31 research outputs found
Numerical Study About the Change in Flow Separation and Velocity Distribution in a 90° Pipe Bend with/without Guide Vane Conditions
A single phase, incompressible turbulent
flow through a 90º pipe bend
with/without guide vane conditions has been studied here. The present work
deals with the numerical simulation to investigate the change in flow
separation and velocity distribution at the downstream
section due to the effect of the guide
vane. The k-? turbulence model has been adopted for simulation purposes to obtain the
results. After the validation of existing experimental and numerical results, a
detailed study has been performed for three different Reynolds number and four
different positions of the guide vane. The value
of the Curvature ratio (Rc/D) has been considered
as one
factor for the present study.
The curvature ratio can be defined as the
ratio between the bend curvature radius and hydraulic diameter of the pipe. The
results obtained from the present study have been presented in graphical form.
A flow separation region has been found at the bend outlet for flow through 90º pipe bend without the guide vane. This flow separation region was
absent for the cases which dealt with
the flow through 90º pipe bend with the guide
vane. Velocity distribution at four different downstream positions for
different cases and different Reynolds numbers have been compared and reported in the present study
Understanding micro-image configurations in quasar microlensing
The micro-arcsecond scale structure of the seemingly point-like images in
lensed quasars, though unobservable, is nevertheless much studied
theoretically, because it affects the observable (or macro) brightness, and
through that provides clues to substructure in both source and lens. A curious
feature is that, while an observable macro-image is made up of a very large
number of micro-images, the macro flux is dominated by a few micro-images.
Micro minima play a key role, and the well-known broad distribution of macro
magnification can be decomposed into narrower distributions with 0,1,2,3,...
micro minima. This paper shows how the dominant micro-images exist alongside
the others, using the ideas of Fermat's principle and arrival-time surfaces,
alongside simulations.Comment: Accepted for publication in MNRA
Radial density profiles of time-delay lensing galaxies
We present non-parametric radial mass profiles for ten QSO strong lensing
galaxies. Five of the galaxies have profiles close to ,
while the rest are closer to r^{-1}, consistent with an NFW profile. The former
are all relatively isolated early-types and dominated by their stellar light.
The latter --though the modeling code did not know this-- are either in
clusters, or have very high mass-to-light, suggesting dark-matter dominant
lenses (one is a actually pair of merging galaxies). The same models give
H_0^{-1} = 15.2_{-1.7}^{+2.5}\Gyr (H_0 = 64_{-9}^{+8} \legacy), consistent
with a previous determination. When tested on simulated lenses taken from a
cosmological hydrodynamical simulation, our modeling pipeline recovers both H_0
and within estimated uncertainties. Our result is contrary to some
recent claims that lensing time delays imply either a low H_0 or galaxy
profiles much steeper than r^{-2}. We diagnose these claims as resulting from
an invalid modeling approximation: that small deviations from a power-law
profile have a small effect on lensing time-delays. In fact, as we show using
using both perturbation theory and numerical computation from a
galaxy-formation simulation, a first-order perturbation of an isothermal lens
can produce a zeroth-order change in the time delays.Comment: Replaced with final version accepted for publication in ApJ; very
minor changes to text; high resolution figures may be obtained at
justinread.ne
Time-delay quasars: scales and orders of magnitudes
We can think of a lensed quasar as taking the Hubble time, shrinking it by
\~10^{-11}, and then presenting the result to us as a time delay; the shrinking
factor is of the order of fractional sky-area that the lens occupies. This cute
fact is a straightforward consequence of lensing theory, and enables a simple
rescaling of time delays. Observed time delays have a 40-fold range, but after
rescaling the range reduces to 5-fold. The latter range depends on details of
the lens and lensing configuration--for example, quads have systematically
shorter rescaled time delays than doubles--and is as expected from a simple
model. The hypothesis that observed time-delay lenses all come from a
generalized-isothermal family can be ruled out. But there is no indication of
drastically different populations either.Comment: To appear in A&
Cobalt(II), Nickel(II) & Copper(II) Complexes of N-Benzylidene-5(3)-methylpyrazole-3(5)-carbohydrazide Schiff Base
203-20
Complexes of Cobalt(II), Nickel(II) & Copper(II) with ɑ -(3,5-Dimethyl-1-pyrazolyl)acetamide
574-57
Chelating Properties of A New Pyrazole-based ONS Tridentate Ligand: Cobalt(II) & Nickel(II) Complexes with 5-Methyl-I-thiocarbamyl-pyrazole-3-carboxylic Acid
680-68