Self-calibrating threshold detector

A self calibrating threshold detector comprises a single demodulating channel which includes a mixer having one input receiving the incoming signal and another input receiving a local replica code. During a short time interval, an incorrect local code is applied to the mixer to incorrectly demodulate the incoming signal and to provide a reference level that calibrates the noise propagating through the channel. A sample and hold circuit is coupled to the channel for storing a sample of the reference level. During a relatively long time interval, the correct replica code provides an output level which ranges between the reference level and a maximum level that represents incoming signal presence and synchronism with the replica code. A summer substracts the stored sample reference from the output level to provide a resultant difference signal indicative of the acquisition of the expected signal

Enhancing apprentice-based learning of Java

Various methods have been proposed in the past to improve student learning by introducing new styles of working with assignments. These include problem-based learning, use of case studies and apprenticeship. In most courses, however, these proposals have not resulted in a widespread significant change of teaching methods. Most institutions still use a traditional lecture/lab class approach with a strong separation of tasks between them. In part, this lack of change is a consequence of the lack of easily available and appropriate tools to support the introduction of new approaches into mainstream courses.In this paper, we consider and extend these ideas and propose an approach to teaching introductory programming in Java that integrates assignments and lectures, using elements of all three approaches mentioned above. In addition, we show how the BlueJ interactive programming environment [7] (a Java development environment aimed at education) can be used to provide the type of support that has hitherto hindered the widespread take-up of these approaches. We arrive at a teaching method that is motivating, effective and relatively easy to put into practice. Our discussion includes a concrete example of such an assignment, followed by a description of guidelines for the design of this style of teaching unit

Synopsis of current satellite snow mapping techniques, with emphasis on the application of near-infrared data

The Skylab EREP S192 Multispectral Scanner data have provided for the first time an opportunity to examine the reflectance characteristics of snowcover in several spectral bands extending from the visible into the near-infrared spectral region. The analysis of the S192 imagery and digital tape data indicates a sharp drop in reflectance of snow in the near-infrared, with snow becoming essentially nonreflective in Bands 11 (1.55-1.75 micron) and 12 (2.10-2.35 micron). Two potential applications to snow mapping of measurements in the near-infrared spectral region are possible: (1) the use of a near-infrared band in conjunction with a visible band to distinguish automatically between snow and water droplet clouds; and (2) the use of one or more near-infrared bands to detect areas of melting snow

Use of synchrotron tomographic techniques in the assessment of diffusion parameters for solute transport in groundwater flow

This technical note describes the use of time-resolved synchrotron radiation tomographic energy dispersive diffraction imaging (TEDDI) and tomographic X-ray fluorescence (TXRF) for examining ion diffusion in porous media. The technique is capable of tracking the diffusion of several ion species simultaneously. This is illustrated by results which compare the movement of Cs+, Ba2+ and La3+ ions from solution into a typical sample of English chalk. The results exhibited somewhat anomalous (non-Fickian) behaviour and revealed heterogeneities (in 1D) on the scale of a few millimetres

Electronic doctoral theses in the UK: a sector-wide survey into policies, practice and barriers to Open Access

Sharing knowledge and research outputs is critical to the progress of science and human development, and a central tenet of academia. The Internet itself is a product of the academic community, and opening access to that community’s most important body of research, doctoral theses, is both a logical and an inevitable development. Progress toward open access to electronic theses has been slow in the UK. Much has been written on the perceived barriers and practical/infrastructural considerations that might explain this, but a comprehensive picture of that progress, and obstacles to it, was lacking. In 2010, a survey of policy and practice in UK HEIs was conducted by UCL (University College London) Library Services (commissioned by the Joint Information Systems Committee, JISC) to address this very issue. Incorporating inputs from 144 institutions currently awarding doctoral degrees, the work provides the first clear and detailed picture of the status of open access to doctoral research in the UK. The mission of the UK Council for Graduate Education (UKCGE) is to promote and support the interests of graduate education, and this it does through dissemination of best practice and intelligence on emergent trends; helping to shape policy and practice for the benefit of the UK HEI sector. This report contributes to that mission by bringing to the membership’s attention the results of this important work by UCL Library Services; a collaboration between UKCGE and the authors of the original work, it sets out the policies and practices that emerged from the survey and also considers what has been learned about the perceived barriers to the implementation of open access to electronic theses. The 2010 survey has enabled, for the first time, a differentiation to be made between barriers that are “real” and those which are unfounded and/or yet to be properly validated. At the same time, the work highlights the progress made in certain critical areas, as well as those that require our greater attention. A positive picture emerges for the UK on the adoption of the electronic thesis, with the majority of HEIs surveyed expected to be providing open access to their theses in five years’ time. A more detailed picture also emerges regarding the primary reasons for requests to restrict access to theses, some of which, notably, apply only to electronic (not print) theses. This has necessarily given rise to new policy developments. There is positive evidence also of collaboration among HEIs to provide an efficient and robust service for accessing electronic theses; pooling their resources and expertise either in the development of their institutional repositories or in operating a joint service. The key driver of open access to electronic theses is the opportunity for UK HEIs to “showcase” their research outputs to the widest possible audience and enhance their impact. There are no reliable means as yet to measure this impact, but there are encouraging early indications that electronic doctoral theses attract significant attention when made openly accessible. Open access to electronic theses may therefore indeed accelerate the sharing of knowledge and the progress of scientific discovery and human development

Lie groups of conformal motions acting on null orbits

Space-times admitting a 3-dimensional Lie group of conformal motions $C_3$ acting on null orbits are studied. Coordinate expressions for the metric and the conformal Killing vectors (CKV) are provided (irrespectively of the matter content) and then all possible perfect fluid solutions are found, although none of these verify the weak and dominant energy conditions over the whole space-time manifold.Comment: 5 pages, Late

High-m Kink/Tearing Modes in Cylindrical Geometry

The global ideal kink equation, for cylindrical geometry and zero beta, is simplified in the high poloidal mode number limit and used to determine the tearing stability parameter, $\Delta^\prime$. In the presence of a steep monotonic current gradient, $\Delta^\prime$ becomes a function of a parameter, $\sigma_0$, characterising the ratio of the maximum current gradient to magnetic shear, and $x_s$, characterising the separation of the resonant surface from the maximum of the current gradient. In equilibria containing a current "spike", so that there is a non-monotonic current profile, $\Delta^\prime$ also depends on two parameters: $\kappa$, related to the ratio of the curvature of the current density at its maximum to the magnetic shear, and $x_s$, which now represents the separation of the resonance from the point of maximum current density. The relation of our results to earlier studies of tearing modes and to recent gyro-kinetic calculations of current driven instabilities, is discussed, together with potential implications for the stability of the tokamak pedestal.Comment: To appear in Plasma Physics and Controlled Fusio