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Full-Text Articles in Physical Sciences and Mathematics
Mode Locking In A Periodically Forced Integrate-And-Fire-Or-Burst Neuron Model, S. Coombes, R. Owen, Gregory D. Smith
Mode Locking In A Periodically Forced Integrate-And-Fire-Or-Burst Neuron Model, S. Coombes, R. Owen, Gregory D. Smith
Arts & Sciences Articles
The minimal “integrate-and-fire-or-burst” (IFB) neuron model reproduces the salient features of experimentally observed thalamocortical relay neuron response properties, including the temporal tuning of both tonic spiking (i.e., conventional action potentials) and post-inhibitory rebound bursting mediated by the low-threshold Ca2+ current, IT. In previous work focusing on experimental and IFB model responses to sinusoidal current injection, large regions of stimulus parameter space were observed for which the response was entrained to periodic applied current, resulting in repetitive burst, tonic, or mixed (i.e., burst followed by tonic) responses. Here we present an exact analysis of such mode-locking in the integrate-and-fire-or-burst model under …
Organization And Bifurcation Of Planar Closed Orbits Of An Atomic Electron In Crossed Fields, D. M. Wang, John B. Delos
Organization And Bifurcation Of Planar Closed Orbits Of An Atomic Electron In Crossed Fields, D. M. Wang, John B. Delos
Arts & Sciences Articles
We describe the patterns of creation and splitting of planar closed orbits of electrons in hydrogen atoms in crossed electric and magnetic fields. These orbits lie in the plane perpendicular to the magnetic field, and they start and end at the nucleus. Using a Poincaré map to study the regular motions, we observe that the bifurcations of planar closed orbits fall into an ordered sequence as energy changes: a “tangent bifurcation” creates one closed orbit that splits into two; subsequently, one of them becomes periodic, and splits by a “pitchfork bifurcation” into two periodic orbits and one closed orbit. Based …
Characterizing And Monitoring Changes In State Of Polymers During Cure And Use -Aging, Andrew Orschel Meyer
Characterizing And Monitoring Changes In State Of Polymers During Cure And Use -Aging, Andrew Orschel Meyer
Dissertations, Theses, and Masters Projects
Multi Angle Laser Light Scattering (MALLS) and Frequency Dependent Electromagnetic Sensing (FDEMS) provide unique characterizations of polymer systems during cure and use-aging. This research illustrates how MALLS is an extremely accurate technique for absolute characterization of macromolecules, giving molecular weight and size information that other widely used and accepted techniques are incapable of measuring. Application of MALLS to monitoring the changing state of a polyamide-11 system in a water aging environment led to the discovery of an equilibrium molecular weight which is the result of two competing reactions, hydrolysis-degradation and a newly discovered recombination-polymerization reaction. The discovery of this recombination …
Single Positive Pion Electroproduction In The First And Second Resonance Regions Using Clas, Hovanes Egiyan
Single Positive Pion Electroproduction In The First And Second Resonance Regions Using Clas, Hovanes Egiyan
Dissertations, Theses, and Masters Projects
The study of single pion electroproduction can provide valuable information on the structure of the nucleon and its excited states. Although these reactions have been studied for decades, never has the npi + channel been measured over the complete phase space of the reaction. The CEBAF Large Acceptance Spectrometer (CLAS) located in Hall B of Jefferson Lab is well-suited for conducting these measurements. The CLAS data were taken using a 1.515 GeV electron beam incident on a liquid H 2 target. The cross sections have been extracted, and their &phis;-dependence has been fit to obtain the sigmaTT, sigma TL and …
Topics In Physics Beyond The Standard Model, Alfredo Aranda
Topics In Physics Beyond The Standard Model, Alfredo Aranda
Dissertations, Theses, and Masters Projects
In this dissertation we address three issues related to physics beyond the Standard model: flavor and the use of discrete gauge symmetries, the dynamical breaking of electroweak symmetry, and the addition of a U(1) gauge symmetry to the Standard model in order to suppress proton decay. We present: (i) A model of flavor based on the double tetrahedral group that leads to acceptable quark and lepton masses as well as mixing angles. Furthermore it gives solutions for the atmospheric and solar neutrino problems. (ii) A model of bosonic topcolor in which the breaking of electroweak symmetry occurs dynamically through the …
Phenomenology Of The Su(2)(L) X Su(2)(I) X U(1)(Y) X U(1)(Y') Model, Shuquan Nie
Phenomenology Of The Su(2)(L) X Su(2)(I) X U(1)(Y) X U(1)(Y') Model, Shuquan Nie
Dissertations, Theses, and Masters Projects
We consider the effective low-energy SU(2) L x SU(2)I x U(1)Y x U(1)Y' model, which is based on the E6 grand unification theory. SU(2)I is a subgroup of SU(3) R and commutes with the electric charge operator.;Higgs bosons in the Standard Model and two-Higgs doublet models are reviewed and studied first. The flavor-changing neutral currents and their effects on the anomalous magnetic moment of the muon are discussed. Bounds on masses of Higgs bosons are obtained by requiring that the vacuum is stable and perturbation theory is valid up to a large scale. We introduce Higgs multiplets including two neutral …
Solid State Nmr Characterization Of Structural And Motional Parameter Distributions In Polyamidoammonium Dendrimers, Dariya Ivanovna Malyarenko
Solid State Nmr Characterization Of Structural And Motional Parameter Distributions In Polyamidoammonium Dendrimers, Dariya Ivanovna Malyarenko
Dissertations, Theses, and Masters Projects
The characterization of narrow distributions of structural and motional parameters, and their evolution during the broad glass transition, is performed for deuterated PAMAM dendrimer salts using solid state NMR. The broadening of deuteron quadrupole echo (QE) lineshapes is consistent with the presence of narrow hydrogen bond length distribution (sigmar < 0.25 A) at the spacer amide and branching tertiary amine sites. The temperature dependent averaging of the experimental lineshapes is explained on the basis of fast planar librations in the dendrimer interior, and fast rotation and intermediate regime libration (in an asymmetric cone) of the dendrimer termini. The amplitudes of libration are temperature dependent and higher for low generation dendrimers, while librational rates show Arrhenius behavior only within the glass transition region. In this region, the width of log-normal distribution of rates increases with temperature at sites associated with chlorine counterions. The largest distributions are still less than one order of magnitude wide, unlike the dendrimer in solution or the linear polymers. Interpenetrated low generations (G < 3), uniform intermediate generations (G = 3--5) with surface network, and backfolded high generations (G > 5), are distinguished by interior and termini dynamics.;In the regime of fast motion QE lineshapes are highly sensitive to the presence of narrow structural and motional parameter distributions, and provide constraints on motional geometry independent of rates. The precise characterization of narrow log-normal rate distributions in the intermediate regime can be …
Measurement Of The Strange Sea Of The Proton, Gary A. Rutledge
Measurement Of The Strange Sea Of The Proton, Gary A. Rutledge
Dissertations, Theses, and Masters Projects
The differential cross section for elastic scattering of longitudinally-polarized electrons from protons exhibits a parity-violating asymmetry, due to the interference between weak and electromagnetic amplitudes. The asymmetry is extracted from the detector counting rates as APV = ( Dr - Dl)/(Dr + D l) where Drl are related to the right (left) differential cross sections sigmar, sigmal respectively. Thus APV = (sigmar - sigma l)/(sigmar + sigmal) for right-handed and left-handed electrons. This asymmetry is sensitive to the presence of strange sea quarks in the proton, in particular to the strange vector matrix elements GsE and GsM .;In an experiment …