A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed. 相似文献
We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show
a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are
found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there
exists no report in literature on any BiNi compound which is magnetic. 相似文献
The tensor character of the first-order density matrix leads to the definition of an MO multicenter bond index for closed-shell systems. It is here applied to three-center bonds. Satisfactory results are obtained for compounds involving secondary bonds, strong and normal hydrogen bonds; the index for the peptide bond is found to be similar to that of strong hydrogen bonds.On leave of absence from Inst. de Física, UFBA, 40000 Salvador, BA, Brasil. 相似文献
A time-of-flight mass spectrometer with a position sensitive ion detector was used to study the dissociative double ionization of benzene by UV synchrotron radiation. The threshold energy for the main dissociative processes, leading to CH(3)(+) + C(5)H(3)(+), C(2)H(3)(+) + C(4)H(3)(+) and C(2)H(2)(+) + C(4)H(4)(+) ion pairs were characterized by exploiting a photoelectron-photoion-photoion-coincidence technique, giving 27.8 ± 0.1, 29.5 ± 0.1, and 30.2 ± 0.1 eV, respectively. The first reaction also proceeds via the formation of a metastable C(6)H(6)(2+) dication. The translational kinetic energy of the ionic products was evaluated by measuring the position of ions arriving to the detector. Theoretical calculations of the energy and structure of dissociation product ions were performed to provide further information on the dynamics of the charge separation reactions following the photoionization event. 相似文献
A fast, sensitive and specific liquid chromatography-mass spectrometry method has been developed for quantification of digoxin in human plasma. The method was optimized to bioequivalence studies aiming higher sensitivity and selectivity than previously published methods, in addition to shorter run time allowing high-throughput sample analyses from volunteers. Chromatographic separation was achieved by an RP-18e column hyphenated to an API 5000 mass spectrometer system set at negative electrospray ionization and operating in the MRM mode. Calibration curve was linear over a wide range of concentration (50.0–6000.0 pg mL−1), with the lower limit of quantification at 50.0 pg mL−1 and without interfering peaks at the retention time of digoxin (2.09 min). Dexamethasone was used as internal standard and samples were cleaned up by liquid-liquid extraction obtaining a mean recovery of 73.8%. Validation results confirmed inter-batch accuracy (−8.66 to 5.78%), precision (4.1–10.6%) and stability, in accordance with the U.S. Food and Drug Administration and the Brazilian National Health Surveillance Agency guidelines. The developed analytical method could be successfully applied to a single oral dose (0.25 mg), one-way, randomized, two-sequence, crossover bioequivalence study validating, up to date, the fastest analysis and the most sensitive and specific method already published for digoxin quantification.
The main contribution of this paper is to provide an alternative strategy to reduce the number of bi-electronic integrals in ab initio quantum mechanics calculations. An analytical procedure to evaluate the energy of a molecule as well as two-electron integrals is proposed. This approach is based on the generalized exponential function (q-exponential) and is particularly advantageous because it reduces substantially the CPU time in quantum mechanical calculations. Some examples of the effectiveness of this methodology are presented. It is important to point out that the new methodology is applicable to any kind of molecular system including relatively large molecular systems in the context of the Hartree–Fock (HF) and density functional theories (DFT). 相似文献