Biomedical subjects

J Ralston

Publications and source records attributed to J Ralston.

At least 19 recordsLinked to original sources

PubMed2002

Electrokinetic properties of methylated quartz capillaries.

Electrokinetic (zeta)-potentials of methylated (trimethylchlorosilane) quartz capillaries (5-6 microm in radius) were determined in 10(-4) M KCl solution. Over the course of time, the absolute values of the zeta-potential decrease, as a result of the formation of small bubbles on the rough methylated surface, generated from the flowing, nitrogen gas-saturated solution. This decrease is attributed to screening of a part of the solid surface. After the passage of time, a sharp increase in the zeta-potentials was observed, as the pressure was increased and the initial potential values were recovered. Sometimes, oscillations in the zeta-potentials were observed. This behaviour was explained by detachment of bubbles from the methylated surfaces by the flowing solution. Addition of non-ionic surfactant, which made the methylated surface hydrophilic, decreased the measured zeta-potentials. This was attributed to suppression of water slippage, an effect known to occur for hydrophobic solid surfaces. A mixed mechanism of charge formation is characteristic for these methylated quartz surfaces and is connected with presence of hydrophobic and hydrophilic areas. The ratio between these areas controls both the formation of surface charge as well as the contact angles.

Journal Article↗

PubMed2002

Wetting film stability and flotation kinetics.

Single bubble experiments performed with different size fractions of quartz particles and different, but known, contact angles revealed two modes of flotation dynamics in superclean water. (1.) A monotonic increase of collection efficiency Ecoll with increasing particle size was observed at high particle hydrophobicity and, correspondingly, a low wetting film stability (WFS). (2.) At low particle hydrophobicity and, correspondingly, high WFS, an extreme dependence of Ecoll on particle size was observed. The use of superclean water in our experiments prevented the retardation of bubble surface movement caused by surfactants or other impurities that is usual for other investigations and where particle-bubble inertial hydrodynamic interactions are suppressed. In the present study the free movement of the bubble surface enhances particle-bubble inertial interaction, creating conditions for different flotation modes, dependent on WFS. At the instant of inertial impact, a particle deforms the bubble surface, which may cause its rebound. Where the stability of the thin water film, formed between opposing surfaces of a bubble and a particle, is low, its rupture is accompanied with three phase contact line extension and contact angle formation before rebound. This prevents rebound, i.e. the first collision is accompanied by attachment. A high WFS prevents rupture during an impact. As a result, a contact angle does not arise and rebound is not prevented. However, rebound is accompanied by a second collision, the kinetic energy of which is smaller and can cause attachment at repetitive collision. These qualitative considerations are confirmed by the model quantification and comparison with measured Ecoll. For the first time the Sutherland equation (SE) for Ecoll is confirmed by experiment for smaller particle sizes and, correspondingly, very small Stokes numbers. The larger the particle size, the larger is the measured deviation from the SE. The SE is generalized, accounting for the centrifugal force, pressing hydrodynamic force and drainage in the low WFS case and, correspondingly, attachment occurs at first collision or during sliding. The derived generalized Sutherland equation (GSE) describes experimental data at low WFS. However, its application without account for possible rebound does not explain the measured extreme dependence in the case of high WFS. The theory for drainage during particle impact and the beginning of rebound enables conditions for either attachment or rebound in terms of the normal component of the impact velocity and the critical film thickness to be derived. Combining this condition with the GSE allowed the equation for Ecoll to be derived, accounting for attachment area shrinkage and attachment during a repetitive collision. This equation predicts the extreme dependence. Thus the WFS determines the modes of flotation dynamics and, in turn, probably affects the mechanisms, which control the flotation domain. At low WFS its upper boundary is controlled by the stability of the particle-bubble aggregate. At high WFS the upper boundary can be controlled by rebound because the latter reduces the attachment efficiency by a factor of 30 or more even with repetitive collision.

Journal Article↗

PubMed2001

Cloning, heterologous expression, and functional characterization of 5-epi-aristolochene-1,3-dihydroxylase from tobacco (Nicotiana tabacum).

Capsidiol is a bicyclic, dihydroxylated sesquiterpene produced by several solanaceous species in response to a variety of environmental stimuli. It is the primary antimicrobial compound produced by Nicotiana tabacum in response to fungal elicitation, and it is formed via the isoprenoid pathway from 5-epi-aristolochene. Much of the biosynthetic pathway for the formation of this compound has been elucidated, except for the enzyme(s) responsible for the conversion of 5-epi-aristolochene to its dihydroxylated form, capsidiol. Biochemical evidence from previous studies with N. tabacum (Whitehead, I. M., Threlfall, D. R., and Ewing, D. F., 1989, Phytochemistry 28, 775-779) and Capsicum annuum Hoshino, T., Yamaura, T., Imaishi, H., Chida, M., Yoshizawa, Y., Higashi, K., Ohkawa, H., Mizutani, J., 1995, Phytochemistry 38, 609-613. suggested that the oxidation of 5-epi-aristolochene to capsidiol was mediated by at least one elicitor-inducible cytochrome P450 hydroxylase. In extending these observations, we developed an in vivo assay for 5-epi-aristolochene hydroxylase activity and used it to demonstrate a dose-dependent inhibition of activity by ancymidol and ketoconazole, two well characterized inhibitors of cytochrome P450 enzymes. Using degenerate oligonucleotide primers designed to the well conserved domains found within most P450 enzymes, including the heme binding domain, cDNA fragments representing four distinct P450 families (CYP71, CYP73, CYP82, and CYP92) were amplified from a cDNA library prepared against mRNA from elicitor-treated cells using PCR. The PCR fragments were subsequently used to isolate full-length cDNAs (CYP71D20 and D21, CYP73A27 and A28, CYP82E1 and CYP92A5), and these in turn were used to demonstrate that the corresponding mRNAs were all induced in elicitor-treated cells, albeit with different induction patterns. Representative, full-length cDNAs for each of the P450s were engineered into a yeast expression system, and the recombinant yeast assessed for functional expression of P450 protein by measuring the CO difference spectra of the yeast microsomes. Only microsomal preparations from yeast expressing the CYP71D20 and CYP92A5 cDNAs exhibited significant CO difference absorbance spectra at 450 nm and were thus tested for their ability to hydroxylate 5-epi-aristolochene and 1-deoxycapsidiol, a putative mono-hydroxylated intermediate in capsidiol biosynthesis. Interestingly, the CYP71D20-encoded enzyme activity was capable of converting both 5-epi-aristolochene and 1-deoxycapsidiol to capsidiol in vitro, consistent with the notion that this P450 enzyme catalyzes both hydroxylations of its hydrocarbon substrate.

Amino Acid Sequence↗

PubMed2000

Particle-bubble collision models--a review

A critical review of the various models existing in the literature for the calculation of the collision efficiency between particles and single, rising gas bubbles is presented. Although all of these collision models predict that the collision efficiency increases with particle size, their dependence on the latter is different because of the various assumptions and hydrodynamic conditions used in each model. Collision efficiencies of quartz particles with single bubbles have been obtained from experimental flotation experiments under conditions where the attachment and stability efficiencies were at, or near, unity. These collision efficiencies were then used to test various collision models. Good agreement between the experimental and calculated collision efficiencies was only obtained with the Generalised Sutherland Equation. The differences in collision efficiencies obtained between the various models were mainly explained in terms of, firstly, the degree of mobility of the bubble surface and, secondly, a consideration of the inertial forces acting on the particles.

Journal Article↗

PubMed1999

Particle-Bubble Attachment in Mineral Flotation.

Attachment efficiencies of rough, angular, methylated quartz particles with nitrogen bubbles are derived from experimental capture efficiency data in conjunction with a collision model termed the Generalized Sutherland Equation (GSE). The methylated quartz particles ranged in size from 7.5 to 70 µm equivalent diameter and had advancing contact angles between 33 degrees and 74 degrees. They heterocoagulated with nitrogen bubbles between 0.77 and 1.52 mm in diameter in 0, 0.01, or 0.1 mol dm(-3) KCl. The attachment efficiencies decreased with increasing particle size and bubble size, but increased with particle contact angle and KCl electrolyte concentration. These attachment efficiency data were then used to test the Dobby-Finch attachment model for potential flow conditions. The latter model was modified so that the conditions of approach of the particle toward the bubble surface are the same as those defined previously in the GSE collision model (Dai et al., 1998, J. Colloid Interface Sci. 197, 275). Satisfactory agreement was obtained between the experimental attachment efficiencies obtained in this study and those calculated with the Dobby-Finch model. In the attachment efficiency calculations, the induction time (t(ind)) varied with particle size (d(p)) according to the well-known equation, t(ind) = Ad(B)(p). The parameter B, with a value of 0.6, was found to be independent of particle size, particle contact angle, bubble size, and KCl electrolyte concentration. Conversely, the value of the parameter A was dependent on the particle contact angle, especially for contact angles smaller than 50 degrees, and on the bubble size but to a lesser extent on the electrolyte concentration. The value of A decreased with an increase in particle contact angle and an increase in bubble size. The values of the induction time obtained in this study are in a reasonable agreement with experimental and calculated induction times reported in the literature. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

The Influence of Interfacial Structuring on Gibbsite Interactions in Synthetic Bayer Liquors.

The interaction forces between gibbsite particles aging in synthetic, supersaturated sodium and potassium aluminate solutions (Bayer liquors) have been investigated. Compliance with DLVO-type behavior was observed in dilute electrolyte. Under synthetic Bayer conditions, non-DLVO, repulsive steric forces exist. Upon aging, this steric repulsion gradually diminishes and disappears. A structured interfacial layer, displaying inner and outer regions of different compressibility, develops as aging occurs and interparticle adhesion increases. At high particle approach velocities, hydrodynamic forces exist which are dependent upon the viscosity of solution. The steric, adhesive, and hydrodynamic interactions are all greater in NaAl(OH)4 compared with KAl(OH)4 liquors of the same concentrations and degree of aging. Solution Al(OH)-4 ion-mediated interfacial structuring is apparently responsible for the time-dependent repulsive and adhesive forces. These interfacial phenomena are perceived to be precursors to, or part of, gibbsite crystal growth and agglomeration mechanisms. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

The Electrochemistry of Nonaqueous Copper Phthalocyanine Dispersions in the Presence of a Metal Soap Surfactant: A Simple Equilibrium Site Binding Model.

The electrophoretic mobilities of copper phthalocyanine particles, dispersed in isoparaffin solutions containing zirconium octanoate, have been determined using phase-analysis light scattering. All the samples studied contained trace concentrations of water. The mobility values were converted to zeta potentials using the Hückel equation. All the systems studied exhibited a pronounced maximum in zeta potential as the zirconium octanoate concentration increased. The maximum occurred at a bulk zirconium octanoate concentration equivalent to that required for complete coverage of the particles. The zeta potential data were converted to surface charge density values through the use of the Poisson-Boltzmann equation. The latter were in the range 0.4 to 2.5 µC m-2. A simple two equation site binding theory, which considered the dissociation of zirconium octanoate and the subsequent adsorption of ions at a generic surface site, was successfully applied to the surface charge data. It is proposed that the maximum in the zeta potential and surface charge as a function of zirconium octanoate concentration was observed due to the preferential location of ZrO2+ ions at the particle surface, followed by charge neutralization with octanoate anions. It is suggested that water facilitates the dissociation process of the zirconium octanoate, although it does not directly contribute to the surface charge itself. Two plausible qualitative mechanisms are described. The first involves the presence of water at the particle-solution interface, whilst the second considers the formation of micelles in the bulk isoparaffin phase. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Copper Phthalocyanine-Mica Interactions in Nonaqueous Media.

The interaction forces and adhesion of copper phthalocyanine particles with a mica substrate in isoparaffin were directly measured using an atomic force microscope. The study was conducted primarily to investigate the stabilization mechanism of copper phthalocyanine dispersions in a nonaqueous medium. The nature of the forces was examined in the presence of various concentrations of water and zirconium octanoate, both of which are present at the particle-isoparaffin interface. A weak attraction, as well as a small adhesion, exists between the copper phthalocyanine particles and the mica surface. These interactions are a function of the water content of the hydrocarbon phase and appear to be a result of capillary forces. The addition of zirconium octanoate produces significant short range repulsive forces with no adhesion between the copper phthalocyanine and mica surfaces. The shape of the force against distance curves suggests that the dispersion stability of the copper phthalocyanine arises through steric stabilization by adsorbed zirconium octanoate. The same qualitative interaction behavior was observed when the copper phthalocyanine particle was coated with a layer of polyvinyl acetate latex. Copyright 1999 Academic Press.

Journal Article↗

PubMed1998

Adsorption of Monoalkyl Phosphates at the Zircon-Aqueous Solution Interface.

The adsorption of a series of monoalkyl phosphates (MAP) of varying alkyl chain lengths (Cn) on a pure natural sample of zircon (ZrSiO4) at 25 degreesC has been studied as a function of concentration and pH. Electrokinetic (zeta-potential) studies showed a significant shift of the isoelectric point of zircon (pH approximately 5.7) to lower pH values, indicating specific interactions between zircon and MAP. Diffuse reflectance infrared Fourier transform spectroscopy and pH increment studies suggested that adsorption of MAP onto zircon proceeded via chelate formation. Adsorption was aided by an attractive lateral alkyl chain interaction energy (phi) of approximately -0.85kT per CH2 group, which suggested that surface aggregates form on the zircon surface. Adsorption isotherms were best described by a Langmuir model, indicating that attractive lateral alkyl chain interactions were compensated by repulsive headgroup interactions, resulting in a pseudo-ideal system. Copyright 1998 Academic Press.

Journal Article↗

PubMed1998

The Inertial Hydrodynamic Interaction of Particles and Rising Bubbles with Mobile Surfaces

The collection efficiency of single bubbles rising through a very dilute pulp of hydrophobized quartz particles has been determined. Measurements have been performed under conditions in which the bubble surface is mobile, as a function of electrolyte concentration, particle diameter (7 to 70 &mgr;m), bubble diameter (0.77 x 10(-3) to 1.52 x 10(-3) m), and particle advancing water contact angle. Situations in which the product of attachment and stability efficiency is at its maximum value have been identified, permitting a stringent, critical test of collision theory to be performed. A collision theory has been developed which accounts for the influence of positive and negative inertial forces in the case of bubbles with mobile surfaces. The approach considers only long-range hydrodynamic interactions under conditions where short-range interactions are strongly suppressed (i.e., high particle contact angle and high electrolyte concentrations) and attachment occurs at first collision. In this instance, good agreement between theory and experiment is achieved for particle diameters between 7 and 60 &mgr;m and Stokes numbers up to 0.27. The analytical equation developed is termed the generalized Sutherland equation (GSE). Copyright 1998 Academic Press. Copyright 1998Academic Press

Journal Article↗

PubMed1997

Inositol triphosphate receptors in sea urchin sperm.

Inositol 1,4,5-triphosphate (Ins(1,4,5)P3) is a second messenger that regulates Ca2+ channels in many important cell signalling pathways. In sea urchin sperm the outer investment of the egg triggers the acrosome reaction (AR) that involves Ins(1,4,5)P3 production and the opening of two Ca2+ channels. Here we have sought to identify a high-affinity Ins(1,4,5)P3 receptor in Strongylocentrotus purpuratus sperm. An Ins(1,4,5)P3 binding component was affinity-purified 12-fold from sperm extracts. It displayed similar characteristics to the Ins(1,4,5)P3 receptor from other sources: pH-dependent high affinity for Ins(1,4,5)P3 (KD = 261 nM), a tau1/2 of association and dissociation of 50 and 40 s, respectively, specificity (IC50 > 5 microM for Ins(1)P1, Ins(1,4)P2 and Ins(1,3,4,5)P4), and pharmacological sensitivity (10 and 100 microg heparin/ml inhibited 75% and 100% binding respectively). An antibody against the carboxy-terminal of the type I Ins(1,4,5)P3 receptor of somatic cells recognised a plasma membrane component in the sperm head and less intensely in the flagella. This antibody also recognised a 240 kDa band from isolated head plasma membranes, and weakly in flagellar membrane. This IP3 receptor-like protein may mediate the sustained uptake of Ca2+ through the second Ca2+ channel opened during the AR.

Animals↗

PubMed1996

Contact Angle Studies of Ethyl Xanthate Coated Galena Particles

The wettability of ethyl xanthate coated galena particles has been determined from measurements of the equilibrium capillary pressure across a packed bed. Both the advancing liquid powder contact angle, thetap, and the specific wettable surface area, Awet, of galena particles have been obtained. The influence of particle size and ethyl xanthate surface coverage on the powder contact angle have been investigated and compared with floatability. Ethyl xanthate at a surface coverage of less than ten percent of an equivalent monolayer significantly increases both thetap and particle floatability.

Journal Article↗

PubMed1995

Comparison of an antigen capture enzyme-linked assay with reverse transcription--polymerase chain reaction and cell culture immunoperoxidase tests for the diagnosis of ruminant pestivirus infections.

A study to compare the merits of three different tests for the diagnosis of ruminant pestivirus infections was carried out. Sensitivity studies using reference strains of bovine viral diarrhoea virus (BVDV) and buffy coat samples from persistently infected (PI) carriers showed the reverse transcription-polymerase chain reaction (RT-PCR) had a greater sensitivity than the other tests. The antigen capture enzyme-linked immunosorbent assay (ELISA) was least sensitive and could only be used on samples containing cells (tissue or blood). When 169 clinical samples were examined, the RT-PCR detected the most positives (42) compared to the ELISA (32) and the immunoperoxidase test (IPT) (20). The RT-PCR was more successful when specific antibody was also present in the sample. The lower sensitivity of the IPT was related to the use of a 1 passage (4-day) test and the testing of toxic or contaminated samples. The ELISA was found to be most suitable for large-scale testing for the diagnosis and control of pestivirus infections.

Animals↗

PubMed1992

Occupational therapists in private practice.

Although increasing numbers of occupational therapists are choosing to work in private practice, little data exist describing this sector of the profession. In the present study, experienced occupational therapists were asked about their moves into private practice, including (a) their motivation, (b) their preparation, and (c) their perceptions of the move's risks and benefits before and after the move. A survey was sent to a national random sample of 105 occupational therapists, 74 of whom responded. According to the survey, autonomy was the most important motivating factor for occupational therapists moving into private practice. However, once they were in private practice, the occupational therapists noted that increased income was a major benefit. These occupational therapists had planned for the risks of reimbursement, referral sources, and overhead but had not anticipated problems with staffing shortages. Incomes increased for occupational therapists who moved into private practice. The survey compared the incomes of occupational therapists before and after they entered private practice. It also compared their income and educational levels. Other comparisons included income and work experience, income and work role, and income and geographic location. Autonomy and financial considerations appear to be the overriding issues for occupational therapists choosing careers in private practice. Almost unanimously, the survey respondents said that private practice was a good career choice.

Adult↗

PubMed1990