Presence Of Curvature Research Articles

High-affinity binding sites for histone H1 in plasmid DNA.

The interaction of histone H1 isolated from chicken erythrocytes with restriction fragments from plasmids pBR322 and pUC19 was studied by gel electrophoresis. Certain restriction fragments exhibited unusually high affinity for the histone, forming high molecular mass complexes at protein to DNA ratios at which the other fragments did not show evidence for binding. The highly preferred fragments are intrinsically curved, as judged by their electrophoretic mobility in polyacrylamide gels, by computer modeling, and by imaging with scanning force microscopy. However, control experiments with either curved portions of the same fragments or highly curved kinetoplast DNA fragments showed that the presence of curvature alone was not sufficient for preferential binding. By using various restriction fragments centered around the highly preferred sequence, it was found that the high-affinity binding required in addition the presence of specific sequences on both sides of the region of curvature. Thus, both curvature and the presence of specific sites seem to be required to generate high affinity.

Approximate elasticity solution for laminated anisotropic finite cylinders

This paper deals with the static response of the axisymmetric problem of arbitrarily laminated, anisotropic cylindrical shells of finite length using three-dimensional elasticity equations. The closed cylinder is simply supported at both ends. The highly coupled partial differential equations (PDEs) are reduced to ordinary differential equations (ODEs) with variable coefficients by choosing the solution composed of trigonometric functions along the axial direction. Through dividing each layer into thin laminas, the variable coefficients in ODEs become constants, and the resulting equations can be solved exactly. Numerical examples are presented for ( - 45/0 deg) and ( - 45/457 - 45 deg) laminations under sinusoidal normal loading on the outer surface and uniform internal pressure. From the present study, it is found that, although the general behavior is similar to that of isotropic shells, the coupling is obvious in general, and the shear effect is very important in the edge region. Moreover, the initial curvature effect plays an essential role, especially in stress distributions. TATIC and dynamic responses of composite laminated closed cylindrical shells and curved panels have received wide attention in recent years. Because of the anisotropy in composites and the presence of curvature in shell structures, obtaining exact three-dimensional elasticity solutions for lami- nated closed cylinders and open panels subjected to general loading and arbitrary boundary conditions becomes a chal- lenging task. The mathematical complexity in analyzing three- dimensional elasticity equations usually makes exact solutions difficult to obtain. However, certain problems in which a three-dimensional approach can be used still exist. Most of these problems can be solved by assuming the solution to be composed of trigonometric functions in the axial and circumferential directions. The main reason is that the partial differential equations (PDEs) governing three-di- mensional problems can be reduced to one-dimension al ordi- nary differential equations (ODEs) with variable coefficients. The solution for the resulting ODEs can be obtained by intro- ducing the displacement potential function. Usually, this method is used with isotropic and transversely isotropic mate- rials, whereas the Frobenius method is used with orthotropic materials. When the three-dimensional elasticity solutions are available, they are very useful in evaluating the accuracy of approximate results, e.g., in the case of two-dimensional shell theories. For the static problem, Flugge and Kelkar1 and Yao2 ob- tained an exact solution for closed isotropic long cylinders under general two-dimensional surface traction. Using the Frobenius method, Srinivas3 developed an exact three-dimen- sional solution for orthotropic finite cylinders with simply supported conditions. However, the numerical results are given for free vibration only. Varadan and Bhaskar4 also performed the static stress analysis using the procedures pro- posed by Srinivas. Pagano5 obtained the stress field for a homogeneous, anisotropic closed cylinder under two-dimen- sional surface loads in which the problems are independent of the axial coordinate. However, numerical results are reported only for a single orthotropic layer. Recently, Ren6'7 presented an exact solution for simply supported laminated cross-ply circular cylindrical panels of infinite and finite length in the

Natural vibrations of composite materials having structures with small-scale curvatures

We have used the continuum theory in [1] to develop an approach to determination of the natural frequency and mode of composite structural elements with locally and regularly curved structures. We used the approach to examine the solution of a specific problem concerning natural vibration. It was shown that the fundamental frequency of the structural elements may be reduced considerably by the presence of curvature in the structure of the composite.

Magnetic curvature drift instability

The semicollisional tearing mode is found to be strongly destabilized by electron temperature gradient in the presence of curvature or cross-field transport of particles or heat. The mode is unstable over a very wide range of parameters for reversed field pinches or spheromaks and appears to be more likely to explain anomalous transport than resistive interchanges. The mode is not so strongly unstable in tokamaks, because of their long shear length, but can be destabilized in a limited range by toroidal effects, principally Pfirsch–Schlüter transport.

Curvature squared terms and string theories

The compatibility between the presence of curvature squared terms and the absence of ghost particles in the low energy limits of string theories is established. The lagrangian ʃ√g d D×(R μνϱσR μνϱσ−4R μνR μν+R 2) leads to ghost-free nontrivial gravitational self-interactions for dimensions higher than four.

Kinematical conditions in the construction of spacetime

We adopt the point of view that a solution of Einstein's equations is an evolution of given initial Cauchy data. Implementing the evolution equations necessarily requires a determination, not directly dictated by the field equations, of the kinematics of the observers in terms of which the evolution is represented. In this paper we study the observers' kinematics (velocities and accelerations) in terms of the geometry of their congruences of world lines relative to families of time slicings of spacetime, which contrasts with the more usual approach of imposing particular "gauge" or "coordinate conditions." The types of conditions we suggest are adapted to the exact Einstein equations for general strong-field, dynamic spacetimes that have to be calculated numerically. Typically, the equations are three-dimensionally covariant, elliptic, and linear in the kinematical functions (the lapse function and shift vector) that they determine. The gravitational field enters in nonlinear form through the presence of curvature in the equations. We present a flat-space model of such elliptic equations (e.g. for maximal slicing) which suggests that this curvature leads to an exponential decrease in the proper time between time slices at late times. We show how the use of maximal slicing with minimal-distortion observers generalizes the notion of a stationary rest frame to dynamical asymptotically flat spacetimes. In cosmological spacetimes the use of minimum-distortion observers is shown to differentiate between those universes which contain only kinematic time dependence (e.g. open Kasner universe) and those in which dynamical degrees of freedom are present (e.g. mixmaster universe). We examine many examples and construct new coordinate systems in both asymptotically flat and cosmological solutions to illustrate these properties.

The Development of Puberty, the Sexual Début and Sexual Function in Hypospadiacs

The development of puberty, the sexual debut and the sexual function were investigated in a longitudinal study of an unselected material of 220 primary cases of hypospadiacs, treated during the period 1965 to 1969 and followed-up during the period 1965 to 1974. The development of puberty in hypospadiacs strongly resembled that in a normal male population. Out of 121 hypospadiacs between 13 and 30 years of age 66 had had sexual intercourse. The median age for the sexual debut was 16.9 years compared to 16.6 years in a normal male population. Thirty out of 55 hypospadiacs without experience of sexual intercourse were in the age-group 13-16. Hypospadiacs with experience of sexual intercourse continued their sexual function was normal. Forty-one out of 66 were married and 24 out of 41 had children. In order to study the influence of the surgical treatment on the sexual debut and sexual function the 121 hypospadiacs were divided into two groups: those in whom treatment was completed before or at the age of 12 years, and those in whom treatment was completed at 13 years of age or later. The median age for the sexual debut was 15.5 years in the former group and 17.6 in the later group. An interesting finding was that almost half of the hypospadiacs in whom treatment was complted at 13 years of age or later had had a preoperative sexual debut despite the presence of curvature in all cases, and despite the fact that all types of hypospadias were represented. The median age for the sexual debut in this group was 17.1 years.

The Effects of Curvature on the Dissolution Kinetics of Spherical Precipitates

AbstractThe effects of curvature on the dissolution kinetics of spherical precipitates is investigated. This is accomplished by using a modified Gibbs–Thompson equation to represent the composition in the matrix at the precipitate/matrix interface as a function of precipitate radius. In this way one can account for the increasing curvature of the dissolving precipitate. The range of physical parameters for which the effect of curvature may appreciably alter the kinetics of diffusion-controlled dissolution is discussed. The presence of curvature tends to speed up dissolution, being particularly important at long times (i.e., small precipitate sizes) and when the difference between the solute concentration at the precipitate/matrix interface (Cr I ) and in the depleted matrix (C M ) is small. It is shown, however, that curvature will, in general, not sensibly affect the dissolution kinetics even at long times unless the concentration difference (Cr I – C M ) is sufficiently small.

The propagation of surface waves in elastic mediums with slightly curved boundaries of sinusoidal type

The effect of slightly curved boundaries (free surfaces and interfaces) of the elastic mediums on the components of displacement of a particle in a medium due to the propagation of the surface waves has been investigated in this paper. It has been found that along with the usual displacement components for stratified boundaries (designated here as primary components), there exist secondary displacement components arising from the presence of curvature in the boundaries. They are constituted of different harmonic components with their amplitudes proportional to the parameters which measure the extent of curvature of the boundaries. The wave numbers of these harmonic constituents are related to those of the primary components in a definite way decided by the shapes of the boundaries.