spectral
resolution measurements of 26Al emission at 1808.65 keV, which demonstrate that
the 26Al source regions corotate with the Galaxy, supporting its Galaxy-wide
origin. We determine a present-day equilibrium mass of 2.8 (+/-0.8) M_sol of
26Al. We use this to estimate that the frequency of core collapse (i.e. type
Ib/c and type II) supernovae to be 1.9(+/- 1.1) events per century.Comment: accepted for publication in Nature, 24 pages including Online
Supplements, 11 figures, 1 tabl
Multisensory causal inference in the brain
At any given moment, our brain processes multiple inputs from its different sensory modalities (vision, hearing, touch, etc.). In deciphering this array of sensory information, the brain has to solve two problems: (1) which of the inputs originate from the same object and should be integrated and (2) for the sensations originating from the same object, how best to integrate them. Recent behavioural studies suggest that the human brain solves these problems using optimal probabilistic inference, known as Bayesian causal inference. However, how and where the underlying computations are carried out in the brain have remained unknown. By combining neuroimaging-based decoding techniques and computational modelling of behavioural data, a new study now sheds light on how multisensory causal inference maps onto specific brain areas. The results suggest that the complexity of neural computations increases along the visual hierarchy and link specific components of the causal inference process with specific visual and parietal regions
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