A multi-scale study on the bubble dynamics of cryogenic cavitation

This study aims to construct a multi-scale cavitation model for unsteady cryogenic cavitation CFD. Many elementary physical processes of bubbles (i.e, nucleation, growth/shrink, evaporation/condensation, coalescence/fission, collapse, bubblebubble interaction, bubble-turbulence interaction, and so on) emerge in cryogenic cavitation where some of the processes have not been understood well. In this paper, we mainly focused the molecular processes in homogeneous liquid-vapor nucleation with noncondensable gas solution by using Molecular Dynamics (MD) method. Bubble nucleation in liquid oxygen including helium, nitrogen, or argon was simulated. Molecular interaction was given by Lennard-Jones potential, and basically, each potential parameter was defined so that a saturation curve obtained by MD data was consistent with an experimental value. In the case that helium was impurity, a bubble nucleus was formed by density fluctuation at a lower concentration while a cluster constituted with helium molecules formed a bubble nucleus at a higher concentration, and the nucleation point becomes closer to the saturation point of pure oxygen when helium molecules form clusters. On the other hand, in the case that nitrogen or argon was the impurity, the above-mentioned clustering was not observed clearly at a concentration where helium made clusters, and these impurities have weaker action to make clusters and cavitation bubble nuclei compared with helium.http://deepblue.lib.umich.edu/bitstream/2027.42/84285/1/CAV2009-final102.pd

One-Center Charge Transfer Transitions in Manganites

In frames of a rather conventional cluster approach, which combines the crystal field and the ligand field models we have considered different charge transfer (CT) states and O 2p-Mn 3d CT transitions in MnO$_{6}^{9-}$ octahedra. The many-electron dipole transition matrix elements were calculated using the Racah algebra for the cubic point group. Simple "local" approximation allowed to calculate the relative intensity for all dipole-allowed $\pi -\pi$ and $\sigma -\sigma$ CT transitions. We present a self-consistent description of the CT bands in insulating stoichiometric LaMn$^{3+}$O$_3$ compound with the only Mn$^{3+}$ valent state and idealized octahedral MnO$_{6}^{9-}$ centers which allows to substantially correct the current interpretation of the optical spectra. Our analysis shows the multi-band structure of the CT optical response with the weak low-energy edge at 1.7 eV, associated with forbidden $t_{1g}(\pi)-e_{g}$ transition and a series of the weak and strong dipole-allowed high-energy transitions starting from 2.5 and 4.5 eV, respectively, and extending up to nearly 11 eV. The most intensive features are associated with two strong composite bands near $4.6\div 4.7$ eV and $8\div 9$ eV, respectively, resulting from the superposition of the dipole-allowed $\sigma -\sigma$ and $\pi -\pi$ CT transitions. These predictions are in good agreement with experimental spectra. The experimental data point to a strong overscreening of the crystal field parameter $Dq$ in the CT states of MnO$_{6}^{9-}$ centers.Comment: 10 pages, 3 figure

A Kinetic Modeling study on the Oxidation of Primary Reference Fuel?Toluene Mixtures Including Cross Reactions between Aromatics and Aliphatics

A detailed chemical kinetic model for the mixtures of Primary Reference Fuel (PRF: n-heptane and iso-octane) and toluene has been proposed. This model is divided into three parts; a PRF mechanism [T. Ogura et al., Energy & Fuels 21 (2007) 3233-3239], toluene sub-mechanism and cross reactions between PRF and toluene. Toluene sub-mechanism includes the low temperature kinetics relevant to engine conditions. A chemical kinetic mechanism proposed by Pitz et al. [Proc. the 2nd Joint Meeting of the U.S. Combust. Institute (2001)] was used as a starting model and modified by updating rate coefficients. Theoretical estimations of rate coefficients were performed for toluene and benzyl radical reactions important at low temperatures. Cross-reactions between alkane, alkene, and aromatics were also included in order to account for the acceleration by the addition of toluene into iso-octane recently found in the shock tube study of the ignition delay [Y. Sakai et al, SAE 2007-01-4014 (2007)]. Validations of the model were performed with existing shock tube and flow tube data. The model well predicts the ignition characteristics of toluene and PRF/Toluene mixtures under the wide range of temperatures (500-1700 K) and pressures (2-50 atm). It is found that reactions of benzyl radical with oxygen molecule determine the reactivity of toluene at low temperature. Although the effect of toluene addition to iso-octane is not fully resolved, the reactions of alkene with benzyl radical have the possibility to account for the kinetic interactions between PRF and toluene

Changing Selective Pressure during Antigenic Changes in Human Influenza H3

The rapid evolution of influenza viruses presents difficulties in maintaining the optimal efficiency of vaccines. Amino acid substitutions result in antigenic drift, a process whereby antisera raised in response to one virus have reduced effectiveness against future viruses. Interestingly, while amino acid substitutions occur at a relatively constant rate, the antigenic properties of H3 move in a discontinuous, step-wise manner. It is not clear why this punctuated evolution occurs, whether this represents simply the fact that some substitutions affect these properties more than others, or if this is indicative of a changing relationship between the virus and the host. In addition, the role of changing glycosylation of the haemagglutinin in these shifts in antigenic properties is unknown. We analysed the antigenic drift of HA1 from human influenza H3 using a model of sequence change that allows for variation in selective pressure at different locations in the sequence, as well as at different parts of the phylogenetic tree. We detect significant changes in selective pressure that occur preferentially during major changes in antigenic properties. Despite the large increase in glycosylation during the past 40 years, changes in glycosylation did not correlate either with changes in antigenic properties or with significantly more rapid changes in selective pressure. The locations that undergo changes in selective pressure are largely in places undergoing adaptive evolution, in antigenic locations, and in locations or near locations undergoing substitutions that characterise the change in antigenicity of the virus. Our results suggest that the relationship of the virus to the host changes with time, with the shifts in antigenic properties representing changes in this relationship. This suggests that the virus and host immune system are evolving different methods to counter each other. While we are able to characterise the rapid increase in glycosylation of the haemagglutinin during time in human influenza H3, an increase not present in influenza in birds, this increase seems unrelated to the observed changes in antigenic properties

Macroscopic traffic models from microscopic car-following models

We present a method to derive macroscopic fluid-dynamic models from microscopic car-following models via a coarse-graining procedure. The method is first demonstrated for the optimal velocity model. The derived macroscopic model consists of a conservation equation and a momentum equation, and the latter contains a relaxation term, an anticipation term, and a diffusion term. Properties of the resulting macroscopic model are compared with those of the optimal velocity model through numerical simulations, and reasonable agreement is found although there are deviations in the quantitative level. The derivation is also extended to general car-following models.Comment: 12 pages, 4 figures; to appear in Phys. Rev.

Criterion for traffic phases in single vehicle data and empirical test of a microscopic three-phase traffic theory

A microscopic criterion for distinguishing synchronized flow and wide moving jam phases in single vehicle data measured at a single freeway location is presented. Empirical local congested traffic states in single vehicle data measured on different days are classified into synchronized flow states and states consisting of synchronized flow and wide moving jam(s). Then empirical microscopic characteristics for these different local congested traffic states are studied. Using these characteristics and empirical spatiotemporal macroscopic traffic phenomena, an empirical test of a microscopic three-phase traffic flow theory is performed. Simulations show that the microscopic criterion and macroscopic spatiotemporal objective criteria lead to the same identification of the synchronized flow and wide moving jam phases in congested traffic. It is found that microscopic three-phase traffic models can explain both microscopic and macroscopic empirical congested pattern features. It is obtained that microscopic distributions for vehicle speed difference as well as fundamental diagrams and speed correlation functions can depend on the spatial co-ordinate considerably. It turns out that microscopic optimal velocity (OV) functions and time headway distributions are not necessarily qualitatively different, even if local congested traffic states are qualitatively different. The reason for this is that important spatiotemporal features of congested traffic patterns are it lost in these as well as in many other macroscopic and microscopic traffic characteristics, which are widely used as the empirical basis for a test of traffic flow models, specifically, cellular automata traffic flow models.Comment: 27 pages, 16 figure

Inferring stabilizing mutations from protein phylogenies : application to influenza hemagglutinin

One selection pressure shaping sequence evolution is the requirement that a protein fold with sufficient stability to perform its biological functions. We present a conceptual framework that explains how this requirement causes the probability that a particular amino acid mutation is fixed during evolution to depend on its effect on protein stability. We mathematically formalize this framework to develop a Bayesian approach for inferring the stability effects of individual mutations from homologous protein sequences of known phylogeny. This approach is able to predict published experimentally measured mutational stability effects (ΔΔG values) with an accuracy that exceeds both a state-of-the-art physicochemical modeling program and the sequence-based consensus approach. As a further test, we use our phylogenetic inference approach to predict stabilizing mutations to influenza hemagglutinin. We introduce these mutations into a temperature-sensitive influenza virus with a defect in its hemagglutinin gene and experimentally demonstrate that some of the mutations allow the virus to grow at higher temperatures. Our work therefore describes a powerful new approach for predicting stabilizing mutations that can be successfully applied even to large, complex proteins such as hemagglutinin. This approach also makes a mathematical link between phylogenetics and experimentally measurable protein properties, potentially paving the way for more accurate analyses of molecular evolution

Open Government Data: A Focus on Key Economic and Organizational Drivers

Grounding the analysis on multidisciplinary literature on the topic, the existing EU legislation and relevant examples, this working paper aims at highlighting some key economic and organizational aspects of the "Open Government Data" paradigm and its drivers and implications within and outside Public Administrations. The discussion intends to adopt an "Internet Science" perspective, taking into account as enabling factors the digital environment itself, as well as specific models and tools. More "traditional" and mature markets grounded on Public Sector Information are also considered, in order to indirectly detect the main differences with respect to the aforementioned paradig