2,600 research outputs found
Estuary Classification Revisited
This paper presents the governing equations of a tidally-averaged,
width-averaged, rectangular estuary in completely nondimensionalized forms.
Subsequently, we discover that the dynamics of an estuary is entirely
controlled by only two variables: (i) the Estuarine Froude number, and (ii) a
nondimensional number related to the Estuarine Aspect ratio and the Tidal
Froude number. Motivated by this new observation, the problem of estuary
classification is re-investigated. Our analysis shows that the two control
variables are capable of completely determining the stratification at the
estuary mouth, and therefore can specify the estuary type. The theoretical
estuary classification scheme proposed in this paper is validated against real
estuarine data collected from existing literature. Our classification scheme on
comparison with the state-of-the-art theory shows significant improvement.Comment: 6 pages, 4 figure
On the stability of plane Couette-Poiseuille flow with uniform cross-flow
We present a detailed study of the linear stability of plane
Couette-Poiseuille flow in the presence of a cross-flow. The base flow is
characterised by the cross flow Reynolds number, and the
dimensionless wall velocity, . Squire's transformation may be applied to the
linear stability equations and we therefore consider 2D (spanwise-independent)
perturbations. Corresponding to each dimensionless wall velocity, ,
two ranges of exist where unconditional stability is observed. In the
lower range of , for modest we have a stabilisation of long
wavelengths leading to a cut-off . This lower cut-off results from
skewing of the velocity profile away from a Poiseuille profile, shifting of the
critical layers and the gradual decrease of energy production. Cross-flow
stabilisation and Couette stabilisation appear to act via very similar
mechanisms in this range, leading to the potential for robust compensatory
design of flow stabilisation using either mechanism. As is increased,
we see first destabilisation and then stabilisation at very large .
The instability is again a long wavelength mechanism. Analysis of the
eigenspectrum suggests the cause of instability is due to resonant interactions
of Tollmien-Schlichting waves. A linear energy analysis reveals that in this
range the Reynolds stress becomes amplified, the critical layer is irrelevant
and viscous dissipation is completely dominated by the energy
production/negation, which approximately balances at criticality. The
stabilisation at very large appears to be due to decay in energy
production, which diminishes like . Our study is limited to two
dimensional, spanwise independent perturbations.Comment: Accepted for publication in Journal of Fluid Mechanic
Generation of higher order nonclassical states via interaction of intense electromagnetic field with third order nonlinear medium
Interaction of intense laser beam with an inversion symmetric third order
nonlinear medium is modeled as a quartic anharmonic oscillator. A first order
operator solution of the model Hamiltonian is used to study the possibilities
of generation of higher order nonclassical states. It is found that the higher
order squeezed and higher order antibunched states can be produced by this
interaction. It is also shown that the higher order nonclassical states may
appear separately, i.e. a higher order antibunched state is not essentially
higher order squeezed state and vice versa.Comment: 7 pages, no figur
The D^4 R^4 term in type IIB string theory on T^2 and U-duality
We propose a manifestly U-duality invariant modular form for the D^4 R^4
interaction in type IIB string theory compactified on T^2. It receives
perturbative contributions upto two loops, and non-perturbative contributions
from D-instantons and (p,q) string instantons wrapping T^2. We provide evidence
for this modular form by showing that the coefficients at tree level and at one
loop precisely match those obtained using string perturbation theory. Using
duality, parts of the perturbative amplitude are also shown to match exactly
the results obtained from eleven dimensional supergravity compactified on T^3
at one loop. Decompactifying the theory to nine dimensions, we obtain a
U-duality invariant modular form, whose coefficients at tree level and at one
loop agree with string perturbation theory.Comment: 25 pages, LaTe
Multijet Discriminators for New Physics in Leptonic Signals at the LHC
Some of the cleanest signals for new physics in the early runs of the LHC
will involve strongly-produced particles which give rise to multiple leptons by
undergoing cascade decays through weakly-interacting states to stable
particles. Some of the most spectacular final states will involve three or more
leptons, multiple jets and generally missing energy-momentum as well. A triad
of the most interesting models of new physics which induce such signals is
known to consist of (i) supersymmetry with R-parity conservation, (ii) a
universal extra dimension with conservation of KK-parity and (iii) little Higgs
models with conserved T-parity. Similar signals could also arise if the
Standard Model is augmented with a fourth sequential generation of heavy
fermions. We study all these possibilities and show that a judiciously chosen
set of observables, critically involving the number of identifiable jets and
leptons, can collectively provide distinct footprints for each of these models.
In fact, simple pairwise correlation of such observables can enable unambiguous
identification of the underlying model, even with a relatively small data
sample.Comment: 43 pages, LaTex2e, 8 embedded eps figure
Stretching force dependent transitions in single stranded DNA
Mechanical properties of DNA, in particular their stretch dependent extension
and their loop formation characteristics, have been recognized as an effective
probe for understanding the possible biochemical role played by them in a
living cell. Single stranded DNA (ssDNA), which, till recently was presumed to
be an simple flexible polymer continues to spring surprises. Synthetic ssDNA,
like polydA (polydeoxyadenosines) has revealed an intriguing force-extension
(FX) behavior exhibiting two plateaus, absent in polydT (polydeoxythymidines)
for example. Loop closing time in polydA had also been found to scale
exponentially with inverse temperature, unexpected from generic models of
homopolymers. Here we present a new model for polydA which incorporates both a
helix-coil transition and a over-stretching transition, accounting for the two
plateaus. Using transfer matrix calculation and Monte-Carlo simulation we show
that the model reproduces different sets of experimental observations,
quantitatively. It also predicts interesting reentrant behavior in the
temperature-extension characteristics of polydA, which is yet to be verified
experimentally.Comment: 5 pages, 3 figure
Local cloning of Bell states and distillable entanglement
The necessary and sufficient amount of entanglement required for cloning of
orthogonal Bell states by local operation and classical communication is
derived, and using this result, we provide here some additional examples of
reversible, as well as irreversible states.Comment: 5 pages, two columns, Latex. Few typos have been corrected. An
explanation of the teleportation map (eqn. (3) in the manuscript) has been
provide
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