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981.
Zahraa S. Al-Taie Barbara Bartholomew Christopher Cartmell Richard T. Froom Russell G. Kerr Rolf Kraehenbuehl Patrick J. Murphy Robert J. Nash Yana B. Penkova Alexander van Teijlingen 《Molecules (Basel, Switzerland)》2022,27(4)
The absolute stereochemistry of the marine alkaloid (+)-(R)-tiruchanduramine was established via a convergent total synthesis in six steps and 15.5% overall yield from Fmoc-D-Dab(Boc)-OH. 相似文献
982.
A general formulation is developed for the contact behavior of a finite circular plate with a tensionless elastic foundation. The gap distance between the plate and elastic foundation is incorporated as an important parameter. Unlike the previous models with zero gap distance and large/infinite plate radius, which assumes the lift-off/separation of a flexural plate from its supporting elastic foundation, this study shows that lift-off may not occur. The results show how the contact area varies with the plate radius, boundary conditions and gap distance. When the plate radius becomes large enough and the gap distance is reduced to zero, the converged contact radius close to the previous ones is obtained. 相似文献
983.
Strain measures consistent with the linear, infinitesimal form of the strain-energy function are obtained within the context of isotropic, homogeneous, compressible, and non-linear elasticity. It will be shown that there are two distinct families of such measures. One family has already been much studied in the literature, the most important member being the strains whose principal values are a function only of the corresponding principal stretches. The second family of strains appears new. The motivation for studying such strains is the intuitive expectation that, for at least moderate deformations, a good fit with experimental data from material characterisation tests will be obtained with the corresponding strain-energy functions. In particular, there is the expectation that such models could prove useful for the modelling of biological soft tissue, whose physiological response is characterised by moderate strains. It will be shown that this is indeed the case for simple tension tests on porcine brain tissue. 相似文献
984.
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
985.
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
986.
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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