4,555 research outputs found
Formation of acetylcholine receptor clusters in mammalian sternohyoid muscle regenerating in the absence of nerves
When the sternohyoid muscle from the rat is grafted, the original muscle fibers, including the membranes at the neuromuscular junction, degenerate irreversibly. New muscle fibers regenerate inside of the basal laminae remaining from the original muscle fibers. In this study rhodamine-[alpha]-bungarotoxin and electron microscopy have been used to demonstrate that acetylcholine receptor (AchR) clusters and synaptic folds are restored to the regenerating myotubes even when innervation to the grafts is prevented. The AchR clusters and synaptic folds colocalized with acetylcholinesterease that persisted at the original synaptic basal lamina. The AchR clusters were not restored if the original innervation band was removed from the muscle at the time of grafting. Lengths of the AchR clusters were measured in animals ranging in weight from 50 to 700 g. The lengths of clusters in the grafts were proportional to the lengths of those in the preoperative controls, suggesting that quantitative morphogenetic information persists through the period of degeneration and regeneration. However, the distribution of the AchRs within the clusters differed slightly from controls. Extrajunctional AchR clusters were present initially, but later disappeared. The sizes of these clusters were unrelated to the sizes of the junctional AchR clusters. This study demonstrates that morphogenetic cues persist within the region of the original motor and plate, possibly associated with the synaptic basal lamina.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25985/1/0000051.pd
Muscle satellite cells in malnourished and nutritionally rehabilitated children
Satellite cells were examined qualitatively and quantitatively in muscle biopsies from children when malnourished, during nutritional rehabilitation, and after clinical recovery. The proportion of satellite cell nuclei relative to myonuclei was significantly lower in malnourished subjects than in well-nourished age-matched controls (4.5 +/- 1% vs. 8.1 +/- 1.0%). The proportion of satellite cells remained low during the early period of "catch-up growth" but was significantly increased in the recovered subjects (10.5 +/- 1.0%). Satellite cells were small and their nuclei were heterochromatic in biopsies from the malnourished subjects. The cells were often partially segregated from the parent fiber by an external lamina. In recovering and recovered subjects many of the satellite cells enlarged, and the appearance of their nuclei and cytoplasmic organelles suggested a more active state. Intervention of external lamina between the satellite cell and the myofibre was uncommon in the recovered subjects.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23597/1/0000559.pd
Fast and accurate modelling of longitudinal and repeated measures neuroimaging data
Despite the growing importance of longitudinal data in neuroimaging, the standard analysis methods make restrictive or unrealistic assumptions (e.g., assumption of Compound Symmetry—the state of all equal variances and equal correlations—or spatially homogeneous longitudinal correlations). While some new methods have been proposed to more accurately account for such data, these methods are based on iterative algorithms that are slow and failure-prone. In this article, we propose the use of the Sandwich Estimator (SwE) method which first estimates the parameters of interest with a simple Ordinary Least Square model and second estimates variances/covariances with the “so-called” SwE which accounts for the within-subject correlation existing in longitudinal data. Here, we introduce the SwE method in its classic form, and we review and propose several adjustments to improve its behaviour, specifically in small samples. We use intensive Monte Carlo simulations to compare all considered adjustments and isolate the best combination for neuroimaging data. We also compare the SwE method to other popular methods and demonstrate its strengths and weaknesses. Finally, we analyse a highly unbalanced longitudinal dataset from the Alzheimer's Disease Neuroimaging Initiative and demonstrate the flexibility of the SwE method to fit within- and between-subject effects in a single model. Software implementing this SwE method has been made freely available at http://warwick.ac.uk/tenichols/SwE
Entangling gates on degenerate spin qubits dressed by a global field
Coherently dressed spins have shown promising results as building blocks for
future quantum computers owing to their resilience to environmental noise and
their compatibility with global control fields. This mode of operation allows
for more amenable qubit architecture requirements and simplifies signal routing
on the chip. However, multi-qubit operations, such as qubit addressability and
two-qubit gates, are yet to be demonstrated to establish global control in
combination with dressed qubits as a viable path to universal quantum
computing. Here we demonstrate simultaneous on-resonance driving of degenerate
qubits using a global field while retaining addressability for qubits with
equal Larmor frequencies. Furthermore, we implement SWAP oscillations during
on-resonance driving, constituting the demonstration of driven two-qubit gates.
Significantly, our findings highlight the fragility of entangling gates between
superposition states and how dressing can increase the noise robustness. These
results represent a crucial milestone towards global control operation with
dressed qubits. It also opens a door to interesting spin physics on degenerate
spins
Radiation hardness qualification of PbWO4 scintillation crystals for the CMS Electromagnetic Calorimeter
This is the Pre-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2010 IOPEnsuring the radiation hardness of PbWO4 crystals was one of the main priorities during the construction of the electromagnetic calorimeter of the CMS experiment at CERN. The production on an industrial scale of radiation hard crystals and their certification over a period of several years represented a difficult challenge both for CMS and for the crystal suppliers. The present article reviews the related scientific and technological problems encountered
Intercalibration of the barrel electromagnetic calorimeter of the CMS experiment at start-up
Calibration of the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector was accomplished, before installation, with cosmic ray muons and test beams. One fourth of the calorimeter was exposed to a beam of high energy electrons and the relative calibration of the channels, the intercalibration, was found to be reproducible to a precision of about 0.3%. Additionally, data were collected with cosmic rays for the entire ECAL barrel during the commissioning phase. By comparing the intercalibration constants obtained with the electron beam data with those from the cosmic ray data, it is demonstrated that the latter provide an intercalibration precision of 1.5% over most of the barrel ECAL. The best intercalibration precision is expected to come from the analysis of events collected in situ during the LHC operation. Using data collected with both electrons and pion beams, several aspects of the intercalibration procedures based on electrons or neutral pions were investigated
Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV
A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay
channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7
TeV is presented. The data were collected at the LHC, with the CMS detector,
and correspond to an integrated luminosity of 4.6 inverse femtobarns. No
significant excess is observed above the background expectation, and upper
limits are set on the Higgs boson production cross section. The presence of the
standard model Higgs boson with a mass in the 270-440 GeV range is excluded at
95% confidence level.Comment: Submitted to JHE
Search for anomalous t t-bar production in the highly-boosted all-hadronic final state
A search is presented for a massive particle, generically referred to as a
Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are
sufficiently massive to produce highly Lorentz-boosted top quarks, which yield
collimated decay products that are partially or fully merged into single jets.
The analysis uses new methods to analyze jet substructure, providing
suppression of the non-top multijet backgrounds. The analysis is based on a
data sample of proton-proton collisions at a center-of-mass energy of 7 TeV,
corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits
in the range of 1 pb are set on the product of the production cross section and
branching fraction for a topcolor Z' modeled for several widths, as well as for
a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any
enhancement in t t-bar production beyond expectations of the standard model for
t t-bar invariant masses larger than 1 TeV.Comment: Submitted to the Journal of High Energy Physics; this version
includes a minor typo correction that will be submitted as an erratu
Combined search for the quarks of a sequential fourth generation
Results are presented from a search for a fourth generation of quarks
produced singly or in pairs in a data set corresponding to an integrated
luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in
2011. A novel strategy has been developed for a combined search for quarks of
the up and down type in decay channels with at least one isolated muon or
electron. Limits on the mass of the fourth-generation quarks and the relevant
Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a
simple extension of the standard model with a sequential fourth generation of
fermions. The existence of mass-degenerate fourth-generation quarks with masses
below 685 GeV is excluded at 95% confidence level for minimal off-diagonal
mixing between the third- and the fourth-generation quarks. With a mass
difference of 25 GeV between the quark masses, the obtained limit on the masses
of the fourth-generation quarks shifts by about +/- 20 GeV. These results
significantly reduce the allowed parameter space for a fourth generation of
fermions.Comment: Replaced with published version. Added journal reference and DO
Measurement of the t t-bar production cross section in the dilepton channel in pp collisions at sqrt(s) = 7 TeV
The t t-bar production cross section (sigma[t t-bar]) is measured in
proton-proton collisions at sqrt(s) = 7 TeV in data collected by the CMS
experiment, corresponding to an integrated luminosity of 2.3 inverse
femtobarns. The measurement is performed in events with two leptons (electrons
or muons) in the final state, at least two jets identified as jets originating
from b quarks, and the presence of an imbalance in transverse momentum. The
measured value of sigma[t t-bar] for a top-quark mass of 172.5 GeV is 161.9 +/-
2.5 (stat.) +5.1/-5.0 (syst.) +/- 3.6(lumi.) pb, consistent with the prediction
of the standard model.Comment: Replaced with published version. Included journal reference and DO
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