Predicted ultrafast dynamic metallization of dielectric nanofilms by strong single-cycle optical fields

We predict a dynamic metallization effect where an ultrafast (single-cycle) optical pulse with a ?1 V/? field causes plasmonic metal-like behavior of a dielectric film with a few-nm thickness. This manifests itself in plasmonic oscillations of polarization and a significant population of the conduction band evolving on a ~1 fs time scale. These phenomena are due to a combination of both adiabatic (reversible) and diabatic (for practical purposes irreversible) pathways.     

Estimation of 99Mo production rates from natural molybdenum in research reactors

Journal of Radioanalytical and Nuclear Chemistry - Molybdenum-99 is one of the most important radionuclides for medical diagnostics. In 2015, the International Atomic Energy Agency organized a...     

Structured construction and simulation of nondeterministic stochastic activity networks

In this work we deal with nondeterministic stochastic activity networks (NDSANs). Their stochastic character results from activity durations, which are given by nonnegative continuous random variables. The nondeterministic behavior of an NDSAN is a consequence of its variable topology, based on two additional features. First, by associating choice probabilities with the immediate successors of an activity, some branches of execution are not always taken. Second, by allowing iterated executions of a group of activities according to predetermined probabilities, the number of times an activity is to be executed is not determined a priori. These properties lead to a wide variety of activity networks, capable of modelling many real situations in process engineering and project management. We describe a simple, recursively structured construction of NDSANs, which both provides a coherent syntactic mechanism to incorporate the two abovementioned nondeterminism features and allows the analytic formulation of completion time. This construction also directly gives rise to a recursive simulation algorithm for NDSANs, whose repeated execution produces an estimate of the probability distribution of the completion time of the network. We also report on real-world case studies, using the Komolgorov–Smirnov statistic for validation.     

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Magnetic characterization of ZnO doped with vanadium

The magnetic properties of vanadium doped ZnO nanorods formed by different growth methods were examined. The samples under investigation were either grown by metallorganic vapour-phase epitaxy (MOVPE) with in situ incorporation of the V atoms or by aqueous chemical growth (ACG) in combination with an ion-implantation process. The V concentration for all samples was less than 2 at.%.Field-cooled SQUID measurements only reveal a weak ferromagnetic signal still in a very sensitive measuring range. However, the MFM micrographs obtained at room temperature show a clear magnetic contrast and complex structures, the images are in good agreement with the phase images expected for vertically aligned magnetic dipoles. This is a strong indication for a ferromagnetic behaviour at room temperature.     

Electric field gradients at the 111In site in the ferroelectric and paraelectric phases of LiTaO3

The temperature dependence of the electric-field gradient of ¹¹¹Cd in single crystalline LiTaO₃ was studied from room temperature to 1040 K in the ferroelectric and paraelectric phases. The data taken at room temperature show unambiguously the presence of two quadrupole interaction frequencies, ν_Q1=230 MHz and ν_Q2=242 MHz, with nonzero asymmetry parameters, while above the Curie temperature (T_C=878 K) the data are well described by a unique frequency. The electric field gradient shows a usual temperature dependence, increasing aproximately in a linear fashion until T_C and then decreasing faster. The initial increase is explained mostly by the lattice expansion, while above T_C it is necessary to consider Li and O displacements. This revised version was published online in August 2006 with corrections to the Cover Date.     

Null geodesics and wave front singularities in the Gödel space–time

We explore wave fronts of null geodesics in the Gödel metric emitted from point sources both at, and away from, the origin. For constant time wave fronts emitted by sources away from the origin, we find cusp ridges as well as blue sky metamorphoses where spatially disconnected portions of the wave front appear, connect to the main wave front, and then later break free and vanish. These blue sky metamorphoses in the constant time wave fronts highlight the non-causal features of the Gödel metric. We introduce a concept of physical distance along the null geodesics, and show that for wave fronts of constant physical distance, the reorganization of the points making up the wave front leads to the removal of cusp ridges.     

Attosecond correlated dynamics of two electrons passing through a transition state

The strong-field induced decay of a doubly excited, transient Coulomb complex Ar**→Ar(2+)+2e(-) is explored by tracing correlated two-electron emission in nonsequential double ionization of Ar as a function of the carrier-envelope phase. Using <6 fs pulses, electron emission is essentially confined to one optical cycle. Classical model calculations support that the intermediate Coulomb complex has lost memory of its formation dynamics and allows for a consistent, though model-dependent definition of "emission time," empowering us to trace transition-state two-electron decay dynamics with sub-fs resolution. We find a most likely emission time difference of ～200±100 as.