Parametric excitation of surface waves at the boundary between a magnetized plasma and a metal

A study is made of the parametric excitation of potential surface waves propagating in a planar plasma-metal waveguide structure in a magnetic field perpendicular to the plasma-metal boundary. An external, spatially uniform, alternating electric field at the second harmonic of the excited wave is used as the source of parametric excitation. A set of equations is derived that describes the excitation of surface waves due to the onset of decay instability. Expressions for the growth rates in the linear stage of instability are obtained, and the threshold amplitudes of the external electric field above which the parametric instability can occur are found. Analytic expressions for the saturation amplitudes are derived with allowance for the self-interaction of each of the excited waves and the interaction between them. The effect of the plasma parameters and the strength of the external magnetic field on the saturation amplitude, growth rates, and the threshold amplitudes of the pump electric field are analyzed.     

Application of the fluctuation theorem to motor proteins: from F<Subscript>1</Subscript>-ATPase to axonal cargo transport by kinesin and dynein

The fluctuation theorem is a representative theorem in non-equilibrium statistical physics actively studied in the 1990s. Relating to entropy production in non-equilibrium states, the theorem has been used to estimate the driving power of motor proteins from fluctuation in their motion. In this review, usage of the fluctuation theorem in experiments on motor proteins is illustrated for biologists, especially those who study mechanobiology, in which force measurement is a central issue. We first introduce the application of the fluctuation theorem in measuring the rotary torque of the rotary motor protein F₁-ATPase. Next, as an extension of this application, a recent trial estimating the force generated during cargo transport in vivo by the microtubule motors kinesin and dynein is introduced. Elucidation of the physical mechanism of such transport is important, especially for neurons, in which deficits in cargo transport are deeply related to neuronal diseases. Finally, perspectives on the fluctuation theorem as a new technique in the field of neuroscience are discussed.     

Excitation of waves in an inhomogeneous plasma

The evolution of initial perturbations in a spatially inhomogeneous cold electron plasma in the absence of an external magnetic field is considered. The excitation of both continuous-spectrum bulk plasma waves and surface plasma waves with a discrete frequency spectrum is investigated. Analytic solutions are obtained in the long-wavelength limit, and the excitation of waves of arbitrary length is analyzed numerically. The local, integral, and spatial spectra are calculated, as well as the field structures and dispersion properties of waves in waveguides filled nonuniformly with a plasma. It is shown that, in a plasma with a smooth boundary, there also exist surface waves with a discrete spectrum (although with somewhat different properties as compared to those in a plasma with a sharp boundary), which are excited together with continuous-spectrum bulk waves during the evolution of the initial perturbation.     

Electric field allowed molecular transitions for one and two photon excitation microscopy

We propose an excitation technique for observing single and two photon excitation in those molecules for which such transitions are forbidden by the selection rules. This is possible by the application of an external electric field that perturbs the molecular orbitals, thereby resulting in a significant shift of energy levels. Such a shift of energy levels may bring those levels in resonance with the radiation field which is normally forbidden by selection rules. Further, parity of the these states may significantly improve the emission process. The external electric field results in the mixing of excited (short lifetime) and metastable states (long lifetime), thus reducing the lifetime of metastable (or near metastable) states. This may provide an effective channel for allowing transition from the metastable states. An application of electric field may result in the excitation of poorly excitable biomolecules. This excitation technique may find applications in single- and multi-photon fluorescence microscopy, bioimaging and optical devices.     

Electric field generated by axial longitudinal vibration modes of microtubule

Microtubules are electrically polar structures fulfilling prerequisites for generation of oscillatory electric field in the kHz to GHz region. Energy supply for excitation of elasto-electrical vibrations in microtubules may be provided from GTP-hydrolysis; motor protein–microtubule interactions; and energy efflux from mitochondria. We calculated electric field generated by axial longitudinal vibration modes of microtubules for random, and coherent excitation. In case of coherent excitation of vibrations, the electric field intensity is highest at the end of microtubule. The dielectrophoretic force exerted by electric field on the surrounding molecules will influence the kinetics of microtubule polymerization via change in the probability of the transport of charge and mass particles. The electric field generated by vibrations of electrically polar cellular structures is expected to play an important role in biological self-organization.     

Extracellular potential field of excited isolated frog muscle fibres immersed in a volume conductor

The extracellular potential field of isolated frog muscle fibres immersed in a volume conductor was studied at radial distances up to 3 mm during excitation. The shape of the field distant from both the point of the origin of the excitation and the end of the fibre as well as changes in the field when depolarization wave approached the fibre end were described. Different amplitude decrease rates in individual phases of the extracellular potential and the peak-to-peak amplitude at different temperatures were found. Extracellular potentials at long radial distances were recorded using an averaging technique. The shape of the extracellular potentials at long radial distances over the fibre and beyond its end were very similar to the shape of extraterritorial potentials of a single motor unit.     

可描述横向电场中外周神经兴奋的电缆方程

传统的电缆方程只能用于描述纵向电场中外周神经的兴奋,无法描述外周神经在横向电场作用下的兴奋,其于两阶段过程模型,提出一种改进的电缆方程,可以描述外周神经在横向电场中的兴奋,其结果和Struijk的离体实验数据相吻合。此改进的电缆方程可用于描述任意电场中外周神经的兴奋。     

Dynamics of pattern formation in lateral-inhibition type neural fields

The dynamics of pattern formation is studied for lateral-inhibition type homogeneous neural fields with general connections. Neural fields consisting of single layer are first treated, and it is proved that there are five types of pattern dynamics. The type of the dynamics of a field depends not only on the mutual connections within the field but on the level of homogeneous stimulus given to the field. An example of the dynamics is as follows: A fixed size of localized excitation, once evoked by stimulation, can be retained in the field persistently even after the stimulation vanishes. It moves until it finds the position of the maximum of the input stimulus. Fields consisting of an excitatory and an inhibitory layer are next analyzed. In addition to stationary localized excitation, fields have such pattern dynamics as production of oscillatory waves, travelling waves, active and dual active transients, etc.This research was supported in part by a Sloan Foundation grant to the Center for Systems Neuroscience, University of Massachusetts at AmherstOn sabbatical leave from the University of Tokyo     

Functional studies of nerve projections in the canine intestine

An in vivo model has been developed to study nerve connections in the canine intestine, using spread of field stimulated contractions recorded proximally and distally with strain gauges and local intra-arterial injections of drugs. Excitation spread orally for several centimetres, more effectively at lower frequencies of field stimulation. This excitation was blocked by local hexamethonium or by a combination of atropine and naloxone (each of which reduced the contractions). Distal excitation occurred after a longer delay than oral excitation; during the delay there was frequently an initial relaxation response. Distal excitation was greater at higher frequencies of field stimulation, but like oral excitation it was blocked by hexamethonium or by a combination of atropine and naloxone. Distal relaxation responses were unaffected by atropine or naloxone, but were abolished by hexamethonium. "Off" contractions, those that followed cessation of field stimulation, occurred at higher frequencies of field stimulation proximally and distally near the site of field stimulation and were blocked by atropine but not by naloxone or hexamethonium. The effects of all agents given locally extended beyond the sites of injection. These results suggest that a chain of cholinergic nerves with nicotinic synapses transmit excitation orally and distally to circular muscle; these effects seem to be facilitated proximally and distally by opioid nerves and to be inhibited initially distally by a noncholinergic mechanism. Explanations of these findings are proposed.     

Neural control of canine colon motor function: studies in vivo

The responses of the circular muscle of canine colon to stimulation of intrinsic nerves and to the probable mediators of these nerves were studied in vivo. In vivo studies were carried out using close intra-arterial injections and local field stimulation of proximal, mid-, and distal colon while recording circumferential contractions. Our results suggest that acetylcholine is the major excitatory mediator, but another excitatory mediator could be released by high frequency field stimulation after atropine. Norepinephrine had mixed inhibitory and excitatory effects, but no evidence was obtained that it was released by field stimulation. Substance P had mainly excitatory effects partly by a mechanism involving nerves and partly by a direct effect on muscle; it in addition to norepinephrine deserves further evaluation as the mediator of noncholinergic excitation to high frequency field stimulation. There is no explanation of the inhibition it produced after initial excitation during field stimulation. Vasoactive intestinal peptide had inhibitory effects but these were incomplete and inconsistent. This may be related to our inability to demonstrate relaxation or inhibition to field stimulation after atropine. Further evaluation of the possible role of vasoactive intestinal peptide and other agents as nonadrenergic, noncholinergic inhibitory mediators is required.     

Relation of unit spike discharges and evoked potentials in the auditory cortex of cats.

Extracellular microelectrode recordings were made from the auditory cortex of anaesthetized cats during acoustic click stimulation. The microelectrode of low resistance allowed to record evoked field potentials and unit discharges simultaneously. In distant extracellular leads the relation of unit discharges and field potentials was equivocal. Near extracellular leads revealed that the antidromic invasion of the somadendritic membrane by excitation is a frequency dependent process (just as evoked field potentials) while spike potentials can reliably be elicited from the initial segment at high frequencies. It is assumed that the excitation spreading from the initial segment to the soma-dendritic membrane represents an important component of the evoked potentials, and their frequency dependence may be traced back to inhibitions activated by afferent impulses.     

Bayes' theorem in paleopathological diagnosis

The utility of Bayes' theorem in paleopathological diagnoses is explored. Since this theorem has been used heavily by modern clinical medicine, its usefulness in that field is described first. Next, the mechanics of the theorem are discussed, along with methods for deriving the prior probabilities needed for its application. Following this, the sources of these prior probabilities and their accompanying problems in paleopathology are considered. Finally, an application using prehistoric rib lesions is presented to demonstrate the utility of this method to paleopathology.     

Neural control of canine colon motor function: studies in vitro

The responses of strips of the canine colon to stimulation of intrinsic nerves and to the probable mediators of these nerves were studied in vitro. Studies were carried out using longitudinal and circular muscle strips from proximal and distal colon with field stimulation and addition of agents to the bath. Overall, these and other studies in vivo suggested that acetylcholine was an ubiquitous mediator of neural excitation. Norepinephrine had mixed inhibitory and excitatory effects, the latter only in circular muscle. Inhibitory effects of norepinephrine seemed to be both pre- and post-synaptic but no evidence that it was released by field stimulation was obtained. Substance P had excitatory effects chiefly by release of acetylcholine. It, in addition to norepinephrine, at least in circular muscle, deserves evaluation as the mediator of noncholinergic excitation to high frequency field stimulation. Although vasoactive intestinal peptide sometimes had inhibitory effects, these were incomplete and inconsistent. However, further evaluation of its possible role as a nonadrenergic, noncholinergic inhibitory mediator is required to determine if it is involved as one component in the response. Few qualitative differences existed between responses of various regions of the colon to potential neuromediators, although there were some consistent differences between responses of longitudinal and circular muscle. Some differences existed in responses obtained earlier in vivo and in vitro. In particular, inhibitory effects following excitation by substance P on field stimulation were found only in vivo. Nonadrenergic, noncholinergic inhibitory responses to field stimulation were consistently present only in vitro. These differences have not been explained.     

Polarization-Controlled TIRFM with Focal Drift and Spatial Field Intensity Correction

Total internal reflection fluorescence microscopy (TIRFM) is becoming an increasingly common methodology to narrow the illumination excitation thickness to study cellular process such as exocytosis, endocytosis, and membrane dynamics. It is also frequently used as a method to improve signal/noise in other techniques such as in vitro single-molecule imaging, stochastic optical reconstruction microscopy/photoactivated localization microscopy imaging, and fluorescence resonance energy transfer imaging. The unique illumination geometry of TIRFM also enables a distinct method to create an excitation field for selectively exciting fluorophores that are aligned either parallel or perpendicular to the optical axis. This selectivity has been used to study orientation of cell membranes and cellular proteins. Unfortunately, the coherent nature of laser light, the typical excitation source in TIRFM, often creates spatial interference fringes across the illuminated area. These fringes are particularly problematic when imaging large cellular areas or when accurate quantification is necessary. Methods have been developed to minimize these fringes by modulating the TIRFM field during a frame capture period; however, these approaches eliminate the possibility to simultaneously excite with a specific polarization. A new, to our knowledge, technique is presented, which compensates for spatial fringes while simultaneously permitting rapid image acquisition of both parallel and perpendicular excitation directions in ∼25 ms. In addition, a back reflection detection scheme was developed that enables quick and accurate alignment of the excitation laser. The detector also facilitates focus drift compensation, a common problem in TIRFM due to the narrow excitation depth, particularly when imaging over long time courses or when using a perfusion flow chamber. The capabilities of this instrument were demonstrated by imaging membrane orientation using DiO on live cells and on lipid bilayers that were supported on a glass slide (supported lipid bilayer). The use of the approach to biological problems was illustrated by examining the temporal and spatial dynamics of exocytic vesicles.     

Excitation of magnetic fields by a circularly polarized laser pulse in a plasma channel

The excitation of quasistatic magnetic fields by a circularly polarized laser pulse in a plasma channel is considered. It is shown that, to second order in the amplitude of the electric field of the laser pulse, circular rotation of the plane of polarization of the laser radiation in a radially nonuniform plasma gives rise to a nonlinear azimuthal current and leads to the excitation of the radial and axial components of the magnetic field. The dependence of the magnetic field distribution over the plasma channel on the spatial dimensions of the pulse and on the channel width is investigated for a moderate-power laser pulse. The structure of the magnetic fields excited by a relativistic laser pulse in a wide plasma channel is analyzed.     

Polarization-Controlled TIRFM with Focal Drift and Spatial Field Intensity Correction

Total internal reflection fluorescence microscopy (TIRFM) is becoming an increasingly common methodology to narrow the illumination excitation thickness to study cellular process such as exocytosis, endocytosis, and membrane dynamics. It is also frequently used as a method to improve signal/noise in other techniques such as in vitro single-molecule imaging, stochastic optical reconstruction microscopy/photoactivated localization microscopy imaging, and fluorescence resonance energy transfer imaging. The unique illumination geometry of TIRFM also enables a distinct method to create an excitation field for selectively exciting fluorophores that are aligned either parallel or perpendicular to the optical axis. This selectivity has been used to study orientation of cell membranes and cellular proteins. Unfortunately, the coherent nature of laser light, the typical excitation source in TIRFM, often creates spatial interference fringes across the illuminated area. These fringes are particularly problematic when imaging large cellular areas or when accurate quantification is necessary. Methods have been developed to minimize these fringes by modulating the TIRFM field during a frame capture period; however, these approaches eliminate the possibility to simultaneously excite with a specific polarization. A new, to our knowledge, technique is presented, which compensates for spatial fringes while simultaneously permitting rapid image acquisition of both parallel and perpendicular excitation directions in ∼25 ms. In addition, a back reflection detection scheme was developed that enables quick and accurate alignment of the excitation laser. The detector also facilitates focus drift compensation, a common problem in TIRFM due to the narrow excitation depth, particularly when imaging over long time courses or when using a perfusion flow chamber. The capabilities of this instrument were demonstrated by imaging membrane orientation using DiO on live cells and on lipid bilayers that were supported on a glass slide (supported lipid bilayer). The use of the approach to biological problems was illustrated by examining the temporal and spatial dynamics of exocytic vesicles.     

Magnetic field effects on the fluorescence of mutant strains of Rhodopseudomonas capsulata

The magnetic field effects on bacteriochlorophyll fluorescence in six strains of Rhodopseudomonas capsulata were investigated. All strains exhibit an increase in fluorescence upon application of a magnetic field. Large magnetic field effects are shown to arise in mutants which contain the B800–850 complex as the only bacteriochlorophyll-containing protein. These fluorescence increases are observed only with carotenoid excitation and are best described by a carotenoid singlet heterofission mechanism. Variations in the magnitudes of the magnetic field effects for the Rps. capsulata strain arise from energy differences in the excited states of the molecules involved in the process. In order to determine the contribution from reaction centers to the magnetic field effects observed in the mutants which contain all three pigment-protein complexes, reaction centers were isolated from these strains. The reaction center contribution to the magnetic field effect on fluorescence in whole cells was determined to be smaller than the antenna contribution when carotenoid excitation was employed.     

Comparison of excitation and emission ratiometric fluorescence methods for quantifying the membrane dipole potential

We are interested in developing fluorescence methods for quantifying lateral variations in the dipole potential across cell surfaces. Previous work in this laboratory showed that the ratio of fluorescence intensities of the voltage-sensitive dye di-8-ANEPPS using excitation wavelengths at 420 and 520 nm correlates well with measurements of the dipole potential. In the present work we evaluate the use of di-8-ANEPPS and an emission ratiometric method for measuring dipole potentials, as Bullen and Saggau (Biophys. J. 65 (1999) 2272-2287) have done to follow changes in the membrane potential in the presence of an externally applied field. Emission ratiometric methods have distinct advantages over excitation methods when applied to fluorescence microscopy because only a single wavelength is needed for excitation. We found that unlike the excitation ratio, the emission ratio does not correlate with the dipole potential of vesicles made from different lipids. A difference in the behaviour of the emission ratio in saturated compared to unsaturated lipid vesicles was noted. Furthermore, the emission ratio did not respond in the same way as the excitation ratio when cholesterol, 6-ketocholestanol, 7-ketocholesterol, and phloretin were added to dimyristoylphosphatidylcholine (DMPC) vesicles. We attribute the lack of correlation between the emission ratio and the dipole potential to simultaneous changes in membrane fluidity caused by changes in membrane composition, which do not occur when the electric field is externally applied as in the work of Bullen and Saggau. Di-8-ANEPPS can, thus, only be used via an excitation ratiometric method to quantify the dipole potential.     

Mutation in autocatalytic reaction networks

A class of kinetic equations describing catalysed and template induced replication, and mutation is introduced. This ODE in its most general form is split into two vector fields, a replication and a mutation field. The mutation field is considered as a perturbation of the replicator equation. The perturbation expansion is a Taylor series in a mutation parameter . First, second and higher order contributions are computed by means of the conventional Rayleigh-Schrödinger approach. Qualitative shifts in the positions of rest points and limit cycles on the boundary of the physically meaningful part of concentration space are predicted from flow topologies. The results of the topological analysis are summarized in two theorems which turned out to be useful in applications: the rest point migration theorem (RPM) and the limit cycle migration theorem (LCM). Quantitative expressions for the shifts of rest points are computed directly from the perturbation expansion. The concept is applied to a collection of selected examples from biophysical chemistry and biology.     

Chirped dissipative ion-cyclotron solitons in the Earth’s low-altitude ionospheric plasma with two ion species

Conditions for the excitation of small-scale nonlinear ion-cyclotron gradient-drift dissipative structures in cold ionospheric plasma are considered. The solution for the wave electric field in this structure in the form of a chirped soliton satisfying the equation of the Ginzburg-Landau type is derived in the electrostatic approach. The dissipative structure as a whole represents the chirped soliton accompanied by the comoving quasineutral plasma hump. The possibility of the excitation of two modes of this type (the high- and low-frequency ones) in plasma containing light and heavy ion impurities is considered. The role of electromagnetic corrections and the possible contribution introduced by these structures to the transport processes in the ionosphere are discussed.