Accurate freezing and melting equations for the Lennard-Jones system

Analyzing three approximate methods to locate liquid-solid coexistence in simple systems, an observation is made that all of them predict the same functional dependence of the temperature on density at freezing and melting of the conventional Lennard-Jones system. The emerging equations can be written as $T={\mathcal A}\rho^4+{\mathcal B}\rho^2$ in normalized units. We suggest to determine the values of the coefficients ${\mathcal A}$ at freezing and melting from the high-temperature limit, governed by the inverse twelfth power repulsive potential. The coefficients ${\mathcal B}$ can be determined from the triple point parameters of the LJ fluid. This produces freezing and melting equations which are exact in the high-temperature limit and at the triple point, and show remarkably good agreement with numerical simulation data in the intermediate region.Comment: 6 pages, 1 figur

Ionization enhanced ion collection by a small floating grain in plasmas

It is demonstrated that the ionization events in the vicinity of a small floating grain can increase the ion flux to its surface. In this respect the effect of electron impact ionization is fully analogous to that of the ion-neutral resonant charge exchange collisions. Both processes create slow ion which cannot overcome grain' electrical attraction and eventually fall onto its surface. The relative importance of ionization and ion-neutral collisions is roughly given by the ratio of the corresponding frequencies. We have evaluated this ratio for neon and argon plasmas to demonstrate that ionization enhanced ion collection can indeed be an important factor affecting grain charging in realistic experimental conditions.Comment: 7 pages, 1 figure, submitted to Physics of Plasma

Real Business Cycle Realizations

Much recent business cycle research focuses on moments of macroeconomic aggregates. We construct examples of real business cycle sample paths for output, consumption, and employment for the U.S. economy. Annual sample paths are generated from an initial condition in 1925, measured technology and government spending shocks since then, and a standard, calibrated, one-sector model of the business cycle. Quarterly sample paths are generated similarly, from an initial condition in 1955. The law of motion for shocks is not parametrized and so decision-rules are estimated by GMM. We compare the paths with actual history graphically and by spectral methods.real business cycles, Solow residuals, US business cycle history

Spin solid phases of spin 1 and spin 3/2 antiferromagnets on a cubic lattice

We study spin S=1 and S=3/2 Heisenberg antiferromagnets on a cubic lattice focusing on spin solid states. Using Schwinger boson formulation for spins, we start in a U(1) spin liquid phase proximate to Neel phase and explore possible confining paramagnetic phases as we transition away from the spin liquid by the process of monopole condensation. Electromagnetic duality is used to rewrite the theory in terms of monopoles. For spin 1 we find several candidate phases of which the most natural one is a phase with spins organized into parallel Haldane chains. For spin 3/2 we find that the most natural phase has spins organized into parallel ladders. As a by-product, we also write a Landau theory of the ordering in two special classical frustrated XY models on the cubic lattice, one of which is the fully frustrated XY model. In a particular limit our approach maps to a dimer model with 2S dimers coming out of every site, and we find the same spin solid phases in this regime as well.Comment: 15 pages, 8 figure

Shielding of a small charged particle in weakly ionized plasmas

In this paper we present a concise overview of our recent results concerning the electric potential distribution around a small charged particle in weakly ionized plasmas. A number of different effects which influence plasma screening properties are considered. Some consequences of the results are discussed, mostly in the context of complex (dusty) plasmas.Comment: This is a short review pape

Statistics of reversible bond dynamics observed in force-clamp spectroscopy

We present a detailed analysis of two-state trajectories obtained from force-clamp spectroscopy (FCS) of reversibly bonded systems. FCS offers the unique possibility to vary the equilibrium constant in two-state kinetics, for instance the unfolding and refolding of biomolecules, over many orders of magnitude due to the force dependency of the respective rates. We discuss two different kinds of counting statistics, the event-counting usually employed in the statistical analysis of two-state kinetics and additionally the so-called cycle-counting. While in the former case all transitions are counted, cycle-counting means that we focus on one type of transitions. This might be advantageous in particular if the equilibrium constant is much larger or much smaller than unity because in these situations the temporal resolution of the experimental setup might not allow to capture all transitions of an event-counting analysis. We discuss how an analysis of FCS data for complex systems exhibiting dynamic disorder might be performed yielding information about the detailed force-dependence of the transition rates and about the time scale of the dynamic disorder. In addition, the question as to which extent the kinetic scheme can be viewed as a Markovian two-state model is discussed.Comment: 25 pages, 10 figures, Phys. Rev. E, in pres

Diabrotica virgifera virgifera LeConte in confrontation mood : simultaneous geographical and host spectrum expansion in southeastern Slovenia

Diabrotica virgifera virgifera LeConte, in its original North American habitat also known as western corn rootworm beetle, actively continues its expansion to new territories and uses Homo sapiens as its prime vector. It took only 15 years to spread to and occupy the southeastern and central parts of Europe, so far with the exception of Denmark where it has not been documented as of 2007. Economic thresholds have been reached and surpassed only in Southeast European countries like Slovakia, Hungary, Serbia, Eastern Croatia, Romania and Northern Italy. But both, the area affected and the severity of symptoms are increasing. Model calculations by a number of authors (Baufeld & Enzian, 2005 a and b; Hongmei Li & al. 2006, CLIMEX model) indicate a definitive propensity of D. v. virgifera to expand its currently occupied territory to regions with moderate temperatures and Zea mays cultivation. East Africa and Eastern Asia are included in the list of potential candidates for future inadvertent introduction. In most discussions it is tacitly and erroneously assumed that Z. mays is the only or the only important host of D. v. virgifera. Our recent observations in Eastern Slovenia on the oil pumpkin Cucurbita pepo indicate, however, that this simplifying assumption is notlonger strictly valid. It has to be modified in light of new evidence. Here, we report a few field experiments conducted in August of 2006 clarifying the host status of C. pepo in a European country.Diabrotica virgifera virgifera LeConte (Coleoptera: Chysomelidae), im deutschsprachigen Raum als Westlicher Maiswurzelbohrer bekannt, ist ein von der Neuen Welt nach Europa eingeschleppter Schädling. Er gelangte in mindestens drei Einwanderungsschüben, die durch molekulargenetische Untersuchungen unterscheidbar sind, nach Europa. Innerhalb der letzten eineinhalb Jahrzehnte wurde, mit Ausnahme von Dänemark, die gesamte Fläche Südost- und Zentraleuropas vom Käfer besiedelt. In mehreren osteuropäischen Ländern ist die ökonomische Schadensschwelle bereits überschritten. Bis 2006 galt Zea mays als einzige bekannte europäische Wirtspflanze. Allerdings deuten neueste Beobachtungen in Ostslowenien vom August 2006 auf kleine Zahlen von Käfern am Ölkürbis Cucurbita pepo und damit auf eine Ausdehnung des Wirtsspektrums von D. v. virgifera hin. Der Käfer tritt in kleinen Zahlen als Besucher von Ölkürbisblüten mit einer Häufigkeit von 0,1 % auf. Er ist aber auch in geringer Häufigkeit in Kairomon- und Pheromonfallen in Ölkürbisfeldern südlich von Gaberje in Ostslowenien anzutreffen. Dieses Ergebnis stellt den zukünftigen Wert des Fruchtwechsels in Frage, der bisher als eine der wirksamsten und nachhaltigsten Methoden des integrierten Pflanzenschutzes galt

Channeling of particles and associated anomalous transport in a 2D complex plasma crystal

Implications of recently discovered effect of channeling of upstream extra particles for transport phenomena in a two-dimensional plasma crystal are discussed. Upstream particles levitated above the lattice layer and tended to move between the rows of lattice particles. An example of heat transport is considered, where upstream particles act as moving heat sources, which may lead to anomalous heat transport. The average channeling length observed was 15 - 20 interparticle distances. New features of the channeling process are also reported