Infinitesimal Force Research Articles

A Rational Approach to Reversibility via Carnot’s Lost-Work

The reversibility definition emerging from Carnot’s ‘lost-work’ notion or, equivalently, from considerations of optimal efficiency and lack of dissipation is here qualified as a rational alternative to that which based on Planck’s constant total-entropy criterion resorts to either a sequence of equilibrium states or the action of infinitesimal forces for the definition of the reversible path.

Three-Dimensional Parabolic Cable Element for Static Analysis of Cable Structures

AbstractThis paper presents a three-dimensional inclined parabolic cable element for static analysis of cable structures. After a catenary cable element is briefly reviewed, the three dimensional parabolic cable considered in this paper is presented. The derivation of the stiffness matrix for the element is described by equating the total differentiations of the cable length and its elastic elongation, and defining the stiffness as the ratio of the infinitesimal force increment to the infinitesimal length increment. The static equilibrium equation for a two-node cable element and the procedure for nonlinear structural analysis using the Newton-Raphson iterative method are presented as well. The proposed element can consider an inclined cable without the need for a transformation, and has explicit and simple stiffness formulas compared with those of a catenary element. To validate the proposed parabolic cable element, four example models subjected to static loadings are analyzed using the proposed element,...

Control of soft tissue deformation during robotic needle insertion

Accurate needle insertion into soft, inhomogeneous tissue is of practical interest because of its importance in percutaneous therapies. In procedures that involve multiple needle insertions such as transrectal ultrasound‐guided prostate brachytherapy, it is important to reduce tissue deformation before puncture and during needle insertion. In order to reduce this deformation, we have studied the effect of different trajectories for a 2‐DOF (degrees of freedom) robot performing needle insertion in soft tissue. To obtain an optimum trajectory, we have compared tissue indentation and frictional forces for different trajectories. According to the results of our experiments, infinitesimal force per tissue displacement is a useful parameter for online trajectory update. In addition, the results show that axial rotation can reduce tissue indentation before puncture and frictional forces after puncture. Our proposed position/force controller is shown to provide considerable improvement in performance with regard to minimizing tissue deformation before puncture.

Bacterial recognition of mineral surfaces: nanoscale interactions between Shewanella and alpha-FeOOH.

Force microscopy has been used to quantitatively measure the infinitesimal forces that characterize interactions between Shewanella oneidensis (a dissimilatory metal-reducing bacterium) and goethite (alpha-FeOOH), both commonly found in Earth near-surface environments. Force measurements with subnanonewton resolution were made in real time with living cells under aerobic and anaerobic solutions as a function of the distance, in nanometers, between a cell and the mineral surface. Energy values [in attojoules (10(-18) joules)] derived from these measurements show that the affinity between S. oneidensis and goethite rapidly increases by two to five times under anaerobic conditions in which electron transfer from bacterium to mineral is expected. Specific signatures in the force curves suggest that a 150-kilodalton putative iron reductase is mobilized within the outer membrane of S. oneidensis and specifically interacts with the goethite surface to facilitate the electron transfer process.

Cutting Dynamics and Stability of Boring Bars

Boring bars with a high lengh-diameter ratio (L/D) tend to chatter. The limit of stability depends not only on the boring bar, its fixation and the machine tool, but also on the selected cutting conditions. A one dimensional model of the regenerative cutting is commonly used for simulation. However, this simple model is able to explain the influence of only a few parameters. Attempts to estimate the boundary of cutting stability by simulations with this model often give wrong results. Therefore, at our laboratory an approach to a more accurate cutting model was studied. Besides extension to three dimensions, the model considers the radius of curvature of the cutting tool corner. This allows the very important differentiation between roughing and finishing work. Modelling the thrust force as a infinite summation of infinitesimal forces perpendicular to the cutting edge, its direction can be calculated. Commonly the size of the forces is estimated by an exponential law depending on the thickness of the chip. Our tests showed that this assumption can be used in dynamics also, if the area of cut and the chip thickness are modelled exactly. This paper presents the new cutting model and illustrates its good accuracy in the estimation of the chatter stability when comparing experimental cutting test with simulation.

A further note on finite-strain force and moment stress elasticity

Earlier considerations [4, 6] of the statics and kinematics of force and moment stresses and strains are complemented by the consideration of constitutive relations for an elastic medium. Known variational theorems for stresses and displacements of finite force stress elasticity, and of infinitesimal force and moment stress elasticity, are generalized to the case of finite force and moment stress elasticity.

Bifurcation Criterion and Plastic Buckling of Plates and Columns

Bifurcation Criterion and Plastic Buckling of Plates and Columns

Miniature Ball Bearings

AN invention which, apart from its intrinsic merits as a mechanical development, promises to be of especial interest in a scientific sense, is the introduction by a Swiss manufacturer of a range of miniature ball bearings. Ordinary bearings of this class have been made in sizes varying from half an inch to five feet in diameter overall ; but nothing small enough has been available to satisfy the requirements of small and sensitive instruments. The bearings now obtainable as a result of this invention are of several different types and vary in size from 1 to 22 millimetres in diameter overall. They are thus of suitable size for use in such devices as small motors, recorders, meters, clockwork, tachometers and scientific instruments of many kinds in which measured movements are produced by infinitesimal forces, and friction must be eliminated as far aome cases so higs possible. Comparative tests on these bearings and the jewelled bearings they are intended to replace show advantages under three different modes of operation. The time to damp down a rotary motion was in sh as eight times that when plain pivots were used and twenty times that when tapered pivots were used, though there is a good deal of variation in the results. In an oscillatory test the corresponding figures were about 4 and 15, while in the deviation test the results claimed are also favourable. As these new bearings are obtainable at moderate prices, it is probable that, after adequate trials, they will play an important part in the future construction of scientific instruments. They are being marketed by International Technical Developments, Ltd., Thames House, Millbank, London, S.W.I.