2,886 research outputs found
Cornering the unphysical vertex
In the classical pure spinor worldsheet theory of AdS5xS5 there are some
vertex operators which do not correspond to any physical excitations. We study
their flat space limit. We find that the BRST operator of the worldsheet theory
in flat space-time can be nontrivially deformed without deforming the
worldsheet action. Some of these deformations describe the linear dilaton
background. But the deformation corresponding to the nonphysical vertex differs
from the linear dilaton in not being worldsheet parity even. The nonphysically
deformed worldsheet theory has nonzero beta-function at one loop. This means
that the classical Type IIB SUGRA backgrounds are not completely characterized
by requiring the BRST symmetry of the classical worldsheet theory; it is also
necessary to require the vanishing of the one-loop beta-function.Comment: LaTeX 40pp; v2: explained the relation to the linear dilaton
background (Section 6), changes in Introduction and Abstrac
Theoretical backgrounds of durability analysis by normalized equivalent stress functionals
Generalized durability diagrams and their properties are considered for a material under a multiaxial loading given by an arbitrary function of time. Material strength and durability under such loading are described in terms of durability, safety factor and normalized equivalent stress. Relations between these functionals are analysed. We discuss some material properties including time and load stability, self-degradation (ageing), and monotonic damaging. Phenomenological strength conditions are presented in terms of the normalized equivalent stress. It is shown that the damage based durability analysis is reduced to a particular case of such strength conditions. Examples of the reduction are presented for some known durability models. The approach is applicable to the strength and durability description at creep and impact loading and their combination
Symmetries of BFKL Equation
We discuss the algebraic structure of the spin chains related to high energy
scattering in QCD. We study the sl(2) Yangian symmetry and possible
generalizations to nonzero spin and anisotropy parameter.Comment: 16 pages, Late
Numerical solution and spectrum of boundary-domain integral equation for the Neumann BVP with variable coefficient
This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2012 Taylor & Francis.In this paper, a numerical implementation of a direct united boundary-domain integral equation (BDIE) related to the Neumann boundary value problem for a scalar elliptic partial differential equation with a variable coefficient is discussed. The BDIE is reduced to a uniquely solvable one by adding an appropriate perturbation operator. The mesh-based discretization of the BDIEs with quadrilateral domain elements leads to a system of linear algebraic equations (discretized BDIE). Then, the system is solved by LU decomposition and Neumann iterations. Convergence of the iterative method is discussed in relation to the distribution of eigenvalues of the corresponding discrete operators calculated numerically.The work was supported by the grant EP/H020497/1 "Mathematical analysis of localised boundary-domain integral equations for BVPs with variable coefficients" of the EPSRC, UK
Endpoint behavior of the pion distribution amplitude in QCD sum rules with nonlocal condensates
Starting from the QCD sum rules with nonlocal condensates for the pion
distribution amplitude, we derive another sum rule for its derivative and its
"integral" derivatives---defined in this work. We use this new sum rule to
analyze the fine details of the pion distribution amplitude in the endpoint
region . The results for endpoint-suppressed and flat-top (or
flat-like) pion distribution amplitudes are compared with those we obtained
with differential sum rules by employing two different models for the
distribution of vacuum-quark virtualities. We determine the range of values of
the derivatives of the pion distribution amplitude and show that
endpoint-suppressed distribution amplitudes lie within this range, while those
with endpoint enhancement---flat-type or CZ-like---yield values outside this
range.Comment: 20 pages, 10 figures, 1 table, conclusions update
History-sensitive accumulation rules for life-time prediction under variable loading
This is the post-print version of the article. The official published version can be obtained from the link below - Copyright @ 2011 SpringerA general form of temporal strength conditions under variable creep loading is employed to formulate several new phenomenological accumulation rules based on the constant-loading durability diagram. Unlike the well-known Robinson rule of linear accumulation of partial life-times, the new rules allow to describe the life-time sensibility to the load sequence, observed in experiments. Comparison of the new rules with experimental data shows that they fit the data much more accurately than the Robinson rule
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