969 research outputs found
On certain cosmological relics of the early string dynamics
The tracing of cosmological relics from the early string dynamics may enhance
the theory and provide new perspectives on the major cosmological problems.
This point is illustrated in a leading-order Bianchi-type string
background, wherein spatial isotropy can be claimed as such a relic. A much
finer one, descending from a premordial gravitational wave, could be retrieved
from its imprint on the small-scale structure of the cosmic microwave
background. In spite of the absence of conventional inflation, there is no
horizon problem thanks to the presence of an equally fundamental mixmaster
dynamics. Implications and certain new perspectives which thus arise for the
more general problem of cosmological mixing are briefly discussed.Comment: Latex file, 11 pages, 0 figures. Re-titled revision of "Mixing
towards isotropization..." to appear in Class. Quantum Gravit
Stability analysis of cosmological models through Liapunov's method
We investigate the general asymptotic behaviour of Friedman-Robertson-Walker
(FRW) models with an inflaton field, scalar-tensor FRW cosmological models and
diagonal Bianchi-IX models by means of Liapunov's method. This method provides
information not only about the asymptotic stability of a given equilibrium
point but also about its basin of attraction. This cannot be obtained by the
usual methods found in the literature, such as linear stability analysis or
first order perturbation techniques. Moreover, Liapunov's method is also
applicable to non-autonomous systems. We use this advantadge to investigate the
mechanism of reheating for the inflaton field in FRW models.Comment: Latex file, 8 pages, no figures, accepted for publication in Class. &
Quant. Gra
Efficacy of Online Training for Improving Camp Staff Competency
Preparing competent staff is a critical issue within the camp community. This quasi-experimental study examined the effectiveness of an online course for improving staff competency in camp healthcare practices among college-aged camp staff and a comparison group (N = 55). We hypothesized that working in camp would increase competency test scores due to opportunities for staff to experientially apply knowledge learned online. Hierarchical linear modeling was used to analyse the cross-level effects of a between-individuals factor (assignment to experimental or comparison group) and within-individual effects of time (pre-test, post-test #1, and post-test #2) on online course test scores. At post-test #2, the difference in average test scores between groups was ~30 points, with the treatment group scoring lower on average than the comparison group. Factors that may have influenced these findings are explored, including fatigue and the limited durability of online learning. Recommendations for research and practice are discussed
Triad representation of the Chern-Simons state in quantum gravity
We investigate a triad representation of the Chern-Simons state of quantum
gravity with a non-vanishing cosmological constant. It is shown that the
Chern-Simons state, which is a well-known exact wavefunctional within the
Ashtekar theory, can be transformed to the real triad representation by means
of a suitably generalized Fourier transformation, yielding a complex integral
representation for the corresponding state in the triad variables. It is found
that topologically inequivalent choices for the complex integration contour
give rise to linearly independent wavefunctionals in the triad representation,
which all arise from the one Chern-Simons state in the Ashtekar variables. For
a suitable choice of the normalization factor, these states turn out to be
gauge-invariant under arbitrary, even topologically non-trivial
gauge-transformations. Explicit analytical expressions for the wavefunctionals
in the triad representation can be obtained in several interesting asymptotic
parameter regimes, and the associated semiclassical 4-geometries are discussed.
In restriction to Bianchi-type homogeneous 3-metrics, we compare our results
with earlier discussions of homogeneous cosmological models. Moreover, we
define an inner product on the Hilbert space of quantum gravity, and choose a
natural gauge-condition fixing the time-gauge. With respect to this particular
inner product, the Chern-Simons state of quantum gravity turns out to be a
non-normalizable wavefunctional.Comment: Latex, 30 pages, 1 figure, to appear in Phys. Rev.
The Concordance Cosmic Star Formation Rate: Implications from and for the Supernova Neutrino and Gamma Ray Backgrounds
We constrain the Cosmic Star Formation Rate (CSFR) by requiring that massive
stars produce the observed UV, optical, and IR light while at the same time not
overproduce the Diffuse Supernova Neutrino Background as bounded by
Super-Kamiokande. With the massive star component so constrained we then show
that a reasonable choice of stellar Initial Mass Function and other parameters
results in SNIa rates and iron yields in good agreement with data. In this way
we define a `concordance' CSFR that predicts the optical SNII rate and the SNIa
contribution to the MeV Cosmic Gamma-Ray Background. The CSFR constrained to
reproduce these and other proxies of intermediate and massive star formation is
more clearly delineated than if it were measured by any one technique and has
the following testable consequences: (1) SNIa contribute only a small fraction
of the MeV Cosmic Gamma-Ray Background, (2) massive star core-collapse is
nearly always accompanied by a successful optical SNII, and (3) the Diffuse
Supernova Neutrino Background is tantalizingly close to detectability.Comment: Improved discussion. Version accepted for publication in JCA
Primordial nucleosynthesis with a varying fine structure constant: An improved estimate
We compute primordial light-element abundances for cases with fine structure
constant alpha different from the present value, including many sources of
alpha dependence neglected in previous calculations. Specifically, we consider
contributions arising from Coulomb barrier penetration, photon coupling to
nuclear currents, and the electromagnetic components of nuclear masses. We find
the primordial abundances to depend more weakly on alpha than previously
estimated, by up to a factor of 2 in the case of ^7Li. We discuss the
constraints on variations in alpha from the individual abundance measurements
and the uncertainties affecting these constraints. While the present best
measurements of primordial D/H, ^4He/H, and ^7Li/H may be reconciled pairwise
by adjusting alpha and the universal baryon density, no value of alpha allows
all three to be accommodated simultaneously without consideration of systematic
error. The combination of measured abundances with observations of acoustic
peaks in the cosmic microwave background favors no change in alpha within the
uncertainties.Comment: Phys. Rev. D accepted version; minor changes in response to refere
The Use of Case Study Competitions to Prepare Students for the World of Work
As we continue into the new millennium, it is imperative that educational institutions equip graduates with the knowledge and skills that are increasingly needed and valued by business and industry. In this article, the authors argue that the case study approach and, specifically, case study competitions constitute an ideal pedagogical strategy for achieving this objective in an effective and efficient manner, with resulting benefits for both students and employers
Assessing student expectations and perceptions of a shortâ term international serviceâ learning experience
ObjectivesDespite nursing studentsâ need for cultural education, few studies have measured what students expect from international serviceâ learning experiences and how their perceptions of the actual experience compare to these expectations. To increase understanding of global nursing experiences, the purpose of this study was to examine the similarities and differences between nursing studentsâ anticipated (preâ travel) personal and professional developmental expectations and reported (posttravel) personal and developmental outcomes.DesignThis study employed a mixed descriptive research design. Quantitative data was secured through survey methodology. Written responses to openâ ended questions provided qualitative data for analysis.SampleBetween 2012 and 2017, 43 undergraduate and graduate nursing students at a Midwestern university completed surveys and narratives about their participation in an international serviceâ learning course in Kenya.ResultsStudentsâ anticipated learning was achieved through their international experiences. Participants also experienced personal growth, professional development, cultural competency enhancement, and transformation from the educational experience. They also described how their experiences would change their personal and professional lives.ConclusionThe depth and breadth of the growth and learning described by students is consistent with the expectations of highâ impact educational practices.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153597/1/phn12669_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153597/2/phn12669.pd
Particle creation, renormalizability conditions and the mass-energy spectrum in gravity theories of quadratic Lagrangians
Massive scalar particle production, due to the anisotropic evolution of a
five-dimensional spacetime, is considered in the context of a quadratic
Lagrangian theory of gravity. Those particles, corresponding to field modes
with non-vanishing momentum component along the fifth dimension, are created
mostly in the neighbourhood of a singular epoch where only their high-frequency
behaviour is of considerable importance. At the 1-loop approximation level,
general renormalizability conditions on the physical quantities relevant to
particle production are derived and discussed. Exact solutions of the resulting
Klein-Gordon field equation are obtained and the mass-energy spectrum
attributed to the scalar field due to the cosmological evolution is being
investigated further. Finally, analytic expressions regarding the number and
the energy density of the created particles at late times, are also derived and
discussed.Comment: LaTeX file, 23 page
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