Search for Kaluza-Klein Graviton Emission in ppˉp\bar{p} Collisions at s=1.8\sqrt{s}=1.8 TeV using the Missing Energy Signature

We report on a search for direct Kaluza-Klein graviton production in a data sample of 84 ${pb}^{-1}$ of \ppb collisions at $\sqrt{s}$ = 1.8 TeV, recorded by the Collider Detector at Fermilab. We investigate the final state of large missing transverse energy and one or two high energy jets. We compare the data with the predictions from a $3+1+n$-dimensional Kaluza-Klein scenario in which gravity becomes strong at the TeV scale. At 95% confidence level (C.L.) for $n$=2, 4, and 6 we exclude an effective Planck scale below 1.0, 0.77, and 0.71 TeV, respectively.Comment: Submitted to PRL, 7 pages 4 figures/Revision includes 5 figure

Measurement of the average time-integrated mixing probability of b-flavored hadrons produced at the Tevatron

We have measured the number of like-sign (LS) and opposite-sign (OS) lepton pairs arising from double semileptonic decays of $b$ and $\bar{b}$-hadrons, pair-produced at the Fermilab Tevatron collider. The data samples were collected with the Collider Detector at Fermilab (CDF) during the 1992-1995 collider run by triggering on the existence of $\mu \mu$ and $e \mu$ candidates in an event. The observed ratio of LS to OS dileptons leads to a measurement of the average time-integrated mixing probability of all produced $b$-flavored hadrons which decay weakly, $\bar{\chi} = 0.152 \pm 0.007$ (stat.) $\pm 0.011$ (syst.), that is significantly larger than the world average $\bar{\chi} = 0.118 \pm 0.005$.Comment: 47 pages, 10 figures, 15 tables Submitted to Phys. Rev.

SmartVote: a full-fledged graph-based model for multi-valued truth discovery

© 2018, Springer Science+Business Media, LLC, part of Springer Nature. In the era of Big Data, truth discovery has emerged as a fundamental research topic, which estimates data veracity by determining the reliability of multiple, often conflicting data sources. Although considerable research efforts have been conducted on this topic, most current approaches assume only one true value for each object. In reality, objects with multiple true values widely exist and the existing approaches that cope with multi-valued objects still lack accuracy. In this paper, we propose a full-fledged graph-based model, SmartVote, which models two types of source relations with additional quantification to precisely estimate source reliability for effective multi-valued truth discovery. Two graphs are constructed and further used to derive different aspects of source reliability (i.e., positive precision and negative precision) via random walk computations. Our model incorporates four important implications, including two types of source relations, object popularity, loose mutual exclusion, and long-tail phenomenon on source coverage, to pursue better accuracy in truth discovery. Empirical studies on two large real-world datasets demonstrate the effectiveness of our approach

Prediction of nano/micro aluminum particles ignition in oxygen atmosphere

Ignition prediction of aluminum particle is of great significance for a variety of propulsion and power systems to achieve optimal energy release within a limited residence time. In this study a heat transfer model employing temperature dependent coefficients was developed and validated to describe the heat exchange between quiescent/flow gas and aluminum particles from nano- to micro-size, covering the free-molecular to continuum regimes. By coupling heat transfer and aluminum oxidation, a theoretical model has been proposed to accurately capture ignition properties of both aluminum nanoparticle and microparticle (ANP and AMP) burning in hot oxygen atmosphere. Two formulas were obtained to predict the ignition temperature and ignition delay time for nano/micro particles, which show good agreements with experimental results, providing a convenient and accurate method for practical application. A parametric study illustrates that AMP ignition is affected by bulk flow velocity, radiation and oxygen concentration, particularly for AMP over 100 mu m in diameter; in contrast, ANP is more sensitive to alumina thickness which generally raises both ignition temperature and ignition delay time. The present study not only deepens the fundamental understanding of aluminum combustion but also provides a guideline for prompting ignition

Reaction Mechanism of the Aluminum Nanoparticle: Physicochemical Reaction and Heat/Mass Transfer

A lack of clarity in the reaction mechanism of the aluminum nanoparticle (ANP) severely restricts its effective applications. By describing the physicochemical evolution of ANP burning in typical oxidizers (CO2, H2O, and O-2 ) at the nanoscale, three principal reaction modes including physical adsorption, chemical adsorption, and reactive diffusion were captured during the reaction. Initially, oxidizer molecules are physically and chemically adsorbed on the ANP surface until ignition in which reaction heat plays a more important role in contrast to heat transfer. Subsequently, partial oxidizer atoms adsorbed by surface diffuse across the shell to react with the Al core, presenting the dominant mode of reactive diffusion. It is assumed that the binding energy between Al and oxidizer atoms is in an inverse relation to atomic diffusivity but is positively correlated to reaction heat, resulting in various ANP structures and heat release rates. Our findings provide design guidelines to control various oxidizer supplies with respect to the reaction stages to balance the energy release and the residence time of ANP

A molecular dynamics simulation on the oxidation of core-shell aluminum nanoparticles in oxygen and water environments

The oxidation mechanisms of core-shell aluminum nanoparticles (ANPs) in high-temperature steam and oxygen are investigated by ReaxFF molecular dynamics (MD) simulation. The details concerning reaction heat release, heat transfer, atomic diffusion process, and ANP structure evolution are studied by examining the temporal variations of temperature, energy, atoms concentration distributions and particle structure, respectively. The atomic-level heat and mass transfer processes reveal that for both ANP/H2O and ANP/O2 systems, at the initial stage of oxidation, the heat transfer between ANP and environmental oxidizer is dominant. Thereafter, the reaction plays an increasingly significant role. The heat transfer efficiency of ANP/H2O is higher than that of ANP/O2, while the reaction exotherm of ANP/H2O is lower than ANP/O2. The final particle temperature for ANP/O2 system is much higher than that of ANP/H2O. The diameter of the former is also larger. During the oxidation of ANP, the core Al atoms diffuse outward into the oxide shell, which pushes the shell Al atoms outward and results in the expansion of ANP. The shell O atoms diffuse inward and left a vacant lattice site, through which the ambient H and O atoms diffuse into the oxide shell. &copy; Asia-Pacific Conference on Combustion, ASPACC 2019.All right reserved.</p

Size-derived reaction mechanism of core-shell aluminum nanoparticle

To prompt the application of aluminum nanoparticles (ANPs) in combustion as the fuel additive and in chemical synthesis as the catalyst, this study examines the reaction dynamics of core-shell ANPs under an oxygen atmosphere via Transient Non-Equilibrium Reactive Molecular Dynamics simulations. Two distinct oxidation modes determined by the competition between the oxide shell melting and core reaction have been identified. One is the fast oxidation mode with a high reaction heat release rate, where core Al and ambient O atoms diffuse into each other to form a homogeneous alumina particle. The other is the moderate oxidation with lower heat release, where only core Al atoms diffuse into the oxide shell to form a hollow spherical structure. By modeling the shell melting and Al core reaction, a size-derived oxidation model has been proposed to conveniently but accurately predict the ANP reaction dynamics. This work also provides fundamental insight into the synthesis of ANPs that serve as a high energy density fuel and high-performance catalyst