2,452 research outputs found
Exact Analysis of Soliton Dynamics in Spinor Bose-Einstein Condensates
We propose an integrable model of a multicomponent spinor Bose-Einstein
condensate in one dimension, which allows an exact description of the dynamics
of bright solitons with spin degrees of freedom. We consider specifically an
atomic condensate in the F=1 hyperfine state confined by an optical dipole
trap. When the mean-field interaction is attractive (c_0 < 0) and the
spin-exchange interaction of a spinor condensate is ferromagnetic (c_2 < 0), we
prove that the system possesses a completely integrable point leading to the
existence of multiple bright solitons. By applying results from the inverse
scattering method, we analyze a collision law for two-soliton solutions and
find that the dynamics can be explained in terms of the spin precession.Comment: 4 pages, 2 figure
Complete integrability of derivative nonlinear Schr\"{o}dinger-type equations
We study matrix generalizations of derivative nonlinear Schr\"{o}dinger-type
equations, which were shown by Olver and Sokolov to possess a higher symmetry.
We prove that two of them are `C-integrable' and the rest of them are
`S-integrable' in Calogero's terminology.Comment: 14 pages, LaTeX2e (IOP style), to appear in Inverse Problem
Space biology initiative program definition review. Trade study 1: Automation costs versus crew utilization
A significant emphasis upon automation within the Space Biology Initiative hardware appears justified in order to conserve crew labor and crew training effort. Two generic forms of automation were identified: automation of data and information handling and decision making, and the automation of material handling, transfer, and processing. The use of automatic data acquisition, expert systems, robots, and machine vision will increase the volume of experiments and quality of results. The automation described may also influence efforts to miniaturize and modularize the large array of SBI hardware identified to date. The cost and benefit model developed appears to be a useful guideline for SBI equipment specifiers and designers. Additional refinements would enhance the validity of the model. Two NASA automation pilot programs, 'The Principal Investigator in a Box' and 'Rack Mounted Robots' were investigated and found to be quite appropriate for adaptation to the SBI program. There are other in-house NASA efforts that provide technology that may be appropriate for the SBI program. Important data is believed to exist in advanced medical labs throughout the U.S., Japan, and Europe. The information and data processing in medical analysis equipment is highly automated and future trends reveal continued progress in this area. However, automation of material handling and processing has progressed in a limited manner because the medical labs are not affected by the power and space constraints that Space Station medical equipment is faced with. Therefore, NASA's major emphasis in automation will require a lead effort in the automation of material handling to achieve optimal crew utilization
A systematic method for constructing time discretizations of integrable lattice systems: local equations of motion
We propose a new method for discretizing the time variable in integrable
lattice systems while maintaining the locality of the equations of motion. The
method is based on the zero-curvature (Lax pair) representation and the
lowest-order "conservation laws". In contrast to the pioneering work of
Ablowitz and Ladik, our method allows the auxiliary dependent variables
appearing in the stage of time discretization to be expressed locally in terms
of the original dependent variables. The time-discretized lattice systems have
the same set of conserved quantities and the same structures of the solutions
as the continuous-time lattice systems; only the time evolution of the
parameters in the solutions that correspond to the angle variables is
discretized. The effectiveness of our method is illustrated using examples such
as the Toda lattice, the Volterra lattice, the modified Volterra lattice, the
Ablowitz-Ladik lattice (an integrable semi-discrete nonlinear Schroedinger
system), and the lattice Heisenberg ferromagnet model. For the Volterra lattice
and modified Volterra lattice, we also present their ultradiscrete analogues.Comment: 61 pages; (v2)(v3) many minor correction
Integrable discretizations of derivative nonlinear Schroedinger equations
We propose integrable discretizations of derivative nonlinear Schroedinger
(DNLS) equations such as the Kaup-Newell equation, the Chen-Lee-Liu equation
and the Gerdjikov-Ivanov equation by constructing Lax pairs. The discrete DNLS
systems admit the reduction of complex conjugation between two dependent
variables and possess bi-Hamiltonian structure. Through transformations of
variables and reductions, we obtain novel integrable discretizations of the
nonlinear Schroedinger (NLS), modified KdV (mKdV), mixed NLS, matrix NLS,
matrix KdV, matrix mKdV, coupled NLS, coupled Hirota, coupled Sasa-Satsuma and
Burgers equations. We also discuss integrable discretizations of the
sine-Gordon equation, the massive Thirring model and their generalizations.Comment: 24 pages, LaTeX2e (IOP style), final versio
Electroencephalographic characteristics of epileptic seizures in preterm neonates
OBJECTIVE:
Although seizures are more common in the neonatal period than in any other stage of childhood, those in preterm neonates are still poorly described. The aim of this study was to assess electro-clinical characteristics of seizures occurring before a corrected age of 40 weeks in neonates born prematurely.
METHOD:
Retrospective analysis of EEG-documented seizures in neonates born prematurely. Seizures in a group of term neonates served as controls.
RESULTS:
Fifty-six prematurely born and 46 term born neonates were included. Median duration of seizures was 52 s in preterm and 96 s in term neonates. Seizures were focal or multifocal. In least mature neonates, they involved smaller regions of onset and remained localised. With increasing corrected age, propagation became more frequent. The electrographic pattern – maximal frequency of oscillation and the onset pattern also evolved with age. Electro-clinical seizures were observed in 25% of preterm versus 50% of term neonates; almost all electro-clinical seizures involved the central (motor) regions.
CONCLUSION:
Ictal EEG features undergo changes depending on corrected age. Most seizures are subclinical, thus EEG is essential for diagnosis.
SIGNIFICANCE:
Relating ictal EEG pattern to corrected age can improve diagnosis and ultimately management
Fast-ion-induced secondary ion emission from submicron droplet surfaces studied using a new coincidence technique with forward-scattered projectiles
A mass spectrometric study of secondary ions emitted from droplet surfaces by MeV-energy heavy ion impact was performed to investigate fast-ion-induced molecular reaction processes on liquid surfaces. Herein, a new coincidence technique was developed between secondary ions and scattered projectile ions at a small forward angle. The advantages of this technique were demonstrated by measurement of the collision between 4-MeV C3+ and ethanol droplets. Secondary ion emission probabilities were obtained directly from the coincidence data. Notably, this technique enabled positive fragment ions that had not been identified in previous measurements to be observed by suppressing the strong background originating from gas-phase molecules more than 104-fold. H+, H3O+, C2H5+, and C2H5O+ were found to be produced as major positive fragment ions, in addition to minor fragments H2+, C2H3+, and CH2OH+. Production of these ions suggests that competition between rapid hydrogen ion emission from multiply ionized states and intermolecular proton transfer accompanied by fragmentation through protonated ethanol occurs after fast heavy-ion collisions. Clarification of the positive fragment ions also revealed the characteristic features of negative ions. Negative ions were realized to exhibit higher degrees of fragmentation and reactivity compared with positive ions. Furthermore, the energy loss by forward-scattered ions during droplet penetration was used to evaluate the target thickness at a submicron level. Variations in secondary ion yield, mass distribution, and kinetic energies depending on the penetration length were observed below 1 µm. These results highlight the unknown mechanism of these “submicron effects” observed in secondary ion emission processes as a new phenomenon
Matter-Wave Solitons in an F=1 Spinor Bose-Einstein Condensate
Following our previous work [J. Ieda, T. Miyakawa, M. Wadati,
cond-mat/0404569] on a novel integrable model describing soliton dynamics of an
F=1 spinor Bose--Einstein condensate, we discuss in detail the properties of
the multi-component system with spin-exchange interactions. The exact multiple
bright soliton solutions are obtained for the system where the mean-field
interaction is attractive (c_0 < 0) and the spin-exchange interaction is
ferromagnetic (c_2 < 0). A complete classification of the one-soliton solution
with respect to the spin states and an explicit formula of the two-soliton
solution are presented. For solitons in polar state, there exists a variety of
different shaped solutions including twin peaks. We show that a "singlet pair"
density can be used to distinguish those energetically degenerate solitons. We
also analyze collisional effects between solitons in the same or different spin
state(s) by computing the asymptotic forms of their initial and final states.
The result reveals that it is possible to manipulate the spin dynamics by
controlling the parameters of colliding solitons.Comment: 12 pages, 9 figures, to appear in J. Phys. Soc. Jpn. Vol.73 No.11
(2004
Stability of Waves in Multi-component DNLS system
In this work, we systematically generalize the Evans function methodology to
address vector systems of discrete equations. We physically motivate and
mathematically use as our case example a vector form of the discrete nonlinear
Schrodinger equation with both nonlinear and linear couplings between the
components. The Evans function allows us to qualitatively predict the stability
of the nonlinear waves under the relevant perturbations and to quantitatively
examine the dependence of the corresponding point spectrum eigenvalues on the
system parameters. These analytical predictions are subsequently corroborated
by numerical computations.Comment: to appear Journal of Physics A: Mathematical and Theoretica
One-Dimensional Integrable Spinor BECs Mapped to Matrix Nonlinear Schr\"odinger Equation and Solution of Bogoliubov Equation in These Systems
In this short note, we construct mappings from one-dimensional integrable
spinor BECs to matrix nonlinear Schr\"odinger equation, and solve the
Bogoliubov equation of these systems. A map of spin- BEC is constructed from
the -dimensional spinor representation of irreducible tensor operators of
. Solutions of Bogoliubov equation are obtained with the aid of the
theory of squared Jost functions.Comment: 2.1 pages, JPSJ shortnote style. Published version. Note and
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