Stress Interference in Axisymmetric Torsion of a Transeversely Isotropic Body

An unbounded transversely isotropic body of revolution containing two spheroidal cavities is subjected to torsion about its axis of elastic symmetry, which coincides with its axis of revolution. At large' distances from the cavities the elastic field approaches the Saint-Venant solution for the torsion of a circular cylinder. The elasticity solution is obtained in series form and numerical results presented for the case of two spherical cavities. Of primary interest is the degree of stress interference between the. two perturbations, as a function of the spacing of the cavities and the values of the elastic constants.Air Force Office of Scientific Research Grant No. AFOSR 82-004

Differential regulation of β2-adrenoceptor and adenosine A2B receptor signalling by GRK and arrestin proteins in arterial smooth muscle

Generation of cAMP through Gs-coupled G protein-coupled receptor (GPCR) [e.g. β2-adrenoceptor (β2AR), adenosine A2B receptor (A2BR)] activation, induces arterial smooth muscle relaxation, counteracting the actions of vasoconstrictors. Gs-coupled GPCR signalling is regulated by G protein-coupled receptor kinases (GRK) and arrestin proteins, and dysregulation of Gs/GPCR signalling is thought play a role in the development of hypertension, which may be a consequence of enhanced GRK2 and/or arrestin expression. However, despite numerous studies indicating that β2AR and A2BR can be substrates for GRK/arrestin proteins, currently little is known regarding GRK/arrestin regulation of these endogenous receptors in arterial smooth muscle. Here, endogenous GRK isoenzymes and arrestin proteins were selectively depleted using RNA-interference in rat arterial smooth muscle cells (RASM) and the consequences of this for β2AR- and A2BR-mediated adenylyl cyclase (AC) signalling were determined by assessing cAMP accumulation. GRK2 or GRK5 depletion enhanced and prolonged β2AR/AC signalling, while combined deletion of GRK2/5 has an additive effect. Conversely, activation of AC by A2BR was regulated by GRK5, but not GRK2. β2AR desensitization was attenuated following combined GRK2/GRK5 knockdown, but not by depletion of individual GRKs, arrestins, or by inhibiting PKA. Arrestin3 (but not arrestin2) depletion enhanced A2BR-AC signalling and attenuated A2BR desensitization, while β2AR-AC signalling was regulated by both arrestin isoforms. This study provides a first demonstration of how different complements of GRK and arrestin proteins contribute to the regulation of signalling and desensitization of these important receptors mediating vasodilator responses in arterial smooth muscle

Three-Dimensional Non-Axisymmetric Anisotropic Stress Concentrations

Unified explicit analytical solutions for the (non-axisymmetric) first and second boundary value problems of elasticity theory for a spheroidal cavity embedded in a transversely isotropic medium are presented. The analysis is based upon solutions of the homogeneous displacement equations of equilibrium in terms of three quasi-harmonic potential functions, each of which is harmonic in a space different from the physical space. Thus, three spheroidal coordinate systems with different metric scales (one for each potential) are introduced such that the three coordinate systems coincide on the surface of the spheroidal cavity. These potential functions are taken in a unique combination of the associated Legendre functions of the first and second kind. Extensive numerical data are obtained for the stress concentration factors associated with axisymmetric and non-axisymmetric problems for a variety of materials. The effect of anisotropy on the stress concentration factor is discussed in much greater detail than has been previously available in the literature.Air Force Office of Scientific Research Grant No. AFOSR 82-004

Distributed of Stresses and Partition of Loads in Gusseted Connections

Load partition and stress distribution in riveted and bolted structural joints are two associated behavioral phenomena which have received continued attention from structural researchers and designers in an attempt to understand better the behavior of multiply fastened joints and to design them adequately. This study presents a basic analysis of various physical parameters and their effects on load partition and stress distribution in gussested connections. The gusseted connection under investigation is a particular type of riveted or bolted connection which has additional variables associated with the shape and size of the gusset plate. Analytical and experimental studies were conducted concurrently to justify the conclusions as well as study the assumptions made in arriving at the analytical models. Analytically, two elastic joint problems were studied: (1) the attachment of tension member by a single row of fasteners to a semi-infinite plate, (2) the similar attachment to a symmetrical tapered gusset plate. The parameters studied include the number of fasteners, the fastener pitch, the edge distance of fasteners, the fastener and tension member flexibilities, and thickness and geometry of the plate. The member to plate connections were evaluated in terms of the load partition among the fasteners as well as the stress distribution at various locations in the plate. It was found that, individually, many of the joint parameters did not appreciably affect the load partition in the connection; however, cumulatively they could have detrimental effects. One parameter, the edge distance severe stress conditions at the edge of plate on the line of loading. The finite geometry plate, studied experimentally, was fabricated and tested with variable geometry or taper of the gusset plate;the plate was loaded by lap plated connected by tight fitting pins. The elastic stress distribution was studied using brittle lacquer techniques and electrical resistance strain gages at specific locations on the gusset. Individual fastener loading was measured using a special technique involving the placement of strain gages on the gusset near the loaded pins. The load partition of the pinned joint was examined for five geometries and variable numbers of fasteners. Geometry did not appreciably affect the load partition until extreme geometries, which resulted in a change of the gusset net cross-sectional area, were reached