970 resultados para Phase angle
Resumo:
Ultraviolet radiation has been generated by tangentially phase-matched sum-frequency mixing in biaxial L-arginine phosphate (LAP) crystal for the first time using Nd:YAG output at 1064 nm and Rh 6G dye laser output at 560 nm as the two input sources. Characterization has also been made of such a cheap, biaxial crystal for its possible use in devices for tangentially phase-matched short wavelength generation. If the crystal is of proper cut, thickness and quality so that its maximum capability can be exploited it can replace the potassium dihydrogen phosphate (KDP) group of crystals for various applications.
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The effect of Raman scattering on co-propagation of two short optical pulses is considered. The intra pulse Raman scattering causes the self-frequency shift of each pulse. The effect of the inter pulse Raman scattering is to enhance the frequency shift while the stimulated Raman scattering (SRS) term suppresses (enhances) the frequency shift if the center frequency difference between the optical pulses falls to the right (left) of the Raman gain peak. An expression for the frequency shift as a function of the propagation distance is obtained.
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Phase-pure, crystalline lanthanide chromates LnCrO4 (V), where Ln = La, Pr, Nd, Sm, Gd, Dy, Ho, Yb, Lu and Y, have been prepared by the controlled combustion of the corresponding lanthanide biscitrato chromium (III) complexes at comparatively low temperatures. Formation of chromates (V) was confirmed by X-ray diffraction, infrared and electronic spectroscopy. Phase purity of the materials has also been confirmed by X-ray photoelectron spectroscopy.
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In the present investigation, unidirectional grinding marks were created on a set of steel plates. Sliding experiments were then conducted with the prepared steel plates using Al-Mg alloy pins and an inclined pin-on-plate sliding tester. The goals of the experiments were to ascertain the influence of inclination angle and grinding mark direction on friction and transfer layer formation during sliding contact. The inclination angle of the plate was held at 0.2 deg, 0.6 deg, 1 deg, 1.4 deg, 1.8 deg, 2.2 deg, and 2.6 deg in the tests. The pins were slid both perpendicular and parallel to the grinding marks direction. The experiments were conducted under both dry and lubricated conditions on each plate in an ambient environment. Results showed that the coefficient of friction and the formation of transfer layer depend on the grinding marks direction and inclination angle of the hard surfaces. For a given inclination angle, under both dry and lubricated conditions, the coefficient of friction and transfer layer formation were found to be greater when the pins slid perpendicular to the unidirectional grinding marks than when the pins slid parallel to the grinding marks. In addition, a stick-slip phenomenon was observed under lubricated conditions at the highest inclination angle for sliding perpendicular to the grinding marks direction. This phenomenon could be attributed to the extent of plane strain conditions taking place at the asperity level during sliding. DOI: 10.1115/1.4002604]
Resumo:
Inovirus is a helical array of agr-helical protein asymmetric units surrounding a DNA core. X-ray fibre diffraction studies show that the Pf1 species of Inovirus can undergo a reversible temperature-induced transition between two similar structural forms having slightly different virion helix parameters. Molecular models of the two forms show no evidence for altered interactions between the protein and either the solvent or the viral DNA; but there are significant differences in the shape and orientation of the protein asymmetric unit, related to the changes in the virion parameters. Normal modes involving libration of whole asymmetric units are in a frequency range with appreciable entropy of libration, and the structural transition may be related to changes in libration.
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Raman investigations of C70 films in the 14-370-K range show significant changes across the orientational phase transitions around 270 and 330 K. Seven of the Raman modes of C70 soften smoothly across the transitions, the magnitude of the decrease in frequencies being in the range of 2-5 cm-1. Linewidths of the bands increase in the transition region over and above the anharmonic contributions.
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Ground-state properties of the two-dimensional Hubbard model with point-defect disorder are investigated numerically in the Hartree-Fock approximation. The phase diagram in the p(point defect concentration)-delta(deviation from half filling) plane exhibits antiferromagnetic, spin-density-wave, paramagnetic, and spin-glass-like phases. The disorder stabilizes the antiferromagnetic phase relative to the spin-density-wave phase. The presence of U strongly enhances the localization in the antiferromagnetic phase. The spin-density-wave and spin-glass-like phases are weakly localized.
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Analysis of gas-particle nozzle flow is carried out with attention to the effect of dust particles on the vibrational relaxation phenomena and consequent effects on the gain of a gasdynamic laser. The phase nonequilibrium between the gas mixture and the particles during the nozzle expansion process is taken into account simultaneously. The governing equations of the two-phase nozzle flow have been transformed into similar form, and general correlating parameters have been obtained. It is shown from the present analysis that the particles present in the mixture affect the optimum gain obtainable from a gasdynamic laser adversely, and the effect depends on the size and loading of the particles in the mixture.
Phase relations and thermodynamic properties of condensed phases in the system calcium-copper-oxygen
Resumo:
The isothermal sections of the phase diagram for the system Ca-Cu-0 at 1073 and 1223 K have been determined. Several compositions in the ternary system were quenched after equilibration, and the phases present were identified by optical microscopy, X-ray diffraction, and electron probe microanalysis. Two ternary compounds Ca2CuO3 and Cao.8&uO1.9s were identified at 1073 K. However, only Ca2CuO3 was found to be stable at 1223 K. The thermodynamic properties of the two ternary compounds were determined using solid-state cells incorporating either an oxide or a fluoride solid electrolyte. The results for both types of cells were internally consistent. The compound C ~ O . ~ & U Ow~h.i~ch~ c, a n also be represented as Ca15Cu18035h, as been identified in an earlier investigation as Cao.828CuOz. Using a novel variation of the galvanic cell technique, in which the emf of a cell incorporating a fluoride electrolyte is measured as a function of the oxygen potential of the gas phase in equilibrium with the condensed phase electrodes, it has been confirmed that the compound Cao.828CuO1.93 (Ca15Cu18035d) oes not have significant oxygen nonstoichiometry. Phase relations have been deduced from the thermodynamic data as a function of the partial pressure of oxygen for the system Ca-Cu-0 at 873, 1073, and 1223 K.
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The phase relations in the system Cu-Gd-O have been determined at 1273 K by X-ray diffrac- tion, optical microscopy, and electron microprobe analysis of samples equilibrated in quartz ampules and in pure oxygen. Only one ternary compound, CuGd2O4, was found to be stable. The Gibbs free energy of formation of this compound has been measured using the solid-state cell Pt, Cu2O + CuGd2O4 + Gd2O3 // (Y2O3) ZrO2 // CuO + Cu2O, Pt in the temperature range of 900 to 1350 K. For the formation of CuGd2O4 from its binary component oxides, CuO (s) + Gd2O3 (s) → CuGd2O4 (s) ΔG° = 8230 - 11.2T (±50) J mol-1 Since the formation is endothermic, CuGd2O4 becomes thermodynamically unstable with respect to CuO and Gd2O3 below 735 K. When the oxygen partial pressure over CuGd2O4 is lowered, it decomposes according to the reaction 4CuGd2O4 (s) → 4Gd2O3 (s) + 2Cu2O (s) + O2 (g) for which the equilibrium oxygen potential is given by Δμo 2 = −227,970 + 143.2T (±500) J mol−1 An oxygen potential diagram for the system Cu-Gd-O at 1273 K is presented.
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The phase relations in the systems Cu–O–R2O3(R = Tm, Lu) have been determined at 1273 K by X-ray diffraction, optical microscopy and electron probe microanalysis of samples equilibrated in evacuated quartz ampules and in pure oxygen. Only ternary compounds of the type Cu2R2O5 were found to be stable. The standard Gibbs energies of formation of the compounds have been measured using solid-state galvanic cells of the type, Pt|Cu2O + Cu2R2O5+ R2O3‖(Y2O3)ZrO2‖CuO + Cu2O‖Pt in the temperature range 950–1325 K. The standard Gibbs energy changes associated with the formation of Cu2R2O5 compounds from their binary component oxides are: 2CuO(s)+ Tm2O3(s)→Cu2Tm2O5(s), ΔG°=(10400 – 14.0 T/K)± 100 J mol–1, 2CuO(s)+ Lu2O3(s)→Cu2Lu2O5(s), ΔG°=(10210 – 14.4 T/K)± 100 J mol–1 Since the formation is endothermic, the compounds become thermodynamically unstable with respect to component oxides at low temperatures, Cu2Tm2O5 below 743 K and Cu2Lu2O5 below 709 K. When the chemical potential of oxygen over the Cu2R2O5 compounds is lowered, they decompose according to the reaction, 2Cu2R2O5(s)→2R2O3(s)+ 2Cu2O(s)+ O2(g) The equilibrium oxygen potential corresponding to this reaction is obtained from the emf. Oxygen potential diagrams for the Cu–O–R2O3 systems at 1273 K are presented.
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Cutting of Y2O3-doped TZP rods by a low-speed diamond saw introduces an unidentified, metastable phase X (x-ZrO2) coexisting with the tetragonal (t-ZrO2) and the monoclinic (m-ZrO2) phases initially present in the sample. Further mechanical deformation of the cut surface by indentation or polishing sustains the x-ZrO2. Chemical etching removes the x-ZrO2 and increases the m-ZrO2content.
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Room-temperature Raman spectra of LiRbSO4 were studied as a function of pressure up to 170 kbar for two different orientations of the crystal. Four pressure-induced phase transitions at about 2, 17, 32 and 57 kbar were observed. The transitions at 17 and 57 kbar have slow kinetics, taking about 4 h for their completion. These phase transitions are associated with the orientations of the SO4 ions in the unit cell.
Resumo:
Proton spin—lattice relaxation time (T1) is measured in [N(CH3)4]PbX3 (X=Cl, Br, I) from 300-77 K at 9.75 MHz. All the compounds show discontinuous changes in T1 values (at 256, 270 and 277 K, respectively), indicating phase transitions. Single T1 minimum is observed in all the cases and the T1 variation is explained in terms of [N(CH3)4] and CH3 group dynamics. The activation energy Eα decreases from chloride to iodide (from 4 to 2 kcal/mol). In bromide and iodide, T1 is found to decrease with increase in temperature at higher temperatures, indicating the presence of spin—rotation interaction.