69 research outputs found
Laminin and α-Dystroglycan Mediate Acetylcholine Receptor Aggregation via a MuSK-Independent Pathway
Specific isoforms of laminin (LN) are concentrated at neuromuscular junctions (NMJs) where they may participate in synaptic organization or function. In myotubes from C2 cells, LN is concentrated within the majority of spontaneous acetylcholine receptor (AChR) aggregates. Neural agrin substantially increases this colocalization, suggesting that agrin can recruit LN into AChR aggregates. Addition of LN to C2 myotubes induces a more than twofold increase in the number of AChR aggregates. These aggregates have a larger size and are more dense than are those induced by agrin, suggesting that LN is involved in the growth and/or stabilization of AChR aggregates. Consistent with this hypothesis, an antiserum to LN reduces the size of individual AChR aggregates but increases their number. In C2 myotubes, extracellular matrix receptors containing the integrin beta1 subunit are poorly colocalized with AChR aggregates, suggesting that integrins may not be involved in LN-induced aggregation. In contrast, almost all AChR aggregates are associated with dystroglycan immunoreactivity, and monoclonal antibody (mAb) IIH6 against alpha-dystroglycan (alpha-DG), a LN and agrin receptor, causes a concentration-dependent inhibition of LN-induced aggregation. Moreover, S27 cells, which lack a functional alpha-DG, and two C2-derived cell lines expressing antisense DG mRNA fail to aggregate AChRs in response to LN. Finally, LN-induced AChR aggregation does not involve the phosphorylation of the muscle-specific tyrosine kinase receptor (MuSK) or the AChR beta subunit. We hypothesize that the interaction of LN with alpha-DG contributes to the growth and/or stabilization of AChR microaggregates into macroaggregates at the developing NMJ via a MuSK-independent mechanism
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using
ultracold atoms in an optical lattice. We investigate the phase evolution of an
array of essentially non-interacting matter waves and observe matter-wave
collapse and revival in the form of a Talbot interference pattern. By using
long expansion times, we image momentum space with sub-recoil resolution,
allowing us to observe fractional Talbot fringes up to 10th order.Comment: 17 pages, 7 figure
Pion, kaon, proton and anti-proton transverse momentum distributions from p+p and d+Au collisions at GeV
Identified mid-rapidity particle spectra of , , and
from 200 GeV p+p and d+Au collisions are reported. A
time-of-flight detector based on multi-gap resistive plate chamber technology
is used for particle identification. The particle-species dependence of the
Cronin effect is observed to be significantly smaller than that at lower
energies. The ratio of the nuclear modification factor () between
protons and charged hadrons () in the transverse momentum
range GeV/c is measured to be
(stat)(syst) in minimum-bias collisions and shows little
centrality dependence. The yield ratio of in minimum-bias d+Au
collisions is found to be a factor of 2 lower than that in Au+Au collisions,
indicating that the Cronin effect alone is not enough to account for the
relative baryon enhancement observed in heavy ion collisions at RHIC.Comment: 6 pages, 4 figures, 1 table. We extended the pion spectra from
transverse momentum 1.8 GeV/c to 3. GeV/
Azimuthal anisotropy at RHIC: the first and fourth harmonics
We report the first observations of the first harmonic (directed flow, v_1),
and the fourth harmonic (v_4), in the azimuthal distribution of particles with
respect to the reaction plane in Au+Au collisions at the Relativistic Heavy Ion
Collider (RHIC). Both measurements were done taking advantage of the large
elliptic flow (v_2) generated at RHIC. From the correlation of v_2 with v_1 it
is determined that v_2 is positive, or {\it in-plane}. The integrated v_4 is
about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8)
harmonics upper limits on the magnitudes are reported.Comment: 6 pages with 3 figures, as accepted for Phys. Rev. Letters The data
tables are at
http://www.star.bnl.gov/central/publications/pubDetail.php?id=3
Light Meson Spectroscopy
We survey the current status of light meson spectroscopy. We begin with a
general introduction to meson spectroscopy and and its importance in
understanding the physical states of Quantum Chromo Dynamics (QCD).
Phemenological models of hadron spectroscopy are described with particular
emphasis on the constituent quark model and the qualitative features it
predicts for the meson spectrum. We next discuss expectations for hadrons lying
outside the quark model, such as hadron states with excited gluonic degrees of
freedom. These states include so-called hybrids glueballs}, as well as
multiquark states. The established meson states are compared to the quark model
predictions and we find that most meson states are well described by the quark
model. However, a number of states in the light-quark sector do not fit in
well, suggesting the existence of hadronic states with additional degrees of
freedom. We end with a brief description of future directions in meson
spectroscopy.Comment: 111 pages with 28 imbedded figures, in LaTeX2e with no special
macros. Submitted to Reviews of Modern Physics, Nov.12, 199
Mid-rapidity anti-proton to proton ratio from Au+Au collisions at GeV
We report results on the ratio of mid-rapidity anti-proton to proton yields
in Au+Au collisions at \rts = 130 GeV per nucleon pair as measured by the
STAR experiment at RHIC. Within the rapidity and transverse momentum range of
and 0.4 1.0 GeV/, the ratio is essentially independent of
either transverse momentum or rapidity, with an average of for minimum bias collisions. Within errors, no
strong centrality dependence is observed. The results indicate that at this
RHIC energy, although the -\pb pair production becomes important at
mid-rapidity, a significant excess of baryons over anti-baryons is still
present.Comment: 5 pages, 3 figures, accepted by Phys. Rev. Let
Transverse-momentum correlations on from mean- fluctuations in Au-Au collisions at 200 GeV
We present first measurements of the pseudorapidity and azimuth
bin-size dependence of event-wise mean transverse momentum
fluctuations for Au-Au collisions at GeV. We invert that
dependence to obtain autocorrelations on differences
interpreted to represent velocity/temperature
distributions on (). The general form of the autocorrelations
suggests that the basic correlation mechanism is parton fragmentation. The
autocorrelations vary strongly with collision centrality, which suggests that
fragmentation is strongly modified by a dissipative medium in the more central
Au-Au collisions relative to peripheral or p-p collisions. \\Comment: 7 pages, 3 figure
Social change and the family: Comparative perspectives from the west, China, and South Asia
This paper examines the influence of social and economic change on family structure and relationships: How do such economic and social transformations as industrialization, urbanization, demographic change, the expansion of education, and the long-term growth of income influence the family? We take a comparative and historical approach, reviewing the experiences of three major sociocultural regions: the West, China, and South Asia. Many of the changes that have occurred in family life have been remarkably similar in the three settings—the separation of the workplace from the home, increased training of children in nonfamilial institutions, the development of living arrangements outside the family household, increased access of children to financial and other productive resources, and increased participation by children in the selection of a mate. While the similarities of family change in diverse cultural settings are striking, specific aspects of change have varied across settings because of significant pre-existing differences in family structure, residential patterns of marriage, autonomy of children, and the role of marriage within kinship systems.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45661/1/11206_2005_Article_BF01124383.pd
Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures
Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo
Expression and phosphorylation of neurofilament proteins in rat pheoichromocytoma (PC 12) cells
The in vitro rephosphorylation of phosphatase-treated neurofilament (NF) subunits was assessed. Enzymatically dephosphorylated NF-L and NF-M proved as good or better substrates for phosphorylation by various exogenous protein kinases, while dephosphorylated NF-H was refractory to phosphorylation, suggesting that a conformational change accompanies the dephosphorylation of NF-H but not NF-L or NF-M.The biosynthesis and phosphorylation of NF subunits were investigated in PC 12 cells. While all three NF subunits were synthesized in PC 12 cells, NF-M and NF-H were synthesized as hypophosphorylated precursors. NF-M was shown to undergo a time-dependent decrease in electrophoretic mobility in both control and NGF treated cells, consistent with its undergoing post-translational phosphorylation. Nerve growth factor (NGF) administration resulted in increased biosynthesis of NF-L and NF-M, increased stability of both NF-L and the slowest migrating form of NF-M, as well as increased incorporation of phosphate into NF-H. A soluble pool of NF subunits was also found in PC 12 cells. Soluble NF-M and NF-H were synthesized as faster migrating electrophoretic forms. Soluble NF-M underwent a time-dependent increase in phosphorylation state, indicating that the extent of phosphorylation does not significantly affect the solubility of this NF subunit.The effect of NGF on NF gene expression PC 12 cells was further explored. NGF treatment resulted in time-dependent increases in the levels of all three NF subunits. However, increases in NF-H levels were delayed relative to those of NF-L and NF-M. NGF treatment resulted in 12- and 14-fold increases in NF-L and NF-M mRNA, respectively, as well as increased transcriptional activity of both genes. The stability of NF-M mRNA was also increased in NGF treated PC 12 cells. However, NGF treatment was found not to affect the levels of NF-H mRNA nor the transcription rate of the NF-H gene, indicating that the effect of NGF on the biosynthesis of NF-H in PC 12 cells may occur at the translational or post-translational level
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