Bifurcation analysis of frequency locking in a semiconductor laser with phase-conjugate feedback

We present a detailed study of the external-cavity modes (ECMs) of a semiconductor laser with phase-conjugate feedback. Mathematically, lasers with feedback are modeled by delay differential equations (DDEs) with an infinite-dimensional phase space. We employ new numerical bifurcation tools for DDEs to continue steady states and periodic orbits, irrespective of their stability. In this way, we show that the periodic orbits corresponding to the ECMs are connected to the steady state solution associated with the locking range of the laser. We also identify symmetric and nonsymmetric homoclinic orbits and hysteresis in the system

Integrated assessment : new assessment methods literature review

The assessment of students in higher education performs a number of functions, some of which may not always be compatible with each other. Traditionally, the role of the assessor has involved determining the level of competence displayed in undertaking the task, and ideally, offering feedback on future learning needs (Rowntree, 1987). Assessment also provides grading for students’ work, allowing comparison of performance across a class, and across the curriculum for individual students. The subsequent gaining of a degree or professional qualification depends on students successfully completing a set of specified assessment tasks across the prescribed curriculum. As such, there may be stakeholders beyond the higher education institution, such as employers, regulatory bodies or clients, who believe the assessment process as being akin to certification or professional gatekeeping (Younes,1998). In professional courses such as social work, passing certain assessment tasks may be associated with notions such as fitness to practice and eligibility for professional registration as a social worker with the Scottish Social Services Council (SSSC) or similar bodies in England, Northern Ireland and Wales, and beyond the United Kingdom. In terms of gatekeeping, assessment tasks may not only restrict who gains certification on exiting an educational programme, but also who is admitted in the first place. For example, requirements by registration authorities that students admitted to social work programmes have achieved specified levels of literacy and numeracy will require appropriate assessment tasks to determine equivalence for those entrants who have not achieved formal qualifications in these areas. Entry point assessments may also be used to determine whether credit should be granted on the basis of prior learning or experience (Slater, 2000) or to identify areas in which additional training may be required (Shera, 2001) In addition to gatekeeping, assessment clearly has a vital role to play in the ongoing development of learning and teaching strategies. It can be crucial in determining what, why and how students learn (Brown, Bull and Pendlebury, 1997) and there is increasing recognition of the necessity to align learning and assessment tasks, so that learning and assessment become aligned rather than being somewhat independent of each other (Biggs, 2003). Furthermore, in an era when evaluation of teaching is often reduced to student satisfaction surveys, critical reflection on work submitted for assessment can serve as an alternative method of evaluating the success of teaching. The nature of assessment has changed considerably since the 1970s, and is ongoing. The key changes have included moves from written examinations to coursework assignments and more emphasis on student participation in assessment (self and peer assessments), processes rather than products, and on competencies rather than content (Brown et al., 1997). Even the more traditional forms of assessment such as essays and examinations have undergone considerable innovations. Yet, in practice these seemingly radical changes may be more a wish list than a statement of fact. In actuality, some new forms of assessment, such as self and peer assessment may simply have been added onto rather than replaced more traditional modes of assessment (Cree, 2000). Changes to assessment in social work tend to reflect changes in higher education more widely such as the emergence of competency based and modular approaches to learning, as well more proceduralised assessment processes necessary to cope with higher numbers of students (Cree, 2000). There is considerable divergence of opinion amongst the social work education community in the United Kingdom as to whether such changes actually benefit social work students and their learning (eg Clark, 1997; Ford and Hayes, 1996; O’Hagan, 1997; Shardlow and Doel, 1996). There have also been concerns expressed as to whether some new forms of assessment are actually capable of achieving the learning they claim to facilitate Boud, 1999; Entwistle, 1990; Taylor, 1993). This report was commissioned by the Scottish Institute for Excellence in Social Work Education (SIESWE) as a resource on assessment for the development of the new social work degree in Scotland and provides an overview of the current literature on assessment methods being utilised in social work education both in the United Kingdom and beyond. This report begins by reviewing the various methods of assessment in social work education which were found in the literature. We then go on to explore the developing literature on the involvement of persons other than social work academics, such as students and service users, in the assessment process. Finally, we consider the importance of developing and assessment strategy which might incorporate these various different forms of assessmen

Anti-D-brane as Dark Matter in Warped String Compactification

It is pointed out that in the warped string compactification, motion of anti-D-branes near the bottom of a throat behaves like dark matter. Several scenarios for production of the dark matter are suggested, including one based on the D/anti-D interaction at the late stage of D/anti-D inflation.Comment: 8 pages, version accepted for publication as a Rapid Communication in PRD, discussion about mass and production of dark matte

Integrated assessment : new assessment methods evaluation of an innovative method of assessment-critical incident analysis

For many people, the term “assessment” is associated with tasks, which are less than inspiring, which are undertaken only because they are hurdles, which must be crossed in order to achieve some form of accreditation or to enable entry into work or a further course of study. In this worldview, what is important for the student is the final determination or grade assigned to their work. While summative assessment, in which students submit work that is marked by experts and which contributes partially or fully to a final grade, plays an important role in the lives of students and educators, contemporary thinking about “assessment” is much more expansive

Demonstration of the range over which the Langley Research Center digital computer charring ablation program (CHAP) can be used with confidence: Comparisons of CHAP predictions and test data for three ablation materials

Comparisons of ablation calculations with the charring ablation computer code and ablation test data are presented over a wide range of environmental conditions in air for three materials: low-density nylon phenolic, Avcoat 5026-39HC/G, and a filled silicon elastomer. Heat fluxes considered range from over 500 Btu/sq ft-sec to less than 50 Btu/sq ft-sec. Pressures range from 0.5 atm to .004 atm. Enthalpies range from about 2000 Btu/lb to 18000 Btu/lb. Predictions of recession, pyrolysis penetration, and thermocouple responses are considered. Recession predictions for nylon phenolic are good as steady state is approached, but strongly transient cases are underpredicted. Pyrolysis penetrations and thermocouple responses are very well predicted. Recession amounts for Avcoat and silicone elastomer are less well predicted, although high heat flux cases near steady state are fairly satisfactory. Pyrolysis penetrations and thermocouple responses are very well predicted