Distribution Of Mechanical Forces Research Articles

Abnormal cancellous bone collagen metabolism in osteoarthritis.

Biochemical investigations into the pathogenesis of osteoarthritis have, for the last two decades, concentrated on the mechanisms involved in the destruction of the articular cartilage. Although bone changes are known to occur, the biochemistry of the collagenous matrix within osteoarthritic bone has received scant attention. We report that bone collagen metabolism is increased within osteoarthritic femoral heads, with the greatest changes occurring within the subchondral zone. Collagen synthesis and its potential to mineralize were determined by the carboxy-terminal propeptide content and alkaline phosphatase activity, respectively. These data supported elevated new matrix formation. Our finding of a three- to fourfold increase in TGF-beta in osteoarthritic bone indicates that this might represent a stimulus for the increased collagen synthesis observed. Of additional significance is the hypomineralization of deposited collagen in the subchondral zone of osteoarthritic femoral heads, supporting a greater proportion of osteoid in the diseased tissue. The cross-linking of collagen was similar to that observed for controls. In addition, the degradative potential of osteoarthritic bone was considerably higher as demonstrated by increased matrix metalloproteinase 2 activity, and again the greater activity was associated with the subchondral bone tissue. The polarization exhibited in the metabolism of bone collagen from osteoarthritic hips might exacerbate the processes involved in joint deterioration by altering joint morphology. This in turn may alter the distribution of mechanical forces to the various tissues, to which bone is a sensitive responder. Bone collagen metabolism is clearly an important factor in the pathogenesis of osteoarthritis and certainly warrants further biochemical study.

Fluid flow during active oblique convergence: A Southern Alps model from mechanical and geochemical observations

On the basis of combined mechanical modeling and isotopic observations, we propose a Southern Alps paradigm for application to fluid-flow regimes of active oblique collision zones subject to orographic precipitation. The model is derived from four spatial correlations among patterns in the distribution of mechanical forces that drive fluid flow, structural permeability, and isotopic signature. (1) A strong meteoric overprint of a deep isotopic signature in the inboard adjacent to the plate boundary is associated with oblique reverse faulting. In these rocks, exhumed rapidly from depth, the isotopic signature is dominated by rock advection and limited vertical movement of fluids. (2) The region along the main divide characterized by net expansion, rotation, and steep failure planes is associated with an isotopic signature of anomalously deep fluids in shallow rocks. (3) A high-strain zone within the root of the deforming orogen produces fluids during strain-induced metamorphism. (4) Basinal and meteoric fluids interact at shallow levels in the outboard region, which undergoes net contraction and rotation in an oblique thrust belt. We suggest that these four correlations represent a predictable pattern that is characteristic of all oblique orographic orogens. Rock advection is the dominant process influencing the isotopic signature adjacent to the plate boundary, where strain and erosion rates are high. Water advection exerts the dominant influence on isotopic signature in the region of net expansion near the main divide, where steep structures tap the source of deep fluids in the underlying high-strain detachment and crustal root.

Differential accumulation of intimal monocyte-macrophages relative to lipoproteins and lipofuscin corresponds to hemodynamic forces on cardiac valves in mice.

We have studied the distribution of monocyte-macrophages, lipids, and lipoproteins in sections of aorta and aortic valves from mice fed an atherogenic diet. By immunocytochemical analysis with Mac-1 and F4/80 antibodies, apolipoprotein B antibody, and oil red O staining, three discrete regions were identified: 1) the aortic wall of the sinus of Valsalva, which contained deposits of lipid that colocalized with lipoproteins and monocyte-macrophages; 2) the sides of the aortic valve leaflets facing the ventricle, which did not contain lipids or lipoproteins but which were lined with macrophages that colocalized with lipofuscin; and 3) the sides of the leaflets facing the aorta, which did not contain lipids, lipoproteins, monocyte-macrophages, or lipofuscin deposits. This pattern of distribution resembles the expected distribution of mechanical forces, especially those of systolic blood flow, which in the three areas are predominantly 1) low-shear disturbed flow, 2) high-shear laminar flow, and 3) low-shear laminar flow, respectively. These findings suggest that lesions in the mouse closely resemble early atherosclerotic lesions in humans and other primates with respect to monocyte-macrophage and lipoprotein accumulation. The results also strikingly demonstrate that the accumulation of monocyte-macrophages and lipoproteins can occur independently, with spatial differences corresponding to the distribution of hemodynamic forces.

Distribution of mechanical forces in magnetised material

Distribution of mechanical forces in magnetised material

Distribution of mechanical forces in magnetised material

Distribution of mechanical forces in magnetised material

Distribution of mechanical forces in magnetised material

Distribution of mechanical forces in magnetised material

Discussion on “Distribution of mechanical forces in magnetised material” and “Evaluation of magnetic energy density in magnetised matter”

Discussion on “Distribution of mechanical forces in magnetised material” and “Evaluation of magnetic energy density in magnetised matter”

On the linearized theory op flow around bodies. Method of force sources

The method of force sources is proposed for solving linear problems related to the interaction between rigid bodies, and fluids, or gases. Method is based on the introduction of perturbation force sources into equation of motion of fluid media. Boundary conditions at the rigid body surface make it possible to reduce the problem of hydrodynamic reactions to an integral equation defining the function of force sources. Method is illustrated by the solution of three simple problems in the field of acoustics, and of viscous, and compressible media flow around bodies. In the linearized theory of flow around rigid bodies, as well as in acoustics, an important part of the sound wave generation analysis concerns the determination of hydrodynamic reactions of the medium on moving, pulsating, or oscillating bodies. Such reactions make themselves felt as constant, or variable mechanical forces, such as drag and lift, or in the case of sound wave emitters, as the wave resistance. Various methods had been proposed for the computation of such forces, as for example, in the monographs [1 to 6]. Here, a different approach to the problem of determination of surface forces exerted by liquids and gases on the rigid body is proposed. By resorting to the formalism of the generalized functions it is possible to introduce into the equations of motion of fluid media a perturbation source in the form volume density of forces exercised by the body on the gas. The distribution of surface tension entering into the expression of this force is selected in such a manner as to satisfy boundary conditions at the body surface. It becomes possible with the use of this device to reduce the problem of determination of forces acting on the body surface to the solution of certain Integral equations. The proposed method is in all respects completely analogous to the well-known method of sources and sinks [1 to 1]. Both methods reduce the problem of interaction between body and gas to the solution of Integral equations. The method of sources and sinks, however, leads to an integral equation which describes the distribution of fictitious sources and sinks in the volume of the body having the density of the medium, while the method of force sources yields an integral equation which directly defines the distribution of mechanical forces over the surface of the body (∗). We may note that the method of force sources had to a certain extent been already used in papers [6 and 7] for the determination of sound radiation by means of point-force sources.

Distribution of mechanical forces in magnetised material

Although the total force on a piece of iron in a magnetic field is calculable by well known methods, the factors governing its distribution over the iron are less well understood. It is shown that the conceptions of iron as an aggregation of dipoles or of current loops are both inadequate for this purpose, but a combination of the two can be used under certain conditions and leads to the Helmholtz force formula. Maxwell's formula, based on the dipole concept, is in error. The effect of nonlinearity in the iron characteristic is discussed, and also that of a permeability which varies when the material is deformed. The latter aspect is developed for a particular ideal material, several examples being discussed; it is thereby shown that the variation of permeability with deformation is crucial in determining the distribution of forces.