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991.
The classical problem of simple shear in nonlinear elasticity has played an important role as a basic pilot problem involving
a homogeneous deformation that is rich enough to illustrate several key features of the nonlinear theory, most notably the
presence of normal stress effects. Here our focus is on certain ambiguities in the formulation of simple shear arising from
the determination of the arbitrary hydrostatic pressure term in the normal stresses for the case of an incompressible isotropic
hyperelastic material. A new formulation in terms of the principal stretches is given. An alternative approach to the determination
of the hydrostatic pressure is proposed here: it will be required that the stress distribution for a perfectly incompressible
material be the same as that for a slightly compressible counterpart. The form of slight compressibility adopted here is that
usually assumed in the finite element simulation of rubbers. For the particular case of a neo-Hookean material, the different
stress distributions are compared and contrasted. 相似文献
992.
During operation, a MEMS switch is activated by an applied voltage. This causes the switch, often a doped silicon microbeam,
to be attracted toward (pulled-into) a substrate. The component–substrate contact completes a circuit and permits the flow
of current. Calculations for the minimum voltage required to achieve quasi-static pull-in are well documented. But for these
quasi-static pull-in voltages to be meaningful, the voltage would have to be increased gradually until the critical value
Vpull-inV_{\mathrm{pull\mbox{-}in}} is reached and the switch closes. Of course, practical considerations might require the switch to cycle on and off quickly,
i.e., dynamically. This is particularly true in the case of radio frequency (RF) MEMS switches. In this paper, a model is
developed and used to consider the dynamic pull-in characteristics of a clamped-clamped microbeam. This model includes inertial effects, structural and air damping
(squeeze-film damping), as well as the impact behavior of the microbeam with the substrate. Parameter combinations leading
to various types of behavior (no pull-in, air-bounce, wall bounce, etc.) are clearly identified. In an attempt to ensure fast
switch closure and limit bouncing, two new applied voltage profiles are considered. 相似文献
993.
Weakly polar interactions between the side-chain aromatic rings and hydrogens of backbone amides (Ar-HN) are found in unique conformational regions. To characterize these conformational regions and to elucidate factors that determine the conformation of the Ar-HN interactions, four 4-ns molecular dynamics simulations were performed using four different low-energy conformations obtained from simulated annealing and one extended conformation of the model tripeptide Ac-Phe-Gly-Gly-NH-CH(3) as starting structures. The Ar(i)-HN(i+1) interactions were 4 times more frequent than were Ar(i)-HN(i+2) interactions. Half of the conformations with Ar(i)-HN(i+2) interactions also contained an Ar(i)-HN(i+1) interaction. The solvent access surface area of the Phe side chain and of the amide groups of Phe1, Gly2, and Gly3 involved in Ar-HN interactions was significantly smaller than in residues not involved in such interactions. The number of hydrogen bonds between the solvent and Phe1, Gly2, and Gly3 amide groups was also lower in conformations with Ar-HN interactions. For each trajectory, structures that contained Ar(i)-HN(i), Ar(i)-HN(i+1), and Ar(i)-HN(i+2) interactions were clustered on the basis of similarity of selected torsion angles. Attraction energies between the aromatic ring and the backbone amide in representative conformations of the clusters ranged from -1.98 to -9.24 kJ mol(-1) when an Ar-HN interaction was present. The most representative conformations from the largest clusters matched well with the conformations from the Protein Data Bank of Phe-Gly-Gly protein fragments containing Ar-HN interactions. 相似文献
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Michael D. Beachy David Chasman Richard A. Friesner Robert B. Murphy 《Journal of computational chemistry》1998,19(9):1030-1038
We have developed a parallel version of our pseudospectral localized Møller–Plesset electronic structure code. We present timings for molecules up to 1010 basis functions and parallel speedup for molecules in the range of 260–658 basis functions. We demonstrate that the code is scalable; that is, a larger number of nodes can be efficiently utilized as the size of the molecule increases. By taking advantage of the available distributed memory and disk space of a scalable parallel computer, the parallel code can calculate LMP2 energies of molecules too large to be done on workstations. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1030–1038, 1998 相似文献
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Highly Efficient Triplet Photosensitizers: A Systematic Approach to the Application of IrIII Complexes containing Extended Phenanthrolines
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Yue Lu Dr. Niamh McGoldrick Dr. Frances Murphy Dr. Brendan Twamley Xiaoneng Cui Dr. Colm Delaney Dr. Gearóid M. Ó Máille Junsi Wang Prof. Dr. Jianzhang Zhao Prof. Dr. Sylvia M. Draper 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(32):11349-11356
A series of IrIII complexes, based on 1,10‐phenanthroline featuring aryl acetylene chromophores, were prepared and investigated as triplet photosensitizers. The complexes were synthesized by Sonogashira cross‐coupling reactions using a “chemistry‐on‐the‐complex” method. The absorption properties and luminescence lifetimes were successfully tuned by controlling the number and type of light‐harvesting group. Intense UV/Vis absorption was observed for the IrIII complexes with two light‐harvesting groups at the 3‐ and 8‐positions of the phenanthroline. The asymmetric IrIII complex (with a triphenylamine (TPA) and a pyrene moiety attached) exhibited the longest lifetime. Red emission was observed for all the complexes in deaerated solutions at room temperature. Their emission at low temperature (77 K) and nanosecond time‐resolved transient difference absorption spectra revealed the origin of their triplet excited states. The singlet‐oxygen (1O2) sensitization and triplet‐triplet annihilation (TTA)‐based upconversion were explored. Highly efficient TTA upconversion (ΦUC=28.1 %) and 1O2 sensitization (ΦΔ=97.0 %) were achieved for the asymmetric IrIII complex, which showed intense absorption in the visible region (λabs=482 nm, ?=50900 m ?1 cm?1) and had a long‐lived triplet excited state (53.3 μs at RT). 相似文献