136 research outputs found
Secondary homotopy groups
Secondary homotopy groups supplement the structure of classical homotopy
groups. They yield a track functor on the track category of pointed spaces
compatible with fiber sequences, suspensions and loop spaces. They also yield
algebraic models of homotopy types with homotopy groups concentrated in two
consecutive dimensions.Comment: We added further commets and references to make the paper more easily
readabl
Optimization of 100 MWe Parabolic-Trough Solar-Thermal Power Plants Under Regulated and Deregulated Electricity Market Conditions
Parabolic-trough solar-thermal power-plant investments are subordinate to radiation availability, thermal-energy storage capacity, and dynamic behavior. Their integration into electricity markets is made by minimizing grid-connection costs, thus improving energy-availability and economic-efficiency levels. In this context, this work analyzes the sizing-investment adequacy of a 100 MWe parabolic-trough solar-thermal power plant regarding solar resources and thermal energy into power-block availability for both regulated and deregulated electricity markets. For this proposal, the design of a mathematical model for the optimal operation of parabolic-trough power plants with thermal storage by two tanks of molten salt is described. Model calibration is made by using a currently operated plant. Solar-resource availability is studied in three different radiation scenarios. The levelized cost of electricity and production profit relating to the investment cost are used to analyze plant sustainability. Thus, the levelized cost of electricity shows the best plant configuration for each radiation scenario within a regulated market. For deregulated markets, the optimal plant configuration tends to enhance the solar multiple and thermal-storage capacity thanks to an increment on selling profit. The gross average annual benefit for electricity generation of deregulated against regulated markets exceeds 21% in all radiation areas under study
Techno-Economic Assessment of Heat Transfer Fluid Buffering for Thermal Energy Storage in the Solar Field of Parabolic Trough Solar Thermal Power Plants
Currently, operating parabolic trough (PT) solar thermal power plants, either solar-only or with thermal storage block, use the solar field as a heat transfer fluid (HTF) thermal storage system to provide extra thermal capacity when it is needed. This is done by circulating heat transfer fluid into the solar field piping in order to create a heat fluid buffer. In the same way, by oversizing the solar field, it can work as an alternative thermal energy storage (TES) system to the traditionally applied methods. This paper presents a solar field TES model for a standard solar field from a 50-MWe solar power plant. An oversized solar model is analyzed to increase the capacity storage system (HTF buffering). A mathematical model has been developed and different simulations have been carried out over a cycle of one year with six different solar multiples considered to represent the different oversized solar field configurations. Annual electricity generation and levelized cost of energy (LCOE) are calculated to find the solar multiple (SM) which makes the highest solar field thermal storage capacity possible within the minimum LCOE
Principal infinity-bundles - General theory
The theory of principal bundles makes sense in any infinity-topos, such as
that of topological, of smooth, or of otherwise geometric
infinity-groupoids/infinity-stacks, and more generally in slices of these. It
provides a natural geometric model for structured higher nonabelian cohomology
and controls general fiber bundles in terms of associated bundles. For suitable
choices of structure infinity-group G these G-principal infinity-bundles
reproduce the theories of ordinary principal bundles, of bundle
gerbes/principal 2-bundles and of bundle 2-gerbes and generalize these to their
further higher and equivariant analogs. The induced associated infinity-bundles
subsume the notions of gerbes and higher gerbes in the literature.
We discuss here this general theory of principal infinity-bundles, intimately
related to the axioms of Giraud, Toen-Vezzosi, Rezk and Lurie that characterize
infinity-toposes. We show a natural equivalence between principal
infinity-bundles and intrinsic nonabelian cocycles, implying the classification
of principal infinity-bundles by nonabelian sheaf hyper-cohomology. We observe
that the theory of geometric fiber infinity-bundles associated to principal
infinity-bundles subsumes a theory of infinity-gerbes and of twisted
infinity-bundles, with twists deriving from local coefficient infinity-bundles,
which we define, relate to extensions of principal infinity-bundles and show to
be classified by a corresponding notion of twisted cohomology, identified with
the cohomology of a corresponding slice infinity-topos.
In a companion article [NSSb] we discuss explicit presentations of this
theory in categories of simplicial (pre)sheaves by hyper-Cech cohomology and by
simplicial weakly-principal bundles; and in [NSSc] we discuss various examples
and applications of the theory.Comment: 46 pages, published versio
An Optical Study of Stellar and Interstellar Environments of Seven Luminous and Ultraluminous X-Ray Sources
We have studied the stellar and interstellar environments of two luminous
X-ray sources and five ultraluminous X-ray sources (ULXs) in order to gain
insight into their nature. Archival Hubble Space Telescope images were used to
identify the optical counterparts of the ULXs Ho IX X-1 and NGC 1313 X-2, and
to make photometric measurements of the local stellar populations of these and
the luminous source IC 10 X-1. We obtained high-dispersion spectroscopic
observations of the nebulae around these seven sources to search for He II
lambda-4686 emission and to estimate the expansion velocities and kinetic
energies of these nebulae. Our observations did not detect nebular He II
emission from any source, with the exception of LMC X-1; this is either because
we missed the He III regions or because the nebulae are too diffuse to produce
He II surface brightnesses that lie within our detection limit. We compare the
observed ionization and kinematics of the supershells around the ULXs Ho IX X-1
and NGC 1313 X-2 with the energy feedback expected from the underlying stellar
population to assess whether additional energy contributions from the ULXs are
needed. In both cases, we find insufficient UV fluxes or mechanical energies
from the stellar population; thus these ULXs may be partially responsible for
the ionization and energetics of their supershells. All seven sources we
studied are in young stellar environments and six of them have optical
counterparts with masses >~7 M_sun; thus, these sources are most likely
high-mass X-ray binaries.Comment: 30 pages, 9 figures. Numerous minor revisions, primarily to more
accurately cite earlier work by Pakull and Mirioni, and to correct
typographical errors. Removed a misleading sentence in the Introduction (re:
X-ray photoionization by ULXs). Accepted for publication in The Astrophysical
Journal. Figures have been reduced in resolution for space requirements;
full-resolution figures may be requested by email to [email protected]
An Optical Study of Stellar and Interstellar Environments of Seven Luminous and Ultraluminous X-Ray Sources
We have studied the stellar and interstellar environments of two luminous
X-ray sources and five ultraluminous X-ray sources (ULXs) in order to gain
insight into their nature. Archival Hubble Space Telescope images were used to
identify the optical counterparts of the ULXs Ho IX X-1 and NGC 1313 X-2, and
to make photometric measurements of the local stellar populations of these and
the luminous source IC 10 X-1. We obtained high-dispersion spectroscopic
observations of the nebulae around these seven sources to search for He II
lambda-4686 emission and to estimate the expansion velocities and kinetic
energies of these nebulae. Our observations did not detect nebular He II
emission from any source, with the exception of LMC X-1; this is either because
we missed the He III regions or because the nebulae are too diffuse to produce
He II surface brightnesses that lie within our detection limit. We compare the
observed ionization and kinematics of the supershells around the ULXs Ho IX X-1
and NGC 1313 X-2 with the energy feedback expected from the underlying stellar
population to assess whether additional energy contributions from the ULXs are
needed. In both cases, we find insufficient UV fluxes or mechanical energies
from the stellar population; thus these ULXs may be partially responsible for
the ionization and energetics of their supershells. All seven sources we
studied are in young stellar environments and six of them have optical
counterparts with masses >~7 M_sun; thus, these sources are most likely
high-mass X-ray binaries.Comment: 30 pages, 9 figures. Numerous minor revisions, primarily to more
accurately cite earlier work by Pakull and Mirioni, and to correct
typographical errors. Removed a misleading sentence in the Introduction (re:
X-ray photoionization by ULXs). Accepted for publication in The Astrophysical
Journal. Figures have been reduced in resolution for space requirements;
full-resolution figures may be requested by email to [email protected]
Nerves and classifying spaces for bicategories
This paper explores the relationship amongst the various simplicial and
pseudo-simplicial objects characteristically associated to any bicategory C. It
proves the fact that the geometric realizations of all of these possible
candidate `nerves of C' are homotopy equivalent. Any one of these realizations
could therefore be taken as the classifying space BC of the bicategory. Its
other major result proves a direct extension of Thomason's `Homotopy Colimit
Theorem' to bicategories: When the homotopy colimit construction is carried out
on a diagram of spaces obtained by applying the classifying space functor to a
diagram of bicategories, the resulting space has the homotopy type of a certain
bicategory, called the `Grothendieck construction on the diagram'. Our results
provide coherence for all reasonable extensions to bicategories of Quillen's
definition of the `classifying space' of a category as the geometric
realization of the category's Grothendieck nerve, and they are applied to
monoidal (tensor) categories through the elemental `delooping' construction.Comment: 42 page
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