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21.
扭摆法是测量物体转动惯量的有效方法,其不确定度分析是关键.本文推导了扭摆法测物体转动惯量准确的不确定度传递公式,得到各直接测量量及其不确定度对转动惯量不确定度的影响.并进行了算例分析.结果表明,扭摆法比三线摆测得物体的转动惯量的误差以及不确定度要小很多.这对实验方法的选择和仪器的研制具有重要的实际意义. 相似文献
22.
23.
Molly Dunkum 《Czechoslovak Mathematical Journal》2009,59(1):241-247
There is a classical result known as Baer’s Lemma that states that an R-module E is injective if it is injective for R. This means that if a map from a submodule of R, that is, from a left ideal L of R to E can always be extended to R, then a map to E from a submodule A of any R-module B can be extended to B; in other words, E is injective. In this paper, we generalize this result to the category q
ω consisting of the representations of an infinite line quiver. This generalization of Baer’s Lemma is useful in proving that
torsion free covers exist for q
ω.
相似文献
24.
Jinsung Park 《Journal of Functional Analysis》2009,257(6):1713-1758
In this paper we derive a relationship of the leading coefficient of the Laurent expansion of the Ruelle zeta function at s=0 and the analytic torsion for hyperbolic manifolds with cusps. Here, the analytic torsion is defined by a certain regularized trace following Melrose [R.B. Melrose, The Atiyah-Patodi-Singer Index Theorem, Res. Notes Math., vol. 4, A.K. Peters, Ltd., Wellesley, MA, 1993]. This extends the result of Fried, which was proved for the compact case in [D. Fried, Analytic torsion and closed geodesics on hyperbolic manifolds, Invent. Math. 84 (3) (1986) 523-540], to a noncompact case. 相似文献
25.
V. N. Paimushin V. A. Ivanov S. A. Lukankin N. V. Polyakova V. A. Firsov S. A. Kholmogorov 《Mechanics of Composite Materials》2009,45(2):113-136
Based on linearized equations of the theory of elastic stability of straight composite bars with a low shear rigidity, which
are constructed using the consistent geometrically nonlinear equations of elasticity theory for small deformations and arbitrary
displacements and a kinematic model of Timoshenko type, exact analytical solutions of nonclassical stability problems are
obtained for a bar subjected to axial compression and torsion for various modes of end fixation. It is shown that the problem
of direct determination of the critical parameter of the compressive load at a given torque parameter leads to transcendental
characteristic equations that are solvable only if bar ends have cylindrical hinges. At the same time, we succeeded in obtaining
solutions to these equations in terms of wave formation parameters of the bar; these parameters, in turn, enabled us to find
the parameter of the critical load at any boundary conditions. Also, an algorithm for numerical solution of the problems stated
is proposed, which is based on reducing the problems to systems of integroalgebraic equations with Volterra-type operators
and on solving these equations by the method of mechanical quadratures (finite sums). It is demonstrated that such numerical
solutions exist only for certain ranges of parameters of the bar and of the parameter of torque. In the general case, they
can not be obtained by the numerical method used. It is also shown that the well-known solutions of the stability problem
for a bar subjected to torsion or to compression with torsion are in correct.
Translated from Mekhanika Kompozitnykh Materialov, Vol. 45, No. 2, pp. 167–200, March–April, 2009. 相似文献
26.
N.J. Popławski 《Annalen der Physik》2011,523(4):291-295
We present a simple and natural way to derive the observed small, positive cosmological constant from the gravitational interaction of condensing fermions. In the Riemann‐Cartan spacetime, torsion gives rise to the axial–axial vector four‐fermion interaction term in the Dirac Lagrangian for spinor fields. We show that this nonlinear term acts like a cosmological constant if these fields have a nonzero vacuum expectation value. For quark fields in QCD, such a torsion‐induced cosmological constant is positive and its energy scale is only about 8 times larger than the observed value. Adding leptons to this picture could lower this scale to the observed value. 相似文献
27.
Tungyang Chen 《Mechanics Research Communications》2011,38(1):68-71
A novel class of graded cylinders is proposed as neutral inclusions inside host shafts of arbitrary cross-section under Saint-Venant's torsion. The graded cylinder is made of cylindrically orthotropic materials with position varying quantities. The profiles of the two distinct shear moduli in the radial and tangential directions follow specific forms based on an arbitrarily selected function along the radial distance. We show that this type of graded cylinders can serve as universal neutral inclusions within host shafts of arbitrary cross-sections. In addition, we find that the associated warping fields can be exactly determined in terms of simple exponents of the selected function. This suggests that, by tuning the gradation parameter, one can manipulate the warping field of the inserted cylinder without disturbing the fields inside the host shaft. This finding is an original contribution to the existing solvable configurations of composite shafts under torsion. 相似文献
28.
C. W. Lim 《Acta Mechanica Solida Sinica》2011,24(6):484-494
The torsional static and dynamic behaviors of circular nanosolids such as nanoshafts, nanorods and nanotubes are established based on a new nonlocal elastic stress field theory. Based on a new expression for strain energy with a nonlocal nanoscale parameter, new higher-order governing equations and the corresponding boundary conditions are first derived here via the variational principle because the classical equilibrium conditions and/or equations of motion can- not be directly applied to nonlocal nanostructures even if the stress and moment quantities are replaced by the corresponding nonlocal quantities. The static twist and torsional vibration of circular, nonlocal nanosolids are solved and discussed in detail. A comparison of the conventional and new nonlocal models is also presented for a fully fixed nanosolid, where a lower-order governing equation and reduced stiffness are found in the conventional model while the new model reports opposite solutions. Analytical solutions and numerical examples based on the new nonlocal stress theory demonstrate that nonlocal stress enhances stiffness of nanosolids, i.e. the angular displacement decreases with the increasing nonlocal nanoscale while the natural frequency increases with the increasing nonlocal nanoscale. 相似文献
29.
We characterize some homogeneous Hopf real hypersurfaces in a nonflat complex space form by studying trajectories for Sasakian magnetic fields whose extrinsic shapes are tangentially of order 2. 相似文献
30.