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991.
In this paper we describe the design and manufacture of an axial-torsion test specimen, and provide relationships needed when
conducting stress-strain characterization experiments with the specimen. The specimen is a short hollow cylinder of rubber
bonded between two steel mounting rings, in which simultaneous axial and shear strains are produced via independently controlled
axial and twist displacements. We present calculations for the strain-displacement and stress-load relationships, and strain
energy density. These relationships have been established and validated via a combination of analytical and experimental techniques,
and finite element analysis. We have investigated the extent and effects of strain and stress field non-uniformity in the
test specimen. The specimen design is sufficiently simple that a closed-form expression for the strain-displacement relationship
has been successfully developed. 相似文献
992.
K. Rßner M. Hümmer A. Benkert A. Forchel 《Physica E: Low-dimensional Systems and Nanostructures》2005,30(1-2):159-163
We have successfully fabricated and characterized room temperature continuous wave (cw) GaInAsSb/AlGaAsSb distributed feedback lasers emitting in the wavelength region between 2.499 and 2.573 μm. To the best of our knowledge, this is the longest emission wavelength realized with a GaSb-based DFB laser diode. The laser structure used for DFB processing was grown by solid source molecular beam epitaxy. A DFB concept requiring no subsequent overgrowth step was used by defining first-order Cr-Bragg gratings laterally patterned to a ridge waveguide. Threshold currents smaller than 60 mA and room temperature cw output powers up to 6.5 mW were obtained. The laser diodes show single mode emission with side mode suppression ratios (SMSR) of up to 32 dB. 相似文献
993.
V. V. Lozhkarev S. G. Garanin R. R. Gerke V. N. Ginzburg E. V. Katin A. V. Kirsanov G. A. Luchinin A. N. Mal’shakov M. A. Mart’yanov O. V. Palashov A. K. Poteomkin N. N. Rukavishnikov A. M. Sergeev S. A. Sukharev G. I. Freidman E. A. Khazanov A. V. Charukhchev A. A. Shaikin I. V. Yakovlev 《JETP Letters》2005,82(4):178-180
In experiments on the parametrical amplification of femtosecond pulses in wide-aperture DKDP crystals, a power of more than 100 TW has been reached, which is much higher than the record level achieved in such lasers. The energy efficiency obtained for the parametric amplifier is equal to 27%. The energy of a 72-fs pulse is equal to 10 J. 相似文献
994.
The Bekenstein–Hawking entropy of certain black holes can be computed microscopically in string theory by mapping the elusive
problem of counting microstates of a strongly gravitating black hole to the tractable problem of counting microstates of a
weakly coupled D-brane system, which has no event horizon, and indeed comfortably fits on the head of a pin. We show here
that, contrary to widely held beliefs, the entropy of spherically symmetric black holes can easily be dwarfed by that of stationary
multi-black-hole “molecules” of the same total charge and energy. Thus, the corresponding pin-sized D-brane systems do not
even approximately count the microstates of a single black hole, but rather those of a zoo of entropically dominant multicentered
configurations.
Fourth Award in the 2007 Essay Competition of the Gravity Research Foundation. 相似文献
995.
M. Vedani G. Angella Paola Bassani D. Ripamonti A. Tuissi 《Journal of Thermal Analysis and Calorimetry》2007,87(1):277-284
Equal channel angular
pressing (ECAP) was carried out on solution annealed samples of Al–Mg–Si–Zr
and Al–Mg–Si–Zr–Sc alloys to achieve a substantial
grain refinement of the materials. Post ECAP aging was then investigated on
the ultrafine grained alloys by DSC and TEM analyses.
DSC scans
were carried out with heating rates ranging from 5 to 30°C min–1.
Peak identification was performed by the support of literature information
and TEM analyses. Precipitation kinetics revealed to be similar for both alloys
but the Sc-free alloy showed a recrystallization peak at temperatures ranging
from 310 to 340°C, depending on the strain accumulated during ECAP. On
the contrary, the Sc-containing alloy showed a greater grain stability. Analyses
of peak positions and of activation energies as a function of ECAP passes
experienced by the samples revealed large modifications of precipitation kinetics
in the ultrafine-grained alloys with respect to the coarse-grained materials. 相似文献
996.
Maxim V. Pavlov 《Communications in Mathematical Physics》2007,272(2):469-505
The algebro-geometric approach for integrability of semi-Hamiltonian hydrodynamic type systems is presented. The class of
symmetric hydrodynamic type systems is defined and the calculation of the associated Riemann surfaces is greatly simplified for this
class. Many interesting and physically motivated examples are investigated. 相似文献
997.
R. Centore P. Riccio S. Fusco A. Carella A. Quatela S. Schutzmann F. Stella F. De Matteis 《Journal of polymer science. Part A, Polymer chemistry》2007,45(13):2719-2725
We have prepared new polyesters containing quadratic, nonlinear optical (NLO) active chromophores covalently incorporated into the main chain. In these polymers, the sequence of the chromophore units along the main chain is rigorously head to tail. All the polyesters are processable, both in the melt and in solution. For one polyester, a full second‐order NLO characterization has been performed. An out‐of‐resonance d33 coefficient of 21 pm/V at 1368 nm has been measured. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2719–2725, 2007 相似文献
998.
K. Ravikumar B. Sridhar M. Mahesh V. V. Narayana Reddy 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(9):o574-o576
The crystal structures of pyranoquinolines 9‐fluoro‐5‐phenyl‐3,4,4a,5,6,10b‐hexahydro‐2H‐pyrano[3,2‐c]quinoline, C18H18FNO, and 9‐methyl‐5‐phenyl‐3,4,4a,5,6,10b‐hexahydro‐2H‐pyrano[3,2‐c]quinoline, C19H21NO, are isomorphous. In both structures, the pyran ring is exo to the six‐membered N‐heterocyclic ring formed in the cycloaddition step. The torsion angles across the phenyl linkage for the two structures are −91.2 (1) and −88.3 (2)°. The striking feature in both crystal packings is that they do not contain the expected conventional hydrogen bonds, in spite of the presence of good hydrogen‐bonding functionalities. Possible C—H⋯π interactions are, however, observed. 相似文献
999.
N. Foroughifar A. Mobinikhaledi M. Amrollahi M. Zendehdel 《Applied magnetic resonance》2004,26(4):483-488
C(2)-H exchange incis-[(en)2Co(HIm)(enH)]Br4 (Im, imidazole; en, ethylenediamine) was studied over a pD range of 9.4 to 10.2 at 60°C where thecis-[(en)2Co(Him)(enH)]4+ andcis-[(en)2Co(HIm)(en)]3+ are the species present in significant concentrations.Cis-[(en)2Co(HIm)(enH)]4+ has pKa1 7.86 and pKa2 9.82 with pKa1 corresponding to coordinated enH ionization and pKa2 to ImH ionization. The kinetic data may be interpreted in terms of an intramolecular H-D exchange mechanism, where the “dangling”-ND2CH2CH2ND2 group acts as a base to remove the imidazole C(2)-H proton from the coordinated DIm moiety. 相似文献
1000.
The microstructure evolution of decagonal quasicrystals in Al72Ni12Co16 alloy was investigated by the electromagnetic melting and cyclic superheating method. Single-phase decagonal quasicrystals have been obtained when the undercoolings were larger than 60 K. The decagonal quasicrystals formed at various undercoolings show different microstructural morphologies. Furthermore, grain refinement was found near the undercooling of 120 K. Based on current thermodynamic and dendrite growth theories, a dimensionless superheating parameter was adopted to explain the effect of processing conditions on the microstructure of Al72Ni12Co16 alloy. The result indicate that the fine equiaxied microstructure of decagonal quasicrystal (D-phase) formed near on undercooling of 120 K originates from the break-up of dendrites. 相似文献