Computer program for transient response of structural rings subjected to fragment impact

Mathematical optimization of containment/deflection system would save time, effort, and material as well as afford designer greater opportunity to investigate new ideas and variety of materials

Analytical Mechanics of Chemical Reactions. V. Application to the Linear Reactive H +H_2 Systems

Natural collision coordinates and a zeroth‐order vibrational–adiabatic approximation are used to treat linear reactive collisions. Nonadiabatic effects on barrier transmission and on vibrational state of products are calculated. The present results are classical and are compared with exact classical numerical results for the H+H_2 reaction in the range 7–20 kcal/mol of initial relative translational energy. The agreement is encouraging and the results support the concepts introduced earlier of statistical adiabaticity and of nonadiabatic leak. At low energies the reaction is adiabatic on the average (initial vibrational phase average), thus justifying activated complex theory for this system. The relative importance of reaction path curvature and of vibrational frequency variation along the reaction path in inducing nonadiabatic effects is described. Implications for a quantum treatment, activated complex theory, and highly nonadiabatic systems are noted

Analytical Mechanics of Chemical Reactions. VI. Rotational and Vibrational Distributions of the H + H_2 Reaction in a Plane

Rotational and vibrational distributions for the exchange reaction H+H_(2)→H_(2)+H are obtained numerically for reaction in a plane and compared with the vibrationally adiabatic solutions. Evidence is obtained regarding the two adiabatic solutions for the final rotational state predicted earlier and for the disappearance of one of these at higher initial relative velocity. Good agreement between calculations based on natural collision coordinates and these based on Cartesian coordinates was found, where tested. The vibrational motion for reaction in a plane is fairly adiabatic on the average at energies of thermal interest. Connections with other properties are noted. The results support the idea of statistical adiabaticity suggested earlier in this series and thus support a derivation of activated complex theory based on this concept

An Upper Limit on Omega_matter Using Lensed Arcs

We use current observations on the number statistics of gravitationally lensed optical arcs towards galaxy clusters to derive an upper limit on the cosmological mass density of the Universe. The gravitational lensing statistics due to foreground clusters combine properties of both cluster evolution, which is sensitive to the matter density, and volume change, which is sensitive to the cosmological constant. The uncertainties associated with the predicted number of lensing events, however, currently do not allow one to distinguish between flat and open cosmological models with and without a cosmological constant. Still, after accounting for known errors, and assuming that clusters in general have dark matter core radii of the order ~ 35 h^-1 kpc, we find that the cosmological mass density, Omega_m, is less than 0.56 at the 95% confidence. Such a dark matter core radius is consistent with cluster potentials determined recently by detailed numerical inversions of strong and weak lensing imaging data. If no core radius is present, the upper limit on Omega_m increases to 0.62 (95% confidence level). The estimated upper limit on Omega_m is consistent with various cosmological probes that suggest a low matter density for the Universe.Comment: 6 pages, 3 figures. Accepted version (ApJ in press

X-ray Polarization Signatures of Compton Scattering in Magnetic Cataclysmic Variables

Compton scattering within the accretion column of magnetic cataclysmic variables (mCVs) can induce a net polarization in the X-ray emission. We investigate this process using Monte Carlo simulations and find that significant polarization can arise as a result of the stratified flow structure in the shock-ionized column. We find that the degree of linear polarization can reach levels up to ~8% for systems with high accretion rates and low white-dwarf masses, when viewed at large inclination angles with respect to the accretion column axis. These levels are substantially higher than previously predicted estimates using an accretion column model with uniform density and temperature. We also find that for systems with a relatively low-mass white dwarf accreting at a high accretion rate, the polarization properties may be insensitive to the magnetic field, since most of the scattering occurs at the base of the accretion column where the density structure is determined mainly by bremsstrahlung cooling instead of cyclotron cooling.Comment: 7 pages, 8 figures, accepted by MNRA

Tunneling Effect Near Weakly Isolated Horizon

The tunneling effect near a weakly isolated horizon (WIH) has been studied. By applying the null geodesic method of Parikh and Wilczek and Hamilton-Jacibi method of Angheben et al. to a weakly isolated horizon, we recover the semiclassical emission rate in the tunneling process. We show that the tunneling effect exists in a wide class of spacetimes admitting weakly isolated horizons. The general thermodynamic nature of WIH is then confirmed.Comment: 7 pages, accepted for publication in Physical Review

Accelerating charging dynamics in sub-nanometer pores

Having smaller energy density than batteries, supercapacitors have exceptional power density and cyclability. Their energy density can be increased using ionic liquids and electrodes with sub-nanometer pores, but this tends to reduce their power density and compromise the key advantage of supercapacitors. To help address this issue through material optimization, here we unravel the mechanisms of charging sub-nanometer pores with ionic liquids using molecular simulations, navigated by a phenomenological model. We show that charging of ionophilic pores is a diffusive process, often accompanied by overfilling followed by de-filling. In sharp contrast to conventional expectations, charging is fast because ion diffusion during charging can be an order of magnitude faster than in bulk, and charging itself is accelerated by the onset of collective modes. Further acceleration can be achieved using ionophobic pores by eliminating overfilling/de-filling and thus leading to charging behavior qualitatively different from that in conventional, ionophilic pores

Towards a guided atom interferometer based on a superconducting atom chip

We evaluate the realization of a novel geometry of a guided atom interferometer based on a high temperature superconducting microstructure. The interferometer type structure is obtained with a guiding potential realized by two current carrying superconducting wires in combination with a closed superconducting loop sustaining a persistent current. We present the layout and realization of our superconducting atom chip. By employing simulations we discuss the critical parameters of the interferometer guide in particular near the splitting regions of the matter waves. Based on measurements of the relevant chip properties we discuss the application of a compact and reliable on-chip atom interferometer.Comment: 14 pages, 7 figures, accepted for New Journal of Physic