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PubMed1998

Effect of initiator concentration, exposure time and particle size of the filler upon the mechanical properties of a light-curing radiopaque dental composite.

Concentration of camphorquinone initiator, exposure time of the light source and particle size of a radiopaque glass filler have been varied for an indigenously developed light-curing dental composite and the changes in the microhardness, compressive strength and diametral tensile strength studied. Higher initiator concentration and exposure times are found to improve the microhardness values while a concentration above 0.25% does not signify any drastic improvement in compressive and diametral strength. Changes in properties are found to be statistically significant at low initiator concentrations. A filler particle size around 1 microm is found to give better properties compared with larger sizes.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1996

Development of methanogenic consortia in fluidized-bed batches using sepiolite of different particle size.

The addition of support materials, such as sepiolite, to fluidized-bed anaerobic digesters enhances the methane production by increasing the colonization by syntrophic microbiota. However, the efficiency in the methanogenesis depends on the particle size of the support material, the highest level of methane production being obtained by the smaller particle size sepiolite. Because of the porosity and physico-chemical characteristics of these support materials, the anaerobic microbial consortia formed quickly (after one week of incubation). The predominant methanogenic bacteria present in the active granules, detected both by immunofluorescence using specific antibodies and by scanning electron microscopy, were acetoclastic methanogens, mainly Methanosarcina and Methanosaeta.

Anaerobiosis↗

PubMed2004

An improvement on the power law for the description of particle size distributions in potable water treatment.

In potable water treatment, the use of the power law to describe particle size distributions (PSDs) in particle counting practice is common. The power law is popular because it allows the reduction of numerous data bits to two meaningful parameters that completely describe the size distribution characteristics of a particle suspension. The model is however flawed. This paper presents the further development of an improved model (the variable-beta model) first proposed by Lawler (1997). Both the power law model and variable-beta model are used to describe the PSDs of a large number of potable water treatment samples taken from full-scale plants and the resulting correlations are compared. The findings from the comparison of data reduction methodologies support the argument that the variable-beta model is fundamentally more correct than the power law model and consequently describes the PSDs better.

Filtration↗

PubMed2005

Modulation of surface charge, particle size and morphological properties of chitosan-TPP nanoparticles intended for gene delivery.

This work investigates the polyanion initiated gelation process in fabricating chitosan-TPP (tripolyphosphate) nanoparticles in the size range of 100-250 nm intended to be used as carriers for the delivery of gene or protein macromolecules. It demonstrates that ionic gelation of cationic chitosan molecules offers a flexible and easily controllable process for systematically and predictably manipulating particle size and surface charge which are important properties in determining gene transfection efficacy if the nanoparticles are used as non-viral vectors for gene delivery, or as delivery carriers for protein molecules. Variations in chitosan molecular weight, chitosan concentration, chitosan to TPP weight ratio and solution pH value were examined systematically for their effects on nanoparticle size, intensity of surface charge, and tendency of particle aggregation so as to enable speedy fabrication of chitosan nanoparticles with predetermined properties. The chitosan-TPP nanoparticles exhibited a high positive surface charge across a wide pH range, and the isoelectric point (IEP) of the nanoparticles was found to be at pH 9.0. Detailed imaging analysis of the particle morphology revealed that the nanoparticles possess typical shapes of polyhedrons (e.g., pentagon and hexagon), indicating a similar crystallisation mechanism during the particle formation and growth process. This study demonstrates that systematic design and modulation of the surface charge and particle size of chitosan-TPP nanoparticles can be readily achieved with the right control of critical processing parameters, especially the chitosan to TPP weight ratio.

Animals↗

PubMed2003

Shear punch strength and flexural strength of model composites with varying filler volume fraction, particle size and silanation.

OBJECTIVE: The effect of filler volume fraction, particle size and silanation on shear punch strength, flexural strength and flexural modulus of model composites has been evaluated. METHODS: Hybrid type glass filled (0-65.2 vol%), composites some without filler silanation (30.7-51.0 vol%) and microfilled type (0-13.0 vol%) resin matrix (UDMA and EGDMA) composites (Shofu Inc., Japan) were used in the study. For the shear punch test, 10 disc specimens, 0.5mm thick and 9 mm diameter, were prepared for each composite and tested with a 3.2mm dia punch at 1.0mm/min. Flexural strength (n=10) was measured by the method outlined in ISO 4049. Data were analyzed using ANOVA and Fisher's multiple-range test. RESULTS: Shear punch strength and flexural strength increased with increasing filler content up to 52.2% for hybrid composites and between 0 and 9.1% for microfilled composites. Shear punch strength and flexural strength decreased with increasing filler volume fraction for un-silanated composites. Flexural modulus for all materials increased with increasing filler volume fraction. Hybrid composites with silanated fillers have significantly higher values of flexural strength, flexural modulus and shear punch strength than equivalent materials with un-silanated fillers. SIGNIFICANCE: The results showed that filler silanation is an important factor for determining material strength. Additions of small quantities of microfillers appeared to have a greater effect on shear strength than equivalent amounts of hybrid filler. The shear punch test may prove beneficial for routine testing of composites as specimen preparation was simple, specimen quality was easy to maintain and the results are meaningful.

Analysis of Variance↗

PubMed1985

Lipoprotein substrates for plasma cholesterol esterification. Influence of particle size and composition of the high density lipoprotein subfraction 3.

Subpopulations of lipoproteins within the high density lipoprotein subfraction 3 (HDL3) have been isolated from human plasma and characterized in terms of their chemical composition and particle size. Since HDL3 are the major substrates for the esterification of plasma cholesterol, and thus play a central role in the transport of cholesterol through the plasma, these studies also examined the relative capacities of different HDL3 subpopulations to interact with lecithin: cholesterol acyltransferase. Substrate reactivity of a given preparation of lipoproteins was defined in terms of the Vmax of the cholesterol esterification reaction in incubations containing a fixed amount of human lipoprotein-free plasma as a source of the enzyme. Substrate reactivity was found to correlate inversely with the radius of HDL3 particles. This inverse relationship between particle size and substrate reactivity was independent of the particle content of cholesteryl ester.

Adult↗

PubMed2000

Particle size of solid food after human mastication and in vitro simulation of oral breakdown.

Mastication, the first step in food digestion, results in the breakdown of solid food and its lubrication with saliva. Although the rate and extent of starch digestion are closely dependent on the way food is chewed, this factor has not been adequately considered in the preparation of food for in vitro digestion experiments. The purpose of this study was to determine the size distribution of starchy food particles before swallowing and to use an in vitro mincing procedure to simulate how food is divided up during chewing. Foods differing in texture and size (bread, spaghetti and tortiglioni) were chewed by 12 healthy subjects and spat out before swallowing. Chewing time and saliva impregnation were measured for each mouthful. The particle sizes resulting from experiments with chewed and minced bread and pasta were analysed respectively by light laser diffraction and image analysis. Chewing time was longer for bread than pasta, resulting in higher saliva impregnation. Chewed bread showed a bimodal distribution of particle size (30 microns, 500 microns), whereas both kinds of pasta produced particles of similar size (0.5 to 30 mm2) after mastication. Mincing reproduced the division of bread and pasta as achieved by chewing in an acceptable way. From our results it seems that the size of particles resulting from mastication depends on food texture. We succeeded by wetting and mincing food to prepare food in a similar bolus-like form before swallowing. Mincing provides a simple means of simulating the reduction of food into particles for in vitro digestion studies.

Adult↗

PubMed1997

Aerodynamic properties of the major dog allergen Can f 1: distribution in homes, concentration, and particle size of allergen in the air.

Exposure and sensitization to dog allergen is a significant cause of asthma. In this study we investigated the distribution, aerodynamic characteristics, and particle-size distribution of the major dog allergen Can f 1. Dust samples were collected in 50 homes with a dog and 50 homes without dogs. Airborne Can f 1 concentration was measured in 28 homes with dogs and 36 homes without a dog. Particle-size distribution was determined by using 10 separate Andersen sampler measurements in a dog-handling facility, and in 10 homes with dogs, and by repeated measurements in a home with one dog. High levels of Can f 1 (> 10 microg/g) were found in dust in all but one home with a dog and in eight of 50 homes without dogs. Airborne Can f 1 levels varied greatly between the homes with dogs (range: 0.3 to 99 ng/m3). Low levels of airborne Can f 1 (range: 0.4 to 1.1 ng/m3) were detected in 11 of 36 homes without a dog. Can f 1 was predominantly associated with large particles collected on the first stage of the Andersen sampler (> 9 microm), which averaged 42 to 49% of the total allergen recovered in the dog-handling facility and in homes with dogs. Small particles (< 5 microm diameter) also carried Can f 1, and these particles comprised approximately 20% of the total airborne allergen load. There was an excellent concordance between the results obtained in different sampling areas, and between the total Can f 1 recovered on the Andersen sampler and on the parallel filter. In conclusion, airborne Can f 1 was detectable in undisturbed conditions in all homes with dogs and in almost one third of the homes without dogs. In houses with dogs, a significant proportion (approximately 20%) of airborne Can f 1 was associated with small particles (< 5 microm diameter). Owing to their aerodynamic characteristics, these particles would be expected to remain airborne for a long period and, when inhaled, could penetrate into the lower airways and initiate asthma attacks.

Air Pollution, Indoor↗

PubMed2006

Genotype of the mutant LDL receptor allele is associated with LDL particle size heterogeneity in familial hypercholesterolemia.

Small, dense LDL particles have been associated with an increased risk of coronary artery disease. In order to assess the potential contribution of the genotype of the LDL receptor to LDL particle size heterogeneity in familial hypercholesterolemia (FH), we examined the electrophoretic characteristics of LDL particles in a large cohort of FH heterozygotes and controls. A total of 259 FH heterozygotes and 208 controls participated in the study. FH subjects were carriers of one of the nine French Canadian mutations in the LDL receptor gene. LDL particles were characterized by polyacrylamide gradient gel electrophoresis following a 6-week lipid-lowering drug-free baseline period. LDL-peak particle diameter (LDL-PPD), representing the most abundant LDL particle subpopulation, was significantly smaller in FH heterozygotes carrying a negative-receptor mutation than in subjects carrying a defective-receptor mutation (negative-receptor = 257.3 +/- 4.1 A versus defective-receptor = 259.0 +/- 4.3 A, p = 0.0006). No significant difference in plasma CETP concentrations was found between these two genotypic groups. Moreover, compared with controls having low triglyceride levels, negative-receptor subjects with high triglyceride levels had a relative risk of 19.6 (p < 0.0001) of having small, dense LDL particles while this risk was not significantly increased among defective-receptor subjects. Multivariate analysis showed that the LDL receptor status accounted for 5.7% of the variance in the LDL-PPD after adjustment for covariates. These results suggest that the genotype of the mutant LDL receptor allele was independently associated with variations in LDL-PPD and could partly explain why negative-receptor FH heterozygotes may be at greater risk of cardiovascular disease than defective-receptor FH subjects.

Adult↗

PubMed1990

Effect of calcium source, particle size, limestone solubility in vitro, and calcium intake level on layer bone status and performance.

Experiments were conducted to examine the effect on layer performance of dietary calcium source, particle size (average United States Screen Numbers 6, 8, 12, 18, 35, and 100) and calcium intake level (2.0, 2.5, 3.0, 3.5, 4.0, and 4.5 g/day). Egg production and egg weight were not affected by any of the treatments. Size and calcium intake level significantly affected shell weight, shell weight per unit surface area, specific gravity, and shell thickness. Bone ash expressed as a percentage of fat-free dry weight was not affected by calcium intake level, but bone ash concentration (bone ash per unit volume) and bone-breaking strength were linearly related to calcium intake level. Regressed shell quality traits and various bone parameters related to solubility instead of particle size produced a better fitted line.

Animals↗

PubMed2002

Fractionation of soybean phospholipids by preparative high-performance liquid chromatography with sorbents of various particle size.

Normal-phase high-performance liquid chromatography was used on a preparative scale to seperate phosphatidylethanolamine (PE), phosphatidylinositol (PI) and phosphatidylcholine (PC) phospholipids from soybean. Separation was achieved using mixtures of three solvents, hexane, methanol and isopropanol. The optimized mobile phase compositions were experimentally determined while operating in a linear gradient mode using 15, 5-20, 25-40, and 40-63 microm preparative particles as well as 4 microm analytical particles. A gradient mobile phase was established on a commmercially available analytical Nova-Pak column such that hexane linearly decreased from 85 to 0 as isopropanol and methanol linearly increased in two gradient steps from 10 to 30 and 5 to 70 respectively. The total run time was 25 min at a flow-rate of 1.5 ml/min. A slight change in mobile phase composition was required to increase the resolution of phospholipids. The 15 microm particle size gave the best separation of the preparative particle sizes examined based on their resolutions between PE and PI and PI and PC. Finally, the retention factors of PE and PC were correlated in terms of mobile phase composition.

Chromatography, High Pressure Liquid↗

PubMed1992

LDL particle size distribution. Results from the Framingham Offspring Study.

Using 2-16% gradient gel electrophoresis, we examined low density lipoprotein (LDL) particle size in relation to plasma lipoproteins in 1,168 women and 1,172 men from the Framingham Offspring Study. In addition, we studied the effect of dietary intake on LDL size in a subset of the population. Seven LDL size peaks were identified, with the largest, LDL 1, being found in the density range 1.019-1.033 g/ml; LDL 2 and LDL 3 in d = 1.033-1.038 g/ml; LDL 4 and LDL5 in d = 1.038-1.050 g/ml; and the smallest, LDL 6 and 7, in d = 1.050-1.063 g/ml. Seventy-seven percent of the population had one major and at least one minor LDL peak. Secondary LDL peaks accounted for 23% of the total LDL relative area, based on laser scanning densitometry. LDL size distribution was skewed toward larger LDL particles in women (prevalence of LDL 1, 30% and of LDL 2, 31%), whereas men exhibited a more symmetric distribution (prevalence of LDL 3, 42%). The prevalence of small (< 255 A), dense (d > 1.038 g/ml) LDL particles 4-7 was 33% in men, 5% in premenopausal women, and 14% in postmenopausal women. In agreement with previous reports, small, dense LDL particles were significantly (p < 0.0001) associated with increased triglyceride and apolipoprotein (apo) B levels and decreased HDL cholesterol and apo A-I levels. In addition, we found a significant (p < 0.0001) association between LDL cholesterol and LDL size. The highest LDL cholesterol levels were found among women with LDL 4 (148 mg/dl) and men with LDL 3-5 (138 mg/dl). In addition, the presence of LDL 3 or 4 as secondary peaks was significantly associated with higher LDL cholesterol levels, while smaller secondary LDL peaks were associated with higher triglyceride levels. We also found that compared with subjects with optimal LDL cholesterol levels (< 130 mg/dl), individuals with high-risk LDL cholesterol levels (> or = 160 mg/dl) had 1) a higher prevalence of LDL 3 and 4 (women only) and a lower prevalence of LDL 1 and 2 (women only) and 2) 11% higher LDL cholesterol to apo B ratios, even when matched for LDL particle size. Furthermore, low saturated fat and cholesterol intakes were significantly associated (p < 0.01) with smaller LDL particles. Therefore, the identification of small, dense LDL particles per se may not be a good indicator of coronary artery disease risk in population studies.(ABSTRACT TRUNCATED AT 400 WORDS)

Apolipoproteins↗

PubMed1976

Changes in the particle size distribution during tableting of sulphathiazole powder.

Five size fractions of sulphathiazole powder (volume surface mean diameter 155, 133, 86, 50 and 41 mum) were compressed into 12 mm diameter tablets on an instrumented single punch tablet machine. The size analysis of the tablet material after compression showed an attrition of the coarser fraction and an agglomeration of the finer fraction. It is postulated that there is a critical particle size where the effects of crushing and bonding cancel each other. The changes in particle size are discussed in relation to some of the compressive characteristics of the powder.

Hardness↗

PubMed2006

Commercial reference shape standards use in the study of particle shape effect on laser diffraction particle size analysis.

The purpose of this paper is to describe the use of LGC Promochem AEA 1001 to AEA 1003 monosized fiber-analog shape standards in the study of the effect of particle shape on laser diffraction (LD) particle size analysis (psa). The psa of the AEA standards was conducted using LD psa systems from Beckman Coulter, Horiba, and Malvern Instruments. Flow speed settings, sample refractive index values, and sample cell types were varied to examine the extent to which the shape effect on LD psa results is modified by these variables. The volume and number probability plots resulting from these measurements were each characterized by a spread in the particle size distribution that roughly extended from the breadth to the longest dimension of the particles. For most of the selected sample refractive index values, the volume probability plots were characterized by apparent bimodal distributions. The results, therefore, provide experimental verification of the conclusions from theoretical studies of LD psa system response to monosized elliptical particles in which this apparent bimodality was the predicted result in the case of flow-oriented particles. The data support the findings from previous studies conducted over the past 10 years that have called into question the verity of the tenets of, and therefore the value of the application of, the equivalent spherical volume diameter theory and the random particle orientation model to the interpretation of LD psa results from measurements made on nonspherical particles.

Drug Evaluation, Preclinical↗

PubMed1989

"Worst case" aerosol testing parameters: I. Sodium chloride and dioctyl phthalate aerosol filter efficiency as a function of particle size and flow rate.

The efficiency of filter media is dependent on the characteristics of the challenge aerosol and the filter's construction. Challenge aerosol parameters, such as particle size, density, shape, electrical charge, and flow rate, are influential in determining the filter's efficiency. In this regard, a so-called "worst case" set of conditions has been proposed for testing respirator filter efficiency in order to ensure wearer protection. Data collected on various types of filters (dust and mist; dust, fume, and mist; paint, lacquer, and enamel mist; and high efficiency) challenged with a worst case-type sodium chloride (NaCl) and dioctyl phthalate (DOP) aerosol are presented. The particle size of maximum penetration varies as a function of filter type and was less than 0.25-micron count mean diameter (CMD) in all cases. The count efficiency for high efficiency filters was greater than 99.97% at worst case testing conditions, but the worst case count efficiencies for dust and mist; dust, fume and mist; and paint, lacquer and enamel mist filters were not nearly as efficient as existing test methods indicate. Also, as the test flow rate is increased, the count efficiency decreases. Thus, respirator filters were found to conform to the prediction of single-fiber filtration theory.

Aerosols↗

PubMed1985

Effect of roughage particle size on ruminal, digestive and metabolic characteristics of early-weaned lambs fed pelleted corncob-concentrate diets.

Two experiments were conducted to determine effects of feeding corncobs of various mean particle size (MPS) on ruminal, digestive and metabolic characteristics of early-weaned lambs fed pelleted 74.9% concentrate:25.1% corncob diets. The MPS of corncobs in diets was 6.5, 5.4, 1.4 and .8 mm, respectively. As particle size decreased, percentage starch decreased and percentage neutral detergent fiber (NDF), acid detergent fiber (ADF) and cellulose increased. In Exp. 1, 28 crossbred rams (seven/treatment, avg initial wt, 15.3 kg) were used in a randomized complete-block design. In Exp. 2, lambs from Exp. 1 were re-weighed (avg initial wt, 16.8 kg) and fed the same diets as in Exp. 1. In Exp. 1 and 2, lambs ingested dry matter (DM) equal to 2.68 and 3.74% of body weight, respectively. In Exp. 1, apparent DM digestibility was unaffected by corncob MPS; however, in Exp. 2, DM digestibility was highest (68.8%) for lambs fed the 6.5-mm diet and lowest (63.8%) for those fed the .8-mm diet. Apparent starch digestibility was high (greater than 98.8%) in both experiments. Neutral detergent fiber and ADF digestibilities were highest for lambs fed the 1.4-mm diet (50.5 and 43.6%, Exp. 1; 39.6 and 28.9%, Exp. 2). A dramatic increase (6.8 to 39.1%) in acid detergent lignin (ADL) digestibility was observed in Exp. 1 as corncob MPS decreased. In Exp. 2, ADL digestibilities were similar for lambs fed the 6.5-, 5.4- or 1.4-mm diets (avg value, 5.9%) and highest for those fed the .8-mm diet (29.7%). Nitrogen metabolism was unaffected by corncob MPS. In Exp. 1, digestible energy intake, corrected for urinary losses, did not differ among treatments but in Exp. 2, lambs consuming the 6.5-mm diet had higher corrected digestibility energy intakes (1,926.6 kcal/d) than did those fed other diets (avg, 1,832.4 kcal/d). Ruminal pH sampled 4 h post-feeding was highest for lambs consuming the 6.5-mm diet (6.25) in Exp. 1 and the 1.4-mm diet (5.89) in Exp. 2. Lowest ruminal pH (5.30 and 5.36, respectively) was for lambs consuming the .8-mm diet in Exp. 1 and the 5.4-mm diet in Exp. 2. Ruminal lactate concentrations were variable within and among treatments. Total ruminal volatile fatty acid (VFA) concentrations were similar across treatments but in Exp. 2, there was a shift in molar proportions from acetate to propionate as corncob MPS decreased.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2005

Particle size distribution and atmospheric metals measurements in a rural area in the South Eastern USA.

Atmospheric particle mass concentrations were measured at a site adjacent to Lake Hartwell, GA, during six dry sampling events in February-March 2003. The overall average PM2.5 mass concentration was 9.5 microg/m3 and the overall average total suspended particles mass concentration was 19.1 microg/m3. Particulate matter was collected on a deposition plate mounted onto a specially designed wind vane and was subsequently analyzed to determine the particle size distribution. The average geometric particle diameter was found to be 2.8 microm. Particulate matter collected was found to be closely approximately at log-normal distribution, with a count median diameter of 1.5 mum and a geometric standard deviation of 1.8. Individual metal concentrations present in airborne particulate matter were determined for cadmium, chromium, copper, iron, lead, manganese, nickel, and zinc using inductively coupled plasma-mass spectrometry analysis of samples collected on Teflon filters. Ambient metal concentrations were found to range from 0.8 ng/m3 for cadmium to 512 ng/m3 for iron. The dry deposition flux of metals was estimated to be in the range of 0.17 mg/(m2 year) for cadmium to 102 mg/(m2 year) for iron. More samples need to be collected and analyzed, both temporally and spatially, in order to establish atmospheric metals fluxes onto surfaces.

Air↗

PubMed1999

Short-term effects of mineral particle sizes on cellular degradation activity after implantation of injectable calcium phosphate biomaterials and the consequences for bone substitution.

This in vivo study investigated the influence of two calcium phosphate particle sizes (40-80 microm and 200-500 microm) on the cellular degradation activity associated with the bone substitution process of two injectable bone substitutes (IBS). The tested biomaterials were obtained by associating a biphasic calcium phosphate (BCP) ceramic mineral phase and a 3% aqueous solution of a cellulosic polymer (hydroxypropylmethylcellulose). Both were injected into osseous defects at the distal end of rabbit femurs for 2- and 3-week periods. Quantitative results for tartrate-resistant acid phosphatase (TRAP) cellular activity, new bone formation, and ceramic resorption were studied for statistical purposes. Positive TRAP-stained degradation cells were significantly more numerous for IBS 40-80 than IBS 200-500, regardless of implantation time. BCP degradation was quite marked during the first 2 weeks for IBS 40-80, and bone colonization occurred more extensively for IBS 40-80 than for IBS 200-500. The resorption-bone substitution process occurred earlier and faster for IBS 40-80 than IBS 200-500. Both tested IBS displayed similar biological efficiency, with conserved in vivo bioactivity and bone-filling ability. Differences in calcium phosphate particle sizes influenced cellular degradation activity and ceramic resorption but were compatible with efficient bone substitution.

Acid Phosphatase↗