Temperature-dependent Cross Sections for Charmonium Dissociation in Collisions with Pions and Rhos in Hadronic Matter

Meson-charmonium dissociation reactions governed by the quark interchange are studied with temperature-dependent quark potentials. Quark-antiquark relative-motion wave functions and masses of charmonia and charmed mesons are determined by the central spin-independent part of the potentials or by the central spin-independent part and a smeared spin-spin interaction. The prominent temperature dependence of the masses is found. Based on the potentials, the wave functions, and the meson masses, we obtain temperature-dependent cross sections for fifteen pion-charmonium and rho-charmonium dissociation reactions. The numerical cross sections are parametrized for future applications in hadronic matter. The particular temperature dependence of the J/psi bound state leads to unusual behavior of the cross sections for endothermic J/psi dissociation reactions. The quantum numbers of psi' and chi_c can not make their difference in mass in the temperature region 0.6T_c < T < T_c, but can make the psi' dissociation different from the chi_c dissociation.Comment: 52 pages, 23 figures, 6 table

Resonant versus anti-resonant tunneling at carbon nanotube A-B-A heterostructures

Narrow antiresonances going to zero transmission are found to occur for general (2n,0)(n,n)(2n,0) carbon nanotube heterostructures, whereas the complementary configuration, (n,n)(2n,0)(n,n), displays simple resonant tunneling behaviour. We compute examples for different cases, and give a simple explanation for the appearance of antiresonances in one case but not in the other. Conditions and ranges for the occurence of these different behaviors are stated. The phenomenon of anti-resonant tunneling, which has passed unnoticed in previous studies of nanotube heterostructures, adds up to the rich set of behaviors available to nanotube based quantum effect devices.Comment: Published in phys. stat. sol. (b); 6 pages, 4 figure

Unraveling the Role of Interfaces on the Spall Failure of Cu/Ta Multilayered Systems.

Molecular dynamics (MD) simulations are carried out to investigate the effects of the type and spacing of FCC/BCC interfaces on the deformation and spall behavior. The simulations are carried out using model Cu/Ta multilayers with six different types of interfaces. The results suggest that interface type can significantly affect the structure and intensity of the incoming shock wave, change the activated slip systems, alter dislocation slip and twinning behavior, affect where and how voids are nucleated during spallation and the resulting spall strength. Moreover, the above aspects are significantly affected by the interface spacing. A transition from homogeneous to heterogeneous dislocation nucleation occurs as the interface spacing is decreased to 6 nm. Depending on interface type and spacing, damage (voids) nucleation and spall failure is observed to occur not only at the Cu/Ta interfaces, but also in the weaker Cu layer interior, or even in the stronger Ta layer interior, although different mechanisms underlie each of these three distinct failure modes. These findings point to the fact that, depending on the combination of interface type and spacing, interfaces can lead to both strengthening and weakening of the Cu/Ta multilayered microstructures

Simultaneous Measurements of Microwave Photoresistance and Cyclotron Reflection in the Multi-Photon Regime

We simultaneously measure photoresistance with electrical transport and plasmon-cyclotron resonance (PCR) using microwave reflection spectroscopy in high mobility GaAs/AlGaAs quantum wells under a perpendicular magnetic field. Multi-photon transitions are revealed as sharp peaks in the resistance and the cyclotron reflection on samples with various carrier densities. Our main finding is that plasmon coupling is relevant in the cyclotron reflection spectrum but has not been observed in the electrical conductivity signal. We discuss possible mechanisms relevant to reflection or dc conductivity signal to explain this discrepancy. We further confirm a trend that higher order multi-photon features can be observed using higher carrier density samples.Comment: 19 pages, 5 figure

Separating the effects of experimental noise from inherent system variability in voltammetry: the [[Fe(CN)6]3−/4−_6]^{3-/ 4-} process

Recently, we have introduced the use of techniques drawn from Bayesian statistics to recover kinetic and thermodynamic parameters from voltammetric data, and were able to show that the technique of large amplitude ac voltammetry yielded significantly more accurate parameter values than the equivalent dc approach. In this paper we build on this work to show that this approach allows us, for the first time, to separate the effects of random experimental noise and inherent system variability in voltammetric experiments. We analyse ten repeated experimental data sets for the $[$Fe(CN)$_6]^{3-/ 4-}$ process, again using large-amplitude ac cyclic voltammetry. In each of the ten cases we are able to obtain an extremely good fit to the experimental data and obtain very narrow distributions of the recovered parameters governing both the faradaic (the reversible formal faradaic potential, $E_0$, the standard heterogeneous charge transfer rate constant $k_0$, and the charge transfer coefficient $\alpha$) and non-faradaic terms (uncompensated resistance, $R_u$, and double layer capacitance, $C_{dl}$). We then employ hierarchical Bayesian methods to recover the underlying "hyperdistribution" of the faradaic and non-faradaic parameters, showing that in general the variation between the experimental data sets is significantly greater than suggested by individual experiments, except for $\alpha$ where the inter-experiment variation was relatively minor. Correlations between pairs of parameters are provided, and for example, reveal a weak link between $k_0$ and $C_{dl}$ (surface activity of a glassy carbon electrode surface). Finally, we discuss the implications of our findings for voltammetric experiments more generally.Comment: 30 pages, 6 figure

Optimal phase space projection for noise reduction

In this communication we will re-examine the widely studied technique of phase space projection. By imposing a time domain constraint (TDC) on the residual noise, we deduce a more general version of the optimal projector, which includes those appearing in previous literature as subcases but does not assume the independence between the clean signal and the noise. As an application, we will apply this technique for noise reduction. Numerical results show that our algorithm has succeeded in augmenting the signal-to-noise ratio (SNR) for simulated data from the R\"ossler system and experimental speech record.Comment: Accepted version for PR