1,366 research outputs found
Theory of x-ray absorption by laser-dressed atoms
An ab initio theory is devised for the x-ray photoabsorption cross section of
atoms in the field of a moderately intense optical laser (800nm, 10^13 W/cm^2).
The laser dresses the core-excited atomic states, which introduces a dependence
of the cross section on the angle between the polarization vectors of the two
linearly polarized radiation sources. We use the Hartree-Fock-Slater
approximation to describe the atomic many-particle problem in conjunction with
a nonrelativistic quantum-electrodynamic approach to treat the photon-electron
interaction. The continuum wave functions of ejected electrons are treated with
a complex absorbing potential that is derived from smooth exterior complex
scaling. The solution to the two-color (x-ray plus laser) problem is discussed
in terms of a direct diagonalization of the complex symmetric matrix
representation of the Hamiltonian. Alternative treatments with time-independent
and time-dependent non-Hermitian perturbation theories are presented that
exploit the weak interaction strength between x rays and atoms. We apply the
theory to study the photoabsorption cross section of krypton atoms near the K
edge. A pronounced modification of the cross section is found in the presence
of the optical laser.Comment: 13 pages, 3 figures, 1 table, RevTeX4, corrected typoe
Analysis of Inelasticity Effect Due to Damage on Stress Distributions in Composite Laminates
A damage mechanics model characterizing damage behavior of composite materials proposed earlier by the authors is employed to analyze the damage effects on stress field near the free edge in symmetrically laminated graphite/epoxy composites of finite dimensions under umaxial tension. A quasi-three-dimensional finite element analy sis is developed for the present investigation. The results from the damaged and undam aged stress distributions of [0/90°]s, [90/0°]s, and [±45°] s laminates are compared and examined. The processes of initiation and development of damage zone in these composite laminates are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68869/2/10.1177_073168449301200805.pd
Pseudo-dynamic method for structural analysis of automobile seats
This work describes the application of a pseudo-dynamic (PsD) method to the
dynamic analysis of passenger seats for the automotive industry. The project of such components
involves a structural test considering the action of dynamic forces arising from a
crash scenario. The laboratory certification of these automotive components consists essentially
on the inspection of the propagation and extension of plastic deformations zones in metallic
members of the seat structure as consequence of the mutual action between the seat and the
passenger fastened to the seat via seat belt anchorages. This work presents a relatively simple
experiment using PsD techniques as a novel method to performa test equivalent to the dynamic
model of a dummy-seat pair subjected to impulsive loads from a car crash.
Essentially, the PsD test method is a hybrid and hierarchic computer-driven testing procedure
where a numerical algorithm and experimental step are used and combined on-line in order to
solve a problem in the scope of structural dynamics. The implementation of the method is not
expensive and has the leading advantage of offering the operator a total control of any intermediate
structure state during the test still keeping the realism of a real dynamic testing.Project: NDT-AUTO Ref 13-02-2003-FDR-01281 (Agencia de Inovação
Analysis of laminated doubly-curved shells by alayerwise theory and radial basis functions collocation, accounting for through-the-thickness deformations
In this paper, the static and free vibration analysis of laminated shells is performed by radial basis functions collocation, according to a sinusoidal shear deformation theory (SSDT). The SSDT theory accounts for through-the-thickness deformation, by considering a sinusoidal evolution of all displacements with the thickness coordinate. The equations of motion and the boundary conditions are obtained by the Carrera's Unified Formulation, and further interpolated by collocation with radial basis functions
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A new flat shell finite element for the linear analysis of thin shell structures
In this paper, a new rectangular flat shell element denoted ‘ACM_RSBE5’ is presented. The new element is obtained by superposition of the new strain-based membrane element ‘RSBE5’ and the well-known plate bending element ‘ACM’. The element can be used for the analysis of any type of thin shell structures, even if the geometry is irregular. Comparison with other types of shell elements is performed using a series of standard test problems. A correlation study with an experimentally tested aluminium shell is also conducted. The new shell element proved to have a fast rate of convergence and to provide accurate results
Oscillatory dissipative conjugate heat and mass transfer in chemically-reacting micropolar flow with wall couple stress : a finite element numerical study
High temperature non-Newtonian materials processing provides a stimulating area for process engineering simulation. Motivated by emerging applications in this area, the present article investigates the time-dependent free convective flow of a chemically-reacting micropolar fluid from a vertical plate oscillating in its own plane adjacent to a porous medium. Thermal radiative, viscous dissipation and wall couple stress effects are included. The Rosseland diffusion approximation is used to model uni-directional radiative heat flux in the energy equation. Darcy’s model is adopted to mimic porous medium drag force effects. The governing two-dimensional conservation equations are normalized with appropriate variables and transformed into a dimensionless, coupled, nonlinear system of partial differential equations under the assumption of low Reynolds number. The governing boundary value problem is then solved under physically viable boundary conditions numerically with a finite element method based on the weighted residual approach. Graphical illustrations for velocity, micro-rotation (angular velocity), temperature and concentration are obtained as functions of the emerging physical parameters i.e. thermal radiation, viscous dissipation, first order chemical reaction parameter etc. Furthermore, friction factor (skin friction), surface heat transfer and mass transfer rates have been tabulated quantitatively for selected thermo-physical parameters. A comparison with previously published paper is made to check the validity and accuracy of the present finite element solutions under some limiting cases and excellent agreement is attained. Additionally, a mesh independence study is conducted. The model is relevant to reactive polymeric materials processing simulation
Metabolic Signatures of Lung Cancer in Biofluids: NMR-Based Metabonomics of Blood Plasma
In this work, the variations in the metabolic profile of blood plasma from lung cancer patients and healthy controls were investigated through NMR-based metabonomics, to assess the potential of this approach for lung cancer screening and diagnosis. PLS-DA modeling of CPMG spectra from plasma, subjected to Monte Carlo Cross Validation, allowed cancer patients to be discriminated from controls with sensitivity and specificity levels of about 90%. Relatively lower HDL and higher VLDL + LDL in the patients' plasma, together with increased lactate and pyruvate and decreased levels of glucose, citrate, formate, acetate, several amino acids (alanine, glutamine, histidine, tyrosine, valine), and methanol, could be detected. These changes were found to be present at initial disease stages and could be related to known cancer biochemical hallmarks, such as enhanced glycolysis, glutaminolysis, and gluconeogenesis, together with suppressed Krebs cycle and reduced lipid catabolism, thus supporting the hypothesis of a systemic metabolic signature for lung cancer. Despite the possible confounding influence of age, smoking habits, and other uncontrolled factors, these results indicate that NMR-based metabonomics of blood plasma can be useful as a screening tool to identify suspicious cases for subsequent, more specific radiological tests, thus contributing to improved disease management.ERDF - Competitive Factors Thematic Operational ProgrammeFCT/PTDC/ QUI/68017/2006FCOMP-01-0124-FEDER-007439SFRH/BD/ 63430/2009National UNESCO Committee - L'Oréal Medals of Honor for Women in Science 200Portuguese National NMR Network - RNRM
Sensitivity Analysis and Optimization Using Energy Finite Element and Boundary Element Methods
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76597/1/AIAA-20811-196.pd
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Beam Energy and Centrality Dependence of Direct-Photon Emission from Ultrarelativistic Heavy-Ion Collisions.
The PHENIX collaboration presents first measurements of low-momentum (0.41 GeV/c) direct-photon yield dN_{γ}^{dir}/dη is a smooth function of dN_{ch}/dη and can be well described as proportional to (dN_{ch}/dη)^{α} with α≈1.25. This scaling behavior holds for a wide range of beam energies at the Relativistic Heavy Ion Collider and the Large Hadron Collider, for centrality selected samples, as well as for different A+A collision systems. At a given beam energy, the scaling also holds for high p_{T} (>5 GeV/c), but when results from different collision energies are compared, an additional sqrt[s_{NN}]-dependent multiplicative factor is needed to describe the integrated-direct-photon yield
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Production of π0 and η mesons in Cu+Au collisions at sNN =200 GeV
Production of π0 and η mesons has been measured at midrapidity in Cu+Au collisions at sNN=200GeV. Measurements were performed in π0(η)→γγ decay channel in the 1(2)-20GeV/c transverse momentum range. A strong suppression is observed for π0 and η meson production at high transverse momentum in central Cu+Au collisions relative to the p+p results scaled by the number of nucleon-nucleon collisions. In central collisions the suppression is similar to Au+Au with comparable nuclear overlap. The η/π0 ratio measured as a function of transverse momentum is consistent with mT-scaling parametrization down to pT=2GeV/c, its asymptotic value is constant and consistent with Au+Au and p+p and does not show any significant dependence on collision centrality. Similar results were obtained in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions as well as in e+e- collisions in a range of collision energies sNN=3-1800 GeV. This suggests that the quark-gluon-plasma medium produced in Cu+Cu collisions either does not affect the jet fragmentation into light mesons or it affects the π0 and η the same way
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