287 research outputs found
Improved Methodology for Estimating Seismic Coefficients for the Pseudo-Static Stability Analysis of Earth Dams
This paper presents an improved methodology for estimating seismic coefficients for the pseudo-static stability analysis of earth dams, which is based on a statistical analysis of input data and results for 112 potential failure surfaces, as estimated from 28 two dimensional seismic response analyses for eight (8) different zoned earth dams and high embankments. The new methodology employs design diagrams and equations and estimates the maximum and the effective seismic coefficients as a function of: (a) the peak ground acceleration at the free-field surface of the foundation soil, (b) the predominant period of the seismic excitation, (c) the eigenperiod of the earth dam, (d) the dam foundation conditions, and (e) the dimensionless ratio z/H of the maximum depth z of the failure surface over the height H of the earth dam. The proposed methodology offers accuracy and consistency with a standard deviation of the relative error in the estimation of the seismic coefficients in the order of ±24
Ship-hull shape optimization with a T-spline based BEM-isogeometric solver
In this work, we present a ship-hull optimization process combining a T-spline based parametric ship-hull model and an Isogeometric Analysis (IGA) hydrodynamic solver for the calculation of ship wave resistance. The surface representation of the ship-hull instances comprise one cubic T-spline with extraordinary points, ensuring C2 continuity everywhere except for the vicinity of extraordinary points where G1 continuity is achieved. The employed solver for ship wave resistance is based on the Neumann-Kelvin formulation of the problem, where the resulting Boundary Integral Equation is numerically solved using a higher order collocated Boundary Element Method which adopts the IGA concept and the T-spline representation for the ship-hull surface. The hydrodynamic solver along with the ship parametric model are subsequently integrated within an appropriate optimization environment for local and global ship-hull optimizations against the criterion of minimum resistance
Holographic Construction of Excited CFT States
We present a systematic construction of bulk solutions that are dual to CFT
excited states. The bulk solution is constructed perturbatively in bulk fields.
The linearised solution is universal and depends only on the conformal
dimension of the primary operator that is associated with the state via the
operator-state correspondence, while higher order terms depend on detailed
properties of the operator, such as its OPE with itself and generally involve
many bulk fields. We illustrate the discussion with the holographic
construction of the universal part of the solution for states of two
dimensional CFTs, either on or on . We compute the
1-point function both in the CFT and in the bulk, finding exact agreement. We
comment on the relation with other reconstruction approaches.Comment: 26 pages, 4 figures, v2: comments adde
Wave-resistance computation via CFD and IGA-BEM solvers : a comparative study
This paper delivers a preliminary comparative study on the computation of wave resistance via a commercial CFD solver (STAR-CCM+®) versus an in-house developed IGA-BEM solver for a pair of hulls, namely the parabolic Wigley hull and the KRISO container ship (KCS). The CFD solver combines a VOF (Volume Of Fluid) free-surface modelling technique with alternative turbulence models, while the IGA-BEM solver adopts an inviscid flow model that combines the Boundary Element approach (BEM) with Isogeometric Analysis (IGA) using T-splines or NURBS. IGA is a novel and expanding concept, introduced by Hughes and his collaborators (Hughes et al, 2005), aiming to intrinsically integrate CAD with Analysis by communicating the CAD model of the geometry (the wetted ship hull in our case) to the solver without any approximation
A consistent truncation of IIB supergravity on manifolds admitting a Sasaki-Einstein structure
We present a consistent truncation of IIB supergravity on manifolds admitting
a Sasaki-Einstein structure, which keeps the metric and five real scalar
fields. This theory can be further truncated to a constrained one-parameter
family that depends on only the metric and one scalar, as well as to a theory
with a metric and three scalars. The reduced theory admits supersymmetric and
non-supersymmetric AdS_5 and AdS_4 x R solutions. We analyze the spectrum
around the AdS critical points and identify the dual operators.Comment: 21 pages; v2: references added and minor improvement
Anatomy of bubbling solutions
We present a comprehensive analysis of holography for the bubbling solutions
of Lin-Lunin-Maldacena. These solutions are uniquely determined by a coloring
of a 2-plane, which was argued to correspond to the phase space of free
fermions. We show that in general this phase space distribution does not
determine fully the 1/2 BPS state of N=4 SYM that the gravitational solution is
dual to, but it does determine it enough so that vevs of all single trace 1/2
BPS operators in that state are uniquely determined to leading order in the
large N limit. These are precisely the vevs encoded in the asymptotics of the
LLM solutions. We extract these vevs for operators up to dimension 4 using
holographic renormalization and KK holography and show exact agreement with the
field theory expressions.Comment: 67 pages, 6 figures; v2: typos corrected, refs added; v3: expanded
explanations, more typos correcte
Topologically Massive Gravity and the AdS/CFT Correspondence
We set up the AdS/CFT correspondence for topologically massive gravity (TMG)
in three dimensions. The first step in this procedure is to determine the
appropriate fall off conditions at infinity. These cannot be fixed a priori as
they depend on the bulk theory under consideration and are derived by solving
asymptotically the non-linear field equations. We discuss in detail the
asymptotic structure of the field equations for TMG, showing that it contains
leading and subleading logarithms, determine the map between bulk fields and
CFT operators, obtain the appropriate counterterms needed for holographic
renormalization and compute holographically one- and two-point functions at and
away from the 'chiral point' (mu = 1). The 2-point functions at the chiral
point are those of a logarithmic CFT (LCFT) with c_L = 0, c_R = 3l/G_N and b =
-3l/G_N, where b is a parameter characterizing different c = 0 LCFTs. The bulk
correlators away from the chiral point (mu \neq 1) smoothly limit to the LCFT
ones as mu \to 1. Away from the chiral point, the CFT contains a state of
negative norm and the expectation value of the energy momentum tensor in that
state is also negative, reflecting a corresponding bulk instability due to
negative energy modes.Comment: 54 pages, v2: added comments and reference
Holographic Non-Gaussianity
We investigate the non-Gaussianity of primordial cosmological perturbations
within our recently proposed holographic description of inflationary universes.
We derive a holographic formula that determines the bispectrum of cosmological
curvature perturbations in terms of correlation functions of a holographically
dual three-dimensional non-gravitational quantum field theory (QFT). This
allows us to compute the primordial bispectrum for a universe which started in
a non-geometric holographic phase, using perturbative QFT calculations.
Strikingly, for a class of models specified by a three-dimensional
super-renormalisable QFT, the primordial bispectrum is of exactly the
factorisable equilateral form with f_nl^eq=5/36, irrespective of the details of
the dual QFT. A by-product of this investigation is a holographic formula for
the three-point function of the trace of the stress-energy tensor along general
holographic RG flows, which should have applications outside the remit of this
work.Comment: 42 pages, 2 figs, published versio
Real-time gauge/gravity duality: Prescription, Renormalization and Examples
We present a comprehensive analysis of the prescription we recently put
forward for the computation of real-time correlation functions using
gauge/gravity duality. The prescription is valid for any holographic
supergravity background and it naturally maps initial and final data in the
bulk to initial and final states or density matrices in the field theory. We
show in detail how the technique of holographic renormalization can be applied
in this setting and we provide numerous illustrative examples, including the
computation of time-ordered, Wightman and retarded 2-point functions in
Poincare and global coordinates, thermal correlators and higher-point
functions.Comment: 85 pages, 13 figures; v2: added comments and reference
Holographic predictions for cosmological 3-point functions
We present the holographic predictions for cosmological 3-point correlators,
involving both scalar and tensor modes, for a universe which started in a
non-geometric holographic phase. Holographic formulae relate the cosmological
3-point functions to stress tensor correlation functions of a holographically
dual three-dimensional non-gravitational QFT. We compute these correlators at
1-loop order for a theory containing massless scalars, fermions and gauge
fields, and present an extensive analysis of the constraints due to Ward
identities showing that they uniquely determine the correlators up to a few
constants. We define shapes for all cosmological bispectra and compare the
holographic shapes to the slow-roll ones, finding that some are distinguishable
while others, perhaps surprisingly, are not.Comment: 51pp; 4 fig
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