Superheating systematics of crystalline solids

Systematics of superheating (theta= T/Tm–1) of crystalline solids as a function of heating rate (Q) are established as beta= A(Q)(theta+ 1)theta2, where the normalized energy barrier for homogeneous nucleation is beta= 16pigammasl3/(3kTmDeltaHm2), T is temperature, Tm melting temperature, A a Q-dependent parameter, gammasl interfacial energy, DeltaHm heat of fusion, and k Boltzmann's constant. For all elements and compounds investigated, beta varies between 0.2 and 8.2. At 1 and 10^12 K/s, A = 60 and 31, theta= 0.05–0.35 and 0.06–0.45, respectively. Significant superheating is achievable via ultrafast heating. We demonstrate that the degree of superheating achieved in shock-wave loading and intense laser irradiation as well as in molecular dynamics simulations (Q~10^12 K/s) agrees with the theta–beta–Q systematics

Feature Enhancement Network: A Refined Scene Text Detector

In this paper, we propose a refined scene text detector with a \textit{novel} Feature Enhancement Network (FEN) for Region Proposal and Text Detection Refinement. Retrospectively, both region proposal with \textit{only} $3\times 3$ sliding-window feature and text detection refinement with \textit{single scale} high level feature are insufficient, especially for smaller scene text. Therefore, we design a new FEN network with \textit{task-specific}, \textit{low} and \textit{high} level semantic features fusion to improve the performance of text detection. Besides, since \textit{unitary} position-sensitive RoI pooling in general object detection is unreasonable for variable text regions, an \textit{adaptively weighted} position-sensitive RoI pooling layer is devised for further enhancing the detecting accuracy. To tackle the \textit{sample-imbalance} problem during the refinement stage, we also propose an effective \textit{positives mining} strategy for efficiently training our network. Experiments on ICDAR 2011 and 2013 robust text detection benchmarks demonstrate that our method can achieve state-of-the-art results, outperforming all reported methods in terms of F-measure.Comment: 8 pages, 5 figures, 2 tables. This paper is accepted to appear in AAAI 201

Melting at the Limit of Superheating

Theories on superheating-melting mostly involve vibrational and mechanical instabilities, catastrophes of entropy, volume and rigidity, and nucleation-based kinetic models. The maximum achievable superheating is dictated by nucleation process of melt in crystals, which in turn depends on material properties and heating rates. We have established the systematics for maximum superheating by incorporating a dimensionless nucleation barrier parameter and heating rate, with which systematic molecular dynamics simulations and dynamic experiments are consistent. Detailed microscopic investigation with large-scale molecular dynamics simulations of the superheating-melting process, and structure-resolved ultrafast dynamic experiments are necessary to establish the connection between the kinetic limit of superheating and vibrational and mechanical instabilities, and catastrophe theories

Polymorphism, superheating, and amorphization of silica upon shock wave loading and release

We present a detailed and quantitative examination of the thermodynamics and phase change mechanisms (including amorphization) that occur upon shock wave loading and unloading of silica. We apply Debye-Grüneisen theory to calculate both the Hugoniot of quartz and isentropic release paths. Quartz converts to stishovite (or a stishovite-like phase) between 15 and 46 GPa, and persistence of the solid phase above its liquidus (i.e., superheating) is confirmed between 77 and 110 GPa. Calculations compare favorably to measurements of shock and post-shock temperatures. For silica, the method of measuring post-shock temperature is insensitive to predicting whether phase transitions actually occur during release. Measurements of release states in pressure-particle velocity space are compared to computed frozen-phase release paths. This comparison suggests transformation of a stishovite-like phase to lower density phases including quartz, liquid, or dense amorphous glass. Transformations to liquid or glass occur upon release from peak pressure of 26 GPa and above. The isentropic release assumption appears to be approximately valid. A shock pressure-temperature scale relating metamorphism of silica in shock-loaded quartz is proposed. Neither recovery of coesite nor substantial quantities of crystalline stishovite-like phases upon shock loading of quartz is predicted. Trace amounts of crystalline stishovite-like phases from shock loading between 15 and 26 GPa are expected

Measurement of the Hall coefficient and electron mobility using Van Der Pauw type Hall effect measurements

Hall effect measurement in the electrical characterization of semiconductor materials is very important. We set up the Hall effect measurement system and examined the system with a standard sample. The experimental results show that this Hall measurement system worked as well as expected. We also used this system to study the GaAs/GaAs and InGaAs/GaAs which grown by MBE. Finally, we disscussed and consided some common problems of Hall measurement. Some useful formulas and plots are presented

QCD at Finite temperature and density with staggered and Wilson quarks

One of the most challenging issues in particle physics is to study QCD in extreme conditions. Precise determination of the QCD phase diagram on temperature $T$ and chemical potential $\mu$ plane will provide valuable information for quark-gluon plasma (QGP) and neutron star physics. We present results for phase structure on the $(\mu, T)$ plane for lattice QCD with Wilson fermions from strong coupling Hamiltonian analysis and Kogut-Susskind Fermions from Lagrangian Monte Carlo simulations at intermediate coupling.Comment: Lattice 2004 (nonzero

Doping dependent time-reversal symmetric nonlinearity of YBa_2Cu_3O_7-d thin films

We have measured the temperature dependent third harmonic response from a series of under-doped YBa_2Cu_3O_7-d thin films to address the mechanism of nonlinearity in these samples. We find that the intrinsic Ginzburg-Landau nonlinearity near Tc is doping dependent, with the sample becoming more nonlinear as it is under-doped. The results are consistent with the doping dependence of the condensation energy of YBa_2Cu_3O_7-d.Comment: 2 pages, 3 figures, submitted to Physica C for M2S-Rio conference pres