Extended states in disordered doped polyacetylene chains

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Computing Fractal Dimension of Signals using Multiresolution Box-counting Method

In this paper, we have developed a method to compute fractal dimension (FD) of discrete time signals, in the time domain, by modifying the box-counting method. The size of the box is dependent on the sampling frequency of the signal. The number of boxes required to completely cover the signal are obtained at multiple time resolutions. The time resolutions are made coarse by decimating the signal. The loglog plot of total number of boxes required to cover the curve versus size of the box used appears to be a straight line, whose slope is taken as an estimate of FD of the signal. The results are provided to demonstrate the performance of the proposed method using parametric fractal signals. The estimation accuracy of the method is compared with that of Katz, Sevcik, and Higuchi methods. In ddition, some properties of the FD are discussed.

Physically consistent simulation of mesoscale chemical kinetics: The non-negative FIS-alpha method

Biochemical pathways involving chemical kinetics in medium concentrations (i.e., at mesoscale) of the reacting molecules can be approximated as chemical Langevin equations (CLE) systems. We address the physically consistent non-negative simulation of the CLE sample paths as well as the issue of non-Lipschitz diffusion coefficients when a species approaches depletion and any stiffness due to faster reactions. The non-negative Fully Implicit Stochastic alpha (FIS alpha) method in which stopped reaction channels due to depleted reactants are deleted until a reactant concentration rises again, for non-negativity preservation and in which a positive definite Jacobian is maintained to deal with possible stiffness, is proposed and analysed. The method is illustrated with the computation of active Protein Kinase C response in the Protein Kinase C pathway. (C) 2011 Elsevier Inc. All rights reserved.

Excretion pattern investigation of urinary normal and modified nucleosides of breast cancer patients by RP-HPLC and factor analysis method

Modified nucleosides, formed post-transcriptionally in RNA by a number of modification enzymes, are excreted in abnormal levels in the urine of patients with malignant tumors. To test their usefulness as tumor markers, and to compare them with the conventional tumor markers, a reversed-phase high-performance liquid chromatographic (RP-HPLC) method and a factor analysis method have been used to study the excretion pattern of nucleosides of breast cancer patients. A clear cut differentiation of the breast cancer group and the healthy individuals in two clusters without overlapping was obtained. Copyright (C) 2000 John Wiley & Sons, Ltd.

A possible way to relate the covariantization and the negative dimensional integration method in the light-cone gauge

Here we present a possible way to relate the method of covariantizing the gauge-dependent pole and the negative dimensional integration method for computing Feynman integrals pertinent to the light-cone gauge fields. Both techniques are applicable to the algebraic light-cone gauge and dispense with prescriptions to treat the characteristic poles.

Evaluating residues and integrals through negative dimensional integration method (NDIM)

The standard way of evaluating residues and some real integrals through the residue theorem (Cauchy's theorem) is well-known and widely applied in many branches of Physics. Herein we present an alternative technique based on the negative dimensional integration method (NDIM) originally developed to handle Feynman integrals. The advantage of this new technique is that we need only to apply Gaussian integration and solve systems of linear algebraic equations, with no need to determine the poles themselves or their residues, as well as obtaining a whole class of results for differing orders of poles simultaneously.

Negative Factor from SIV Binds to the Catalytic Subunit of the V-ATPase to Internalize CD4 and to Increase Viral Infectivity

The accessory protein negative factor (Nef) from human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) is required for optimal viral infectivity and the progression to acquired immunodeficiency syndrome (AIDS). Nef interacts with the endocytic machinery, resulting in the down-regulation of cluster of differentiation antigen 4 (CD4) and major histocompatibility complex class I (MHCI) molecules on the surface of infected cells. Mutations in the C-terminal flexible loop of Nef result in a lower rate of internalization by this viral protein. However, no loop-dependent binding of Nef to adaptor protein-2 (AP-2), which is the adaptor protein complex that is required for the internalization of proteins from the plasma membrane, could be demonstrated. In this study we investigated the relevance of different motifs in Nef from SIVmac239 for its internalization, CD4 down-regulation, binding to components of the trafficking machinery, and viral infectivity. Our data suggest that the binding of Nef to the catalytic subunit H of the vacuolar membrane ATPase (V-ATPase) facilitates its internalization. This binding depends on the integrity of the whole flexible loop. Subsequent studies on Nef mutant viruses revealed that the flexible loop is essential for optimal viral infectivity. Therefore, our data demonstrate how Nef contacts the endocytic machinery in the absence of its direct binding to AP-2 and suggest an important role for subunit H of the V-ATPase in viral infectivity.

Inhibition of human immunodeficiency virus type 1 and vaccinia virus infection by a dominant negative factor of the interferon regulatory factor family expressed in monocytic cells.

ICSBP is a member of the interferon (IFN) regulatory factor (IRF) family that regulates expression of type I interferon (IFN) and IFN-regulated genes. To study the role of the IRF family in viral infection, a cDNA for the DNA-binding domain (DBD) of ICSBP was stably transfected into U937 human monocytic cells. Clones that expressed DBD exhibited a dominant negative phenotype and did not elicit antiviral activity against vesicular stomatitis virus (VSV) infection upon IFN treatment. Most notably, cells expressing DBD were refractory to infection by vaccinia virus (VV) and human immunodeficiency virus type 1 (HIV-1). The inhibition of VV infection was attributed to defective virion assembly, and that of HIV-1 to low CD4 expression and inhibition of viral transcription in DBD clones. HIV-1 and VV were found to have sequences in their regulatory regions similar to the IFN-stimulated response element (ISRE) to which IRF family proteins bind. Accordingly, these viral sequences and a cellular ISRE bound a shared factor(s) expressed in U937 cells. These observations suggest a novel host-virus relationship in which the productive infection of some viruses is regulated by the IRF-dependent transcription pathway through the ISRE.

INSULATOR-TO-METAL TRANSITION IN POLYTHIOPHENE

In the present work, the electronic structure of polythiophene at several doping levels is investigated by the use of the Huckel Hamiltonian with sigma-bond compressibility. Excess charges are assumed to be stored in conformational defects of the bipolaron type. The Hamiltonian matrix elements representative of a bipolaron are obtained from a previous thiophene oligomer calculation, and then transferred to very long chains. Negative factor counting and inverse iteration techniques have been used to evaluate densities of states and wave functions, respectively. Several types of defect distributions were analyzed. Our results are consistent with the following: (i) the bipolaron lattice does not present a finite density of states at the Fermi energy at any doping level; (ii) bipolaron clusters show an insulator-to-metal transition at 8 mol% doping level; (iii) segregation disorder shows an insulator-to-metal transition for doping levels in the range 20-30 mor %.

Disordered distribution of defects in polythiophene

In this work we study the electronic structure associated to a disordered distribution of bipolarons in polythiophene. The polymer chain is modelled by a tight-binding Hamiltonian with explicit treatment of electron-phonon coupling and the elastic energy of the sigma framework. The model also includes the electrostatic interaction due to the counterions. The density of states of the disordered system is obtained by the use of the Negative Factor Counting technique. Our results show that ion-induced conformational disorder can account for the closure of the gap and that the states around the Fermi level are extended. © 1993.

A Phase Space Box-counting based Method for Arrhythmia Prediction from Electrocardiogram Time Series

Arrhythmia is one kind of cardiovascular diseases that give rise to the number of deaths and potentially yields immedicable danger. Arrhythmia is a life threatening condition originating from disorganized propagation of electrical signals in heart resulting in desynchronization among different chambers of the heart. Fundamentally, the synchronization process means that the phase relationship of electrical activities between the chambers remains coherent, maintaining a constant phase difference over time. If desynchronization occurs due to arrhythmia, the coherent phase relationship breaks down resulting in chaotic rhythm affecting the regular pumping mechanism of heart. This phenomenon was explored by using the phase space reconstruction technique which is a standard analysis technique of time series data generated from nonlinear dynamical system. In this project a novel index is presented for predicting the onset of ventricular arrhythmias. Analysis of continuously captured long-term ECG data recordings was conducted up to the onset of arrhythmia by the phase space reconstruction method, obtaining 2-dimensional images, analysed by the box counting method. The method was tested using the ECG data set of three different kinds including normal (NR), Ventricular Tachycardia (VT), Ventricular Fibrillation (VF), extracted from the Physionet ECG database. Statistical measures like mean (μ), standard deviation (σ) and coefficient of variation (σ/μ) for the box-counting in phase space diagrams are derived for a sliding window of 10 beats of ECG signal. From the results of these statistical analyses, a threshold was derived as an upper bound of Coefficient of Variation (CV) for box-counting of ECG phase portraits which is capable of reliably predicting the impeding arrhythmia long before its actual occurrence. As future work of research, it was planned to validate this prediction tool over a wider population of patients affected by different kind of arrhythmia, like atrial fibrillation, bundle and brunch block, and set different thresholds for them, in order to confirm its clinical applicability.

Dimensional approaches to schizophrenia: A comparison of the Bern Psychopathology scale and the five-factor model of the Positive and Negative Syndrome Scale

The aim was to examine to what extent the dimensions of the BPS map the five factors derived from the PANSS in order to explore the level of agreement of these alternative dimensional approaches in patients with schizophrenia. 149 inpatients with schizophrenia spectrum disorders were recruited. Psychopathological symptoms were assessed with the Bern Psychopathology Scale (BPS) and the Positive and Negative Syndrome Scale (PANSS). Linear regression analyses were conducted to explore the association between the factors and the items of the BPS. The robustness of patterns was evaluated. An understandable overlap of both approaches was found for positive and negative symptoms and excitement. The PANSS positive factor was associated with symptoms of the affect domain in terms of both inhibition and disinhibition, the PANSS negative factor with symptoms of all three domains of the BPS as an inhibition and the PANSS excitement factor with an inhibition of the affect domain and a disinhibition of the language and motor domains. The results show that here is only a partial overlap between the system-specific approach of the BPS and the five-factor PANSS model. A longitudinal assessment of psychopathological symptoms would therefore be of interest.

The positive impact of multiple sclerosis (MS) on carers: Associations between carer benefit finding and positive and negative adjustment domains

Purpose. This study examined benefit finding in MS carers including the dimensionality of benefit finding, relations between carer and care recipient benefit finding, and the effects of carer benefit finding on carer positive and negative adjustment domains. Method. A total of 267 carers and their care recipients completed questionnaires at Time 1 and 3 months later, Time 2 (n=155). Illness data were collected at Time 1, and number of problems, stress appraisal, benefit finding, negative (global distress, negative affect) and positive (life satisfaction, positive affect, dyadic adjustment) adjustment domains were measured at Time 2. Results. Qualitative data revealed seven benefit finding themes, two of which were adequately represented by the Benefit Finding Scale (BFS) [1] (Mohr et al. Health Psychology 1999; 18: 376). Factor analyses indicated two factors (Personal Growth, Family Relations Growth) which were psychometrically sound and showed differential relations with illness and adjustment domains. Although care recipients reported higher levels of benefit finding than carers, their benefit finding reports regarding personal growth were correlated. The carer BFS factors were positively related to carer and care recipient dyadic adjustment. Care recipient benefit finding was unrelated to carer adjustment domains. After controlling for the effects of demographics, care recipient characteristics, problems and appraisal, carer benefit finding was related to carer positive adjustment domains and unrelated to carer negative adjustment domains. Conclusion. Findings support the role of benefit finding in sustaining positive psychological states and the communal search for meaning within carer-care recipient dyads.

Negative sequence compensation within fundamental positive sequence reference frame for a stiff micro-grid generation in a wind power system using slip ring induction machine

An isolated wind power generation scheme using slip ring induction machine (SRIM) is proposed. The proposed scheme maintains constant load voltage and frequency irrespective of the wind speed or load variation. The power circuit consists of two back-to-back connected inverters with a common dc link, where one inverter is directly connected to the rotor side of SRIM and the other inverter is connected to the stator side of the SRIM through LC filter. Developing a negative sequence compensation method to ensure that, even under the presence of unbalanced load, the generator experiences almost balanced three-phase current and most of the unbalanced current is directed through the stator side converter is the focus here. The SRIM controller varies the speed of the generator with variation in the wind speed to extract maximum power. The difference of the generated power and the load power is either stored in or extracted from a battery bank, which is interfaced to the common dc link through a multiphase bidirectional fly-back dc-dc converter. The SRIM control scheme, maximum power point extraction algorithm and the fly-back converter topology are incorporated from available literature. The proposed scheme is both simulated and experimentally verified.