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Query: UMLS:C0851184 (thinning)
 11,252 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Detailed viscosity measurements have been made of barium sulfate mixtures over a wide range of viscosities for use in radiography of the esophagus, stomach, and duodenum. A new methodology was developed for more accurate estimation of viscosity in non-Newtonian fluids in conventional cylinder-type viscometers. As base cases, the variation of viscosity with shear rate was measured for standard commercial mixes of e.z.hd (250% w/v) and a diluted mixture of liquid e.z.paque (40% w/v). These suspensions are strongly shear thinning at low shear rates. Above about 3s-1 the viscosity is nearly constant, but relatively low. To increase the viscosity of the barium sulfate mixture, Knott's strawberry syrup was mixed to different proportions with e.z.hd powder. In this way viscosity was systematically increased to values 130,000 times that of water. For these mixtures the variation of viscosity with temperature, and the change in mixture density with powder-syrup ratio are documented. From least-square fits through the data, simple mathematical formulas are derived for approximate calculation of viscosity as a function of mixture ratio and temperature. These empirical formulas should be useful in the design of "test kits" for systematic study for pharyngeal and esophageal motility, and clinical analysis of motility disorders as they relate to bolus consistency.
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PMID:Viscosity measurements of barium sulfate mixtures for use in motility studies of the pharynx and esophagus. 142 24

This paper proposes and studies a new three-parameter constitutive equation for whole human blood, tau = tau y+eta 2 gamma 1/2 + eta 1 gamma. The model aims at a proper description of the shear thinning behavior of blood at both low and high shear rates. While empirically based, it relies on continuum constitutive theories. The model has been verified by fitting the experimental data available in the literature using the weighted least squares. Results show that the proposed model fits the experimental data with nearly constant parameters in a wide shear range, and with average deviations epsilon less than 6.24%. Formulae to calculate the velocity profile and flow rate of the proposed model in a straight tube flow were deduced. Compared to Casson's and Newtonian models, it is concluded that the proposed model is more effective in describing the shear thinning behavior of blood within a wide shear range.
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PMID:A study on the constitutive equation of blood. 163 37

A decreased count of retinal photoreceptors all over the fundus and a loss of retinal pigment epithelium cells mainly in the parapapillary region have been reported to be associated with glaucoma. This study addressed the question whether this cell loss in the deep retinal layers may be connected with a change of the choroidal thickness in glaucomatous eyes. Histological sections of 12 eyes with secondary angle closure glaucoma due to a malignant melanoma of the ciliary body and 20 eyes with a malignant choroidal melanoma and normal intraocular pressure were histomorphometrically evaluated. Before enucleation the intraocular pressure was significantly higher in the glaucoma group compared with the control group. Thickness of the choroid was measured at 12 locations from the posterior pole to the fundus periphery. The choroid was significantly thinner in the glaucoma group than in the control group. The decreased choroidal thickness was mainly due to a diminished choroidal vessel diameter. The differences were more marked at the optic disc border than in the fundus periphery. The decreased choroidal thickness in the glaucomatous eyes suggests a reduced choroidal perfusion. It fits with the reported lack of autoregulation of the choroidal blood circulation. Considering the diminished choroidal thickness especially in the parapapillary region, it may be one among other factors explaining the changes of the deep retinal layers in eyes with glaucoma. It indicates that thinning of the choroid, besides the chorioretinal atrophy in the parapapillary region, should be added to the panoply of histological changes in glaucoma.
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PMID:Decreased choroidal thickness in eyes with secondary angle closure glaucoma. An aetiological factor for deep retinal changes in glaucoma? 834 72

Broiler chicks in different groups were fed furazolidone (0, 400 and 800 mg/kg feed) and sodium chloride (500 and 1510 mg/kg feed) separately and concurrently from 1 to 30 days of age. Furazolidone (Fz) induced ascites, leg weakness, convulsions, depression and mortality was exacerbated by concurrent feeding of 1510 mg NaCl. Hemorrhages in the liver, swollen kidneys, pallor of the kidneys and cystic testes were present in all birds fed furazolidone either alone or in combination with NaCl. However, at microscopic level, necrotic changes were observed in the liver and kidneys of birds fed NaCl only. Fz-induced cardiac ventricular dilatation and thinning of walls were more severe when 400 mg Fz was fed concurrently with 1510 mg NaCl but feeding of 800 mg Fz with the same level of NaCl resulted in partial amelioration of cardiac changes. It is suggested that high dietary NaCl may exacerbate and alter the clinical and morphological picture of Fz toxicosis.
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PMID:Effect of concurrent feeding of furazolidone and sodium chloride upon some clinical, pathological and cardiac morphometric parameters in broiler chicks. 859 92

The rheological properties of aqueous polystyrene latex dispersions from three synthetic batches, with nearly the same z-average particle sizes, 400 nm, but varying degrees of polydispersity, 0.085, 0.301, and 0.485, respectively, were systematically investigated using steady-state shear and oscillatory shear measurements. The particles were sized with photon correlation spectroscopy and transmission electron microscopy and were stabilized sterically with PEO-PPO-PEO triblock copolymer (Synperonic F127). Results from steady-state shear measurements show that the viscosities of the systems exhibit shear-thinning behavior at high solid fractions. However, the degree of shear thinning depends on the breadth of particle size distribution, with the narrowest distribution suspension exhibiting the highest degree of shear thinning. The Herschel-Bulkley relationship best describes the flow curves. The relative viscosities as a function of volume fraction data were compared, and it was found that the broadest distribution suspension had the lowest viscosity for a given volume fraction. In addition, the data were fitted to the Krieger-Dougherty equation for hard spheres. A reasonable agreement of theory with experiment is observed, particularly and surprisingly for the very broad distribution. However, when the contribution to the volume due to the adsorbed polymer layer is considered, the agreement between experiment and theory becomes closer for all the suspensions, although the agreement for the broad distribution suspension is now worse. Fitting the Dougherty-Krieger theory to the experimental data based on our experimental maximum packing fractions gives very good agreement for all the systems studied. From oscillatory shear measurements, the moduli were obtained as a function of frequency at various latex volume fractions. The results show general change of the dispersions from viscous (G" > G') at low volume fractions (0.25-0.30) to moderately elastic (G' > G") at moderately high volume fractions (0.41-0.45). The change at this concentration level is likely due to some compression and interpenetration of the stabilizing polymer chain at the periphery, indicating the dominance of the interparticle forces. Overall, the very broad distribution was found to have the lowest elastic modulus for a given volume fraction. Copyright 1999 Academic Press.
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PMID:Effect of Particle Size Distribution on the Rheology of Dispersed Systems. 1060 51

Defects in mitochondrial enzymes, such as pyruvate dehydrogenase and cytochrome oxidase, cause hereditary disorders which lead to modifications in cellular pH due to the accumulation of pyruvate and lactic acid. Mitochondrial diseases include severe neonatal diseases and less severe forms of adult diseases. We report the case of lactic acidosis in a newborn girl who was delivered at 36 weeks of gestation and who died 3 months after birth. Her family history revealed a relative with tetraparesis and mental retardation. Her clinical findings, such as tonic-clonic convulsions and accumulation of pyruvate and lactic acid in blood, urine and cerebrospinal fluid, were refractory to treatment and developed soon after birth. Ultrasound scans of the brain some days before death revealed cerebral atrophy with ventricular dilatation and thinning of the corpus callosum and septum pellucidum. The clinical diagnosis of metabolic lactic acidosis was confirmed by macroscopic, microscopic and ultrastructural findings seen at autopsy. On macroscopic examination, the heart was hypertrophic, and the brain was atrophic with ventricular dilatation and thinning of corpus callosum. Small cystic lesions were present in the basal ganglia. On microscopic examination, the latter were characterized by loss of neurons, gliosis and capillary proliferation. Ultrastructural examination of the heart and skeletal muscle showed lysis of myofibrils, mitochondrial pleomorphism and hyperplasia, and crystalline inclusion in mitochondria and in the matrix compartment. In reporting this case, we emphasize the importance of accurate postmortem examination and clinical data for the diagnosis of metabolic lactic acidosis.
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PMID:[An autopsy case of neonatal lactic acidosis]. 1129 18

A Landau theory for surface-enhanced ordering in smectic-A free-standing films is described, based on a generalization of de Gennes' model for a "presmectic" fluid confined between two walls. According to the theory, smectic ordering in free-standing films heated above the bulk smectic melting temperature is due to an intrinsic surface contribution rather than an external field. The theory yields a persistent finite-size effect, in that the film melting temperatures do not tend to the bulk transition temperature in the limit of infinite film thickness. It also predicts that a continuous transition from (N+1)- to N-layer films is impossible without an external field. The theory closely fits existing experimental data on layer-thinning transitions in compounds which exhibit a bulk smectic-A to nematic phase transition. Possible origins of the intrinsic surface contribution are discussed.
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PMID:Landau-de Gennes theory of surface-enhanced ordering in smectic films. 1130 63

A new preparation method has been developed in order to avoid the breaking of brittle samples for plan-view TEM investigation during and after mechanical and ion beam thinning. The thinning procedure is carried out on a reduced size piece of the sample (about 1.6 x 0.8 mm(2) or about 1-1.6 mm diameter) that is embedded into a 3-mm-diameter Ti disk, which fits the sample holder of the TEM. The small sample size and the supporting metal disk assure the mechanical stability and minimize the possibility of breaking during and after the preparation: The Ti disk is placed on adhesive kapton tape, a cut piece of the sample is put into the slot of the disk, pressed onto the tape and embedded with glue. The tape keeps the parts in place and in the same plane, keeps the sample surface safe from the embedding glue and can be removed easily after the glue solidifies. Subsequently, the embedded sample is thinned from the rear by well-known mechanical and ion beam techniques until electron transparency. This simple solution lowers the risk of failed sample preparation remarkably and makes it possible to reduce the thickness of the sample to about 50 microm by mechanical thinning. As a result, dimpling becomes unnecessary and low angle ion milling gives a large transparent area for TEM. Its efficiency has been proved by successful preparation of numerous thin film samples on Si, sapphire, and glass substrates. The method is compatible with the widespread cross-sectional thinning procedures, and can be easily adopted by TEM laboratories.
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PMID:Novel method for the plan-view TEM preparation of thin samples on brittle substrates by mechanical and ion beam thinning. 1187 8

Keratoconus is a debilitating corneal thinning disease that principally develops in the second and third decades of life. Our group previously developed a novel approach to studying keratoconus, based on the observation that there is a gradient of damage across the keratoconic cone. We identified a number of cellular characteristics of keratoconus such as discrete incursions of fine cellular processes from the anterior keratocytes in association with localised indentation of the basal epithelium, and increased levels of the lysosomal enzymes Cathepsin B and G in aberrant keratocytes, located beneath compromised regions of Bowman's layer, but also deeper in the stroma. Enzyme activity by these cells seemed to be causing localised structural degradation of the anterior stroma, leading to near-complete destruction of both Bowman's layer and the stroma, often necessitating a full-thickness corneal graft for sight restoration. This current study extends our initial findings by investigating the role of corneal nerves passing between the stroma and epithelium at the sites of early degradative change observed previously, and may be facilitating the keratocyte-epithelial interactions in this disease. Cells in sections of normal and keratoconic human corneas were labelled with the fixable fluorescent viability dye 5-chloromethylfluorescein diacetate, antibodies to alpha-tubulin (nerves), alpha3beta1 integrin, Cathepsin B and G, and the nuclear dye DAPI, and then examined with a confocal microscope. Anterior keratocyte nuclei were seen wrapping around the nerves as they passed through the otherwise acellular Bowman's layer, and as the disease progressed and Bowman's layer degraded, these keratocytes were seen to express higher levels of Cathepsin B and G, and become displaced anteriorly into to the epithelium. Localised nerve thickenings also developed within the epithelium in association with Cathepsin B and G expression, and appeared to be very destructive to the cornea. Insight into the molecular mechanisms of keratoconic disease pathogenesis and progression can be gained from the process of extracellular matrix remodelling known from studies of connective tissues other than the cornea, and wound healing studies in the cornea. Further studies are required to determine how well this model fits the actual molecular basis of the pathogenesis of keratoconus.
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PMID:Involvement of corneal nerves in the progression of keratoconus. 1295 50

The shear-thickening behavior of an equimolar semidilute aqueous solution of 40 mM/L cetylpyridinium chloride and sodium salicylate was studied in this work by using a combined method of rheometry and particle image velocimetry (PIV). Experiments were conducted at 27.5 degrees C with Couette, vane-bob, and capillary rheometers in order to explore a wide shear stress range as well as the effect of boundary conditions and time of flow on the creation and destruction of shear-induced structures (SIS). The use of the combined method of capillary rheometry with PIV allowed the detection of fast spatial and temporal variations in the flow kinematics, which are related to the shear-thickening behavior and the dynamics of the SIS but are not distinguished by pure rheometrical measurements. A rich-in-details flow curve was found for this solution, which includes five different regimes. Namely, at very low shear rates a Newtonian behavior was found, followed by a shear thinning one in the second regime. In the third, shear banding was observed, which served as a precursor of the SIS and shear-thickening. The fourth and fifth regimes in the flow curve were separated by a spurtlike behavior, and they clearly evidenced the existence of shear-thickening accompanied by stick-slip oscillations at the wall of the rheometer, which subsequently produced variations in the shear rate under shear stress controlled flow. Such a stick-slip phenomenon prevailed up to the highest shear stresses used in this work and was reflected in asymmetric velocity profiles with spatial and temporal variations linked to the dynamics of creation and breakage of the SIS. The presence of apparent slip at the wall of the rheometer provides an energy release mechanism which leads to breakage of the SIS, followed by their further reformation during the stick part of the cycles. In addition, PIV measurements allowed the detection of apparent slip at the wall, as well as mechanical failures in the bulk of the fluid, which suggests an extra contribution of the shear stress field to the SIS dynamics. Increasing the residence time of the fluid in the flow system enhanced the shear-thickening behavior. Finally, the flow kinematics is described in detail and the true flow curve is obtained, which only partially fits into the scheme of existing theoretical models for shear-thickening solutions.
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PMID:Rheometry-PIV of shear-thickening wormlike micelles. 1661 40


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