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.

Drift compensation of gas sensor array data by common principal component analysis

A new drift compensation method based on Common Principal Component Analysis (CPCA) is proposed. The drift variance in data is found as the principal components computed by CPCA. This method finds components that are common for all gasses in feature space. The method is compared in classification task with respect to the other approaches published where the drift direction is estimated through a Principal Component Analysis (PCA) of a reference gas. The proposed new method ¿ employing no specific reference gas, but information from all gases ¿has shown the same performance as the traditional approach with the best-fitted reference gas. Results are shown with data lasting 7-months including three gases at different concentrations for an array of 17 polymeric sensors.

Nanoscale electrical conductivity of the purple membrane monolayer

Nanoscale electron transport through the purple membrane monolayer, a two-dimensional crystal lattice of the transmembrane protein bacteriorhodopsin, is studied by conductive atomic force microscopy. We demonstrate that the purple membrane exhibits nonresonant tunneling transport, with two characteristic tunneling regimes depending on the applied voltage (direct and Fowler-Nordheim). Our results show that the purple membrane can carry significant current density at the nanometer scale, several orders of magnitude larger than previously estimated by macroscale measurements.

Petróleo y gas en África: viejas realidades, nuevos escenarios

[cat] En els últims temps es parla molt del nou paper dels hidrocarburs d'Àfrica, fins i tot s'al·ludeix a un oil rush o a un african oil scramble , que inevitablement desembocarà en una confrontació bipolar entre la Xina i els Estats Units, pel control de les reserves de petroli del subsòl del continent africà. Així, el propòsit d'aquest text és, en primer lloc, realitzar una anàlisi descriptiva que ajudi a valorar la hipòtesi d'aquest african oil scramble. A continuación, amb les dades obtingudes, es discutirà sobre la possibilitat de que aquest fenomen desemboqui en un escenari de confrontació xinoamericana. Aquesta especulació ens durà a concloure que hi ha suficients indicis per a argumentar que el joc petrolífer africà podria desenvolupar-se en un escenari marcat per la multilateralitat.

Systematics of properties of the electron gas in deep-etched quantum wires

An efficient method is developed for an iterative solution of the Poisson and Schro¿dinger equations, which allows systematic studies of the properties of the electron gas in linear deep-etched quantum wires. A much simpler two-dimensional (2D) approximation is developed that accurately reproduces the results of the 3D calculations. A 2D Thomas-Fermi approximation is then derived, and shown to give a good account of average properties. Further, we prove that an analytic form due to Shikin et al. is a good approximation to the electron density given by the self-consistent methods.

Edge excitations and topological order in rotating Bose gas

The edge excitations and related topological orders of correlated states of a fast rotating Bose gas are studied. Using exact diagonalization of small systems, we compute the energies and number of edge excitations, as well as the boson occupancy near the edge for various states. The chiral Luttinger-liquid theory of Wen is found to be a good description of the edges of the bosonic Laughlin and other states identified as members of the principal Jain sequence for bosons. However, we find that in a harmonic trap the edge of the state identified as the Moore-Read (Pfaffian) state shows a number of anomalies. An experimental way of detecting these correlated states is also discussed.

Liquid-gas phase transition in nuclear matter from realistic many-body approaches

The existence of a liquid-gas phase transition for hot nuclear systems at subsaturation densities is a well-established prediction of finite-temperature nuclear many-body theory. In this paper, we discuss for the first time the properties of such a phase transition for homogeneous nuclear matter within the self-consistent Green's function approach. We find a substantial decrease of the critical temperature with respect to the Brueckner-Hartree-Fock approximation. Even within the same approximation, the use of two different realistic nucleon-nucleon interactions gives rise to large differences in the properties of the critical point.

Tearing and folding of the retinal internal limiting membrane associated with macular epiretinal membrane

PURPOSE: To describe the clinical and histologic features of a particular form of macular epiretinal membrane. METHODS: The charts of all patients operated for macular epiretinal membrane by a single surgeon (E.H.B.) between June 2001 and January 2005 were retrospectively reviewed. Patients with macular epiretinal membrane associated with tearing and folding of the internal limiting membrane (ILM) were identified and the following parameters were recorded when available: age, gender, best-corrected visual acuity before and after vitrectomy; optical coherence tomography; pre-, intra-, and postoperative macular status; intraoperative staining by indocyanine green; histology. RESULTS: Twenty-three of 268 eyes (8.6%) with macular epiretinal membrane were associated with tearing and folding of the ILM, forming a whitish prominent band on the surface of the retina. The mean age of the patients was 68.6 years with a significant female predominance (78.3%). The vitreous was completely detached in 21 eyes. After surgical peeling, the mean visual gain was 3.2 Early Treatment Diabetic Retinopathy Study lines. No recurrence was observed. CONCLUSION: Tearing and folding of the ILM was associated with macular epiretinal membranes in 8.6% of cases. The ILM was probably torn during posterior hyaloid detachment, but the pathogenesis has not been clearly elucidated. The surgeon should begin to peel the macular epiretinal membrane by grasping the folded ILM to ensure complete removal of the ILM together with the epiretinal membrane. The postoperative visual prognosis was good

An improved method for measuring soil microbial activity by gas phase flow injection analysis

The rate of carbon dioxide production is commonly used as a measure of microbial activity in the soil. The traditional method of CO2 determination involves trapping CO2 in an alkali solution and then determining CO2 concentration indirectly by titration of the remaining alkali in the solution. This method is still commonly employed in laboratories throughout the world due to its relative simplicity and the fact that it does not require expensive, specific equipment. However, there are several drawbacks: the method is time-consuming, requires large amounts of chemicals and the consistency of results depends on the operator's skills. With this in mind, an improved method was developed to analyze CO2 captured in alkali traps, which is cheap and relatively simple, with a substantially shorter sample handling time and reproducibility equivalent to the traditional titration method. A comparison of the concentration values determined by gas phase flow injection analysis (GPFIA) and titration showed no significant difference (p > 0.05), but GPFIA has the advantage that only a tenth of the sample volume of the titration method is required. The GPFIA system does not require the purchase of new, costly equipment but the device was constructed from items commonly found in laboratories, with suggestions for alternative configurations for other detection units. Furthermore, GPFIA for CO2 analysis can be equally applied to samples obtained from either the headspace of microcosms or from a sampling chamber that allows CO2 to be released from alkali trapping solutions. The optimised GPFIA method was applied to analyse CO2 released from degrading hydrocarbons from a site contaminated by diesel spillage.