Synaptic transmission at visualized sympathetic boutons: stochastic interaction between acetylcholine and its receptors

Excitatory postsynaptic currents (EPSCs) were recorded with loose patch electrodes placed over visualized boutons on the surface of rat pelvic ganglion cells. At 34 degrees C the time to peak of the EPSC was about 0.7 ms, and a single exponential described the declining phase with a time constant of about 4.0 ms; these times were not correlated with changes in the amplitude of the EPSC. The amplitude-frequency histogram of the EPSC at individual boutons was well described by a single Gaussian-distribution that possessed a variance similar to that of the electrical noise. Nonstationary fluctuation analysis of the EPSCs at a bouton indicated that about 120 ACh receptor channels were available beneath boutons for interaction with a quantum of ACh. The characteristics of these EPSCs were compared with the results of Monte Carlo simulations of the quantal release of 9000 acetylcholine (ACh) molecules onto receptor patches of density 1400 microns-2 and 0.41 micron diameter, using a kinetic scheme of interaction between ACh and the receptors similar to that observed at the neuromuscular junction. The simulated EPSC generated in this way had temporal characteristics similar to those of the experimental EPSC when either the diffusion of the ACh is slowed or allowance is made for a finite period of transmitter release from the bouton. The amplitude of the simulated EPSC then exhibited stochastic fluctuations similar to those of the experimental EPSC

The effect of spring burning on competitive ranking of prairie species

A common explanation for the changes in species abundance following a fire is a shift in competitive ranking. However, experimental tests have been inconsistent and generally do not support this explanation. I examined the competitive ability of an abundant C 4 grass, Andropogon gerardii , and a C 3 forb, Ratibida pinnata , in a prairie remnant in northern Ohio, USA, for each of three years following a spring burn in 1996. While the abiotic environment directly influenced both species similarly, relative competitive abilities in terms of growth changed markedly: in 1996 Andropogon was less inhibited by neighbors; in 1997 both Andropogon and Ratibida had similar competitive abilities; and in 1998 Ratibida was less inhibited by neighbors. This shift in competitive response ranking paralleled the changes in relative abundance for the two species. In contrast, the effect of neighbors on survival changed markedly over time but did not differ among the two species. Thus, fire may influence species abundance through changing species competitive response ranking, at least in terms of growth.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72362/1/3236873.pd

Characterization and immunomodulatory effects of canine adipose tissue- and bone marrow-derived mesenchymal stromal cells

Background Mesenchymal stromal cells (MSC) hold promise for both cell replacement and immune modulation strategies owing to their progenitor and non-progenitor functions, respectively. Characterization of MSC from different sources is an important and necessary step before clinical use of these cells is widely adopted. Little is known about the biology and function of canine MSC compared to their mouse or human counterparts. This knowledge-gap impedes development of canine evidence-based MSC technologies. Hypothesis and Objectives We hypothesized that canine adipose tissue (AT) and bone marrow (BM) MSC (derived from the same dogs) will have similar differentiation and immune modulatory profiles. Our objectives were to evaluate progenitor and non-progenitor functions as well as other characteristics of AT- and BM-MSC including 1) proliferation rate, 2) cell surface marker expression, 3) DNA methylation levels, 4) potential for trilineage differentiation towards osteogenic, adipogenic, and chondrogenic cell fates, and 5) immunomodulatory potency in vitro. Results 1) AT-MSC proliferated at more than double the rate of BM-MSC (population doubling times in days) for passage (P) 2, AT: 1.69, BM: 3.81; P3, AT: 1.80, BM: 4.06; P4, AT: 2.37, BM: 5.34; P5, AT: 3.20, BM: 7.21). 2) Canine MSC, regardless of source, strongly expressed cell surface markers MHC I, CD29, CD44, and CD90, and were negative for MHC II and CD45. They also showed moderate expression of CD8 and CD73 and mild expression of CD14. Minor differences were found in expression of CD4 and CD34. 3) Global DNA methylation levels were significantly lower in BM-MSC compared to AT-MSC. 4) Little difference was found between AT- and BM-MSC in their potential for adipogenesis and osteogenesis. Chondrogenesis was poor to absent for both sources in spite of adding varying levels of bone-morphogenic protein to our standard transforming growth factor (TGF-β3)-based induction medium. 5) Immunomodulatory capacity was equal regardless of cell source when tested in mitogen-stimulated lymphocyte reactions. Priming of MSC with pro-inflammatory factors interferon-gamma and/or tumour necrosis factor did not increase the lymphocyte suppressive properties of the MSC compared to untreated MSC. Conclusions/Significance No significant differences were found between AT- and BM-MSC with regard to their immunophenotype, progenitor, and non-progenitor functions. Both MSC populations showed strong adipogenic and osteogenic potential and poor chondrogenic potential. Both significantly suppressed stimulated peripheral blood mononuclear cells. The most significant differences found were the higher isolation success and proliferation rate of AT-MSC, which could be realized as notable benefits of their use over BM-MSC

Ionization degree of the electron-hole plasma in semiconductor quantum wells

The degree of ionization of a nondegenerate two-dimensional electron-hole plasma is calculated using the modified law of mass action, which takes into account all bound and unbound states in a screened Coulomb potential. Application of the variable phase method to this potential allows us to treat scattering and bound states on the same footing. Inclusion of the scattering states leads to a strong deviation from the standard law of mass action. A qualitative difference between mid- and wide-gap semiconductors is demonstrated. For wide-gap semiconductors at room temperature, when the bare exciton binding energy is of the order of T, the equilibrium consists of an almost equal mixture of correlated electron-hole pairs and uncorrelated free carriers.Comment: 22 pages, 6 figure

First Measurement of Z/gamma* Production in Compton Scattering of Quasi-real Photons

We report the first observation of Z/gamma* production in Compton scattering of quasi-real photons. This is a subprocess of the reaction e+e- to e+e-Z/gamma*, where one of the final state electrons is undetected. Approximately 55 pb-1 of data collected in the year 1997 at an e+e- centre-of-mass energy of 183 GeV with the OPAL detector at LEP have been analysed. The Z/gamma* from Compton scattering has been detected in the hadronic decay channel. Within well defined kinematic bounds, we measure the product of cross-section and Z/gamma* branching ratio to hadrons to be (0.9+-0.3+-0.1) pb for events with a hadronic mass larger than 60 GeV, dominated by (e)eZ production. In the hadronic mass region between 5 GeV and 60 GeV, dominated by (e)egamma* production, this product is found to be (4.1+-1.6+-0.6) pb. Our results agree with the predictions of two Monte Carlo event generators, grc4f and PYTHIA.Comment: 18 pages, LaTeX, 5 eps figures included, submitted to Physics Letters

Search for Higgs Bosons in e+e- Collisions at 183 GeV

The data collected by the OPAL experiment at sqrts=183 GeV were used to search for Higgs bosons which are predicted by the Standard Model and various extensions, such as general models with two Higgs field doublets and the Minimal Supersymmetric Standard Model (MSSM). The data correspond to an integrated luminosity of approximately 54pb-1. None of the searches for neutral and charged Higgs bosons have revealed an excess of events beyond the expected background. This negative outcome, in combination with similar results from searches at lower energies, leads to new limits for the Higgs boson masses and other model parameters. In particular, the 95% confidence level lower limit for the mass of the Standard Model Higgs boson is 88.3 GeV. Charged Higgs bosons can be excluded for masses up to 59.5 GeV. In the MSSM, mh > 70.5 GeV and mA > 72.0 GeV are obtained for tan{beta}>1, no and maximal scalar top mixing and soft SUSY-breaking masses of 1 TeV. The range 0.8 < tanb < 1.9 is excluded for minimal scalar top mixing and m{top} < 175 GeV. More general scans of the MSSM parameter space are also considered.Comment: 49 pages. LaTeX, including 33 eps figures, submitted to European Physical Journal

A Measurement of the Product Branching Ratio f(b->Lambda_b).BR(Lambda_b->Lambda X) in Z0 Decays

The product branching ratio, f(b->Lambda_b).BR(Lambda_b->Lambda X), where Lambda_b denotes any weakly-decaying b-baryon, has been measured using the OPAL detector at LEP. Lambda_b are selected by the presence of energetic Lambda particles in bottom events tagged by the presence of displaced secondary vertices. A fit to the momenta of the Lambda particles separates signal from B meson and fragmentation backgrounds. The measured product branching ratio is f(b->Lambda_b).BR(Lambda_b->Lambda X) = (2.67+-0.38(stat)+0.67-0.60(sys))% Combined with a previous OPAL measurement, one obtains f(b->Lambda_b).BR(Lambda_b->Lambda X) = (3.50+-0.32(stat)+-0.35(sys))%.Comment: 16 pages, LaTeX, 3 eps figs included, submitted to the European Physical Journal

Measurement of the Michel Parameters in Leptonic Tau Decays

The Michel parameters of the leptonic tau decays are measured using the OPAL detector at LEP. The Michel parameters are extracted from the energy spectra of the charged decay leptons and from their energy-energy correlations. A new method involving a global likelihood fit of Monte Carlo generated events with complete detector simulation and background treatment has been applied to the data recorded at center-of-mass energies close to sqrt(s) = M(Z) corresponding to an integrated luminosity of 155 pb-1 during the years 1990 to 1995. If e-mu universality is assumed and inferring the tau polarization from neutral current data, the measured Michel parameters are extracted. Limits on non-standard coupling constants and on the masses of new gauge bosons are obtained. The results are in agreement with the V-A prediction of the Standard Model.Comment: 32 pages, LaTeX, 9 eps figures included, submitted to the European Physical Journal

LSST: from Science Drivers to Reference Design and Anticipated Data Products

(Abridged) We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). A vast array of science will be enabled by a single wide-deep-fast sky survey, and LSST will have unique survey capability in the faint time domain. The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. LSST will be a wide-field ground-based system sited at Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg$^2$ field of view, and a 3.2 Gigapixel camera. The standard observing sequence will consist of pairs of 15-second exposures in a given field, with two such visits in each pointing in a given night. With these repeats, the LSST system is capable of imaging about 10,000 square degrees of sky in a single filter in three nights. The typical 5$\sigma$ point-source depth in a single visit in $r$ will be $\sim 24.5$ (AB). The project is in the construction phase and will begin regular survey operations by 2022. The survey area will be contained within 30,000 deg$^2$ with $\delta<+34.5^\circ$, and will be imaged multiple times in six bands, $ugrizy$, covering the wavelength range 320--1050 nm. About 90\% of the observing time will be devoted to a deep-wide-fast survey mode which will uniformly observe a 18,000 deg$^2$ region about 800 times (summed over all six bands) during the anticipated 10 years of operations, and yield a coadded map to $r\sim27.5$. The remaining 10\% of the observing time will be allocated to projects such as a Very Deep and Fast time domain survey. The goal is to make LSST data products, including a relational database of about 32 trillion observations of 40 billion objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures available from https://www.lsst.org/overvie

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters