Nonlinear inverse dynamic models of gas sensing systems based on chemical sensor arrays for quantitative measurements

Gas sensing systems based on low-cost chemical sensor arrays are gaining interest for the analysis of multicomponent gas mixtures. These sensors show different problems, e.g., nonlinearities and slow time-response, which can be partially solved by digital signal processing. Our approach is based on building a nonlinear inverse dynamic system. Results for different identification techniques, including artificial neural networks and Wiener series, are compared in terms of measurement accuracy.

Reggies/flotillins regulate E-cadherin-mediated cell contact formation by affecting EGFR trafficking.

The reggie/flotillin proteins are implicated in membrane trafficking and, together with the cellular prion protein (PrP), in the recruitment of E-cadherin to cell contact sites. Here, we demonstrate that reggies, as well as PrP down-regulation, in epithelial A431 cells cause overlapping processes and abnormal formation of adherens junctions (AJs). This defect in cell adhesion results from reggie effects on Src tyrosine kinases and epidermal growth factor receptor (EGFR): loss of reggies reduces Src activation and EGFR phosphorylation at residues targeted by Src and c-cbl and leads to increased surface exposure of EGFR by blocking its internalization. The prolonged EGFR signaling at the plasma membrane enhances cell motility and macropinocytosis, by which junction-associated E-cadherin is internalized and recycled back to AJs. Accordingly, blockage of EGFR signaling or macropinocytosis in reggie-deficient cells restores normal AJ formation. Thus, by promoting EGFR internalization, reggies restrict the EGFR signaling involved in E-cadherin macropinocytosis and recycling and regulate AJ formation and dynamics and thereby cell adhesion.

Changes in running mechanics and spring-mass behaviour induced by a 5-hour hilly running bout.

Abstract The aim of this study was to investigate changes in running mechanics and spring-mass behaviour with fatigue induced by 5-hour hilly running (5HHR). Running mechanics were measured pre- and post-5HHR at 10, 12 and 14 km · h(-1) on an instrumented treadmill in eight ultramarathon runners, and sampled at 1000 Hz for 10 consecutive steps. Contact (t(c) ) and aerial (t(a) ) times were determined from ground reaction force (GRF) signals and used to compute step frequency (f). Maximal GRF, loading rate, downward displacement of the centre of mass (Δz), and leg length change (ΔL) during the support phase were determined and used to compute both vertical (K(vert) ) and leg (K(leg) ) stiffness. A significant decrease in t(c) was observed at 12 and 14 km · h(-1) resulting in an increase of f at all speeds. Duty factor and F(max) significantly decreased at 10 km · h(-1). A significant increase in K(vert) and K(leg) was observed at all running speeds with significant decreases in Δz and ΔL. Despite the shorter duration, the changes in running mechanics appeared to be in the same direction (increased f and K(vert) , decrease in Δz and F(max) ) but of lower amplitude compared with those obtained after an ultra-trail or an ultramarathon.

On the consequences of misspecifing assumptions concerning residuals distribution in a repeated measures and nonlinear mixed modelling context

In this paper we describe the results of a simulation study performed to elucidate the robustness of the Lindstrom and Bates (1990) approximation method under non-normality of the residuals, under different situations. Concerning the fixed effects, the observed coverage probabilities and the true bias and mean square error values, show that some aspects of this inferential approach are not completely reliable. When the true distribution of the residuals is asymmetrical, the true coverage is markedly lower than the nominal one. The best results are obtained for the skew normal distribution, and not for the normal distribution. On the other hand, the results are partially reversed concerning the random effects. Soybean genotypes data are used to illustrate the methods and to motivate the simulation scenarios

Impact of incorrect assumptions on the covariance structure of random effects and/or residuals in nonlinear mixed models for repeated measures data

In this paper we analyse, using Monte Carlo simulation, the possible consequences of incorrect assumptions on the true structure of the random effects covariance matrix and the true correlation pattern of residuals, over the performance of an estimation method for nonlinear mixed models. The procedure under study is the well known linearization method due to Lindstrom and Bates (1990), implemented in the nlme library of S-Plus and R. Its performance is studied in terms of bias, mean square error (MSE), and true coverage of the associated asymptotic confidence intervals. Ignoring other criteria like the convenience of avoiding over parameterised models, it seems worst to erroneously assume some structure than do not assume any structure when this would be adequate.

Force volume and stiffness tomography investigation on the dynamics of stiff material under bacterial membranes.

The determination of the characteristics of micro-organisms in clinical specimens is essential for the rapid diagnosis and treatment of infections. A thorough investigation of the nanoscale properties of bacteria can prove to be a fundamental tool. Indeed, in the latest years, the importance of high resolution analysis of the properties of microbial cell surfaces has been increasingly recognized. Among the techniques available to observe at high resolution specific properties of microscopic samples, the Atomic Force Microscope (AFM) is the most widely used instrument capable to perform morphological and mechanical characterizations of living biological systems. Indeed, AFM can routinely study single cells in physiological conditions and can determine their mechanical properties with a nanometric resolution. Such analyses, coupled with high resolution investigation of their morphological properties, are increasingly used to characterize the state of single cells. In this work, we exploit the capabilities and peculiarities of AFM to analyze the mechanical properties of Escherichia coli in order to evidence with a high spatial resolution the mechanical properties of its structure. In particular, we will show that the bacterial membrane is not mechanically uniform, but contains stiffer areas. The force volume investigations presented in this work evidence for the first time the presence and dynamics of such structures. Such information is also coupled with a novel stiffness tomography technique, suggesting the presence of stiffer structures present underneath the membrane layer that could be associated with bacterial nucleoids.

Open elbow arthrolysis for posttraumatic elbow stiffness.

OBJECTIVES: The elbow joint is vulnerable to stiffness, especially after trauma. The aim of this study was to evaluate the results of open arthrolysis for posttraumatic elbow stiffness. DESIGN: Cohort retrospective study. PATIENTS: Eighteen consecutive patients were evaluated by an independent observer at an average of 16 months (6 to 43) after open elbow arthrolysis was performed for posttraumatic stiffness. Initial traumas were: isolated fractures (11) or dislocation (1) and complex fracture-dislocations (6). Initial treatments were: nonoperative (3), radial head resection (1), and ORIF (14). Patients presented predominantly with mixed contractures (combined extrinsic and intrinsic contractures). INTERVENTION: Open elbow arthrolysis. MAIN OUTCOME MEASUREMENTS: Elbow function and patient satisfaction were the principal outcome measures. At follow-up European Society for Shoulder and Elbow Surgery (SECEC) elbow scores were calculated. RESULTS AND CONCLUSIONS: Three patients had minor postoperative complications: 1 partial wound dehiscence, 1 subcutaneous infection, and one seroma. None of these complications influenced the final result clinically. The mean total increase in range of motion was 40 degrees (13 to 112 degrees), with a mean gain in flexion of 14 degrees (0 to 45 degrees) and 26 degrees in extension (5 to 67 degrees). No patient showed signs of elbow instability. There was no radiographic evidence of osteoarthritis progression at follow-up. We did not find any correlations between the type of stiffness, the approaches used, and the results. However, patients with the greatest preoperative stiffness had significantly better improvement of mobility (P<0.001). The best results were obtained in patients who had arthrolysis done within 1 year after the initial trauma (P=0.008). The mean SECEC scores were 88 (52 to 100) for the injured elbows, and 96 (88 to 100) for the contralateral elbows. CONCLUSION: Open elbow arthrolysis for patients with posttraumatic stiffness improves joint function and provides patient satisfaction. The best results, in terms of gain of motion and patient satisfaction, were obtained in patients with severe stiffness who had operations within the first year after initial trauma.

Effects of new nonlinear couplings in relativistic effective field theory

We extend the relativistic mean field theory model of Sugahara and Toki by adding new couplings suggested by modern effective field theories. An improved set of parameters is developed with the goal to test the ability of the models based on effective field theory to describe the properties of finite nuclei and, at the same time, to be consistent with the trends of Dirac-Brueckner-Hartree-Fock calculations at densities away from the saturation region. We compare our calculations with other relativistic nuclear force parameters for various nuclear phenomena.

Transient and preparation colored-noise effects: The nonlinear relaxation-time approach

We develop a singular perturbation approach to the problem of the calculation of a characteristic time (the nonlinear relaxation time) for non-Markovian processes driven by Gaussian colored noise with small correlation time. Transient and initial preparation effects are discussed and explicit results for prototype situations are obtained. New effects on the relaxation of unstable states are predicted. The approach is compared with previous techniques.

Decay of unstable states in the presence of colored noise and random initial conditions. I. Theory of nonlinear relaxation times

The general theory of nonlinear relaxation times is developed for the case of Gaussian colored noise. General expressions are obtained and applied to the study of the characteristic decay time of unstable states in different situations, including white and colored noise, with emphasis on the distributed initial conditions. Universal effects of the coupling between colored noise and random initial conditions are predicted.

Hepatic amyloidosis increases liver stiffness measured by transient elastography.

Liver stiffness values in transient elastography (TE) have to be interpreted with caution. Steatosis, congestion, acute inflammation and extrahepatic cholestasis can indeed influence measurements. Obtained stiffness values in the cirrhotic range can also be present in the absence of fibrosis as in hepatic amyloidosis. Here we report two cases of systemic amyloidosis with hepatic involvement where high stiffness values were measured at TE. In fact, deposits of amyloid may increase the rigidity of the liver parenchyma resulting in higher liver stiffness values. Therefore, results of TE should always be interpreted in their clinical context and if inconsistent, the performance of a liver biopsy might be necessary.

Nonlinear Saffman-Taylor instability

We show, both theoretically and experimentally, that the interface between two viscous fluids in a Hele-Shaw cell can be nonlinearly unstable before the Saffman-Taylor linear instability point is reached. We identify the family of exact elastica solutions [Nye et al., Eur. J. Phys. 5, 73 (1984)] as the unstable branch of the corresponding subcritical bifurcation which ends up at a topological singularity defined by interface pinchoff. We devise an experimental procedure to prepare arbitrary initial conditions in a Hele-Shaw cell. This is used to test the proposed bifurcation scenario and quantitatively asses its practical relevance.

Systematic weakly nonlinear analysis of interfacial instabilities in Hele-Shaw flows

We develop a systematic method to derive all orders of mode couplings in a weakly nonlinear approach to the dynamics of the interface between two immiscible viscous fluids in a Hele-Shaw cell. The method is completely general: it applies to arbitrary geometry and driving. Here we apply it to the channel geometry driven by gravity and pressure. The finite radius of convergence of the mode-coupling expansion is found. Calculation up to third-order couplings is done, which is necessary to account for the time-dependent Saffman-Taylor finger solution and the case of zero viscosity contrast. The explicit results provide relevant analytical information about the role that the viscosity contrast and the surface tension play in the dynamics of the system. We finally check the quantitative validity of different orders of approximation and a resummation scheme against a physically relevant, exact time-dependent solution. The agreement between the low-order approximations and the exact solution is excellent within the radius of convergence, and is even reasonably good beyond this radius.

Systematic weakly nonlinear analysis of radial viscous fingering

We present a weakly nonlinear analysis of the interface dynamics in a radial Hele-Shaw cell driven by both injection and rotation. We extend the systematic expansion introduced in [E. Alvarez-Lacalle et al., Phys. Rev. E 64, 016302 (2001)] to the radial geometry, and compute explicitly the first nonlinear contributions. We also find the necessary and sufficient condition for the uniform convergence of the nonlinear expansion. Within this region of convergence, the analytical predictions at low orders are compared satisfactorily to exact solutions and numerical integration of the problem. This is particularly remarkable in configurations (with no counterpart in the channel geometry) for which the interplay between injection and rotation allows that condition to be satisfied at all times. In the case of the purely centrifugal forcing we demonstrate that nonlinear couplings make the interface more unstable for lower viscosity contrast between the fluids.

The nonlinear relaxation time and quasideterministic-theory approaches to characterize the decay of unestable states

We present the relationship between nonlinear-relaxation-time (NLRT) and quasideterministic approaches to characterize the decay of an unstable state. The universal character of the NLRT is established. The theoretical results are applied to study the dynamical relaxation of the Landau model in one and n variables and also a laser model.