597 research outputs found
IMPACTS OF POWER SYSTEM-TIED DISTRIBUTED GENERATION ON THE PERFORMANCE OF PROTECTION SYSTEMS
The dispersed integration of smaller power units in the existing utility grid is the new trend. This is largely due to changes in the power generation and distribution markets. The combination of rising cost of new construction, deregulations and improved newer power equipment technologies suitable for deferred expansions make the new trend very attractive to power companies and independent investors. Until recently, other contributions to power distribution systems from such sources as standby units were considered negligible and therefore unaccounted for during the design and operation of power systems. This view has drastically changed, largely due to the increasing penetration levels of these newer technologies termed Distributed Generation Resources. This thesis work is a continuation of ongoing work in the validation of the benefits and pitfalls of grid integrated Distributed Generation using modern modeling and simulation techniques. The proposed simplified but more robust symmetrical components based protection relay system is shown to be immune to the mis-coordination, mis-operation and blinding caused by the bidirectional power flow resulting from the high shares of Distributed renewable resource integration
Distinguishing among Scalar Field Models of Dark Energy
We show that various scalar field models of dark energy predict degenerate
luminosity distance history of the Universe and thus cannot be distinguished by
supernovae measurements alone. In particular, models with a vanishing
cosmological constant (the value of the potential at its minimum) are
degenerate with models with a positive or negative cosmological constant whose
magnitude can be as large as the critical density. Adding information from CMB
anisotropy measurements does reduce the degeneracy somewhat but not
significantly. Our results indicate that a theoretical prior on the preferred
form of the potential and the field's initial conditions may allow to
quantitatively estimate model parameters from data. Without such a theoretical
prior only limited qualitative information on the form and parameters of the
potential can be extracted even from very accurate data.Comment: 15 pages, 5 figure
Response of distance measures to the equation of state
We show that the distance measures (such as the luminosity and angular
diameter distances) are linear functionals of the equation-of-state function
w(z) of the dark energy to a fair degree of accuracy in the regimes of
interest. That is, the distance measures can be expressed as a sum of (i) a
constant and (ii) an integral of a weighting function multiplied by the
equation of state parameter w(z). The existence of such an accurate linear
response approximation has several important implications: (a) Fitting a
constant w model to the data drawn from an evolving model has a simple
interpretation as a weighted average of w(z). (b) Any polynomial (or other
expansion coefficients can also be expressed as weighted sums of the true w(z).
(c) A replacement for the commonly used heuristic equation for the effective
w(z), as determined by the CMB, can be derived and the result is found to be
quite close to the heuristic expression commonly used. (d) The reconstruction
of w(z) by Huterer et al. (2002) can be expressed as a matrix inversion. In
each case the limitations of the linear response approximation are explored and
found to be surprisingly small.Comment: 6 pages, 5 figures, minor changes, accepted to MNRA
Pipe dreams or digital dreams: Technology, pedagogy and content knowledge in the vocational educational and training sector
Regional Australia provides fertile ground for the integration of online technologies to support the vocational education and training (VET) sector. This paper examines teachers’ beliefs about teaching with technology in a regional VET institute. VET teachers must demonstrate teaching expertise (pedagogical knowledge) and industry expertise (content knowledge) for diverse learners and contexts; however, the emergence of new digital technologies illustrates an increasing need for teachers to embrace ‘technology’ knowledge commensurate with industry practice. Recent surveys have revealed that teachers’ use of online digital technology within the VET sector is not effectively incorporated nor has it been embraced in pedagogically defensible ways. This paper adopts a mixed methods approach to understand how the epistemic beliefs of VET teachers influence their teaching and how the TPACK is applied in practice. Finally, this paper illuminates the need for professional development programmes to focus on developing teacher knowledge across all TPACK domains
Evolution of density perturbations in double exponential quintessence models
In this work we investigate the evolution of matter density perturbations for
quintessence models with a self-interaction potential that is a combination of
exponentials. One of the models is based on the Einstein theory of gravity,
while the other is based on the Brans-Dicke scalar tensor theory. We constrain
the parameter space of the models using the determinations for the growth rate
of perturbations derived from data of the 2-degree Field Galaxy Redshift
Survey.Comment: 5 pages, 3 eps figure
Opportunities for future supernova studies of cosmic acceleration
We investigate the potential of a future supernova dataset, as might be
obtained by the proposed SNAP satellite, to discriminate among different ``dark
energy'' theories that describe an accelerating Universe. We find that many
such models can be distinguished with a fit to the effective
pressure-to-density ratio, , of this energy. More models can be
distinguished when the effective slope, , of a changing is also fit,
but only if our knowledge of the current mass density, , is improved.
We investigate the use of ``fitting functions'' to interpret luminosity
distance data from supernova searches, and argue in favor of a particular
preferred method, which we use in our analysis.Comment: Four pages including figures. Final published version. No significant
changes from v
Impairment in predictive processes during auditory mismatch negativity in ScZ: evidence from event-related fields
Patients with schizophrenia (ScZ) show pronounced dysfunctions in auditory perception but the underlying mechanisms as well as the localization of the deficit remain unclear. To examine these questions, the current study examined whether alterations in the neuromagnetic mismatch negativity (MMNm) in ScZ-patients could involve an impairment in sensory predictions in local sensory and higher auditory areas. Using a whole-head MEG-approach, we investigated the MMNm as well as P300m and N100m amplitudes during a hierarchical auditory novelty paradigm in 16 medicated ScZ-patients and 16 controls. In addition, responses to omitted sounds were investigated, allowing for a critical test of the predictive coding hypothesis. Source-localization was performed to identify the generators of the MMNm, omission responses as well as the P300m. Clinical symptoms were examined with the positive and negative syndrome scale. Event-related fields (ERFs) to standard sounds were intact in ScZ-patients. However, the ScZ-group showed a reduction in the amplitude of the MMNm during both local (within trials) and global (across trials) conditions as well as an absent P300m at the global level. Importantly, responses to sound omissions were reduced in ScZ-patients which overlapped both in latency and generators with the MMNm sources. Thus, our data suggest that auditory dysfunctions in ScZ involve impaired predictive processes that involve deficits in both automatic and conscious detection of auditory regularities
Quantized Non-Abelian Monopoles on S^3
A possible electric-magnetic duality suggests that the confinement of
non-Abelian electric charges manifests itself as a perturbative quantum effect
for the dual magnetic charges. Motivated by this possibility, we study vacuum
fluctuations around a non-Abelian monopole-antimonopole pair treated as point
objects with charges g=\pm n/2 (n=1,2,...), and placed on the antipodes of a
three sphere of radius R. We explicitly find all the fluctuation modes by
linearizing and solving the Yang-Mills equations about this background field on
a three sphere. We recover, generalize and extend earlier results, including
those on the stability analysis of non-Abelian magnetic monopoles. We find that
for g \ge 1 monopoles there is an unstable mode that tends to squeeze magnetic
flux in the angular directions. We sum the vacuum energy contributions of the
fluctuation modes for the g=1/2 case and find oscillatory dependence on the
cutoff scale. Subject to certain assumptions, we find that the contribution of
the fluctuation modes to the quantum zero point energy behaves as -R^{-2/3} and
hence decays more slowly than the classical -R^{-1} Coulomb potential for large
R. However, this correction to the zero point energy does not agree with the
linear growth expected if the monopoles are confined.Comment: 18 pages, 5 figures. Minor changes, reference list update
Fitting inverse power-law quintessence models using the SNAP satellite
We investigate the possibility of using the proposed SNAP satellite in
combination with low-z supernova searches to distinguish between different
inverse power-law quintessence models. If the true model is that of a
cosmological constant, we determine the prospects of ruling out the inverse
power-law potential. We show that SNAP combined with e.g. the SNfactory and an
independent measurement of the mass energy density to 17% accuracy can
distinguish between an inverse power-law potential and a cosmological constant
and put severe constraints on the power-law exponent.Comment: 5 pages, 6 figure
Temporal niche expansion in mammals from a nocturnal ancestor after dinosaur extinction
Most modern mammals, including strictly diurnal species, exhibit sensory adaptations to nocturnal activity that are thought to be the result of a prolonged nocturnal phase or ‘bottleneck’ during early mammalian evolution. Nocturnality may have allowed mammals to avoid antagonistic interactions with diurnal dinosaurs during the Mesozoic. However, understanding the evolution of mammalian activity patterns is hindered by scant and ambiguous fossil evidence. While ancestral reconstructions of behavioural traits from extant species have the potential to elucidate these patterns, existing studies have been limited in taxonomic scope. Here, we use an extensive behavioural dataset for 2,415 species from all extant orders to reconstruct ancestral activity patterns across Mammalia. We find strong support for the nocturnal origin of mammals and the Cenozoic appearance of diurnality, although cathemerality (mixed diel periodicity) may have appeared in the late Cretaceous. Simian primates are among the earliest mammals to exhibit strict diurnal activity, some 52–33 million years ago. Our study is consistent with the hypothesis that temporal partitioning between early mammals and dinosaurs during the Mesozoic led to a mammalian nocturnal bottleneck, but also demonstrates the need for improved phylogenetic estimates for Mammalia
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