Time history speckle pattern under statistical view

The dynamic speckle analysis has been done because speckle interference began to be evaluated as an important source of information, especially those related to biological samples under laser beam. The time history speckle pattern, a THSP image, is an approach to analyze, which allows a summary to represent the activity monitored. THSP adoption has compelled the research to evaluate the information and the reliability of its inner pattern. This study presents a statistical approach to analyze the data using white noise tests and cross-spectrum analysis. The data analyzed was a set of THSP from animal sperm samples. The evaluation of white noise among lines was conducted using the Fischer test over eight THSP and the cross-spectral approach has been conducted by comparing the information in each THSP. The results presented that the THSP of the sperm did not behave as a white noise in a global evaluation, and specifically in the Gaussian white noise test over 4096 lines; only six lines presented the behavior of a white noise pattern. The strong rejection of white noise test confirms that the THSP pattern allows reliable information. The results obtained with the cross-spectral analysis presented differences between lines within the same THSP, showing that the information of an inner pattern varies in relation to space, which is against the findings in literature.     

Biospeckle laser spectral analysis under Inertia Moment, Entropy and Cross-Spectrum methods

Biospeckle or dynamic speckle can be used as a method for analysing activity, biologic or not, from materials illuminated with laser beam. The Spatial Temporal Speckle (STS) contains data of time information of dynamic speckle and it is used as input for many techniques allowing the analysis of the activity which is being monitored. One question that rises from the manipulation of the STS is related with the information inside it, in particular, whether it is possible to access different frequency behaviors in the time series presented in the STS pattern. This study presents the Inertia Moment, the Wavelets based Entropy and the Cross-Spectrum analysis as approaches that can be used for evaluating the STS spectral content. In a simulation, STS lines have been created based on many frequencies of the fundamental harmonic. This was done for verifying as each method acts when analysing different frequencies, varying harmonics offset and amplitude. These techniques were applied to real database, to validate their action mechanism in real samples. The results present that all techniques were able to verify the spectral content of different harmonics. Inertia Moment was more efficient on analysing high frequencies, because it is a second order moment, being able to obtain more information from high variations on activity. Entropy and Cross-Spectrum, in turn, were better on differing lower frequencies. This was attributed to the convolution proccess, which is present in both methods, filtering high frequencies. Although, any of them returned informations on both high and low frequencies at the same time, they can be used simultaneously, since Entropy and Cross-Spectrum were complementary to Inertia Moment.     

Influence of Coloured Correlated Noises on Probability Distribution and Mean of Tumour Cell Number in the Logistic Growth Model

An approximate Fokker-Planck equation for the logistic growth model which is driven by coloured correlated noises is derived by applying the Novikov theorem and the Fox approximation. The steady-state probability distribution （SPD） and the mean of the tumour cell number are analysed. It is found that the SPD is the single extremum configuration when the degree of correlation between the multiplicative and additive noises, λ is in -1 〈λ≤0 and can be the double extrema in 0〈λ〈1. A configuration transition occurs because of the variation of noise parameters. A minimum appears in the curve of the mean of the steady-state tumour cell number, （x）, versus λ The position and the value of the minimum are controlled by the noise-correlated times.     

Microstructure and osteoblast response of gradient bioceramic coating on titanium alloy fabricated by laser cladding

To construct a bioactive interface between metal implant and the surrounding bone tissue, the gradient calcium phosphate bioceramic coating on titanium alloy (Ti-6Al-4V) was designed and fabricated by laser cladding. The results demonstrated that the gradient bioceramic coating was metallurgically bonded to the titanium alloy substrate. The appearance of hydroxyapatite and β-tricalcium phosphate indicated that the bioactive phases were synthesized on the surface of coating. The microhardness gradually decreased from the coating to substrate, which could help stress relaxation between coating and bone tissue. Furthermore, the methyl thiazolyl tetrazolium (MTT) assay of cell proliferation revealed that the laser-cladded bioceramic coating had more favorable osteoblast response compared with the surface of untreated titanium alloy substrate.     

Comment on: “Dynamical analysis of Cohen-Grossberg neural networks with continuously distributed delays” [Phys. Lett. A 364 (2007) 38]

Recently, Mao and Zhao [Z. Mao, H. Zhao, Phys. Lett. A 364 (2007) 38] considered the existence and uniqueness of the equilibrium point of the Cohen-Grossberg neural network model with continuously distributed delays. Mao and Zhao established Theorem 1. In this Letter, we would like to point out that Theorem 1 given by Mao and Zhao is incorrect in general.     

Effects of Nonlinear Time-Delay on a Stochastic Asymmetric System

We numerically investigate the effects of nonlinear time-delay on the stochastic system. With the delay time increasing, it is found that the peak of probability distribution in low steady states is decreased, and the peak of probability distribution in high steady states is increased. The mean of state variable, the normalized variance, and the normalized autocorrelation function which quantifies the concentrated degree are slowly varied for small delay time. However, the mean of state variable is rapidly increased, and the normalized variance and the normalized autocorrelation function is rapidly decreased for large delay time.     

Study of the human postural control system during quiet standing using detrended fluctuation analysis

The detrended fluctuation analysis is used to study the behavior of different time series obtained from the trajectory of the center of pressure, the output of the activity of the human postural control system. The results suggest that these trajectories present two different regimes in their scaling properties: persistent (for high frequencies, short-range time scale) to antipersistent (for low frequencies, long-range time scale) behaviors. The similitude between the results obtained for the measurements, done with both eyes open and eyes closed, indicate either that the visual system may be disregarded by the postural control system while maintaining the quiet standing, or that the control mechanisms associated with each type of information (visual, vestibular and somatosensory) cannot be disentangled with the type of analysis performed here.     

Generalization ability and information gain of clock-model perceptrons

We study the generalization abilityg _Q ofQ-state Clock-model perceptrons for (i) Hebbian and for certain Non-Hebbian learning procedures, namely (ii) learning with maximal stability, (iii) zero stability and (iv) optimal generalization, for the case of random training sets. Among other results we find thatg _Q behaves quite different in the Hebbian and in the Non-Hebbian cases in the limitQ. E.g. in the Hebbian case for finite ,g _Q vanishes always 1/Q, whereas in the Non-Hebbian cases considered,g _Q converges forQ to a non-trivial continuous functiong (), which vanishes for <2, but increases rapidly for >2. This means that for (ii), (iii) and (iv), as a function of atQ=, there is a 2nd-order phase transition from a non-generalizing phase for 2 to a generalizing phase for >2. Different behaviour of the Hebbian and Non-Hebbian cases, respectively, is also observed for the information gain obtained through learning. For the particular case of AdaTron Learning, which is identical to case (ii), we find a geometrical formulation forg _Q (), which is applicable to more general models.     

Improved delay-dependent stability criterion for neural networks with time-varying delays

In this Letter, the problem of stability analysis for neural networks with time-varying delays is considered. By constructing a new Lyapunov functional, a new delay-dependent stability criterion for the network is established in terms of LMIs (linear matrix inequalities) which can be easily solved by various convex optimization algorithms. Two numerical examples are included to show the effectiveness of proposed criterion.     

Calculus removal on a root cement surface by ultrashort laser pulses

Ultrashort-pulse-laser ablation of dental calculus (tartar) and cement is performed on root surfaces. The investigation shows that the threshold fluence for ablation of calculus is a factor of two to three times smaller than that of a healthy root cement surface. This indicates that ultrashort laser pulses may provide an appropriate tool for selective removal of calculus with minimal damage to the underlying root cement. Future application of an in situ profiling technique allows convenient on-line monitoring of the ablation process.     

Modulated Wave Packets in DNA and Impact of Viscosity

We study the nonlinear dynamics of a DNA molecular system at physiological temperature in a viscous media by using the Peyrard-Bishop model. The nonlinear dynamics of the above system is shown to be governed by the discrete complex Cinzburg-Landau equation. In the non-viscous limit, the equation reduces to the nonlinear Schroedinger equation. Modulational instability criteria are derived for both the cases. On the basis of these criteria, numerical simulations are made, which confirm the analytical predictions. The planar wave solution used as the initial condition makes localized oscillations of base pairs and causes energy localization. The results also show that the viscosity of the solvent in the surrounding damps out the amplitude of wave patterns.     

Dynamical Analysis of Protein Regulatory Network in Budding Yeast Nucleus

Recent progresses in the protein regulatory network of budding yeast Saccharomyces cerevisiae have provided a global picture of its protein network for further dynamical research. We simplify and modularize the protein regulatory networks in yeast nucleus, and study the dynamical properties of the core 37-node network by a Boolean network model, especially the evolution steps and final fixed points. Our simulation results show that the number of fixed points N（k） for a given size of the attraction basin k obeys a power-law distribution N（k） χ k^-2.024. The yeast network is more similar to a scale-free network than a random network in the above dynamical properties.     

Frequency Selectivity Behaviour in the Auditory Midbrain： Implications of Model Study

By numerical simulations on frequency dependence of the spiking threshold, i.e. on the critical amplitude of periodic stimulus, for a neuron to fire, we find that bushy cells in the cochlear nuclear exhibit frequency selec- tivity behaviour. However, the selective frequency band of a bushy cell is far away from that of the preferred spectral range in human and mammal auditory perception. The mechanism underlying this neural activity is also discussed. Further studies show that the ion channel densities have little impact on the selective frequency band of bushy cells. These findings suggest that the neuronal behaviour of frequency selectivity in bushy cells at both the single cell and population levels may be not functionally relevant to frequency discrimination. Our results may reveal a neural hint to the reconsideration on the busily cell functional role in auditory information processing of sound frequency.     

Thermal Vibration and Twist Induced Semiconducting Behaviour in Short DNA Wires

We study the transport properties of electrons in a short homogeneous DNA molecule where thermal vibrations and twist fluctuations of the base molecules are considered. The nonlinear current-voltage curves can be derived by using the equivalent single-particle multichannel network. The voltage gap is sensitive to the strength of thermal vibrations and twist fluctuations of the base molecules. Our results are in good agreement with the recent finding of semiconducting behaviour in short poly（G）-poly（C） DNA oligomers. The present method can also be used to calculate the other molecular wires.     

Nonlinear adaptive synchronization rule for identification of a large amount of parameters in dynamical models

The existing adaptive synchronization technique based on the stability theory and invariance principle of dynamical systems, though theoretically proved to be valid for parameters identification in specific models, is always showing slow convergence rate and even failed in practice when the number of parameters becomes large. Here, for parameters update, a novel nonlinear adaptive rule is proposed to accelerate the rate. Its feasibility is validated by analytical arguments as well as by specific parameters identification in the Lotka-Volterra model with multiple species. Two adjustable factors in this rule influence the identification accuracy, which means that a proper choice of these factors leads to an optimal performance of this rule. In addition, a feasible method for avoiding the occurrence of the approximate linear dependence among terms with parameters on the synchronized manifold is also proposed.     

Stochastic resonance in a bias monostable system with frequency mixing force and multiplicative and additive noise

The stochastic resonance in a bias monostable system subject to frequency mixing force and multiplicative and additive noise is investigated. Based on the adiabatic elimination theory, the analytic expressions of the signal-to-noise ratio (SNR) for the fundamental and higher harmonics are obtained. It is shown that the SNR is a non-monotonic function of the intensities of the multiplicative and additive noise, as well as the system parameter. Moreover, the SNR for the fundamental harmonic decreases with the increase of the system bias, while the SNR for the higher harmonics behaves non-monotonically as the system bias varies.     

A semi-analytic method for computing the long-time order parameter dynamics in mean-field coupled overdamped oscillators with colored noises

The order parameter dynamics of a mean-field model is frequently investigated in macroscopic cumulant dynamics, from which a bifurcation can be predicted qualitatively. In this Letter, for quantitatively investigating the long-time order parameter dynamics, a semi-analytic method is proposed based on approximate nonlinear Fokker-Planck equations. Applying the new method to the mean-field model of periodically driven overdamped bistable oscillators with colored noise, we exhibit the bifurcation behavior and the nonlinear stochastic resonance of the order parameter by tuning noise intensity or coupling coefficient, and the accuracy of the new method are verified by direct simulation. Our observations disclose some new properties about the order parameter dynamics of the mean-field model. For example, the periodic signal shifts the critical coupling coefficient to a larger value, while the nonzero correlation time of the colored noise shifts it to a lower value. Our observation also discloses that there is no quantitatively corresponding relation between the resonant peak and the critical bifurcation parameter of the Gaussian moment system.     

Multifractal Analysis of Human Heartbeat in Sleep

We study the dynamical properties of heart rate variability （HRV） in sleep by analysing the scaling behaviour with the multifractal detrended fluctuation analysis method. It is well known that heart rate is regulated by the interaction of two branches of the autonomic nervous system： the parasympathetic and sympathetic nervous systems. By investigating the multifractal properties of light, deep, rapid-eye-movement （REM） sleep and wake stages, we firstly find an increasing multifractal behaviour during REM sleep which may be caused by augmented sympathetic activities relative to non-REM sleep. In addition, the investigation of long-range correlations of HRV in sleep with second order detrended fluctuation analysis presents irregular phenomena. These findings may be helpful to understand the underlying regulating mechanism of heart rate by autonomic nervous system during wake-sleep transitions.     

Note on Two-Phase Phenomena in Financial Markets

The two-phase behaviour in financial markets actually means the bifurcation phenomenon, which represents the change of the conditional probability from an unimodal to a bimodal distribution. We investigate the bifurcation phenomenon in Hang-Sang index. It is observed that the bifurcation phenomenon in financial index is not universal, but specific under certain conditions. For Hang-Sang index and randomly generated time series, the phenomenon just emerges when the power-law exponent of absolute increment distribution is between 1 and 2 with appropriate period. Simulations on a randomly generated time series suggest the bifurcation phenomenon itself is subject to the statistics of absolute increment, thus it may not be able to reflect essential financial behaviours. However, even under the same distribution of absolute increment, the range where bifurcation phenomenon occurs is fax different from real market to artificial data, which may reflect certain market information.     

Analysis of hydroxyapatite laser ablation plumes in a water atmosphere

4 m/s, shows the development of a shock wave in its front, resulting from the interaction between the species released from the target and the background gas. The water vapor slows down this component up to values of about 3×10³ m/s following a behavior that can be well described by the dynamics of a spherical shock wave. The low intensity of emission of the second component has not allowed us to analyze its dynamics. The third and slowest component expands at a constant velocity of 5×10² m/s and is constituted by hot particulates leaving the target. Spectra recorded in the shock front have shown the presence of emission lines arising from Ca I, Ca II, P I and some impurities, and two strong emission bands that can be assigned to some sort of calcium oxide. Received: 7 November 1997/Accepted: 17 February 1998