13,780 research outputs found
Comparative performance analysis of Vacuum Insulation Panels in thermal window shutters
Windows are a major area of heat loss in buildings and can lose up to 10 times more energy than other building elements. In a typical house, around 10% of heat is lost through the windows. Thermal shutters could considerably reduce heat losses through windows and improve the energy performance of buildings. Insulation plays a major role in overall performance of thermal shutters. Advance insulation material such as Vacuum Insulation Panel (VIP) can help in improving the performance of thermal window shutters. VIP with a thermal conductivity of 0.005-0.008 W/mK is a high thermal resistance and energy efficient alternative to conventional thermal insulation materials. In this paper, effect of VIP and conventional insulation has been investigated and compared for enhancing the thermal performance of window shutters using computer simulations. Results indicate significant reduction in heat loss through windows when VIP insulation was employed in internal thermal window shutters. Thermal bridging was found to be the significant factor that deteriorated the performance of the shutter. Reducing heat loss through the frame and surrounding walls could improve the VIP insulated shutter thermal performance by approximately nine times
Can Heavy WIMPs Be Captured by the Earth?
If weakly interacting massive particles (WIMPs) in bound solar orbits are
systematically driven into the Sun by solar-system resonances (as Farinella et
al. have shown is the case for many Earth-crossing asteroids), then the capture
of high-mass WIMPs by the Earth would be affected dramatically because
high-mass WIMPs are captured primarily from bound orbits. WIMP capture would be
eliminated for M_x>630 GeV and would be highly suppressed for M_x>~150 GeV.
Annihilation of captured WIMPs and anti-WIMPs is expected to give rise to
neutrinos coming from the Earth's center. The absence of such a neutrino signal
has been used to place limits on WIMP parameters. At present, one does not know
if typical WIMP orbits are in fact affected by these resonances. Until this
question is investigated and resolved, one must (conservatively) assume that
they are. Hence, limits on high-mass WIMP parameters are significantly weaker
than previously believed.Comment: 8 pages + 1 figure. Submitted to Ap
Structural, elastic, and electronic properties of newly discovered Li2PtSi3 superconductor: Effect of transition metals
First-principles calculations within the density functional theory (DFT) with
GGA-PBE exchange-correlation scheme have been employed to predict the
structural, the elastic and the electronic properties of newly discovered
lithium silicide superconductor, Li2PtSi3, for the first time. All the
theoretical results are compared with those calculated recently for
isostructural Li2IrSi3. The present study sheds light on the effect of
replacement of transition metal element Ir with Pt on different mechanical,
electronic, and superconducting properties. The effect of spin-orbit coupling
on electronic band structure was found to be insignificant for Li2PtSi3. The
difference in superconducting transition temperatures of Li2PtSi3 and Li2IrSi3
arises primarily due to the difference in electronic energy density of states
at the Fermi level. Somewhat reduced Debye temperature in Li2PtSi3 plays a
minor role. We have discussed the implications of the theoretical results in
details in this study.Comment: Submitted for publicatio
No realistic wormholes from ghost-free scalar-tensor phantom dark energy
It is proved that no wormholes can be formed in viable scalar-tensor models
of dark energy admitting its phantom-like () behaviour in cosmology,
even in the presence of electric or magnetic fields, if the non-minimal
coupling function is everywhere positive and the scalar field
itself is not a ghost. Some special static, spherically symmetric wormhole
solutions may exist if is allowed to reach zero or to become
negative, so that the effective gravitational constant becomes negative in some
region making the graviton a ghost. If remains non-negative, such solutions
require severe fine tuning and a very peculiar kind of model. If is
allowed, it is argued (and confirmed by previous investigations) that such
solutions are generically unstable under non-static perturbations, the
instability appearing right near transition surfaces to negative .Comment: 8 pages, late
Biodiesel From Mustard Oil: a Sustainable Engine Fuel Substitute for Bangladesh
Various attractive features of mustard oil based biodiesel as a potential substitute for engine fuel are investigated in this paper for use in Bangladesh. Although the use of mustard oil as edible oil has been reduced, Bangladesh still produces 0.22 million metric tons of mustard oil per year. This surplus mustard oil would satisfactorily be used as an alternative to diesel fuel, and thus could contribute in reducing the expenses for importing fuel from foreign countries. Moreover, the rural people of Bangladesh are capable of producing mustard oil themselves using indigenous machines. Fuel properties of biodiesel obtained from mustard oil were determined in the laboratory using standard procedure and an experimental setup was constructed to study the performance of a small diesel engine. It is observed that with biodiesel, the engine is capable of running without difficulty. Initially different lower blends of biodiesel (e.g., B20, B30 etc.) have been used to avoid complicated modification of the engine and the fuel supply system. It is also found in some condition that mustard oil based biodiesel have better properties than those made from other vegetable oils. These properties of mustard oil based biodiesel were evaluated to validate its sustainability in Bangladesh
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