Optical piston in glasses

Abstract

Light-driven electron transitions between different traps in the direction opposite to an electric force eE (e is the electron charge and E is the static electric field) are studied. We show that in Ge-doped silica fibres the electrons are transfered predominantly between different Ge centres at concentrations ≥ 10 mol.% and dominate over the ordinary electron mobility in the direction of the force eE. Light acts as an optical piston, moving electrons against the acting force and therefore resulting in positive feedback in response to static electric field. This feedback amplifies the weak initial electric field up to magnitudes of the order of 10⁵?10⁶ Vcm^?1. This strong field breaks the initial inversion symmetry and allows effective second harmonic generation.     

Atomic force/tunneling microscope and its application to the study of dielectric breakdown of a diamond film on silicon

A simple design is proposed for an atomic force microscope where the force of interaction between the tip and the surface of the sample is recorded directly using the piezoceramic of an XYZ-manipulator. The force signal is used as a feedback signal to keep the gap between the tip and the surface constant, and its electrical conductivity is recorded at the same time. Results of modifying the electrical conductivity of a thin diamond film after electrical breakdown are presented. Pis’ma Zh. Tekh. Fiz. 25, 80–86 (March 12, 1999)     

Quality control and monitoring of NSM CFRP systems: E-modulus evolution of epoxy adhesive and its relation to the pull-out force

BackgroundIn Fibre-Reinforced Polymer (FRP) applications, the mechanical behaviour of the strengthening system strongly depends on the epoxy adhesive, particularly at early ages.MethodsThe present paper describes the application of an innovative technique (termed EMM-ARM: Elasticity Modulus Monitoring through Ambient Response Method) for continuous monitoring of the stiffening process of an epoxy adhesive used in structural reinforcements applications. A simultaneous study of direct pull-out tests with concrete specimens strengthened with near-surface mounted (NSM) carbon FRP laminate strips was carried out to compare the evolution of bond performance with the E-modulus of epoxy since early ages.ResultsThe peak pull-out force and the epoxy E-modulus obtained by EMM-ARM exhibit very similar evolution kinetics.ConclusionsA relationship between the evolution of epoxy E-modulus and the maximum pull-out force is assessed, highlighting the potential of applying EMM-ARM for quality control and decision-making assistance of NSM systems.     

A New Computer-Aided Apparatus for Simultaneous Measurements of Water Uptake and Swelling Force in Tablets

Abstract

Water uptake and disintegrating force development have frequently been related to tablet disintegration properties.

Water penetration into compressed tablets has been studied by many authors using modified Enslin apparatus. Meanwhile, in previous papers by our group, a great deal of attention has been paid to the measurements of disintegrating force and to the kinetics of force development.

Given the fact that water penetration and swelling force development are related to each other, a new apparatus was set up which allows simultaneous measurements of water penetration and force development. It consists of a modified apparatus for force measurements, integrated with a modified Enslin apparatus. Both force and water uptake data were collected by a computer and stored for subsequent analysis.

Fitting of both water penetration and force development curves was performed with a commercially available software package for non-linear regression analysis.

This enables an examination of the relationships between force development and water penetration on the basis of homogeneous rate parameters. The apparatus was validated on a model tablet formulation based on dicalcium phosphate dihydrate with carboxymethylstarch.

Besides application in fast disintegrating tablets, this approach could be useful to study the behaviour of swelling-controlled release systems, in which the release mechanism (swelling force) is triggered by water penetration.     

Analysis and model of the crack bridging mechanisms in a ductile fiber reinforced ceramic matrix composite

The force resisting the opening of a crack in a brittle matrix composite that is bridged by ductile fibers was studied (Acta Mater. 46(18) (1998) 6381; Acta Mater. 45(9) (1997) 3609). to gain a generic understanding of the crack-bridging process by ductile reinforcements. The matrix was alumina, initially containing a parallel array of fine cylindrical holes. Molten Al was cast into the holes to produce the fibers in situ. A crack was gently introduced to traverse the specimen. The matrix halves were pulled apart in a controlled manner to open the crack. The resisting force increased proportionally to the crack opening over a wide range until a force plateau was reached. Thereafter the force diminished very gradually until failure intervened. Analysis of this counter-intuitive behavior indicated that the excellent adhesion between the fiber and the matrix in combination with the large thermal expansion mismatch must have led to extensive but spotty debonding already from the start of the start of the crack opening. In spite of the well-known ductility of the fibers, the bridging showed quasi-elastic behavior over much of the crack opening. Necking appeared to be suppressed until the separation approached failure. Detailed modeling is offered to provide interpretation of this observed behavior.     

The damping of sandwich cantilever beam

Abstract

The natural vibration damping of sandwich cantilever beam has been investigated. A theoretical development for damping calculation has been carried out by considering shear force, normal force and bending moment for both face and core layers. The ratio of thickness between the face and core layer is not constrained. Experimental results show that theoretical calculation is quite satisfied. When the elastic modulus of the core layer is larger than that of the face layer, a simpler and more convenient formula has been developed to calculate the loss factor.     

Adhesion mechanism of friction in nanotribocontacts

An adhesion mechanism is proposed for the frictional force between the tip of an atomic force (friction) microscope and a surface, whereby the frictional force is determined by the energy of breaking and formation of adhesive bonds for a discrete microslide step of length close to the atomic radii of the contacting bodies. Calculations were made of the frictional force as a function of the radius of curvature and the distance between the tip and the surface for silicon-silicon and tungsten-iron contacts. Pis’ma Zh. Tekh. Fiz. 24, 44–50 (October 12, 1998)     

Normalized load‐deflection curves of lateral piles in homogeneous elasto‐plastic soils

Abstract

In this paper, the procedure of normalizing load‐deflection curves of lateral piles in a homogeneous elasto‐plastic soil is presented. An analytical method using subgrade reactions reveals that the normalized relation of load‐deflection exists for force, moment or combined load. The normalized curves for force and moment load fit very well with the predictions using the equations. For the combined load, the normalized curves are distributed between the force and moment load curves, so it is easy to use interpolation from a family of curves. These normalized curves provide a very convenient way for calculating the pile load or deflection in the design stage.     

Ergonomics as a foundation for a science of purpose

The argument here is at once simple and profound. The first premise is that technology is the most powerful 'shaping' force on the planet today. The second premise is that individual impact on this force is most evident at the human-machine interface. A corollary of the second premise is that unity in intention is to be found in the aggregate of individual actions. Ergonomics, as the pursuit that mediates between operator and technology, is, therefore, the first step along the path to a science of intention as expressed in 'world' changes. Some initial observations on the integration of existing behavioural theories represent the first step along this royal road.     

THE RESPONSE OF UNSYMMETRIC LAMINATES TO SIMPLE APPLIED FORCES

SUMMARY

The snap-through behaviour from one cylindrical configuration to another of an unsymmetric (O₂/90₂)T cross-ply laminate is modelled using a simple Rayleigh-Ritz approach. Snap-through is caused by two opposing moments which are produced by opposing forces acting through known moment arms. The snap-through force is predicted, and the predictions are compared with experimental measurements. Correlation is good. The experimental set-up used to measure the force is described, as are the details of the Rayleigh-Ritz approach.     

Comparison of glide mechanisms in hcp Ti and Ti3Al

Several dislocation glide mechanisms are studied in Ti and Ti₃Al by means of in situ straining experiments in a transmission electron microscope at various temperatures. The prismatic glide of α titanium occurs by the jerky motion of straight screw a-dislocations subjected to a frictional force. An explanation for the discontinuity in the temperature dependence of the corresponding activation area is proposed, on the basis of the experimentally measured variation of the corresponding dislocation jump length. In Ti₃Al, superlattice 2a-dislocations exhibit two different dissociation modes in prismatic planes corresponding to highly different antiphase boundary energies. The properties of these two types of dislocation are compared and discussed. It is shown that the motion of 2c+a superlattice dislocations in pyramidal planes is controlled by a new mechanism: the self-nucleation of small-size obstacles as the result of irreversible atomic displacements. The tension/compression asymmetry observed between type 1 and type 2 pyramidal planes is finally discussed.     

The Measurement of Resulting Forces on a Roller Compactor

Abstract

In this study, a Pharma 250 Sahut-Conreur roller compactor and a MG 333 Frewitt oscillating granulator is used in order to obtain granules to be compressed. The compactor is fitted with strain gauges which measure the forces during compaction. The autors demonstrate that the force measured is a fonction of the rate between the speed of the feeding screw and the speed of the wheeles; its depends on the pressure applied and on the configuration of the machine.     

Liquid film simulation of Zener grain boundary pinning by second phase particles

Abstract

The geometry of the interaction of second phase particles with migrating grain boundaries has been studied using a liquid film simulation. The geometries observed show that the perimeter of intersection between boundary and particle can be complex, often not lying in a single plane through the particle. The curvature of the boundary when in contact with the particle is also complex, sometimes displaying double curvature and often of opposite sign. These observations have been used to modify previous calculations quantifying the grain boundary pinning effect. Measurements from the photographs of these interactions have been applied to a force equilibrium approach for calculating the pinning force and these results are found to be in good agreement with values obtained using an energy analysis based on grain boundary shape change.

MST/1259     

Three-dimensional force calibration of optical tweezers

Abstract

We demonstrate a method for 3-dimensional force calibration of optical tweezers by recording the trapping dynamics of polystyrene beads. This is realized by time-resolved detection of the horizontal and vertical position of a bead which is drawn to the focus of a laser beam. The method provides real time characterization of the force profile of an optical trap in all directions.     

Stress induced martensite transformation texture in AISI 304 austenitic stainless steel

Abstract

The phenomenological theory of martensitic transformation was applied to a tension induced martensitic transformation in an AISI 304 austenitic stainless steel in order to estimate the transformation texture. Input data were obtained from the published literature. Calculated pole figures were constructed assuming a variant selection process based on Patel and Cohen’s theory, which emphasises that a mechanical component of free energy is the driving force for martensitic transformation at temperatures above martensite start M_s. The results showed a remarkably good match between the calculated and published measured data.     

Instability of the stressed surface of a highly viscous liquid

A new type of hydrodynamic instability is observed in a highly viscous liquid whose free surface is exposed to an external force acting at a certain angle to the normal. The physical reason for this instability is the redistribution of energy between the tangential and normal components of the free surface stresses. Pis’ma Zh. Tekh. Fiz. 25, 1–6 (November 26, 1999)     

Cavity generation in dental enamel using a copper-HyBrID laser

Applications of Cu-HyBrID laser (copper laser with Hydrogen Bromide In Discharge) in Dentistry and AFM (atomic force microscopy) evaluations of dental tissues irradiated by laser are seldom reported in the literature. This work presents an AFM investigation of the cross-section of a cavity generated in human dental enamel by laser thermal evaporation using the Cu-HyBrID laser. The results exposed the structural and morphological differences between the fused and non-fused dental enamel, provide qualitative information about the susceptibility of these tissues to abrasive polishing, and revealed the extension of the thermal damage. Quantitative information concerning the wall thickness and the dimensions of the cross-section of non-fused enamel rod were also obtained.     

Time and frequency domain identification and analysis of a permanent magnet synchronous servo motor

Abstract

This study employed the approach of non‐linear autoregressive moving average model with exogenous inputs (NARMAX) to analyze the dynamics of a Permanent Magnet Synchronous Motor (PMSM). The non‐linearity in PMSM including cogging force, reluctance force and force ripple is difficult to estimate. By using the NARMAX approach, thrust‐speed relationship and thrust‐position relationship could be analyzed by identifying both time and frequency domain models of the system. The frequency domain analysis is studied by mapping the discrete‐time NARMAX models into generalized frequency response functions (GFRFs) to reveal the non‐linear coupling between the various input spectral components and the energy transfer mechanisms in the system. From the results, the interpretation of the higher‐order GFRFs has been comprehensively studied and non‐linear effects have been related to the physical models of the systems.     

PARAMETERS INFLUENCING TONER CHARGING CHARACTERISTICS IN ELECTROPHOTOGRAPHIC PRINTING

ABSTRACT

The charge-to-mass ratio, q/m, of a two-component developer is the important factor in an electrophotographic system, since the toner charge controls the developed tone mass and the print quality. This article investigates the charging properties of differently shaped toners (spherical and irregular), and carrier particles that differ in their composition and surface oxide layer thickness by adjusting the applied current. The parameters for toner charging involving the mixing force, the toner concentration, the shape of the toner, the carrier type, and the current of the carrier surface are studied. The print quality is evaluated by focusing on the solid density, 60 and 40% halftone densities, background density, and edge sharpness of the characters. An explanation of the force between the toner and carrier particles is proposed.     

Characterization of Talc Samples from Different Sources

Abstract

Nine different kinds of U.S.P. grade talc samples were examined for variations in density, particle size, surface area, tendency of preferred orientation, and maximum ejection force. It was found that U.S.P. grade talcs varied in physical properties. The relationships between various physical properties of talc were analyzed using the Pearson's correlation of coefficient. The results suggested that the talc sample with a higher tendency of preferred orientation has closer bulk packing and talc with lower bulk density and higher surface area requires less peak force to break the tablet/die-wall adhesion.