The elastic potential energy of a thin foil deformed by an in-plane 60° dislocation

An explicit expression of the elastic potential energy, W ^p, stored in a thin foil by a dissociated dislocation running parallel to the free surfaces is obtained in isotropic elasticity. It is used to discuss the metastable elastic equilibrium of a 60° dislocation in an ultrathin silicon foil when the fault plane is slightly inclined with respect to the free surfaces. The energy W ^p depends in particular on the positions of the two partials in the foil and on the thickness h, a situation not fully considered previously. For such ultrathin foils, propitious to the observation of partial dislocations cores at near atomic resolution, the theory predicts rapid changes with h of the separation distance S. This result is in accordance with previous experimental observations of S realized with the so-called “forbidden-reflection lattice imaging” technique.     

Simulation of 200–400 Me V/u ~(12)C+~(12)C elastic scattering on SHARAQ spectrometer

In order to further obtain the information of three-body force(TBF) from 200–400 Me V/u12C+12C elastic scattering, we plan to perform this experiment on a SHARAQ spectrometer. Based on the experimental condition of the Radioactive Ion Beam Factory(RIBF)-SHARAQ facility, a simulation is given to find a compromise between the better energy and angular resolutions, and higher yield by optimizing the target thickness, beam transport mode, beam intensity and angular step. From the simulation, we found that the beam quality mainly limits the improvements of energy and angular resolutions. A beam tracking system as well as a lateral and angular dispersionmatching technique are adopted to reduce the influence of beam quality. According to the two angular settings of SHARAQ as well as the expected cross sections on the basis of the theoretical model, the energy and angular resolutions, and statistical accuracy are estimated.     

Measurement of all electro-elastic constants of lithium tetraborate(Li_2B_4O_7)crystal

A new approach to determine all the electro-elastic constants of thepiezoelectric crystals in class 4mm has been put forward.As an example,all theconstants of Lithium Tetraborate(Li_2B_4O_7)crystal have been measured bymeans of the approach.The outstanding advantage of the approach is that it on-ly needs to employ in measurement three crystal plates differently oriented.     

Effect of the low-temperature (20–60°C) heating of silicon on its microhardness

Changes in the microhardness of silicon samples exposed to temperatures of 20–60°C are studied. It is found that the microhardness increases; this effect is preserved at room temperature for 20 min and non-monotonically depends on the temperature and exposure time (the changes are maximal at ～40°C and ～100 s, respectively). The microhardness of samples with native oxide removed does not change. The results are discussed in terms of a model of processes in the silicon-oxide system, which was previously proposed for the case of irradiation of silicon with light. The practical importance of the effect is discussed.     

Relaxation and hysteresis internal friction in ultra-fine-grained copper at temperatures of up to 400°C

The temperature- and amplitude-dependent internal friction and elastic moduli of copper samples (99.95% Cu) subjected to deformation by equal channel angular pressing with a pass number of 1, 4, and 8 along the Bc route in the hertz range of loading frequencies at room temperature and temperatures of up to 400°C are investigated. The effect of deformation and subsequent recrystallization on the parameters of thermally activated internal friction peaks due to grain-boundary relaxation and the recrystallization of intensively deformed copper, and on amplitude-dependent internal friction due to dislocation hysteresis, is determined.     

Dielectric loss relaxation maxima of undoped and calcium doped NaCl crystals between 20 and 400°C

When studying the dielectric loss dependence of undoped (pure) and CaCl₂ doped NaCl crystals on temperature and frequency, some further maxima were observed apart from the wellknown relaxation maxima of calcium complexes. The temperature of these maxima shifts with rising calcium content to lower temperatures (from 259 to 142°C), whereas the value of the maxima does not change with concentration and remains unchanged even with the purest crystals. It seems probable that the observed maxima are due to the relaxation loss of the crystal lattice itself.     

Fracture Mechanisms of Low Activation 12% Chromium Ferritic-Martensitic Steel EK-181 in the Temperature Range from –196 to 800°C

Russian Physics Journal - A comparative study of the fracture features of a promising low-activation 12% chromium ferritic-martensitic steel EK-181 after uniaxial tensile tests in the temperature...     

Thermal expansion and phase changes of 16Kh12V2FTaR steel in temperature range from 20 to 1000 °C

The article presents the results of investigation of thermal expansion of 16Kh12V2FTaR steel in the temperature range 20–1000 °C. Measurements were carried out by dilatometric method with the error (1.5–2)×10^?7 K^?1. The temperature dependences of thermal coefficient of linear expansion of steel have been obtained in ferrite-martensite and ferrite-perlite states, and reference tables have been calculated. Influence of samples cooling rate on martensite phase formation is shown.     

A System for Determination of Precise Isotopic Vapor Pressure Differences from —20 to 110 °C,including Temperature Control to 0·001 over that Range)

An experimental system for the precise measurement of small vapor pressure differences over the range —20 to 110°C is described.     

Melting properties of mixed Ni13-xAlx(x=0 to 13) clusters

Starting from the configuration full optimized by Genetic Algorithm (GA), the melting behaviors of Binary Ni13-xAlx(x=0 to 13) clusters have been investigated by Monte Carlo (MC) simulations with Metropolis algorithm with a n-body Gupta potential. In contrast to bulk, these clusters have smeared first order transitions occurring over a range of temperature. The melting temperature Tm calculated from Lindemanns criterion vary drastically with concentrations x. For most clusters studied, the average energy per atom E, the relative root-mean-square (rms) bond length fluchuation δ and the heat capacity C per atom related to the energy fluctuation of the system change with temperature in the transition region in manners differing from LJ and alkali metal clusters. For Ni12Al, Ni7Al6, Ni6Al7, Ni5Al8 clusters, there are behaviors characteristic of magic number in C, which do not exist in the pure TM clusters.     

Influence of High-Temperature Annealing on the Resistance to High Strain Rate and Fracture of Tantalum at Temperatures of 20 and 500°C

Technical Physics - Two series of shock-wave experiments have been conducted in order to measure the Hugoniot elastic limit and determine the strain rate dependence of critical fracture stress for...     

Molecular structure of a gold β-octakis(trifluoromethyl)-meso-triarylcorrole: an 85° difference in saddling dihedral relative to copper

Copper corroles exhibit inherent saddling, driven by ligand non-innocence, which may be viewed as a form of multideterminantal character. The saddling is enhanced by sterically hindered peripheral substituents. The sterically hindered complex Cu[(CF₃)₈T(pFP)C] (wherein the ligand is β-octakis(trifluoromethyl)-meso-tris(p-fluorophenyl)corrolato) is thus exceedingly saddled with adjacent pyrrole rings nearly orthogonal to one another. By contrast, Au[(CF₃)₈T(pFP)C] has a nearly planar corrole macrocycle, implying an innocent corrole ligand.     

The structure of 99Ru from (α,3n) reaction

The results of in-beam investigations of excited states of ⁹⁹Ru using the ⁹⁸Mo(α,3n) reaction are presented. Angular distributions of γ–rays and γ–γ coincidences have been measured. Excited states have been identified up to an energy of E = 5603 keV and spin of I^π= 31/2⁻. Mean lifetimes τ have been determined using the DSA method for eleven levels. Aligned angular momenta are discussed and the probable (νh _11/2) origin of a backbending at frequency about 0.5 MeV was confirmed. The possible role of (νd _5/2) alignment at frequencies above 0.5 MeV was pointed out. Received: 13 January 1999 / Revised version: 26 March 1999     

The crystal structure of meta-zeunerite Cu(UO2)2(AsO4)2⋅8 H2O

The structure of the mineral zeunerite (deposits at Rotava near Kraslice, Ore Mountains) was determined. The tetragonal unit cell, having the dimensionsa=7.10₅Å andc=17.70₄Å, contains two structure units of Cu(UO₂)₂(AsO₄)₂8H₂O. The space group isP4₂/nmc. The distribution of the atoms in the unit cell was determined from the Patterson projectionP(vw) and by means of (F ₀-F _c) synthesis. Meta-Zeunerite has a layer type structure. The sheets [(UO₂)(AsO₄)] are separated by layers containing the cations (Cu(H₂O)₄)²⁺ and molecules of water. The uranium is coordinated octahedrally with six oxygen atoms at distances: U-O₁ 1.94 Å, U-O₂ 1.78 Å, U-O₃₍₄₎ 2.18 Å (4×). The uranyl radical O₁-U-O₂ is linear. In the tetrahedron AsO₄ the interatomic distances are As-O 1.77 Å and the bond angles 102°, 102°, 113° and 113°. Each oxygen atom of the tetrahedron AsO₄ is simultaneously bonded to the uranium atom. The bond angle As-O-U is 137°. The layers [(UO₂)₂(AsO₄)] are bonded together by the cations (Cu(H₂O)₄)²⁺. The distances Cu-O₁ and Cu-O₂ are 2.55 and 2.58Å respectively. The structural changes during hydration and dehydration are explaned.

---

- Cu(UO₂)₂(AsO₄)₂8 H₂O

( , ). =7,10₅ Å,=17,70₄ Å Cu(UO₂)₂(AsO₄)₂8 ₂O. P4₂/nmc. P(v w) (F ₀-F _c) . . , [(UO₂)(AsO₄)], , [u(₂)₄]²⁺ . : U-O₁ 1,94 Å, U-O₂ 1,78 Å, U-O₃₍₄₎ 2,18 Å ( ). ₁-U-₂. AsO₄ As- 1,77 Å -102°, 102°, 113° 113°. AsO₄ . As--U 137°. [(UO₂)₂(AsO₄)] [u(₂O)₄]²⁺. u-O₁ 2,55 Å, u-O₂ 2,58 Å. .

---

---

In conclusion the author thanks T. Veselská for assistance in the calculations and workers of the National Museum in Prague, and primarily Dr. ípek, for supplying the sample. The experimental work was carried out at the Department of Physics of the Natural Science Faculty of Komenský University.     

Leed study of Fe epitaxially grown at 190°C on Cu(100)

We report a LEED study of iron deposited on Cu(100) at 190°C. Very sharp LEED patterns were obtained for high iron coverages. We observed evidence of an ill defined Fe/Cu interface for one monolayer of iron deposited at 190°C. The stability of the iron overlayers was tested as a function of time for various coverages. For one monolayer the intensity versus energy curve for the (00) beam shows time dependence at 190°C. For four layers, no significant changes were observed in the LEED spectra over a period of one hour. We measured for five layers of iron a top layer expansion of 2.8% relative to the bulk. The interplanar spacing for bulk fcc Fe at 190°C remains equal to the room value. In these experiments the samples were deposited at 190°C and kept at this temperature during the LEED measurements.     

The nature of hydrogen bonding in R22(8) crystal motifs – a computational exploration

R²₂(8), a commonly occurring motif in organic crystals, has been examined here through ab initio and density functional theory (DFT) methods. The 11 R²₂(8) motifs reported by Allen et al. have been classified into five types; their structural features, hydrogen-bonding patterns and the kind of interactions stabilising these motifs have been studied. Results reveal that the electronegativity of donor atoms plays a major role in directing the hydrogen bonds, whereas their positions in the motif have been found to be less important. Quantum theory of atoms in molecules (QTAIM) and reduced density gradient-based non-covalent-interaction analyses have been used to understand the weak interactions between monomers. Homonuclear interactions within the motifs have been found to be stronger with higher covalent character at the bond critical points than heteronuclear interactions. In addition, a localised molecular orbital energy decomposition analysis (LMOEDA) has been accomplished to provide useful insight into various long- and short-range interactions that contribute to the total stabilisation energies. The stabilising n → σ* interactions have been explained using natural bond orbital (NBO) analysis. Overall, this study provides the essential criteria for an organic crystal to be in an R²₂(8) motif and further discusses the different combinations of hydrogen-bonding features within the R²₂(8) motifs.