The configuration of moving crack tip zones

The dynamic elasticity solution of a steady state crack is used for determination of the geometrical characteristics and of the displacement rates within the discrete crack zones which are formed as a result of the selective propagation of cleavage microcracks ahead of the tip of a running brittle crack in a mild steel plate. The zone length and the stress distribution in the zone are found to be strongly dependent on the assumed form of the stress-displacement relation for the progressively fracturing metal. On the other hand, the crack opening displacement rate is much less sensitive to the assumed form. The magnitudes of the nominal plastic strain rates, found by an approximate procedure, are of the order of 10⁵ to 10⁶ sec^?1. A comparison with the results of dynamic tension tests on similar steels indicates that the flow stress at these strain rates would exceed the twinning stress, and therefore, it is suggested in agreement with experimental observations, that twinning is the principal deformation mode in the crack zone. Accordingly, the crack tip boundary conditions considered in the solution of crack propagation problems can be assumed as independent of crack velocity. Also, their possible dependence on temperature would not be related to the deformation mode in the crack zone.     

Biomechanics of whiplash injury

The cooling effect of topicals has been used in the dermatological therapy as "physical effect" on the skin for more than hundred years. This effect of dermatologicals releasing free water is widely accepted, but current knowledge does not correspond to today's possibilities of experimental thermographic tests in man. The present paper describes the results published up to now and the current testing methods in vivo and in vitro.     

Initial Failure Maps for Fibrous CMC Laminates

A simple micromechanics-based procedure is used to evaluate initial failure maps for brittle composite laminates under combined in-plane loads and temperature changes. The maps are derived from local stresses in the fiber, matrix and at their interfaces, and from selected magnitudes of the respective strengths. In a particular loading plane or space, the maps indicate the damage-free load range of the laminate, and the source of likely initial failure by fiber or matrix cracking, or by fiber debonding. An application to Al₂O₃/MoSi₂ laminates with unidirectional and (0/±45)_slayups is presented. In this system, the thermal stresses are very small in the 1200°–20°C range; hence laminate failure is dominated by mechanical loads. Propensity to fiber debonding appears to limit the load magnitudes that can be safely applied to the angle-ply laminate.     

Supersonic Flow Structure in the Entrance Part of a Mixing Chamber of 2D Model Ejector

The paper deals with experimental and numerical results of investigation into supersonic and transonic flow past a two-dimensional model ejector. Results of optical measurements show a flow structure and flow parameter development in the entrance part of the mixing chamber of the ejector. Numerical results are obtained by means of both the straight solution of shock waves in supersonic flow field using classical relations of parameters of shock waves and the Fluent 6 program. Results of numerical solutions are compared with experimental pictures of flow fields. Flow structure development in the mixing chamber is analysed in detail.     

Development and application of quantum dots for immunocytochemistry of human erythrocytes

Recent developments in quantum dot technology have resulted in the introduction of new fluorescence immunocytochemical probes. In contrast to organic fluorophores, which are not photostable, the high quantum yield and remarkable photostability of quantum dots solve major problems associated with immunocytochemical studies of erythrocytes. We report here the first application of quantum dots to immunocytochemical studies of human erythrocytes capable of being used in high‐magnification, three‐dimensional erythrocyte reconstruction techniques. The procedure consists of stabilizing human erythrocytes with a homofunctional imidoester cross‐linker to minimize fixative‐induced autofluorescence followed by reacting with a quantum dot – monoclonal antibody complex to label band 3 protein. Our new procedure clearly showed a non‐homogeneous, raft‐like distribution of band 3 protein in the erythrocyte membrane. We also demonstrate the applicability of our technique to studies of erythrocyte membrane modifications occurring during the invasion of a malaria parasite.     

Compatibility of Spread-Spectrum Signals with Narrow-Band FM Receivers in VHF Mobile Networks

The feasibility of a tentative introduction of the spread- spectrum (SS) scheme in VHF mobile bands on an area-and frequency-sharing basis with existing FDM service is investigated. It is shown that compatibility can be attained only for cellular SS networks with small cell area. The approach outlined may be useful in the treatment of general compatibility problems involving variable geometry of the transmitter/receiver configuration.     

Impact ionization suppression by quantum confinement: Effects onthe DC and microwave performance of narrow-gap channel InAs/AlSb HFET's

InAs/AlSb heterostructure field-effect transistors (HFET's) are subject to impact ionization induced short-channel effects because of the narrow InAs channel energy gap. In principle, the effective energy gap to overcome for impact ionization can be increased by quantum confinement (channel quantization) to alleviate impact ionization related nonidealities such as the kink effect and a high gate leakage current. We have studied the effects of quantum well thickness on the dc and microwave performance of narrow-gap InAs/AlSb HFET's fabricated on nominally identical epitaxial layers which differ only by their quantum well thickness. We show that a thinner quantum well postpones the onset of impact ionization and suppresses short-channel effects. As expected, the output conductance g_DS and the gate leakage current are reduced. The f_MAX/f_T ratio is also significantly improved when the InAs well thickness is reduced from 100 to 50 Å. The use of the thinner well reduces the cutoff frequency f_T, the transconductance g_m, and the current drive because of the reduced low-field mobility due to interface roughness scattering in thin InAs/AlSb channel layers: the low-field mobility was μ=21 000 and 9000 cm²/Vs for the 100- and 50-Å quantum wells, respectively. To our knowledge, the present work is the first study of the link between channel quantization, in-plane impact ionization, and device performance in narrow-gap channel HFET's     

Reaction analysis in stripline circuits

In this paper, a full-wave layered-interconnect simulator (UA-FWLIS), which is capable of simulating EM effects in packaging-interconnect problems, is introduced. Standard integral-equation-based method of moment (MoM) techniques are employed in UA-FWLIS. However, instead of using standard time-consuming numerical integration techniques, we have analytically evaluated the MoM reaction elements, thereby greatly improving the computational efficiency of the simulator. This paper illustrates the application of the simulator by employing it in the studies of coupling in a stripline structure and S-parameters for an interconnect