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Biomedical subjects

L Friedland

Publications and source records attributed to L Friedland.

At least 19 recordsLinked to original sources
PubMed2006

Emergence and control of breather and plasma oscillations by synchronizing perturbations.

Large amplitude standing waves of spatially periodic sine-Gordon equations are excited and controlled by sweeping the frequency of a small, spatially modulated driving oscillation through resonances in the system. The approach is based on capturing the system into resonances and subsequent adiabatic, persistent phase locking (autoresonance) yielding control via a single external parameter (the driving frequency). Plasma oscillations in the system are excited by using a small amplitude drive in the form of a chirped frequency standing wave, while emergence of autoresonant breather oscillations requires driving by a combination of small amplitude oscillation and standing waves.

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PubMed2006

Autoresonant phase-space holes in plasmas.

Electron phase-space holes are formed and controlled in a plasma by adiabatic nonlinear phase locking (autoresonance) with a chirped frequency driving wave. The process has a threshold on the driving amplitude and involves dragging a void region in phase space into the bulk of the distribution via persistent Cherenkov-type resonance.

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PubMed2005

Multiphase autoresonant excitations in discrete nonlinear Schrödinger systems.

Large amplitude, multiphase solutions of periodic discrete nonlinear Schrödinger (NLS) systems are excited and controlled by starting from zero and using a small perturbation. The approach involves successive formation of phases in the solution by driving the system with small amplitude plane wavelike perturbations (drives) with chirped frequencies, slowly passing through a system's resonant frequency. The system is captured into resonance and enters a continuing phase-locking (autoresonance) stage, if the drive's amplitude surpasses a certain sharp threshold value. This phase-locked solution is efficiently controlled by variation of an external parameter (driving frequency). Numerical examples of excitation of multiphase waves and periodic discrete breathers by using this approach for integrable (Ablowitz-Ladik) and nonintegrable NLS discretizations are presented. The excited multiphase waveforms are analyzed via the spectral theory of the inverse scattering method applied to both the integrable and nonintegrable systems. A theory of autoresonant excitation of 0- and 1-phase solutions by passage through resonances is developed. The threshold phenomenon in these cases is analyzed.

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PubMed2005

Excitation of multiphase waves of the nonlinear Schrödinger equation by capture into resonances.

A method for adiabatic excitation and control of multiphase ( N -band) waves of the periodic nonlinear Schrödinger (NLS) equation is developed. The approach is based on capturing the system into successive resonances with external, small amplitude plane waves having slowly varying frequencies. The excitation proceeds from zero and develops in stages, as an (N+1) -band (N=0,1,2,...) , growing amplitude wave is formed in the (N+1) th stage from an N -band solution excited in the preceding stage. The method is illustrated in simulations, where the excited multiphase waves are analyzed via the spectral approach of the inverse scattering transform method. The theory of excitation of 0- and 1-band NLS solutions by capture into resonances is developed on the basis of a weakly nonlinear version of Whitham's averaged variational principle. The phenomenon of thresholds on the driving amplitudes for capture into successive resonances and the stability of driven, phase-locked solutions in these cases are discussed.

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PubMed2004

Robust autoresonant excitation in the plasma beat-wave accelerator.

A modified version of the plasma beat-wave accelerator scheme is proposed, based on autoresonant phase locking of the Langmuir wave to the slowly chirped beat frequency of the driving lasers by passage through resonance. Peak electric fields above standard detuning limits seem readily attainable, and the plasma wave excitation is robust to large variations in plasma density or chirp rate. This scheme might be implemented in existing chirped pulse amplification or CO2 laser systems.

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PubMed2003

Multiphase control of a nonlinear lattice.

Large amplitude, multiphase excitations of the periodic Toda lattice (n-gap solutions) are created and controlled by small forcing. The approach uses passage through an ensemble of resonances and subsequent multiphase self-locking of the system with adiabatic wave-like perturbations. The synchronization of each phase in the excited lattice proceeds from the weakly nonlinear stage, where the problem can be reduced to that for a number of independent, driven, one-degree-of-freedom oscillatory systems. Due to this separability, the phase locking at this stage is robust, provided the amplitude of the corresponding forcing component exceeds a threshold, which scales as 3/4 power of the corresponding frequency chirp rate. The adiabatic synchronization continues into a fully nonlinear stage, as the driven lattice self-adjusts its state to remain in a persisting and stable multifrequency resonance with the driving perturbation. Thus, a complete control of the n-gap state becomes possible by slow variation of external parameters.

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PubMed2003

Direct excitation of high-amplitude chirped bucket-BGK modes.

For the first time, high amplitude (Deltan/n approximately 40%), high Q (up to 100 000) Bernstein, Greene, and Kruskal modes have been controllably excited in a plasma. The modes are created by sweeping an excitation voltage downwards in frequency, thereby dragging a phase space "bucket" of low density into the bulk of the plasma velocity distribution. The modes have no linear limit and differ markedly from plasma waves and Trivelpiece-Gould modes.

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PubMed2003

Emergence and control of multiphase nonlinear waves by synchronization.

Large amplitude multiphase solutions of the periodic Korteweg-de Vries equation are excited and controlled by a small forcing. The approach uses passage through an ensemble of resonances and subsequent multiphase self-locking of the system with eikonal-type perturbations. The synchronization of each phase in the Korteweg-de Vries wave is robust, provided the corresponding driving amplitude exceeds a threshold.

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PubMed2002

Spatial control of a classical electron state in a Rydberg atom by adiabatic synchronization.

An adiabatic synchronization approach is used to control orbital eccentricity and inclination of a highly excited electron in a hydrogen atom. The approach is based on persisting nonlinear phase locking (autoresonance) between spatially uniform, chirped frequency oscillating electric field, and the classical Keplerian motion of the electron in the atom. Efficient control in three dimensions is achieved by slow passage through and capture into different resonances. Scenarios guaranteeing the capture and continuing synchronization in the system are outlined, all requiring the driving field amplitude to exceed a threshold. The threshold scales as A(3/4), where A is the sweep rate of the driving frequency at resonance. The adiabatic synchronization allows one to accelerate the electron gradually by using dipolar fields, until approaching the stochastic ionization limit.

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PubMed2000

Resonant formation and control of 2D symmetric vortex waves.

It is shown that m-fold symmetric vortex waves in two dimensions ( V states) preserve their functional form in a weak straining flow having appropriate symmetry, but arbitrary time dependence. This phenomenon is used in driving the V states into a highly nonlinear excitation by subjecting a circular vortex patch to rotation and strain with oscillating strain rate and varying the rotation angular velocity. The effect is due to autoresonance in the system as the excited vortex state boundary self-adjusts its aspect ratio to synchronize with the external flow.

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PubMed2000

Subharmonic autoresonance

Adiabatic passage through higher order resonances in a perturbatively driven dynamical system with a slow control parameter, yields persisting phase locking and a strong long time response. The phenomenon has a sharp threshold on the driving amplitude, which scales with the control parameter chirp rate A and resonance order n, as A(3/(4n)).

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PubMed2000

Second harmonic autoresonant control of the l=1 diocotron mode in pure-electron plasmas

An oscillator whose frequency is amplitude dependent can be controlled by a drive whose frequency sweeps through a resonance with the oscillator's fundamental frequency. This phenomenon is called autoresonance, and has been previously investigated for drives with frequencies near the oscillator's fundamental or subharmonic frequencies. This paper examines autoresonance for drives at twice the fundamental frequency, i.e, second harmonic autoresonance. The l=1 diocotron mode in pure-electron plasmas, a very high Q nonlinear oscillator, is the focus of the paper. The theory for this oscillator is derived, and compared to experimental results. The results can be generalized to any Duffing-like driven nonlinear oscillator in which the coupling between the drive and the oscillator depends at least weakly on the oscillator amplitude.

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PubMed1999

Characterization of single-nucleotide polymorphisms in coding regions of human genes.

A major goal in human genetics is to understand the role of common genetic variants in susceptibility to common diseases. This will require characterizing the nature of gene variation in human populations, assembling an extensive catalogue of single-nucleotide polymorphisms (SNPs) in candidate genes and performing association studies for particular diseases. At present, our knowledge of human gene variation remains rudimentary. Here we describe a systematic survey of SNPs in the coding regions of human genes. We identified SNPs in 106 genes relevant to cardiovascular disease, endocrinology and neuropsychiatry by screening an average of 114 independent alleles using 2 independent screening methods. To ensure high accuracy, all reported SNPs were confirmed by DNA sequencing. We identified 560 SNPs, including 392 coding-region SNPs (cSNPs) divided roughly equally between those causing synonymous and non-synonymous changes. We observed different rates of polymorphism among classes of sites within genes (non-coding, degenerate and non-degenerate) as well as between genes. The cSNPs most likely to influence disease, those that alter the amino acid sequence of the encoded protein, are found at a lower rate and with lower allele frequencies than silent substitutions. This likely reflects selection acting against deleterious alleles during human evolution. The lower allele frequency of missense cSNPs has implications for the compilation of a comprehensive catalogue, as well as for the subsequent application to disease association.

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PubMed1999

Double autoresonance in two-dimensional dynamical systems.

The phenomenon of double autoresonance in dynamical systems with two degrees of freedom is examined. We analyze the motion of a particle in a two-dimensional centrally symmetric potential, subject to a homogeneous quasiperiodic external field of elliptical polarization. It is shown that if the particle has a sufficiently small initial energy, a double resonance is established when the slowly varying driving frequency approaches the linear resonance frequency. As the driving frequency is changed further, the double resonance is maintained, causing a continuous excitation of the oscillator. When nonlinearity becomes significant, the motion transforms into nearly circular oscillations. The necessary conditions for the persistence of the autoresonance are studied in detail.

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PubMed1999

Passage through resonance and autoresonance in x(2n)-type potentials.

Resonant dynamics of a particle in an x(2n)-type potential driven by an oscillation with adiabatically varying frequency is investigated. It is shown that, under certain conditions, when the driving frequency increases in time and passes the resonance with the unperturbed system, the oscillator phase locks to the drive and, later, this phase locking is sustained, i.e., the system remains in autoresonance. The initial phase locking by passage through resonance is the main ingredient of the transition to autoresonance and comprises the generalization of previous results for nearly parabolic potentials.

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