970 research outputs found
Solar-powered adsorption refrigeration cycle optimization
Solar energy is an attractive energy source among various renewable energy resources in Malaysia as relatively high solar radiation is available throughout the year. This solar energy can be utilized for air-conditioning by using solar-powered adsorption refrigeration cycle. Intermittent nature of the solar radiation leads to a challenge for continuous air-conditioning operation. In the present study, a combination of solar-powered adsorption refrigeration system and thermal storage is studied. Activated carbon-ammonia and activated carbon-methanol are the working pairs of the adsorption reaction. Analytical calculation results show that activated carbon-methanol pair indicates higher coefficient of performance (COP) than activated carbon-ammonia pair, while adsorption chiller system with hot water thermal storage has higher COP than the system with ice thermal storage. For the activated carbon-methanol case with hot water thermal storage, the COP is 0.79. Since this COP analysis is based on the ideal case with uniform temperature distribution within the reactor beds, which achieves equilibrium states at the end of the reactions. In more realistic situation, the reaction process will be terminated before reaching to the equilibrium states because of the non-uniform temperature distribution and the time required for the reaction. Transient simulation in which heat transfer and reaction equation are combined will be performed to model actual reactors
Space laser interferometers can determine the thermal history of the early Universe
It is shown that space-based gravitational wave detectors such as DECIGO
and/or Big Bang Observer (BBO) will provide us with invaluable information on
the cosmic thermal history after inflation and they will be able to determine
the reheat temperature provided that it lies in the range preferred by
the cosmological gravitino problem, GeV. Therefore it is
strongly desired that they will be put into practice as soon as possible.Comment: 5 page
Fibrations of genus two on complex surfaces
We consider fibrations of genus 2 over complex surfaces. The purpose of this
paper is primarily to provide a geometric description of the possible
structures of the fibration on a neighborhood of a singular fiber. In
particular it is shown that the "geometric data" of the singular fiber
determines the fibration on its neighborhood up to a transversely holomorphic
-diffeomorphism. The method employed is quite flexible and it
applies to good extent to fibrations of arbitrary genus.Comment: This is the final version, June 201
Concept study of microgrid dispatch strategy for solar thermal power plant with thermal storage
Complex grid systems have been gradually replaced by smaller and simpler grid systems called Microgrids. Integration of a solar thermal power generation systems into Microgrids open a new horizon of renewable energy power generation to achieve the supply and demand balance of electricity. Microgrid dispatch strategy is a control method of energy balance between power generation and electricity consumption. A thermal storage integrated into the system buffers the intermittency of solar radiation used as the heat source of the power generation system. The daily starting time for the power generation is determined by the dispatch strategy in search of minimum power from the conventional grid and maximum electricity generation from the solar thermal power generation system. In the simulation stage, the heat energy available for power generation and amount of thermal energy saved in the thermal storage is calculated at each time step using measured solar radiation data as the heat source and load profile data as the consumption required. Based on the simulation result, the power generation starting time for the next day is determined. The effectiveness of the proposed dispatch strategy is demonstrated by obtaining the best starting time and identifying minimum power requiredfrom the conventional grid. The power supply from the conventional grid is reduced by 10% by applying the proposed methodology
Cluster Morphologies as a Test of Different Cosmological Models
We investigate how cluster morphology is affected by the cosmological
constant in low-density universes. Using high-resolution cosmological
N-body/SPH simulations of flat (\Omega_0 = 0.3, \lambda_0 = 0.7, \Lambda CDM)
and open (\Omega_0 = 0.3, \lambda_0 = 0, OCDM) cold dark matter universes, we
calculate statistical indicators to quantify the irregularity of the cluster
morphologies. We study axial ratios, center shifts, cluster clumpiness, and
multipole moment power ratios as indicators for the simulated clusters at z=0
and 0.5. Some of these indicators are calculated for both the X-ray surface
brightness and projected mass distributions. In \Lambda CDM all these
indicators tend to be larger than those in OCDM at z=0. This result is
consistent with the analytical prediction of Richstone, Loeb, & Turner, that
is, clusters in \Lambda CDM are formed later than in OCDM, and have more
substructure at z=0. We make a Kolmogorov-Smirnov test on each indicator for
these two models. We then find that the results for the multipole moment power
ratios and the center shifts for the X-ray surface brightness are under the
significance level (5%). We results also show that these two cosmological
models can be distinguished more clearly at z=0 than z = 0.5 by these
indicators.Comment: 30pages, 6figures, Accepted for publication in Ap
Effect of Collective Neutrino Oscillations on the Neutrino Mechanism of Core-Collapse Supernovae
In the seconds after collapse of a massive star, the newborn proto-neutron
star (PNS) radiates neutrinos of all flavors. The absorption of electron-type
neutrinos below the radius of the stalled shockwave may drive explosions (the
"neutrino mechanism"). Because the heating rate is proportional to the square
of neutrino energy, flavor conversion of mu and tau neutrinos to electron-type
neutrinos via collective neutrino oscillations (CnuO) may in principle increase
the heating rate and drive explosions. In order to assess the potential
importance of CnuO for the shock revival, we solve the steady-state boundary
value problem of spherically-symmetric accretion between the PNS surface (r_nu)
and the shock (r_S), including a scheme for flavor conversion via CnuO. For a
given r_nu, PNS mass (M), accretion rate (Mdot), and assumed values of the
neutrino energies from the PNS, we calculate the critical neutrino luminosity
above which accretion is impossible and explosion results. We show that CnuO
can decrease the critical luminosity by a factor of at most ~1.5, but only if
the flavor conversion is fully completed inside r_S and if there is no matter
suppression. The magnitude of the effect depends on the model parameters (M,
Mdot, and r_nu) through the shock radius and the physical scale for flavor
conversion. We quantify these dependencies and find that CnuO could lower the
critical luminosity only for small M and Mdot, and large r_nu. However, for
these parameter values CnuO are suppressed due to matter effects. By
quantifying the importance of CnuO and matter suppression at the critical
neutrino luminosity for explosion, we show in agreement with previous studies
that CnuO are unlikely to affect the neutrino mechanism of core-collapse
supernovae significantly.Comment: 8 pages, 3 figures, accepted to MNRA
An approximate theory for substructure propagation in clusters
The existence of dark matter can be proved in an astrophysical context by the
discovery of a system in which the observed baryons and the inferred dark
matter are spatially segregated, such as the bullet cluster (1E0657-558). The
full descriptions of the dark matter halo and X-ray gas substructure motions
are necessary to forecast the location of the dark halo from X-ray maps, which
can be confirmed by the detection of a galaxy concentration or by gravitational
lensing. We present an analytical hydrodynamic model to determine the distance
between the X-ray and dark-matter components and the Mach number of the merger
shock. An approximate solution is given for the problem of the substructure
propagation in merging clusters. A new method to predict the position of a dark
matter halo in clusters, where there is a separation between the X-ray gas and
the dark halo, is proposed and applied to the clusters 1E0657-558 and Abell
1763.Comment: Accepted for publication in Astronomy & Astrophysic
Do food scares explain supplier concentration? An analysis of EU agri-food imports
We investigate how rising sanitary risk of agri-food products affects the geographical concentration of European Union (EU) imports at the product level. We first estimate a product-specific measure of sanitary risk based on the count of food alerts at EU borders. Then we regress the evolution of geographical concentration indices on our measure of product risk and year. We find that product sanitary risk indeed affected the EU import pattern. Overall, the EU diversified its import sources, but with diversification at the extensive margin and concentration at the intensive margin. This pattern is stronger for risky products, leading to a two-tier system
Interacting Ricci Dark Energy and its Statefinder Description
In this paper we have considered an interacting Ricci dark energy in flat FRW
universe. We have reconstructed the Hubble's parameter under this interaction.
Also, we have investigated the statefinder diagnostics. It has been revealed
that the equation of state parameter behaves like quintessence in this
interaction and from the statefinder diagnostics it has been concluded that the
interacting Ricci dark energy interpolates between dust and CDM stages
of the universe.Comment: 9 pages, 3 figure
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