Performance of the piezoelectric microbalance respirable aerosol sensor

A battery-portable respirable aerosol sensor has been experimentally evaluated. Calibration procedures are described. For instruments calibrated with welding smoke, test results show agreement within +/- 15% of parallel filter samples for 10 laboratory and industrial aerosols including welding and tobacco smoke, oil mist, cotton and asbestos mill dusts, powdered metal and walnut shell dusts, and atmospheric urban aerosol in the 0.05-5.5 mg/m3 range. Results show that an average of several piezobalance measurements can accurately simulate a time-integrated filter sample in many industrial environments.     

Laboratory investigation of the mass stability of sampling cassettes from inhalable aerosol samplers

A study was conducted to evaluate the mass stability of the materials used in the construction of samplers with internal cassettes for the gravimetric measurement of inhalable aerosol exposures. The internal cassettes from IOM samplers were studied. Results indicate that the mass stability of filters is uniform, but the mass stability of the cassette material may dramatically affect the results of the measurement. Cassettes constructed from plastic exhibited drastic shifts in mass depending on the environmental conditions of their storage. Under room humidity, the plastic cassettes absorbed 1 to 2 mg of water over several days. When these cassettes were placed in a desiccator, they lost mass consistently but did not approach a stable mass. Studies repeated with cassettes made of stainless steel showed negligible mass variability. Based on this study, the use of stainless steel cassettes is recommended for gravimetric determinations of aerosol exposure, although field blanks may in some cases be used for correction of data from plastic cassettes. This study shows the need to evaluate the mass stability of the cassette material of any sampling device where an internal cassette is weighed together with the filter.     

粉末烧结法制备开孔泡沫铝压缩性能的研究

采用粉末烧结工艺制备开孔泡沫铝并研究了其压缩性能，不同形态的尿素和氯化钠颗粒作为造孔剂使泡沫铝的孔隙度控制在70％。结果表明：粉末烧结法制备的泡沫铝呵以容易地控制孔隙度及孔径的大小，并且孔结构很好地保持了造孔剂的形状。不同的孔结构对泡沫铝的压缩性能具有显著影响，球形孔结构得到了最佳的压缩效果。     

Semi-empirical model for the aspiration efficiencies of personal aerosol samplers of the type widely used in occupational hygiene

This paper extends what it known about the aspiration efficiencies of blunt aerosol samplers at large angles and under 'orientation-averaged' conditions to the important case of personal samplers worn by workers. Attention is focused on three sampling devices which have particular relevance to industrial hygiene sampling in Britain, the United States and elsewhere. A semi-empirical model for aspiration efficiency is described, based on physical considerations of the nature of air and particle motion near an asymmetric sampling system, like that relevant to personal sampling. The resultant model contains a number of coefficients which are fitted by non-linear regression to experimental data sets which were available from previously published experiments for the three samplers in question. Agreement for all three data sets is good, with an overall Rcorr2 of 68%. Such semi-empirical models can be useful for predicting and interpreting sampler performance until practical versions of more rigorous mathematical and numerical models become available.     

Field testing of new aerosol sampling method with a porous curved surface as inlet

A new aerosol sampling method, utilizing a porous curved surface as the sampling inlet, has recently been developed. Previous laboratory evaluations of this method have demonstrated its important features, such as low wind sensitivity and good filter collection uniformity. In this study a prototype incorporating the new method was evaluated in the field as a stationary and personal sampling device. The small sampler, utilizing a 25-mm filter is called the button aerosol sampler and was evaluated for collecting total airborne dust and fungal spores. The study was performed in nine poorly maintained inner-city houses during environmental cleanups at different cleanliness levels. The button sampler was used in parallel with the standard 37-mm closed-face filter cassette. Four collocated samplers of each type were tested at all sites as stationary samplers, and three samplers of each type were tested at two sites as personal samplers. Aerosol samples were collected on filters and analyzed using the gravimetric method for total dust and epifluorescence microscopy for fungal spores. The average particle concentration values measured with the button sampler and with the standard sampling cassette were found to correlate well within ranges of 10(1)-10(3) micrograms/m3 for total dust and 10(3)-10(5) spores/m3 for airborne fungi. The measurement results obtained with the new button sampler showed lower intersample variations of the measured concentration levels and higher uniformity of the particle deposits on the filters than those obtained with the standard cassette.     

Surveillance of respirable crystalline silica dust using OSHA compliance data (1979-1995)

BACKGROUND: The objective of this work was to estimate the percentage of workers by industry that are exposed to defined concentrations of respirable crystalline silica dust. METHODS: An algorithm was used to estimate the percentage of total workers exposed to crystalline silica in 1993 at concentrations of at least 1, 2, 5, and 10 times the National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL) of 0.05 mg/m3. Respirable crystalline silica air sampling data from regulatory compliance inspections performed by the Occupational Safety and Health Administration (OSHA), for the years 1979-1995, and recorded in the Integrated Management Information System (IMIS) were used to estimate exposures. Therefore, this work does not include industries such as mining and agriculture that are not covered by OSHA. The estimates are stratified by Standard Industrial Classification (SIC) codes. RESULTS: This work found that some of the highest respirable crystalline silica dust concentrations occurred in construction (masonry, heavy construction, and painting), iron and steel foundries (casting), and in metal services (sandblasting, grinding, or buffing of metal parts). It was found that 1.8% (13,800 workers) of the workers in SIC 174--Masonry, Stonework, Tile Setting, and Plastering--were exposed to at least 10 times the NIOSH REL. For SIC 162--Heavy Construction, Except Highway and Street Construction--this number is 1.3% (6,300 workers). SIC 172--Painting and Paper Hanging--which includes construction workers involved in sandblasting was found to have 1.9% (3,000 workers) exposed to at least 10 times the NIOSH REL. The industry that was found to have the highest percentage of workers (6%) exposed to at least the NIOSH REL was the cut stone and stone products industry. CONCLUSION: Not enough is being done to control exposure to respirable crystalline silica. Engineering controls should be instituted in the industries indicated by this work.     

Comparison of recommended respirable mass dust sampling devices

The draft, "Revised Guide for Respirable Mass Sampling," prepared by the AIHA-ACGIH Aerosol Hazards Committee, recommends five respirable mass sampling devices that sample in accordance with the "Los Alamos" respirable dust criterion. The spectrum of recommended sampling rates for these devices ranges from 1.8 to 430. liters per minute. A study was conducted to determine if simultaneous measurements with these devices yielded comparable respirable mass concentrations. The penetration characteristics of the first stage separators were also evaluated and compared.     

MAX phase foams produced via powder metallurgy process using water soluble space holder

Abstract

There have been few systematic studies of the fabrication and properties of porous MAX phase microstructures despite the potential applications of these materials. A simple, low cost, eco-friendly PM method has been developed to prepare MAX phase foams from commercial Ti₂AlC powder, using crystalline carbohydrate as space holder. This method involves: mixing Ti₂AlC powder with crystalline carbohydrate, pressing to form a green body, removal of the space holder and sintering. Compaction was achieved by uniaxial pressing (UP) and cold isostatic pressing (CIP). Control of porosity was achieved by varying the particle size (three ranges between 250 and 1000?μm), and volume fractions (20, 40 and 60%) of space holder. The foams were characterised and the porosity compared with the expected values. Optimal conditions for this novel processing technique were established with the aim of controlling the final microstructures and properties of the Ti₂AlC foams.     

Flow visualisation study in porous media using X-rays

An X-ray technique has been developed to visualise the fluid flow behaviour in three-phase packed column. It can be used in both static and transient conditions. This technique is capable of differentiating between various liquids or solids or both. It can be used to visualise the flow in one, two or three dimensions. The technique has been used to study the complex flow behaviour of fluid (rivulets/droplets/film formation, dispersion, etc.) in a porous medium in both static and dynamic conditions. It is shown that X-ray is a powerful and simple tool for visualisation and is very useful in research.     

Calculation of dendrite settling velocities using a porous envelope

The convective transport and gravitational settling of unattached equiaxed grains and dendrite fragments can cause macrosegregation and influence the structure of the equiaxed zone in a variety of solidification arrangements. An understanding of how the highly nonspherical geometry of the dendrite influences its settling and transport characteristics is needed to determine the motion of unattached dendrites and predict structure and segregation in castings. The empirical results of previous works have been used to develop a FORTRAN 77 computer program to calculate the settling velocity of various dendritic shapes and a number of other parameters of interest, such as the volume and surface area of the dendrite. Required inputs to the code are the physical properties of the system and some simple geometric parameters of the dendrite being considered, such as the average radius of the primary arm. The predicted settling velocities were on average within ±5 pct of those measured for model dendrites and were consistent and in good agreement with three other experimental investigations. Future development of the code will attempt to overcome many of its present limitations by including particle-particle interactions and the effects of tertiary arms, for example. Formerly Graduate Student at the University of Iowa.     

Reconstruction of saddle nose deformities using porous polyethylene implant

Background: Troglitazone is a new drug for the treatment of type 2 diabetes. Although mild liver injury occurred in 1.9% of participants in controlled trials, the U.S. Food and Drug Administration has received reports of five postmarketing cases of severe liver disease that resulted in death or liver transplantation. OBJECTIVE: To report the clinical and histopathologic characteristics of a patient with troglitazone-associated severe liver injury leading to transplantation. DESIGN: Case report. SETTING: Two university hospitals. PATIENT: A 55-year-old woman taking troglitazone, 400 mg/d, and insulin, 120 U/d. INTERVENTION: Discontinuation of troglitazone therapy, pretransplantation liver biopsy, and liver transplantation. RESULTS: Early nonspecific symptoms were attributed to other causes and were not evaluated. After the patient had used troglitazone for 3.5 months, massive loss of liver parenchyma and symptoms of liver failure developed, necessitating liver transplantation. CONCLUSION: Troglitazone may cause subfulminant liver failure.     

Pharmacokinetic/pharmacodynamic aspects of aerosol therapy using glucocorticoids as a model

Glucocorticoids are predominantly prescribed in asthma therapy as aerosols to achieve high pulmonary effects with reduced systemic spill-over and pronounced pulmonary selectivity. A variety of pharmacokinetic parameters are potentially important for determining pulmonary selectivity. The intent of this article, is to provide a practice-relevant theoretical approach to put the importance of these parameters on pulmonary targeting using pharmacokinetic/pharmacodynamic modeling as a tool in perspective. The applied pulmonary pharmacokinetic/pharmacodynamic model revealed that, in addition to recognized parameters such as systemic clearance, oral bioavailability, and efficiency of pulmonary deposition, other factors, such as the pulmonary release (dissolution) rate and dose, are relevant. However, the volume of distribution (for effect parameters not undergoing a diurnal rhythm) and the receptor affinity of a given glucocorticoid are not important for achieving lung targeting.     

Clinical pulmonary tuberculosis in an asthmatic patient using a steroid aerosol

A patient who was receiving a steroid aerosol for treatment of asthma developed clinical pulmonary tuberculosis. Continued administration of the steroid aerosol along with antituberculosis chemotherapy did not adversely influence healing of the pulmonary lesion.     

The deformation of aluminum foams

The compressive flow behavior of Al, Al-7 pct Mg and 7075 Al alloy foams has been determined in structures whose void fraction varies from 0.80 to 0.95 of the total volume. In all cases, a greater than linear increase in flow strength with increase in density was exhibited, indicating that bending stresses within the foam structure are an important feature of the collapse mode. The flow strength did not follow proportionately changes in bulk flow strength in comparisons of either alloy or of heat-treatment conditions. Ancillary tensile and metallographic observations show that this lack of correlation arises because the different foams collapse by different modes with localized fracture becoming dominant in the higher strength 7075 alloy. The energy absorbing efficiency was found to be independent of foam density for all the materials. However, the efficiency was found to be a strong function of the alloy and heat treatment increasing from about 30 pct in Al, to 43 pct in Al-7 pct Mg and to 50 pct in the solution heat treated and aged 7075 alloy. The increase in efficiency occurs because of an increase in the propensity to fracture in the higher strength alloys which introduces the potential for a propagating constant-stress collapse process.     

Fracture toughness of brittle foams

Existing models for the fracture toughness of brittle cellular materials have two limitations: the crack is assumed to be large relative to the cell size and the modulus of rupture of the cell wall material is assumed to be constant. In the previous companion paper, we reanalyzed the fracture toughness using a finite element analysis for short cracks and assuming that the modulus of rupture of the cell wall material followed a Weibull distribution. The finite element analysis gave a reduction factor for the effective fracture toughness for short cracks which was independent of the cell geometry. The Weibull analysis showed that the effect of cell size on the fracture toughness of brittle honeycombs is dependent upon the Weibull modulus of the cell wall material. We now apply similar ideas to the analysis of the fracture toughness of brittle foams.     

Creep of aluminum-based closed-cell foams

Metal foams creep when loaded mechanically at high homologous temperatures. We have studied the creep behavior of closed-cell aluminum-based foams with relative densities of 0.092, 0.112, and 0.163. Compressive creep tests were performed at 300 °C at strain rates ranging from 10⁻⁹ to 10⁻⁴ s⁻¹. Special efforts were made to produce and characterize a bulk reference material exhibiting the same chemical composition. Results show that the foams exhibit a lower creep strength and a higher stress exponent than predicted by the Gibson-Ashby model for regular foams. The possible mechanisms responsible for this deviation are discussed. A semi-empirical rate equation is established which describes the experimental data well.     

The Deformation of aluminum foams

The compressive flow behavior of Al, Al−7 pct Mg and 7075 Al alloy foams has been determined in structures whose void fraction varies from 0.80 to 0.95 of the total volume. In all cases, a greater than linear increase in flow strength with increase in density was exhibited, indicating that bending stresses within the foam structure are an important feature of the collapse mode. The flow strength did not follow proportionately changes in bulk flow strength in comparisons of either alloy or of heat-treatment conditions. Ancillary tensile and metallographic observations show that this lack of correlation arises because the different foams collapse by different modes with localized fracture becoming dominant in the higher strength 7075 alloy. The energy absorbing efficiency was found to be independent of foam density for all the materials. However, the efficiency was found to be a strong function of the alloy and heat treatment increasing from about 30 pct in Al, to 43 pct in Al−7 pct Mg and to 50 pct in the solution heat treated and aged 7075 alloy. The increase in efficiency occurs because of an increase in the propensity to fracture in the higher strength alloys which introduces the potential for a propagating constant-stress collapse process.     

Estimation of porous media flow functions using NMR imaging data

Nuclear magnetic resonance (NMR) imaging data measured during two-phase displacement experiments on porous rock core samples are used in an inverse problem methodology to estimate the two-phase flow functions relative permeability and capillary pressure. Nuclear magnetic resonance imaging data contain valuable information about variation of fluid states within the core sample and are therefore important for accurate estimation of these properties. A precise agreement between measured data, which also includes pressure drop across the core samples, and the data simulated by using the estimated flow functions is found, indicating accurate flow function estimates.     

Stiffness variation of porous titanium developed using space holder method

Abstract

The excellent properties of Ti have resulted in its generalised use for bone implants. However, Ti is very stiff in comparison with human cortical bone, and this creates problems of bone weakening and loosening of the implant. This article discusses the mechanical properties (flexural and compressive strength, and stiffness) of porous Ti–6Al–4V specimens developed using the space holder method. These properties are examined relative to the production process parameters: compacting pressure and sintering time, as well as temperature, and the addition of spacer and its particle size. It is seen that when spacer is added, compressive strength decreases with the application of compacting pressure and that these are the most influential parameters. The developed pieces show a closed and unconnected porosity. Small additions of spacer (25 vol.-%) reduce stiffness to around half of that shown by the solid material, and the resulting pieces are strong enough to be used as bone substitute.