Wire Displacement Research Articles

The application of percolation theory of the analysis of sieve blinding

Percolation theory is applied to interpret the patterns formed on the surface of sieves by blinding. A stochastic model has been developed to simulate the blinding process. The results from this model are compared with predictions using statistical theory, giving rise to polynomials in P, the probability of blinding of an aperture, and with experimental results. The agreement between these models is good, indicating that the approach is valid in describing conditions of a sieve after processing. The critical probability computed from the model is in excellent agreement with published data for a square lattice. Under certain conditions experimental results were found to deviate from the predictions of the model. The frequency of formation of linear clusters was much higher than expected. This was shown to be due to displacement of wires on the surface of the sieves and was probably due to the method used to clean the sieves, that of brushing the surface. Subsequent experiments have proved this to be the case and careful cleaning with air jets was shown to overcome this problem. By modifying the simulation model to account for displacement of wires identical results were obtained, confirming both the experimental observations and the applicability of the model to this process. General wear over a sieve brought about by erosion was also investigated. This was shown to have little effect on the cluster pattern produced. This analysis is able to detect defects in a sieve or screen by analysing the blinding pattern and it could be used to assess the quality of material for manufacture of sieves or to check the performance of sieves in use.

多軸応力下のコンクリートのひずみ測定方法

The purpose of this study is to propose a method of strain measurements under multi-axial stress condition. By adopting the cube specimen, we can apply the load different from each other in three directions. At the triaxial test, six steel brushes covered the specimen, and there was no space to put wire strain gages or displacement devices on the surfaces of the specimen. Therefore, the cube specimen with chamfered edges was selected to measure strains by utilizing the chamfered edges. Six pairs of displacement measuring devices were set on the chamfered edges of the specimen in three directions (α, β, γ) as shown in Fig.2. The deformation in a specific direction was measured as the sum of the outputs from a pair of displacement devices placed in the diagonal and opposite edges in the same direction of the specimen. The strains, ε_X, Ε_Y and E_Z in X, Y and Z directions can be written in the equation (10), as the terms higher than the second order are negligibly small. The experimental strains that were measured in the manner described above are compared with the strains that were measured with wire strain gages mounted on its sides, both in the uniaxial compression test of the same specimen. The stress-strain relations of the two were almost the same, so that the validity of the method of strain measurement proposed in this study is experimentally proved.

Revision hip surgery using the straight-stem Muller prosthesis

Thirty-two cemented revision hip arthroplasties done with a straightstem Muller prosthesis were reviewed an average of 3 years after operation (range, 2–4.4 years). Acetabular revision, performed in 29 cases, was done with a support ring, mesh, or bone graft in 18 of 29 (62%) cases. Acetabular and femoral cement pressurization techniques were not used. Trochanteric osteotomy was done in 15 cases (47%). The average patient age was 60.2 years (range, 20–85 years). Based on the clinical rating system of Swanson and Evarts, there were 21 (65.6%) excellent, 2 (6.3%) good, 8 (25%) fair, and 1 (3.1%) poor results. The clinical outcome was better after revision from a resurfacing arthroplasty (87.5% good/excellent results) than from uni/bipolar or total hip arthroplasty (60%). Radiographic examination suggests that two femoral components and one acetabular component are loose. These patients have a fair clinical rating. None have been revised. Trochanteric wire breakage (60%) and displacement (26.7%) was common if trochanteric osteotomy was done

Displacement of optic nerve head in response to short-term intraocular pressure elevation in human eyes.

Mechanical movement, reflecting compression within the lamina cribrosa, has been suggested as an initiating event in the production of damage in glaucoma. Reversible movements within the lamina cribrosa were sought and studied by characterizing the displacement of fine platinum wire following short-term elevation of intraocular pressure in 13 enucleated human eyes. With IOP elevation, maximum movement in the optic nerve occurred near its center, with minimum movement at its periphery. The difference in movement between these two locations increased with increases in IOP. However, the greatest displacement per unit of IOP elevation occurred at the lowest IOP. Resistance to further displacement occurred as higher IOP was reached. The differential mechanical displacement observed may initiate damage in open-angle glaucoma by causing compression of the vessels and/or shearing of axons within the lamina cribrosa.

A two-component dynamic wind tunnel balance for mounted insects

A dynamic force balance has been developed for the measurement of the instantaneous lift and drag components of an insect flying fixed in a wind tunnel. The force balance is a simple taut 'string' with fixed ends; in this work a live insect is mounted near the string midpoint. The miniscule wire displacements due to imposed forces are optically detected and interpreted as forces by an electromagnetic calibration procedure. The system response is strongly frequency-dependent, but this posed no serious problem for the measurement of periodic forces such as lift and drag fluctuations due to wing beat.

Effects of ultrasonically produced shearing stresses on enzyme systems

Solutions of the enzymes catalase and malate dehydrogenase have been exposed to ultrasonically produced shearing stresses for period of up to 90 min. These enzymes were sonated by placing a resonant length of tungsten wire into a 0.3‐ml sample and driving the wire in transverse oscillation at 20 KHz. After sonation, the enzyme activity was determined spectrophotometrically. Catalase was not inactivated under any of the experimental conditions used. Malate dehydrogenase was found to be inactivated for wire displacements greater than 30 μm. Since no temperature rise or cavitation were detected in the treatment vessel, the mechanism for inactivation is believed to be shearing stresses associated with acoustic micro‐streaming. For conditions of the experiment, the magnitude and duration of the shearing stress are, respectively, 3000 dyn/cm2 and 2 ms. The enzyme was inactivated at an exponential rate which was inversely proportional to enzyme concentration. [This work was supported in part by the American Heart Association‐Maine Affiliate.]

Pacemaker failures characterized by continuous direct current leakage

Pulse generator failure caused by continuous leakage of direct current through an output capacitor has not previously been appreciated. Routine post-explant electronic evaluation has identified the defect in six implanted and one external pulse generator. The constant direct current in the implantable units, 0.14 to 0.26 milliamperes, is in the range that produces ventricular arrhythmias in dogs although this did not occur in our patients. Evidence of local myocardial damage existed in four cases and of electrode deterioration in three. The implant failures occurred without warning and in four cases within 2 weeks of demonstrated normal function, blunting the predictive benefits of pacemaker monitoring programs. Capacitor discharge circuits used in many pacers are inherently capable of developing direct current leakage in the event of output capacitor short circuit. In one model of pacemakers such continuous direct current leakage caused 8.3 percent (3 of 36) of pulse generator failures, widely scattered in time at 23, 27 and 46 months after implant. Capacitor short circuit causing constant direct current leakage can masquerade as primary battery failure and should be suspected when cessation of pacer function is associated with increased threshold or poor myocardial electrogram without evidence of wire break or displacement.

Release of serotonin from human platelets by hydrodynamic shear

Fresh human platelet-rich plasma was prepared from adult blood anticoagulated with EDTA. The platelets were allowed to incorporate tritiated serotonin, washed twice, and resuspended in autologous plasma. Samples of 0.2 ml were sheared for 5 min at 23°C by the acoustic microstreaming field generated around submerged portions of a transversely oscillating steel wire (115-μm radius driven at 20 kHz). Immediately following irradiation, each sample was centrifuged for 5 rain to sediment intact cells and debris, and the quantity of serotonin released into the supernatant was measured using a liquid scintillation counter. It was found that there was no measurable threshold below which serotonin was not liberated, after allowances had been made for the spontaneous release of serotonin induced by the centrifugation procedure. In addition, it was found that the amount of serotonin released by irradiation alone varied with the square of the wire displacement amplitude. Hydrodynamic shear stress and velocity gradient are both proportional to the square of the wire displacement amplitude and are probably the agents responsible for the release of serotonin (together with the simultaneous release of clot promoting and/or accelerating factors).

DNA degradation by acoustic microstreaming

Calf thymus DNA in saline buffer (SSC) was irreversibly degraded by the acoustic microstreaming field generated around submerged portions of a transversely oscillating steel wire. Free radical scavenging agents (e.g., I131) were firmly (covalently?) bound to sheared fragments, strongly indicating covalent bond rupture during cleavage of the DNA backbone. All molecular weight estimations were made by viscometry under “zero-shear” conditions and showed that DNA of initial average molecular weight 9.34 × 106 daltons was not degraded until the wire displacement amplitude exceeded 18 μm. At any given amplitude above this threshold, the measured molecular weight decreased asymptotically with time of exposure and was usually within 5% of its limiting value after 5 min. Each original average molecule was halved after 5 min shear at 28 μm and quartered at a displacement amplitude of 59 μm. Approximate lower limits were estimated for the velocity gradients existing near the wedge-shaped wire trip; this gave a critical shear rate of about 105 sec−1 to cleave each original DNA molecule, and an average breeding force of about 5 × 10−5 dyn.

A mechanical resonance detector for multiwire proportional chambers

The mechanical tension in the anode wires of a multiwire proportional chamber must be sufficient to prevent wire displacement due to electrostatic forces between wires but must not exceed the breaking strength of the wires. A technique is described for interferring the tension by measuring the mechanical resonant frequency of the wires. It employs a servomechanism which uses the small capacitance change of the selected wire to tune a variable frequency oscillator to the mechanical resonance. Since it is not necessary to observe the wires visually, the technique is applicable to closed chambers in inaccessible locations.

A possible alteration in the permeability of ascites cell membranes after exposure to acoustic microstreaming.

ABSTRACT Single-cell suspensions of mouse Ehrlich ascites cells in isotonic saline were subjected to a small-scale acoustic microstreaming field generated around a transversely oscillating wire. Cells sheared at wire displacement amplitudes below the threshold for membrane rupture contained more fluid than their controls. Evidence is presented which suggests that a slight change has occurred in the permeability of the plasma membranes of the intact sheared cells.

An experimental method of measuring the damping of a structure when subjected to a spatially-distributed random vibration

The design of a railway catenary is subject to multiple decisions regarding the geometry of the system. In particular, the horizontal geometry of the contact wire determines the evolution of the wear of the contact wire and contact strip over time. The horizontal geometry is obtained through the stagger, a lateral displacement of the contact wire at the supports. The value of the stagger, length of the span, curvature of the track, and train speed within the span determine the speed at which the contact point between the wire and the pantograph moves over the contact strip from side to side. A wider stagger corresponds to a larger area of the wear distribution over the contact strip. However, the speed at which the contact point moves over the strip is also important to the wear due to the sliding contact. Thus, the catenary design affects the contact strip wear through the lateral speed of the contact point. In this paper, a study of the lateral speed effects on contact strip wear is presented. The findings include a model of the lateral speed effect on the wear and a recommendation for a lower limit value for the lateral speed of 330 mm/s.

Disorganization and Disruption of Mammalian and Amoeboid Cells by Acoustic Microstreaming

Single-cell suspensions of mouse Ehrlich ascites carcinoma and the amoeba Hartmanella castellanii were subjected to the small-scale acoustic microstreaming field set up around a partially submerged transversely oscillating wire. A resonant length (1.69 cm) of thin steel wire (0.023-cm diam) was driven transversely from one end at 20 kHz and a system of flexural standing waves developed. The free end of the wire was immersed in 0.3 ml of the dilute cell suspension and the maximum displacement amplitude of the submerged portion measured with a traveling microscope. The amoebae and mouse cells were disrupted in a reproducible manner when the maximum wire displacement amplitude exceeded the critical values of about 10 and 28 μm respectively. Electron micrographs of amoebae sonicated for 5 min at displacement amplitudes close to the critical value for disruption suggest that some form of intracellular streaming might have occurred. However, this is unlikely in the mouse cells where intracellular adhesion is so strong that the cell membrane may be partially or completely removed without dispersing the cell contents. Intact sonicated mouse cells exhibit a variety of changes which suggest that a small alteration in fluid transport has occurred.

The dynamics of a current collection system for an electric locomotive

The motion of an overhead trolley wire, suspended at equal intervals by stiff springs, in response to a pantograph moving with constant speed is analysed. The pantograph is modelled by two discrete masses connected by springs and dampers. Away from the supports the inertia and elasticity of the pantograph can be neglected and a simple solution for the wire and pantograph displacement is obtained. Near a support this solution is not valid as it predicts discontinuities in the vertical pantograph velocity. A different first approximation is then required in which the support elasticity and the pantograph inertia and elasticity must be included. This problem is reduced to that of solving a system of four linear differential equations containing one term with a stretched argument. The numerical and asymptotic solution of such a system is discussed and results are obtained for the contact force and pantograph displacement near a support in typical operating conditions. This disturbance at the support is propagated with the wire wave speed and reflected at the subsequent support, thus interacting with the pantograph again. This interaction is analysed and a uniformly valid solution obtained for the contact force over a complete span. Some conclusions are made about possible operating conditions in which loss of contact between the pantograph and the wire may occur.

Diffusion chimique et effet kirkendall dans la phase cubique centree du systeme plutonium zirconium

Soluté diffusion and thé Kirkendall effect were studied in the εβ body centred cubic phase of the Pu-Zr system, with the technique of welded couples. The concentration/penetration curves obtained by electron probe microanalysis, using the Lα 1 wavelength of plutonium, use of which leads directly to true concentrations, were interpreted by the methods of Hall and Matano. The chemical diffusion coefficients measured from 650 to 900 °C increase with plutonium concentration and obey Arrhenius' law. Activation energies range from 44 to 18 kcal/mole as the concentration ranges from 20 to 60 at% plutonium. They vary, therefore, in the same sense as the melting point of the εβ phase (melting point of plutonium 660 °C; melting point of zirconium 1853 °C). The existence of a Kirkendall effect in the Pu-Zr system has been shown by the displacement of inert wires, initially placed in the welding plane, towards the element which diffuses more rapidly. Each of the elements which constitutes the diffusion couple is therefore characterised by its own intrinsic diffusion coefficient D Pu or d zr . The variation of the intrinsic diffusion coefficients, of the flux j pu and J Zr of the two species and of the mean “lattice velocity” V as a function of concentration, was studied by the technique of “incremental couples”. These couples were made from a pellet of pure zirconium attached to a pellet of Pu-Zr alloy of different compositions in the various samples. Two methods are possible for measuring D Pu and d zr . The first makes use of the two equations of Darken: D ̃ = N PuD Zr + N ZrD Pu (1) ( D Pu − D Zr )( ∂N Pu / ∂x) (2) where V is the speed of displacement of the Kirkendall plane measured micrographically, D ̃ is the chemical diffusion coefficient calculated from the composition of the Kirkendall plane. The second method uses eq. (1) together with Heumann's relation: D Pu / D Zr = J' Pu / J' Zr (3) where J' Pu and j' zr are the integrated fluxes during the diffusion anneal across the marked plane. J' Pu and J' Zr are determined micrographically from concentration/penetration curve when, by micrography, one knows the position of the plane of the wires. A statistical error calculation shows that the second method, which is in any case experimentally simpler, is more exact than the first method, but it presupposes that the Kirkendall plane is displaced as the square root of time. In the range of concentrations studied (15 to 16 at% plutonium) it is plutonium which diffuses the more rapidly. The ratio D Pu / D Zr increases with plutonium concentration, and ranges from 1.5 to 6. The flux j pu and the mean atomic velocity have their largest value near the Kirkendall plane, while on the other hand J Pu and J Zr do not appear to reach extreme values simultaneously. This study has shown that the equations of Darken and Heumann are well able to interpret the phenomenon we have studied, within the limits of our experimental errors. On the other hand, the Kirkendall effect observed in the Pu-Zr system shows in an unambiguous manner that diffusion in this system takes place by a mechanism which involves the nonconservative migration of defects (vacancies or interstitials).