On the applicability of the Heliosat-2 method to assess surface solar irradiance in the Intertropical Convergence Zone,French Guiana

Measurements of daily means of surface solar irradiance made at four ground stations in French Guiana are compared to estimates from the HelioClim-3 database produced by the Heliosat-2 method applied to Meteosat satellite images. The bias ranges from 12 W m^?2 (6% of the mean of measurements) to 23 W m^?2 (12%), depending on the stations. The root mean square difference ranges between 23 W m^?2 (11%) and 35 W m^?2 (18%). The correlation coefficient (r) is close to 0.9. Better results are observed during the rainy season than during the dry season. Uncertainties are mainly due to the presence of clouds, large viewing angles of the Meteosat satellite, and limitations of the atmospheric transmittance model under the tropical atmospheric conditions. It is concluded that the Heliosat-2 method provides new knowledge about solar radiation in French Guiana.     

New hypotheses for hydrogenase implication in the corrosion of mild steel

The influence of [Fe]-hydrogenase from Clostridium acetobutylicum was studied on the anaerobic corrosion of mild steel. Two short-circuited mild steel electrodes were exposed to the same solution and hydrogenase was retained on the surface of only one electrode thanks to a dialysis membrane. The galvanic current and the electrode potential were measured as a function of time in order to monitor the difference in electrochemical behaviour induced by the presence of hydrogenase. A sharp potential decrease of around 500 mV was controlled by the deoxygenating phase. When hydrogenase was introduced after complete deoxygenation, significant heterogeneous corrosion was observed under the vivianite deposit on the electrode in contact with hydrogenase, while the other electrode only showed the vivianite deposit, which was analysed by MEB and EDX. The effect of hydrogenase was then confirmed by monitoring the free potential of single coupons exposed or not to the enzyme in a classical cell after complete deoxygenating. In both phosphate and Tris-HCl buffers, the presence of hydrogenase increased the free potential around 60 mV and induced marked general corrosion. It was concluded that [Fe]-hydrogenase acts in the absence of any final electron acceptor by catalysing direct proton reduction on the mild steel surface.     

Two approaches for waveform coding of 9.6 kbit/s voiceband datasignals through 32 kbit/s ADPCM

Two approaches are presented for accommodating 9.6 kb/s modem signals (e.g. V.29) through 32 kb/s ADPCM (adaptive digital pulse-code modulation) links. These are small changes in the existing algorithm and coding with ADPCM incorporating a 5-bit, rather than 4-bit quantizer. For each approach, tradeoffs between performance and implementation complexity are described     

Electroactive biofilms: new means for electrochemistry

This work demonstrates that electrochemical reactions can be catalysed by the natural biofilms that form on electrode surfaces dipping into drinking water or compost. In drinking water, oxygen reduction was monitored with stainless steel ultra-microelectrodes under constant potential electrolysis at −0.30 V/SCE for 13 days. 16 independent experiments were conducted in drinking water, either pure or with the addition of acetate or dextrose. In most cases, the current increased and reached 1.5–9.5 times the initial current. The current increase was attributed to biofilm forming on the electrode in a similar way to that has been observed in seawater. Epifluorescence microscopy showed that the bacteria size and the biofilm morphology depended on the nutrients added, but no quantitative correlation between biofilm morphology and current was established. In compost, the oxidation process was investigated using a titanium based electrode under constant polarisation in the range 0.10–0.70 V/SCE. It was demonstrated that the indigenous micro-organisms were responsible for the current increase observed after a few days, up to 60 mA m⁻². Adding 10 mm acetate to the compost amplified the current density to 145 mA m⁻² at 0.50 V/SCE. The study suggests that many natural environments, other than marine sediments, waste waters and seawaters that have been predominantly investigated until now, may be able to produce electrochemically active biofilms.     

From technological acceptability to appropriation by users: Methodological steps for device assessment in road safety

This article presents the methodology developed within the framework of the research project SARI (Automated Road Surveillance for Driver and Administrator Information). This methodology is based on the logic of action research. The article presents the different stages in the development of technological innovation addressing vehicle control loss when driving on a curve. The results observed in speed reduction illustrate that no matter how optimal an innovation may be technologically speaking, it is only as effective as it is acceptable from a user standpoint. This acceptability can only be obtained if the technology is developed by engineers in liaison with social science specialists.     

1 H and 29Si NMR Spectroscopy as a Powerful Analytical Tool to Evaluate the Activity of Various Platinum-Based Catalysts in Model Olefin Hydrosilylation

The structure of polysiloxane copolymers obtained by hydrosilylation of 1-octene with polymethylhydrosiloxane (PMHS) was analyzed by ²⁹Si NMR spectroscopy and revealed a tendency to form block copolymers. Although all the platinum catalysts that were used showed a tendency to form some block structures, only Karstedt catalyst led to well defined block copolymers. However, the tacticity of these copolymers could not be determined using Heteronuclear Multiple Bond Correlation (HMBC) 2D (¹H/ ²⁹Si) NMR technique. The following criteria were found to affect the structure of the hydrosilylation product: low SiH conversion, the “age” of the Karstedt catalyst (low TON) and high octene/SiH ratios.     

Solubility and mobility of phosphorus recycled from dairy effluents and pig manures in incubated soils with different characteristics

Phosphorus (P) nutrition of plants in croplands is managed by fertilization. Commercial P fertilizers are manufactured from phosphate rocks, which are non-renewable and the only fossil resource of P. As an alternative, P in human and animal wastes can be recovered and concentrated in products that can be used as P fertilizers. Here, we studied four recycled P products derived from pig manures (hereafter referred as “RPPM”) and another one derived from dairy effluents (“RPDE”). The RPDE product is composed of Ca–P (partly as hydroxyapatite, HA), while RPPM products include recovered struvite (ST) and Ca–P in variable proportions. The objective was to assess the ability of RPPM and RPDE products to increase available P in a range of soils differing in their characteristics (seven soils used), and to compare these recycled P products with a standard fertilizer [commercial triple super phosphates (TSP)], reference HA and reference ST. To this end, products were mixed to the soils and the mixtures were incubated at 75 % water holding capacity and 28 °C. After incubation, the amounts of phosphate ions (iP) in solution (Q_W) and isotopically exchangeable iP (E) in soils were quantified using an isotopic labeling (³²P) and dilution procedure. In each soil, Q_W and E were significantly affected by treatments (control and P-treated soils) and increased due to the application of the different products. However, reference HA and RPDE products were generally less effective than TSP, reference ST and RPPM products. The soil response (variation in Q_W or E) in TSP treatment was compared to those in other treatments. It enabled the calculation of a relative effectiveness index. Relative effectiveness of HA and RPDE varied among soils (from 5 to 124 %) and increased with decreasing soil pH. Results however showed that the RPDE product tends to be more effective than reference HA, probably due to different degrees of crystallization of Ca–P. Relative effectiveness of RPPM products (80–116 %) was high in all soils and was similar to that of reference ST (90–104 %). To conclude, the present study suggests that RPDE products are effective only in acidic or slightly acidic soils. In contrast, P recycling from pig manures through chemical precipitation can provide effective P fertilizers, independently on soil conditions.     

Competition Between Rashba Effect and Exchange Interaction in a Hg0.98Mn0.02Te Magnetic 2DEG

Magnetotransport measurements are used to study the peculiar properties of a modulation doped n-type Hg_0.98Mn_0.02Te magnetic 2DEG. The Rashba effect and giant Zeeman spin splitting are observed simultaneously and can be separated by temperature and gate voltage dependent Shubnikov-de Haas oscillations. The Rashba effect is found to be the dominant term up to 5 T.     

A Digital Codec Simulation Facility

This paper describes a minicomputer facility developed to aid in the evaluation of the grade-of-service impact of digital codecs. Two minicomputers are interfaced with 15 bit A/D and D/A converters so that an analog signal such as speech can be quantized and stored in real time at sampling rates up to 72 kHz. The acquired digital samples can then be processed by various PCM, ADPCM, and ADM algorithms programmed on the system. After the processing is completed, the facility can automatically generate high quality audio tapes which are suitable for subjective evaluation in an absolute judgment or balance test format. The two minicomputers operate on a stand-alone basis so that the capability exists for simulating either similar or dissimilar tandem encodings in a synchronous or asynchronous mode. A few sample outputs of the facility are also given in the form of subjective test results for single and tandem encodings of μ255 PCM and Nearly Instantaneous Companded (NIC) PCM.