Field enhancement in microfluidic semiconductor nanowire array.

Nano-material integrated microfluidic platforms are increasingly being considered to accelerate biological sample preparation and molecular diagnostics. A major challenge in this context is the generation of high electric fields for electroporation of cell membranes. In this paper, we have studied a novel mechanism of generating a high electric field in the microfluidic channels by using an array of semiconductor nanowires. When an electrostatic field is applied across a semiconductor nanowire array, the electric field is localized near the nanowires and the field strength is higher than what was reported previously with various other micro-geometries. Nanowires made of ZnO, Si, and Si-SiO2 and their orientation and array spacing are considered design parameters. It is observed that for a given ratio of the spacing between nanowires to the diameter, the electric field enhancement near the edges of ZnO nanowires is nearly 30 times higher compared to Si or Si-SiO2 nanowire arrays. This enhancement is a combined effect of the unique geometry with a pointed tip with a hexagonal cross section, the piezoelectric and the spontaneous polarization in the ZnO nanowires, and the electro-kinetics of the interface fluid. Considering the field localization phenomena, the trajectories of E. coli cells in the channel are analyzed. For a given inter-nanowire spacing and an applied electric field, the channels with ZnO nanowire arrays have a greater probability of cell lysis in comparison to Si-based nanowire arrays. Detailed correlations between the cell lysis probability with the inter-nanowire spacing and the applied electric field are reported.

Review on nanomaterials-enabled electrochemical sensors for ascorbic acid detection.

This review (with 307 refs.) addresses the recent advances in electrochemical nonenzymatic ascorbic acid (AA) sensors using various nanomaterials as sensing elements. In general, nanomaterials have paved the way for a novel and advanced sensing device due to their unique physical and chemical properties. AA sensors based on noble metals, their nanoparticles, transition metals/metal nanoparticles, alloys/bimetallic nanoparticles, conducting polymers and carbon nanomaterials have been reviewed. Also, there has been a focus on describing the details of many significant articles explaining the design of sensors and utilities of the prepared sensors, so that readers might get the principles behind such devices and relevant detection strategies. Finally, the challenges and prospects for the application of nanomaterials-enabled electrochemical sensors for AA analysis have also been incorporated.

Modeling and simulation of vibro-thermography including nonlinear contact dynamics of ultrasonic actuator.

In this paper, a thermodynamically consistent generalized three-dimensional modeling scheme is developed to simulate vibro-thermography and subsequently perform a quantitative investigation on a test structure. Simulation results are analyzed considering a plate with Structural Features (SF) which are used in a gas turbine engine structural components to reduce structural mass and enhance cooling. The modeling framework includes (i) coupled thermo-elastic heat generation and (ii) effects of various sources of nonlinear vibration arising due to the amplitude of the excitation, the engagement force on the target structure due to the ultrasonic horn, and structural boundary conditions. Transient heat generation behavior in the target structure with SF is analyzed. Dynamic contact models are used to capture the nonlinear harmonics. The effects of engagement force on the dynamic response are analyzed. Simulation results are obtained by incorporating the model in a finite element scheme. The simulation results show that the thermographic inspection can be optimally designed using a relationship between the SF sizes with reference to wavelength based resonance phenomenon. The spectral components obtained at various locations in the SF reveals the presence of both sub- and super-harmonics.

Incidental Mesenteric Paraganglioma: A Case Report and Literature Review

Mesenteric paragangliomas are a rare entity; consequently, only 12 cases have been reported to date. Although considered benign and often found incidentally, they have the potential to metastasize and are an important diagnosis to consider for patients with a mesenteric tumor. We report the case of a 71-year-old woman who was found on magnetic resonance imaging to have an incidental, large, complex, intra-abdominal mass that had initially been misdiagnosed as ovarian in origin. She underwent an open resection of the tumor and adjacent small bowel with no perioperative complications; histology confirmed the mass to be a mesenteric paraganglioma. This case report highlights several important key issues regarding paraganglioma, including diagnosis, imaging, genetic testing, and surgical resection. The results of a literature review are also discussed.

Temperature-pressure-induced solid-solid <100> to <110> reorientation in FCC metallic nanowire: a molecular dynamic study.

Atomistic simulation of initial <100> oriented FCC Cu nanowires shows a novel coupled temperature-pressure dependent reorientation from <100> to <110> phase. A temperature-pressure-induced solid-solid <100> to <110> reorientation diagram is generated for Cu nanowire with varying cross-sectional sizes. A critical pressure is reported for Cu nanowires with varying cross-sectional sizes, above which an initial <100> oriented nanowire shows temperature independent reorientation into the <110> phase. The effect of surface stresses on the <100> to <110> reorientation is also studied. The results indicate that above a critical cross-sectional size for a given temperature-pressure, <100> to <110> reorientation is not possible. It is also reported here that for a given applied pressure, an increase in temperature is required for the <100> to <110> reorientation with increasing cross-sectional size of the nanowire. The temperature-pressure-induced solid-solid <100> to <110> reorientation diagram reported in the present paper could further be used as guidelines for controlling the reorientations/shape memory in nano-scale applications of FCC metallic nanowires.

Electromechanical interactions in a carbon nanotube based thin film field emitting diode.

Carbon nanotubes (CNTs) have emerged as promising candidates for biomedical x-ray devices and other applications of field emission. CNTs grown/deposited in a thin film are used as cathodes for field emission. In spite of the good performance of such cathodes, the procedure to estimate the device current is not straightforward and the required insight towards design optimization is not well developed. In this paper, we report an analysis aided by a computational model and experiments by which the process of evolution and self-assembly (reorientation) of CNTs is characterized and the device current is estimated. The modeling approach involves two steps: (i) a phenomenological description of the degradation and fragmentation of CNTs and (ii) a mechanics based modeling of electromechanical interaction among CNTs during field emission. A computational scheme is developed by which the states of CNTs are updated in a time incremental manner. Finally, the device current is obtained by using the Fowler-Nordheim equation for field emission and by integrating the current density over computational cells. A detailed analysis of the results reveals the deflected shapes of the CNTs in an ensemble and the extent to which the initial state of geometry and orientation angles affect the device current. Experimental results confirm these effects.

Lamb wave characteristics of thickness-graded piezoelectric IDT.

An equivalent single layer model of Lamb wave generation by thickness-graded piezoelectric IDT on host structure is developed. Various additional complexities, such as the coupling between the Lamb wave modes, complicated nature of the electro-mechanical excitation are considered. The model of infinite IDT is extended to deal with the finite IDT with edge discontinuities. The effects of electromechanical coupling and thickness gradation on the wavelength shifts are investigated. The problem of electrically driven instability within the IDT is analyzed. Numerical results are reported by considering Al2O3/PZT IDT as integral part of the host structure, which show that there are significant changes and improvements in the Lamb wave characteristics due to the graded configuration. Most important among these is the reduced dispersiveness of the Lamb wave modes, which is useful in launching a SAW that propagates with narrower pulse width and less attenuation.