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Notes: Three different thermal carbonization processes of porous silicon (PS) surface by acetylene occurring between 400 and 950 °C were observed by in situ measurements. The peak temperature of oxidation shifts from 300 to 600 °C and the activation energy from 130 to 500 kJ/mole in the samples treated at 900 °C compared to untreated PS. Using Fourier transform infrared spectroscopy (FTIR), the bonding configurations associated with the temperature dependent processes were found. In the samples treated at or below 600 °C, traces of C–Hx bonds were clearly seen, but above 600 °C the FTIR spectra started resemble those of the SiC. The graphitization process was found to take place on the surface of PS samples treated above 800 °C. By changing the time between the C2H2 flush and thermal treatment, the graphitization can be controlled and even avoided. The weight increase was observed to be nearly proportional to the reduction of the surface area while the decrease in the surface area due to the thermal carbonization was found to be small. The origin of this phenomenon and the effects of other preparation parameters have been discussed. © 2002 American Institute of Physics.

Notes: We have investigated the photoluminescence quenching of porous silicon in different atmospheres and in vacuum. We observe a much faster quenching in vacuum than reported before, which we propose is caused by the difference of structure in p- and n-type porous silicon, or a re-reaction with an electrolyte vapor. We have also investigated the recovery of the photoluminescence. We observe the luminescence intensity to partially recover under the influence of a hydrogen atmosphere, up to 0.1 of its initial value. We propose that this is associated with the stabilization of surface dangling bonds. When the hydrogen atmosphere was changed to the normal atmosphere of air, the photoluminescence intensity started to decrease again due to oxidation. © 1996 American Institute of Physics.

Notes: We have studied the thermal oxidation of free-standing porous silicon films from room temperature to 730 °C with a differential scanning calorimeter and a thermogravimeter. We have observed three different thermal oxidation processes for the porous silicon. The change of enthalpy (ΔH) and activation energy (Ea) for the first reaction has been calculated. The oxidation of a fresh sample has been compared with those of aged samples, which were stored in dry relative humidity (RH 0%), humid (RH 100%) and normal (RH 25%–35%) laboratory air atmospheres. We also used Fourier transform infrared spectroscopy to clarify the bonds for each process. © 1997 American Institute of Physics.

Notes: We have used an isothermal microcalorimetric method to study photoinduced effects in porous silicon (PS). In the photo-oxidation investigations using constant wavelength, sharp threshold behavior with threshold energies 3.9 eV for n-PS and 4.7 eV for p+-PS were observed. The two discussed origins for the different threshold energies are based either on the energy gap transitions and enhanced electron transfer from the conduction band to the electron-affinity level of oxygen molecules, or the Si–O bond energy. Also nonlinear dependence on the irradiation intensity was found. Surprisingly, high exothermic signals were observed in measurements made under an inert perfusion. It is proposed that this is associated with relaxation of PS structure, which seems to be more efficiently induced by illumination than thermal treatment. © 1999 American Institute of Physics.

Notes: The oxidation behavior of porous silicon (PS) has been found to be related to illumination during etching. The autocatalytic oxidation behavior at room temperature arises from the unrelaxed surface induced by the preparation under illumination and can be removed using thermal treatment in a nitrogen atmosphere. The effect is absent in the case of degenerate PS and smaller in p type than in n-type PS. The correlation between the oxidation behavior and the microstructural dimensions is also discussed. © 1999 American Institute of Physics.

Notes: The complement system is regarded as an important component of the innate defence system against invading bacteria. However, synergistic actions between the complement and the other components of innate immunity are incompletely known. Human group IIA phospholipase A2 (hGIIA PLA2) is an effective antibacterial enzyme in serum of patients with severe bacterial infections. Our aim was to investigate the significance of complement and hGIIA PLA2 in acute phase serum. Serum samples were collected from patients with acute bacterial infections and from healthy control subjects. We prepared hGIIA PLA2-depleted serum by immunoadsorption and inhibited the activity of complement by a specific inhibitor, compstatin. The bactericidal effects of treated and untreated serum were compared by incubating Staphylococcus aureus and Listeria monocytogenes in the presence of serum. Acute phase serum effectively killed S. aureus and L. monocytogenes, and depletion of hGIIA PLA2 significantly reduced the antibacterial effect. Complement had a weak bactericidal effect against L. monocytogenes. We conclude that hGIIA PLA2 is the major antibacterial factor in human acute phase serum against the gram-positive bacteria S. aureus and L. monocytogenes, exceeding complement in efficiency.

Notes: Reduction of the dose of MCPA/mecoprop and MCPA/fluroxypyr mixtures to half or one-third of the recommended rates still provided good weed control efficacy in spring wheat (Triticum aestivum L.) and particularly in spring barley (Hordeum vulgare L). The average yield of treated plots was 8% higher in wheat and 1% higher in barley compared with untreated plots. However, yield reductions were observed in 32% of wheat plots and in 43% of barley plots treated with herbicides. The yield responses were poorly correlated with the weed density of mixed weed flora at the time of spraying. No reliable threshold density for chemical weed control was found. Réponses au rendement de céréales de printemps, à des doses d'herbicides réduites La réduction de la dose de MCPA/mecoprop et MCPA/fluroxypyr a la moitié ou au tiers des taux recommandés a encore assure une bonne efficacité herbicide chez le blé de printemps (Triticum aestivum L.) et specialement chez l'orge de printemps (Hordeum vulgare L.). Le rendement moyen des parcelles traitées était de 8% plus élevé chez le blé et de 1%élevé chez l'orge que dans les parcelles non traitees. Cependant, des reductions de rendement ont été observées dans 32% des parcelles de blé et dans 43% des parcelles d'orge traitées aux herbicides. Les reponses du rendement étaient faiblement liées a la densité en adventices d'une flore mixte au moment du traitement. Aucune densité seuil-sérieuse pour le desherbage n'a été trouvée. Ertragsbildung von Sommergetreide bei reduziertem Aufwand von Herbiziden Eine Reduzierung des Aufwands von MCPA-Mecoprop- und MCPA-Fluroxypyr-Mischungen auf die Halfte oder ein Drittel des empfohlenen Aufwands ergab in Sommerweizen (Triticum aestivum L.) und besonders in Sommergerste (Hordeum vulgare L.) noch eine gute Unkrautbekampfung. Im Mittel war der Ertrag der behandelten Parzellen beim Weizen um 8% und bei der Gerste um 1% höher als in den unbehandelten, aber in 32% der Herbizidparzellen mit Weizen und in 43% der mit Gerste wurden Ertragsminderungen beobachtet. Die Ertragsbildung stand kaum in Beziehung zur Unkrautdichte zur Zeit der Behandlung. Es wurde keine verläßliche Schadensschwelle gefunden.

Notes: The effect of dose reduction on the efficacy of MCPA/mecoprop and MCPA/fluroxypyr mixtures in the control of broad-leaved weeds was studied in spring barley (Hordeum vulgare L.) and spring wheat (Triticum aestivum L.), Five crop densities were sown to obtain crop stands of different competitive ability. Halving the highest recommended dose decreased the control efficacy by 5–15 percentage units, but still provided a good weed control. Further reduction of the dose resulted in high variation in efficacy. The level of weed suppression was mainly determined by the competitiveness of the crop, environmental conditions and weed spectrum with differential sensitivity of species to the herbicides. No changes in the weed infestation were detected after continuous use of low herbicide doses for 3 years. The seed bank of weeds in soil was higher after a wheat-dominated rotation than after a barley-dominated rotation. Efficacité de doses réduites d'herbicides chez des céréales de printemps d'aptitudes à la compétitivé différentes L'impact de la réduction des doses sur l'efficacité de melange MCPA/mecoprop et MCPA/ fluroxypyr en matiere de desherbage des dicotyledones a étéétudié chez l'orge de printemps (Hordeum vulgare L.) et le blé de printemps (Triticum aestivum L.) 5 densités de culture ont été semées pour obtenir des cultures d'aptitudes a la compétitivité différentes. La réduction de moitié de la dose recommandée la plus élevée a reduit l'efficacité herbicide de 5 à 15% mais a encore fourni un bon résultat. Des reductions plus élevées de la dose ont conduit à de fortes variations dans l'efficacité. Le niveau de suppression des adventices était principalement déterminé par la compétitivité de la culture, les conditions environnementales et le spectre des adventices avec une sensibilité differentes des espèces aux herbicides, Aucun changement dans l'infestation en adventices n'a été observé après une utilisation continue de faibles doses d'herbicide pendant 3 ans, Le stock grainier d'adventices du sol était plus élevé après une rotation à dominante blé, qu'après une rotation à dominante orge. Wirksamkeit reduzierten Aufwands von Herbiziden in Sommergetreide mit unterschiedlicher Konkurrenzkraft In Sommergerste (Hordeum vulgare L.) und Sommerweizen (Triticum aestivum L.) wurde untersucht, wie die Reduzierung des Aufwands die Wirksamkeit von MCPA-Mecoprop- und MCPA-Fluroxypyr-Mischungen beeinflußt, Die Getreide wurden in 5 Dichten gesät, um Pflanzenbestände unterschiedlicher Konkurrenzkraft zu haben. Die Halbierung des hochsten empfohlenen Aufwands verminderte die Wirksamkeit um 5 bis 15 Prozentpunkte, ergab dennoch eine gute Unkrautbekämpfung, Eine weitere Reduzierung des Aufwands brachte sehr unterschiedliche Wirksamkeit. Der Grad der Unkrautunterdrückung wurde überwiegend durch die Konkurrenzkraft des Getreides, die Umweltbedingungen und das Unkrautspektrum mit gegenüber den Herbiziden verschieden empfindlichen Arten bestimmt. Nach 3 Jahren niedrigen Herbizidaufwands ließen sich Änderungen der Verunkrautung nicht erkennen. Der Unkrautsamenvorrat im Boden war nach einer weizen-dominierten Fruchtfolge größer als nach einer gerstendominierten.

Notes: For implementation of simple yield loss models into threshold-based weed management systems, a thorough validation is needed over a great diversity of sites. Yield losses by competition wsth Sinapis alba L. (white mustard) as a model weed, were studied in 12 experiments in sugar beet (Beta vulgaris L.) and in 11 experiments in spring wheat (Triticum aestivum L.). Most data sets were heller described by a model based on the relative leaf area of the weed than by a hyperbolic model based on weed density. This leaf area model accounted for (part of) the effect of different emerging times of the S. alba whereas the density model did not. A parameter that allows the maximum yield loss to be smaller than 100% was mostly not needed to describe the effects of weed competition. The parameter that denotes the competitiveness of the weed species with respect to the crop decreased the later the relative leaf area of the mustard was determined. This decrease could be estimated from the differences in relative growth rate of the leaf area of crop and S. alba. However, the accuracy of this estimation was poor. The parameter value of the leaf area model varied considerably between sites and years. The results strongly suggest that the predictive ability of the leaf area model needs to be improved before it can be applied in weed management systems. Such improvement would require additional information about effects of abiotic factors on plant development and morphology and the definition of a time window for predictions with an acceptable level of error.