2,069 research outputs found
Optimization of shallow arches against instability using sensitivity derivatives
The author discusses the problem of optimization of shallow frame structures which involve a coupling of axial and bending responses. A shallow arch of a given shape and of given weight is optimized such that its limit point load is maximized. The cross-sectional area, A(x) and the moment of inertia, I(x) of the arch obey the relationship I(x) = rho A(x) sup n, n = 1,2,3 and rho is a specified constant. Analysis of the arch for its limit point calculation involves a geometric nonlinear analysis which is performed using a corotational formulation. The optimization is carried out using a second-order projected Lagrangian algorithm and the sensitivity derivatives of the critical load parameter with respect to the areas of the finite elements of the arch are calculated using implicit differentation. Results are presented for an arch of a specified rise to span ratio under two different loadings and the limitations of the approach for the intermediate rise arches are addressed
On the calculation of derivatives of eigenvalues and eigenvectors in the simultaneous design and control of structures
Independent Modal Space Control (IMSC) is a technique that is often used for the control of large order structural systems. The pertinent optimization problem in the simultaneous design and control of structures is a min - min problem that minimizes with respect to the structural design variables, the minimum value of the performance index with respect to the control forces obtained using the IMSC technique. The minimization process requires derivatives of eigenvalues and eigenvectors with respect to the design variables. These derivatives can be computed by a rather involved analytical procedure or a relatively simple finite difference procedure. The computer cost effectiveness of these two procedures for the derivative calculations is examined
SAPNEW: Parallel finite element code for thin shell structures on the Alliant FX/80
The results of a research activity aimed at providing a finite element capability for analyzing turbo-machinery bladed-disk assemblies in a vector/parallel processing environment are summarized. Analysis of aircraft turbofan engines is very computationally intensive. The performance limit of modern day computers with a single processing unit was estimated at 3 billions of floating point operations per second (3 gigaflops). In view of this limit of a sequential unit, performance rates higher than 3 gigaflops can be achieved only through vectorization and/or parallelization as on Alliant FX/80. Accordingly, the efforts of this critically needed research were geared towards developing and evaluating parallel finite element methods for static and vibration analysis. A special purpose code, named with the acronym SAPNEW, performs static and eigen analysis of multi-degree-of-freedom blade models built-up from flat thin shell elements
Flavor Changing Neutral Currents, an Extended Scalar Sector, and the Higgs Production Rate at the LHC
We study extensions of the standard model with additional colored scalar
fields which can couple directly to quarks. Natural suppression of flavor
changing neutral currents implies minimal flavor violation, and fixes the
scalars to transform as (8,2)_1/2 under the SU(3) X SU(2) X U(1) gauge
symmetry. We explore the phenomenology of the standard model with one
additional (8,2)_1/2 scalar, and discuss how this extension can modify flavor
physics and the Higgs boson production rate at the LHC. Custodial SU(2)
symmetry can be implemented for the octet scalars since they transform as a
real color representation. Additional weak scale degrees of freedom needed for
gauge unification are discussed.Comment: Minor change
How bright is the proton? A precise determination of the photon parton distribution function
It has become apparent in recent years that it is important, notably for a
range of physics studies at the Large Hadron Collider, to have accurate
knowledge on the distribution of photons in the proton. We show how the photon
parton distribution function (PDF) can be determined in a model-independent
manner, using electron-proton () scattering data, in effect viewing the
process as an electron scattering off the photon field of the
proton. To this end, we consider an imaginary, beyond Standard Model process
with a flavour changing photon-lepton vertex. We write its cross section in two
ways, one in terms of proton structure functions, the other in terms of a
photon distribution. Requiring their equivalence yields the photon distribution
as an integral over proton structure functions. As a result of the good
precision of data, we constrain the photon PDF at the level of 1-2% over a
wide range of momentum fractions.Comment: 6 pages, 5 figures; v3 includes small textual changes and an updated
CT14 comparison in Fig. 4, as published. LUXqed_PDF4LHC15_nnlo_100 set
available from LHAPDF, further information at http://cern.ch/luxqed
Motion detection in astronomical and ice floe images
Two approaches are presented for establishing correspondence between small areas in pairs of successive images for motion detection. The first one, based on local correlation, is used on a pair of successive Voyager images of the Jupiter which differ mainly in locally variable translations. This algorithm is implemented on a sequential machine (VAX 780) as well as the Massively Parallel Processor (MPP). In the case of the sequential algorithm, the pixel correspondence or match is computed on a sparse grid of points using nonoverlapping windows (typically 11 x 11) by local correlations over a predetermined search area. The displacement of the corresponding pixels in the two images is called the disparities to cubic surfaces. The disparities at points where the error between the computed values and the surface values exceeds a particular threshold are replaced by the surface values. A bilinear interpolation is then used to estimate disparities at all other pixels between the grid points. When this algorithm was applied at the red spot in the Jupiter image, the rotating velocity field of the storm was determined. The second method of motion detection is applicable to pairs of images in which corresponding areas can experience considerable translation as well as rotation
The Photon Content of the Proton
The photon PDF of the proton is needed for precision comparisons of LHC cross
sections with theoretical predictions. In a recent paper, we showed how the
photon PDF could be determined in terms of the electromagnetic proton structure
functions and measured in electron-proton scattering experiments,
and gave an explicit formula for the PDF including all terms up to
next-to-leading order. In this paper we give details of the derivation. We
obtain the photon PDF using the factorisation theorem and applying it to
suitable BSM hard scattering processes. We also obtain the same PDF in a
process-independent manner using the usual definition of PDFs in terms of
light-cone Fourier transforms of products of operators. We show how our method
gives an exact representation for the photon PDF in terms of and ,
valid to all orders in QED and QCD, and including all non-perturbative
corrections. This representation is then used to give an explicit formula for
the photon PDF to one order higher than our previous result. We also generalise
our results to obtain formul\ae\ for the polarised photon PDF, as well as the
photon TMDPDF. Using our formula, we derive the subset of DGLAP
splitting functions to order and , which agree with
known results. We give a detailed explanation of the approach that we follow to
determine a photon PDF and its uncertainty within the above framework.Comment: 75 pages, 25 figures, data files corresponding to the figures
available at http://doi.org/10.5281/zenodo.837233, LUXqed17 PDF files
available in LHAPDF, references added in v
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