25,369 research outputs found
Nearly chirp- and pedestal-free pulse compression in nonlinear fiber Bragg gratings
Peer reviewedPublisher PD
Quantum State Transfer Characterized by Mode Entanglement
We study the quantum state transfer (QST) of a class of tight-bonding Bloch
electron systems with mirror symmetry by considering the mode entanglement.
Some rigorous results are obtained to reveal the intrinsic relationship between
the fidelity of QST and the mirror mode concurrence (MMC), which is defined to
measure the mode entanglement with a certain spatial symmetry and is just the
overlap of a proper wave function with its mirror image. A complementarity is
discovered as the maximum fidelity is accompanied by a minimum of MMC. And at
the instant, which is just half of the characteristic time required to
accomplish a perfect QST, the MMC can reach its maximum value one. A large
class of perfect QST models with a certain spectrum structure are discovered to
support our analytical results.Comment: 6 pages, 3 figures. to appear in PR
Determination of Dark Matter Halo Mass from Dynamics of Satellite Galaxies
We show that the mass of a dark matter halo can be inferred from the
dynamical status of its satellite galaxies. Using 9 dark-matter simulations of
halos like the Milky Way (MW), we find that the present-day substructures in
each halo follow a characteristic distribution in the phase space of orbital
binding energy and angular momentum, and that this distribution is similar from
halo to halo but has an intrinsic dependence on the halo formation history. We
construct this distribution directly from the simulations for a specific halo
and extend the result to halos of similar formation history but different
masses by scaling. The mass of an observed halo can then be estimated by
maximizing the likelihood in comparing the measured kinematic parameters of its
satellite galaxies with these distributions. We test the validity and accuracy
of this method with mock samples taken from the simulations. Using the
positions, radial velocities, and proper motions of 9 tracers and assuming
observational uncertainties comparable to those of MW satellite galaxies, we
find that the halo mass can be recovered to within 40%. The accuracy can
be improved to within 25% if 30 tracers are used. However, the dependence
of the phase-space distribution on the halo formation history sets a minimum
uncertainty of 20% that cannot be reduced by using more tracers. We
believe that this minimum uncertainty also applies to any mass determination
for a halo when the phase space information of other kinematic tracers is used.Comment: Accepted for publication in ApJ, 18 pages, 13 figure
Mechanisms controlling vertical variability of subsurface chlorophyll maxima in a mode-water eddy
An intense subsurface chlorophyll enhancement was found repeatedly within the core of a mode-water eddy during a 2-month period. Two controls on chlorophyll concentrations in this deep chlorophyll maximum (DCM) layer are noted: chlorophyll concentration is controlled by nutrients at low nutrient concentrations and by light when nutrients are saturating. To synthesize these results, a simple one-dimensional nutrient-phytoplankton model is developed by including the effects of phytoplankton self-shading for light attenuation, depth-dependent phytoplankton specific loss, and density-associated nutrient fluctuation in the deep layer. The model is parameterized using eddy data including not only vertical diffusivity, sinking velocity, and chlorophyll-to-carbon ratios, but also rates of phytoplankton growth and nutrient regeneration. Our results suggest that the observed DCM variability is controlled by nutrient-light interaction leading to a change of phytoplankton physiology and hence vertical enrichment of chlorophyll within the core of the stratified eddy. Further theoretical analyses indicate that variation of nutrient and light availability in the DCM layer of the eddy core is largely driven by change of the vertical nutrient fluxes as a result of isopycnal motions in the deep layer, which is also subject to influences by processes including vertical mixing, particle sinking, and nutrient regeneration
Two-loop gluino contributions to neutron electric dipole moment in CP violating MSSM
We analyze two-loop gluino corrections to the neutron electric dipole moment
(EDM) in the minimal supersymmetry extension of the standard model (MSSM). The
dependence of two-loop corrections on the relevant CP violating phases differs
from that of the one-loop contributions, and there is a region in the parameter
space where the two-loop contributions are comparable with the one-loop
contributions. Our numerical results show that the two-loop corrections can be
as large as 30% of the one-loop results.Comment: Revtex, 27 pages, including 11 ps figure
Robust visual tracking via speedup multiple kernel ridge regression
Most of the tracking methods attempt to build up feature spaces to represent the appearance of a target. However, limited by the complex structure of the distribution of features, the feature spaces constructed in a linear manner cannot characterize the nonlinear structure well. We propose an appearance model based on kernel ridge regression for visual tracking. Dense sampling is fulfilled around the target image patches to collect the training samples. In order to obtain a kernel space in favor of describing the target appearance, multiple kernel learning is introduced into the selection of kernels. Under the framework, instead of a single kernel, a linear combination of kernels is learned from the training samples to create a kernel space. Resorting to the circulant property of a kernel matrix, a fast interpolate iterative algorithm is developed to seek coefficients that are assigned to these kernels so as to give an optimal combination. After the regression function is learned, all candidate image patches gathered are taken as the input of the function, and the candidate with the maximal response is regarded as the object image patch. Extensive experimental results demonstrate that the proposed method outperforms other state-of-the-art tracking methods
Feasability of Introducing a Thioether Ring in Vasopressin by nisBTC Co-expression in Lactococcus lactis
Introducing one or more intramolecular thioether bridges in a peptide provides a
promising approach to create more stable molecules with improved pharmacodynamic
properties and especially to protect peptides against proteolytic degradation.
Lanthipeptides are compounds that naturally possess thioether bonds in their structure.
The model lanthipeptide, nisin, is produced by Lactococcus lactis as a core peptide
fused to a leader peptide. The modification machinery responsible for nisin production,
including the Ser/Thr-dehydratase NisB and the cyclase NisC, can be applied for
introducing a thioether bridge into peptides fused to the nisin leader peptide, e.g., to
replace a disulfide bond. Vasopressin plays a key role in water homeostasis in the
human body and helps to constrict blood vessels. There are two cysteine residues in the
structure of wild type vasopressin, which form a disulfide bridge in the mature peptide.
Here, we show it is possible to direct the biosynthesis of vasopressin variants in such a
way that the disulfide bridge is replaced by a thioether bridge using the nisin modification
machinery NisBTC, albeit at low efficiency. Vasopressin mutants were fused either to the
nisin leader peptide directly (Type A), after the first three rings of nisin (Type B/C), or after
full nisin (Type D). The type B strategy was optimal for expression. LC-MS/MS data
verified the formation of a thioether bridge, which provides proof of principle for this
modification in vasopressin. This is a first step prior to the necessary increase of the
production yield and further purification of these peptides to finally test their biological
activity in tissue and animal models.Chinese Scholarship Council (No.
201306770012)MM-L was supported by a grant of the EU
FW7 Project SynPeptide
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