Biomedical subjects

A B Yu

Publications and source records attributed to A B Yu.

15 recordsLinked to original sources

PubMed2006

Role of interparticle forces in the formation of random loose packing.

We present a physical and numerical study of the settling of uniform spheres in liquids and show that interparticle forces play a critical role in forming the so-called random loose packing (RLP). Different packing conditions give different interparticle forces and, hence, different RLP. Two types of interparticle forces are identified: process dependent and process independent. The van der Waals force, as the major cohesive force in the present study, plays a critical role in effecting the process-dependent forces such as drag and lift forces. An equation is formulated to describe the relationship between the macroscopic packing fraction and microscopic interparticle forces in a packing. We argue there is no lowest packing fraction for a mechanically stable RLP; hence, the packing fractions of RLP can range from 0 to 0.64 depending on the cohesive and frictional conditions between particles.

Journal Article↗

PubMed2006

Pore structure of the packing of fine particles.

This paper presents a numerical study of the pore structure of fine particles. By means of granular dynamics simulation, packings of mono-sized particles ranging from 1 to 1000 microm are constructed. Our results show that packing density varies with particle size due to the effect of the cohesive van der Waals force. Pores and their connectivity are then analysed in terms of Delaunay tessellation. The geometries of the pores are represented by the size and shape of Delaunay cells and quantified as a function of packing density or particle size. It shows that the cell size decreases and the cell shape becomes more spherical with increasing packing density. A general correlation exists between the size and shape of cells: the larger the cell size relative to particle size, the more spherical the cell shape. This correlation, however, becomes weaker as packing density decreases. The connectivity between pores is represented by throat size and channel length. With decreasing packing density, the throat size increases and the channel length decreases. The pore scale information would be useful to understand and model the transport and mechanical properties of porous media.

Journal Article↗

PubMed2005

Micromechanical simulation and analysis of one-dimensional vibratory sphere packing.

We present a numerical method capable of reproducing the densification process from the so-called random loose to dense packing of uniform spheres under vertical vibration. The effects of vibration amplitude and frequency are quantified, and the random close packing is shown to be achieved only if both parameters are properly controlled. Two densification mechanisms are identified: pushing filling by which the contact between spheres is maintained and jumping filling by which the contact between particles is periodically broken. In general, pushing filling occurs when the vibration intensity is low and jumping filling becomes dominant when the vibration intensity is high.

Journal Article↗

PubMed2005

The interlayer swelling and molecular packing in organoclays.

Understanding the interlayer swelling and molecular packing in organoclays is important to the formation and design of polymer nanocomposites. This paper presents recent experimental and molecular simulation studies on a variety of organoclays that show a linear relationship between the increase of d-spacing and the mass ratio between organic and clay. A denser molecular packing is observed in organoclays containing surfactants with hydroxyl-ethyl units. Moreover, our simulation results show that the head (nitrogen) groups are essentially tethered to the clay surface while the long hydrocarbon chains tend to adopt a layering structure with disordered conformation, which contrasts with the previous assumptions of either the chains lying parallel to the clay surface or being tilted at rather precise angles.

Journal Article↗

PubMed2005

Clay-based polymer nanocomposites: research and commercial development.

This paper reviews the recent research and development of clay-based polymer nanocomposites. Clay minerals, due to their unique layered structure, rich intercalation chemistry and availability at low cost, are promising nanoparticle reinforcements for polymers to manufacture low-cost, lightweight and high performance nanocomposites. We introduce briefly the structure, properties and surface modification of clay minerals, followed by the processing and characterization techniques of polymer nanocomposites. The enhanced and novel properties of such nanocomposites are then discussed, including mechanical, thermal, barrier, electrical conductivity, biodegradability among others. In addition, their available commercial and potential applications in automotive, packaging, coating and pigment, electrical materials, and in particular biomedical fields are highlighted. Finally, the challenges for the future are discussed in terms of processing, characterization and the mechanisms governing the behaviour of these advanced materials.

Aluminum Silicates↗

PubMed2004

Packing structure of cohesive spheres.

This paper presents the first set of measured data to probe into the loose packing structure of wet particles featured with large pores, aggregated and chain-connected particles. The structure is also analyzed in terms of radial distribution function and coordination number, and compared with that of the random dense packing.

Journal Article↗

PubMed2002

Averaging method of granular materials.

This paper presents an averaging method to link discrete to continuum variables of granular materials. Compared to the other methods proposed in the literature, it has advantages of being applicable to all flow regimes, and to granular flows with or without the effect of physical boundaries. Its application is demonstrated in the determination of the macroscopic properties such as mass density, velocity, stress, and couple stress distributions of a hopper flow, where the discrete results are generated by means of discrete particle simulation. While highlighting the need for considering properly the effect of physical boundaries, the results indicate that the proposed method is an effective way to determine the flow properties of granular materials.

Journal Article↗

PubMed2002

Voronoi tessellation of the packing of fine uniform spheres.

The packing of uniform fine spherical particles ranging from 1 to 1000 microm has been simulated by means of discrete particle simulation. The packing structure is analyzed, facilitated by the well established Voronoi tessellation. The topological and metric properties of Voronoi polyhedra are quantified as a function of particle size and packing density. The results show that as particle size or packing density decreases, (i) the average face number of Voronoi polyhedra decreases, and the distributions of face number and edge number become broader and more asymmetric; (ii) the average perimeter and area of polyhedra increase, and the distributions of polyhedron surface area and volume become more flat and can be described by the log-normal distribution. The topological and metric properties depicted for the packing of fine particles differ either quantitatively or qualitatively from those reported in the literature although they all can be related to packing density. In particular, our results show that the average sphericity coefficient of Voronoi polyhedra varies with packing density, and although Aboav-Weaire's law is generally applicable, Lewis's law is not valid when packing density is low, which are contrary to the previous findings for other packing systems.

Journal Article↗

PubMed2001

Numerical investigation of the angle of repose of monosized spheres.

This paper presents a numerical study of the angle of repose, a most important macroscopic parameter in characterizing granular materials, by means of a modified distinct element method. Emphasis is given to the effect of variables related to factors such as particle characteristics, material properties, and geometrical constraints. The results show that sliding and rolling frictions are the primary reasons for the formation of a sandpile; particle size and container thickness significantly influence the angle of repose; and the angle of repose is not so sensitive to density, Poisson's ratio, damping coefficient, and Young's modulus. Increasing rolling friction coefficient or sliding friction coefficient increases the angle of repose. Conversely, increasing particle size or container thickness decreases the angle of repose. The underlying mechanisms for these effects are discussed in terms of particle-particle and particle-wall interactions.

Journal Article↗

PubMed1990

Oxidation kinetics of an antiasthmatic, 2-[(4-hydroxyphenyl)amino]-5-methoxybenzenemethanol, and stabilization with ascorbic acid.

A novel antiasthmatic, 2-[(4-hydroxyphenyl)amino]-5-methoxybenzenemethanol (1), oxidizes to the corresponding iminoquinone in aqueous solutions. The reaction was monitored by a paired-ion reversed-phase HPLC method. The oxidation rate was highly dependent on the solution pH, with a large rate increase occurring above pH 6.1. In nonaqueous solution, the oxidation reaction was significantly slower. Ascorbic acid protects 1 from oxidation. The aqueous solution of the decomposed product is reduced to 1 in the presence of ascorbic acid.

Aminophenols↗

PubMed1987

Particle-size distribution of bitolterol mesylate solution delivered by four compressed-air nebulizer devices.

The particle-size distribution of bitolterol mesylate solution delivered by four types of compressed-air nebulizers was determined. Before nebulization, bitolterol mesylate solution 0.2% w/v was diluted to 0.0833% w/v with 0.9% sodium chloride solution. The following commercially available nebulizers were tested: DeVilbiss Nebulizer Model 645, Hudson 1720 (Updraft) Hand Held Nebulizer, Bard Inspiron 002220 Mini-Neb Nebulizer, and Bunn Mini Mist Set model 0140-041. The particle-size distribution of nebulized solutions was determined with a cascade impactor contained in an in vitro apparatus designed to simulate use by a patient. Assays of bitolterol mesylate in the cascade impactor apparatus were done by high-performance liquid chromatography. Only slight differences were found in the particle-size distributions among the four types of nebulizers; the calculated average particle size ranged from 3.0 to 3.6 micron. All nebulizers tested showed satisfactory, comparable particle-size distributions and performance with bitolterol mesylate solution.

Aerosols↗

PubMed1981

Effect of antacid on bioavailability of theophylline from rapid and timed-release drug products.

Magnesium aluminum hydroxide suspension (an antacid) was given concurrently with either theophylline anhydrous tablets or theophylline anhydrous timed-release capsules to 13 volunteers using a four-way crossover design. Serum theophylline was measured by reversed-phase high-pressure liquid chromatography. The serum level-time curves were individually fitted to an oral absorption one-compartment open model. The pharmacokinetic parameters (mean +/- SD) KA, K, AUC, and F/V for theophylline from the rapid release theophylline anhydrous tablets were 2.1 +/- 1.3 hr-1, 0.15 +/- 0.06 hr-1, 89.2 +/0 39 microgram hr/ml, and 0.0023 +/- 0.002 kg/ml, respectively; from the anhydrous timed-release capsules, they were 0.27 +/- 0.08 hr-1, 0.20 +/- 0.07 hr-1, 79.0 +/- 27 microgram hr/ml, and 0.0030 +/- 0.007 kg/ml, respectively. The concurrent administration of 15 ml of antacid (magnesium aluminum hydroxide suspension) with the theophylline products did not significantly affect any of these pharmacokinetic parameters. The extent of theophylline bioavailability from all drug products was consistent and similar as shown by the F/V and AUC values.

Adult↗

PubMed1979

High-pressure liquid chromatographic analysis of antipyrine in small plasma samples.

A high-pressure liquid chromatographic (HPLC) method was developed for the assay of antipyrine in small (0.1-ml) plasma samples using aminopyrine as the internal standard and a reversed-phase microparticulate column. The assay sensitivity (1 microgram/ml) permits development of a plasma level--time curve using a single rat. The mean (+/- SE) plasma elmination half-life in rats was 1.28 +/- 0.14 hr. A comparison of the spectrophotometric method with the HPLC method yielded a correlation coefficient of 0.98. The HPLC assay for antipyrine is rapid and precise and can be used for hepatic drug metabolism study in a single animal.

Animals↗

PubMed1977

Rapid sensitive fluorometric analysis of cephalosporin antibiotics.

A rapid and sensitive fluorometric analysis for cephalosporins, which can also be applied to penicillins, is presented. The method involves reaction with 0.1 N sodium hydroxide at 100 degrees, producing stable fluorescent products. This method was applied to cephalexin and ampicillin with detection at concentrations as low as 0.01 mug/ml.

Ampicillin↗

PubMedDate not supplied

Use of continuous ambulatory infusions of concentrated subcutaneous (s.q.) hydromorphone versus intravenous (i.v.) morphine: cost implications for palliative care.

Health care practitioners are increasingly under pressure to curtail spending while trying to deliver excellent patient care. These issues are also affecting palliative care, particularly now that palliative care programs are expanding. A comparison of cost-effectiveness and feasibility of using continuous subcutaneous (s.q.) ambulatory infusion of hydromorphone versus intravenous (i.v.) ambulatory morphine is illustrated in this study. With the high doses of morphine required in chronic cancer pain, the use of subcutaneous morphine is not feasible due to the volume of solution required to be delivered. Hydromorphone can be prepared in concentrated solutions enabling it to be delivered by the subcutaneous route. Morphine stability data are available. However, hydromorphone stability has only been verified for seven days; thus, stability data were needed post-seven days. Concentrations of 10 mg/ml, 20 mg/ml, 50 mg/ml, and 100 mg/ml, in 0.9 percent normal saline or dextrose 5 percent water, were analyzed via high-performance liquid chromatography (HPLC) at seven and 28 days. Cost comparisons of supplies and associated costs with subcutaneous versus intravenous solutions were obtained. Hydromorphone was found to be stable for 28 days in both dilutants. Cost analysis of a hydromorphone 28-day supply resulted in substantial savings over the equivalent costs of morphine infusions.

Ambulatory Care↗