779 research outputs found
Evolving a DSL implementation
Domain Specific Languages (DSLs) are small languages designed for use in a specific domain. DSLs typically evolve quite radically throughout their lifetime, but current DSL implementation approaches are often clumsy in the face of such evolution. In this paper I present a case study of an DSL evolving in its syntax, semantics, and robustness, implemented in the Converge language. This shows how real-world DSL implementations can evolve along with changing requirements
Phase noise contribution of EOMs and HF cables
Two key components of LISA's inter-spacecraft clock tone transfer chain are electro-optic modulators (EOMs) and high-frequency (HF) cable assemblies. At modulation frequencies of 2 GHz, we characterized the excess phase noise of these components in the LISA frequency range (0.1 mHz to 1 Hz). The upper phase noise limit was found to be almost an order of magnitude better than required. In addition, phase dependencies on temperature were determined. The measured coefficients are within a few milliradians per Kelvin and thereby negligible due to the specified on-board temperature stability
Nonlinear resonant tunneling in systems coupled to quantum reservoirs
An adiabatic approximation in terms of instantaneous resonances is developed
to study the steady-state and time-dependent transport of interacting electrons
in biased resonant tunneling heterostructures. The resulting model consists of
quantum reservoirs coupled to regions where the system is described by
nonlinear ordinary differential equations and has a general conceptual
interest.Comment: 4 pages, 3 postscript figure
Quasi-two-dimensional MHD duct flow around a 180-degree sharp bend in a strong magnetic field
This study considers the quasi-two-dimensional flow of an electrically conducting fluid subjected to a strong out-of-plane magnetic field in a rectangular duct. The effect of Hartmann number on flow features such as the length of the downstream recirculation bubbles and the threshold Reynolds numbers between steady-state and unsteady flow regimes for values of the ratio between the throat of the bend and the duct height, β = 1 are identified. The simulations reveal that the primary recirculation bubble length decreases with increasing Hartmann number,
and simultaneously the secondary recirculation bubble is significantly damped compared to the corresponding non-MHD case. The critical Reynolds number where the transitions from steady to unsteady flow occurs was found to increase with increasing of Hartman number. This study provides information that will be useful for refining the design of heat exchanger ducting in MHD systems to maximise the useful mass transport adjacent to the duct walls where heating is applied
Linear stability of confined flow around a 180-degree sharp bend
This study seeks to characterise the breakdown of the steady two-dimensional solution
in the flow around a 180-degree sharp bend to infinitesimal three-dimensional
disturbances using a linear stability analysis. The stability analysis predicts that
three-dimensional transition is via a synchronous instability of the steady flows.
A highly accurate global linear stability analysis of the flow was conducted with
Reynolds number Re < 1150 and bend opening ratio (ratio of bend width to inlet
height) 0.26β 65. This range of Re and β captures both steady-state two-dimensional
flow solutions and the inception of unsteady two-dimensional flow. For 0.2 6 β 6 1,
the two-dimensional base flow transitions from steady to unsteady at higher Reynolds
number as β increases. The stability analysis shows that at the onset of instability,
the base flow becomes three-dimensionally unstable in two different modes, namely
a spanwise oscillating mode for β = 0.2 and a spanwise synchronous mode for
β > 0.3. The critical Reynolds number and the spanwise wavelength of perturbations
increase as β increases. For 1 < β 6 2 both the critical Reynolds number for onset
of unsteadiness and the spanwise wavelength decrease as β increases. Finally, for
2 < β 6 5, the critical Reynolds number and spanwise wavelength remain almost
constant. The linear stability analysis also shows that the base flow becomes unstable
to different three-dimensional modes depending on the opening ratio. The modes are
found to be localised near the reattachment point of the first recirculation bubbl
Going SOLO to assess novice programmers
This paper explores the programming knowledge of novices using Biggs' SOLO taxonomy. It builds on previous work of Lister et al. (2006) and addresses some of the criticisms of that work. The research was conducted by studying the exam scripts for 120 introductory programming students, in which three specific questions were analyzed using the SOLO taxonomy. The study reports the following four findings: when the instruction to students used by Lister et al. - "In plain English, explain what the following segment of Java code does" - is replaced with a less ambiguous instruction, many students still provide multistructural responses; students are relatively consistent in the SOLO level of their answers; student responses on SOLO reading tasks correlate positively with performance on writing tasks; postgraduates students manifest a higher level of thinking than undergraduates. Copyright 2008 ACM
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