2,274 research outputs found
Anisotropically Shaped Magnetic/Plasmonic Nanocomposites for Information Encryption and Magnetic-Field-Direction Sensing.
Instantaneous control over the orientation of anisotropically shaped plasmonic nanostructures allows for selective excitation of plasmon modes and enables dynamic tuning of the plasmonic properties. Herein we report the synthesis of rod-shaped magnetic/plasmonic core-shell nanocomposite particles and demonstrate the active tuning of their optical property by manipulating their orientation using an external magnetic field. We further design and construct an IR-photoelectric coupling system, which generates an output voltage depending on the extinction property of the measured nanocomposite sample. We employ the device to demonstrate that the nanocomposite particles can serve as units for information encryption when immobilized in a polymer film and additionally when dispersed in solution can be employed as a new type of magnetic-field-direction sensor
Topological Stable Rank of Nest Algebras
We establish a general result about extending a right invertible row over a
Banach algebra to an invertible matrix. This is applied to the computation of
right topological stable rank of a split exact sequence. We also introduce a
quantitative measure of stable rank. These results are applied to compute the
right (left) topological stable rank for all nest algebras. This value is
either 2 or infinity, and rtsr(T(N)) = 2 occurs only when N is of ordinal type
less than omega^2 and the dimensions of the atoms grows sufficiently quickly.
We introduce general results on `partial matrix algebras' over a Banach
algebra. This is used to obtain an inequality akin to Rieffel's formula for
matrix algebras over a Banach algebra. This is used to give further insight
into the nest case
Generalized parton distributions of the pion in a Bethe-Salpeter approach
We calculate generalized parton distribution functions in a field theoretic
formalism using a covariant Bethe-Salpeter approach for the determination of
the bound-state wave function. We describe the procedure in an exact
calculation in scalar Electrodynamics proving that the relevant corrections
outside our scheme vanish. We extend the formalism to the Nambu--Jona-Lasinio
model, a realistic theory of the pion. We go in both cases beyond all previous
calculations and discover that all important features required by general
physical considerations, like symmetry properties, sum rules and the
polynomiality condition, are explicitly verified. We perform a numerical study
of their behavior in the weak and strong coupling limits.Comment: 19 pages, 21 eps figures, accepted for publication in EPJ
Impact-parameter dependence of the generalized parton distribution of the pion in chiral quark models
We compute the off-forward diagonal non-singlet generalized parton
distribution of the pion in two distinct chiral quark models: the
Nambu-Jona-Lasinio model with the Pauli-Villars regulator and the Spectral
Quark Model. The analysis is carried out in the impact-parameter space.
Leading-order perturbative QCD evolution is carried out via the inverse Mellin
transform in the index space. The model predictions agree very reasonably with
the recent results from transverse-lattice calculations, reproducing
qualitatively both the Bjorken-x and the impact-parameter dependence of the
data.Comment: 13 pages, 3 figures, to appear in Phys. Lett.
Genomic characterization of Gli-activator targets in sonic hedgehog-mediated neural patterning
Sonic hedgehog (Shh) acts as a morphogen to mediate the specification of distinct cell identities in the ventral neural tube through a Gli-mediated (Gli1-3) transcriptional network. Identifying Gli targets in a systematic fashion is central to the understanding of the action of Shh. We examined this issue in differentiating neural progenitors in mouse. An epitope-tagged Gli-activator protein was used to directly isolate cis-regulatory sequences by chromatin immunoprecipitation (ChIP). ChIP products were then used to screen custom genomic tiling arrays of putative Hedgehog (Hh) targets predicted from transcriptional profiling studies, surveying 50-150 kb of non-transcribed sequence for each candidate. In addition to identifying expected Gli-target sites, the data predicted a number of unreported direct targets of Shh action. Transgenic analysis of binding regions in Nkx2.2, Nkx2.1 (Titf1) and Rab34 established these as direct Hh targets. These data also facilitated the generation of an algorithm that improved in silico predictions of Hh target genes. Together, these approaches provide significant new insights into both tissue-specific and general transcriptional targets in a crucial Shh-mediated patterning process
Simulations of a Magnetic Fluctuation Driven Large Scale Dynamo and Comparison with a Two-scale Model
Models of large scale (magnetohydrodynamic) dynamos (LSD) which couple large
scale field growth to total magnetic helicity evolution best predict the
saturation of LSDs seen in simulations. For the simplest so called "{\alpha}2"
LSDs in periodic boxes, the electromotive force driving LSD growth depends on
the difference between the time-integrated kinetic and current helicity
associated with fluctuations. When the system is helically kinetically forced
(KF), the growth of the large scale helical field is accompanied by growth of
small scale magnetic (and current) helicity which ultimately quench the LSD.
Here, using both simulations and theory, we study the complementary
magnetically forced(MF) case in which the system is forced with an electric
field that supplies magnetic helicity. For this MF case, the kinetic helicity
becomes the back-reactor that saturates the LSD. Simulations of both MF and KF
cases can be approximately modeled with the same equations of magnetic helicity
evolution, but with complementary initial conditions. A key difference between
KF and MF cases is that the helical large scale field in the MF case grows with
the same sign of injected magnetic helicity, whereas the large and small scale
magnetic helicities grow with opposite sign for the KF case. The MF case can
arise even when the thermal pressure is approximately smaller than the magnetic
pressure, and requires only that helical small scale magnetic fluctuations
dominate helical velocity fluctuations in LSD driving. We suggest that LSDs in
accretion discs and Babcock models of the solar dynamo are actually MF LSDs.Comment: 12 pages, 34 figure
Short-Pulse, Compressed Ion Beams at the Neutralized Drift Compression Experiment
We have commenced experiments with intense short pulses of ion beams on the
Neutralized Drift Compression Experiment (NDCX-II) at Lawrence Berkeley
National Laboratory, with 1-mm beam spot size within 2.5 ns full-width at half
maximum. The ion kinetic energy is 1.2 MeV. To enable the short pulse duration
and mm-scale focal spot radius, the beam is neutralized in a 1.5-meter-long
drift compression section following the last accelerator cell. A
short-focal-length solenoid focuses the beam in the presence of the volumetric
plasma that is near the target. In the accelerator, the line-charge density
increases due to the velocity ramp imparted on the beam bunch. The scientific
topics to be explored are warm dense matter, the dynamics of radiation damage
in materials, and intense beam and beam-plasma physics including select topics
of relevance to the development of heavy-ion drivers for inertial fusion
energy. Below the transition to melting, the short beam pulses offer an
opportunity to study the multi-scale dynamics of radiation-induced damage in
materials with pump-probe experiments, and to stabilize novel metastable phases
of materials when short-pulse heating is followed by rapid quenching. First
experiments used a lithium ion source; a new plasma-based helium ion source
shows much greater charge delivered to the target.Comment: 4 pages, 2 figures, 1 table. Submitted to the proceedings for the
Ninth International Conference on Inertial Fusion Sciences and Applications,
IFSA 201
Mode attraction, rejection and control in nonlinear multimode optics
Novel fundamental notions helping in the interpretation of the complex
dynamics of nonlinear systems are essential to our understanding and ability to
exploit them. In this work we predict and demonstrate experimentally a
fundamental property of Kerr-nonlinear media, which we name mode rejection and
takes place when two intense counter-propagating beams interact in a multimode
waveguide. In stark contrast to mode attraction phenomena, mode rejection leads
to the selective suppression of a spatial mode in the forward beam, which is
controlled via the counter-propagating backward beam. Starting from this
observation we generalise the ideas of attraction and rejection in nonlinear
multimode systems of arbitrary dimension, which paves the way towards a more
general idea of all-optical mode control. These ideas represent universal tools
to explore novel dynamics and applications in a variety of optical and
non-optical nonlinear systems. Coherent beam combination in
polarization-maintaining multicore fibres is demonstrated as example
A Model for the Pion Structure Function
The pion structure function is investigated in a simple model, where pion and
constituent quark fields are coupled through the simplest pseudoscalar
coupling. The imaginary part of the forward gamma* pi-> gamma* pi scattering
amplitude is evaluated and related to the structure functions. It is shown that
the introduction of non-perturbative effects, linked to the size of the pion
and preserving gauge invariance, allows a connection with the quark
distribution. It is predicted that higher-twist terms become negligible for Q2
larger than about 2 GeV2 and that quarks in the pion have a momentum fraction
smaller than in the proton case.Comment: 14 pages, 6 figures, LaTeX, elsart clas
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