7,001 research outputs found
Renewable Energy Resources Impact on Clean Electrical Power by developing the North-West England Hydro Resource Model.
This paper describes the development of a sequential decision support system to promote hydroelectric power in North-West England. The system, composed of integrated models, addresses barriers to the installation of hydroelectric power schemes. Information is linked through an economic assessment which identifies different turbine options, assesses their suitability for location and demand; and combines the different types of information in a way that supports decision making. The system is structured into five components: the hydrological resource is modelled using Low Flows 2000, the turbine options are identified from hydrological, environmental and demand requirements; and the consequences of different solutions will be fed into other components so that the environmental impacts and public acceptability can be assessed and valued. A preliminary case study is presented on an old gunpowder works to illustrate how the resource model may be employed. Historical architectural structures, power uptake and educational instruction of hydro power technology are considered
Validity of the linear coupling approximation in heavy-ion fusion reactions at sub barrier energies
The role of higher order coupling of surface vibrations to the relative
motion in heavy-ion fusion reactions at near-barrier energies is investigated.
The coupled channels equations are solved to all orders, and also in the linear
and the quadratic coupling approximations. Taking Ni + Zr
reactions as examples, it is shown that all order couplings lead to
considerably improved agreement with the experimentally measured fusion cross
sections and average angular momenta of the compound nucleus for such heavy
nearly symmetric systems. The importance of higher order coupling is also
examined for asymmetric systems like O + Cd, Sm, for
which previous calculations of the fusion cross section seemed to indicate that
the linear coupling approximation was adequate. It is shown that the shape of
the barrier distributions and the energy dependence of the average angular
momentum can change significantly when the higher order couplings are included,
even for systems where measured fusion cross sections may seem to be well
reproduced by the linear coupling approximation.Comment: Latex file, 15 pages, 6 figure
The effects of a background potential in star cluster evolution: a delay in the relaxation time-scale and runaway collision processes
Runaway stellar collisions in dense star clusters are invoked to explain the
presence of very massive stars or blue stragglers in the center of those
systems. This process has also been explored for the first star clusters in the
Universe and shown to yield stars that may collapse at some points into an
intermediate mass black hole. Although the early evolution of star clusters
requires the explicit modeling of the gas out of which the stars form, these
calculations would be extremely time-consuming and often the effects of the gas
can be accurately treated by including a background potential to account for
the extra gravitational force. We apply this approximation to model the early
evolution of the first dense star clusters formed in the Universe by performing
-body simulations, our goal is to understand how the additional
gravitational force affects the growth of a very massive star through stellar
mergers in the central parts of the star cluster. Our results show that the
background potential increases the velocities of the stars, causing an overall
delay in the evolution of the clusters and in the runaway growth of a massive
star at the center. The population of binary stars is lower due to the
increased kinetic energy of the stars, initially reducing the number of stellar
collisions, and we show that relaxation processes are also affected. Despite
these effects, the external potential enhances the mass of the merger product
by a factor 2 if the collisions are maintained for long times.Comment: 16 pages. Accepted for publication in Astronomy and Astrophysic
Importance of Non-Linear Couplings in Fusion Barrier Distributions and Mean Angular Momenta
The effects of higher order coupling of surface vibrations to the relative
motion on heavy-ion fusion reactions at near-barrier energies are investigated.
The coupled channels equations are solved to all orders, and also in the linear
and the quadratic coupling approximations. It is shown that the shape of fusion
barrier distributions and the energy dependence of the average angular momentum
of the compound nucleus can significantly change when the higher order
couplings are included. The role of octupole vibrational excitation of ^{16}O
in the ^{16}O + ^{144}Sm fusion reaction is also discussed using the all order
coupled-channels equations.Comment: 8 pages, 6 figures, To be published in the Proceedings of the FUSION
97 Conference, South Durras, Australia, March 1997 (J. Phys. G
Another Leigh-Strassler deformation through the Matrix model
In here the matrix model approach, by Dijkgraaf and Vafa, is used in order to
obtain the effective superpotential for a certain deformation of N=4 SYM
discovered by Leigh and Strassler. An exact solution to the matrix model
Lagrangian is found and is expressed in terms of elliptic functions.Comment: 15 pages,2 figure
Potassium homeostasis in vacuolate plant cells
Plant cells contain two major pools of K+, one in the vacuole and one in the cytosol. The behavior of K+ concentrations in these pools is fundamental to understanding the way this nutrient affects plant growth. Triple-barreled microelectrodes have been used to obtain the first fully quantitative measurements of the changes in K+ activity (aK) in the vacuole and cytosol of barley (Hordeum vulgare L.) root cells grown in different K+ concentrations. The electrodes incorporate a pH-selective barrel allowing each measurement to be assigned to either the cytosol or vacuole. The measurements revealed that vacuolar aK declined linearly with decreases in tissue K+ concentration, whereas cytosolic aK initially remained constant in both epidermal and cortical cells but then declined at different rates in each cell type. An unexpected finding was that cytoplasmic pH declined in parallel with cytosolic aK, but acidification of the cytosol with butyrate did not reveal any short-term link between these two parameters. These measurements show the very different responses of the vacuolar and cytosolic K+ pools to changes in K+ availability and also show that cytosolic K+ homeostasis differs quantitatively in different cell types. The data have been used in thermodynamic calculations to predict the need for, and likely mechanisms of, active K+ transport into the vacuole and cytosol. The direction of active K+ transport at the vacuolar membrane changes with tissue K+ status
AdS Taub-Nut Space and the O(N) Vector Model on a Squashed 3-Sphere
In this note, motivated by the Klebanov-Polyakov conjecture we investigate
the strongly coupled O(N) vector model at large on a squashed three-sphere
and its holographic relation to bulk gravity on asymptotically locally
spaces. We present analytical results for the action of the field theory as the
squashing parameter , when the boundary becomes effectively one
dimensional. The dual bulk geometry is AdS-Taub-NUT space in the corresponding
limit. In this limit we solve the theory exactly and show that the action of
the strongly coupled boundary theory scales as .
This result is remarkably close to the scaling of the
Einstein gravity action for AdS-Taub-NUT space. These results explain the
numerical agreement presented in hep-th/0503238, and the soft logarithmic
departure is interpreted as a prediction for the contribution due to higher
spin fields in the bulk geometry.Comment: 11 pages, 3 figures. References adde
Duality and Superconvergence Relation in Supersymmetric Gauge Theories
We investigate the phase structures of various N=1 supersymmetric gauge
theories including even the exceptional gauge group from the viewpoint of
superconvergence of the gauge field propagator. Especially we analyze in detail
whether a new type of duality recently discovered by Oehme in gauge
theory coupled to fundamental matter fields can be found in more general gauge
theories with more general matter representations or not. The result is that in
the cases of theories including matter fields in only the fundamental
representation, Oehme's duality holds but otherwise it does not. In the former
case, superconvergence relation might give good criterion to describe the
interacting non-Abelian Coulomb phase without using some information from dual
magnetic theory.Comment: 20 pages, LaTe
Creation of Fundamental Strings by Crossing D-branes
We study the force balance between orthogonally positioned -brane and
-brane. The force due to graviton and dilaton exchange is repulsive in
this case. We identify the attractive force that balances this repulsion as due
to one-half of a fundamental string stretched between the branes. As the
-brane passes through the -brane, the connecting string changes
direction, which may be interpreted as creation of one fundamental string. We
show this directly from the structure of the Chern-Simons terms in the D-brane
effective actions. We also discuss the effect of string creation on the 0-brane
quantum mechanics in the type I' theory. The creation of a fundamental string
is related by U-duality to the creation of a 3-brane discussed by Hanany and
Witten. Both processes have a common origin in M-theory: as two M5-branes with
one common direction cross, a M2-brane stretched between them is created.Comment: 6 pages, Late
Evidence of Double Phonon Excitations in ^{16}O + ^{208}Pb Reaction
The fusion cross-sections for ^{16}O + ^{208}Pb, measured to high precision,
enable the extraction of the distribution of fusion barriers. This shows a
structure markedly different from the single-barrier which might be expected
for fusion of two doubly-closed shell nuclei. The results of exact coupled
channel calculations performed to understand the observations are presented.
These calculations indicate that coupling to a double octupole phonon excited
state in ^{208}Pb is necessary to explain the experimental barrier
distributions.Comment: 6 pages, 2 figures, To be published in the Proceedings of the FUSION
97 Conference, South Durras, Australia, March 1997 (J. Phys. G
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