Antifactors of regular bipartite graphs

Let $G=(X,Y;E)$ be a bipartite graph, where $X$ and $Y$ are color classes and $E$ is the set of edges of $G$. Lov\'asz and Plummer \cite{LoPl86} asked whether one can decide in polynomial time that a given bipartite graph $G=(X,Y; E)$ admits a 1-anti-factor, that is subset $F$ of $E$ such that $d_F(v)=1$ for all $v\in X$ and $d_F(v)\neq 1$ for all $v\in Y$. Cornu\'ejols \cite{CHP} answered this question in the affirmative. Yu and Liu \cite{YL09} asked whether, for a given integer $k\geq 3$, every $k$-regular bipartite graph contains a 1-anti-factor. This paper answers this question in the affirmative

Density of States Monte Carlo Method for Simulation of Fluids

A Monte Carlo method based on a density-of-states sampling is proposed for study of arbitrary statistical mechanical ensembles in a continuum. A random walk in the two-dimensional space of particle number and energy is used to estimate the density of states of the system; this density of states is continuously updated as the random walk visits individual states. The validity and usefulness of the method are demonstrated by applying it to the simulation of a Lennard-Jones fluid. Results for its thermodynamic properties, including the vapor-liquid phase coexistence curve, are shown to be in good agreement with high-accuracy literature data.Comment: 5 pages, 3 figures, accepted by J Chem Phy

Seguimiento online de la conductividad eléctrica del vino inducido por ultrasonido

We assessed the effects of ultrasonic frequency, power, temperature and exposure time on the electric conductivity (EC) of wine to evaluate the feasibility of the online EC monitoring as an indicator to reflect the changes of wine quality under the ultrasound irradiation. Results showed that the continuously monitored curve of EC was significantly different from the values recorded at the beginning and end of sonication. An abrupt rise and a rapid drop of wine EC were observed at the start and end points of sonication, respectively, in all working conditions. With regards to the assayed wine temperatures, the effect exerted by this parameter on EC before sonication was totally different from that observed when the samples were cooled down after ultrasound treatment. All in all, these results suggest that the online EC monitoring of wine may be used as an efficient indicator to control and reflect the real changes of wine under ultrasound treatment.Hemos estudiado los efectos de la frecuencia de ultrasonido, la potencia, la temperatura y el tiempo de exposición en la conductividad eléctrica (EC) del vino para evaluar la viabilidad del seguimiento EC online como indicador para reflejar los cambios en la calidad del vino bajo irradiación de ultrasonido. Los resultados mostraron que la curva de EC supervisada en continuo fue significativamente diferente de los valores registrados al principio y al final de la sonicación. Se observaron un aumento brusco y una rápida caída de EC del vino al principio y al final de la sonicación, respectivamente, para todas las condiciones estudiadas. En referencia a las temperaturas testadas del vino, el efecto ejercido por este parámetro en EC antes de la sonicación fue totalmente distinto de aquel observado cuando se enfriaron las muestras después del tratamiento de ultrasonido. En resumen, estos resultados sugieren que el seguimiento online de EC del vino podría ser utilizado como un indicador eficiente para controlar y reflejar los cambios reales en el vino con el uso de tratamiento de ultrasonido.National Natural Science Foundation of China [grant number 31101324]Natural Science Foundation of Shaanxi Province, China [grant number 2015JM3097]Technology Transfer Promotion Project of Xi’an, Shaanxi Province, China [grant number CXY1434(5)]Fundamental Research Funds for the Central Universities of China [grant number GK201302039], [grant number GK201404006], [grant number GK201505128

Multicanonical Parallel Tempering

We present a novel implementation of the parallel tempering Monte Carlo method in a multicanonical ensemble. Multicanonical weights are derived by a self-consistent iterative process using a Boltzmann inversion of global energy histograms. This procedure gives rise to a much broader overlap of thermodynamic-property histograms; fewer replicas are necessary in parallel tempering simulations, and the acceptance of trial swap moves can be made arbitrarily high. We demonstrate the usefulness of the method in the context of a grand-multicanonical ensemble, where we use multicanonical simulations in energy space with the addition of an unmodified chemical potential term in particle-number space. Several possible implementations are discussed, and the best choice is presented in the context of the liquid-gas phase transition of the Lennard-Jones fluid. A substantial decrease in the necessary number of replicas can be achieved through the proposed method, thereby providing a higher efficiency and the possibility of parallelization.Comment: 8 pages, 3 figure, accepted by J Chem Phy