SEARCH · PubMed Health

Results for “Particle Size”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources

PubMed1996

A simple method for the analysis of particle sizes of forage and total mixed rations.

A simple separator was developed to determine the particle sizes of forage and TMR that allows for easy separation of wet forage into three fractions and also allows plotting of the particle size distribution. The device was designed to mimic the laboratory-scale separator for forage particle sizes that was specified by Standard S424 of the American Society of Agricultural Engineers. A comparison of results using the standard device and the newly developed separator indicated no difference in ability to predict fractions of particles with maximum length of less than 8 and 19 mm. The separator requires a small quantity of sample (1.4 L) and is manually operated. The materials on the screens and bottom pan were weighed to obtain the cumulative percentage of sample that was undersize for the two fractions. The results were then plotted using the Weibull distribution, which proved to be the best fit for the data. Convenience samples of haycrop silage, corn silage, and TMR from farms in the northeastern US were analyzed using the forage and TMR separator, and the range of observed values are given.

Animal Feed↗

PubMed1982

Effect of surface charge and particle size on gel structure of aluminum hydroxycarbonate gel.

The effect of surface charge and particle size on the gel structure of aluminum hydroxycarbonate gel was studied through the use of a specially designed tension cell. Surface charge has a major effect on the coefficient of bulk compressibility. The charged state is more compressible at lower tensions while the neutral gel is more compressible at higher tensions. In addition, physical properties of gels having a small particle size are more profoundly influenced by interparticle forces than are gels consisting of larger particles. The effect of surface charge and particle size on gel structure is applied to physical properties such as viscosity and dewatering.

Aluminum Hydroxide↗

PubMedDate not supplied

Recirculation-type Amplatz clot macerator: determination of particle size and distribution.

PURPOSE: A high-speed mechanical clot macerator was tested in vitro, and the distributions and sizes of residual particles produced by this device were determined. MATERIALS AND METHODS: Human thrombi aged for 4 days and 10 days were macerated using a recirculation-type Amplatz thrombectomy device with an 8-F, high-speed screw propeller. The device was activated for 15, 30, and 60 seconds. Two different methods of particle measurement were used to determine overall particle distribution and to determine the size and number of large particles. RESULTS: The recirculation device liquefied 99.2% of 4-day-old and 98.8% of 10-day-old thrombi, producing particles ranging in size from 13 to 1,000 microns; all particles were smaller than 1,000 microns. Particle size and distribution results were identical for the 30-second and 60-second activation times. CONCLUSION: The recirculation-type thrombectomy device appears to perform well as a method of macerating human thrombi. Clinical trials need to be conducted to test the device further and to determine if it can be used safely on venous as well as arterial occlusions.

Humans↗

PubMed2002

Characterization of LDL particle size among carriers of a defective or a null mutation in the lipoprotein lipase gene: the Québec LIPD Study.

OBJECTIVE: The objective of the present study was to compare the impact of the null P207L and defective D9N mutations in the LPL gene on LDL particle size among heterozygous carriers. METHODS AND RESULTS: LDL particle size was measured on whole plasma by 2% to 16% non-denaturing polyacrylamide gradient gel electrophoresis in a cohort of 206 heterozygous carriers of either the P207L or the D9N mutation. The P207L carriers (N=88) presented with a more atherogenic lipoprotein-lipid profile compared with the D9N carriers (N=118). Accordingly, LDL particle size was smaller in the P207L carriers than in the D9N subjects (248.8+/- 1.0 vs 254.5+/-1.0 A, P< 0.001), and the difference remained significant after adjustment for plasma triglyceride (TG) levels. The difference in LDL diameter between the P207L and the D9N carriers was 3-fold greater in individuals with plasma TG levels >3.5 mmol/L than in subjects with TG < or =3.5 mmol/L. The factors that statistically contributed to LDL particle size variation in multivariate analyses were plasma TG levels (11.6%) and age (6.4%) in subjects with TG levels < or =3.5 mmol/L and HDL cholesterol levels (15.5%) and the LPL gene mutation (null versus defective, 7.0%) in patients with TG levels >3.5 mmol/L. CONCLUSIONS: These results suggest that the null P207L mutation in the LPL gene has a greater impact on LDL particle size than the defective D9N mutation and that this mutation-specific effect is amplified at greater plasma TG concentrations.

Cohort Studies↗

PubMed1998

Low density lipoprotein particle size is associated with glycosylated hemoglobin levels regardless of plasma lipid levels.

We evaluated the influence of the levels of glycosylated hemoglobin (HbA1C) and fasting plasma glucose on the variation in low density lipoprotein (LDL) peak particle size in 210 subjects who were undergoing an annual check-up. Univariate analysis showed that LDL particle size was significantly and positively correlated with high density lipoprotein (HDL) cholesterol levels, and was inversely correlated with the levels of total plasma cholesterol, triglycerides, fasting glucose, fasting insulin, HbA1C, and body mass index (BMI). Stepwise regression analysis selected four independent contributing variables that could affect LDL particle size; triglyceride levels, HDL cholesterol levels, LDL cholesterol levels, and HbA1C levels. Similar regression analysis performed for men and for normotensive subjects showed that HbA1C levels also independently influenced LDL particle size. The results indicate that HbA1C levels have a significant effect on LDL particle size. This suggests that small LDL particles would be present in subjects with non-insulin-dependent diabetes mellitus regardless of plasma lipid concentrations.

Adult↗

PubMed1986

The effect of the relationship between punch velocity and particle size on the compaction behaviour of materials with varying deformation mechanisms.

The effect of punch velocity over the range 0.033-300 mm s-1 on the compaction properties of lactose, microcrystalline cellulose and a drug substance (a phthalazine derivative) for a range of particle sizes has been studied using the yield pressure derived from the Heckel relationship and a strain rate sensitivity index (SRS index), as the criteria to describe their behaviour. For lactose, a material which deforms by a mixed mechanism of particle fracture and plastic deformation at the contact points, the yield pressure increased and the SRS index decreased as particle size decreased, due to a reduction in the amount of fragmentation of the particles. For microcrystalline cellulose, a material which is known to deform plastically, the yield pressure and the SRS index were independent of particle size. For the phthalazine derivative the yield pressure increased as particle size decreased; however the SRS index reduced from 41% to zero, indicating that the deformation mechanism was changing from plastic flow to brittle behaviour. This decrease in the SRS index has been explained in terms of the relative amounts of strain-hardened material produced as milling severity increased, resulting in an increasing resistance to deformation and thus an apparent increase in brittle behaviour as particle size decreased.

Cellulose↗

PubMed1999

A simple model for estimating the particle size dependence of absolute efficiency of fluorescent screens.

The absolute efficiency of a phosphor screen is the ratio of the light energy per unit area at the screen surface to the incident x-ray energy fluence. Particle size is a critical factor in determining the absolute efficiency, but in most models its influence is not accounted for. To allow derivation of the particle size dependence, a model is proposed that describes the optical properties of the screen by means of a single parameter, the light extinction factor, xi, and assumes that the intrinsic efficiency (light energy/energy imparted to the phosphor material) is independent of particle size. The value of xi depends on the type of screen (phosphor, reflective backing, coating and binder) and has to be determined from measurements on at least two screens with known particle size and thickness. The absolute efficiency can then be calculated for an extended range of particle sizes and/or screen thicknesses. To test the model, experimental data from the literature were used to derive values of xi for screens of La2O2S:Tb, LaOBr:Tm and ZnCdS:Ag. The extinction factor was found to vary between -6 and +20%. The non-physical negative value for xi, found from one set of experiments on La2O2S:Tb screens, may be explained as resulting from a lack of accurate knowledge of the actual tube potential, influencing calculated values of the energy imparted to the screen. The results are promising but further well-controlled experiments (including improved dosimetric calculations to account forescape of K-radiation from the screen) are needed to confirm the model.

Biophysical Phenomena↗

PubMed2003

De-agglomeration of micronized benzodiazepines in dissolution media measured by laser diffraction particle sizing.

The objective of this research was to develop a method to characterize the degree of particle agglomeration using laser diffraction particle sizing, following the addition of benzodiazepine interactive mixtures to water. Interactive mixtures of diazepam, nitrazepam and oxazepam (up to 20% w/w) were prepared by mixing micronized benzodiazepines with lactose granules (250-355 microm). Micronized sodium lauryl sulfate and cetrimide (up to 5% w/w) were added to the benzodiazepine-lactose interactive mixes to produce ternary mixtures. Particle size distributions of benzodiazepines, after addition of the interactive mixtures to water, were determined using laser diffraction particle sizing. Bimodal distributions representing dispersed particles and agglomerates were observed initially after lactose carrier dissolution. Partial agglomerate to dispersed particle transition occurred during a 60-min observation period for all mixtures, reaching a constant level of agglomeration after this time. Interactive mixtures with higher benzodiazepine concentrations displayed transition profiles with higher levels of agglomeration. The presence of surfactant in interactive mixtures dramatically decreased agglomeration. Sodium lauryl sulfate was more effective than cetrimide in dispersing agglomerates. The shape of the transition curves during de-agglomeration demonstrated the presence of stable agglomerates that remained after the initial transition; these may be important in explaining dissolution and absorption rates.

Benzodiazepines↗

PubMed2005

Effect of plant sterols and endurance training on LDL particle size and distribution in previously sedentary hypercholesterolemic adults.

BACKGROUND: Plant sterols and exercise favourably alter lipid profiles in a way that protect against future coronary heart disease (CHD). However, their effects on other indicators of CHD risk, such as LDL particle size, still need further clarification. OBJECTIVE: This study examined the effect of plant sterols, exercise, and the combination of plant sterols and exercise, on LDL particle size and distribution in previously sedentary, hypercholesterolemic adults. DESIGN: In an 8-week, placebo-controlled, parallel-arm clinical trial, 84 subjects were randomized to one of four intervention groups: (1) combination of sterols and exercise, (2) exercise, (3) sterol, or (4) control. RESULTS: Exercise significantly (P < 0.05) reduced post-treatment LDL peak particle size from 255 to 253 A. Additionally, exercise significantly (P < 0.05) decreased the proportion of large LDL particles within plasma. Sterol supplementation significantly (P < 0.05) decreased the estimated cholesterol concentrations within small, medium, and large LDL particles by 13.4, 13.5, and 14.4%, respectively, yet had no effect on the distribution of cholesterol among various LDL particle sizes. Furthermore, decreased body weight post-training was associated with increased cholesterol in small LDL particles (r = -0.52, P < 0.0001). Decrease in body fat percent (BF%) post-training was associated with increased cholesterol concentrations in small LDL particles (r = -0.29, P < 0.01). CONCLUSION: On the basis of modulating LDL electrophoretic characteristics, the present study demonstrates that plant sterols have no effect on CHD risk, while short-term exercise may potentially increase CHD risk by decreasing LDL peak particle size. SPONSORSHIP: This study was sponsored by The Heart and Stroke Foundation of Canada.

Adult↗

PubMed2003

Effect of different forms of dietary hydrogenated fats on LDL particle size.

BACKGROUND: Dietary trans fatty acids (FAs), which are formed during the process of hydrogenating vegetable oil, are known to increase plasma LDL-cholesterol concentrations. However, their effect on LDL particle size has yet to be investigated. OBJECTIVE: We investigated the effect of trans FA consumption on the electrophoretic characteristics of LDL particles. DESIGN: Eighteen women and 18 men each consumed 5 experimental diets in random order for 35-d periods. Fat represented 30% of total energy intake in each diet, with two-thirds of the fat in the form of semiliquid margarine (0.6 g trans FAs/100 g fat), soft margarine (9.4 g trans FAs/100 g fat), shortening (13.6 g trans FAs/100 g fat), stick margarine (26.1 g trans FAs/100 g fat), or butter, which was low in trans FAs (2.6 g trans FAs/100 g fat) but rich in saturated fat. LDL particle size and distribution were characterized by nondenaturing, 2-16% polyacrylamide gradient gel electrophoresis. RESULTS: Relative to the LDL particle size observed after consumption of the butter-enriched diet, LDL particle size decreased significantly and in a dose-dependent fashion with increasing amounts of dietary trans FAs (P < 0.001). Cholesterol concentrations in large (> 260 A) and medium-sized (255-260 A) LDL particles also increased proportionately to the amount of trans FAs in the diet. CONCLUSION: Consumption of dietary trans FAs is associated with a deleterious increase in small, dense LDL, which further reinforces the importance of promoting diets low in trans FAs to favorably affect the lipoprotein profile.

Aged↗

PubMed2003

Improving relative bioavailability of dicumarol by reducing particle size and adding the adhesive poly(fumaric-co-sebacic) anhydride.

PURPOSE: This study was carried out to show the effect of particle size reduction and bioadhesion on the dissolution and relative bioavailability of dicumarol. METHODS: Formulations were produced by a variety of methods including a novel technique to reduce particle size as well as phase inversion with poly(fumaric-co-sebacic)anhydride p(FA:SA) to create nanospheres. Drug was administered to groups of pigs and rats via oral gavage of a suspension, and dicumarol concentration in the blood was measured using a double extraction technique. RESULTS: In vitro results showed improved dissolution in both the micronized formulation and the encapsulated p(FA:SA) nanospheres. In vivo, relative bioavailability of a spray-dried formulation was increased by 17% in the rat and 72% in the pig by further reduction in particle size. The bioadhesive p(FA:SA) formulation also improved relative bioavailability over the spray-dried drug, increasing it by 55% in the rat and 96% in the pig. Additionally, the p(FA:SA) formulation prolonged Tmax and decreased Cmax in both species. CONCLUSION: This work demonstrates the importance of particle size and bioadhesion to improve oral bioavailability of ducumarol.

Adhesives↗

PubMed2006

[Influence of particle size and MePEG molecular weight on in vitro macrophage uptake and in vivo long circulating of stealth nanoparticles in rats].

AIM: To investigate the influence of particle size and methoxypolyethyleneglycol (MePEG) molecular weight on the in vitro macrophage uptake and in vivo long circulating of recombinant human tumor necrosis factor-alpha (rHuTNF-alpha)-loaded stealth nanoparticles in rats. METHODS: Three sizes (approximately 80, 70 and 240 nm) of poly (methoxypolyethyleneglycol cyanoacrylate-co-n-hexadecyl cyanoacrylate) (PEG-PHDCA) nanoparticles loading rHuTNF-alpha were prepared at different MePEG molecular weights (Mr 2,000, 5,000, 10,000) using the double emulsion method. The in vitro macrophage uptake and in vivo long circulating properties in rats were examined and compared. RESULTS: The uptake by macrophages decreased and the half-life of rHuTNF-alpha in rat increased with the increase of MePEG molecular weight or the decrease of particle size. The linear-ships between particle size and MePEG molecular weight and the in vitro macrophage uptake and in vivo long circulating properties were fairly good. Having the highest MePEG surface density (1.32 nm(-2)) , the shortest average distance between neighboring MePEG chain (0.87 nm) and the thicker fixed aqueous layer thickness (FALT, 5.16 nm), PEG5,000-PHDCA nanoparticles (80.0 nm) earned the strongest potency of decreasing uptake by macrophages and prolonging the half-life of rHuTNF-alpha in rat. CONCLUSION: Within the experimental limits, particle size and MePEG molecular weight had dramatic influence on in vitro macrophage uptake and in vivo long circulating properties of rHuTNF-alpha-loaded stealth nanoparticles.

Animals↗

PubMed1994

Particle size: the key to the atherogenic lipoprotein?

Using different analytical methods, up to 12 low-density lipoprotein (LDL) subfractions can be separated. LDL particle size decreases with increasing density. Smaller, denser LDL particles seem more atherogenic than the larger, lighter particles, based on the experimental findings that smaller LDL particles are more susceptible for oxidation in vitro, have lower binding affinity for the LDL receptors and lower catabolic rate, have a higher concentration of polyunsaturated fatty acids, and potentially interact more easily with proteoglycans of the arterial wall. Clinical studies have shown that a smaller LDL subfraction profile is associated with an increased risk of heart disease, even when total cholesterol level is only slightly raised. There is a strong inverse association between LDL particle size and triglyceride concentrations. Although LDL particle size is genetically determined, its phenotypic expression may also be affected by environmental factors such as drugs, diet, obesity, exercise or disease. Factors that shift the LDL subfractions profile towards larger particles may reduce the risk of heart disease.

Arteries↗

PubMedDate not supplied

Examination of parameters determining particle size distribution: acetylsalicylic acid microcapsules.

A method of preparation of acetylsalicylic acid microcapsules has been elaborated. The active ingredient was made suitable for microencapsulation by recrystallization before phase separation coating. Experiments were performed on the basis of factorial design, and parameters which influence the particle size and particle size distribution of microcapsules were characterized quantitatively.

Aspirin↗

PubMed2004

The effect of ultrasound on the particle size and structural disorder of a well-ordered kaolinite.

The present study examined the effect of sonication on the particle size and structure of a well-crystallized (KGa-1) kaolinite from Georgia. Sonication produced an important delamination effect as well as a reduction of the other particle-size dimensions. The experiments, carried out under different experimental conditions, showed that particle-size reduction can be controlled through different variables such as power of ultrasonic processor, amount of sample (kaolinite + water), and time of treatment. As a consequence of this particle-size reduction the surface area increases sharply with the sonication time from 8.5 to 83 m2/g after 20 h with the most energetic treatment. Contrary to what is observed in the grinding treatment, sonication did not cause the amorphization of kaolinite, as observed by XRD and FTIR data. Nevertheless, ultrasound treatment increased the structural disorder, which consisted in increases in the proportion of specific translations (-a/3+b/3) between adjacent layers in the first hours of treatment, followed by increases in the proportion of random translations between layers.

Journal Article↗

PubMedDate not supplied

A combinatorial approach to the study of particle size effects on supported electrocatalysts: oxygen reduction on gold.

A novel high-throughput technique has been developed for the investigation of the influence of supported metal particle size and the support on electrocatalytic activity. Arrays with a gradation of catalyst particle sizes are fabricated in a physical vapor deposition system that also allows selection of the support material. Simultaneous electrochemical measurements at all electrodes in the array, together with determination of the actual particle size distribution on each of the electrodes by transmission electron microscopy (TEM), then allows rapid determination of the activity as a function of catalyst center size. The procedure is illustrated using data for the reduction of oxygen on gold nanoparticles supported on both substoichiometric titanium dioxide (TiO(x)()) and carbon and the conclusions are verified using voltammetry at rotating disk electrodes. Gold centers with diameters in the range 1.4-6.3 nm were investigated and it is demonstrated that, with both supports, the catalytic activity for oxygen reduction decays rapidly for particle sizes below 3.0 nm. This may be observed as a decrease in current at constant potential or an increase in the overpotential for oxygen reduction.

Catalysis↗

PubMed1999

Influence of drug:hydroxypropylmethylcellulose ratio, drug and polymer particle size and compression force on the release of diclofenac sodium from HPMC tablets.

This study evaluates the relationship and influence of formulation and technological factors such as drug:hydroxypropylmethylcellulose (HPMC) ratio, particle size of the drug, particle size of HPMC and compression force, on drug release from matrices containing HPMC and diclofenac sodium as a model drug. The influence of these variables was assessed by multi-way analysis of variance. The results of the present study point out that the rate and mechanism of diclofenac sodium release from HPMC K15M matrices are mainly controlled by the drug:HPMC ratio. The drug and HPMC particle size also influence the drug release parameters, although to a lesser extent. Finally, the independence of the drug release from matrix tablets with respect to the compression force is reported.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2004

Analysis of ambient particle size distributions using Unmix and positive matrix factorization.

Hourly averaged particle size distributions measured at a centrally located urban site in Seattle were analyzed through the application of bilinear positive matrix factorization (PMF) and Unmix to study underlying size distributions and their daily patterns. A total of 1051 samples each with 16 size intervals from 20 to 400 nm were obtained from a differential mobility particle sizer operating between December 2000 and February 2001. Both PMF and Unmix identify four similar underlying factors in the size distributions. Factor 1 is an accumulation mode particle size spectrum that shows a regular nocturnal pattern, and factor 2 is a larger particle distribution. Factor 3 is assigned as a traffic-related particle distribution, based on its correlations with accompanying gas-phase measurements, and has a regular weekday-high rush-hour pattern. Factor 4 is a traffic-related particle size distribution that has a regular rush-hour pattern on weekdays as well as weekends. Conditional probability functions (CPF) were computed using wind profiles and factor contributions. The results of CPF analysis suggest that these factors are correlated with surrounding particle sources of wood burning, secondary aerosol, diesel emissions, and motor vehicle emissions.

Aerosols↗