L'equation experimentale I—V du developpement d'oxyde poreux d'aluminium

The steady-state I—V relationship for the development of the thin oxide layer on aluminium has been established:

where ΔE = 10–12 kcal/mol and V^x is a limiting value of the voltage. The relationship describes the behaviour of the barrier layer and holds for sulfuric, oxalic and phosphoric acid solutions as well. The experimental data may be interpreted as the behaviour of an insulator layer working in Poole domain.     

UV Raman imaging--a promising tool for astrobiology: comparative Raman studies with different excitation wavelengths on SNC Martian meteorites

The great capabilities of UV Raman imaging have been demonstrated on the three Martian meteorites: Sayh al Uhaymir, Dar al Gani, and Zagami. Raman spectra without disturbing fluorescence and with high signal-to-noise-ratios and full of spectral features were derived. This result is of utmost importance for the development of powerful instruments for space missions. By point scanning the surfaces of the meteorite samples, it was possible for the first time to construct UV-Raman images out of the array of Raman spectra. Deep-UV Raman images are to the best of our knowledge presented for the first time. The images were used for a discussion of the chemical-mineralogical composition and texture of the meteorite surfaces. Comparative Raman studies applying visible and NIR Raman excitation wavelengths demonstrate a much better performance for UV Raman excitation. This comparative study of different Raman excitation wavelengths at the same sample spots was done by constructing a versatile, robust sample holder with a fixed micro-raster. The overall advantages of UV resonance Raman spectroscopy in terms of sensitivity and selectivity are demonstrated and discussed. Finally the application of this new technique for a UV Raman instrument for envisaged astrobiological focused space missions is suggested.     

Nucleophile Substitutionen an Kohlensäurederivaten. XIX. Alkoholyse und Hydrolyse des Bis(trichlormethyl)carbonates

Nucleophilic Substitutions at Carbonic Acid Derivatives. XIX. Alcoholysis and Hydrolysis of Bis(trichloromethyl)carbonate The rate constants of hydrolysis and alcoholysis of bis(trichlormethyl)carbonate in xan have been determinated conductometrically. The effects of the water and alcohol concentrations, the temperature and deuterium have been studied. By the hydrolysis and alcoholysis of bis(trichlormethyl)carbonate the nucleophilic attack of water and alcohol is the rate-determining step, followed by a fast elimination of unstable trichloro-methanol.     

The Role of NiO Doping in Reducing the Impact of Humidity on the Performance of SnO2‐Based Gas Sensors: Synthesis Strategies,and Phenomenological and Spectroscopic Studies

The humidity dependence of the gas‐sensing characteristics in SnO₂‐based sensors, one of the greatest obstacles in gas‐sensor applications, is reduced to a negligible level by NiO doping. In a dry atmosphere, undoped hierarchical SnO₂ nanostructures prepared by the self‐assembly of crystalline nanosheets show a high CO response and a rapid response speed. However, the gas response, response/recovery speeds, and resistance in air are deteriorated or changed significantly in a humid atmosphere. When hierarchical SnO₂ nanostructures are doped with 0.64–1.27 wt% NiO, all of the gas‐sensing characteristics remain similar, even after changing the atmosphere from a dry to wet one. According to diffuse‐reflectance Fourier transform IR measurements, it is found that the most of the water‐driven species are predominantly absorbed not by the SnO₂ but by the NiO, and thus the electrochemical interaction between the humidity and the SnO₂ sensor surface is totally blocked. NiO‐doped hierarchical SnO₂ sensors exhibit an exceptionally fast response speed (1.6 s), a fast recovery speed (2.8 s) and a superior gas response (R_a/R_g = 2.8 at 50 ppm CO (R_a: resistance in air, R_g: resistance in gas)) even in a 25% r.h. atmosphere. The doping of hierarchical SnO₂ nanostructures with NiO is a very‐promising approach to reduce the dependence of the gas‐sensing characteristics on humidity without sacrificing the high gas response, the ultrafast response and the ultrafast recovery.     

A reconfigurated rack-tool for the generation of gears

The cutting processes with tools that generate “through-winding straight-involute teeth-gears”, tools associated with couples of centrodes-in-rolling (such as the rack-tool), are characterized by a fairly complicated cutting scheme, due to the specific shape of the tools and, at the same time, due to the rolling process of the axodes associated with the tool and the blank. The present solutions are not accorded well enough to the process and lead to significant variations in the detached chip area value regarding the machined wheel teeth number. It is accepted that the main cutting force size depends on the size of the area of the cutting layer (the geometrical area of the once detached chip by the assembly of operative edges of this kind of tools). The geometrical modeling of the generation process proves this and it could be considered a criterion for the reconfiguration of the cutting tool. In this work, there is defined a criterion so as to describe the cutting scheme, and based on this criterion we can compare the variation laws for the chip area size when generating the modeling of the cylindrical straight teethed gears. We propose a modeling of the cutting schemes in order to get new constructive forms of the cutting tools that will lead to cutting schemes adaptable to the number of teeth of the processed gear with the purpose of diminishing the teething cutting force. Also, there is presented a constructive solution for a rack-tool with reconfigurable structure with the purpose of according the teething process with the processed gear number of teeth.     

Effects of the Lipid Profile,Type 2 Diabetes and Medication on the Metabolic Syndrome—Associated Gut Microbiome

Metabolic syndrome (MetSyn) is a major health problem affecting approximately 25% of the worldwide population. Since the gut microbiota is highly connected to the host metabolism, several recent studies have emerged to characterize the role of the microbiome in MetSyn development and progression. To this end, our study aimed to identify the microbiome patterns which distinguish MetSyn from type 2 diabetes mellitus (T2DM). We performed 16S rRNA amplicon sequencing on a cohort of 70 individuals among which 40 were MetSyn patients. The microbiome of MetSyn patients was characterised by reduced diversity, loss of butyrate producers (Subdoligranulum, Butyricicoccus, Faecalibacterium prausnitzii) and enrichment in the relative abundance of fungal populations. We also show a link between the gut microbiome and lipid metabolism in MetSyn. Specifically, low-density lipoproteins (LDL) and high-density lipoproteins (HDL) display a positive effect on gut microbial diversity. When interrogating the signature of gut microbiota in a subgroup of patients harbouring both MetSyn and T2DM conditions, we observed a significant increase in taxa such as Bacteroides, Clostridiales, and Erysipelotrichaceae. This preliminary study shows for the first time that T2DM brings unique signatures of gut microbiota in MetSyn patients. We also highlight the impact of metformin treatment on the gut microbiota. Metformin administration was linked to changes in Prevotellaceae, Rickenellaceae, and Clostridiales. Further research focusing on the microbiome-metabolome patterns is needed to clarify the exact association of various gut microbial communities with the progression of T2DM and the occurrence of various complications in MetSyn patients.     

The study of the vapor-liquid interfacial polycondensation of the cyclohexylphosphonic dichloride with bisphenol AThe influence of temperature, reaction time, base concentration and molar ratio on yield, inherent viscosity and molecular weight

Summary Polyphosphonate esters of molecular weights ∼ 10⁴ were synthesized by base promoted liquid-vapor polycondensation of cyclohexylphosphonic dichloride with bisphenol A. The effect of temperature, reaction time, base concentration and molar ratio of reagents on yield, inherent viscosity and molecular weight of the obtained polymer was studied. A second order, central composite, rotatable experimental design was used to find domain experimental field for optimal yields and high inherent viscosities. Received: 4 August 2000/Revised version: 14 February 2001/Accepted: 5 March 2001     

Parabolic and hyperbolic flexure hinges: flexibility, motion precision and stress characterization based on compliance closed-form equations

The parabolic and hyperbolic flexure hinges are introduced as new rotation joints to be utilized in two-dimensional monolithic mechanisms. Closed-form equations are formulated for compliances to characterize both the active rotation and all other in- and out-of-plane parasitic motions. The stress levels are also evaluated in terms of compliances. Checked against finite element analysis and experimental measurement data, the model predictions are within 8% error margins. Further simulation is performed to compare geometrically-equivalent parabolic and hyperbolic flexure hinges. The results indicate that the parabolic flexures are more rotation-compliant and induce less stress, while the hyperbolic flexures are less sensitive to parasitic effects.     

Two improved nyquist filters with piece-wise rectangular-polynomial frequency characteristics

In this article a novel method for constructing a family of improved Nyquist filters is provided, as well as some guidelines on how the inter-symbol interference (ISI) problem can be approached. The proposed solution for the design of Nyquist pulses is based on a piece-wise rectangular-polynomial frequency characteristic using second and third degree polynomials. The characteristic property of the novel family of ISI-free pulses generated by the proposed filters is the asymptotic decay rate of t⁻². By introducing this approach, comparable or better results are obtained in terms ISI performance as compared to several recently proposed pulses.     

Kinetics and mechanism of isocyanate reactions. I. Reactions of Aryl Isocyanates with Alcohols

The reaction of aryl isocyanates with alcohols has been kinetically studied as a model reaction for polyurethane formation under conditions similar to those of industrial scale production. Considering the isocyanate and alcohol structure, kinetic isotopic effect, activation enthalpy and entropy and solvent effects it has been found that the most probable mechanism is the alcohol addition through a four-membered cyclic transition state.