159,514 research outputs found
Thermodynamics and kinetics of the undercooled liquid and the glass transition of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 alloy
Differential scanning calorimetry (DSC) was used to determine the thermodynamic functions of the undercooled liquid and the amorphous phase with respect to the crystalline state of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5bulk metallic glass forming alloy. The specific heat capacities of this alloy in the undercooled liquid, the amorphous state and the crystal were determined. The differences in enthalpy, āH, entropy, āS, and Gibbs free energy, āG, between crystal and the undercooled liquid were calculated using the measured specific heat capacity data as well as the heat of fusion. The results indicate that the Gibbs free energy difference between metastable undercooled liquid and crystalline solid, āG, stays small compared to conventional metallic glass forming alloys even for large undercoolings. Furthermore, the Kauzmann temperature, TK, where the entropy of the undercooled liquid equals to that of the crystal, was determined to be 560 K. The Kauzmann temperature is compared with the experimentally observed rate-dependent glass transition temperature, Tg. Both onset and end temperatures of the glass transition depend linearly on the logarithm of the heating rate based on the DSC experiments. Those characteristic temperatures for the kinetically observed glass transition become equal close to the Kauzmann temperature in this alloy, which suggests an underlying thermodynamic glass transition as a lower bound for the kinetically observed freezing process
QCD effective action with a most general homogeneous field background
We consider one-loop effective action of SU(3) QCD with a most general
constant chromomagnetic (chromoelectric) background which has two independent
Abelian field components. The effective potential with a pure magnetic
background has a local minimum only when two Abelian components H_{\mu\nu}^3
and H_{\mu\nu}^8 of color magnetic field are orthogonal to each other. The
non-trivial structure of the effective action has important implication in
estimating quark-gluon production rate and p_T-distribution in quark-gluon
plasma. In general the production rate depends on three independent Casimir
invariants, in particular, it depends on the relative orientation between
chromoelectric fields.Comment: 6 pages, 3 figures (9 pages in published version
Searching for Ground Truth: a stepping stone in automating genre classification
This paper examines genre classification of documents and
its role in enabling the effective automated management of digital documents by digital libraries and other repositories. We have previously presented genre classification as a valuable step toward achieving automated extraction of descriptive metadata for digital material. Here, we present results from experiments using human labellers, conducted to assist in genre characterisation and the prediction of obstacles which need to be overcome by an automated system, and to contribute to the process of creating a solid testbed corpus for extending automated genre classification and testing metadata extraction tools across genres. We also describe the performance of two classifiers based on image and stylistic modeling features in labelling the data resulting from the agreement of three human labellers across fifteen genre classes.
Experimental determination of a timeātemperature-transformation diagram of the undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 alloy using the containerless electrostatic levitation processing technique
High temperature high vacuum electrostatic levitation was used to determine the complete timeātemperatureātransformation (TTT) diagram of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass forming alloy in the undercooled liquid state. This is the first report of experimental data on the crystallization kinetics of a metallic system covering the entire temperature range of the undercooled melt down to the glass transition temperature. The measured TTT diagram exhibits the expected "C" shape. Existing models that assume polymorphic crystallization cannot satisfactorily explain the experimentally obtained TTT diagram. This originates from the complex crystallization mechanisms that occur in this bulk glass-forming system, involving large composition fluctuations prior to crystallization as well as phase separation in the undercooled liquid state below 800 K
Metallic glass formation in highly undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 during containerless electrostatic levitation processing
Various sample sizes of Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 with masses up to 80 mg were undercooled below Tg (the glass transition temperature) while electrostatically levitated. The final solidification product of the sample was determined by x-ray diffraction to have an amorphous phase. Differential scanning calorimetry was used to confirm the absence of crystallinity in the processes sample. The amorphous phase could be formed only after heating the samples above the melting temperature for extended periods of time in order to break down and dissolve oxides or other contaminants which would otherwise initiate heterogeneous nucleation of crystals. Noncontact pyrometry was used to monitor the sample temperature throughout processing. The critical cooling rate required to avoid crystallization during solidification of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 alloy fell between 0.9 and 1.2 K/s
Analysis of resonant inelastic x-ray scattering at the edge in NiO
We analyze the resonant inelastic x-ray scattering (RIXS) spectra at the Ni
edge in an antiferromagnetic insulator NiO by applying the theory developed
by the present authors. It is based on the Keldysh Green's function formalism,
and treats the core-hole potential in the intermediate state within the Born
approximation. We calculate the single-particle energy bands within the
Hartree-Fock approximation on the basis of the multi-orbital tight-binding
model. Using these energy bands together with the density of states from
an ab initio band structure calculation, we calculate the RIXS intensities as a
function of energy loss. By taking account of electron correlation within the
random phase approximation (RPA), we obtain quantitative agreement with the
experimental RIXS spectra, which consist of prominent two peaks around 5 eV and
8 eV, and the former shows considerable dispersion while the latter shows no
dispersion. We interpret the peaks as a result of a band-to-band transition
augmented by the RPA correlation.Comment: 11 pages, 10 figures, submitted to PR
Hemispherical total emissivity and specific heat capacity of deeply undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 melts
High-temperature high-vacuum electrostatic levitation (HTHVESL) and differential scanning calorimetry (DSC) were combined to determine the hemispherical total emissivity epsilon T, and the specific heat capacity cp, of the undercooled liquid and throughout the glass transition of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass forming alloy. The ratio of cp/epsilon T as a function of undercooling was determining from radiative cooling curves measured in the HTHVESL. Using specific heat capacity data obtained by DSC investigations close to the glass transition and above the melting point, epsilon T and cp were separated and the specific heat capacity of the whole undercooled liquid region was determined. Furthermore, the hemispherical total emissivity of the liquid was found to be about 0.22 at 980 K. On undercooling the liquid, the emissivity decreases to approximately 0.18 at about 670 K, where the undercooled liquid starts to freeze to a glass. No significant changes of the emissivity are observed as the alloy undergoes the glass transition
Weak Localization Effect in Superconductors
We study the effect of weak localization on the transition temperatures of
superconductors using time-reversed scattered state pairs, and find that the
weak localization effect weakens electron-phonon interactions. With solving the
BCS equation, the calculated values for are in good agreement
with experimental data for various two- and three-dimensional disordered
superconductors. We also find that the critical sheet resistance for the
suppression of superconductivity in thin films does not satisfy the universal
behavior but depends on sample, in good agreement with experiments. but depends
on sample, in good agreement with experiments.Comment: 14 pages, Revtex, 5 ps figure
Limits on Interactions between Weakly Interacting Massive Particles and Nucleons Obtained with NaI(Tl) crystal Detectors
Limits on the cross section for weakly interacting massive particles (WIMPs)
scattering off nucleons in the NaI(Tl) detectors at the Yangyang Underground
Laboratory are obtained with a 2967.4 kg*day data exposure. Nuclei recoiling
are identified by the pulse shape of scintillating photon signals. Data are
consistent with no nuclear recoil hypothesis, and 90% confidence level upper
limits are set. These limits partially exclude the DAMA/LIBRA region of
WIMP-sodium interaction with the same NaI(Tl) target detector. This 90%
confidence level upper limit on WIMP-nucleon spin-independent cross section is
3.26*10^-4 pb for a WIMP mass at 10 GeV/c^2
- ā¦