From Marsquakes to Terraforming: the Role of Planetary Geology in Science Fiction Literature

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Gallium nitride high electron mobility transistors in chip scale packaging: evaluation of performance in radio frequency power amplifiers and thermomechanical reliability characterization

2017 Summer.Includes bibliographical references.Wide bandgap semiconductors such as Gallium Nitride (GaN) have many advantages over their Si counterparts, such as a higher energy bandgap, critical electric field, and saturated electron drift velocity. These parameters translate into devices which operate at higher frequency, voltage, and efficiency than comparable Si devices, and have been utilized in varying degrees for power amplification purposes at >1 MHz for years. Previously, these devices required costly substrates such as sapphire (Al2O3), limiting applications to little more than aerospace and military. Furthermore, the typical breakdown voltage ratings of these parts have historically been below ~200 V, with many targeted as replacements for 50 V Si LDMOS as used in cellular infrastructure and industrial, scientific, and medical (ISM) applications between 1 MHz and 1 GHz. Fortunately within the past five years, devices have become commercially available with attractive key specifications: GaN on Si subtrates, with breakdown voltages of over 600 V, realized in cost effective chip scale packages, and with inherently low parasitic capacitances and inductances. In this work, two types of inexpensive commercially available AlGaN/GaN high electron mobility transistors (HEMTs) in chip scale packages are evaluated in a set of three interconnected experiments. The first explores the feasibility of creating a radio frequency power amplifier for use in the ISM bands of 2 MHz and 13.56 MHz, at power levels of up to 1 kW, using a Class E topology. Experiments confirm that a DC to RF efficiency of 94% is easily achievable using these devices. The second group of experiments considers both the steady state and transient thermal characterization of the HEMTs when installed in a typical industrial application. It is shown that both types of devices have acceptable steady state thermal resistance performance; approximately 5.27 °C/W and 0.93 °C/W are achievable for the source pad (bottom) cooled and top thermal pad cooled device types, respectively. Transient thermal behavior was found to exceed industry recommended maximum dT/dt by over 80x for the bottom cooled devices; a factor of 20x was noted with the top cooled devices. Extrapolations using the lumped capacitance method for transient conduction support even higher initial channel dT/dt rates. Although this rate of change decays to recommended levels within one second, it was hypothesized that the accumulated mechanical strain on the HEMTs would cause early life failures if left uncontrolled. The third set of experiments uses the thermal data to design a set of experiments with the goal of quantifying the cycles to failure under power cycling. It is confirmed that to achieve a high number of thermal cycles to failure as required in high reliability industrial systems, the devices under test require significant thermal parameter derating to levels on the order of 50%

Clamping devices to enable concurrent mechanical and electrical connections of a power semiconductor

2011 Fall.Includes bibliographical references.In response to the restrictions of lead bearing solders in the European Union Restriction of Hazardous Substances Directive of 2002, new strategies for solderless electrical connections are desired. In this work, such concepts are used in the simultaneous electrical connection of power semiconductor leads to a PCBA and mechanical attachment of the device package to a heat sink. These concepts are specifically designed for use in an industrial high power (kW to tens of kW) radio frequency generator. The many constraints of such a system, some of which are directly contradictory to each other, are considered throughout, including manufacturability, mechanical tolerances, system reliability, and cost. Theoretical models predict that in the expected usage environment, the transistor leads in the clamped connection under consideration will move 5.1 micrometers for a thermal excursion of 50°C. SEM micrographs showing that the size of z-axis asperities is on the order of 1 micrometers and calculations estimating adhesive junctions with surface energies on the order of 100 N/mm2 demonstrate that contact wear is likely. A survey of available materials has been conducted, with beryllium copper and polyetherimide being the favored options for clamp construction. Four concepts are modeled, noting the benefits and drawbacks of each. The preferred embodiment is found to be a clamping mechanism fabricated from electrically insulating material, specifically injection molded 30% fiberglass filled polyetherimide, incorporating cantilevered beams which deflect upon installment into the system with fasteners, thus forming the electrical connections. Test regimens have been performed, including room temperature aging, elevated temperature aging at 50°C and 80°C, thermal cycling, highly accelerated life testing, and thermal analysis in both the steady state and transient regimes. The results of the experiments show this clamping system to have a useful life in the intended environment of multiple years

Organisational capacity for responsive regulation

In April 1998, the Australian Taxation Office (Tax Office) adopted a policy of responsive regulation of tax compliance by small firms in the building and construction industry. Known as the Australian Taxation Office Compliance Model (ATO Compliance Model), the new approach is grounded in past research into regulation of business entities. As seen by its promoters, it promises to improve significantly tax compliance in the cash economy. Drawing from survey and interview data, we explore the Tax Office’s capacity for successful implementation of the ATO Compliance Model. Specifically, we examine the extent to which it had the leadership and staff commitment to implement the policy successfully. We also explore whether or not project field-level staff saw merit in the program and eventually came to support it. We conclude by examining whether the owners of small building and construction firms changed their perspectives on the Tax Office and tax compliance following introduction of the ATO Compliance Model

Listening and learning : the reciprocal relationship between worker and client

The relationship between worker and client has for the best part of 100 years been the mainstay of probation, and yet has recently been eroded by an increased emphasis on punishment, blame and managerialism. The views of offenders are in direct contradiction to these developments within the criminal justice system and this article argues that only by taking account of the views of those at the 'coal face' will criminologists, policy makers and practitioners be able to effect real change in crime rates. The article thus focuses on the views of a sample of previously persistent offenders in Scotland about offending, desistance and how the system can help them. It explores not only their need for friendship and support in youth but also the close association between relationships and the likelihood of offending. It also demonstrates the views of offenders themselves about the importance of the working relationship with supervising officers in helping them desist from crime. The article concludes that the most effective way of reducing offending is to re-engage with the message of the Probation Act of 100 years ago, namely, to 'advise, assist and befriend' offenders rather than to 'confront, challenge and change' offending behaviour

Diseño estructural de una vivienda multifamiliar sismo resistente utilizando software, en el CP. Alto Trujillo, El Porvenir, Trujillo - La Libertad

Este proyecto tuvo como objetivo primordial llevar a cabo el proceso de construcción de la vivienda multifamiliar de 3 pisos, contemplando el factor económico como punto de partida, por lo tanto, este análisis y diseño se hizo con el fin de comprender los distintos comportamientos que tiene la estructura frente a un posible sismo y así tener un factor de seguridad. Con los planos arquitectónicos y los parámetros de zona que contempla la norma E030, se predimensionó y analizó la estructura. Para el proceso del análisis lineal estático y dinámico se utilizó el software ETABS 16 como elemento primordial para obtener datos relevantes. El tipo de sistema estructural es mixto, ya que se consideró para la dirección “x” un sistema de muros de albañilería y para la dirección paralela placas de concreto armado. Comprobado todos los puntos del análisis sismorresistente y, el buen manejo y la simplicidad de los programas ETABS 16, SAP 2000 y SAFE 2016 se hizo el diseño de cada uno de los elementos estructurales tales como vigas, columnas, placas de concreto armado, muros de albañilería, losas, escalera y cimentación. Los resultados del análisis estructural han sido comprobados por los parámetros mínimos que exigen las normas peruanas, por lo que se concluyó con los detalles de cada uno de los elementos que conforma la vivienda multifamiliar.Tesi