Multi-mode coupling wave theory for helically corrugated waveguide

Helically corrugated waveguide has been used in various applications such as gyro-backward wave oscillators, gyro-traveling wave amplifier and microwave pulse compressor. A fast prediction of the dispersion characteristic of the operating eigenwave is very important when designing a helically corrugated waveguide. In this paper, multi-mode coupling wave equations were developed based on the perturbation method. This method was then used to analyze a five-fold helically corrugated waveguide used for X-band microwave compression. The calculated result from this analysis was found to be in excellent agreement with the results from numerical simulation using CST Microwave Studio and vector network analyzer measurements

Economic Impacts of Farm Program Payment Limits

The high levels of government payments to farmers resulting from the 1985 farm bill have once again led the Congress to examine the payment limit issue. Payment limits were initially established in 1970 and have since been revised several times. In this report, policy and farm management economists analyze the consequences of alternative payment limits on economic efficiency, economic viability of family-size farms, international competitiveness, and consumer food costs. Effective payment limits encourage reduced farm size and in the presence of economies of size, tend to increase production costs for program crops. The Agricultural and Food Policy Center is charged with evaluating economic impacts of policy alternatives -- not recommending, advocating, or opposing particular policies. The Center's orientation is toward Texas agriculture -- evaluating policy impacts on its producers and consumers. Farm prices and income, however, are determined in world markets that are influenced by national economic policy and farm programs. Texas impacts, therefore, must be evaluated in a much broader national and international market and policy context.Agricultural and Food Policy,

Subnanometer traceability of localization microscopy

In localization microscopy, subnanometer precision is possible but supporting accuracy is challenging, and no study has demonstrated reliable traceability to the International System of Units (SI). To do so, we measure the positions of nanoscale apertures in a reference array by traceable atomic-force microscopy, creating a master standard. We perform correlative measurements of this standard by optical microscopy, correcting position errors from optical aberrations by a Zernike calibration. We establish an uncertainty field due to localization errors and scale uncertainty, with regions of position traceability to within a 68 % coverage interval of +/- 1.0 nm. These results enable localization metrology with high throughput, which we apply to measure working standards, validating the subnanometer accuracy of lithographic pitch

Low loss transmission line for a 3.4-kW, 93-GHz gyro-traveling-wave amplifier

In this article, a transmission line system for the propagation of millimeter-wave radiation is presented. The full system includes a TE11-to-TE01 mode converter, waveguide tapers, miter bends, and many straight sections. The design of each of these components is described, and the optimized simulation results are given. The mode converter shows a greater than 96% mode conversion efficiency that can be achieved over a 2% bandwidth at the ${W}$ -band. The miter bends demonstrate a transmission loss of 0.04 dB each over the same bandwidth when they are configured to introduce a mixture of higher order waveguide modes before the reflecting surface. An example transmission line system with a propagation length of 20 m, inclusive of four 90° bends with an oxygen-free high conductivity (OFHC) copper waveguide material, was studied over a 90-96-GHz frequency range and showed a 0.84-dB transmission loss at 93 GHz

The effect of journal metrics on academic resume assessment

It has been widely argued that journal metrics are used in assessing publication records on resumes for academic jobs and assessments. Within that debate, two important considerations emerge. Firstly, academics belonging to different career cohorts may have different experiences which are reflected in their recommendations related to targeting and assessing publication records. Secondly, recruitment or assessment expectations that include publishing in highly rated journals may lead to the targeting of a smaller number of high rated publications, with perceived lower rated journal outlets being discouraged. Using an experimental design, an online survey collected data from 1011 academics across management and psychology disciplines in the UK and USA, exploring the association between journal ratings, the number of publications on a resume, and the length of time spent in academia. Analysis indicated that when assessing an academic resume, the discouraging of lower rated journal publications may be dependent on the length of time spent in academia. Specifically, in the context of exactly the same high rated journal publications on a resume, those who had been in academia for 10–20 years were less favorable towards the inclusion of additional low rated journals. The findings contribute to how we view the socialization of institutional influences on career decision making in higher education. The results add to emergent evidence of behavioral responses to the institutional pressures on academic careers, and how individuals at different career stages may be impacted differently. This has implications for the management of academic career progression and academic recruitment processes.Output Status: Forthcoming/Available Onlin

Feedhorn synthesis using a parameterized aperture field distribution

In this letter, we present an improved method for synthesizing smooth-profiled horns. A direct connection between the mode compositions and far-field parameters was established by utilizing a parameterized aperture field distribution and the field decomposition method. It speeds up the optimization process by a factor of 5. The requirements for the aperture field to maintain a constant directivity were studied based on the method. A feedhorn was optimized for a W-band gyro-TWA with a 0.7 dB variation of the directivity within a bandwidth of 10%

A high-power Ka-band free electron maser, defined by a 2D – 1D Bragg lasing cavity

One of the on-going research programs, at the University of Strathclyde, involves the development of high-power, pulsed, Free-Electron Masers (FEMs) with the lasing cavity defined using periodic corrugations on the drift-tube walls 1-4 . These corrugations form 1D and 2D Bragg resonators, whose reflection bands determine the dominant resonance of the maser 5 . Proper selection of the FEM undulator magnetic field strength, allows for efficient extraction of energy from a mildly relativistic (400 - 500 keV) electron beam at the resonant frequency of the lasing cavity, leading to monochromatic output at power levels of several tens of megawatts and pulse durations of ~150ns (determined primarily by the pulse duration of the driving power supply of ~250ns)

Experimental study of microwave pulse compression using a five-fold helically corrugated waveguide

This paper presents the experimental study of microwave pulse compression using a five-fold helically corrugated waveguide. In the experiment, the maximum power compression ratio of 25.2 was achieved by compressing an input microwave pulse of 80 ns duration and 9.65 GHz to 9.05 GHz frequency swept range into a 1.6 ns Gaussian-envelope pulse. For an average input power of 5.8 kW generated by a conventional traveling wave tube, a peak pulse output power of 144.8 kW was measured corresponding to an energy efficiency of 66.3%

The Metabolic Stress Response to Burn Trauma: Current Understanding and Therapies

Summary Severe burns incur a profound stress response, which is unrivaled in terms of its magnitude and duration. Recent evidence suggests that the pathophysiological stress response to severe burns persists for several years post injury. Thus, there is a pressing need for novel strategies that mitigate this response and restore normal metabolic function in burn survivors. This is the first installment of a three-part series exploring the stress response to severe burn trauma. In this article we aim to distill the current knowledge pertaining to the stress response to burn trauma, highlighting recent developments and important knowledge gaps that need to be pursued in order to develop novel therapeutic strategies which improve outcomes in burn survivors