Characterization of Cu/CeO2/γ-Al2O3 Thin Film Catalysts by Thermal Desorption Spectroscopy

Thermal desorption spectroscopy (TDS) under ultra high vacuum (UHV) condition has been used to investigate the desorption characteristics of Cu/CeO₂/γ-Al₂O₃ thin film catalysts coated onto the microchannel of a microreactor. TDS results demonstrate that surface desorption profiles and chemical properties (acid–base and redox properties) are remarkably influenced by the catalyst composition, i.e. the loading of copper and ceria. The enhanced basicity with the increase of ceria loading and the decrease of copper loading is evident from the shifted desorption maximum of CO₂ in TDS spectra. Three oxygen species, ranging from weakly bound oxygen desorbed at low temperature to the strongly held lattice oxygen desorbed at high temperature, are easily discernible and clearly identified by O₂ TDS spectra, depending on the catalyst compositions. The concomitant thermal desorption of O₂, CO₂, and H₂O at low temperature indicates the unique chemical properties of copper/ceria catalyst with appropriate copper and ceria contents. The observed low-temperature feature is ascribed to the role of porthole of copper/ceria interfacial area for several desorbed species. The weakly bound oxygen species is attributed to the enhanced abundance of copper/ceria interfacial anionic vacancies created by the intimate contact between copper and ceria entities and its impact on steam reforming of methanol (SRM) reaction is tentatively discussed in terms of reverse oxygen spillover.     

The Esterase PfeE,the Achilles’ Heel in the Battle for Iron between Pseudomonas aeruginosa and Escherichia coli

Bacteria access iron, a key nutrient, by producing siderophores or using siderophores produced by other microorganisms. The pathogen Pseudomonas aeruginosa produces two siderophores but is also able to pirate enterobactin (ENT), the siderophore produced by Escherichia coli. ENT-Fe complexes are imported across the outer membrane of P. aeruginosa by the two outer membrane transporters PfeA and PirA. Iron is released from ENT in the P. aeruginosa periplasm by hydrolysis of ENT by the esterase PfeE. We show here that pfeE gene deletion renders P. aeruginosa unable to grow in the presence of ENT because it is unable to access iron via this siderophore. Two-species co-cultures under iron-restricted conditions show that P. aeruginosa strongly represses the growth of E. coli as long it is able to produce its own siderophores. Both strains are present in similar proportions in the culture as long as the siderophore-deficient P. aeruginosa strain is able to use ENT produced by E. coli to access iron. If pfeE is deleted, E. coli has the upper hand in the culture and P. aeruginosa growth is repressed. Overall, these data show that PfeE is the Achilles’ heel of P. aeruginosa in communities with bacteria producing ENT.     

Evidence by EIS of the interaction between proteins and tin oxide electrode surface

Macromolecules like proteins are able to adhere to tin oxide electrodes at open circuit potential as proved by electrogravimetry experiments. In this work, electrochemical impedance studies were performed at aqueous electrolyte/F- or Sb-doped semiconducting tin oxide interfaces, including natural seawater. By this way, it was possible to characterize the potential dependence of the interfacial capacitance in various physicochemical conditions, without or in the presence of bovine serum albumin (BSA). In the potential range where tin oxide is in the depletion regime (blocking interface), a capacitance excess is evidenced which can be attributed to the formation of surface states which are the signature of chemical bonding. By simulating the so-called surface state capacitance, three states have been pointed out. They are centred at 0.7, 0.9 and 1.1 eV in the tin oxide bandgap. On the basis of experimental arguments, the state at 1.1 eV was ascribed to the OH-terminated tin oxide surface, the two other states were found to be specific of the interaction of organic matter with the oxide surface. In the presence of BSA, the density of surface atoms (about 10¹³ cm⁻²) involved in bonding is of the order of magnitude of the surface concentration of one BSA monolayer. The lasting character of these bonds was also shown. This finding shows the definitive protein immobilisation at the SnO₂ surface.     

The Electrodeposition of Chromium from Tervalent Chromium Salt Solutions. Part I. Chromium Chloride and Chromium Sulphate Baths

The “imponderables” which affect the framework within which the Plating Shop must be planned are listed. The grouping of vats, cleaners and rinses are discussed and alternative methods of hand operation of plating vats described. The importance of depth of plating vats is stressed and various methods of constructing floors, drainage and vat supports are briefly indicated. Layouts for barrel plating shops both with inclined and horizontal barrels are suggested, and the importance of correct housing for electrical and other ancillary plant is emphasised.     

The effect of microstructure on hydrogen permeability of high strength steels

Hydrogen diffusivity and trapping have been studied in two advanced high strength steel grades and model samples using electrochemical permeation test. Microstructures of CP1000 and DP1000 steels consist of ferrite, martensite and a small fraction of retained austenite. In addition, bainite is present in CP1000. Model phases with predominance of a particular phase have been prepared by specific heat treatment. DP1000 has shown the lowest diffusivity among all materials, while ferritic model sample has shown the highest. Differences in hydrogen diffusion coefficient values are linked to trapping microstructural characteristics and grain size.     

Inhibition tests for detection and presumptive identification of tetracyclines, beta-lactam antibiotics and quinolones in poultry meat

A combination of three plates, seeded with strains of Micrococcus luteus, Bacillus cereus or Escherichia coli, can be used for detection of residues of betalactam antibiotics, tetracyclines and fluoroquinolones. The sensitivity of each plate is optimal for only one of these groups, resulting in detection limits (LOD) lower than the corresponding maximum residue limits (MRL) and in distinct inhibition patterns typical for each antibiotic family. Beta-lactam antibiotics such as penicillin G, ampicillin and amoxicillin give only inhibition zones on the plate with M. luteus. Tetracyclines are detected up to the MRL level with B. cereus, and fluoroquinolones with E. coli. The LODs of the antibiotics tested were as follows: penicillin G (PENG) 0.9 ng, ampicillin (AMPI) 0.6 ng and amoxicillin (AMOX) 1.0 ng on the plate with M. luteus; tetracycline (TET) 4 ng, oxytetracycline (OXY) 3 ng, doxycycline (DOX) 0.6 ng, and chlortetracycline (CHL) 0.3 ng on the plate with B. cereus; enrofloxacin (ENRX) 1.5 ng, ciprofloxacin (CIPX) 0.5 ng and flumequine (FLUM) 1.5 ng on the plate with E. coli. The combination of plates enables the laboratory to select appropriate chromatographic techniques for identification and quantification of the residues. On the other hand, the three groups can also be detected on one plate seeded with Bacillus subtilis, although the limits of detection are higher: PENG 0.4 ng, AMPI and AMOX 3 ng; TET 5 ng, OXY 8 ng, DOX 1 ng, CHL 0.5 ng, ENRX 4 ng, CIPX 10 ng and FLUM 4 ng. The test was applied to 228 broiler fillets and to 27 turkey thighs, originating from different poultry slaughterhouses. Nineteen broiler fillets contained inhibiting substances. The positive results of the inhibition tests were confirmed with a chromatographic technique. Doxycycline residues were found in 16 samples and amoxicillin in two.     

Some elements in domestic and imported fresh fruits marketed in the Netherlands

Summary Sodium, potassium, arsenic, selenium and tin have been determined in 38 different types of domestic and imported fresh fruits. All samples (n=242) were analysed for Na und K whereas a limited number of samples (n=85) of each fruit type was selected for the determination of As, Se and Sn. The median contents, in mass fractions of the edible portion, found for fresh fruits are: Na<0.001%; K 0.17%; As 4 g/kg; Se 2 g/kg and Sn< 0.05 mg/kg. The corresponding 90th percentile values are: Na 0,002%, K 0.34%; As 12 g/kg; Se 10 g/kg and Sn 0.10 mg/kg. Results for selenium reported here differ substantially from those given for a number of fresh fruits in the German Food Composition Tables 1986/1987. The average consumption of 129 g fresh fruit by Dutch citizens in the age category of 22–75 years contributes, in general, marginally to the total daily dietary intake of sodium, arsenic, selenium and tin. Fresh fruit can contribute substantially, up to 23%, to the average oral daily intake of potassium.

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Einige Mineralstoffe im einheimischen und importierten Frischobst vom niederländischen Markt

Zusammenfassung Natrium, Kalium, Arsen, Selen und Zinn wurden in 38 verschiedenen Sorten von in- und ausländischem Frischobst bestimmt. Alle Proben (n=242) wurden auf Na und K untersucht; während nur eine beschränkte Zahl von Proben (n=85) für die Bestimmung von As, Se und Sn ausgewählt wurde. Die Medianwerte, in Massenanteilen der eßbaren Portionen, betrugen für frisches Obst: Na<0,001%; K 0,17% As 4 g/kg; Se 2 g/kg und Sn<0,05 mg/kg. Die dazugehörigen Werte für den 90 Perzentil sind: Na 0,002%; K 0,34%; As 12 g/kg; Se 10 g/kg und Sn 0,10 mg/kg. Für einige Obstsorten wurden Selenwerte erhalten, die erheblich von denen der Deutschen Nährwert-Tabellen 1986/1987 abweichen. Frischobst, dessen Verzehr für Einwohner der Niederlande in der Altersklasse von 22–75 Jahre im Schnitt 129 g/Tag beträgt, liefert einen vernachlässigbaren Beitrag zur täglichen Einnahme von Natrium, Arsen, Selen und Zinn; für Kalium hingegen kann dieser Beitrag, mit bis zu 23%, erheblich sein.

     

小型亚热带半日潮河口中的湍流

在天然河口,污染物的输送是由湍流动量混合驱动的,而弥散的大小却难以被准确地预测。这是由于对河口的湍流结构缺乏基础的认识而造成的。介绍在一个小型的亚热带半日潮河口进行的高频率及连续50 h的湍流实地测量的情况。在研究的浅水(低潮水深小于0．5 m)小型河口中,使用了最适用于这种水体的声学多普勒流速仪进行测量,并进行了完整的后处理工作。河口水流是一个波动的过程,各种宏观流动参数随潮周期和其它大尺度的过程而波动,但是湍流特性是由即时局部流动特性所决定,它们基本不受流动历程的影响,其结构和瞬时变化受多种机理影响。这导致其只与水流剪切力引起的湍流边界层平衡相关。所有湍流特性在潮周期中均有大波动是本次研究数据的一个显著特征,这一特征在此前少有记载,但本次的测量数据与过往数据的一大差别是,数据连续测量的时间长且频率高。这将为波动特性的动量交换系数及积分时间和长尺度提供新的信息,这些湍流特性不应被视为不变的。