369 research outputs found
Quantum Lattice Solitons
The number state method is used to study soliton bands for three anharmonic
quantum lattices: i) The discrete nonlinear Schr\"{o}dinger equation, ii) The
Ablowitz-Ladik system, and iii) A fermionic polaron model. Each of these
systems is assumed to have -fold translational symmetry in one spatial
dimension, where is the number of freedoms (lattice points). At the second
quantum level we calculate exact eigenfunctions and energies of pure
quantum states, from which we determine binding energy , effective
mass and maximum group velocity of the soliton bands as
functions of the anharmonicity in the limit . For arbitrary
values of we have asymptotic expressions for , , and
as functions of the anharmonicity in the limits of large and small
anharmonicity. Using these expressions we discuss and describe wave packets of
pure eigenstates that correspond to classical solitons.Comment: 21 pages, 1 figur
Wannier functions analysis of the nonlinear Schr\"{o}dinger equation with a periodic potential
In the present Letter we use the Wannier function basis to construct lattice
approximations of the nonlinear Schr\"{o}dinger equation with a periodic
potential. We show that the nonlinear Schr\"{o}dinger equation with a periodic
potential is equivalent to a vector lattice with long-range interactions. For
the case-example of the cosine potential we study the validity of the so-called
tight-binding approximation i.e., the approximation when nearest neighbor
interactions are dominant. The results are relevant to Bose-Einstein condensate
theory as well as to other physical systems like, for example, electromagnetic
wave propagation in nonlinear photonic crystals.Comment: 5 pages, 1 figure, submitted to Phys. Rev.
An autoinhibitory control element defines calcium-regulated isoforms of nitric oxide synthase
Nitric oxide synthases (NOSs) are classified functionally, based on whether calmodulin binding is Ca2+-dependent (cNOS) or Ca2+-independent (iNOS). This key dichotomy has not been defined at the molecular level. Here we show that cNOS isoforms contain a unique polypeptide insert in their FMN binding domains which is not shared with iNOS or other related flavoproteins. Previously identified autoinhibitory domains in calmodulin-regulated enzymes raise the possibility that the polypeptide insert is the autoinhibitory domain of cNOSs. Consistent with this possibility, three-dimensional molecular modeling suggested that the insert originates from a site immediately adjacent to the calmodulin binding sequence. Synthetic peptides derived from the 45-amino acid insert of endothelial NOS were found to potently inhibit binding of calmodulin and activation of cNOS isoforms. This inhibition was associated with peptide binding to NOS, rather than free calmodulin, and inhibition could be reversed by increasing calmodulin concentration. In contrast, insert-derived peptides did not interfere with the arginine site of cNOS, as assessed from [3H]NG-nitro-L-arginine binding, nor did they potently effect iNOS activity. Limited proteolysis studies showed that calmodulin's ability to gate electron flow through cNOSs is associated with displacement of the insert polypeptide; this is the first specific calmodulin-induced change in NOS conformation to be identified. Together, our findings strongly suggest that the insert is an autoinhibitory control element, docking with a site on cNOSs which impedes calmodulin binding and enzymatic activation. The autoinhibitory control element molecularly defines cNOSs and offers a unique target for developing novel NOS activators and inhibitors
Tunneling of quantum rotobreathers
We analyze the quantum properties of a system consisting of two nonlinearly
coupled pendula. This non-integrable system exhibits two different symmetries:
a permutational symmetry (permutation of the pendula) and another one related
to the reversal of the total momentum of the system. Each of these symmetries
is responsible for the existence of two kinds of quasi-degenerated states. At
sufficiently high energy, pairs of symmetry-related states glue together to
form quadruplets. We show that, starting from the anti-continuous limit,
particular quadruplets allow us to construct quantum states whose properties
are very similar to those of classical rotobreathers. By diagonalizing
numerically the quantum Hamiltonian, we investigate their properties and show
that such states are able to store the main part of the total energy on one of
the pendula. Contrary to the classical situation, the coupling between pendula
necessarily introduces a periodic exchange of energy between them with a
frequency which is proportional to the energy splitting between
quasi-degenerated states related to the permutation symmetry. This splitting
may remain very small as the coupling strength increases and is a decreasing
function of the pair energy. The energy may be therefore stored in one pendulum
during a time period very long as compared to the inverse of the internal
rotobreather frequency.Comment: 20 pages, 11 figures, REVTeX4 styl
Perturbation-induced radiation by the Ablowitz-Ladik soliton
An efficient formalism is elaborated to analytically describe dynamics of the
Ablowitz-Ladik soliton in the presence of perturbations. This formalism is
based on using the Riemann-Hilbert problem and provides the means of
calculating evolution of the discrete soliton parameters, as well as shape
distortion and perturbation-induced radiation effects. As an example, soliton
characteristics are calculated for linear damping and quintic perturbations.Comment: 13 pages, 4 figures, Phys. Rev. E (in press
An embedded cohesive crack model for finite element analysis of brickwork masonry fracture
This paper presents a numerical procedure for fracture of brickwork masonry based on the strong discontinuity approach. The model is an extension of the cohesive model prepared by the authors for concrete, and takes into account the anisotropy of the material. A simple central-force model is used for the stress versus crack opening curve. The additional degrees of freedom defining the crack opening are determined at the crack level, thus avoiding the need of performing a static condensation at the element level. The need for a tracking algorithm is avoided by using a consistent procedure for the selection of the separated nodes. Such a model is then implemented into a commercial code by means of a user subroutine, consequently being contrasted with experimental results. Fracture properties of masonry are independently measured for two directions on the composed masonry, and then input in the numerical model. This numerical procedure accurately predicts the experimental mixed-mode fracture records for different orientations of the brick layers on masonry panels
Njihanje i upravljanje stabilnošću koturajućeg Acrobota
In this paper the Wheeled Acrobot (WAcrobot), a novel mechanical system consisting of an underactuated double inverted pendulum robot (Acrobot) equipped with actuated wheels, is described. This underactuated and highly nonlinear system has potential applications in mobile manipulators and leg-wheeled robots. It is also a testbed for researchers studying advanced methodologies in nonlinear control. The control system for swing-up of the WAcrobot based on collocated or non-collocated feedback linearisation to linearise the active or passive Degree Of Freedom (DOF) followed by Linear Quadratic Regulator (LQR) to stabilise the robot is discussed. The effectiveness of the proposed scheme is validated with numerical simulation. The numerical results are visualised by graphical simulation to demonstrate the correlation between the numerical results and the WAcrobot physical response.U članku je opisan koturajući Acrobot (WAcrobot), novi mehanički sustav koji se sastoji od podupravljanog robota u obliku dvostrukog inverznog njihala (Acrobot) opremljenog s aktuiranim kotačem. Ovaj podupravljani i izrazito nelinearni sustav ima potencijalnu primjenu u mobilnim manipulatorima i robotima na kotačima. Također služi kao testni model za istraživače koji proučavaju napredne metode nelinearnog upravljanja. U radu je opisan sustav upravljanja za podizanje WAcrobot-a u ispravan položaj baziran na metodama kolocirane i nekolocirane eksterne linearizacije za linearizaciju aktivnog ili pasivnog stupnja slobode, i linearnom kvadratičnom regulatoru za stabilizaciju robota. Učinkovitost predvi.ene metode je validirana simulacijskim rezultatima. Rezultati su prikazani u obliku animacije kako bi se demonstrirala korelacija izme.u simulacijskih odziva i fizičkog odziva WAcrobota-a
A novel 65 kDa RNA-binding protein in squid presynaptic terminals
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Neuroscience 166 (2010): 73-83, doi:10.1016/j.neuroscience.2009.12.005.A polyclonal antibody (C4), raised against the head domain of chicken myosin Va,
reacted strongly towards a 65 kDa polypeptide (p65) on western blots of extracts from squid optic
lobes but did not recognize the heavy chain of squid myosin V. This peptide was not recognized by
other myosin Va antibodies, nor by an antibody specific for squid myosin V. In an attempt to
identify it, p65 was purified from optic lobes of Loligo plei by cationic exchange and reverse phase
chromatography. Several peptide sequences were obtained by mass spectroscopy from p65 cut from
SDS-PAGE gels. BLAST analysis and partial matching with ESTs from a Loligo pealei data bank
indicated that p65 contains consensus signatures for the hnRNP A/B family of RNA-binding
proteins. Centrifugation of post mitochondrial extracts from optic lobes on sucrose gradients after
treatment with RNase gave biochemical evidence that p65 associates with cytoplasmic RNP
complexes in an RNA-dependent manner. Immunohistochemistry and immunofluorescence studies
using the C4 antibody showed partial co-labeling with an antibody against squid synaptotagmin in
bands within the outer plexiform layer of the optic lobes and at the presynaptic zone of the stellate
ganglion. Also, punctate labeling by the C4 antibody was observed within isolated optic lobe
synaptosomes. The data indicate that p65 is a novel RNA-binding protein located to the presynaptic
terminal within squid neurons and may have a role in synaptic localization of RNA and its
translation or processing.REL, JCR and JEM received
financial support from the Fundação de Amparo à Pesquisa do Estado de Sao Paulo (FAPESP), the
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and the Fundação de
Apoio ao Ensino, Pesquisa e Assistência do Hospital das Clínicas da FMRP-USP (FAEPA). JAD
received financial support from the RI-INBRE Program Grant #P20RR016457 from the Nation
Center for Research Resources, NIH, Bethesda, MD. DTPL, LC, SBFT, EJRV and MMAB were
recipients of research fellowships from FAPESP and CNPq. REL and JEM received Productivityin-
Research fellowships from CNPq
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
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