Toshihiro Iwaki

A thermoelastic analysis of the thermal stress produced in a semi-infinite cylindrical single crystal during the Czochralski growth

Abstract The thermal stress produced in a semi-infinite single crystal during the growth by temperature variations is analytically obtained and numerically calculated for various Biot numbers and Peclet numbers. The magnitude of the thermal stress is mainly determined by the Biot number. The Peclet number modifies its profile along the axis. The residual stress after the growth is explicitly obtained. Its magnitude is as high as a third of the maximum thermal stress produced in the crystal during the growth and it is never negligible. The resolved shear stresses for {111}〈110〉 slip systems in an fcc crystal are also calculated for the following growth directions: 〈;100〉, 〈110〉 and 〈111〉. From the cross-sectional patterns of the total resolved shear stress with and without the plane strain assumption , it is concluded that the plane strain assumption is not always satisfactory in evaluating the thermal stress in the crystal during growth. Finally, the relation between the resolved shear stress and the dislocation distribution in the crystal is discussed.

Stress-optic law in a single crystal and its application to photo-anisotropic elasticity

A general stress-optic law in a plate made of a single crystal with birefringence is developed, the plate has an arbitrary crystallographic direction. From the general stressoptic law, a condition for obtaining stress distributions in the plate under a plane stress state is derived. Some optical and mechanical properties when the plate is used as a photoanisotropic model are also explained. Experiments on silicon beams in pure bending are performed by using an infrared photoelastic method. Experimental results show that the stress-optic law is valid. The optical and mechanical properties of silicon beams are shown in tables.

Transient thermal stresses in fully and partly cooled circular rings

The constraint associated with the direction of the thickness of a thin photoelastic circular-ring model is experimentally proved to occur and it is compared with the theoretical result; the constraint is induced by thermal loads. The method for dealing with the constraint and for obtaining a transient thermal stress under plane-stress conditions is applied to study the thermal stress of the circular ring partly cooled from the inside cylindrical surface. It is found that the thermal stress of the fully cooled circular ring is not always greater than the partly cooled one.

Transient thermal stresses in a strip with an eccentric hole

A procedure is presented for dealing with the constraint associated with the direction of the thickness of a thin model and for obtaining transient thermal stresses under plane-stress conditions; the stresses are induced by severe thermal loads. Thermal-stress-concentration factor in an unrestrained strip with an eccentric circular hole placed near the thermally loaded edge is obtained. One straight edge of the strip is cooled and the others are insulated. Consequently, two cases for which the hole acts remarkably as a stress raiser are found.

Molecular Dynamics Simulation of Heat Transport in a Nanoribbon by the Thermal Wave at Different Durations of Pulse Heating

In recent year, progress has been made in the study of ballistic heat flow and phonon scattering by phonon spectroscopy and phonon-imaging techniques. Regarding the femtosecond laser application to nanostructures, phonon generation in nanoscale electronics is the focus of interest in the investigation of the mechanism of thermal wave formation at different heating pulses and conditions for heat flux propagation in nanostructures. We test an atomic model of thermal transport in a nanoribbon after a few picosecond pulse heating that leads to the simultaneous presence of two modes, namely, coherent phonons and diffusion, by molecular dynamics (MD) simulation. Our main goal is to investigate the characteristics of the highest magnitude vibrational motion of wave front atoms at different heating pulses and ascertain their correspondence to a single longitudinal optical phonon. To this end it is shown that in the MD model, the equations of heat flux taken through the boundaries of a corresponding sampling area can resolve coherent phonon motion with high resolution when translational and vibrational modes are evaluated separately. Such a definition of heat flux allows the tracing of formation and dynamics of a single phonon. It is applied for different times of heating of a nanoribbon sample. The mechanism underlying the decay of phonons into diffusion is also probed, and energy conversion over the nanoribbon is evaluated. The relevant size of the area for the temporal and spatial flux resolution of a coherent phonon in the MD model is confirmed.

Effect of pulling direction on resolved shear stress produced in single crystal during Czochralski growth

Abstract The resolved shear stresses (RSSs) in a Czochralski grown fcc single crystal during and after pulling are calculated numerically for various growth directions. The fcc crystal has twelve RSSs of which only five are independent. The total of twelve RSSs, the total of five larger RSSs, and the maximum RSSs are obtained to evaluate the contribution of each RSS to dislocation generation or dislocation density. From their cross-sectional patterns, it is found that the 〈111〉 growth direction is the most advantageous for the reduction of RSS. Finally, the relation between the cross-sectional patterns of the three RSS measures and some etch-patterns is discussed.

Finite-dimensional decentralized VS-MRAC of non-linear interconnected distributed parameter systems

Abstract We propose a design method for finite-dimensional decentralized VS-MRAC of a class of large-scale non-linear interconnected distributed parameter systems with bounded input and output disturbances. Each equivalent control is approximated by each average control and the norm of the output error vector can be made asymptotically arbitrarily small without the ℳ-matrix condition, independently of the reference inputs and in spite of the presence of non-linear interconnections, unmodelled dynamics and disturbances. Furthermore, it is assured that all signals in the closed-loop system are globally ultimately uniformly bounded. Finally, we show the effectiveness of the proposed method by using a numerical example.

New rubber-band loader to facilitate use of hemorrhoid ligator

The placement of rubber bands on a ligator is often difficult and frustrating, especially when the operator is wearing gloves. A newly designed rubber-band loader with grooves and a pusher places the bands on the ligator easily, simultaneously, and quickly even under these conditions.

Finite-dimensional VS-MRAC of distributed parameter systems with boundary inputs

A design method is proposed for actual finite-dimensional VS-MRAC (variable structure model reference adaptive control) of asymptotically stable distributed systems with bounded disturbances, boundary inputs and arbitrary relative degree. Ideal finite-dimensional VS-MRAC is first stated and then actual finite-dimensional VS-MRAC is stated by using the results. The main results obtained in this paper are as follows. First, in the case of the ideal finite-dimensional VS-MRAC, each ideal sliding mode is always attained in a finite time, independently of the reference input and in spite of the presence of unmodelled dynamics and disturbances. The output error converges exponentially to zero, and it is assured that all signals in the closed-loop system are ultimately uniformly bounded. Next, in the case of the actual finite-dimensional VS-MRAC, each equivalent control is approximated by each average control, and the absolute value of the output error can be made asymptotically arbitrarily small, independently of the reference input and in spite of the presence of unmodelled dynamics and disturbances. Furthermore, it is assured that all signals in the closed-loop system are ultimately bounded. Finally, the effectiveness of the proposed method is demonstrated by using a numerical example

Finite-dimensional model reference adaptive control of a class of nonlinear distributed systems with quasi-sliding mode

Abstract We propose a new design method for a finite-dimensional model reference adaptive control of a class of non-linear distributed systems with input and output disturbances, when only input and output measurements are available. We consider the case where the relative degree of the dominant part of the plant is arbitrary, and introduce the idea of quasi-sliding mode in variable structure systems theory which can avoid the chattering problem. The proposed method assures that any accuracy of the output error is obtained in any finite time, independently of the presence of bounded disturbances, non-linearity and unmodelled dynamics and that all signals in the closed-loop system are uniformly bounded. Finally, we show the effectiveness of the proposed method by a simple numerical example.