Traveling-wave tube circuit simplifies microwave relay

Circuit with a sawtooth-modulated traveling-wave tube, which acts as a frequency converter and as an amplifier, simplifies microwave transmission. Lower power losses and reduced size and weight are also realized in this circuit

Traveling wave tube development for a serrodyne re-entrant amplifier

Traveling wave tube development for serrodyne re-entrant amplifie

Self Piercing Riveting for Metal-Polymer Joints

Self-Piercing Riveting (SPR) is a sheet metal joining technique based on the insertion of a rivet into two or more sheets, with no preparatory hole. This process has gained wide diffusion in the automotive industry, due to the increasing use of materials alternative to steel, that are difficult or impossible to join with traditional techniques. In particular, polymeric materials are becoming increasingly used, due to their favorable weight/strength ratio. This paper reports the results of experimental investigations, aimed at identifying the variables affecting the mechanical characteristics of mixed metal-plastic joints. A statistic model for the optimization of the geometrical parameters has been computed. The paper demonstrates that self-piercing riveting appears competitive for metal/polymer junction. The results analyzed in light of statistical techniques show that some geometrical parameters affect joint performance more than others and can therefore be used as independent variables for joint performance optimizatio

Perspectives on procedure based assessments: a thematic analysis of semi-structured interviews with ten UK surgical trainees

Objectives: The introduction of competency-based training has necessitated development and implementation of accompanying mechanisms for assessment. Procedure based assessments (PBAs) are an example of workplace-based assessments that are used to examine focal competencies in the workplace. The primary objective was to understand surgical trainees’ perspective on the value of PBA. Design: Semi-structured interviews with 10 surgical trainees individually interviewed to explore their views. Interviews were audio-recorded and transcribed, following this they were open and axial coded. Thematic analysis was then performed. Results: Semi-structured interviews yielded several topical and recurring themes. In trainees’ experience the use of PBAs as a summative tool limits their educational value. Trainees reported a lack of support from seniors and variation in the usefulness of the tool based on stage of training. Concerns related to the validity of PBAs for evaluating trainees’ performance with reports of ‘gaming’ the system and trainees completing their own assessments. Trainees’ did identify the significant value of PBAs when used correctly. Benefits included the identification of additional learning opportunities, standardisation of assessment and their role in providing a measure of progress. Conclusions: The UK surgical trainees interviewed identified both limitations and benefits to PBAs, however we would argue based on their responses and our experience that their use as a summative tool limits their formative use as an educational opportunity. PBAs should either be used exclusively to support learning or solely used as a summative tool, if so further work is needed to audit, validate and standardise them for this purpose

Phase sensitive detection of dipole radiation in a fiber-based high numerical aperture optical system

We theoretically study the problem of detecting dipole radiation in an optical system of high numerical aperture in which the detector is sensitive to \textit{field amplitude}. In particular, we model the phase sensitive detector as a single-mode cylindrical optical fiber. We find that the maximum in collection efficiency of the dipole radiation does not coincide with the optimum resolution for the light gathering instrument. The calculated results are important for analyzing fiber-based confocal microscope performance in fluorescence and spectroscopic studies of single molecules and/or quantum dots.Comment: 12 pages, 2 figure

Palladium nanowire hydrogen sensor based on a SAW transducer

Palladium (Pd) nanowires were synthesized by electro chemical deposition technique. Pd nanowires were transferred onto a ZnO/36deg LiTaO3 surface acoustic wave (SAW) transducer with an approximate operating frequency of 100 MHz. This operational frequency approximately corresponds to the device's highest conductometric sensitivity. These devices were investigated for hydrogen (H2) sensing at the room temperature. It was observed that the device exposure to the H2 gas resulted to a measurable increase in the device operating frequenc

A layered SAW device based on ZnO/LiTaO3 for liquid media sensing applications

Surface Acoustic Wave (SAW) sensors comprising a zinc oxide guiding layer deposited on a 36°-YX lithium tantalate substrate were developed. They were found to have greater mass sensitivity than other LiTaO3 based SAW sensors, such as the -SiO2/LiTaO3 configuration. In this paper, the fabrication of the ZnO/LiTaO3 sensor is described and micro-characterisation of the deposited films is presented. Sensitivity of these devices to surface mass and dielectric perturbations is then presented, followed by an analysis of temperature stability

Atomistic structure of amorphous silicon nitride from classical molecular dynamics simulations

By means of molecular dynamics simulations based on the Billeter et al. [S. R. Billeter, A. Curioni, D. Fischer, and W. Andreoni, Phys. Rev. B {\bf 73}, 155329] environment-dependent classical force field we studied the structural features of SiN$_x$ samples at various stoichiometries. Our results are in good agreement with experimental data and are able to reproduce some features which so far were not reproduced by simulations. In particular, we identified units containing N--N bonds, which are thought to be responsible for an unassigned peak in the radial distribution function obtained from neutron diffraction data and signals observed in electron spin resonance, X-ray photoemission spectroscopy, electron-energy-loss spectroscopy and optical absorption experiments. We have identified defects which are thought to be the responsible for the high concentration of charge traps that makes this material suitable for building non-volatile memory devices. We analyzed the dependency of the concentration of these defects with the stoichiometry of the sample

Finite element modelling of flexural plate devices

A two dimensional finite element model has been developed for the simulation of a layered flexural plate wave device using the ANSYS package. The simulated device consists of a 2.0 µm silicon nitride thin film, followed by a 0.4 µm aluminum ground layer. A 0.6 µm zinc oxide piezoelectric layer was defined to excite acoustic waves. Good agreement of device frequency response and displacement profiles have been achieved in comparison with other numerical simulation methods. In this paper, the finite element (FE) method is proposed as a benchmark for an alternative analysis based upon a Green's function method. Furthermore, the FE method can be used to obtain other device parameters, such as insertion loss and charge density, which are presented

On attributes of a Rotating Neutron star with a Hyperon core

We study the effect of rotation on global properties of neutron star with a hyperon core in an effective chiral model with varying nucleon effective mass within a mean field approach. The resulting gross properties of the rotating compact star sequences are then compared and analyzed with other theoretical predictions and observations from neutron stars. The maximum mass of the compact star predicted by the model lies in the range $(1.4-2.4) ~M_{\odot}$ at Kepler frequency $\Omega_K$, which is consistant with recent observation of high mass stars thereby reflecting the sensitivity of the underlying nucleon effective mass in the dense matter EoS. We also discuss the implications of the experimental constraints from the flow data from heavy-ion collisions on the global properties of the rotating neutron stars.Comment: 11 Pages, 10 Figures and 2 Table