Nonlinear elasticity imaging: theory and phantom study

In tissue the Young's modulus cannot be assumed constant over a wide deformation range. For example, direct mechanical measurements on human prostate show up to a threefold increase in Young's modulus over a 10% deformation. In conventional elasticity imaging, these effects produce strain-dependent elastic contrast. Ignoring these effects generally leads to suboptimal contrast (stiffer tissues at lower strain are contrasted against softer tissues at higher strain), but measuring the nonlinear behavior results in enhanced tissue differentiation. To demonstrate the methods extracting nonlinear elastic properties, both simulations and measurements were performed on an agar-gelatin phantom. Multiple frames of phase-sensitive ultrasound data are acquired as the phantom is deformed by 12%. All interframe displacement data are brought back to the geometry of the first frame to form a three-dimensional (3-D) data set (depth, lateral, and preload dimensions). Data are fit to a 3-D second order polynomial model for each pixel that adjusts for deformation irregularities. For the phantom geometry and elastic properties considered in this paper, reconstructed frame-to-frame strain images using this model result in improved contrast to noise ratios (CNR) at all preload levels, without any sacrifice in spatial resolution. From the same model, strain hardening at all preload levels can be extracted. This is an independent contrast mechanism. Its maximum CNR occurs at 5.13% preload, and it is a 54% improvement over the best case (preload 10.6%) CNR for frame-to-frame strain reconstruction. Actual phantom measurements confirm the essential features of the simulation. Results show that modeling of the nonlinear elastic behavior has the potential to both increase detectability in elasticity imaging and provide a new independent mechanism for tissue differentiation.     

Optimization of the Second-Order Logarithmic Machining Economics Problem by Extended Geometric Programming Part II: Posynomial Constraints

An algorithm is presented for solution of the machining economics problem with a Quadratic Posylognomial (QPL) objective function and single term posynomial constraints, meeting certain sufficient conditions. The algorithm applies to minimum cost or maximum productivity when the tool-life equation is a single term QPL and the removal rate is a single-term posynomial. A peripheral end-milling example, using the same tool-life equation and cost parameters as Part I, with the addition of experimentally derived constraints, is solved to illustrate the computational aspects of the algorithm. The QPL and posynomial (Taylor) formulations of the constrained machining problem are compared using the same experimental tool-life data. The QPL formulation is based on a quadratic logarithmic model whereas the posynomial formulation is based on a linear logarithmic tool-life model. An optimum without active constraints is possible using the QPL formulation in several independent machining variables, such as feed, speed, and depth, whereas the posynomial optimum, by nature, requires active constraints for more than one independent variable. This is tantamount to having additional “degrees of freedom” for optimization, as illustrated by the example problem.     

Effect of inoculum size, relative humidity, storage temperature, and ripening stage on the attachment of Salmonella Montevideo to tomatoes and tomatillos

The influence of inoculum populations and environmental factors on attachment of Salmonella Montevideo to the surface of tomatoes and tomatillos was evaluated. To study the effect of inoculum size, red, ripe tomatoes were spot-inoculated with bacterial suspensions (10(5) and 10(8) CFU/fruit) and stored at 22 degrees C under 100% relative humidity. The effects of temperature (12, 22, and 30 degrees C) and relative humidity (75, 85, and 97%) on attachment of the pathogen (10(7) CFU/fruit) to tomatoes (red and green) and ripe tomatillos were also evaluated. Inoculated fruits were stored for 90 min at all combinations of temperature and relative humidity, and after rinsing with water, the number of cells attached to the surface was determined. Salmonella Montevideo attached to the surface of tomatoes within 90 min. A direct correlation between the number of attached cells and the population in the inoculum was observed. The percentage of cells that attached immediately after inoculation was approximately 0.3% for the three test products. After storage for 90 min at various temperature and relative humidity conditions, the number of adhering cells ranged from 4.0 to 5.4 log CFU/fruit (1.2% of inoculum). Both the type of product and the temperature/relative humidity combination had a significant (P < 0.05) effect on attachment of Salmonella Montevideo to the surfaces of tomatoes and tomatillos. Scanning electron micrographs of the cuticles of inoculated washed tomatoes and tomatillos revealed typical skin cell patterns, and only a few randomly dispersed Salmonella Montevideo were observed. Deposition of Salmonella Montevideo on the surface of tomatoes and tomatillos could result in attachment and subsequent colonization under suitable conditions.     

AC-coupled front-end for biopotential measurements

AC coupling is essential in biopotential measurements. Electrode offset potentials can be several orders of magnitude larger than the amplitudes of the biological signals of interest, thus limiting the admissible gain of a dc-coupled front end to prevent amplifier saturation. A high-gain input stage needs ac input coupling. This can be achieved by series capacitors, but in order to provide a bias path, grounded resistors are usually included, which degrade the common mode rejection ratio (CMRR). This paper proposes a novel balanced input ac-coupling network that provides a bias path without any connection to ground, thus resulting in a high CMRR. The circuit being passive, it does not limit the differential dc input voltage. Furthermore, differential signals are ac coupled, whereas common-mode voltages are dc coupled, thus allowing the closed-loop control of the dc common mode voltage by means of a driven-right-leg circuit. This makes the circuit compatible with common-mode dc shifting strategies intended for single-supply biopotential amplifiers. The proposed circuit allows the implementation of high-gain biopotential amplifiers with a reduced number of parts, thus resulting in low power consumption. An electrocardiogram amplifier built according to the proposed design achieves a CMRR of 123 dB at 50 Hz.     

Operational Remote Sensing of Aerosols over Land to Account for Directional Effects

The assumption that the ground is a Lambertian reflector is commonly adopted in operational atmospheric corrections of spaceborne sensors. Through a simple modeling of directional effects in radiative transfer following the second simulation of the satellite signal in the solar spectrum (6S) approach, we propose an operational method to account for the departure from Lambertian behavior of a reflector covered by a scattering medium. This method relies on the computation of coupling terms between the reflecting and the scattering media and is able to deal with a two-layer atmosphere. We focus on the difficult problem of aerosol remote sensing over land. One popular sensing method relies on observations over dense dark vegetation, for which the surface reflectance is low and quite well defined in the blue and in the red. Therefore a study was made for three cases: (1) dark vegetation covered by atmospheric aerosols, (2) atmospheric aerosols covered by molecules, and finally (3) dark vegetation covered by atmospheric aerosols covered by molecules. Comparisons of top-of-the-atmosphere reflectances computed with our modeling and reference computations made with the successive-order-of-scattering code show the robustness of the modeling in the blue and in the red for aerosol optical thicknesses as great as 0.6 and solar zenith angles as large as 60 degrees . The model begins to fail only in the blue for large solar zenith angles. The benefits expected for aerosol remote sensing over land are evaluated with an aerosol retrieval scheme developed for the Medium-Resolution Imaging Spectrometer. The main result is a better constraint on the aerosol model with inclusion of directional effects and a weaker effect on the optical thickness of the retrieved aerosol. The directional scheme is then applied to the aerosol remote-sensing problem in actual Indian Remote Sensing Satellite P3/Modular Optoelectronic Scanner images over land and shows significant improvement compared with a Lambertian algorithm. Moreover, it confirms our main theoretical conclusion.     

Ab initio insights into the visible luminescent properties of ZnO

The luminescence spectrum of ZnO exhibits, besides a UV band-edge recombination line, a broad visible band around 2.2-2.4 eV whose origin has not been satisfactorily established. Recently, analysis of the luminescence of nanostructured materials with high surface-to-volume ratios has led some authors to suggest that the band could be related to surface states. This work presents a novel ab initio study of the most relevant ZnO surfaces and their intrinsic point defects. It reveals the existence of intragap surface states 0.5 eV above the valence band maximum. If additional bulk defect levels are considered, several bulk-to-surface transitions are compatible with the observed visible luminescence.     

Stress Power Dependent Self-Heating Degradation of Metal-Induced Laterally Crystallized n-Type Polycrystalline Silicon Thin-Film Transistors

Using a fluorinated high-k/metal gate stack combined with a stress relieved preoxide (SRPO) pretreatment before high-k deposition, we show significant device reliability and performance improvements. This is a critical result since threshold voltage instability may be a fundamental problem, and performance degradation for high-fc is a concern. The novel fluorinated Ta_infinC_y/HfZrO_infin/SRPO gate stack device exceeds the positive-bias-temperature-instability and negative-bias-temperature-instability targets with sufficient margin and has electron mobility at 1 MV/cm comparable to the industrial high-quality polySi/SiON device on bulk silicon.