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At least 685 records · Page 38Linked to original sources

PubMed2006

Numerical simulation of film coating process in a novel rotating fluidized bed.

In this study, numerical simulation of film coating process in a novel rotating fluidized bed (RFB) was conducted by using a Discrete Element Method (DEM)-Computational Fluid Dynamics (CFD) coupling model. Particle movements and fluid motions in a centrifugal force field were simulated at three-dimensional cylindrical coordinate, and this model was applied to film coating process. Film coating process in a RFB was numerically analyzed by using a simplified assumption that a particle was coated only when a particle existed within a spray zone. The experiments were also conducted and uniformity of sprayed material was evaluated by investigating color difference of the coated particles. As a result of the numerical simulation, three-dimensional bubble movements and particle circulation could be well simulated. In addition, mass of the sprayed material on a single particle in a RFB could be visualized by using our proposed model. The relationship between distribution of the sprayed material and the coating time was also analyzed. Calculated mass distributions of the sprayed material could be expressed by a normal distribution function, showing qualitative good agreement with the previous studies. Effect of the operating parameters, such as gas velocity and centrifugal acceleration, on the uniformity of the sprayed material was also investigated by both numerical and experimental approaches. Comparison of the coating process in a RFB with that in a conventional fluidized bed was also conducted by the numerical simulation. The result showed that uniformity of the sprayed material was greatly improved in a RFB due to the much smaller circulation time.

Chemistry, Pharmaceutical↗

PubMed1997

[New aspects of the mechanism of Ca2+ entry in non-excitable cells].

The capacitative Ca2+ entry has been accepted to play a crucial role in Ca2+ signaling in non-excitable cells, and the mechanisms linking the depletion of intracellular Ca2+ stores to the activation of Ca2+ entry are presently the subject of intensive investigation. There are two hypotheses to explain the molecular mechanism of capacitative Ca2+ entry. One is that a diffusible second messenger released from intracellular Ca2+ stores may activate a Ca2+ channel at the plasma membrane. Numerous molecules, including CIF, cGMP, arachidonic acid, and a small G-protein, are proposed as the candidates for the diffusible messenger. In addition, the capacitative Ca2+ entry has been suggested to be modulated by protein phosphorylation/dephosphorylation. Another hypothesis is termed the "conformational coupling model". This model suggests that information between the IP3 receptor and a plasma membrane Ca2+ channel may be transferred directly through conformational protein-protein interactions. The plasma membrane Ca2+ channel involved in the capacitative Ca2+ entry is still neither purified nor cloned, but recent studies suggest that the mammalian homologue of the Drosophila protein Trp may function as a capacitative Ca2+ entry channel.

Animals↗

PubMed2003

Vacuum evaporated porous silicon photonic interference filters.

Porous materials with nanometer-scale structure are important in a wide variety of applications including electronics, photonics, biomedicine, and chemistry. Recent interest focuses on understanding and controlling the properties of these materials. Here we demonstrate porous silicon interference filters, deposited in vacuum with a technique that enables continuous variation of the refractive index between that of bulk silicon and that of the ambient (n approximately 3.5 to 1). Nanometer-scale oscillations in porosity were introduced with glancing angle deposition, a technique that combines oblique deposition onto a flat substrate of glass or silicon in a high vacuum with computer control of substrate tilt and rotation. Complex refractive index profiles were achieved including apodized filters, with Gaussian amplitude modulations of a sinusoidal index variation, as well as filters with index matching antireflection regions. A novel quintic antireflection coating is demonstrated where the refractive index is smoothly decreased to that of the ambient, reducing reflection over a broad range of the infrared spectrum. Optical transmission characterstics of the filters were accurately predicted with effective medium modeling coupled with a calibration performed with spectroscopic ellipsometry.

Journal Article↗

PubMed2006

Optimal design of predenitrification systems.

A coupled model of biological and settling phases aimed at optimal design of predenitrification systems is presented. Each unknown is obtained in explicit form, and is expressed as a function of the system's required performance. A model, taking into account both suspended and dissolved substrates, is adopted for the biological phase, while the limiting solid flux theory is assumed for the design of the settling phase. Finally, a relationship correlating the two phases is obtained expressing opportunely the sludge recycle flow and the sludge waste flow, without recourse to empirical parameters. The effect of different influent and effluent wastewater characteristics on the model's results is also analyzed.

Biodegradation, Environmental↗

PubMed1987

New criteria for the diagnosis of ankylosing spondylitis.

Criteria for ankylosing spondylitis are useful for two main purposes. First, to provide unity of diagnosis in population surveys; secondly, in the field of therapeutic assessment. This paper is concerned with criteria used largely in the former role, i.e. as an epidemiological tool. Critical formulation and subsequent evaluation of criteria is important if a realistic measure of disease prevalence is to be obtained. The New York criteria have provided the general currency for diagnosis epidemiologically in recent years, but their value, in their originally published form, has been questioned for various reasons. Attempts have been made to improve these criteria or to suggest alternatives. Although increased sophistication of the original New York criteria has doubtless been achieved, the position regarding the diagnosis of ankylosing spondylitis continues to represent a challenge. The main concern is that the present "index of truth" for the disease, radiological sacroiliitis, is all too often a delayed feature, presenting only after pain has been present for some time. A second problem is the difficulty in diagnosing with confidence the early changes of sacroiliac sclerosis and erosion, and the degree of intra- and inter-observer error arising from these changes. Newer techniques such as radioisotope scintigraphy and computerised tomography (CT) are unlikely to replace the traditional pelvic radiograph. The way forward is more likely to be in the direction of how existing data are processed rather than what is used to obtain them. In this vein, suitable mathematical/biological models coupled with computer technology could provide realistic tools through a system of probability weighting of existing criteria.

Humans↗

PubMedDate not supplied

Do band 3 protein conformational changes mediate shape changes of human erythrocytes?

The bilayer-couple model predicts a reversible membrane crenation for an increasing ratio of external to internal monolayer area. This was comprehensively proven. However, individual erythrocytes may undergo dramatic shape changes within seconds when the suspension medium is changed. In contrast, under physiological conditions with no addition of membrane active compounds, active phospholipid translocation and passive flip-flops are comparatively slow. We propose that conformational changes of the anion-exchange protein, band 3, may rapidly alter the monolayer area ratio. Band 3 occupies about 10% of the total membrane area of human erythrocytes. Under physiological conditions, its conformers are asymmetrically distributed with about 90% of the transport sites facing the cytoplasm. This distribution is altered when external conformations are recruited by changing the transmembranous Cl- gradient, the external pH, or by the application of inhibitors. In experiments, recruitment by low ionic strength caused a rapid, temporary formation of echinocytes. This suspension effect could also be found at high ionic concentrations, when Cl- was replaced by SO4(2-). Inhibitors known to recruit the external band 3 conformation, like DIDS, SITS and flufenamic acid, are echinocytogenic. For inhibitors not recruiting a certain conformation, e.g. phenylglyoxal and niflumic acid, no shape effect was found. Since band 3 ensures a fast equilibrium of internal and external anions these ions are usually distributed according to the transmembrane potential (TMP). In the literature, a correlation of TMP and band 3 conformation, as well as a correlation of TMP and red cell shape, is described. In the proposed model, low external Cl- concentrations, inhibitors, or a negative TMP may recruit the transport sit outwards.(ABSTRACT TRUNCATED AT 250 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1984

Investigation of drug-receptor interactions by means of irreversible receptor inhibitors: binding of oxytocin and angiotensin II to their receptors in rat uterus.

A stimulus-response coupling model in which individual steps follow hyperbolic or Hill-type laws has been employed to mimic phenomena associated with irreversible receptor inhibition (receptor reserve) in a responding biological system. Two methods for computation of ligand-receptor dissociation constant (KA) have been derived from this model: 1) The relation between pD2 and maximal attainable response allows a rough estimate of KA; 2) A generalization of the earlier Furchgott-Bursztyn procedure employing equipotent doses for noninhibited and partially inhibited systems, has been achieved by introduction of Hill equation into the model. Applied to oxytocin and angiotensin II receptors in rat uterus, these pharmacological methods indicate rather low affinity of the two receptors for the respective peptides (around 2 X 10(-8) for angiotensin II and 2 X 10(-7) mol/l for oxytocin), in case of oxytocin much lower than values reported from binding studies. Apparently, several binding sites are present on the target tissue cells from which the methods based on cellular response can pick up those corresponding to the receptors. Biophysical methods are lacking this ability. Single pD2 values in noninhibited systems cannot themselves deliver any relevant information about receptor binding.

Angiotensin II↗

PubMed2000

Hyperosmotic hemolysis and antihemolytic activity of the saponin fraction and triterpene glycosides from Panax ginseng C. A. Meyer.

A saponin fraction and triterpene glycosides Rb1, Rb2 and Rg1 from Panax ginseng C. A. Meyer (saponins) were shown to inhibit the hyperosmotic hemolysis of erythrocytes. Using scanning electron microscopy and light scattering, saponins were found to restore the shape of the cells by inhibiting their contraction and the formation of echinocytes and microspherocytes. Scanning microcalorimetry demonstrated that an increase in osmomolarity and ionic strength of the medium eliminated structural transitions of erythrocyte ghost membranes. The hyperosmotic conditions were shown to cause the destruction of the erythrocyte membrane skeleton, except for the cytoplasmic and membrane domains of band 3 proteins. Saponins changed the parameters of all membrane structural transitions, induced new reversible transitions in the membranes and eliminated the ripple phase of dipalmitoylphosphatidylcholine. The mechanism of the antihemolytic action is discussed based on the bilayer couple model hypothesis.

Erythrocytes↗

PubMed2001

Membrane active compounds that affect the shape of cells and cellular organelles.

Amphiphilic membrane active compounds are considered that affect the shapes of cells and cellular organelles by intercalation into the phospholipid part of their membranes. It is taken into consideration that amphiphile-membrane interaction modifies membrane mechanical properties. The relationship between membrane mechanical properties and vesicle shapes and the concept of the bilayer couple model are shortly reviewed. Then it is put forward that the strength of the amphiphile-membrane interaction may depend on the lateral packing of phospholipid molecules. It is shown that in such a case the amphiphile molecules bind to the membrane in a cooperative manner. Moreover, the amphiphile binding makes the ratio between the nonlocal and local membrane bending constants to be effectively larger and thus widens the range of possible stable vesicle and cellular shapes.

Animals↗

PubMed2003

[Effects of actin cytoskeleton rearrangements on channel activation by calcium entry into A431 cells].

Using patch clamp and ion-selective fluorescence dye techniques, we investigated the influence of actin cytoskeleton rearrangements on the activity of calcium entry channels in plasma membrane of human carcinoma A431 cells. It is shown that disruption of actin microfilaments by cytohalasin D has no significant effect on calcium release from the stores and its entry from the extracellular space. It also does not interfere with the activation of inositol 1,4,5-trisphosphate (IP3)-dependent high-selective low-conductance calcium channels Imin. The treatment of cells with calyculin A induces the formation of actin filament layer beneath plasma membrane and also inhibits Imin activation and calcium entry through the plasma membrane, though calcium efflux from the stores was nearly unchanged. Thus, it is concluded that calcium signalling in A431 cells can be modulated by actin cytoskeleton rearrangements, and may be well described in terms of "conformational coupling" model.

Actins↗

PubMed2006

[Study on photoluminescence spectra of Cd(1-x)Mn(x)Te/CdTe diluted semiconductor superlattices with high Mn compositions].

The electronic properties of Cd(1-x)Mn(x)Te/CdTe semiconductor superlattices (SLs) with high Mn concentrations (x up to 0.8) were studied by means of low and room temperature photoluminescence (PL). The samples were grown by MBE on GaAs substrates with CdTe buffers. PL allowed the investigation of the optical emission from the fundamental 11H excitonic transition, revealing the high quantum efficiency and quality of the SLs. The temperature dependence of the excitonic PL energy position and excitonic line-shape broadening were studied. An exciton-longitudinal optical phonon couple model can be used to explain the experimental results very well. Photoreflectance (PR) spectra were also performed in order to compare with the authors' photoluminescence results. The combined use of PL and PR allowed a full understanding of the electronic states and optical emission characteristics of the authors' SLs. The authors' results indicate that high quality Cd(1-x)Mn(x)Te/CdTe SLs with high Mn concentrations can be grown using MBE on GaAs substrates. The possibility to have magnetic semiconductor nanostructures opens the way to applications in the field of spintronics toward devices based on new concepts.

English Abstract↗

PubMed1987

On the mechanism and measurement of shape transformations of constant volume of human red blood cells.

A method is described for measuring the rate of disc-sphere transformations of constant volume by recording changes in the intensity and noise envelope of light transmitted through a stirred suspension of human red blood cells. We used this method to determine the rates and characteristics of disc-sphere transitions induced by various sphering agents (uranyl nitrate, rose bengal, Na glycocholate). It was found that, when sphered by any of these agents, cells spontaneously reverted to discs upon continued incubation in the presence of the agent. The rate of sphering was directly proportional and the rate of spontaneous reversal inversely related to the concentration of sphering agent used. Plasma added before an agent is added prevents subsequent sphering; plasma added after sphering had occurred accelerated reversal. During spontaneous reversal of the spheres to discs, sphering could again be induced prior to subsequent return to discs either by the addition of more agent or, in certain circumstances, by the addition of plasma. Spontaneous reversal of discs to spheres qualitatively correlates with the uptake rate of agent (rose bengal), the cells becoming discs as uptake is completed. Furthermore, establishment of temporary proton gradients across the membrane promotes sphering with return to discs as pH equilibrium takes place. Evidently, the spherical shape is a transient form representing the unequal distribution of agent across the membrane. The spherical form could thus be associated with a change in the relative surface energies between the outer and inner lipid leaflets, such as a difference in their relative surface areas, as hypothesized in the "bilayer couple" models. The molecular mechanism(s) underlying the action of sphering agents and protons may not be the same.

Adult↗

PubMed1984

Evidence for the formation of a linear [3Fe-4S] cluster in partially unfolded aconitase.

Beef heart aconitase, as isolated under aerobic conditions, is inactive and contains a [3Fe-4S]1+ cluster. On incubation at pH greater than 9.5 (or treatment with 4-8 M urea) the color of the protein changes from brown to purple. This purple form is stable and can be converted back in good yield to the active [4Fe-4S]2+ form by reduction in the presence of iron. Active aconitase is converted to the purple form at alkaline pH only after oxidative inactivation. The Fe/S2- ratio of purple aconitase is 0.8, indicating the presence of [3Fe-4S] clusters. The number of SH groups readily reacting with 5,5'-dithiobis(2-nitrobenzoic acid) is increased from approximately 1 in the enzyme as isolated to 7-8 in the purple form, indicating a partial unfolding of the protein. On conversion of inactive aconitase to the purple form, the EPR signal at g = 2.01 (S = 1/2) is replaced by signals at g = 4.3 and 9.6 (S = 5/2). Mössbauer spectroscopy shows that purple aconitase has high-spin ferric ions, each residing in a tetrahedral environment of sulfur atoms. The three iron sites are exchange-coupled to yield a ground state with S = 5/2. Analysis of the data within a spin coupling model shows that J13 congruent to J23 and 2 J12 less than J13, where the Jik describe the antiferromagnetic (J greater than 0) exchange interactions among the three iron pairs. Comparison of our data with those reported for synthetic Fe-S clusters (Hagen, K. S., Watson, A. D., and Holm, R. H., (1983) J. Am. Chem. Soc. 105, 3905-3913) shows that purple aconitase contains a linear [3Fe-4S]1+ cluster, a structural isomer of the S = 1/2 cluster of inactive aconitase. Our studies also show that protein-bound [2Fe-2S] clusters can be generated under conditions where partial unfolding of the protein occurs.

Aconitate Hydratase↗

PubMed1982

Mössbauer study of a bacterial cytochrome oxidase: cytochrome c1aa3 from Thermus thermophilus.

Cytochrome c1aa3 from Thermus thermophilus has optical and EPR properties similar to bovine cytochrome c oxidase. We have studied 87Fe-enriched samples with Mössbauer spectroscopy in the fully oxidized and fully reduced states and in the oxidized state complexed with cyanide. The cytochromes a and c1 yielded spectra quite similar to those reported for the cytochromes c and b5; in the oxidized state the spectra reflect noninteracting, low spin ferric hemes, whereas the a- and c1-sites of the reduced enzyme are typical of low spin ferrous hemochromes. The spectra of the reduced enzyme show that reduced cytochrome a3 is high spin ferrous, with Mössbauer parameters quite similar to those of deoxymyoglobin. Upon addition of cyanide to the oxidized enzyme, the a3-site exhibits in the absence of an applied magnetic field and at temperatures down to 1.3 K a quadrupole doublet with parameters typical of low spin ferric heme-CN complexes. The low temperature spectra taken in applied magnetic fields show that the electronic ground state of the a3-CN complex has integer electronic spin, suggesting ferromagnetic coupling of the low spin ferric heme (S = 1/2) to Cu2+ (S = 1/2) to yield as S = 1 ground state. We have examined the oxidized enzyme from two different preparations. Both had good activity and identical optical and EPR spectra. The Mössbauer spectra, however, revealed that the a3-site had a substantially different electronic structure in the two preparations. Neither configuration had properties in accord with the widely accepted spin-coupling model proposed for the bovine enzyme.

Cyanides↗

PubMed1997

Renal toxicities of antineoplastic drugs and bone marrow transplantation.

A number of antineoplastic chemotherapeutic drugs may produce fluid and electrolyte disturbances or nephrotoxic reactions extending across the clinical spectrum, from subclinical renal dysfunction to progressive chronic renal insufficiency to severe acute failure. Although some of the drugs that are highly nephrotoxic are now seldom used, others are tremendously useful in modern clinical oncology. Some newer antineoplastic therapies such as interleukin-2 and bone marrow transplantation are commonly associated with nephrotoxicity. Although our understanding of the pathophysiological mechanisms underlying these toxic reactions is still rather rudimentary, information derived from animal models, coupled with clinical experience, has in many circumstances generated clinical interventions that can successfully limit treatment-related renal injury.

Animals↗

PubMed1998

Immunoglobulin transgenes as targets for somatic hypermutation.

This review describes studies on somatic hypermutation of immunoglobulin genes that were started in the mid-80s in collaboration with Ralph Brinster. Almost all of the experiments were carried out using Ig transgenes as targets for the somatic mutation mechanism. Ig transgenes can be very good targets of somatic mutation, despite many different transgene integration sites. Thus, the required cis-acting elements must be present within the approximately 10 kb of the transgene. Only the Ig variable region and its proximate flanks are mutated, not the constant region in unmanipulated sequences. Several Ig gene enhancers are permissive for somatic mutation and they do not have to be associated with the Ig promoter they normally interact with. However, the mutation process does seem to be specific for Ig genes. No mutations were found in several housekeeping genes isolated from cells that had very high levels of somatic hypermutation of their Ig genes. This suggests that the Ig enhancers provide the lg gene specificity. An exception is the Bcl-6 gene, encoding a transcription factor, which was found to be mutated in normal human memory B cells. When the transcriptional promoter that is located upstream of the variable region is duplicated upstream of the constant region, this region is mutated as well. This suggests a transcription coupled model in which a mutator factor associates with the RNA polymerase at the initiation of transcription, travels with the polymerase during elongation, and causes mutations during polymerase pausing. Our recent data with an artificial substrate for somatic mutation suggest that the mutations are increased by increased stability of the secondary structures in the nascent RNA, and the specific nucleotides that are mutated are due to preferences of a mutator factor.

Animals↗

PubMed1994

Simulation Model of the Coupling between Nitrification and Denitrification in a Freshwater Sediment.

A model was constructed to simulate the results of experiments which investigated nitrification and denitrification in the freshwater sediment of Lake Vilhelmsborg, Denmark (K. Jensen, N. P. Sloth, N. Risgaard-Petersen, S. Rysgaard, and N. P. Revsbech, Appl. Environ. Microbiol. 60:2094-2100, 1994). The model output faithfully represented the profiles of O(2) and NO(3) and rates of nitrification, denitrification, and O(2) consumption as the O(2) concentration in the overlying water was increased from 10 to 600 muM. The model also accurately predicted the response, to increasing O(2) concentrations, of the integrated (micromoles per square meter per hour) rates of nitrification and denitrification. The simulated rates of denitrification of NO(3) diffusing from the overlying water (D(w)) and of NO(3) generated by nitrification within the sediment (D(n)) corresponded to the experimental rates as the O(2) concentration in the overlying water was altered. The predicted D(w) and D(n) rates, as NO(3) concentration in the overlying water was changed, closely resembled those determined experimentally. The model was composed of 41 layers 0.1 mm thick, of which 3 represented the diffusive boundary layer in the water. Large first-order rate constants for nitrification and denitrification were required to completely oxidize all NH(4) diffusing from the lower sediment layers and to remove much of the NO(3) produced. In addition to the flux of NH(4) from below, the model required a flux of an electron donor, possibly methane. Close coupling between nitrification and denitrification, achieved by allowing denitrification to tolerate some O(2) ( approximately 10 muM), was necessary to reproduce the real data. Spatial separation of the two processes (no toleration by denitrification of O(2)) resulted in too high NO(3) concentrations and too low rates of denitrification.

Journal Article↗

PubMed1998

Using coupling with the Gibbs sampler to assess convergence in animal models.

The coupling method was investigated as a method to assess the convergence of the Gibbs sampler when drawing marginal inferences with an animal model. This method is based on the output of two Markov chains with different starting values but the same conditional deviates. The coupling method shows that the Gibbs sampler has an exponential convergence when the variance components are assumed to be known. All the variables in the model have the same rate of convergence, and it is closely related with the largest eigenvalue of a matrix derived from the coefficient matrix of the mixed model equations. Models including the variance components as unknowns showed a rate of convergence equal for all the variables, and this rate of convergence was approximately exponential. The coupling method provides an estimation of the convergence at the current iteration, and it does not require a post-Gibbs analysis as do the single chain-based methods. The coupling method is less computationally demanding than multiple chain methods, because only two chains are required to assess convergence.

Analysis of Variance↗