Heat transfer in a compact tubular heat exchanger with helium gas at 3.5 MPa

A compact heat exchanger was constructed consisting of circular tubes in parallel brazed to a grooved base plate. This tube specimen heat exchanger was tested in an apparatus which radiatively heated the specimen on one side at a heat flux of up to 54 W/sq cm, and cooled the specimen with helium gas at 3.5 MPa and Reynolds numbers of 3000 to 35,000. The measured friction factor of the tube specimen was lower than that of a circular tube with fully developed turbulent flow, although the uncertainty was high due to entrance and exit losses. The measured Nusselt number, when modified to account for differences in fluid properties between the wall and the cooling fluid, agreed with past correlations for fully developed turbulent flow in circular tubes

A J-Spectral Factorization Approach to ℋ∞ Control

Necessary and sufficient conditions for the existence of suboptimal solutions to the standard model matching problem associated with ℋ∞ control, are derived using J-spectral factorization theory. The existence of solutions to the model matching problem is shown to be equivalent to the existence of solutions to two coupled J-spectral factorization problems, with the second factor providing a parametrization of all solutions to the model matching problem. The existence of the J-spectral factors is then shown to be equivalent to the existence of nonnegative definite, stabilizing solutions to two indefinite algebraic Riccati equations, allowing a state-space formula for a linear fractional representation of all controllers to be given. A virtue of the approach is that a very general class of problems may be tackled within a conceptually simple framework, and no additional auxiliary Riccati equations are required

A massively parallel SIMD processor for neural network and machine vision applications

This thesis describes the MM32k, a massively parallel SIMD computer which is easy to program, high in performance, low in cost and effective for implementing highly parallel neural network architectures. The MM32k has 32768 bit serial processing elements, each of which has 512 bits of memory, and all of which are interconnected by a switching network. The entire system resides on a single PC-AT compatible card. It is programmed from the host computer using a C++ language class library which supports variable precision vector arithmetic. The MM32k also supports direct video input and output for machine vision applications

Development as unfreedom : the role of mine migrant labour institutions as agents of development in the Transkei, 1886-1980s

Early liberal historians predominantly criticised the migrant labour system for its economic irrationality. After high GDP growth and steady benefits from gold mining in the 1960s, Marxist scholars in the 1970s pointed to the destructive impact of the system. Since 1994, the challenge inter alia has been to forge a new developmental path for the economy. In 2012 the National Development Plan set out its aim to “eliminate poverty and reduce inequality by 2030”.1 This is the challenge. For the country or region to ‘develop’ and eliminate ‘poverty’ we need to know what we are trying to eliminate and what our development is trying to achieve. This thesis examines the migrant labour system in the Transkei through a lens of development and asks how and to what extent the system inhibited the development of the Transkei and its peoples. Using Amartya Sen’s conception of development - which sees development as a process of expanding social, political, and economic freedoms/capabilities - this thesis offers a view of migrant labour institutions in terms of how they created and engendered deprivation and unfreedom in the Transkei. It is an attempt to understand our ‘developmental past’ and to understand how development in the Transkei has been frustrated and inhibited by formal institutions. Amartya Sen’s notions of ‘development’ and ‘deprivation’ offer an autonomy- and freedom-centred approach to thinking about poverty and development. Specifically the thesis examines the nexus of formal institutions underpinning the migrant labour system - including state laws, the Native Affairs Department, and the Native Recruiting Corporation - in terms of how they acted to inhibit the development of mineworkers and labour exporting regions like the Transkei

We\u27re Listening: A Study of Music Preference in Modern Society

The purpose of this study was to investigate the formation of music preference in an effort to identify specific ages when preferred music is likely to be discovered. One hundred one individuals participated in an online survey, answering questions about their listening habits, music preferences, and the social elements that contributed most to those preferences. Participants were asked to identify their current, second, and third favorite music at the time of the study and whether their preferences had changed over time. According to findings, males were likely to discover their current favorite music at the age of 12.46 years, and females were likely to discover their current favorite music at the age of 13.23 years. Parents, friends, and the radio were shown to be the most common influences towards preference discovery. Of those surveyed, 69.3 % of participants acknowledged that their preferences had changed over time. However, the current methodology lacked the specificity to determine the scope of that change, leaving room for future study. The results hold implications for not only the field of music therapy, but also for any other fields utilizing preferred music to achieve a specific result

Design, Layout, and Testing of a Silicon Carbide-based Under Voltage Lock-out Circuit

Silicon carbide-based power devices play an increasingly important role in modern power conversion systems. Finding a means to reduce the size and complexity of these systems by even incremental amounts can have a significant impact on cost and reliability. One approach to achieving this goal is the die-level integration of gate driver circuitry with the SiC power devices. Aside from cost reductions, there are significant advantages to the integration of the gate driver circuits with the power devices. By integrating the gate driver circuitry with the power devices, the parasitic inductances traditionally seen between the gate driver and the switching devices can be significantly reduced, allowing faster switching speeds, which in turn leads to higher efficiencies, less aggressive thermal management requirements, and physically smaller passives. Collaborators from Toyota, Cree, the University of Arkansas, Oak Ridge National Labs, and Arkansas Power Electronics International have designed, fabricated, and tested a custom gate driver circuit implemented in a low-voltage SiC-based process by Cree. This gate driver implementation is the first step toward the goal of a completely integrated system. One key sub-component of this gate driver is the Under Voltage Lock-Out (UVLO) circuit, which asserts a signal whenever the supply voltage to the die falls below a set threshold and allows circuitry both on- and off-chip to take steps to prevent damage to the system. The work presented herein is the design, layout, and testing of a UVLO circuit implemented in the low-voltage silicon carbide process available from Cree. The UVLO was demonstrated to operate over a temperature range between -55 oC and 300 oC. An overview of the gate driver design, the fabrication process, and the trade-offs made during the UVLO circuit design process will be presented, as well as the integrated circuit layout workflow. A synopsis of the die testing apparatus and results will also be provided

Rock-shape and its role in rockfall dynamics

Rockfall threaten infrastructure and people throughout the world. Estimating the runout dynamics of rockfall is commonly performed using models, providing fundamental data for hazard management and mitigation design. Modelling rockfall is made challenging by the complexity of rock-ground impacts. Much research has focused on empirical impact laws that bundle the rock-ground impact into a single parameter, but this approach fails to capture characteristics associated with the impact configuration and, in particular, the effects of rock-shape. While it is apparent that particular geological settings produce characteristic rock-shapes, and that different rock-shapes may produce characteristic runout dynamics, these aspects of rockfall are poorly understood. This study has focused on investigating the mechanics behind the notion that different rock-shapes produce characteristic runout dynamics and trajectories. The study combines field data on rockfall runout, trajectory and dynamics, laboratory analogue testing in controlled conditions, and numerical modelling of the influence of rock-shape. Initially rock-shape, deposition patterns and rockfall dynamics were documented at rockfall sites in Switzerland and New Zealand. This informed a detailed study of individual rock-ground impacts on planar slopes in which laboratory-scale and numerical rockfall experiments were combined to isolate the role of rock-shape on runout. Innovatively, the physical experiments captured the dynamics of impacts and runout paths using high speed video tracking and a sensor bundle with accelerometers and gyroscopes. Numerical experiments were performed using a 3-D rigid-body rockfall model that considers rock-shape, and has allowed the variability of rockfall behaviour to be explored beyond the limitations of physical experimentation. The main findings of the study were on understanding rockfall-ground impacts, the influence of rock-shape on rockfall dynamics, and influence of rock sphericity. By measuring velocity, rotational speed, impact and runout character, it has been possible to quantify the variability of individual rock-ground impacts as a function of rock-shape. Investigation of single rebounds reveals that if classical restitution coefficients are applied, $R_n$ values greater than unity are common and rebounds are highly variable regardless of constant contact parameters. It is shown that this variability is rooted in the inherent differences in the magnitudes of the principal moment of inertia of a rock body brought about by rock-shape. Any departure from a perfect sphere induces increased range and variability in rock-ground rebound characteristics. In addition to the popular description of a rock bouncing down slope, rebounds involve the pinning of an exterior edge point on the rock, creating a moment arm which effectively levers the rock into ballistic trajectory as it rotates. Observations reveal that the angle of the impact configuration plays a key role in the resulting rebound, whereby low angles produce highly arched rebounds, while large impact angles produce low flat rebounds. The type of rebound produced has a strong bearing on the mobility of the rocks and their ability to maintain motion over a long runout. The mobility of rocks is also shown to be related to rotation, which is governed by the differences in the principal inertial axes as a function of rock-shape. Angular velocity measurements about each principal inertial axis indicate that rocks have a tendency to seek rotation about the axis of largest inertia, as the most stable state. Rotations about intermediate and small axes of inertia and transitions between rotational axes are shown to be unstable and responsible for the dispersive nature of runout trajectories, which are inherent characteristics of different rock-shapes. The findings of this research demonstrate the importance of rock-shape in rockfall runout dynamics and illustrate how it is essential that the rock-shape is included in rockfall modelling approaches if the variability of rockfall behaviour is to be simulated

The Higgs Boson Lineshape and Perturbative Unitarity

We discuss the lineshape of a heavy Higgs boson, and the behaviour well above resonance. Previous studies concluded that the energy-dependent Higgs width should be used in the resonance region, but must not be used well away from it. We derive the full result and show that it smoothly extrapolates these limits. It is extremely simple, and would be straightforward to implement in existing calculations.Comment: 10 pages, 10 figures A postscript version of this paper can be obtained http://surya11.cern.ch/users/seymour/pubs/higgswidth.ps.

Earnings Predictability And Broker-Analysts’ Earnings Forecast Bias

Scholars have reasoned that analysts issue optimistic forecasts to improve their access to managers’ private information when earnings are unpredictable. While this requires a managerial preference for analyst forecast optimism, the observed walk-down of analyst expectations to beatable forecasts is consistent with a managerial preference for pessimism in short-horizon forecasts. Using data from various sample periods, alternative model specifications, and various measures of earnings unpredictability, we find that pessimism, not optimism, in short-horizon forecasts is associated with increasingly unpredictable earnings. Our results suggest that firms can more effectively manage analysts’ earnings expectations downward when earnings are relatively unpredictable