Earlier Experimental Values Research Articles

Constant electrical resistivity of Ni along the melting boundary up to 9 GPa

AbstractCharacterization of transport properties of liquid Ni at high pressures has important geophysical implications for terrestrial planetary interiors, because Ni is a close electronic analogue of Fe and it is also integral to Earth's core. We report measurements of the electrical resistivity of solid and liquid Ni at pressures 3–9 GPa using a 3000 t multianvil large volume press. A four‐wire method, in conjunction with a rapid acquisition meter and polarity switch, was used to overcome experimental challenges such as melt containment and maintaining sample geometry and to mitigate the extreme reactivity/solubility of liquid Ni with most thermocouple and electrode materials. Thermal conductivity is calculated using the Wiedemann‐Franz law. Electrical resistivity of solid Ni exhibits the expected P dependence and is consistent with earlier experimental values. Within experimental uncertainties, our results indicate that resistivity of liquid Ni remains invariant along the P‐dependent melting boundary, which is in disagreement with earlier prediction for liquid transition metals. The potential reasons for such behavior are examined qualitatively through the impact of P‐independent local short‐range ordering on electron mean free path and the possibility of constant Fermi surface at the onset of Ni melting. Correlation among metals obeying the Kadowaki‐Woods ratio and the group of late transition metals with unfilled d‐electron band displaying anomalously shallow melting curves suggests that on the melting boundary, Fe may exhibit the same resistivity behavior as Ni. This could have important implications for the heat flow in the Earth's core.

Experimental study and modelling of overheating of electrical catenary-pantograph interface for trains supplied with power in station

For railroads and trains, there have been many incidents involving catenary overheating at the contact with the pantograph when a train is supplied with power while standing still. The overheating of the catenary-pantograph interface can sometimes cause the contact wire to break. In order to anticipate the occurrence of such costly problems, the FEMTO-ST Institute has carried out theoretical and experimental studies in collaboration with the French National Railway Company (SNCF) to better understand this phenomenon. First, a 2D transient electrical model was developed for the contact wire. This allows the current distribution in the wire to be estimated to obtain an accurate measure of the internal heat generation. The heat produced by the interface was considered and split between the catenary and pantograph with an analytical model. Finally, the heat transfer equation for the wire under particular boundary conditions was solved for the entire finite difference network based on Euler’s implicit method. The transient modelling results of the wire heating were compared with earlier experimental values, and a parametric study was performed.

A comparative density functional study of newly proposed ‘122’ compounds with their parent low-temperature superconductors

The full potential-linearized augmented plane wave method has been used to calculate structural, electronic and transport properties of proposed ‘122’ compounds namely SrNi2Bi2 and BaNi2Bi2 using first principle calculations. These compounds belong to ThCr2Si2-type tetragonal structure and are isostructural with SrNi2(P/As)2 and BaNi2(P/As)2 compounds. The lattice constants of SrNi2Bi2 and BaNi2Bi2 are derived from their respective parent compounds. Optimized lattice constant, energy band structure, electron density plots and superconducting transition temperature are computed for the parent compounds. The calculated results are in reasonable agreement with earlier experimental values and theoretical results. The proposed compounds show similar electronic and bonding characteristics of their respective parent low temperature superconductors.

Thermochemical investigation of Sm–Mg alloys

Abstract The paper focuses on the thermochemical behaviour of the binary Sm–Mg alloys. The enthalpies of formation of the Sm–Mg intermetallic compounds have been determined at 300 K by high temperature direct synthesis calorimetry. The following results in kJ/mole of atoms are reported: −18.5±2 (SmMg), −16.0±2 (SmMg 2 ), −12.0±2 (SmMg 3 ), −8.5±2 (SmMg 5 ) and −5.5±2 (Sm 5 Mg 41 ). The results are compared with the earlier experimental value obtained by vapour pressure.

Performance of dispersion-corrected double hybrid density functional theory: A computational study of OCS-hydrocarbon van der Waals complexes

The performance of double hybrid density functionals (DHDFs) has been assessed by studying the spectroscopic properties and potential energy curves of OCS-C2H4 (carbonyl sulfide-ethylene) and OCS-C4H6 (carbonyl sulfide-dimethylacetylene) van der Waals complexes. Both dispersion corrected and uncorrected DHDF theories have been applied to study the intermolecular interaction energies, stability, spectroscopic parameters, rigidity, and binding energies or depths of the potential well of the weakly bound complexes and also to explore the possibility of formation of three isomers of each complex. The correlation consistent valence triple zeta quality basis set is used to investigate the complexes. The calculated results provide insight into the computational methods applied to the weakly bound complexes. The double hybrid density functional B2PLYP and mPW2PLYP methods with dispersion corrections (B2PLYP-D2, B2PLYP-D3 and mPW2PLYP-D2, mPW2PLYP-D3) performed better over the B2PLYP and mPW2PLYP density functional methods without dispersion correction to deal with the weak dispersion interaction that prevails in these complexes. The results obtained by the dispersion-corrected density functional mPW2PLYP-D2 and mPW2PLYP-D3 methods agree very well with the earlier experimental values wherever available. The contributing components of the interaction energy have been analyzed by the symmetry-adapted perturbation theory (SAPT, here, SAPT0) to get insight into the interaction energy.

Tsunami simulation with Green–Naghdi theory

Green–Naghdi (GN) theory is a fully nonlinear wave theory which has been used with success to simulate nonlinear water waves. In previous applications of GN theory to water wave problems the ocean bottom was assumed to be time invariant. In this work no such restriction is made and GN theory is used to simulate tsunami caused by bottom fluctuation. As first test cases we simulate two-dimensional nonlinear surface waves generated by positive bottom movements. The results in the generation region for three different seabed movements compare well against earlier experimental data. The results in the downstream region for impulsive seabed movements show some discrepancies in wave phase and amplitude compared with earlier experimental values. It is suspected that the viscous effects may have played a role. The GN theory is then used to study three-dimensional near-field tsunami amplitudes caused by submarine landslides and slumps spreading in two orthogonal directions. The GN results agree with previous linear solution very well when the ratio of the velocities is v 1/ v 2=1.0. But GN theory give more believable results for the case of v T / v=0.1 and v 1/ v 2=0.1.

Nuclear quadrupole moment of theT99cground state

By combining first-principles calculations and existing nuclear magnetic resonance (NMR) experiments, we determine the quadrupole moment of the 9/2{sup +} ground state of {sup 99}Tc to be (-)0.14(3)b. This confirms the value of -0.129(20)b, which is currently believed to be the most reliable experimental determination, and disagrees with two earlier experimental values. We supply ab initio calculated electric-field gradients for Tc in YTc{sub 2} and ZrTc{sub 2}. If this calculated information would be combined with yet to be performed Tc-NMR experiments in these compounds, the error bar on the {sup 99}Tc ground state quadrupole moment could be further reduced.

Calculation of the crystal-melt interfacial free energy of succinonitrile from molecular simulation

The crystal-metal interfacial free energy for a six-site model of succinonitrile [N triple bond C-(CH(2))(2)-C triple bond N] has been calculated using molecular-dynamics simulation from the power spectrum of capillary fluctuations in interface position. The orientationally averaged magnitude of the interfacial free energy is determined to be (7.0+/-0.4)x10(-3) J m(-2). This value is in agreement (within the error bars) with the experimental value [(7.9+/-0.8)x10(-3) J m(-2)] of Marasli et al. [J. Cryst. Growth 247, 613 (2003)], but is about 20% lower than the earlier experimental value [(8.9+/-0.5)x10(-3) J m(-2)] obtained by Schaefer et al. [Philos. Mag. 32, 725 (1975)]. In agreement with the experiment, the calculated anisotropy of the interfacial free energy of this body-centered-cubic material is small. In addition, the Turnbull coefficient from our simulation is also in agreement with the experiment. This work demonstrates that the capillary fluctuation method of Hoyt et al. [Phys. Rev. Lett. 86, 5530 (2001)] can be successfully applied to determine the crystal-melt interfacial free energy of molecular materials.

Theoretical investigation of the lower bend-stretch states of the Cl−H2 anion complex and its isotopomers

Coupled-cluster [CCSD(T)] calculations of the potential energy surface of the Cl−H2 complex were carried out, subsequently averaged over the vibrational motion of the H2 moiety and then fitted. The lower bend-stretch levels of the anion complex were then determined, for the H2 molecule in its ground and first excited vibrational levels. The resulting rotational constants agree with earlier experimental values, almost to within the experimental precision. The predicted dissociation energies are 5–8% larger than the experimentally derived values. The bend-stretch wave function of the lowest state of the Cl−oD2 complex encompasses a considerably larger range of bending motion than in the complexes with oH2 and pD2.

Electric field gradients of water: A systematic investigation of basis set, electron correlation, and rovibrational effects

Electric field gradients at the oxygen and hydrogen nuclei of water have been calculated using high level ab initio methods. Systematic studies of basis set truncation errors have been carried out at the Hartree–Fock and coupled cluster singles and doubles (CCSD) levels using extended correlation consistent basis sets with up to 398 basis functions. Correlation effects are investigated using a hierarchy of correlation methods extending up to the approximate inclusion of triples excitations by means of the CCSD(T) method. Rovibrational effects have been calculated combining accurate ab initio electric field gradient data and accurate experimental force fields. On the basis of the most accurate results for the electric field gradients, the nuclear quadrupole coupling constants for deuterium and oxygen-17 have been discussed including the temperature dependence. The final results are discussed in view of existing experimental data. Our best values for the nuclear quadrupole coupling constants are in excellent agreement (within 1%) of recent experimental results, while some earlier experimental values are shown to be less reliable.

Tλ depression in 4He by a heat current along the λ-line

We report measurements of the depression of the superfluid transition temperature by a heat current ( 1⩽Q⩽100 μW/ cm 2 ) along the λ-line (SVP⩽ P⩽21.6 bar). Experimental data can be represented by Δ T λ / T λ =( Q/ Q 0) x . The exponent, x, is universal and pressure independent as expected, but its value (about 0.9) is higher than the theoretical prediction (0.745) and the earlier experimental value (0.813) at SVP. The amplitude, Q 0, shows a pressure dependence that is in qualitative agreement with the theoretical prediction, but its value is lower than the predicted and earlier experimental values at SVP. At P=21.6 bar, measurements were also performed in a reduced effective gravity (0.2 g), and these results show that the gravity effect in our measurements is small.

Partition Function and Dissociation Energy for Sc2X5Σ−u

An improved partition function for the Sc2 dimer including eight low-lying states has been computed at the multireference internally contracted ACPF level using large, generally contracted basis sets. The experimental third-law value for the dissociation energy is recomputed using the new dimer partition function giving an experimental dissociation energy of 1.05 eV, a reduction by 0.07 eV compared with the earlier experimental value. The computed spectrum is very strongly affected by dynamical correlation so that lower-level theoretical approaches such as CASSCF are shown to give unreliable results.

Standard enthalpy of formation of CrSi 2 by high-temperature mixing calorimetry

The standard molar enthalpy of formation of CrSi 2 has been determined by mixing calorimetry at (1400 ± 2) K. In these experiments the liquid alloy Cu 0.70Si 0.25Cr 0.05 is formed in the calorimeter from the elements or from CrSi 2. The following result is reported: Δf H m o(298.15 K) = −(77.4 ± 13.2) kJ · mol −1. This result is compared with earlier experimental values and with the recently predicted value of Niessen and Miedema. Among the disilicides of the first-row transition metals from Sc to Cr the least negative enthalpy of formation is found for CrSi 2.

Determination of the K-shell internal conversion coefficient for the 37.2 keV transition in the decay of121mSn

TheK-shell internal conversion coefficientα K for the 37.2 keV transition (7/2+→5/2+) occuring in121Sb afterβ − decay of121 mSn has been redetermined applying theX- toγ-peak method (XPG). Measurements of photon spectra from thin sources have been performed at various source-detector distances with a high resolution, efficiency calibrated Si(Li) detector. Values ofα K have been deduced from the number of emittedKX rays compared to that of the emittedγ rays. TheK-shell fluorescence yield for antimony has been taken from the literature. From in total 14 experimental runs a mean result ofα K =9.52±0.27 has been obtained. The quoted uncertainty comprising statistical and systematic parts is discussed in detail. The present result is compared with the few existing earlier experimental values and with the theoretical value interpolated from the most recent tabulations.

Experimental correction for primary and secondary extinction. II. Application to beryllium

The profiles of the first three reflections from a parallel-sided crystal slab of Be are measured on an absolute scale with polarized Cu Kα radiation and unpolarized Mo Kα radiation. The effects of secondary extinction are corrected by measuring the transmitted intensity and using the conservation of energy. Primary extinction is determined by comparing two measurements where the extinction distances are different; this is realized by changing the wavelength or polarization of the incident radiation. The calculated average secondary-extinction factor, {\bar Y}s, ranges from 0.98 to 0.74, and the average primary extinction factor, {\bar Y}p, from 0.96 to 0.42. The room-temperature values of the structure factors, F(10.1) = 1.90 ± 0.01, F(00.2) = 3.37 ± 0.02, F(10.1) = 2.78 ± 0.03, differ substantially from earlier experimental values and from the values calculated for a free atom, but agree very closely with the results of a LCAO calculation.

Positron impact inner shell ionization

The positron impact ionization cross section for theK-shell was determined in the case of Ni, Y and Ag at 670 and 490 keV as well as for theL-shell in the case of Yb, Ta, Au and Pb at 490 keV using a beta-ray spectrometer as a source of monoenergetic electrons and anX-e+ coincidence arrangement. The results for theK-shell are compared with the theoretical calculations according to Kolbenstvedt and with the earlier experimental values.

Capture Cross Sections of Intermediate Neutrons

Radiative neutron capture cross sections for the isotopes /sup 59/Co, / sup 68/Zn/, /sup 86/Sr, /sup 87/Rb,/sup 976/Ryu, /sup 98/Mo, /sup 100/Mo, /sup 102/Ru, /sup 104/Ru, / sup 113/In, /sup 115/In, /sup 122/Sn and /sup 133/Cs were remeasured at the neutron energy 24 plus or minus 5 keV in view of the wide discrepancies in their values as reported in literature. The activation method and 4 pi geometry absolute gamma counting technique were used to obtain the cross sections. By making a critical comparison of the present results with the earlier experimental values on the one hand and with semi-theoretical estimates on the other, an attempt is made to resolve the discrepancies. (auth)

Level density parameter in the mass region 24–48

The cross sections for several (n, p), (n, α) and (n, 2n) reactions leading to residual nuclei in the mass range 24–48 at 14.2 MeV neutron energy are calculated by the statistical model using the level density parameter a = 1 8 A . The following values for the cross sections are obtained in mb: 27Al(n,p) 27Mg, 82.3 42Ca(n,p) 42K, 203.1 43Ca(n,p) 44Ca(n,p) 44K, 13.4 41K(n,p) The theoretical values are compared with our earlier experimental values. From this comparison, it is concluded that the value of the level density parameter (a = 1 8 A used in these calculations is approximately correct in the mass region 24–48.

The Exchange of Energy Between Organic Molecules and Solid Surfaces Part I. Accommodation Coefficients and Specific Heats of Hydrocarbon Molecules

A molecular beam method primarily devised for the investigation of heterogeneous thermal decomposition of hydrocarbon-molecules (to be published later) was used to determine the accommodation coefficients of various hydrocarbon molecules at 20°C on an ordinarily clean nickel surface at 140°C and at pressures in the region of 10-6 mm Hg. The absolute values of the accommodation coefficients were obtained by relative measurements with the help of the following simple relation that was found to exist for paraffin hydrocarbons between the accommodation coefficient α, the specific heat per mole at constant pressure for the ideal gas state Cv0, and the molecular weight M,α(Cv0+R/2)/M=constant=0.352,where R is the gas constant per mole. This equation supports a further relation which can be set up for the mean specific heat between 20° and 140°C for the paraffins by using a few reliable Cv0 values: Cv0 = 0.352M +1.80. A combination of both relations gives the simple equation for α of the paraffins: α=c1M/(c1M+c2),where c1 = 0.352 and c2 = 1.80+R/2. The accommodation coefficient for hydrogen was found to be 0.310, in excellent agreement with earlier experimental values. The accommodation coefficients of ethane and ethylene whose specific heats are known from normal frequencies were found to be equal within a few tenths of a percent; acetylene was found to be 3 percent lower. Specific heats have been calculated for paraffin gases and vapors up to n-heptane by a combination of the results of this work and the specific heat of ethane from the normal frequencies. The specific heats are given to 300°C. Under the assumption of equal accommodation coefficients for paraffins and corresponding olefines based on the accommodation coefficient measurements of ethane and ethylene and on their specific heats, specific heats are given for propylene and n- and isobutylene at 300°C. It was found that the absolute difference between the specific heats of a paraffin and the corresponding olefine decreases with the chain length. The Cv0 values of the following pairs were found to be equal within the experimental error of one percent: n- and isobutane, n- and isobutylene, methyl acetylene and allene. Approximate values for the mean specific heats between 20° and 140 C are given for methyl acetylene and allene. A discussion is given of the relationship of the present work to spectroscopic work in the field.