An algorithm for real-time tomography of gas concentrations,using prior information about spatial derivatives

We present a new computed tomography method, the low third derivative (LTD) method, that is particularly suited for reconstructing the spatial distribution of gas concentrations from path-integral data for a small number of optical paths. The method finds a spatial distribution of gas concentrations that (1) has path integrals that agree with measured path integrals, and (2) has a low third spatial derivative in each direction, at every point. The trade-off between (1) and (2) is controlled by an adjustable parameter, which can be set based on analysis of the path-integral data. The method produces a set of linear equations, which can be solved with a single matrix multiplication if the constraint that all concentrations must be positive is ignored; the method is therefore extremely rapid. Analysis of experimental data from thousands of concentration distributions shows that the method works nearly as well as smooth basis function minimization (the best method previously available), yet is about 100 times faster.     

A mass transfer based method for measuring the reaction coefficients of a photocatalyst

We have developed a new method, the mass transfer based (MTB) method, for measuring the Langmuir–Hinshelwood (L–H) rate form reaction coefficients of photocatalysts. The conventional method for determining the reaction coefficients disregards the effect of mass transfer on the reaction surface by designing and controlling a reaction process to be reaction-limited. In contrast, the new MTB method takes the mass transfer effect into account by using a computational fluid dynamics (CFD) method. The reaction coefficients can be regressed by the measured reaction rates and the calculated VOC concentrations in the air adjacent to the reaction surface. Thus, by using the new method, the reaction coefficient of a reaction process can be accurately determined even if it is not reaction-limited. This is very important in cases where it is difficult to realize reaction-limited processes, such as photocatalytic oxidation of VOCs with strong UV radiation intensity. The relative error of the regressed reaction coefficients obtained by the new method is analyzed. To illustrate, we apply this method to measuring the reaction coefficients of TiO₂ photocatalytic decomposing formaldehyde. This method is very useful in determining the reaction coefficients of the photocatalytic oxidation of various VOCs simultaneously.     

A new method for determining concentrations of Endod-S (Phytolacca dodecandra) in water during mollusciciding

A hemolytic method was developed for the quantitative determination of oleanane saponin (Endod-S) in Phytolacca dodecandra (Phytolaccaceae), a plant with potent molluscicidal properties. A chemical method based on thin-layer chromatography (TLC) was used as a control for comparison with a hemolysis test. Standard curves for calibration of both tests of Endod-S gave high correlation coefficients. The hemolysis method gave a correlation coefficient of 0.98 for saponin (Endod-S) levels ranging from 1.6 to 4.2 mg/l. The TLC method gave a correlation coefficient of 0.99 for saponin levels above 1.5 micrograms. Due to the action of saponins on erythrocytes, the hemolysis method could not be used at levels below 1.6 and above 4.2 mg/l. Similarly, sample size limited TLC quantitation of these saponins at levels below 1 microgram. Both the TLC and the hemolysis methods on identical Endod-S water samples gave comparable results at saponin levels between 2 and 6 mg/l. A snail bioassay showed that the LC50 and the LC90 concentrations of Endod-S to the snail Biomphalaria glabrata (albino) were 2.57 and 2.92 mg/l respectively. These values fell in the standard curve range for the hemolysis method thus indicating that the hemolysis method is of practical value for testing Endod-S concentrations that would actually be used in field applications for snail control. The hemolysis method is less expensive than TLC and can be easily adapted to field conditions.     

一种活性污泥总DNA提取方法的优化

对3种活性污泥DNA提取方法———传统蛋白酶K-SDS-氯仿异戊醇法(CPSCI法)、液氮研磨法和脱腐处理法进行了对比,并针对CPSCI法从污泥量、保温时间、裂解方式及沉淀时间等4个方面进行了优化。结果表明,优化的蛋白酶K-氯仿-异戊醇法(OPSCI法)采用污泥量0.10 g、37℃静置10 min,加SDS常温旋涡振荡及异丙醇直接离心等条件可获得长度在23.1 kb左右的DNA,OD260nm/OD280nm为1.86,稀释10倍后即可进行16S rDNA PCR。该方法重复性好,提取得率高,纯度好,操作简便,为常规实验室开展活性污泥微生物多样性研究提供了帮助。     

The Hygienic Aspects of the Production and Use of Lead Antiknock Compounds

Hydrogen sulfide and other sulfides can be determined in the part per billion range in air if the air is bubbled through an absorption mixture of an alkaline suspension of cadmium hydroxide contained in a macro impinger. Rates as high as 1 cubic foot per minute can be used, or 0.1 cubic foot per minute with a midget impinger. The concentration of the trapped sulfides is then estimated by the methylene blue method. A colorimetric method and a spectrophotometric method are described.     

水质模型参数识别的遗传算法

Ｏ’ｃｏｎｎｏｒ模型是一个比广泛应用的Ｓｔｒｅｅｔｅｒ－Ｐｈｉｌｉｐｓ模型更精确的水质模型,由于该模型参数率定的困难性,限制它在实际中应用。     

Fluorophotometric Determination of Trace Amounts of Atmospheric Ozone

This work was initiated in an effort to obtain a better method for the manual determination of trace amounts of atmospheric ozone. The method described depends upon the fact that ozone oxidizes nonfluorescent 9, 10-dihydroacridine to fluorescent acridine. When the ethyl alcohol solution of acridine is acidified by 6N acetic acid, the fluorescence maximum occurs approximately at 482 mμ and its intensity is sufficiently strong to be useful in this analysis. Linear relationships between acridine concentrations and fluorescence intensities were obtained from 0.1 to 3.5 μg per ml. by measurement with a commercial fluorophotometer. The results indicated that the low concentrations of experimentally prepared ozone measured by this method were in good agreement with those obtained by the phenolphthalin method. This method appeared to be about twice as sensitive as the phenolphthalin method, but it is subject to some interference from nitrogen dioxide.     

Validation of an evacuated canister method for measuring part-per-billion levels of chemical warfare agent simulants

The National Institute for Occupational Safety and Health (NIOSH) research on direct-reading instruments (DRIs) needed an instantaneous sampling method to provide independent confirmation of the concentrations of chemical warfare agent (CWA) simulants. It was determined that evacuated canisters would be the method of choice. There is no method specifically validated for volatile organic compounds (VOCs) in the NIOSH Manual of Analytical Methods. The purpose of this study was to validate an evacuated canister method for sampling seven specific VOCs that can be used as a simulant for CWA agents (cyclohexane) or influence the DRI measurement of CWA agents (acetone, chloroform, methylene chloride, methyl ethyl ketone, hexane, and carbon tetrachloride [CCl4]). The method used 6-L evacuated stainless-steel fused silica-lined canisters to sample the atmosphere containing VOCs. The contents of the canisters were then introduced into an autosampler/preconcentrator using a microscale purge and trap (MPT) method. The MPT method trapped and concentrated the VOCs in the air sample and removed most of the carbon dioxide and water vapor. After preconcentration, the samples were analyzed using a gas chromatograph with a mass selective detector. The method was tested, evaluated, and validated using the NIOSH recommended guidelines. The evaluation consisted of determining the optimum concentration range for the method; the sample stability over 30 days; and the accuracy, precision, and bias of the method. This method meets the NIOSH guidelines for six of the seven compounds (excluding acetone) tested in the range of 2.3-50 parts per billion (ppb), making it suitable for sampling of these VOCs at the ppb level.     

A method for predicting the performance of packed columns operating with a reactive scrubbing liquid that control gaseous air pollutants

A method for predicting the performance of packed columns that control gaseous air pollutants has been developed that exploits the advances in both computer software and hardware commonly used by practicing engineers. The solution of the simultaneous partial differential equations that describe the absorption process in packed columns that occurs in the presence of chemical reaction is obtained by converting the partial differential equations to systems of ordinary differential equations. These systems of ordinary differential equations are then solved using the method of lines along with a variable step, variable order numerical method. The method is applicable to systems in which there are multiple reactions within the liquid phase. The reactions can be of any order and can be reversible. The programming is simple and the machine running time is minimal. The method is illustrated here with an example.     

HPLC-screening method for the determination of the adsorption-coefficient on soil-comparison of different stationary phases

The application of a HPLC method for the determination of soil sorption constants was tested and validated. Different stationary and mobile phases including buffer solutions were compared using a large set of reference substances from different chemical classes. Cyanopropyl columns turned out to be the most suitable. The results show that the investigated HPLC method provides a quick and reliable method to determine the sorption constants.     

Convenient dioxin measuring method using an efficient sampling train, an efficient HPLC system and a highly sensitive HRGC/LRMS with a PTV injector

An efficient sampling method for dioxins from flue gas, an efficient automatic purification and fractionation method by a new HPLC system using a sulfuric acid-silica/silica column, a Nitro column and a PGC column, and sensitive determination method by an economical HRGC/LRMS using a programmable temperature vaporization (PTV) injector were developed. It was confirmed that the dioxins could be easily collected by the proposed simple sampling train consisting of only two bottles, and the extracted sample could be purified sufficiently and separated as mono-ortho PCBs, non-ortho PCBs and PCDDs/PCDFs completely with the proposed HPLC system. The peak areas of GC/MS were increased linearly with the injection volume up to 40 microl by the PTV technique, and the sensitivity could be increased to 20 times higher than usual. This convenient measuring method can drastically reduce operation time, consumption of hazardous solvent and cost.     

Changes in pesticide adsorption with time at high soil to solution ratios

Adsorption of six pesticides (2,4-D, dicamba, fluroxypyr, fluazifop-P, metsulfuron-methyl and flupyrsulfuron-methyl) in nine contrasting soils was measured using two techniques: (i) a classical batch method and (ii) a centrifugation method that allowed the measurement of adsorption at a realistic soil to solution ratio after one and seven days. Although the batch method gived significantly higher values of Kd than the centrifugation method for the more strongly sorbed molecules in the more sorptive soils, it tended to give lower adsorption coefficients compared to the centrifugation method when adsorption was lower. Discrepancies between the two methods were probably mainly due to the vigorous shaking applied in the batch technique that artificially enhances the availability of adsorption sites. This implies that shortly after application, more pesticide may be present in the soil solution and thus be available for degradation, plant uptake or leaching than will be predicted from adsorption coefficient determined using the batch method. Adsorption significantly increased between one and seven days and the extractability of total residues decreased with time. The increase in adsorption was not directly related to the level of adsorption although it was more important in soils containing more organic carbon (p=0.022). These results confirm the importance of time-dependent processes and the necessity to include them in risk assessment procedures. The centrifugation technique is a useful method to measure adsorption of pesticides at realistic soil moisture contents and seems to be an adequate technique to characterise the fraction of pesticide that is available for leaching at a given time after application.     

A Method for Predicting the Performance of Packed Columns Operating with a Reactive Scrubbing Liquid That Control Gaseous Air Pollutants

Abstract

A method for predicting the performance of packed columns that control gaseous air pollutants has been developed that exploits the advances in both computer software and hardware commonly used by practicing engineers. The solution of the simultaneous partial differential equations that describe the absorption process in packed columns that occurs in the presence of chemical reaction is obtained by converting the partial differential equations to systems of ordinary differential equations. These systems of ordinary differential equations are then solved using the method of lines along with a variable step, variable order numerical method. The method is applicable to systems in which there are multiple reactions within the liquid phase. The reactions can be of any order and can be reversible. The programming is simple and the machine running time is minimal. The method is illustrated here with an example.     

A method for determining pyrene in mucus using synchronous fluorimetry with multiple standard additions

A new method was proposed to determine pyrene in mucus, which combined the synchronous fluorimetry with the multiple standard addition method (SFMSA). The method was used to determine pyrene in mucus directly without pretreatment. The method detection limit (MDL) for pyrene in mucus was measured as 0.47 ng/ml with a relative standard deviation of 12.7% (n = 7). The standard addition graph was linear in the range 0.05-50.00 ng/ml (r(2) = 0.9989). SFMSA was validated using a GC/MS method as a reference method, and nice agreement was found. The pyrene in mucus can be directly monitored by SFMSA without solvent extraction of samples. This indicates that SFMSA is more timesaving, less laborious and cheaper than the GC/MS method with solvent extraction. SFMSA has lower MDL and higher average recovery than the GC/MS method.     

The relationship between flow and bacteria in streams

A method is proposed to relate the statistics of in-stream bacteria concentrations to the surface-runoff fraction of stream flow. The parameters of this relationship include the characteristic concentration of bacteria in surface runoff and the characteristic concentration of bacteria in the base flow, and these parameters can be derived from synoptic bacteria and flow measurements. The effectiveness of the proposed method is demonstrated at several U.S. locations for both Escherichia coli and fecal coliform bacteria. Application of the proposed method at a particular location showed that the method can be used to identify the most effective bacteria source controls and that conventional application of the load-duration curve might lead to erroneous identification of target sources.     

Modelling radionuclide transport for time varying flow in a channel network

Water flowrates and flow directions may change over time in the subsurface for a number of reasons. In fractured rocks flow takes place in channels within fractures. Solutes are carried by the advective flow. In addition, solutes may diffuse in and out of stagnant waters in the rock matrix and other stagnant water regions. Sorbing species may sorb on fracture surfaces and on the micropore surfaces in the rock matrix. We present a method by which solute particles can be traced in flowing water undergoing changes in flowrate and direction in a complex channel network where the solutes can also interact with the rock by diffusion in the rock matrix. The novelty of this paper is handling of diffusion in the rock matrix under transient flow conditions. The diffusive processes are stochastic and it is not possible to follow a particle deterministically. The method therefore utilises the properties of a probability distribution function for a tracer moving in a fracture where matrix diffusion is active. The method is incorporated in a three dimensional channel network model. Particle tracking is used to trace out a multitude of flowpaths, each of which consists of a large number of channels within fractures. Along each channel the aperture and velocity as well as the matrix sorption properties can vary. An efficient method is presented whereby a particle can be followed along the variable property flowpath. For stationary flow conditions and a network of channels with advective flow and matrix diffusion, a simple analytical solution for the residence time distribution along each pathway can be used. Only two parameter groups need to be integrated along each path. For transient flow conditions, a time stepping procedure that incorporates a stochastic Monte-Carlo like method to follow the particles along the paths when flow conditions change is used. The method is fast and an example is used for illustrative purposes. It is exemplified by a case where land rises due to glacial rebound. It is shown that the effects of changing flowrates and directions can be considerable and that the diffusive migration in the matrix can have a dominating effect on the results.     

A column method for determination of leaching of polycyclic aromatic hydrocarbons from aged contaminated soil

In this study a column leaching method for investigation of hydrophobic organic contaminants (HOCs) leaching from soil was developed. The method set-up is based on a recycled flow of sterile water through a soil column with a sedimentation chamber mounted on top of the column, in connection with on-line filtration. The combination of a sedimentation chamber and an on-line filtration enables the measurement of leaching concentrations from contaminated materials consisting of very fine particle fractions. In addition, by using on-line solid phase extraction, minute amounts of leaching HOCs may be captured and quantified with high accuracy and reproducibility. The method was applied successfully on a contaminated aged soil sample and the leaching behavior of seven PAHs, with three to six aromatic rings, was monitored for more than 1600 h under saturated conditions. The tested PAHs were fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)pyrene and benzo(ghi)perylene. The method proved to be reliable and capable of providing data on leachable amounts of the PAHs under field-like conditions and over a longer period of time. The results indicated low availability of the studied contaminants since only a minor fraction (0.3%) of the initial amount of PAHs in the soil was removed during the experiment (liquid/solid-ratio of 700 l/kg). Thus PAHs in aged contaminated soil are not to be expected to be released to any great extent only by leaching with water.     

Steady-state modelling of hydroxyl radical concentrations at Mace Head during the EASE ’97 campaign,May 1997

Two different steady-state methods are applied to calculate OH radical concentrations based on the rates of known source and sink processes. The first method, which calculates only OH radical concentrations from measured data including HO₂ gives good correlation with measured OH concentrations but overpredicts by 30%. The second method applied calculates OH, HO₂ and RO₂ radical concentrations simultaneously. This second method overestimates the measured concentrations of OH by almost 3 times. This apparent overprediction may be a result of calculated concentrations of HO₂ which appear too high and may be indicative of a gap in our understanding of the relevant peroxy radical chemistry or a result of the limited peroxy radical chemistry assumed by the method.     

A Filter Test Method For Rapid Weight Distribution Of Dust in Gas Streams To Evaluate Dust Collectors

The purpose of this paper is to describe a simple gravimetric test method that was used as a field tool to diagnose variations and malfunctions in dust collector performance. This method is not considered a replacement for accepted standard test methods for stacks.^1,2,3 Nevertheless, the reproducibility, ease, and value of this short term monitor test method over a two year period, covering over 1000 tests suggest that this method may be used effectively in the field.

The article published below is a condensed version of a paper (67-117) presented at 1967 Annual Meeting.     

Through-electromigration: a new method of investigating pore connectivity and obtaining formation factors

The retardation of radionuclides and other contaminants in fractured crystalline rock is strongly associated with the diffusive properties of the rock matrix. At present, the scientific community is divided concerning the question of long-range pore connectivity in intrusive igneous rock. This paper presents a fast new method, called the through-electromigration method, of obtaining formation factors and investigating pore connectivity. The method involves the migration of an ionic tracer through a rock sample with an electrical potential gradient as the main driving force. The method is analogous to the through-diffusion method but the experimental time is reduced by orders of magnitude. This enables investigations of pore connectivity, as measurements can be made on longer samples. In a preliminary investigation, the new method is compared to the traditional through-diffusion method as well as to rock resistivity methods. The diffusive properties of nine granitic rock samples from Laxemar in Sweden, ranging from 15 to 121 mm in length, have been investigated and the results are compared.