A millimeter-wave slot-V antenna

A V-shaped slot antenna built on a dielectric substrate is presented. The antenna is a nonresonant, traveling-wave design, with a predicted impedance in the range from 50 Ω to 80 Ω. Calculations indicate that this antenna should have a gain of 15 dB with 3 dB beamwidths of 10° in the H plane and 64° in the E plane. Pattern measurements at 90 GHz support the theory. It should be possible to equalize the two beamwidths with a cylindrical lens. The broad bandwidth and high gain characteristics make the slot- V a good candidate for picosecond optoelectronic measurements. Fabrication is simple, and it should be possible to make this antenna at wavelengths as short as 10 μm with conventional photolithography

Workplace Flexibility Practices in SMEs: Relationship with Performance via Redundancies, Absenteeism, and Financial Turnover

This workplace flexibility study uses primary data on private sector small and medium-sized enterprises (SMEs) in Lancashire, United Kingdom, collected in 2009 during the recent “credit crunch” recession. Key features include: (1) objective measures of SME performance; (2) a focus on the previously relatively neglected relationship between workplace flexibility practices (WFPs) and three SME performance indicators, namely, redundancies, absenteeism, and financial turnover; and (3) a timely contribution to research on SMEs. Numerical, functional, and cost WFPs analyses, via zero-inflated Poisson and linear regressions, control for SME and market characteristics. Despite SMEs having limited resources, the results show a significant section of SMEs to be innovative and entrepreneurial organizations, embracing advancements in employment relations regarding employee discretion, training, participative working arrangements, and/or job security. Moreover, results indicate that WFPs have the potential to assist SMEs in responding to periods of constrained demand. Flexitime and job sharing are associated with low permanent-employee redundancies. Training, job security, and family-friendly practices relate to low absenteeism with reductions of up to six annual days per worker. Job security and profit-related pay are associated with high financial turnover. Staff pay-freeze links with high financial turnover, but to the detriment of redundancies and absenteeism, whereas management pay-cuts or management pay-freeze relate to low financial turnover. On a cautionary note, spending cuts, often enforced by policymakers, may be of limited benefit to SMEs, and thus other approaches would appear more fruitful

Properties of periodic arrays of symmetric complementary structuresand their application to grid amplifiers

Deschamps' theorem for n-terminal complementary structures is reviewed. An extension to Deschamps' theorem for a class of three-terminal bounded structures with one axis of symmetry is presented. It is shown that, for these structures, a simple relationship between the impedances of the odd mode of the original structure and the admittances of the even mode of the complementary structure exists, and that these modes are orthogonal. Using this, a self-complementary grid amplifier is designed and the measured results are presented

Is There Extra Cost of Institutional Care for MS Patients?

Throughout life, patients with multiple sclerosis (MS) require increasing levels of support, rehabilitative services, and eventual skilled nursing facility (SNF) care. There are concerns that access to SNF care for MS patients is limited because of perceived higher costs of their care. This study compares costs of caring for an MS patient versus those of a typical SNF patient. We merged SNF cost report data with the 2001-2006 Nursing Home Minimum Data Set (MDS) to calculate percentage of MS residents-days and facility case-mix indices (CMIs). We estimated the average facility daily cost using hybrid cost functions, adjusted for facility ownership, average facility wages, CMI-adjusted number of SNF days, and percentage of MS residents-days. We describe specific characteristics of SNF with high and low MS volumes and examine any sources of variation in cost. MS patients were no longer more costly than typical SNF patients. A greater proportion of MS patients had no significant effect on facility daily costs (P = 0.26). MS patients were more likely to receive care in government-owned facilities (OR = 1.904) located in the Western (OR = 2.133) and Midwestern (OR = 1.3) parts of the USA (P < 0.05). Cost of SNF care is not a likely explanation for the perceived access barriers that MS patients face

Stability of grid amplifiers

We present a stability model for quasi-optical grid amplifiers. This model is useful for predicting and suppressing the common-mode oscillations that often occur in amplifier grids. Three stabilization techniques will be discussed. The first technique uses a capacitor to stabilize the grid. The second approach employs resistance to suppress the oscillations. The final technique stabilizes the grid by reducing the on-chip common-mode resistance, allowing greatly increased amplifier efficiencies. Experimental evidence will be presented to confirm the validity of our stability model

Self-Complementary Structures and Their Application in Grid Amplifiers

An extension to Deschamps’s theorem for a class of 3-terminal bounded structures with one axis of symmetry is presented. For these structures, a simple relationship between the impedance matrix of the odd mode excitation of the original structure and the admittance matrix of the even mode excitation of its complement exists. Using this, a self-complementary grid amplifier is designed and the measured results are presented

Quantification of thermally-driven flows in microsystems using Boltzmann equation in deterministic and stochastic contexts

When the flow is sufficiently rarefied, a temperature gradient, for example, between two walls separated by a few mean free paths, induces a gas flow---an observation attributed to the thermo-stress convection effects at microscale. The dynamics of the overall thermo-stress convection process is governed by the Boltzmann equation---an integro-differential equation describing the evolution of the molecular distribution function in six-dimensional phase space---which models dilute gas behavior at the molecular level to accurately describe a wide range of flow phenomena. Approaches for solving the full Boltzmann equation with general inter-molecular interactions rely on two perspectives: one stochastic in nature often delegated to the direct simulation Monte Carlo (DSMC) method; and the others deterministic by virtue. Among the deterministic approaches, the discontinuous Galerkin fast spectral (DGFS) method has been recently introduced for solving the full Boltzmann equation with general collision kernels, including the variable hard/soft sphere models---necessary for simulating flows involving diffusive transport. In this work, the deterministic DGFS method; Bhatnagar-Gross-Krook (BGK), Ellipsoidal statistical BGK, and Shakhov kinetic models; and the widely-used stochastic DSMC method, are utilized to assess the thermo-stress convection process in MIKRA---Micro In-Plane Knudsen Radiometric Actuator---a microscale compact low-power pressure sensor utilizing the Knudsen forces. BGK model under-predicts the heat-flux, shear-stress, and flow speed; S-model over-predicts; whereas ESBGK comes close to the DSMC results. On the other hand, both the statistical/DSMC and deterministic/DGFS methods, segregated in perspectives, yet, yield inextricable results

Modelling shear bands in a volcanic conduit: Implications for over-pressures and extrusion-rates

Shear bands in a volcanic conduit are modelled for crystal-rich magma flow using simplified conditions to capture the fundamental behaviour of a natural system. Our simulations begin with magma crystallinity in equilibrium with an applied pressure field and isothermal conditions. The viscosity of the magma is derived using existing empirical equations and is dependent upon temperature, water content and crystallinity. From these initial conduit conditions we utilize the Finite Element Method, using axi-symmetric coordinates, to simulate shear bands via shear localisation. We use the von Mises visco-plasticity model with constant magma shear strength for a first took into the effects of plasticity. The extent of shear bands in the conduit is explored with a numerical model parameterized with values appropriate for Soufriere Hills Volcano, Montserrat, although the model is generic in nature. Our model simulates shallow (up to approximately 700 in) shear bands that occur within the upper conduit and probably govern the lava extrusion style due to shear boundaries. We also model the change in the over-pressure field within the conduit for flow with and without shear bands. The pressure change can be as large as several MPa at shallow depths in the conduit, which generates a maximum change in the pressure gradient of 10's of kPa/m. The formation of shear bands could therefore provide an alternative or additional mechanism for the inflation/deflation of the volcano flanks as measured by tilt-metres. Shear bands are found to have a significant effect upon the magma ascent rate due to shear-induced flow reducing conduit friction and altering the over-pressure in the upper conduit. Since we do not model frictional controlled slip, only plastic flow, our model calculates the minimum change in extrusion rate due to shear bands. However, extrusion rates can almost double due to the ton nation of shear bands, which may help suppress volatile loss. Due to the paucity of data and large parameter space available for the magma shear strength our model results can only allow for a qualitative comparison to a natural system at this stage. (c) 2007 Elsevier B.V. All rights reserved