Elasticity behavior, phonon spectra, and the pressure-temperature phase diagram of HfTi alloy: A density-functional theory study

The pressure-induced phase transition, elasticity behavior, thermodynamic properties, and $P\mathtt{-}T$ phase diagram of $\alpha$, $\omega$, and $\beta$ equiatomic HfTi alloy are investigated using first-principles density-functional theory (DFT). The simulated pressure-induced phase transition of the alloy follows the sequence of $\alpha\mathtt{\rightarrow}\omega\mathtt{\rightarrow}\beta$, in agreement with the experimental results of Hf and Ti metals. Our calculated elastic constants show that the $\alpha$ and $\omega$ phases are mechanically stable at ambient pressure, while the $\beta$ phase is unstable, where a critical pressure of 18.5 GPa is predicted for its mechanical stability. All the elastic constants, bulk modulus, and shear modulus increase upon compression for the three phases of HfTi. The ductility of the alloy is shown to be well improved with respect to pure Hf and Ti metals. The Mulliken charge population analysis illustrates that the increase of the d-band occupancy will stabilize the $\beta$ phase under pressure. The phonon spectra and phonon density of states are studied using the supercell approach for the three phases, and the stable nature of $\alpha$ and $\omega$ phases at ambient pressure are observed, while the $\beta$ phase is only stable along the [110] direction. With the Gibbs free energy calculated from DFT-parametrized Debye model as a function of temperature and pressure, the phase transformation boundaries of the $\alpha$, $\omega$, and $\beta$ phases of HfTi are identified.Comment: 18 pages, 10 figure

Controlled Singular Volterra Integral Equations and Pontryagin Maximum Principle

This paper is concerned with a class of controlled singular Volterra integral equations, which could be used to describe problems involving memories. The well-known fractional order ordinary differential equations of the Riemann--Liouville or Caputo types are strictly special cases of the equations studied in this paper. Well-posedness and some regularity results in proper spaces are established for such kind of questions. For the associated optimal control problem, by using a Liapounoff's type theorem and the spike variation technique, we establish a Pontryagin's type maximum principle for optimal controls. Different from the existing literature, our method enables us to deal with the problem without assuming regularity conditions on the controls, the convexity condition on the control domain, and some additional unnecessary conditions on the nonlinear terms of the integral equation and the cost functional.Comment: 30 page

First-principles study of temperature-dependent diffusion coefficients: Hydrogen, deuterium, and tritium in α\alpha-Ti

We report the prediction of temperature-dependent diffusion coefficients of interstitial hydrogen, deuterium, and tritium atoms in $\alpha$-Ti using transition state theory. The microscopic parameters in the pre-factor and activation energy of the impurity diffusion coefficients are obtained from first-principles total energy and phonon calculations including the full coupling between the vibrational modes of the diffusing atom with the host lattice. The dual occupancy case of impurity atom in the hcp matrix are considered, and four diffusion paths are combined to obtain the final diffusion coefficients. The calculated diffusion parameters show good agreement with experiments. Our numerical results indicate that the diffusions of deuterium and tritium atoms are slower than that of the hydrogen atom at temperatures above 425 K and 390 K, respectively.Comment: 11 pages, 4 figure

Photon production in Pb+Pb collisions at sNN\sqrt{s_{NN}}=2.76 TeV

We calculate the high energy photon production from the Pb+Pb collisions for different centrality classes at $\sqrt{s_{NN}}$=2.76 TeV Large Hadron Collider (LHC) energy. The jet energy loss in the jet fragmentation, jet-photon conversion and jet bremsstrahlung is considered by using the Wang-Huang-Sarcevic (WHS) and Baier-Dokshitzer-Mueller-Peigne-Schiff (BDMPS) models. We use the (1+1)-dimensional ideal relativistic hydrodynamics to study the collective transverse flow and space-time evolution of the quark gluon plasma (QGP). The numerical results agree well with the ALICE data of the direct photons from the Pb+Pb collisions ($\sqrt{s_{NN}}$=2.76 TeV) for 0-20\%, 20-40\% and 40-80\% centrality classes.Comment: 4 figure

Jet-dilepton conversion in expanding quark-gluon plasma

We calculate the production of large mass dileptons from the jet-dilepton conversion in the expanding quark-gluon plasma at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies. The jet-dilepton conversion exceeds the thermal dilepton production and Drell-Yan process in the large mass region of 3.9 GeV$<M<$5.8 GeV and 6.3 GeV$<M<$8.7 GeV in central Pb+Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV and 5.5 TeV, respectively. We present the numerical solution of ideal fluid hydrodynamics. We find that the transverse flow leads to a rapid cooling of the fire ball. The suppression due to transverse flow is appeared from small to large mass, the transverse flow effect becomes important at LHC energies. The energy loss of jets in the hot and dense medium is also included.Comment: 7 pages, 8 figure

Intermediate mass dileptons from the passage of jets and high energy photons through quark-gluon plasma

The production of the intermediate mass dileptons originating from the annihilation and Compton scattering of the jets and high energy photons (resolved photons) passing through the quark-gluon plasma is calculated. The contribution of the dilepton yield due to the jet-plasma and high energy photon-plasma interaction is pronounced compared to the thermal and Drell-Yan dilepton spectrum at intermediate mass. The ordinary spectrum of thermal and Drell-Yan processes is enhanced by the jet and photon-plasma mechanism. The numerical results match to the PHENIX data accurately in the intermediate mass region for Au-Au 200 GeV/A collisions at RHIC.Comment: 2 figure

Anomalous gauge couplings of the Higgs boson at the LHC II: Study of additional backgrounds in semileptonic mode of WW scatterings

Searching for the Higgs boson is of first priority in LHC experiments. Once a Higgs candidate is found, we then need to know whether it is the standard model (SM) Higgs boson or a Higgs boson in new physics beyond the SM. So far we do not know what model of new physics will actually reflect the property of the nature. A model-independent way of measuring the anomalous couplings of the Higgs boson will provide a no-lose study, i.e., if we find nonvanishing anomalous couplings (deviation from the SM couplings), we can conclude that it is a new physics effect. In a previous paper \cite{QKLZ09}, we gave a hadron level study of a model-independent test of the anomalous gauge couplings of the Higgs boson at the 14 TeV LHC via the semileptonic mode of weak-boson scatterings $pp\to W^+W^\pm j^f_1 j^f_2\to l^+\nu^{}_lj^{}_1j^{}_2j^f_1j^f_2$, and the conclusion is that, with certain kinematical cuts imposed, the measurement can start for an integrated luminosity of 50 fb$^{-1}$. For higher integrated luminosity, say 100 fb$^{-1}$, the two main anomalous coupling constants $f^{}_{WW}/\Lambda^2$ and $f^{}_W/\Lambda^2$ can be determined separately which may provide a clue for figuring out the underlying theory of new physics.Comment: 4 pages RevTex4 file with 6 eps files for the figures. Format improve

Comment on "Enhanced transmission through periodic arrays of subwavelength holes: the role of localized waveguide resonances"

Comment on "Enhanced transmission through periodic arrays of subwavelength holes: the role of localized waveguide resonances" [Phys.Rev.Lett. 96, 233901 (2006)]Comment: 3 pages, 1 figur

First-principles study of temperature-dependent diffusion coefficients for helium in α\alpha-Ti

The temperature-dependent diffusion coefficients of interstitial helium atom in $\alpha$-Ti are predicted using the transition state theory. The microscopic parameters in the pre-factor and activation energy of the impurity diffusion coefficients are obtained from first-principles total energy and phonon calculations including the full coupling between the vibrational modes of the diffusing atom and the host lattice. The climbing image nudged elastic band (CINEB) method is used to search for the minimum energy pathways and associated saddle point structures. It is demonstrated that the diffusion coefficients within the \emph{xy} plane ($D_{xy}$) is always higher than that along the \emph{z} axis ($D_{z}$), showing remarkable anisotropy. Also, it is found that the formation of helium dimer centered at the octahedral site reduces the total energy and confines the diffusion of helium atoms.Comment: 6 pages, 5 figure

Content-based similar document image retrieval using fusion of CNN features

Rapid increase of digitized document give birth to high demand of document image retrieval. While conventional document image retrieval approaches depend on complex OCR-based text recognition and text similarity detection, this paper proposes a new content-based approach, in which more attention is paid to features extraction and fusion. In the proposed approach, multiple features of document images are extracted by different CNN models. After that, the extracted CNN features are reduced and fused into weighted average feature. Finally, the document images are ranked based on feature similarity to a provided query image. Experimental procedure is performed on a group of document images that transformed from academic papers, which contain both English and Chinese document, the results show that the proposed approach has good ability to retrieve document images with similar text content, and the fusion of CNN features can effectively improve the retrieval accuracy