Changes In Nonlinear Parameters Research Articles

ANSIEDADE, DEPRESSÃO E ANÁLISE NÃO LINEAR DA VARIABILIDADE DA FREQUÊNCIA CARDÍACA EM INGRESSANTES NO ENSINO SUPERIOR

The non-linear analysis of the heart rate variability (HRV) is a potential correlation tool between physiological and emotional states. The aim of this study was correlate changes in non-linear parameters of the HRV with anxiety and depression indices in higher education entrants from Federal University of Goiás (UFG). To record HRV, the Polar Frequency Metermodel Polar® RS800cx (Electro Oi, Finland) was used. To analyze the levels of depression, the Beck Depression Inventory-I (BDI) was used, and for analysis of anxiety, the Inventories of State and Trace (IDATE T and E). Altogether, 50 (19.4±2.48 years) volunteers participated in the study. The scores of the depression and anxiety inventories indicated that the public had low and moderate indices of both conditions, respectively. Statistically significant correlations were found between the SD2 parameter (from the Poincaré plot in the HRV analysis), entropy data (ApEn and SampEn) and fractal property (DFA: α1) and trait and state anxiety levels. Although ApEn e SampEn still do not have well-defined physiological correspondences, DFA: α1 has been associated with parasympathetic modulation of heart rate. Therefore, it is concluded that chronic negative emotional states, such as anxiety and humor disorders, can be accompanied by parasympathetic increase in HRV, so the organism would be able to not wear out against long-term stressors. New studies are necessary to understand the physiological and evolutional bases of depression and anxiety.

Features of Raman spectra of mechanically activated graphite

The prolonged mechanoactivation treatment (MAT) of graphite and carbon materials causes nonequilibrium processes, accompanied by stepwise changes in the characteristics of the structure of the material and its phase constituents. Using the techniques of electron microscopic analysis and Raman spectroscopy, the research task was to study the effect of short-term high-energy MAT on the possibility and regularity (sequence) of the transformation of chemical bonds between carbon atoms in the produced micro- and nanopowder materials. To compare the rate of change, graphite MPG-7 was processed for no more than an hour at 1000 and 1500 rpm. The changes were evaluated not only by the shift of the Raman spectrum lines, but also by the structural ordering of the substance and the degree of disorder, by thedegree ofamorphization. Similar nonlinear parameter changes for the two processing modes are detected. It is shown that treatment with less energy for an hour leads to a greater accumulation of energy in the material, which is reflected in the internal pressure corresponding to the difference Raman spectrum lines (S1-D1).

Characterizing the nonlinear interaction of S- and P-waves in a rock sample

The nonlinear elastic response of rocks is known to be caused by the rocks' microstructure, particularly cracks and fluids. This paper presents a method for characterizing the nonlinearity of rocks in a laboratory scale experiment with a unique configuration. This configuration has been designed to open up the possibility of using the nonlinear characterization of rocks as an imaging tool in the field. In our experiment, we study the nonlinear interaction of two traveling waves: a low-amplitude 500 kHz P-wave probe and a high-amplitude 50 kHz S-wave pump in a room-dry 15 × 15 × 3 cm slab of Berea sandstone. Changes in the arrival time of the P-wave probe as it passes through the perturbation created by the traveling S-wave pump were recorded. Waveforms were time gated to simulate a semi-infinite medium. The shear wave phase relative to the P-wave probe signal was varied with resultant changes in the P-wave probe arrival time of up to 100 ns, corresponding to a change in elastic properties of 0.2%. In order to estimate the strain in our sample, we also measured the particle velocity at the sample surface to scale a finite difference linear elastic simulation to estimate the complex strain field in the sample, on the order of 10−6, induced by the S-wave pump. We derived a fourth order elastic model to relate the changes in elasticity to the pump strain components. We recover quadratic and cubic nonlinear parameters: β̃=−872 and δ̃=−1.1×1010, respectively, at room-temperature and when particle motions of the pump and probe waves are aligned. Temperature fluctuations are correlated to changes in the recovered values of β̃ and δ̃, and we find that the nonlinear parameter changes when the particle motions are orthogonal. No evidence of slow dynamics was seen in our measurements. The same experimental configuration, when applied to Lucite and aluminum, produced no measurable nonlinear effects. In summary, a method of selectively determining the local nonlinear characteristics of rock quantitatively has been demonstrated using traveling sound waves.

Characteristics of ultrasonic nonlinearity by thermal fatigue

The deterioration conditions of nuclear power plants and chemical plants have raised deep concerns about the safety of high-risk structures. The safety of a structure can be secured by evaluations of breakages and lifespan in the early stage. Therefore, the material condition of a structure needs to be estimated. A nonlinear ultrasonic evaluation method is reportedly more sensitive on microscopic changes of a material than a linear evaluation method. Therefore, the nonlinear ultrasonic technique based on ultrasonic nonlinearity is considered a promising method of evaluation for breakages and lifespan. This study measured the changes in nonlinear parameters by using a nonlinear ultrasonic method, observed the microstructure of a heated material, and analyzed the relation between the size of the microstructure and the changes in the nonlinear parameters.

Nonlinear optical manipulation, patterning and control in nano- and micro-scale systems

Nonlinearities are becoming more and more important for a variety of applications in nanosciences, bio-medical sciences, information processing and photonics. For applications at the crossings of these fields, especially microscopic and nanoscopic imaging and manipulation, nonlinearities play a key role. They may range from simple nonlinear parameter changes up to applications in manipulating, controlling and structuring material by light, or the manipulation of light by light itself. It is this area between basic nonlinear optics and photonic applications that includes `hot' topics such as ultra-resolution optical microscopy, micro- and nanomanipulation and -structuring, or nanophotonics. This special issue contains contributions in this field, many of them from the International Conference on Nonlinear Microscopy and Optical Control held in conjunction with a network meeting of the ESF COST action MP0604 `Optical Micromanipulation by Nonlinear Nanophotonics', 19–22 February 2008, Munster, Germany. Throughout this special issue, basic investigations of material structuring by nonlinear light--matter interaction, light-induced control of nanoparticles, and novel nonlinear material investigation techniques, are presented, covering the basic field of optical manipulation and control. These papers are followed by impressive developments of optical tweezers. Nowadays, optical phase contrast tweezers, twin and especially multiple beam traps, develop particle control in a new dimension: particles can be arranged, sorted and identified with high throughput. One of the most prominent forthcoming applications of optical tweezers is in the field of microfluidics. The action of light on fluids will open new horizons in microfluidic manipulation and control. The field of optical manipulation and control is a very broad field that has developed in an impressive way, in a short time, in Europe with the installation of the MP0604 network. Top researchers from 19 countries are collaborating in this network. The editors are grateful for the active participation of all colleagues in this network, in the network meeting, and in making this special issue a success. We also extend our thanks to a great Journal of Optics A staff that have supported the editing of this special issue, especially the Publishing Editor, Julia Dickinson. Among the active colleagues in our network was also Associate Professor Erik Fallman, Umea University, Sweden. It was with great sadness that we learnt of the death of our colleague and friend in June 2008. We dedicate this special issue to his memory, and the active and always engaged contribution he made both to our conference and to the field of optical micromanipulation and optical control. Erik will be particularly remembered for his applications of optical force measurements on bacterial pili adhesion, which has stimulated a worldwide experimental and theoretical interest in this field.

Reduced signal complexity of intracellular recordings: a precursor for epileptiform activity?

Recent studies have shown that time windowed extraction of nonlinear parameters like an effective correlation dimension from intracranially recorded EEG of epileptic patients often allows to detect and identify an unequivocal “pre-ictal phase” preceding an epileptic seizure. In another study, however, such an anticipation could not be made. These conflicting findings may indicate that observed changes in nonlinear parameters probably depend on the type of elementary mechanisms underlying epileptic processes and/or the spatial distribution of neurons primarily involved in generation of epileptiform discharges. To test the existence of such dependencies, the transition from normal to epileptiform activity (EA) of CA3-neurons in hippocampal slices was analyzed in four epilepsy models, using a time windowed computation of an effective correlation dimension. Indeed, in xanthine and penicillin models, signal complexity in intracellular recordings was reduced before manifestation of paroxysmal depolarization shifts (PDS), whereas a preceding loss of complexity was missing in low-magnesium and veratridine models. These findings indicate that interictal-like EA is predictable only in some epilepsy models.

Existence of a bistable polarization state in a Kerr medium in the presence of two-photon absorption

An elliptically polarized beam is sent into a cell filled with nitrobenzol. The output polarization shows two stable states for a single set of input parameters when the excitation is above the two-photon absorption threshold. Transverse field effects combined with third-order nonlinear parameter changes at high intensities can be used to explain the observations.

Dependence of the rate of convergence of the Rayleigh-Ritz method on a nonlinear parameter.

Numerical computation of optimum values for nonlinear parameters in a Rayleigh-Ritz variational trial function is considerably more difficult than numerical computation of optimum values for linear parameters. Thus, an analytic understanding of the mechanisms that determine these optimum values can be quite useful. Uniform asymptotic expansions can be used to explore these mechanisms for the nonlinear parameter that sets the length scale for a basis set. These uniform asymptotic expansions usually involve two or more different kinds of terms whose relative importance changes as the nonlinear parameter changes, with two different terms being equally important at the point where the nonlinear parameter has its optimum value. Interference effects between these different terms are typical, and tend to become most pronounced near the optimum value. These different kinds of terms arise from singularities of the wave function, from the neighborhood of the classical turning point for the basis functions, and/or from saddle points. Comparisons of theory with (numerical) experiment will be given for Rayleigh-Ritz calculations on three model problems that illustrate the kinds of terms listed above.