340 research outputs found
Microsegregation and inclusion development during the casting of steel
The enrichment of composition in the residual liquid during solidification is of itself an important parameter regarding the fitness for purpose of the alloy and, furthermore, will have a major influence on the precipitates and oxide inclusions that can nucleate and/or grow in the mushy zone. Corus sought a relatively simple, rapid model for this microsegregation and its associated inclusion type and size, for predictions across the thickness of continuously cast steels, suitable for use in
conjunction with macro-models but demonstrably superior to the use of analytical equations. Notably, the analytical equations employ constant temperature equilibrium and diffusivity data for a process that can cover a very wide temperature range, and the assumed growth laws coupled with these data have an implied thermal history at odds with the environment of the macroscopic model within which the algorithm is to be used. The development and use of this model are described, along with its validation against a proven but time-consuming Finite Difference program for this purpose
Q7-branes and their coupling to IIB supergravity
We show how, by making use of a new basis of the IIB supergravity
axion-dilaton coset, SL(2,R)/SO(2), 7-branes that belong to different conjugacy
classes of the duality group SL(2,R) naturally couple to IIB supergravity with
appropriate source terms characterized by an SL(2,R) charge matrix Q. The
conjugacy classes are determined by the value of the determinant of Q. The
(p,q) 7-branes are the branes in the conjugacy class detQ = 0. The 7-branes in
the conjugacy class detQ > 0 are labelled by three numbers (p,q,r) which
parameterize the matrix Q and will be called Q7-branes. We construct the full
bosonic Wess--Zumino term for the Q7-branes. In order to realize a gauge
invariant coupling of the Q7-brane to the gauge fields of IIB supergravity it
is necessary to introduce an SL(2,R) doublet of two distinct Born--Infeld
fields on the Q7-brane world-volume.Comment: 31 pages, Latex fil
New Superembeddings for Type II Superstrings
Possible ways of generalization of the superembedding approach for the
supersurfaces with the number of Grassmann directions being less than the half
of that for the target superspace are considered on example of Type II
superstrings. Focus is on n=(1,1) superworldsheet embedded into D=10 Type II
superspace that is of the interest for establishing a relation with the NSR
string.Comment: 26 pages, LaTeX, JHEP.cls and JHEP.bst style files are used; v2:
misprints corrected, comments, acknowledgments, references adde
Two-Dimensional Helioseismic Power, Phase, and Coherence Spectra of {\it Solar Dynamics Observatory} Photospheric and Chromospheric Observables
While the {\it Helioseismic and Magnetic Imager} (HMI) onboard the {\it Solar
Dynamics Observatory} (SDO) provides Doppler velocity [], continuum
intensity [], and line-depth [] observations, each of which is
sensitive to the five-minute acoustic spectrum, the {\it Atmospheric Imaging
Array} (AIA) also observes at wavelengths -- specifically the 1600 and 1700
Angstrom bands -- that are partly formed in the upper photosphere and have good
sensitivity to acoustic modes. In this article we consider the characteristics
of the spatio--temporal Fourier spectra in AIA and HMI observables for a
15-degree region around NOAA Active Region 11072. We map the
spatio--temporal-power distribution for the different observables and the HMI
Line Core [], or Continuum minus Line Depth, and the phase and coherence
functions for selected observable pairs, as a function of position and
frequency. Five-minute oscillation power in all observables is suppressed in
the sunspot and also in plage areas. Above the acoustic cut-off frequency, the
behaviour is more complicated: power in HMI is still suppressed in the
presence of surface magnetic fields, while power in HMI and the AIA bands
is suppressed in areas of surface field but enhanced in an extended area around
the active region, and power in HMI is enhanced in a narrow zone around
strong-field concentrations and suppressed in a wider surrounding area. The
relative phase of the observables, and their cross-coherence functions, are
also altered around the active region. These effects may help us to understand
the interaction of waves and magnetic fields in the different layers of the
photosphere, and will need to be taken into account in multi-wavelength local
helioseismic analysis of active regions.Comment: 18 pages, 15 figures, to be published in Solar Physic
N=2 Sigma Models for Ramond-Ramond Backgrounds
Using the U(4) hybrid formalism, manifestly N=(2,2) worldsheet supersymmetric
sigma models are constructed for the Type IIB superstring in Ramond-Ramond
backgrounds. The Kahler potential in these N=2 sigma models depends on four
chiral and antichiral bosonic superfields and two chiral and antichiral
fermionic superfields. When the Kahler potential is quadratic, the model is a
free conformal field theory which describes a flat ten-dimensional target space
with Ramond-Ramond flux and non-constant dilaton. For more general Kahler
potentials, the model describes curved target spaces with Ramond-Ramond flux
that are not plane-wave backgrounds. Ricci-flatness of the Kahler metric
implies the on-shell conditions for the background up to the usual four-loop
conformal anomaly.Comment: 19 pages harvma
String-Loop Corrected Magnetic Black Holes
We discuss the form of the string-loop-corrected effective action obtained by
compactification of the heterotic string theory on the manifold
or on its orbifold limit and the loop-corrected magnetic black hole solutions
of the equations of motion. Effective 4D theory has N=2 local supersymmetry.
Using the string-loop-corrected prepotential of the N=2 supersymmetric theory,
which receives corrections only from the string world sheets of torus topology,
we calculate the loop corrections to the tree-level gauge couplings and solve
the loop-corrected equations of motion. At the string-tree level, the effective
gauge couplings decrease at small distances from the origin, and in this region
string-loop corrections to the gauge couplings become important. A possibility
of smearing the singularity of the tree-level supersymmetric solution with
partially broken supersymmetry by quantum corrections is discussed.Comment: Improved version. Mixing of the dilaton with other moduli properly
taken into account. Explanatory notes adde
String Propagator: a Loop Space Representation
The string quantum kernel is normally written as a functional sum over the
string coordinates and the world--sheet metrics. As an alternative to this
quantum field--inspired approach, we study the closed bosonic string
propagation amplitude in the functional space of loop configurations. This
functional theory is based entirely on the Jacobi variational formulation of
quantum mechanics, {\it without the use of a lattice approximation}. The
corresponding Feynman path integral is weighed by a string action which is a
{\it reparametrization invariant} version of the Schild action. We show that
this path integral formulation is equivalent to a functional ``Schrodinger''
equation defined in loop--space. Finally, for a free string, we show that the
path integral and the functional wave equation are {\it exactly } solvable.Comment: 15 pages, no figures, ReVTeX 3.
Universality of the Operator Product Expansions of SCFT_4
We study the operator product algebra of the supercurrent J and Konishi
superfield K in four-dimensional supersymmetric gauge theories. The Konishi
superfield appears in the JJ OPE and the algebra is characterized by two
central charges c and c' and an anomalous dimension h for K. In free field
(one-loop) approximation, c~3N_v+N_\chi and c'~N_\chi, where N_v and N_\chi
are, respectively, the number of vector and chiral multiplets in the theory. In
higher order c, c' and h depend on the gauge and Yukawa couplings and we obtain
the two-loop contributions by combining earlier work on c with our own
calculations of c'. The major result is that the radiative corrections to the
central charges cancel when the one-loop beta-functions vanish, suggesting that
c and c' (but not h) are invariant under continuous deformations of
superconformal theories. The behavior of c and c' along renormalization group
flows is studied from the viewpoint of a c-theorem.Comment: LaTeX file, 11 pages, no figur
Supergravity Solutions for BI Dyons
We construct partially localized supergravity counterpart solutions to the
1/2 supersymmetric non-threshold and the 1/4 supersymmetric threshold bound
state BI dyons in the D3-brane Dirac-Born-Infeld theory. Such supergravity
solutions have all the parameters of the BI dyons. By applying the IIA/IIB
T-duality transformations to these supergravity solutions, we obtain the
supergravity counterpart solutions to 1/2 and 1/4 supersymmetric BIons carrying
electric and magnetic charges of the worldvolume U(1) gauge field in the
Dirac-Born-Infeld theory in other dimensions.Comment: 17 pages, REVTeX, revised version to appear in Phys. Rev.
Type IIB superstring action in AdS_5 x S^5 background
We construct the covariant kappa-symmetric superstring action for a type IIB
superstring on AdS_5 x S^5 background. The action is defined as a 2d
sigma-model on the coset superspace SU(2,2|4) / SO(4,1) x SO(5) and is shown to
be the unique one that has the correct bosonic and flat space limits.Comment: 18 pages, latex. v2: Minor corrections, extended comment on conformal
invariance of the 2d theory; v3,v4: Few signs correcte
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