6,859 research outputs found
Ultrafast control of inelastic tunneling in a double semiconductor quantum
In a semiconductor-based double quantum well (QW) coupled to a degree of
freedom with an internal dynamics, we demonstrate that the electronic motion is
controllable within femtoseconds by applying appropriately shaped
electromagnetic pulses. In particular, we consider a pulse-driven AlxGa1-xAs
based symmetric double QW coupled to uniformly distributed or localized
vibrational modes and present analytical results for the lowest two levels.
These predictions are assessed and generalized by full-fledged numerical
simulations showing that localization and time-stabilization of the driven
electron dynamics is indeed possible under the conditions identified here, even
with a simultaneous excitations of vibrational modes.Comment: to be published in Appl.Phys.Let
Global analysis by hidden symmetry
Hidden symmetry of a G'-space X is defined by an extension of the G'-action
on X to that of a group G containing G' as a subgroup. In this setting, we
study the relationship between the three objects:
(A) global analysis on X by using representations of G (hidden symmetry);
(B) global analysis on X by using representations of G';
(C) branching laws of representations of G when restricted to the subgroup
G'.
We explain a trick which transfers results for finite-dimensional
representations in the compact setting to those for infinite-dimensional
representations in the noncompact setting when is -spherical.
Applications to branching problems of unitary representations, and to spectral
analysis on pseudo-Riemannian locally symmetric spaces are also discussed.Comment: Special volume in honor of Roger Howe on the occasion of his 70th
birthda
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Discrete Wavelet Transform-Based Whole-Spectral and Subspectral Analysis for Improved Brain Tumor Clustering Using Single Voxel MR Spectroscopy
On duality symmetries of supergravity invariants
The role of duality symmetries in the construction of counterterms for
maximal supergravity theories is discussed in a field-theoretic context from
different points of view. These are: dimensional reduction, the question of
whether appropriate superspace measures exist and information about non-linear
invariants that can be gleaned from linearised ones. The former allows us to
prove that F-term counterterms cannot be E7(7)-invariant in D=4, N=8
supergravity or E6(6)-invariant in D=5 maximal supergravity. This is confirmed
by the two other methods which can also be applied to D=4 theories with fewer
supersymmetries and allow us to prove that N=6 supergravity is finite at three
and four loops and that N=5 supergravity is three-loop finite.Comment: Clarification of arguments and their consistency with higher
dimensional divergences added, e.g. we prove the 5D 4L non-renormalisation
theorem. The 4L N=6 divergence is also ruled out. References adde
Parent Actions, Dualities and New Weyl-invariant Actions of Bosonic p-branes
By using the systematic approach of parent action method, we derive one
Weyl-noninvariant and two Weyl-invariant actions of bosonic -branes () starting from the Nambu-Goto action, and establish the duality symmetries
in this set of four actions. Moreover, we discover a new bosonic -brane
action (including the string theory) and deduce two corresponding
Weyl-invariant formulations by proposing a new special parent action. We find
that the same duality symmetries as those mentioned above exist in this new set
of actions. The new -brane actions are also briefly analyzed.Comment: 19 pages, 14 figures. The first section is modified slightly, and
references are adde
Characterization of mRNA Polyadenylation in the Apicomplexa
Messenger RNA polyadenylation is a universal aspect of gene expression in eukaryotes. In well-established model organisms, this process is mediated by a conserved complex of 15â20 subunits. To better understand this process in apicomplexans, a group of unicellular parasites that causes serious disease in humans and livestock, a computational and high throughput sequencing study of the polyadenylation complex and poly(A) sites in several species was conducted. BLAST-based searches for orthologs of the human polyadenylation complex yielded clear matches to only twoâpoly(A) polymerase and CPSF73âof the 19 proteins used as queries in this analysis. As the human subunits that recognize the AAUAAA polyadenylation signal (PAS) were not immediately obvious, a computational analysis of sequences adjacent to experimentally-determined apicomplexan poly(A) sites was conducted. The results of this study showed that there exists in apicomplexans an A-rich region that corresponds in position to the AAUAAA PAS. The set of experimentally-determined sites in one species, Sarcocystis neurona, was further analyzed to evaluate the extent and significance of alternative poly(A) site choice in this organism. The results showed that almost 80% of S. neurona genes possess more than one poly(A) site, and that more than 780 sites showed differential usage in the two developmental stagesâextracellular merozoites and intracellular schizontsâstudied. These sites affected more than 450 genes, and included a disproportionate number of genes that encode membrane transporters and ribosomal proteins. Taken together, these results reveal that apicomplexan species seem to possess a poly(A) signal analogous to AAUAAA even though genes that may encode obvious counterparts of the AAUAAA-recognizing proteins are absent in these organisms. They also indicate that, as is the case in other eukaryotes, alternative polyadenylation is a widespread phenomenon in S. neurona that has the potential to impact growth and development
Oscillation mode linewidths and heights of 23 main-sequence stars observed by Kepler
Solar-like oscillations have been observed by Kepler and CoRoT in many
solar-type stars, thereby providing a way to probe the stars using
asteroseismology. We provide the mode linewidths and mode heights of the
oscillations of various stars as a function of frequency and of effective
temperature. We used a time series of nearly two years of data for each star.
The 23 stars observed belong to the simple or F-like category. The power
spectra of the 23 main-sequence stars were analysed using both maximum
likelihood estimators and Bayesian estimators, providing individual mode
characteristics such as frequencies, linewidths, and mode heights. We study the
source of systematic errors in the mode linewidths and mode heights, and we
present a way to correct these errors with respect to a common reference fit.
Using the correction, we could explain all sources of systematic errors, which
could be reduced to less than 15% for mode linewidths and heights, and
less than 5% for amplitude, when compared to the reference fit. The effect
of a different estimated stellar background and a different estimated splitting
will provide frequency-dependent systematic errors that might affect the
comparison with theoretical mode linewidth and mode height, therefore affecting
the understanding of the physical nature of these parameters. All other sources
of relative systematic errors are less dependent upon frequency. We also
provide the dependence of the so-called linewidth dip, in the middle of the
observed frequency range, as a function of effective temperature. We show that
the depth of the dip decreases with increasing effective temperature. The
dependence of the dip on effective temperature may imply that the mixing length
parameter or the convective flux may increase with effective
temperature.Comment: Accepted by A&A, 38 pages, 35 figures, 26 table
Evidence for the classical integrability of the complete AdS(4) x CP(3) superstring
We construct a zero-curvature Lax connection in a sub-sector of the
superstring theory on AdS(4) x CP(3) which is not described by the
OSp(6|4)/U(3) x SO(1,3) supercoset sigma-model. In this sub-sector worldsheet
fermions associated to eight broken supersymmetries of the type IIA background
are physical fields. As such, the prescription for the construction of the Lax
connection based on the Z_4-automorphism of the isometry superalgebra OSp(6|4)
does not do the job. So, to construct the Lax connection we have used an
alternative method which nevertheless relies on the isometry of the target
superspace and kappa-symmetry of the Green-Schwarz superstring.Comment: 1+26 pages; v2: minor typos corrected, acknowledgements adde
Universal properties of superconformal OPEs for 1/2 BPS operators in
We give a general analysis of OPEs of 1/2 BPS superfield operators for the
superconformal algebras OSp(8/4,R), PSU(2,2), F and
OSp() which underlie maximal AdS supergravity in . \\
The corresponding three-point functions can be formally factorized in a way
similar to the decomposition of a generic superconformal UIR into a product of
supersingletons. This allows for a simple derivation of branching rules for
primary superfields. The operators of protected conformal dimension which may
appear in the OPE are classified and are shown to be either 1/2 or 1/4 BPS, or
semishort. As an application, we discuss the "non-renormalization" of extremal
-point correlators.Comment: To be published in NJP Focus Issue: Supersymmetry in condensed matter
and high energy physic
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