On the Entropy and the Density Matrix of Cosmological Perturbations

We look at the transition to the semiclassical behaviour and the decoherence process for the inhomogeneous perturbations in the inflationary universe. Two different decoherence mechanisms appear: one dynamical, accompanied with a negligible, if at all, entropy gain, and the other, effectively irreversible dephasing, due to a rapid variation in time of the off-diagonal density matrix elements in the post-inflationary epoch. We thus settle the discrepancies in the entropy content of perturbations evaluated by different authors.Comment: LaTeX2e with the epsf packag

Revisiting the Benefits of Higher Education

The economic returns of higher education (HE) in terms of enhanced earnings are well established. The wider set of ‘non-economic benefits’ in the areas of health, generic skills and citizenship are less widely recognised. In an earlier report, we presented preliminary findings on the wider benefits, drawing on data collected at age 33 from the National Child Development Study (based on a cohort born in 1958). This report updates the earlier conclusions through new findings from a more extensive analysis involving both the 1958 cohort and the more recent 1970 British Cohort Study cohort (based on a cohort born in 1970). The current analysis incorporates more recent data collected in both cohorts in 2000 and at an older age (1958 cohort). We report findings in five major areas. First, we examine the mobility of graduates. To what extent do some parts of the country gain and lose graduates and graduate types of occupation at the expense of others? We then report findings on the ‘marginal returns’ to higher education in four domains of life: health, labour market, citizenship and values, and parenting

Penrose Limits, the Colliding Plane Wave Problem and the Classical String Backgrounds

We show how the Szekeres form of the line element is naturally adapted to study Penrose limits in classical string backgrounds. Relating the "old" colliding wave problem to the Penrose limiting procedure as employed in string theory we discuss how two orthogonal Penrose limits uniquely determine the underlying target space when certain symmetry is imposed. We construct a conformally deformed background with two distinct, yet exactly solvable in terms of the string theory on R-R backgrounds, Penrose limits. Exploiting further the similarities between the two problems we find that the Penrose limit of the gauged WZW Nappi-Witten universe is itself a gauged WZW plane wave solution of Sfetsos and Tseytlin. Finally, we discuss some issues related to singularity, show the existence of a large class of non-Hausdorff solutions with Killing Cauchy Horizons and indicate a possible resolution of the problem of the definition of quantum vacuum in string theory on these time-dependent backgrounds.Comment: Some misprints corrected. Matches the version in print. To appear in Classical & Quantum Gravit

Higher education, mature students and employment goals: policies and practices in the UK

This article considers recent policies of Higher Education in the UK, which are aimed at widening participation and meeting the needs of employers. The focus is on the growing population of part-time students, and the implications of policies for this group. The article takes a critical perspective on government policies, using data from a major study of mature part-time students, conducted in two specialist institutions in the UK, a London University college and a distance learning university. Findings from this study throw doubt on the feasibility of determining a priori what kind of study pathway is most conducive for the individual in terms of employment gains and opportunities for upward social mobility. In conclusion, doubts are raised as to whether policies such as those of the present UK government are likely to achieve its aims. Such policies are not unique to the UK, and lessons from this country are relevant to most of the developed world

Gravitational Optics: Self-phase modulation and harmonic cascades

Nonlinear wave interaction of low amplitude gravitational waves in flat space-time is considered. Analogy with optics is established. It is shown that the flat metric space-time is equivalent to a centro-symmetric optical medium, with no second order susceptibility. The lowest order nonlinear effects are those due to the third order nonlinearity and include self-phase modulation and high harmonic generation. These processes lead to an efficient energy dilution of the gravitational wave energy over an increasingly large spectral range.Comment: 12 pages, REVTEX

Stellar Rotation in Young Clusters. II. Evolution of Stellar Rotation and Surface Helium Abundance

We derive the effective temperatures and gravities of 461 OB stars in 19 young clusters by fitting the H-gamma profile in their spectra. We use synthetic model profiles for rotating stars to develop a method to estimate the polar gravity for these stars, which we argue is a useful indicator of their evolutionary status. We combine these results with projected rotational velocity measurements obtained in a previous paper on these same open clusters. We find that the more massive B-stars experience a spin down as predicted by the theories for the evolution of rotating stars. Furthermore, we find that the members of binary stars also experience a marked spin down with advanced evolutionary state due to tidal interactions. We also derive non-LTE-corrected helium abundances for most of the sample by fitting the He I 4026, 4387, 4471 lines. A large number of helium peculiar stars are found among cooler stars with Teff < 23000 K. The analysis of the high mass stars (8.5 solar masses < M < 16 solar masses) shows that the helium enrichment process progresses through the main sequence (MS) phase and is greater among the faster rotators. This discovery supports the theoretical claim that rotationally induced internal mixing is the main cause of surface chemical anomalies that appear during the MS phase. The lower mass stars appear to have slower rotation rates among the low gravity objects, and they have a large proportion of helium peculiar stars. We suggest that both properties are due to their youth. The low gravity stars are probably pre-main sequence objects that will spin up as they contract. These young objects very likely host a remnant magnetic field from their natal cloud, and these strong fields sculpt out surface regions with unusual chemical abundances.Comment: 50 pages 18 figures, accepted by Ap

On the evolution of a large class of inhomogeneous scalar field cosmologies

The asymptotic behaviour of a family of inhomogeneous scalar field cosmologies with exponential potential is studied. By introducing new variables we can perform an almost complete analysis of the evolution of these cosmologies. Unlike the homogeneous case (Bianchi type solutions), when k^2<2 the models do not isotropize due to the presence of the inhomogeneitiesComment: 23 pages, 1 figure. Submitted to Classical and Quantum Gravit

Exact non-singular waves in the anti-de Sitter universe

A class of radiative solutions of Einstein's field equations with a negative cosmological constant and a pure radiation is investigated. The space-times, which generalize the Defrise solution, represent exact gravitational waves which interact with null matter and propagate in the anti-de Sitter universe. Interestingly, these solutions have homogeneous and non-singular wave-fronts for all freely moving observers. We also study properties of sandwich and impulsive waves which can be constructed in this class of space-times.Comment: 15 pages, 3 figures, To appear in Gen. Rel. Gra

A Summary of the Collaborative IS Curriculum Specification of the Joint DPMA, ACM, AIS Task Force

Information Systems \u2795 (IS \u2795), a model curriculum for a bachelor\u27s degree in Information Systems (IS), is the resulting development of collaborative work of a Joint Task Force of the Data Processing Management Association (DPMA), the Association for Computing Machinery (ACM), and Academy for Information Systems (AIS). Representation on the task force includes both academic and industrial members. This paper summarizes the full report (Figure 1). A definition of the IS discipline and its relevance within the business and university community is discussed. Resources needed to support a viable program are identified, including faculty, and information technology. Courses are identified and the characteristics of graduates defined. A paradigm is provided which couples a definition of the IS discipline and its underlying principles to the of characteristics of the IS graduate. An updated IS body of knowledge is presented. It is based on previous efforts of DPMA and ACM (Longenecker and Feinstein 1991a,b,c; Ashenhurst 1972; Couger 1972; ACM 1983 and ACM 1990; DPMA 1981, 1986). The current body of knowledge contains the Computer Science and Engineering body of knowledge (Turner and Tucker 1991). A cognitive behavioral metric is presented for specifying and evaluating depth of knowledge. The specification includes a numeric depth indicator and appropriate language to describe presentation goals and resultant behavior expected of students completing study of specific aspects of the curriculum. A modular concept of learning units is defined and utilized in specifying proposed courses. Methods for mapping the learning units to alternate course plans are discussed. Elements from the body of knowledge are combined in a logical top-down manner to form Learning Units (LU). Each LU contains a goal statement, behavioral objectives and associated elements from the body of knowledge. Five curriculum areas with 20 sub-areas form clusters of these learning units. A complete set of 128 learning units form meta-presentation units which can be organized in different schemes to meet individual institutional missions. One possible organization of these units into ten courses is presented. This paper provides curriculum guidelines for implementing undergraduate programs in information systems. The full report, IS\u2795, provides the detail necessary for design and implementation of courses. Dissemination of the curriculum and plans for review and updating the curriculum are presented

Disks in Expanding FRW Universes

We construct exact solutions to Einstein equations which represent relativistic disks immersed into an expanding FRW Universe. It is shown that the expansion influences dynamical characteristics of the disks such as rotational curves, surface mass density, etc. The effects of the expansion is exemplified with non-static generalizations of Kuzmin-Curzon and generalized Schwarzschild disks.Comment: Revised version to appear in ApJ, Latex, 17 pages, 10 figures, uses aaspp4 and epsf style file