Uncertainty analysis in environmental modelling under a change of spatial scale

Although environmental processes at large scales are to a great degree the resultant of processes at smaller scales, models representing these processes can vary considerably from scale to scale. There are three main reasons for this. Firstly, different processes dominate at different scales, and so different processes are ignored in the simplification step of the model development. Secondly, input data are often absent or of a much lower quality at larger scales, which results in a tendency to use simpler, empirical models at the larger scale. Third, the support of the inputs and outputs of a model changes with change of scale, and this affects the relationships between them. Given these reasons for using different models at different scales, application of a model developed at a specific scale to a larger scale should be treated with care. Instead, models should be modified to suit the larger scale, and for this purpose uncertainty analyses can be extremely helpful. If upscaling disturbed the balance between the contributions of input and model error to the output error, then an uncertainty analysis will show this. Uncertainty analysis will also show how to restore the balance. In practice, application of uncertainty analysis is severely hampered by difficulties in the assessment of input and model error. Knowledge of the short distance spatial variability is of paramount importance to input error assessment with a change of support, but current geographical databases rarely convey this type of information. Model error can only be estimated reliably by validation, but this is not easy because the support of model predictions and validation measurements is usually not the same.     

Aging of polypropylene using high oxygen pressure: Influence of sample thickness and stabilization

Thin films (0.05–0.08 mm thick) of stabilized and unstabilized polypropylene were aged under 4.24 MPa (614 psi) of oxygen at 90°C. The oxidation of these films was monitored using transmission infrared spectroscopy. Previously it was shown that embrittlement for the thin unstabilized polypropylene films occurred 3.6 times faster in 4.24 MPa of oxygen than in air at atmospheric pressure. For thick stabilized polypropylene (3.18 mm thick), the oxidative induction time at 120°C and 4.24 MPa of oxygen was drastically reduced compared with conventional air aging at this temperature. Specifically, sample embrittlement occured in 1 week during the high oxygen pressure aging in stark contrast to 70 weeks for conventional air aging. Consequently, due to the shortening of time to age samples at high oxygen pressures, aging can be conducted at this lower temperature (nearer the service temperature) rather than at this commonly used aging temperature of 150°C.     

Directed molecular evolution by somatic hypermutation

After rearrangement of immunoglobulin gene segments, the immune system evolves the antibody repertoire by mutating the immunoglobulin variable region at a high rate. While this somatic hypermutation was thought to occur only at the variable region, recent studies suggest that hypermutation can occur at locations throughout the genome. Building upon this notion, we sought to exploit this mechanism as a mutagenesis tool. We created a substrate based on GFP that could be screened using flow cytometry and showed that retroviral infection can deliver the transgene to genomic locations that support hypermutation. Infected cells generated various GFP mutants with increased fluorescence intensity and analysis revealed mutations not only at the chromophore, but also an unexpected mutation at a distant residue. Our results demonstrate in principle that immunoglobulin somatic hypermutation can be a potent means of mutagenesis. With appropriate selection conditions it may be utilized to evolve gene products with desired properties.     

Freezing as a method of study of early cement paste hydration

A method for studying early stage hydration of cement paste is proposed. The method consists in freezing the specimens at specific times in liquid nitrogen at ?195°C. These are then vacuum dried and studied under scanning electron microscope. By this method the hydration can be stopped at any time and exactly the same structure of hydration products, which was present at the freezing time, can be studied under microscope. It is though that this method can be useful specially to study structure of the fresh cement paste. Chemical reactions (phase identification) in different ceramic materials at various stages may also be studied by this method.     

Onset Temperatures in Hot Wire Ignition of AN‐Based Emulsions

Hot wire ignition experiments were carried out recently at the Canadian Explosives Research Laboratory on a few emulsion formulations. The data indicate that there is a pressure‐dependent onset temperature beyond which the wire temperature increases at an accelerated rate. In order to explain this observation and to detect this temperature more consistently, particularly at low pressures, the data are reanalysed by comparing the experimental wire temperature with that predicted from theory for the heating of an inert material. For this purpose, an analytical theory from the literature is reviewed and the numerical solution developed in this report is described. The latter can deal with more general solutions with variable thermal properties and chemical reactions in the condensed medium surrounding the wire.     

企业建立总承包项目HSE培训体系的探讨

建筑业是一个高危行业,其HSE培训是安全管理工作的重点。针对目前国内总承包项目HSE培训工作中存在的问题与不足,文章提出建立企业总承包项目HSE培训体系,重点阐述了建立该体系需要落实的几项基础工作,并详实介绍了该体系运行流程,希望对规范企业总承包项目HSE培训有一定的借鉴意义。     

Mechanism of the enhanced spreading of some mixtures of anionic and cationic hydrocarbon chain surfactants on a highly hydrophobic polyethylene surface

The objective of this investigation was to measure the interfacial properties and interactions among mixtures of different cationic and anionic surfactants at the hydrophobic solid/aqueous solution interface to explain the different spreading factors or behavior of the mixed surfactants on a highly hydrophobic polyethylene (PE) film. A synergistic effect in the spreading of the mixed surfactant solutions on the PE film was observed when the surfactants were added sequentially. Other interfacial phenomena related to this surfactant spreading, such as interaction parameters at the solid/liquid (S/L) and liquid/air (L/A) interfaces in the mixtures adsorbed at various interfaces and dynamic contact angles of the mixed surfactant solutions during the process of spreading on the PE substrate, were investigated to obtain insight into this enhanced spreading. All the interaction parameters were more negative than −20, indicating very strong interaction between these cationic and anionic surfactants. The interaction parameters at the S/L interface were more negative than at the L/A interface, showing that the attractive interaction at the S/L interface was stronger than at the L/A interface. The spreading was related to the difference in the interaction parameters at the S/L and L/A interfaces and to the dynamic contact angle.     

New developments in corrosion and blister formation in coatings

Many polymers take up more water at equilibrium at higher temperatures than they do at lower temperatures. Water exposure with cycling temperatures can lead to excess free water when films saturated with water at a higher temperature are quenched or rapidly cooled. This mechanism has been called microfogging with soluble water exuded at lowered temperatures (SWEAT) being the undesired result. The water freed by this process can cause microcavities, blisters, and even total delamination. Means to counteract these failures include increasing permeation coefficients using micaceous iron oxide or other void-containing filler, for example. The intended incorporation of microvoids (microsponges) also allows the SWEAT water to collect in the coating without causing excess damage. A polymeric binder which dissolves the same amount of water at all temperatures would eliminate this effect at its source.     

Effect of high aspect ratio flaky aluminum on mechanical properties of epoxy-based particulate composites

Epoxy-based polymer composites are used in the aerospace industry due to high strength, less shrinkage, and ready availability. However, they are brittle and this limitation is usually addressed by using additives. Soft additives typically increase the toughness at the cost of stiffness and are usually not preferred for high strength applications. On the contrary, rigid additives such as carbon nanotubes (CNTs) and nanoclay increase the stiffness and tensile strength, but at the expense of strain at failure, indicating embrittlement. Also, these additives are expensive and this adds up to the overall product cost, limiting its application. Thus, this study aims to introduce a new low-cost, high aspect ratio additive that toughens epoxy without compromising on its strength. Tensile test and impact test were conducted to procure mechanical properties for the composite, along with fractography using electron microscopy. These tests revealed that this new additive increased the tensile strength, impact strength, and strain at failure by 56%, 60%, and 200% for a very low weight fraction of 0.5% of the additive.     

Quaternary reactive dyes containing a thioether‐ethylsulphone group. Part 2; Application methods for the dyeing of nylon†

A member of the new series of cationic reactive dyes containing a thioether‐ethylsulphone grouping referred to in Part 1 of this series has been applied to nylon at pH 3–10. The dye is water soluble and shows excellent substantivity for nylon 6.6 when dyed at the boil at pH 8–10. Under alkaline conditions, gradual β‐elimination back to the vinylsulphone dye occurs and covalent bond formation quickly takes place with the fibre; the higher the pH the more rapidly this occurs. Dyeings carried out at pH 10 showed very good brightness and levelling, together with good wash fastness. The light fastness of dyeings at moderate depth was 4–5 on the Blue Wool scale.     

Effect of calcination temperature on the low-temperature oxidation of CO over CoOx/TiO2 catalysts

A 5 wt% CoO_x/TiO₂ catalyst has been used to study the effect of calcination temperature on the activity of this catalyst for CO oxidation at 100 °C under a net oxidizing condition in a continuous flow type fixed-bed reactor system, and the catalyst samples have been characterized using TPD, XPS and XRD measurements. The catalyst after calcination at 450 °C gave highest activity for this low-temperature CO oxidation, and XPS measurements yielded that a 780.2-eV Co 2p_3/2 main peak appeared with this catalyst sample and this binding energy was similar to that measured with pure Co₃O₄. After calcination at 570 °C, the catalyst, which had possessed practically no activity in the oxidation reaction, gave a Co 2p_3/2 main structure peak at 781.3 eV which was very similar to those obtained for synthesized Co_nTiO_n+2 compounds (CoTiO₃ and Co₂TiO₄), and this catalyst sample had relatively negligible CO chemisorption as observed by TPD spectra. XRD peaks indicating only the formation of Co₃O₄ particles on titania surface were developed in the catalyst samples after calcination at temperatures ≥350 °C. Based on these characterization results, five types of Co species could be modeled to exist with the catalyst calcined at different temperatures. Among these surface Co species, the Type A clean Co₃O₄ particles were predominant on a sample of the catalyst after calcination at 450 °C and highly active for CO oxidation at 100 °C, and the calcination at 570 °C gave the Type B Co₃O₄ particles with complete Co_nTiO_n+2 overlayers inactive for this oxidation reaction.     

Graft polymerization of methyl methacrylate onto gelatin

In order to extend the application of grafting for the modification of natural polymers, the graft polymerization of methyl methacrylate onto gelatin by radical initiators was studied in aqueous solution at temperatures between 60°C and 80°C. Among the initiators used (peroxy-sulfates, α,α′-azobisisobutylonitrile, and benzoyl peroxide), potassium peroxysulfate was found to be the most efficient initiator in this particular graft polymerization. From the kinetic data with this initiator, it was shown that (1) efficiency of grafting is higher at lower temperature; (2) a sharp increase in the efficiency of grafting occurs at the later period of the polymerization at high temperature, which is attributable to the combination between homopolymer and backbone gelatin; and (3) generally, the number of branches was small and the molecular weight of the branch polymer was high in this polymerization.     

Oxidation of some reducing agents used in electroless plating baths at gold anodes in aqueous media

The oxidation of four reductants, two of direct interest in electroless plating baths, at gold electrodes in base was investigated using cyclic voltammetry and the results were interpreted in terms of the incipient hydrous oxide model of electrocatalysis. Dimethylamine borane and tert-butylamine borane reacted in a similar manner; the results were interpreted in terms of the oxidation of the hydroxytri-hydroborate anion; potential/pH studies indicate that the important mediator at the interface for this reaction is a cationic, Au(I), species. Pyridine borane reacted in a significantly different manner; the mediating species in this case appeared to be an Au(III) hydrous oxide; further work is required to explain the behaviour of this system. The oxidation of hypophosphite on gold in base was quite sluggish, as was the oxidation of hypophosphorous aicd at low potentials in solutions of low pH; it was assumed here that in this system there is a complication due to phosphorous atoms adsorbing at, and thus deactivating, the gold surface.     

The effect of various anti-setting systems in wool dyeing. Part 4; Sodium tetrathionate based systems

The tetrathionate anion has the potential to oxidise thiols specifically to disulphides; this property has been investigated in this paper from the point of view of using tetrathionate as an anti-setting agent in wool dyebaths. It was found that at pH 3 the addition of tetrathionate actually made the degree of permanent set greater than in its absence; however at pH 5 and pH 7 significant anti-setting benefits were achieved. The reason for the apparently contradictory result at pH 3 was found to be the substantivity and subsequent reactivity of thiosulphate anion for wool – this anion is a product of the reduction of tetrathionate by wool cysteinyl thiol residues.     

The volume adsorption capacity of activated carbon for selected trace contaminants

By measuring the time-dependent transmission of a trace contaminant gas through an adsorber bed, we obtained the volume adsorption capacity of (Columbia type 4 LXC 12/28) activated carbon at 25.0°C for four trace contaminants (acetaldehyde, ethanol, acetone and freon-113) each selected to represent an important class of organic compounds (i.e. aldehydes, primary alcohols, ketones and halocarbons). The transmission is the ratio of the concentration at the outlet of the adsorber bed to that at the inlet. Each measurement was carried out at a steady inlet concentration of about 100 ppm in helium at a total pressure of one atmosphere. Adsorption capacities at this low concentration can be determined more readily by this dynamic transmission method than by the conventional static method.     

Effects of pH and temperature on the sorption of sodium dodecyl sulfate by cellulose acetate/polyaniline blend membranes

Cellulose acetate/polyaniline (PANi) blends show a selective response to the presence of sodium dodecyl sulfate (SDS). Such detection can be monitored by visible absorption spectroscopy. In this article, we show how this is dependent on the pH and temperature. At pH 2, the redshift of the maximum absorbance wavelength of blend films is essentially dependent on hydrochloric acid; however, at pH 3, this effect clearly decreases, and at pH values between 4 and 6, the alteration of the blend color depends only on SDS. The selective detection of SDS is faster with a higher percentage of PANi in the blend. At 25°C, the mechanism of sorption is essentially Fickian for short times, but this changes at higher temperatures, and at temperatures of 40°C and higher, the sorption kinetics show an initial time lag in which no visible response from the blend to SDS is detected. The response rate of blends to SDS detection increases with the temperature and PANi content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electron-Beam-Induced Structural Variations of Divanadium Pentoxide (V2O5) at Liquid Helium Temperature

The electron-beam-induced changes in V₂O₅ crystals were investigated by means of electron microscopy at liquid helium temperature (4.2 K). We obtained high-resolution images of this system, but observed an amorphization process during a prolonged exposure to the electron beam. The average oxidation state of the amorphous phase was estimated to be about 4+. This phase was stable at room temperature, but a partial recrystallization occurs by further irradiation at room temperature and it can be reduced to VO. These observations are discussed with respect to the reduced diffusion rate of oxygen and lattice collapses at this very low temperature.     

Partial oxidation of butadiene on platinized Pt and Au anodes in acid aqueous solutions

At 30°C butadiene is only partially oxidized on Pt and Au anodes in H₂SO₄Na₂SO₄ solutions. On Pt, ethanol is the principal resulting substance at this temperature. On Au, tert-butyl alcohol and propanone are obtained at 30°C and a hydroxylated polymer, together with butanone, are produced at 70°C. Polarization curves run at this temperature and at 30°C allow some mechanistic conclusions: on Pt electrodes the role of surface must be recognized in analyzing this kind of reactions; on Au, it is suggested that hydration of butadiene must take place homogeneously prior to adsorption of the organic molecule.     

Conversion of N2O to N2 on TiO2(1 1 0)

In this study, we examine the interaction of N₂O with TiO₂(1 1 0) in an effort to better understand the conversion of NO_x species to N₂ over TiO₂-based catalysts. The TiO₂(1 1 0) surface was chosen as a model system because this material is commonly used as a support and because oxygen vacancies on this surface are perhaps the best available models for the role of electronic defects in catalysis. Annealing TiO₂(1 1 0) in vacuum at high temperature (above about 800 K) generates oxygen vacancy sites that are associated with reduced surface cations (Ti³⁺ sites) and that are easily quantified using temperature programmed desorption (TPD) of water. Using TPD, X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS), we found that the majority of N₂O molecules adsorbed at 90 K on TiO₂(1 1 0) are weakly held and desorb from the surface at 130 K. However, a small fraction of the N₂O molecules exposed to TiO₂(1 1 0) at 90 K decompose to N₂ via one of two channels, both of which are vacancy-mediated. One channel occurs at 90 K, and results in N₂ ejection from the surface and vacancy oxidation. We propose that this channel involves N₂O molecules bound at vacancies with the O-end of the molecule in the vacancy. The second channel results from an adsorbed state of N₂O that decomposes at 170 K to liberate N₂ in the gas phase and deposit oxygen adatoms at non-defect Ti⁴⁺ sites. The presence of these O adatoms is clearly evident in subsequent water TPD measurements. We propose that this channel involves N₂O molecules that are bound at vacancies with the N-end of the molecule in the vacancy, which permits the O-end of the molecule to interact with an adjacent Ti⁴⁺ site. The partitioning between these two channels is roughly 1:1 for adsorption at 90 K, but neither is observed to occur for moderate N₂O exposures at temperatures above 200 K. EELS data indicate that vacancies readily transfer charge to N₂O at 90 K, and this charge transfer facilitates N₂O decomposition. Based on these results, it appears that the decomposition of N₂O to N₂ requires trapping of the molecule at vacancies and that the lifetime of the N₂O–vacancy interaction may be key to the conversion of N₂O to N₂.     

冷氨泵汽化原因分析及最小流量校核计算

分析冷氨泵低速运行时打量突然下降的主要原因是由于泵打量过低,不足以将热量带走,液氨在泵的某一级或几级入口过热汽化造成的。根据机组已知的设计参数计算实际工况下冷氨泵在2608r／min转速运转时,为保证泵内液氨不汽化,散热所需的最小流量为13．54m^3／h。