Shake-Modified Resonant Autoionization In Magnesium

Anomalous features in the resonantly excited 2p autoionization spectrum of Mg are attributed to overlapping shake transitions of the excited bound (spectator) electron. Universal features of the shake spectrum are displayed and related to the post-collision interaction

Vanadium pentoxide nanobelt-reduced graphene oxide nanosheet composites as high-performance pseudocapacitive electrodes: Ac impedanc spectroscopy data modeling and theoretical calculations

Graphene nanosheets and graphene nanoribbons, G combined with vanadium pentoxide (VO) nanobelts (VNBs) and VNBs forming GVNB composites with varying compositions were synthesized via a one-step low temperature facile hydrothermal decomposition method as high-performance electrochemical pseudocapacitive electrodes. VNBs from vanadium pentoxides (VO) are formed in the presence of graphene oxide (GO), a mild oxidant, which transforms into reduced GO (rGOHT), assisting in enhancing the electronic conductivity coupled with the mechanical robustness of VNBs. From electron microscopy, surface sensitive spectroscopy and other complementary structural characterization, hydrothermally-produced rGO nanosheets/nanoribbons are decorated with and inserted within the VNBs\u27 layered crystal structure, which further confirmed the enhanced electronic conductivity of VNBs. Following the electrochemical properties of GVNBs being investigated, the specific capacitance Csp is determined from cyclic voltammetry (CV) with a varying scan rate and galvanostatic charging-discharging (V-t) profiles with varying current density. The rGO-rich composite V1G3 (i.e., VO/GO = 1:3) showed superior specific capacitance followed by VO-rich composite V3G1 (VO/GO = 3:1), as compared to V1G1 (VO/GO = 1:1) composite, besides the constituents, i.e., rGO, rGOHT and VNBs. Composites V1G3 and V3G1 also showed excellent cyclic stability and a capacitance retention of \u3e80% after 500 cycles at the highest specific current density. Furthermore, by performing extensive simulations and modeling of electrochemical impedance spectroscopy data, we determined various circuit parameters, including charge transfer and solution resistance, double layer and low frequency capacitance, Warburg impedance and the constant phase element. The detailed analyses provided greater insights into physical-chemical processes occurring at the electrode-electrolyte interface and highlighted the comparative performance of thin heterogeneous composite electrodes. We attribute the superior performance to the open graphene topological network being beneficial to available ion diffusion sites and the faster transport kinetics having a larger accessible geometric surface area and synergistic integration with optimal nanostructured VO loading. Computational simulations via periodic density functional theory (DFT) with and without V2O5 adatoms on graphene sheets are also performed. These calculations determine the total and partial electronic density of state (DOS) in the vicinity of the Fermi level (i.e., higher electroactive sites), in turn complementing the experimental results toward surface/interfacial charge transfer on heterogeneous electrodes

FISSION DYNAMICS WITH MICROSCOPIC LEVEL DENSITIES

We present a consistent framework for treating the energy and angularmomentum dependence of the shape evolution in the nuclear fission. It combines microscopically calculated level densities with the Metropolis-walk method, has no new parameters, and can elucidate the energy-dependent influence of pairing and shell effects on the dynamics of warm nuclei

Local Spectral Density for a Periodically Driven System of Coupled Quantum States with Strong Imperfection in Unperturbed Energies

A random matrix theory approach is applied in order to analyze the localization properties of local spectral density for a generic system of coupled quantum states with strong static imperfection in the unperturbed energy levels. The system is excited by an external periodic field, the temporal profile of which is close to monochromatic one. The shape of local spectral density is shown to be well described by the contour obtained from a relevant model of periodically driven two-states system with irreversible losses to an external thermal bath. The shape width and the inverse participation ratio are determined as functions both of the Rabi frequency and of parameters specifying the localization effect for our system in the absence of external field.Comment: 6 pages, 5 figures, submitted to Optics and Spectroscop

Thermodynamic ground states of platinum metal nitrides

We have systematically studied the thermodynamic stabilities of various phases of the nitrides of the platinum metal elements using density functional theory. We show that for the nitrides of Rh, Pd, Ir and Pt two new crystal structures, in which the metal ions occupy simple tetragonal lattice sites, have lower formation enthalpies at ambient conditions than any previously proposed structures. The region of stability can extend up to 17 GPa for PtN{sub 2}. Furthermore, we show that according to calculations using the local density approximation, these new compounds are also thermodynamically stable at ambient pressure and thus may be the ground state phases for these materials. We further discuss the fact that the local density and generalized gradient approximations predict different values of the absolute formation enthalpies as well different relative stabilities between simple tetragonal and the pyrite or marcasite structures

Unconventional decay law for excited states in closed many-body systems

We study the time evolution of an initially excited many-body state in a finite system of interacting Fermi-particles in the situation when the interaction gives rise to the ``chaotic'' structure of compound states. This situation is generic for highly excited many-particle states in quantum systems, such as heavy nuclei, complex atoms, quantum dots, spin systems, and quantum computers. For a strong interaction the leading term for the return probability $W(t)$ has the form $W(t)\simeq \exp (-\Delta_E^2t^2)$ with $\Delta_E^2$ as the variance of the strength function. The conventional exponential linear dependence $W(t)=C\exp (-\Gamma t)$ formally arises for a very large time. However, the prefactor $C$ turns out to be exponentially large, thus resulting in a strong difference from the conventional estimate for $W(t)$.Comment: RevTex, 4 pages including 1 eps-figur

Calculation of the photoionization with de-excitation cross sections of He and helium-like ions

We discuss the results of the calculation of the photoionization with de-excitation of excited He and helium-like ions Li$^{+}$ and B$^{3+}$ at high but non-relativistic photon energies $\omega$. Several lower $^{1}S$ and $^{3}S$ states are considered. We present and analyze the ratios $R_{d}^{+\ast}$ of the cross sections of photoionization with de-excitation, $\sigma_{(d)}^{+\ast}(\omega)$, and of the photo-ionization with excitation, $\sigma ^{+\ast}(\omega)$. The dependence of $R_{d}^{+\ast}$ on the excitation of the target object and the charge of its nucleus is presented. Apart to theoretical interest, results obtained can be verified using such long living excited state as $2^{3}S$ of He.Comment: 10 pages, 6 table

Cluster Interpretation of Properties of Alternating Parity Bands in Heavy Nuclei

The properties of the states of the alternating parity bands in actinides, Ba, Ce and Nd isotopes are analyzed within a cluster model. The model is based on the assumption that cluster type shapes are produced by the collective motion of the nuclear system in the mass asymmetry coordinate. The calculated spin dependences of the parity splitting and of the electric multipole transition moments are in agreement with the experimental data.Comment: 29 pages, 10 figure