Successive Jumps Research Articles

Relaxation Oscillation Enhancement and Coherence Collapse in Semiconductor Lasers with Optical Feedback

The dynamic characteristics of a semiconductor laser with optical feedback are strongly dependent on the injection current and the reflectivity and position of the external feedback reflector. We investigated the relaxation oscillation enhancement and coherence collapse state of the laser oscillation based on the laser rate equations. It is well known that laser output power jumps with increase of the injection current due to external mode transition. But here for the first we time demonstrate the existence of a chaotic scenario within successive laser power jumps. The results calculated by numerical simulations based on the rate equations are compared with those of the experiments and good coincidence between them is found.

Theoretical description of adatom migration in two-dimensional highly-ordered states

Analytical expressions for chemical, jump, and tracer diffusion coefficients are obtained for interacting lattice gases on a square lattice. Strongly repulsive nearest neighbor interactions cause the formation of a highly-ordered c( ) state in the vicinity of half coverage. It is shown that only strongly correlated successive adatom jumps contribute to the particle flow. This allows to describe the adatom kinetics by considering an almost ideal lattice gas of defects. Two types of defects are considered, adatoms in the empty sublattice and vacancies in the filled sublattice of the c( ) ordered state. The diffusion equations for these defects are developed considering the generation and recombination of defects. In addition we have considered adatom transport caused by the motion of defect pairs (dimers). Dimer transport mechanism prevails in the high coverage region. The characteristic features of the various diffusion coefficients near half coverage are analyzed and discussed. The theory is compared with the results of sophisticated Monte-Carlo simulations which have been executed with the use of a fully parallelized algorithm on a Cray T3E (LC784-128). The agreement between theoretical and MC results is excellent if the motion of dimers at is taken into account.

Neotectonics in the eastern North Anatolian fault region (Turkey) advocates crustal extension: mapping from SAR ERS imagery and Digital Elevation Model

This paper concerns the neotectonics of the eastern part of the Anatolian block bounded, respectively, to the north and the east by the North Anatolian (NAF) and the East Anatolian faults (EAF), meeting at Karlıova. The study is based on imagery of Synthetic Aperture Radar (SAR), scenes acquired by the European Remote Sensing (ERS) satellite and on views of a Digital Elevation Model (DEM), complemented with fault analysis in the field. We show that extensional tectonics associated with transcurrent displacements prevail in the Karlıova triangle and beyond. New local releasing bends or pull-apart basins and push-up structures along the NAF have been demonstrated. More importantly, Anatolia is composed of blocks less than 50 km in width, that are tilted and move relative to each other. They are compatible with a detachment within the crust of Anatolia. We argue that an escape wedge has migrated through time from west to east, with successive jumps to form the present-day Karlıova triangle. At each stage, the escape wedge was easterly bounded by a NE–SW-striking fault zone similar to the EAF. In each escape wedge, clockwise block rotations predate strike-slip tectonics along the N110°E-striking NAF. This is the case for instance for the Erzincan Basin where the first movements were parallel to the SW-striking Ovacık Fault, an early equivalent of the EAF, and turned later to the west. The detached crustal blocks moved southwestward, then westward and extended at the same time in order to occupy the increasing surface within the successive escape wedges. This is not the behaviour of simple lateral extrusion of the Anatolian lithospheric block induced by forces applied at its boundaries by the adjacent plates, but rather that of detached crustal blocks submitted to extension as a consequence of backward retreat of the Hellenic slab and buoyancy forces arising from crustal thickness differences.

Reliability of leg muscle electromyography in vertical jumping.

In this study we aimed to determine the reliability of the surface electromyography (EMG) of leg muscles during vertical jumping between two test sessions, held 2 weeks apart. Fifteen females performed three maximal vertical jumps with countermovement. The displacement of the body centre of mass (BCM), duration of propulsion phase (time), range of motion (ROM) and angular velocity of the knee and surface EMG of four leg muscles (rectus femoris, vastus medialis. biceps femoris and gastrocnemius) were recorded during the jumps. All variables were analysed throughout the propulsion and mid-propulsion phases. Intraclass correlation coefficients (ICC) for the rectus femoris, vastus medialis, biceps femoris and gastrocnemius were calculated to be 0.88, 0.70, 0.24 and 0.01, respectively. BCM, ROM and time values all indicated ICC values greater than 0.90, and the mean knee angular velocity was slightly lower, at 0.75. ICCs between displacement of the BCM and integrated EMG (IEMG) of the muscles studied were less than 0.50. The angular velocity of the knee did not correlate well with muscle activity. Factors that may have affected reliability were variations in the position of electrode replacement, skin resistance, cross-talk between muscles and jump mechanics. The results of this study suggest that while kinematic variables are reproducible over successive vertical jumps, the degree of repeatability of an IEMG signal is dependent upon the muscle studied.

The average jump rate and diffusion in disordered systems

The average jump rate for particles undergoing diffusion in disordered systems is calculated for arbitrary concentrations of particles. The disorder model considered is a combination of site-energy and barrier-energy disorder. Uniform and Gaussian distribution functions are used as examples. The average jump rate does not show Arrhenius behaviour in general, but can in particular cases. The tracer diffusion coefficient is deduced from the average jump rate in the low-concentration limit for the site-energy disorder model for which there are no spatial correlations in successive jumps. For models where spatial correlations do occur, expressions for the diffusion coefficient and the average jump rate can be used to obtain information about the correlations.

Collective jumps in a soft-sphere glass

Relaxations in a soft-sphere glass are studied by molecular dynamics. We observe local jumps where groups of ten and more atoms move collectively forming chainlike structures. At the lowest temperatures the total jump length is of the order of the nearest neighbor distance whereas a single atom moves only a fraction of this distance. Both the displacements and the numbers of participating atoms increase with temperature. Successive jumps tend to involve the same atoms. Relaxations and soft quasilocalized vibrations are correlated. In the glass and in the liquid state near the glass transition a markedly non-Gaussian distribution of the mean square displacements is observed.

A weight-bearing, water-based exercise program for osteopenic women: Its impact on bone, functional fitness, and well-being

Objective: To evaluate the effects of a weight-bearing, waterbased, exercise program designed for women with low bone mass. Design: A test-retest cross-sectional, prospective study. Setting: Community-dwelling women from a Canadian city. Participants: Seventy-seven postmenopausal women, 50 to 70 years of age, with spinal or femoral bone density below the fracture threshold. Intervention: Subjects exercised in a pool with waist-high water for 60 minutes, 3 days a week, over a 12-month period. Forty minutes of each session were devoted to successive jumps and muscular exercises designed to promote bone accretion, strength, and endurance. Main Outcome Measures: Spinal and femoral bone mineral density (BMD) measured by dual-energy X-ray absorptiometry, functional fitness (flexibility, coordination, agility, strength/endurance, and cardiorespiratory endurance) assessed with the American Alliance for Health, Physical Education, Recreation and Dance battery, and psychological states evaluated with Dupuy's General Well-Being Schedule. Results: Spinal BMD decreased significantly ( p < .001), whereas there was no change in femoral neck BMD ( p = .90). Four of the parameters chosen to assess functional fitness, namely, flexibility, agility, strength/endurance, and cardiorespiratory endurance, were affected positively by the exercise program (all p values <.001). Psychological well-being also improved significantly after participation in the exercise program ( p < .001). Conclusion: The intervention was successful in improving the functional fitness and psychological well-being of the participants, despite a lack of effect on the skeletal system. Future studies are needed to identify water exercises that are safe yet exert enough stress on the bones to initiate a bone response.

Estimating the Time Course of the Excitatory Synaptic Conductance in Neocortical Pyramidal Cells Using a Novel Voltage Jump Method

We introduce a method that permits faithful extraction of the decay time course of the synaptic conductance independent of dendritic geometry and the electrotonic location of the synapse. The method is based on the experimental procedure of Pearce (1993), consisting of a series of identical somatic voltage jumps repeated at various times relative to the onset of the synaptic conductance. The progression of synaptic charge recovered by successive jumps has a characteristic shape, which can be described by an analytical function consisting of sums of exponentials. The voltage jump method was tested with simulations using simple equivalent cylinder cable models as well as detailed compartmental models of pyramidal cells. The decay time course of the synaptic conductance could be estimated with high accuracy, even with high series resistances, low membrane resistances, and electrotonically remote, distributed synapses. The method also provides the time course of the voltage change at the synapse in response to a somatic voltage-clamp step and thus may be useful for constraining compartmental models and estimating the relative electrotonic distance of synapses. In conjunction with an estimate of the attenuation of synaptic charge, the method also permits recovery of the amplitude of the synaptic conductance. We use the method experimentally to determine the decay time course of excitatory synaptic conductances in neocortical pyramidal cells. The relatively rapid decay time constant we have estimated (tau approximately 1.7 msec at 35 degrees C) has important consequences for dendritic integration of synaptic input by these neurons.

I. Tracer diffusion in bond-disordered square lattices

A model of the diffusion of a tagged particle moving by hopping on a lattice, where a finite concentration c of background particles gives rise to blocking due to forbidden multiple occupancy of sites, is extended to the situation where disorder exists on the lattice. In this paper the specific case of variable bond hopping rates is considered in the strongly disordered limit where a finite concentration p of the bonds are completely blocked. The resulting self-diffusion coefficient takes the form where is the percolation limit and f is the dynamical correlation factor. It is expected that f is affected by the disorder and this is estimated by random-walk theory through a calculation of where is the angle between successive jumps of a particle and a vacancy. Also a quite comprehensive simulation study of tracer diffusion in a two-dimensional square lattice for 0 < c < 1 and is performed. The results are in good agreement with the analytical results which are known for small concentrations. Our approximate theory gives a good description over the entire range provided that the corrected form of is used.

The Inviscid Burgers Equation with Initial Value of Poissonian Type

We study the discontinuities (shocks) of the solution to the Burgers equation in the limit of vanishing viscosity (the inviscid limit) when the initial value is the opposite of the standard Poisson process p. We show that this solution is only defined for t e (0, 1). Let T 0 = 0 and T n , n≧1, be the successive jumps of p. We prove that for all M > 0 the inviscid limit is characterized on the region x e (-∞, M], t e (0, 1) by the increasing process $$N(t) = \sup \{ n \in \mathbb{N} {\text{| }}M + nt > T_n \} $$ and the random set I(x) = {n e {0,..., N(t)}‖T n -nt≦x<T n+1 - nt}. The positions of shocks are given in a precise manner. We give the distribution of N(t) and also the distribution of its first jump. We also prove similar results when the initial value is u μ(y, 0) = -μp(y/μ2) + μ-1 max(y, 0), μ e (0, 1).

Internal friction due to hydrogen jumps between tunnel systems in Nb-Ti alloy

Abstract Low-frequency internal friction was measured for single-crystal Nb-2 at.% Ti specimens charged with H in the temperature range 5–100 K. An internal friction peak was observed at around 60 K. The peak appears under both S 44 and S 11 - S 12 shear stress modes. It is suggested that two configurations of a Ti-H pair exist simultaneously: one is a 4T configuration where a H atom forms a tunnel system among four tetrahedral interstitial sites in the {100} face of the cubic cell containing a Ti atom, and another is a 2T configuration where a H atom forms a tunnel system between two tetrahedral interstitial sites which belong to two neighbouring {100} faces of the cubic cell. The internal friction peak is considered to be due to successive jumps of the H atoms between the two tunnel systems.

Self-diffusion on low-index metallic surfaces: Ag and Au (100) and (111).

Using molecular-dynamics simulations and the embedded-atom method, we study the homodiffusion of single adatoms on flat Ag and Au (100) and (111) surfaces. Our results for the (111) surfaces indicate that when the thermal energies of the atoms become larger than the energy barriers, diffusion can no longer be represented by a simple random walk since correlations between successive jumps become important. We present a simple model that takes into account these correlated jumps and reproduces the molecular dynamics data very well. We also demonstrate that knowledge of the energy barriers is not sufficient to determine the preferred mechanism for diffusion on the (100) surface, since the prefactors for the various mechanisms can vary significantly from the value that is usually assumed. The ability of a simple transition-state theory to describe diffusion is also tested. We find, in the cases considered here, that the static barrier is equivalent to the dynamical activation energy and that the prefactor is also well described as long as the relaxation of the substrate remains small. \textcopyright{} 1996 The American Physical Society.

Continuous time random walk model as a model of anomalous relaxation

The microscopic models of anomalous structural relaxation are proposed and studied within the framework of the continuous time random walk. The Cole-Cole type relaxation is observed in the model with the fractal nature where the waiting time distribution, ψ( t), of the random walker is given by the power-law, ψ( t) ∝ t −1− a , with a < 1. The relaxation also becomes of the Cole-Cole type even when we introduce the correlation between the direction of two successive jumps, suggesting the robustness of this property. On the other hand, the stretched-exponential type relaxation appears when the fractal nature of the model is removed by the upper cutoff of the waiting time. These results show that the type of the relaxation is strongly related to the (non-) fractal nature of the system.

Asymptotic distributions of continuous-time random walks: A probabilistic approach

We provide a systematic analysis of the possible asymptotic distributions o one-dimensional continuous-time random walks (CTRWs) by applying the limit theorems of probability theory. Biased and unbiased walks of coupled and decoupled memory are considered. In contrast to previous work concerning decoupled memory and Levy walks, we deal also with arbitrary coupled memory and with jump densities asymmetric about its mean, obtaining asymmetric Levy-stable limits. Suprisingly, it is found that in most cases coupled memory has no essential influence on the form of the limiting distribution. We discuss interesting properties of walks with an infinite mean waiting time between successive jumps.

特集： 細胞機能からみた生体膜研究 原子間力顕微鏡と光ピンセット法による細胞膜裏打ち構造の解析

Movements of transferrin and α2-macroglobulin receptor molecules in the plasma membrane of cultured normal rat kidney (NRK) fibroblastic cells were investigated by video-enhanced optical microscopy with 1.8 nm spatial precision and 33 ms temporal resolution by labeling the receptors with the ligand-coated nanometer-sized colloidal gold particles. For both receptor species, approximately 90% of the movement trajectories are of the confined diffusion type, within domains of=0.25 μm2 (500-700 nm in diagonal length). Movement within the domains is random with a microscopic diffusion coeffcient (Dmicro) =10-9cm2/s, which is consistent with that expected for free Brownian diffusion of proteins in the plasma membrane. The receptor molecules move from one domain to one of the adjacent domains at an average frequency of 0.034s-1 (the residence time within a domain=29s), indicating that the plasma membrane is compartmentalized for diffusion of membrane receptors and that longrange diffusion is the result of successive intercompartmental jumps. The macroscopic diffusion coefficients for these two receptor molecules calculated on the basis of the compartment size and the intercompartmental jump rate are=2.4 × 10-11cm2/s, which is consistent with those determimed determined by averaging the long-term movements of many particles. Partial destruction of the cytoskeleton decreased the confined diffusion mode, increased the simpple diffusion mode, and induced the directed diffusion (transport) mode, Those resules suggest that the boundaries between compartments are made of dynamically fluctuating membrane skeletons (membrane-skeletion fence model).The mechanical properties of intercompartmental boundaries were then studied by tagging transferrin receptor (TR) with either 210 nm-φ latex or 40nm-φ colloidal gold particles, and by dragging the particle-TR complexes laterally along the plasma membrane using laser tweezers. Approximately 90% of the TR-particle complexes that showed confined-type diffusion with Dmicro of=10-9cm2/s could be dragged past the intercompartmental boundaries in their path by laser tweezers at a trapping force of 0.35-0.8 pN. At the dragging forces between 0.05 and 0.1 pN, particle-TR complexes tended to escape from the laser trap at the boundaries, and such escape occurred in both the forward and backward directions of dragging. The average distance dragged was half of the confined distance of TR, which further indicates that particle-TR complexes escape at the compartment boundaries. The boundaries are likely present in the cytoplasmic domain, and are elastic. These results are consistent with the proposal that the compartment boundaries consist of membrane skeleton or a membrane-associated part of the cytoskeleton. Approximately 10% or TR exhibited slower diffusion (Dmicro=10-10-10-11cm2/s) and binding to elastic structures.

Compartmentalized structure of the plasma membrane for receptor movements as revealed by a nanometer-level motion analysis.

Movements of transferrin and alpha 2-macroglobulin receptor molecules in the plasma membrane of cultured normal rat kidney (NRK) fibroblastic cells were investigated by video-enhanced contrast optical microscopy with 1.8 nm spatial precision and 33 ms temporal resolution by labeling the receptors with the ligand-coated nanometer-sized colloidal gold particles. For both receptor species, most of the movement trajectories are of the confined diffusion type, within domains of approximately 0.25 microns2 (500-700 nm in diagonal length). Movement within the domains is random with a diffusion coefficient approximately 10(-9) cm2/s, which is consistent with that expected for free Brownian diffusion of proteins in the plasma membrane. The receptor molecules move from one domain to one of the adjacent domains at an average frequency of 0.034 s-1 (the residence time within a domain approximately 29 s), indicating that the plasma membrane is compartmentalized for diffusion of membrane receptors and that long-range diffusion is the result of successive intercompartmental jumps. The macroscopic diffusion coefficients for these two receptor molecules calculated on the basis of the compartment size and the intercompartmental jump rate are approximately 2.4 x 10(-11) cm2/s, which is consistent with those determined by averaging the long-term movements of many particles. Partial destruction of the cytoskeleton decreased the confined diffusion mode, increased the simple diffusion mode, and induced the directed diffusion (transport) mode. These results suggest that the boundaries between compartments are made of dynamically fluctuating membrane skeletons (membrane-skeleton fence model).

The 'pennies drop'. Genetic discoveries of medical significance

Discovery, examined closely, I said to Crick, seemed curiously difficult to pin to a moment or to an insight or even to a single person. "No, I don't think that's curious," Crick said. "I think that's the nature of discoveries, many times: that the reason they're difficult to make is that you've got to take a series of steps, three or four steps, which if you don't make them you won't get there, and if you go wrong in any one of them you won't get there. It isn't a matter of one jump—that would be easy. You've got to make several successive jumps. And usually the pennies drop one after another until eventually it all clicks . Otherwise it would be too easy!" 1 This issue of JAMA is an extension of previousJOURNALpublications this year (1993;269:1040-1045, 1966-1994) designed to mark the 40th anniversary of the 1953 publication of

The 'Pennies Drop'

Discovery, examined closely, said to Crick, seemed curiously difficult to pin to a moment or to an insight or even to a single person. No, don't think that's curious, Crick said. I think that's the nature of discoveries, many times: that the reason they're difficult to make is that you've got to take a series of steps, three or four steps, which if you don't make them you won't get there, and if you go wrong in any one of them you won't get there. It isn't a matter of one jump—that would be easy. You've got to make several successive jumps. And usually the pennies drop one after another until eventually it all clicks . Otherwise it would be too easy! 1 This issue of JAMA is an extension of previousJOURNALpublications this year (1993;269:1040-1045, 1966-1994) designed to mark the 40th anniversary of the 1953 publication of

Quantum-jump approach to dissipative processes: application to amplification without inversion

Several recent studies have shown that the time evolution of an atom submitted to coherent laser fields and to dissipative processes, such as spontaneous emission of photons or excitation by a broadband incoherent field, can be considered to consist of a sequence of coherent evolution periods separated by quantum jumps occurring at random times. A general statistical analysis of this random sequence is presented for the case in which the number of relevant atomic states is finite and the delay functions giving the distribution of the time intervals between two successive jumps can easily be calculated. These general considerations are then applied to a simple model recently proposed for demonstrating the possibility of amplification without inversion of populations. We show how the quantum-jump approach allows one to calculate the respective contributions of the various physical processes responsible for the amplification or the attenuation of the probe field and to get new insights into the relevant physical mechanisms.

Computer simulation of collective correlation effects for diffusion in a random alloy

Abstract In the present study the assumptions used and the analytical results derived by Qin and Murch (1992, Phil. Mag. A, 66, 957) are tested by computer simulation using the binary random alloy model. The simulation focuses on the calculation of collective cosines which are the average cosines of the angles between a jump of some atom and the successive jumps of any atom of the same or a different species. It is found that the results of the calculations of the , the first term of the collective cosine series, are in reasonable agreement with the analytical results which employ the six-vacancy-jump approximation when the correlation effect is weak. Discrepancies become pronounced, however, when the correlation effect is strong. Calculation of the collective correlation factors by summing up the appropriate gives very good agreement with the results obtained by the ‘displacement method’. Calculation using the approximate equations based only on are only roughly correct imply...