Microscopic study of Ca++Ca fusion

We investigate the fusion barriers for reactions involving Ca isotopes $\mathrm{^{40}Ca}+\mathrm{^{40}Ca}$, $\mathrm{^{40}Ca}+\mathrm{^{48}Ca}$, and $\mathrm{^{48}Ca}+\mathrm{^{48}Ca}$ using the microscopic time-dependent Hartree-Fock theory coupled with a density constraint. In this formalism the fusion barriers are directly obtained from TDHF dynamics. We also study the excitation of the pre-equilibrium GDR for the $\mathrm{^{40}Ca}+\mathrm{^{48}Ca}$ system and the associated $\gamma$-ray emission spectrum. Fusion cross-sections are calculated using the incoming-wave boundary condition approach. We examine the dependence of fusion barriers on collision energy as well as on the different parametrizations of the Skyrme interaction.Comment: 11 pages, 13 figure

Angular Dependence in Proton-Proton Correlation Functions in Central 40Ca+40Ca^{40}Ca+^{40}Ca and 48Ca+48Ca^{48}Ca+^{48}Ca Reactions

The angular dependence of proton-proton correlation functions is studied in central $^{40}Ca+^{40}Ca$ and $^{48}Ca+^{48}Ca$ nuclear reactions at E=80 MeV/A. Measurements were performed with the HiRA detector complemented by the 4$\pi$ Array at NSCL. A striking angular dependence in the laboratory frame is found within p-p correlation functions for both systems that greatly exceeds the measured and expected isospin dependent difference between the neutron-rich and neutron-deficient systems. Sources measured at backward angles reflect the participant zone of the reaction, while much larger sources observed at forward angles reflect the expanding, fragmenting and evaporating projectile remnants. The decrease of the size of the source with increasing momentum is observed at backward angles while a weaker trend in the opposite direction is observed at forward angles. The results are compared to the theoretical calculations using the BUU transport model.Comment: 8 pages, 3 figures, submitted to PR

Mineral Utilization in Rams Fed Ration Supplemented with Different Levels of Chromium, Calcium, and Cation-Anion Balances

Chromium (Cr) is an essential mineral for ruminants. Its metabolism and interactions with other minerals has not been widely known. This experiment was designed to evaluate the utilization of minerals and growth of Garut ram fed ration supplemented with Cr and different Dietary Cation Anion Balance (DCAB) and Ca level. Dietary treatments, namely: R0 (Ration with DCAB+14); R1 (Ration with DCAB+14 + Cr 3ppm,); R2 (Ration with DCAB 0 + Ca); R3 (Ration with DCAB 0 + Cr 3 ppm + Ca), were allocated in twenty four of 1.5-2 years old Garut rams in a randomized block design. The results showed that Cr supplementation in rations containing different levels of Ca did not affect feed intake, body weight gain, and dry matter digestibility, but reduced the absorption of Cr and Ca of the low Ca diet. Supplementation of Cr had no effect on Cr, Ca, Zn, and Mg status in blood and semen of the rams. Level of Cr intake had negative correlation with Ca absorption and positive correlation with blood Cr levels. There is a positive relationship between level of Ca intake with Ca and Mg absorption and blood Ca and Zn levels. Intake of Cr and Ca was not related to the semen Cr and Ca levels

Influence of inelastic collisions with hydrogen atoms on the non-LTE modelling of Ca I and Ca II lines in late-type stars

We perform the non-local thermodynamic equilibrium (NLTE) calculations for Ca I-II with the updated model atom that includes new quantum-mechanical rate coefficients for Ca I + H I collisions from two recent studies, that is, by Barklem and by Mitrushchenkov, Guitou, Belyaev, Yakovleva, Spielfiedel, and Feautrier, and investigate the accuracy of calcium abundance determinations using the Sun, Procyon, and five metal-poor (MP) stars with well-determined stellar parameters. We show that both collisional recipes lead to very similar NLTE results. When using the subordinate lines of Ca I and the high-excitation lines of Ca II, NLTE provides the smaller line-to-line scatter compared with the LTE case for each star. For Procyon, NLTE removes a steep trend with line strength among strong Ca I lines seen in LTE and leads to consistent [Ca/H] abundances from the two ionisation stages. In the MP stars, the NLTE abundance from Ca II 8498 A agrees well with that from the Ca I subordinate lines. NLTE largely removes abundance discrepancies between the high-excitation lines of Ca I and Ca II 8498 A obtained for our four [Fe/H] < -2 stars under the LTE assumption. We investigate the formation of the Ca I resonance line in the [Fe/H] < -2 stars. Consistent NLTE abundances from the Ca I resonance line and the Ca II lines are found for two hyper metal-poor stars HE0107-5240 and HE1327-2326. We provide the NLTE abundance corrections for 28 lines of Ca I in a grid of model atmospheres suitable for abundance analysis of FGK-type dwarfs and subgiants.Comment: 12 pages, 3 tables, 10 figures; accepted for publication in A&

Modeling effects of L-type ca(2+) current and na(+)-ca(2+) exchanger on ca(2+) trigger flux in rabbit myocytes with realistic T-tubule geometries.

The transverse tubular system of rabbit ventricular myocytes consists of cell membrane invaginations (t-tubules) that are essential for efficient cardiac excitation-contraction coupling. In this study, we investigate how t-tubule micro-anatomy, L-type Ca(2+) channel (LCC) clustering, and allosteric activation of Na(+)/Ca(2+) exchanger by L-type Ca(2+) current affects intracellular Ca(2+) dynamics. Our model includes a realistic 3D geometry of a single t-tubule and its surrounding half-sarcomeres for rabbit ventricular myocytes. The effects of spatially distributed membrane ion-transporters (LCC, Na(+)/Ca(2+) exchanger, sarcolemmal Ca(2+) pump, and sarcolemmal Ca(2+) leak), and stationary and mobile Ca(2+) buffers (troponin C, ATP, calmodulin, and Fluo-3) are also considered. We used a coupled reaction-diffusion system to describe the spatio-temporal concentration profiles of free and buffered intracellular Ca(2+). We obtained parameters from voltage-clamp protocols of L-type Ca(2+) current and line-scan recordings of Ca(2+) concentration profiles in rabbit cells, in which the sarcoplasmic reticulum is disabled. Our model results agree with experimental measurements of global Ca(2+) transient in myocytes loaded with 50 μM Fluo-3. We found that local Ca(2+) concentrations within the cytosol and sub-sarcolemma, as well as the local trigger fluxes of Ca(2+) crossing the cell membrane, are sensitive to details of t-tubule micro-structure and membrane Ca(2+) flux distribution. The model additionally predicts that local Ca(2+) trigger fluxes are at least threefold to eightfold higher than the whole-cell Ca(2+) trigger flux. We found also that the activation of allosteric Ca(2+)-binding sites on the Na(+)/Ca(2+) exchanger could provide a mechanism for regulating global and local Ca(2+) trigger fluxes in vivo. Our studies indicate that improved structural and functional models could improve our understanding of the contributions of L-type and Na(+)/Ca(2+) exchanger fluxes to intracellular Ca(2+) dynamics

Resampling from the past to improve on MCMC algorithms

We introduce the idea that resampling from past observations in a Markov Chain Monte Carlo sampler can fasten convergence. We prove that proper resampling from the past does not disturb the limit distribution of the algorithm. We illustrate the method with two examples. The first on a Bayesian analysis of stochastic volatility models and the other on Bayesian phylogeny reconstruction.Monte Carlo methods, Resampling, Stochastic volatility models, Bayesian phylogeny reconstruction.

Mechanisms altering airway smooth muscle cell Ca(2+) homeostasis in two asthma models

Background: Asthma is characterized by airway remodeling, altered mucus production and airway smooth muscle cell (ASMC) contraction causing extensive airway narrowing. In particular, alterations of ASMC contractility seem to be of crucial importance. The elevation of the cytoplasmic Ca(2+) concentration is a key event leading to ASMC contraction and changes in the agonist- induced Ca(2+) increase in ASMC have been reported in asthma. Objective: The aim of this study was to investigate mechanisms underlying these changes. Methods: Murine tracheal smooth muscle cells (MTSMC) from T- bet KO mice and human bronchial smooth muscle cells (HBSMC) incubated with IL-13 and IL-4 served as asthma models. Acetylcholine- induced changes in the cytoplasmic Ca(2+) concentration were recorded using fluorescence microscopy and the expression of Ca(2+) homeostasis regulating proteins was investigated with Western blot analysis. Results: Acetylcholine- induced Ca(2+) transients were elevated in both asthma models. This correlated with an increased Ca(2+) content of the sarcoplasmic reticulum (SR). In MTSMC from T-bet KO mice, the expression of the SR Ca(2+) buffers calreticulin and calsequestrin was higher compared to wild- type mice. In HBSMC incubated with IL-13 or IL-4, the expression of ryanodine receptors, inositol-3-phosphate receptors and sarcoplasmic/ endoplasmic reticulum Ca 2+ ATPases 2 was increased compared to HBSMC without incubation with interleukins. The enlarged acetylcholine- induced Ca(2+) transients could be reversed by blocking inositol-3- phosphate receptors. Conclusions: We conclude that in the murine asthma model the SR Ca(2+) buffer capacity is increased, while in the human asthma model the expression of SR Ca(2+) channels is altered. The investigation of the Ca(2+) homeostasis of ASMC has the potential to provide new therapeutical options in asthma. Copyright (C) 2008 S. Karger AG, Basel