Modeling of Spiking-Bursting Neural Behavior Using Two-Dimensional Map

A simple model that replicates the dynamics of spiking and spiking-bursting activity of real biological neurons is proposed. The model is a two-dimensional map which contains one fast and one slow variable. The mechanisms behind generation of spikes, bursts of spikes, and restructuring of the map behavior are explained using phase portrait analysis. The dynamics of two coupled maps which model the behavior of two electrically coupled neurons is discussed. Synchronization regimes for spiking and bursting activity of these maps are studied as a function of coupling strength. It is demonstrated that the results of this model are in agreement with the synchronization of chaotic spiking-bursting behavior experimentally found in real biological neurons.Comment: 9 pages, 12 figure

Localized transverse bursts in inclined layer convection

We investigate a novel bursting state in inclined layer thermal convection in which convection rolls exhibit intermittent, localized, transverse bursts. With increasing temperature difference, the bursts increase in duration and number while exhibiting a characteristic wavenumber, magnitude, and size. We propose a mechanism which describes the duration of the observed bursting intervals and compare our results to bursting processes in other systems.Comment: 4 pages, 8 figure

Hysteresis and bi-stability by an interplay of calcium oscillations and action potential firing

Many cell types exhibit oscillatory activity, such as repetitive action potential firing due to the Hodgkin-Huxley dynamics of ion channels in the cell membrane or reveal intracellular inositol triphosphate (IP$_3$) mediated calcium oscillations (CaOs) by calcium-induced calcium release channels (IP$_3$-receptor) in the membrane of the endoplasmic reticulum (ER). The dynamics of the excitable membrane and that of the IP$_3$-mediated CaOs have been the subject of many studies. However, the interaction between the excitable cell membrane and IP$_3$-mediated CaOs, which are coupled by cytosolic calcium which affects the dynamics of both, has not been studied. This study for the first time applied stability analysis to investigate the dynamic behavior of a model, which includes both an excitable membrane and an intracellular IP$_3$-mediated calcium oscillator. Taking the IP$_3$ concentration as a control parameter, the model exhibits a novel rich spectrum of stable and unstable states with hysteresis. The four stable states of the model correspond in detail to previously reported growth-state dependent states of the membrane potential of normal rat kidney fibroblasts in cell culture. The hysteresis is most pronounced for experimentally observed parameter values of the model, suggesting a functional importance of hysteresis. This study shows that the four growth-dependent cell states may not reflect the behavior of cells that have differentiated into different cell types with different properties, but simply reflect four different states of a single cell type, that is characterized by a single model.Comment: 29 pages, 6 figure

Bremsstrahlung corrections to the decay b→sγb \to s \gamma

We calculate the O($\alpha_s$) gluon Bremsstrahlung corrections to the inclusive decay $b \rightarrow s \gamma$, involving the full operator basis $\hat O_1$ -- $\hat O_8$. Confirming and extending earlier calculations of Ali and Greub, we give formulas for the total decay width as well as the perturbative photon spectrum, regarding the former as a necessary part of the forthcoming complete NLO analysis. We explore in detail the renormalization scale dependence of our results and find it considerably increased.Comment: 23 pages, LaTeX, uses epsf.sty and rotate.sty. 4 figures (uuencoded postscript) appended as seperate file. A complete postscript version may be obtained from URL ftp://feynman.t30.physik.tu-muenchen.de/pub/preprints/tum-93-95.ps.gz Final version as to appear in Physical Review D. Some minor errors corrected, without changes in the numerical results. One reference adde

Optimized Variables of the Study of Λb\Lambda_b Polarization

The value of the $b$-baryon polarization can be extracted from inclusive data at LEP with better than 10\% precision based on current statistics. We present a new variable by which to measure the polarization, which is the ratio of the average electron energy to the average neutrino energy. This variable is both sensitive to polarization and insensitive to fragmentation uncertainties.Comment: 10 pages (LaTeX), 2 figures, MIT-CTP-2270, CERN-PPE/94-0

QCD-based description of one-particle inclusive B decays

We discuss one-particle inclusive B decays in the limit of heavy b and c quarks. Using the large-N_C limit we factorize the non-leptonic matrix elements, and we employ a short distance expansion. Modeling the remaining nonperturbative matrix elements we obtain predictions for various decay channels and compare them with existing data.Comment: LaTeX, 22 pages, 6 figures (eps); analytical and numerical results unchanged, misrepresentation of experimental data in Fig. 5 corrected, final published versio

Association of proinflammatory cytokines and chemotherapy-associated cognitive impairment in breast cancer patients: a multi-centered, prospective, cohort study.

BackgroundExisting evidence suggests that proinflammatory cytokines play an intermediary role in postchemotherapy cognitive impairment. This is one of the largest multicentered, cohort studies conducted in Singapore to evaluate the prevalence and proinflammatory biomarkers associated with cognitive impairment in breast cancer patients.Patients and methodsChemotherapy-receiving breast cancer patients (stages I-III) were recruited. Proinflammatory plasma cytokines concentrations [interleukin (IL)-1β, IL-2, IL-4, IL-6, IL-8, IL-10, granulocyte-macrophage colony-stimulating factor, interferon-γ and tumor necrosis factor-α] were evaluated at 3 time points (before chemotherapy, 6 and 12 weeks after chemotherapy initiation). The FACT-Cog (version 3) was utilized to evaluate patients' self-perceived cognitive disturbances and a computerized neuropsychological assessment (Headminder) was administered to evaluate patients' memory, attention, response speed and processing speed. Changes of cognition throughout chemotherapy treatment were compared against the baseline. Linear mixed-effects models were applied to test the relationships of clinical variables and cytokine concentrations on self-perceived cognitive disturbances and each objective cognitive domain.ResultsNinety-nine patients were included (age 50.5 ± 8.4 years; 81.8% Chinese; mean duration of education = 10.8 ± 3.3 years). Higher plasma IL-1β was associated with poorer response speed performance (estimate: -0.78; 95% confidence interval (CI) -1.34 to -0.03; P = 0.023), and a higher concentration of IL-4 was associated with better response speed performance (P = 0.022). Higher concentrations of IL-1β and IL-6 were associated with more severe self-perceived cognitive disturbances (P = 0.018 and 0.001, respectively). Patients with higher concentrations of IL-4 also reported less severe cognitive disturbances (P = 0.022).ConclusionsWhile elevated concentrations of IL-6 and IL-1β were observed in patients with poorer response speed performance and perceived cognitive disturbances, IL-4 may be protective against chemotherapy-associated cognitive impairment. This study is important because cytokines would potentially be mechanistic mediators of chemotherapy-associated cognitive changes

Non-factorizable Contributions to B→ππB \to \pi\pi Decays

We investigate to what extent the experimental information on $B \to \pi\pi$ branching fractions and CP asymmetries can be used to better understand the QCD dynamics in these decays. For this purpose we decompose the independent isospin amplitudes into factorizable and non-factorizable contributions. The former can be estimated within the framework of QCD factorization for exclusive $B$ decays. The latter vanish in the heavy-quark limit, $m_b \to \infty$, and are treated as unknown hadronic parameters. We discuss at some length in which way the non-factorizable contributions are treated in different theoretical and phenomenological frameworks. We point out the potential differences between the phenomenological treatment of power-corrections in the ``BBNS approach'', and the appearance of power -suppressed operators in soft-collinear effective theory (SCET). On that basis we define a handful of different (but generic) scenarios where the non-factorizable part of isospin amplitudes is parametrized in terms of three or four unknowns, which can be constrained by data. We also give some short discussion on the implications of our analysis for $B \to \pi K$ decays. In particular, since non-factorizable QCD effects in $B \to \pi \pi$ may be large, we cannot exclude sizeable non-factorizable effects, which violate $SU(3)_F$ flavour symmetry, or even isospin symmetry (via long-distance QED effects). This may help to explain certain puzzles in connection with isospin-violating observables in $B \to \pi K$ decays.Comment: published version, minor correction

Extracting V_{ub} Without Recourse to Structure Functions

We present a closed form expression for |V_{ub}|^2/ |V_{tb} V_{ts}^*|^2 in terms of the endpoint photon and lepton spectra from the inclusive decays B -> X_s\gamma and B -> X_u\ell\nu, respectively, which includes the resummation of the endpoint logs at next to leading order and is completely independent of the B meson structure function. The use of this expression for extracting V_{ub} would eliminate the large systematic errors usually incurred due to the modeling of the heavy quarks' Fermi motion.Comment: 20 pages, no figures, minor typos correcte

Determining V(ub) from B+ --> D*+(s) e+ e- and B+ --> D*+ e+ e-

It was recently pointed out that the decays B^+ --> D^{*+}_s gamma and B^+ --> D^{*+} gamma can be used for an extraction of |V_{ub}|. The theory of these decays is poorly understood. It was shown that in a world of almost degenerate b and c-quarks the decay would be computable. The severe difficulties that are encountered in the realistic calculation stem primarily from the very hard photon produced in the two body decay. We point out that in the decays B^+ --> D^{*+}_s e^+e^- and B^+ --> D^{*+} e^+e^- the photon vertex is soft when the charmed meson is nearly at rest (in the B^+ rest frame). This allows us to compute with some confidence the decay rate in a restricted but interesting kinematic regime. Given enough data the extraction of V_{ub} with reasonably small uncertainties could proceed through an analysis of these exclusive decays much as is done in the determination of V_{cb}.Comment: 9 pages, latex (revtex), replaced with published versio