2,926 research outputs found
Planning Instrumentation Monitoring in Dams
This paper outlines the seismic instrumentation being adopted for river valley projects in India, More than 60% of Indian sub-continent lies in an active seismic belt. Of this the middle and lower Himalayas constitute a major area wherein lies a huge untapped hydro-power potential, Being primarily constituted of younger rock formations, frequented by faults, thursts and shear zones and lying in a high seismic risk zone, observations through instruments play a significant role in perspective planning of projects in this area. Setting up of seismological observatories in advance of construction of dam projects, forms a part of investigative planning to assess the seismic status of the area. The observations are continued after construction to monitor any changes in seismicity due to reservoir impounding. Present approach is to also provide instrumentation and continued observation to a possible prediction of earthquake. A typical case of instrumentation for a dam on active fault is also cited
Boiling Heat Transfer from an Array of Round Jets with Hybrid Surface Enhancements
The effect of a variety of surface enhancements on the heat transfer achieved with an array of impinging jets is experimentally investigated using the dielectric fluid HFE-7100 at different volumetric flow rates. The performance of a 5x5 array of jets, each 0.75mm in diameter, is compared to that of a single 3.75mm diameter jet with the same total open orifice area, in single-and two-phase operation. Four different target copper surfaces are evaluated: a baseline smooth flat surface, a flat surface coated with a microporous layer, a surface with macroscale area enhancement (extended square pin–fins), and a hybrid surface on which the pin–fins are coated with the microporous layer; area-averaged heat transfer and pressure drop measurements are reported. The array of jets enhances the single-phase heat transfer coefficients by 1.13–1.29 times and extends the critical heat flux (CHF) on all surfaces compared to the single jet at the same volumetric flow rates. Additionally, the array greatly enhances the heat flux dissipation capability of the hybrid coated pin–fin surface, extending CHF by 1.89–2.33 times compared to the single jet on this surface, with a minimal increase in pressure drop. The jet array coupled with the hybrid enhancement dissipates a maximum heat flux of 205.8 W/cm2 (heat input of 1.33 kW) at a flow rate of 1800 ml/min (corresponding to a jet diameter-based Reynolds number of 7800) with a pressure drop incurred of only 10.9 kPa. Compared to the single jet impinging on the smooth flat surface, the array of jets on the coated pin–fin enhanced surface increased CHF by a factor of over four at all flow rates
Embankment Design in Seismic Areas — Indian Practice
A number of river valley projects for the development of water and power resources, particularly in the Northern and North Eastern part of India, lie on the foothills of Himalayas which is seismically active. In the developmental activity of dam building, aseismic design of dam is therefore recognized and adopted. The paper presents the current Indian practice in the aseismic design of embankment dams with illustrations from studies carried out on some recent dams
The temperature dependent bandstructure of a ferromagnetic semiconductor film
The electronic quasiparticle spectrum of a ferromagnetic film is investigated
within the framework of the s-f model. Starting from the exact solvable case of
a single electron in an otherwise empty conduction band being exchange coupled
to a ferromagnetically saturated localized spin system we extend the theory to
finite temperatures. Our approach is a moment-conserving decoupling procedure
for suitable defined Green functions. The theory for finite temperatures
evolves continuously from the exact limiting case. The restriction to zero
conduction band occupation may be regarded as a proper model description for
ferromagnetic semiconductors like EuO and EuS. Evaluating the theory for a
simple cubic film cut parallel to the (100) crystal plane, we find some marked
correlation effects which depend on the spin of the test electron, on the
exchange coupling, and on the temperature of the local-moment system.Comment: 11 pages, 9 figure
PKS 0537-286, carrying the information of the environment of SMBHs in the early Universe
We present the results of a multifrequency campaign on the high-redshift (z =
3.1) blazar PKS 0537-286. The source was observed at different epochs from 2006
to 2008 with INTEGRAL and Swift, and nearly simultaneously with ground-based
near-IR/optical telescopes. The SEDs are compatible with a model based on
synchrotron radiation and external inverse Compton scattering. The campaign
gives an insight into the physical environment of the blazar.Comment: 8 pages, 5 figures, accepted for publication in A&
The kinetic description of vacuum particle creation in the oscillator representation
The oscillator representation is used for the non-perturbative description of
vacuum particle creation in a strong time-dependent electric field in the
framework of scalar QED. It is shown that the method can be more effective for
the derivation of the quantum kinetic equation (KE) in comparison with the
Bogoliubov method of time-dependent canonical transformations. This KE is used
for the investigation of vacuum creation in periodical linear and circular
polarized electric fields and also in the case of the presence of a constant
magnetic field, including the back reaction problem. In particular, these
examples are applied for a model illustration of some features of vacuum
creation of electron-positron plasma within the planned experiments on the
X-ray free electron lasers.Comment: 17 pages, 3 figures, v2: a reference added; some changes in tex
The Environment of M85 optical transient 2006-1: constraints on the progenitor age and mass
M85 optical transient 2006-1 (M85 OT 2006-1) is the most luminous member of
the small family of V838 Mon-like objects, whose nature is still a mystery.
This event took place in the Virgo cluster of galaxies and peaked at an
absolute magnitude of I~-13. Here we present Hubble Space Telescope images of
M85 OT 2006-1 and its environment, taken before and after the eruption, along
with a spectrum of the host galaxy at the transient location. We find that the
progenitor of M85 OT 2006-1 was not associated with any star forming region.
The g and z-band absolute magnitudes of the progenitor were fainter than about
-4 and -6 mag, respectively. Therefore, we can set a lower limit of ~50 Myr on
the age of the youngest stars at the location of the progenitor that
corresponds to a mass of <7 solar mass. Previously published line indices
suggest that M85 has a mean stellar age of 1.6+/-0.3 Gyr. If this mean age is
representative of the progenitor of M85 OT 2006-1, then we can further
constrain its mass to be less than 2 solar mass. We compare the energetics and
mass limit derived for the M85 OT 2006-1 progenitor with those expected from a
simple model of violent stellar mergers. Combined with further modeling, these
new clues may ultimately reveal the true nature of these puzzling events.Comment: 4 pages, accepted to Ap
Doublet structures in quantum well absorption spectra due to Fano-related interference
In this theoretical investigation we predict an unusual interaction between a
discrete state and a continuum of states, which is closely related to the case
of Fano-interference. It occurs in a GaAs/AlxGa1-xAs quantum well between the
lowest light-hole exciton and the continuum of the second heavy-hole exciton.
Unlike the typical case for Fano-resonance, the discrete state here is outside
the continuum; we use uniaxial stress to tune its position with respect to the
onset of the continuum. State-of-the art calculations of absorption spectra
show that as the discrete state approaches the continuum, a doublet structure
forms which reveals anticrossing behaviour. The minimum separation energy of
the anticrossing depends characteristically on the well width and is unusually
large for narrow wells. This offers striking evidence for the strong underlying
valence-band mixing. Moreover, it proves that previous explanations of similar
doublets in experimental data, employing simple two-state models, are
incomplete.Comment: 21 pages, 5 figures and 5 equations. Accepted for publication in
Physical Review
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