Diffraction effects in insertion mode estimation of ultrasonicgroup velocity

We describe diffraction effects in ultrasonic group velocity estimation using an insertion technique. We characterize the estimation error produced by diffraction as a function of distance and nominal velocity values. A new method termed Group Velocity Diffraction Correction (GVDC) which corrects for the diffraction effect is presented. Experimental validation of the technique is also presented using measurements made with both 1 MHz and 500 kHz ultrasonic transducer pairs. The results demonstrate that diffraction effects on ultrasonic group velocity estimation are usually small, and may often be neglected. Significant improvement, up to about 50%, in the accuracy of the group velocity estimate can however be obtained using the method described here in those cases in which higher degrees of accuracy are required     

Engineering Transport in Manganites by Tuning Local Nonstoichiometry in Grain Boundaries

Interface‐dominated materials such as nanocrystalline thin films have emerged as an enthralling class of materials able to engineer functional properties of transition metal oxides widely used in energy and information technologies. In particular, it has been proven that strain‐induced defects in grain boundaries of manganites deeply impact their functional properties by boosting their oxygen mass transport while abating their electronic and magnetic order. In this work, the origin of these dramatic changes is correlated for the first time with strong modifications of the anionic and cationic composition in the vicinity of strained grain boundary regions. We are also able to alter the grain boundary composition by tuning the overall cationic content in the films, which represents a new and powerful tool, beyond the classical space charge layer effect, for engineering electronic and mass transport properties of metal oxide thin films useful for a collection of relevant solid‐state devices.     

Impatt characterization as a mildly nonlinear devices

The first-order nonlinear analysis of IMPATT diodes is performed and a model is obtained in which the nonlinear effects due to avalanche are separated from the activity and transit-time effects. Such a mildly nonlinear model is suitable for CAD applications. The determination of the model parameters by means of small signal measurements is outlined, and the applicability of the proposed model is demonstrated on real devices.     

Enhancement of the interaction between low‐intensity R.F. e.m. fields and ligand binding due to cell basal metabolism

Power absorption by biological tissues, due to lowintensity electromagnetic exposure at radio frequencies, as those generated by personal telecommunication systems, is typically negligible. Nevertheless, the electromagnetic field is able to affect biological processes, like the binding of a messenger ion to a cell membrane receptor, if some specific conditions occur. The depth of the attracting potential energy well of the binding site must be comparable with the radio frequency photon energy. The dependance of the binding potential energy on the spatial coordinates must be highly nonlinear. The ion–receptor system, in absence of the exogenous electromagnetic exposure, must be biased out of thermodynamic equilibrium by the cell basal metabolism. When the above conditions concur a lowintensity radio frequency sinusoidal field is able to induce a steady change of the ion binding probability, which overcomes thermal noise. The model incorporates the effects of both thermal noise and basal metabolism, so that it offers a plausible biophysical basis for potential bioeffects of electromagnetic fields, e.g., those generated by mobile communication systems.     

Small-signal theory of transit-time diodes

Transit-time diodes, in which the effects of carrier diffusion and generation or recombination are not important, have recently been investigated both theoretically and experimentally. The impedance of these devices, mainly due to one type of carriers, has been computed by several authors with different simplifying assumptions. In this paper a more general expression of the impedance of the transit-time diode is given, accounting for the spatial non-uniform d.c. distributions of the electric field and of the carrier velocity, and by allowing any dependance of the carrier mobility on the d.c. electric field. The impedance is given in closed form in the case where the mobility is constant. The impedance of a metal-semiconductor-metal structure is then computed, and the frequency and bias range over which a negative resistance arises is found to be consistent with known experimental data.     

A neural network approach for bone fracture healing assessment

An approach based on auscultatory percussion, a technique used by some orthopedists both for bone fracture detection and bone fracture healing assessment, is described. Low-frequency, low-intensity mechanical power, very much like the finger tap of orthopedists, is used to evaluate the vibrational response of the bone. The novel element is the data processing, which incorporates specialized preprocessing and a neural network for estimating fractured bone strength. In addition, a new mathematical model for the vibrational response of a fractured limb, which provides data to design and test the neural network processing scheme, is presented. An experimental procedure is described for acquiring real data from animal and human fractures in a form necessary for neural network input.     

Reconstruction of Low Dimensional Electronic States by Altering the Chemical Arrangement at the SrTiO3 Surface

Developing reliable methods for modulating the electronic structure of the 2D electron gas (2DEG) in SrTiO₃ is crucial for utilizing its full potential and inducing novel properties. Herein, it is shown that relatively simple surface preparation reconstructs the 2DEG at the SrTiO₃ (STO) surface, leading to a Lifshitz-like transition. Combining experimental methods, such as angle-resolved photoemission spectroscopy (ARPES) and X-ray photoemission spectroscopy with ab initio calculations, that the modulation of the surface band structures can be effectively achieved via transforming the chemical composition at the atomic scale is found. In addition, ARPES experiments demonstrate that vacuum ultraviolet light can be efficiently employed to alter the band renormalization of the 2DEG system and control the electron-phonon interaction . This study provides a robust and straightforward route to stabilize and tune the low-dimensional electronic structure via the chemical degeneracy of the STO surface.