Rheology

Linear-low-density polyethylene (LLDPE) is steadily gaining importance in a wide variety of applications due to its excellent performance characteristics in the final product. The rheological properties of LLDPE in the dynamic and steady state are of great pragmatic importance and these have been studied in the present work. A correlation between the dynamic and steady-state rheological properties has been attempted and good agreement has been found.

Purpose: To evaluate the efficiency of transvaginal ultrasound in the early diagnosis of ovarian cancer. Methods: Screening transvaginal ultrasound has been annually performed during the last 2 years in asymptomatic women without familial history of ovarian cancer. When abnormalities were detected, the procedure was repeated after 4-6 weeks. If the findings disappeared, the study was repeated after 1 year. If the abnormality persisted, study was complemented with tumor markers, computed tomography and laparoscopic surgery. The findings were compared with a control group of women in whom ovarian transvaginal ultrasonography was formally indicated. Results: A total of 26007 transvaginal ultrasound were performed: 8813 (33.8%) belonged to the screening group and 17194 (66.2%) to the control group. In 14 patients of the screening group, a malignant tumor was diagnosed and histologically confirmed. The mean age of these patients was 45 years old (SD 12). Eleven of these tumors were stage I (seven Ia, and four Ic), two stage IIIc and one was a metastatic melanoma in both ovaries. Six lesions were borderline tumors (five serous and one mucinous). In the control group, 27 ovarian cancers were diagnosed in patients with a mean age of 48 years (SD 17). In this group, 11 tumors were in stage I, and six were borderline. Conclusions: Although consensus about the benefits of using transvaginal ultrasound as a screening procedure is not conclusive, our data reveals that tumors detected in patients screened with transvaginal ultrasound are in earlier stages when compared with those diagnosed in the control group. No differences were found in age and number of borderline tumors between both groups. Additional studies are needed to support this preliminary findings.

In the present work, the current status of the hydrodynamic cavitation reactors has been reviewed discussing the bubble dynamics analysis, optimum design considerations, design correlations for cavitational intensity (in terms of collapse pressure)/cavitational yield and different successful chemical synthesis applications clearly illustrating the utility of these types of reactors. The theoretical discussion based on the modeling of the bubble dynamics equations aims at understanding the design information related to the dependency of the cavitational intensity on the operating parameters and recommendations have been made for the choice of the optimized conditions of operating parameters. The design information based on the theoretical analysis has also been supported with some experimental illustrations concentrating on the chemical synthesis applications. Assessment of the hydrodynamic cavitation reactors and comparison with the sonochemical reactors has been done by citing the different industrially important reactions (oxidation of toluene, o-xylene, m-xylene, p-xylene, mesitylene, o-nitrotoluene, p-nitrotoluene, m-nitrotoluene, o-chlorotoluene and p-chlorotoulene, and trans-esterification reaction i.e., synthesis of bio-diesel). Some recommendations have also been made for the future work to be carried out as well as the choice of the operating conditions for realizing the dream of industrial scale applications of the cavitational reactors.

It has been previously described that when a sample's particle size is determined using different sizing techniques, the results can differ considerably. The purpose of this study was to review several in-process techniques for particle size determination (Spatial Filtering Velocimetry, Focused Beam Reflectance Measurements, Photometric Stereo Imaging, and the Eyecon Ò technology) and compare them to well-known and widespread off-line reference methods (laser diffraction and sieve analysis). To start with, a theoretical explanation of the working mechanism behind each sizing technique is presented, and a comparison between them is established. Secondly, six batches of granules and pellets (i.e., spherical particles) having different sizes were measured using these techniques. The obtained size distributions and related D 10 , D 50 , and D 90 values were compared using the laser diffraction wet dispersion method as reference technique. As expected, each technique provided different size distributions with different D values. These dissimilarities were examined and explained considering the measurement principles behind each sizing technique. The particle property measured by each particle size analyzer (particle size or chord length) and how it is measured as well as the way in which size information is derived and calculated from this measured property and how results are presented (e.g., volume or mass distributions) are essential for the interpretation of the particle size data.

The application of a new class of organogels as cleaning tools for painted surfaces is described. It combines some of the most attractive features of cleaning liquids and normal gels while diminishing the deleterious characteristics of both. Thus, the 'latent' gellant, polyethyleneimine (PEI), reacts with CO 2 at room temperature in solutions of several organic liquids to produce an ammonium carbamate form (PEICO 2 ). This charged species organizes itself into 3D polymer networks which immobilize the liquids as gels. The properties of the original solution (i.e. a free-flowing liquid) are re-established immediately after addition of a small amount of a weak acid which displaces the CO 2 molecules and makes the PEI chains positively charged. The visual changes are substantiated by rheological analyses. Results from analytical tests to determine the utility of these gels as cleaning tools for painted surfaces of historical and artistic interest, have been obtained from contact angle and FTIR measurements as well as visual comparisons of the surfaces before and after application of the gels. The analyses indicate that the PEICO 2 -based organogels were very effective in removing different surface patinas from painted supports. A surface layer of dammar was completely removed from a test canvas with oil paint, an aged painting from the XIX century, and a XV century oil-on-wood panel attributed to Mariotto di Cristoforo. Finally, a surface acrylic polymeric resin (used in a restoration performed during the 1960s) was also successfully removed from Renaissance wall paintings decorating the Santa Maria della Scala Sacristy in Siena, Italy. The isothermally rheoreversible gel approach described in this work represents a new, highly versatile, and very efficient method for removing aged surface patinas from works of art.

The performance of a hollow fibre artificial lung ('Capiox E') was analysed by measurement of the 'parallel deadspace' of the device under varying conditions in 21 patients. The efficiency with which carbon dioxide was exchanged was determined by the time available for equilibration between the blood and gas phases. When this equilibration coefficient was less than 12 seconds per litre of blood flow per litre of gas flow, there was a marked reduction in the efficiency of gas exchange. Under certain conditions, the 'counter-current' design of the device apparently permitted the clearance of carbon dioxide at a partial pressure greater than that which was found in the mixed venous blood. This anomalous behaviour may represent in vivo confirmation of the Haldane effect.

Large-scale periodic undulations within the oceanic and continental lithospheres revealed by a number of observations, are often treated as compressive instabilities, i.e. lithospheric buckling or folding. These undulations are normally associated with intensive faulting, which raises questions on the role of faulting in the folding process, and even on the possibility of folding in highly faulted media. In this study, we demonstrate that folding can "survive" faulting and that both processes may develop concurrently, so that faulting may serve as a mechanism of folding in the brittle domain. We support this hypothesis by direct numerical modeling. The results are compared with the data on three most prominent and well-known cases of the oceanic and continental folding-like deformation ("Indian Ocean" type, "Western Gobi (central Asia)" type and "Central Australian" type). We demonstrate that under reasonable tectonic stresses, folds can develop from faults cutting through the brittle parts of the lithosphere. The predicted wavelengths and nite growth rates are in agreement with the observations. We also show that within a continental lithosphere with thermotectonic age greater than 400 My, either a bi-harmonic mode (two superimposed wavelengths, crustal and mantle one) or a coupled mode (mono-layer deformation) of inelastic folding can develop, depending on the strength and thickness of the lower crust.

Calcium-alginate hydrogel has been widely studied as a material for cell encapsulation for tissue engineering. At present, the effect that cells have on the degradation of alginate hydrogel is largely unknown. We have shown that fibroblasts encapsulated at a density of 7.5 Â 10 5 cells ml À1 in both 2% and 5% w/v alginate remain viable for at least 60 days. Rheological analysis was used to study how the mechanical properties exhibited by alginate hydrogel changed during 28 days in vitro culture. Alginate degradation was shown to occur throughout the study but was greatest within the first 7 days of culture for all samples, which correlated with a sharp release of calcium ions from the construct. Fibroblasts were shown to increase the rate of degradation during the first 7 days when compared with acellular samples in both 2% and 5% w/v gels, but after 28 days both acellular and cell-encapsulating samples retained disc-shaped morphologies and gel-like spectra. The results demonstrate that although at an early stage cells influence the mechanical properties of encapsulating alginate, over a longer period of culture, the hydrogels retain sufficient mechanical integrity to exhibit gel-like properties. This allows sustained immobilization of the cells at the desired location in vivo where they can produce extracellular matrix and growth factors to expedite the healing process.

This article presents a preparation methodology for making clear yield pseudoplastic fluids so that repetitive and consistent rheological measurements can be made using two types of Carbopol 980 and Carbopol Ultrez-10. The methodology calls for gentle agitation while dispersing the polymer, leaving it static for 30 minutes for air bubble removal and neutralization while agitating with NaOH followed by 1 hour for the 980 type and 5 hours for the Ultrez-10. Results are presented for the change of rheological parameters with polymer type, polymer concentration, with hydration time, and temperature. Almost all samples exhibited rheological behavior which could be very well described by the Herschel-Bulkley rheological model. Carbopol 980 solutions appear to be very suitable as model clear yield pseudoplastic fluids while Ultrez-10 solutions present some peculiarities rendering them not so suitable as model fluids.

Aims: Magnesium hydroxide (Mg (OH) 2) is an alkaline compound that is used as an anti-acid and laxative agent. The objective of the study was to find the effect of electrolyte concentration and polymers on the rheological behavior of Mg (OH) 2 suspension.

RESUME. L'approche proposée dans cette étude consiste à étudier le comportement d'un béton à partir du comportement des suspensions qui le composent : le fluide de référence, constitué par l'eau et les adjuvants, la pâte de ciment, le mortier et le béton. Des essais rhéométriques en contraintes ou en vitesses imposées sont réalisés sur chacune des suspensions. Les données expérimentales nous ont permis de réaliser une analyse paramétrique élargie. L'influence de la concentration et de la taille des éléments solides sur l'évolution des paramètres rhéologiques tels que le seuil de mise en écoulement et la viscosité a été identifiée. Le comportement rhéologique d'une suspension est directement gouverné par le comportement de la suspension de classe granulaire immédiatement inférieure. ABSTRACT. The proposed approach consists in studying the behaviour of a concrete starting from four uncoupled suspensions scales: suspending fluid, corresponding to water and the additives, cement paste, mortar and concrete. Rheometric tests using controlled shear rates or shear stresses were carried out on each uncoupled suspension. The experimental data exploitation led us to propose a widened parametric analysis. The influence solid concentration and the particles size on the evolution of the rheological parameters such as the yield stress and the apparent viscosity was identified. In addition, the rheological behaviour of an uncoupled suspension is directly controlled by the behaviour of the uncoupled suspension from size range immediately below.

Exposure of poly(DL-lactic acid) (P DL LA), and related polymers, to supercritical CO 2 (scCO 2 ) at or below, physiological temperatures leads to very effective plasticization and liquefying of the polymers. The phenomenon arises from the high solubility and interaction of the scCO 2 in the polymer. Under these unique conditions, temperature and solvent labile molecules can be mixed efficiently into the liquefied polymer. This liquefied polymer/drug/CO 2 mixture can then be sprayed into a collecting chamber, and during this process particles of drug-loaded polymer are formed. This process is very different from rapid expansion and antisolvent based techniques that have been previously reported. In this article, we describe a method of controlling particle size during the spray process by introducing a backpressure of N 2 in the collecting chamber. This backpressure dynamically regulates the loss of CO 2 from the issuing polymer/CO 2 mixture, leading to control over sprayed particle size. In situ observation of the viscosity of the plasticized polymer indicates that a backpressure of 68 bar or greater is necessary to ensure the production of fine particles. The influences of backpressure and saturation temperature on particle size for the sprayed products are discussed in terms of observed P DL LA/CO 2 mixture viscosities. ß

Self-Compacting Concrete (SCC) is a flowable concrete that exerts high pressure on formwork. SCC is the most commonly used concrete worldwide for construction applications due to its costeffectiveness. The high flow of SCC reduces both the number of workers and the casting time required. It also eliminates vibration and removes noise pollution. This study is a review of previous investigations into the pressure exerted by fresh-state SCC on formwork. The paper discussed various factors that affect lateral pressure on formwork. These factors are included theoretical predictions, the effect of temperature, casting rate, rheology, types of pressure sensors, geometry and workability. Considering these various factors, the paper discussed major factors related to lateral pressure of SCC at early ages. However, internal temperature measurement of concrete effects at fresh state appears to be an important factor.

In this study, rheological properties of several food hydrocolloids (carrageenan, pectin, gelatin, starch and xanthan) were evaluated using a rotational viscometer at three concentrations (1-6%, depending on the type of hydrocolloid) and four temperatures (20, 40, 60 and 80 C). Samples were subjected to a programmed shear rate increasing linearly from 0 to 300 s À1 in 3 min, followed by a steady shear at 300 s À1 for 10 min and finally a linearly decreasing shear rate from 300 s À1 to 0 in 3 min. Experiments were performed in duplicate. In general, the power law model fitted most of the experimental results. Xanthan gum and carrageenan (at 20 o C) were exceptions, characterized by a yield stress and hence the rheograms were fitted with the Herschel-Bulkley model. Furthermore, gelatin showed a Newtonian behavior. Three models (power, exponential and polynomial) were used to evaluate the concentration effect on apparent viscosity. Arrhenius model was used to describe the temperature effect. Among the samples, carrageenan showed the most temperature dependency and xanthan gum, the least.

An association between hemorheological alterations (i.e., whole-blood and plasma hyperviscosity, reduced erythrocyte deformability, increased red cell aggregation, hyperfibrinogenemia and increased acute-phase protein levels) and the mild stage of senile dementia of the Alzheimer's type (DAT) was suggested in the present study. In particular, hyperfibrinogenemia and the increase of erytrhocyte aggregation were correlated with the increased generation and release of TNF-␣ and IFN-␥ (spontaneous release and IL-2-modulated release) from natural killer (NK) lymphocytes (CD16ϩ, CD56ϩ, CD3-cells) of patients with DAT; whereas a normal cytokine release from NK cells was found in healthy old subjects and in patients with vascular dementia (VaD). The in vitro and in vivo administration of the hemorheologic drug pentoxifylline (PTX) significantly reduced spontaneous and IL-2-modulated cytokine overproduction from NK cells (in vitro effects with 500 U/ml and 1000 U/ml/NK cells) and improved all the hemorheological parameters. Taken together, these data suggest that disturbances of cerebrovascular flow and of hemorheology could be considered a negative component related to the pathogenesis and progression of DAT neurodegeneration. The association between hemorheological changes and alterations of TNF-␣ and IFN-␥ release from NK may indicate a potential immunorheologic mechanism associated with cerebrovascular damage in DAT and could suggest the use of vascular protective drugs as support of the main pharmacological and non-pharmacological therapy of AD.

The aim of this work was to characterize lipid nanoparticles from a rheological point of view, intended for drug delivery after parenteral administration. The conditions to obtain a re-dispersible powder using freeze-drying and spray-drying have also been investigated. Lipid nanoparticles (179.9 ± 6.2 nm) were prepared with the high pressure homogenization technique, using previously established optimal conditions (lipid volume fraction of 0.121), though particle size increased (285.9 ± 4.3 nm) in suspensions produced with higher lipid volume fractions (0.255). Rheology evidenced an expected increase of viscosity with the volume fraction and Newtonian behaviour was observed for volume fractions up to 0.161, while higher volume fractions showed shear thinning and shear thickening. In the suspension with a volume fraction of 0.255, a change of the complex modulus was observed at low shear stress. Freeze-drying and nano spray-drying were suitable only when trehalose was employed as an additive. In the former case, particle size was increased by 18% (198.7 ± 1.1 nm) using 20 fold water dilution. With spray-drying, the use of 20 fold dilution in water:ethanol (8:2) led to particle dimensions of 207.7 ±10.0 ( size 20%). In conclusion, cetylpalmitate nanoparticles seem to be suitable for parenteral application, up to volume fractions of 0.16, and pharmaceutical operations, which submit suspensions to shear stress, should not be a critical issue.

Microrheology is a technique that is increasingly used to investigate the local viscoelastic properties of complex fluids non-invasively, by tracking the motion of micron-sized probe spheres. In this work, passive Particle Tracking Microrheology (PTM) is used to study network formation in the milk protein β-lactoglobulin at 80 • C and pH 2. In these conditions the protein aggregates to form thread-like structures known as amyloid fibrils, which can further aggregate into elastic networks. Using PTM, gels were observed to form at significantly lower concentrations than determined by bulk rheometry, where the oscillatory shear forces may disrupt either fibril or network formation. During incubation, the Mean Square Displacement (MSD) of the probe particles exhibited time-cure superposition, allowing the critical relaxation exponent to be calculated as ∼ 0.63, consistent with other biopolymer gels. Combined with the gel-like appearance of the complex modulus at long incubation times, this confirms that a true gel is forming, with physical or chemical crosslinks forming between the fibrils, refining the conclusions of other workers in the field.

Geopolymers are presented in many studies as alternatives to ordinary Portland cement. Previous studies have focused on their chemical and mechanical properties, their microstructures and their potential applications, but very few have focussed on their rheological behaviour. Our work highlights the fundamental differences in the flow properties, which exist between geopolymers made from metakaolin and Ordinary Portland Cement (OPC). We show that colloidal interactions between metakaolin particles are negligible and that hydrodynamic effects control the rheological behaviour. Metakaolin-based geopolymers can then be described as Newtonian fluids with the viscosity controlled mainly by the high viscosity of the suspending alkaline silicate solution and not by the contribution of direct contacts between metakaolin grains. This fundamental difference between geopolymers and OPC implies that developments made in cement technology to improve rheological behaviour such as plasticizers will not be efficient for geopolymers and that new research directions need to be explored.

Addition of calcium chloride to milk has positive effects on cheese-making because it decreases coagulation time, creates firmer gels, and increases curd yield. Although addition of calcium chloride is a widely used industrial practice, the effect of soluble calcium on the preliminary stages of gelation is not fully understood. In addition, it is not known whether the manner of addition and equilibration of the soluble calcium would affect the rennetability of the casein micelles. Therefore, the aim of this paper was to study the details of the coagulation behavior of casein micelles in the presence of additional calcium, and to elucidate whether the manner in which this cation is added (directly as calcium chloride or by gradual exchange through dialysis) affects the functionality of the micelles. Calcium was added as CaCl(2) (1 mM final added concentration) directly to skim milk or indirectly using dialysis against 50 volumes of milk. Additional soluble calcium did not affect the ...

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Physicochemical and functional changes of jumbo squid (Dosidicus gigas) mantle muscle stored in ice for 15 days were evaluated. Proximate analysis, pH, protein solubility (PS) and SDS-PAGE profile changes were monitored for muscle proteins, while texture profile analysis (TPA) (gel strength, elasticity and cohesiveness), water holding capacity (WHC) and colour changes were monitored for gels produced from this muscle. Fresh muscle chemical composition varied according to fishing season and/or physiological status presented by specimens. pH and PS were stable (p P 0.05) throughout the study with a slight tendency to decrease towards the end of study. SDS-PAGE revealed no drastic changes in proteins influencing gelation (i.e., myosin). TPA and WHC of gels decreased towards the end of experiment; however, due to sampling variability, no significant differences (p P 0.05) were found over storage time. Changes in gel colour were observed with hue angle decreasing towards yellow hues. Improved post-capture management of mantle muscle preserved its integrity and functionality for up to two weeks.

The spatiotemporal evolution of field-induced structures in very dilute polarizable colloidal suspensions subject to rotating magnetic fields has been experimentally studied using video microscopy. We found that there is a crossover Mason number ͑ratio of viscous to magnetic forces͒ above which the rotation of the field prevents the particle aggregation to form chains. Therefore, at these high Mason numbers, more isotropic clusters and isolated particles appear. The same behavior was also found in recent scattering dichroism experiments developed in more concentrated suspensions, which seems to indicate that the dynamics does not depend on the volume fraction. Scattering dichroism experiments have been used to study the role played by the volume fraction in suspensions with low concentration. As expected, we found that the crossover Mason number does not depend on the volume fraction. Brownian particle dynamics simulations are also reported, showing good agreement with the experiments.

A theoretical approach was used to determine the distribution of a poly(methylmethacrylate) cement after its injection into a porous structure. The predictions of the model were then compared to experimental results obtained by injecting a polymethylmethacrylate cement into an open-porous ceramic filter. The goal was to define a model that could predict what factors affect the risk of cement extravasation and hence how the risk of cement extravasation can be minimized. The calculations were based on two important rheological laws: the law of Hagen-Poiseuille and the law of Darcy. The law of Hagen-Poiseuille describes the flow of a fluid in a cylindrical tube. The law of Darcy describes the flow of a fluid through a porous media. The model predicted that the extravasation risk was decreased when the cement viscosity, the bone pore size, the bone permeability and the bone porosity were increased, and when the diameter of the extravasation path and the viscosity of the marrow were decreased. Experimentally, the effect of the marrow viscosity and extravasation path could be evidenced. Therefore, the model was believed to be an adequate approximation of the experimental behavior. In conclusion, the experimental results demonstrated that the model was adequate and that the best practical way to decrease the risk of extravasation is to increase the cement viscosity. r

The effect of shear on dewatering behaviour and particle interactions of Na-exchanged smectite and kaolinite clay dispersions has been investigated at pH 7.5, using hydrolysable Ca(II) and Mn(II) ions as coagulants and high molecular weight anionic and non-ionic polyacrylamide (PAM A and PAM N, respectively) and polyethylene oxide (PEO) flocculants. Metal ion addition enhanced the flocculation performance by dramatically reducing the magnitude of the particle zeta potential and, in the case of smectite pulp, suppressing osmotic swelling. Under optimum orthokinetic flocculation conditions of controlled agitation rate and duration, PAM A and PEO-based flocs settled faster than those of PAM N whilst kaolinite pulps produced higher sedimentation rates than smectite pulps. The settling rates are nearly an order of magnitude greater than those observed under standard flocculant -pulp mixing/flocculation methods of inversion and plunging. The difference in the flocculant behaviour is attributed to the more expanded conformation of PAM A and PEO polymer chains in contrast to PAM N, whilst the lower yield stresses, reflecting inter-particle bridging and floc network structure strength that are conducive to faster clarification, were displayed by kaolinite pulps. Following shear, similar consolidation enhancement of å 5 -7 wt.% solid for both pulps was achieved at an optimum agitation range of 100 -200 rpm. This was accompanied by decreased yield stress in the case of PAM A-based pulps, indicating non-reversible disruption of polymer mediated particle and floc network structure. In contrast, the yield stresses of PAM N and PEO flocculated dispersions indicated similar and stronger particle interactions, respectively, upon consolidation following shear. The findings show clear links between effect of shear, interfacial chemistry and polymer structure on pulp particle interactions and dewaterability. D

High quality flow kinematics reconstruction from noisy and spatially scattered data requires the use of regularization techniques but remains a challenge. We set out to test the effect and practical relevance of additional incompressibility constraints. To this end, we present two methods for reconstructing smooth velocity and velocity gradient fields from such data in an incompressible two-dimensional complex flow. One is based on a generalized Tikhonov regularization combined with a finite element approximation and uses a stream function formulation, which enforces incompressibility (hard constraint). This approach is compared to that in which incompressibility is asymptotically achieved by adding a divergence penalty term in the regularization expression (soft constraint). The methods are compared on synthetic velocity data, obtained for an incompressible Oldroyd-B fluid in a cross-slot channel with added noise. For such data sets, both methods are seen to lead to essentially identical results. However, for a given grid size, the stream function formulation uses a single regularization parameter and less degrees of freedom to provide the required continuity of the gradient fields. The fidelity of the reconstruction is investigated in terms of the quality of the streamlines and velocity gradient history. Incompressibility constraints turn into significant and valuable improvement for applications as we demonstrate by analyzing the stress and optical signal fields obtained by applying a constitutive equation to the reconstructed flow fields. V C 2011 The Society of Rheology.

Both Laponite and scleroglucan can find several applications in various fields (from industrial to biomedical one) in virtue of their peculiar features and rheological properties displayed in aqueous phases. Structural states of Laponite dispersions strongly depend on concentration and ionic strength. When attractive and repulsive interparticle interactions are so effective that they lead to arrested states (attractive gel or repulsive glass), the rheological behavior of the dispersion undergoes a sharp transition, from quasi-Newtonian to markedly shear thinning and viscoelastic. Conversely, scleroglucan solutions gradually change to weak gels with increasing polymer concentration. The present work is concerned with aqueous Laponite-scleroglucan mixed systems, obtained according to different preparation modes, and is aimed at examining how much the content and proportion of both components affect the viscoelastic and flow properties of the mixed system.

series of progressively smaller vessels-arteries, arterioles, Depts. of Physiology, Neurological Surgery, and Anesthesiology and capillaries. From a solitary aorta, the flow is partitioned Columbia University College of Physicians and Surgeons into more than a billion capillaries. It is in the capillaries that one of the most important functions of blood occurs, i.e., THE CIRCULATORY system is uniquely designed for sevoxygen transfer to the tissue cells. The blood flows from Teral functions, one of the most important being oxygen capillaries into a series of venules, veins, and the superior and transport. This is accomplished through the interaction of the inferior vena cavae, and the number of vessels decreases heart, lungs, blood vessels, and the blood. Blood is a complex with successive generations of converging flow. fluid consisting of plasma and cells, primarily red blood cells, suspended in it. The ability to deliver oxygen depends partly BASIC RHEOLOGICAL PRINCIPLES on the relative concentrations of these elements and the As blood flows from the aorta to the capillaries, most of the interactions between them. It also depends on the properties pressure head generated by the heart is dissipated, particuof the vessels through which the blood flows. Blood rheology larly in the arterioles, which are the primary resistance is the study of blood flow and the response of blood to vessels. The flow of blood across the circulatory system (0) deforming forces in the circulatory system.

Bench testing is a useful method to characterize the response of different automatic positive airway pressure (APAP) devices under well-controlled conditions. However, previous models did not consider the diversity of obstructive sleep apnea (OSA) patients' characteristics and phenotypes. The objective of this proof-of-concept study was to design a new bench test for realistically simulating an OSA patient's night, and to implement a one-night example of a typical female phenotype for comparing responses to several currently-available APAP devices. We developed a novel approach aimed at replicating a typical night of sleep which includes different disturbed breathing events, disease severities, sleep/wake phases, body postures and respiratory artefacts. The simulated female OSA patient example that we implemented included periods of wake, light sleep and deep sleep with positional changes and was connected to ten different APAP devices. Flow and pressure readings were recorded; each device was tested twice. The new approach for simulating female OSA patients effectively combined a wide variety of disturbed breathing patterns to mimic the response of a predefined patient type. There were marked differences in response between devices; only three were able to overcome flow limitation to normalize breathing, and only five devices were associated with a residual apnea-hypopnea index of <5/h. In conclusion, bench tests can be designed to simulate specific patient characteristics, and typical stages of sleep, body position, and wake. Each APAP device behaved differently when exposed to this controlled model of a female OSA patient, and should lead to further understanding of OSA treatment.

The aim of this article is to study experimentally and numerically the influence of the inclination of a plate placed near a wall on flows of Newtonian and yield stress fluids. The drag and lift forces were particularly studied. The inclination of the plate varies between 0°and 90°. The inertia of the fluid is considered negligible. The effects of the Oldroyd number, the shear-thinning index and the inclination of the plate on drag and lift are shown. Experimentally, an instrumented flume was used with a Carbopol gel as a yield stress fluid model. The measured lift and drag forces are compared to the numerical results and the literature data. The elasticity and plasticity effects are discussed.

In the present study, EPS secreted by the endophytic bacterium Bacillus licheniformis was isolated and characterized. The molecular masses of the EPS were 1540 and 44,565 kDa and 1 H NMR, FT-IR and UV-Vis spectral analyses revealed prevalence of characteristic primary amine-group, aromatic-compound, halide and aliphatic alkyl-group in addition to Na, P, Ca, C, O, Cl and S as inferred from EDX analysis. XRD and DSC analysis confirmed the amorphous nature of EPS, showing an average particle size of 24.977 m (d 0.5) with 191 nm average roughness. The positive ion reflector mode of MALDI TOF-TOF MS exhibited a series of low and high mass peaks corresponding to various oligosaccharides and polysaccharides respectively. Further, GC-MS analysis revealed its four monosaccharide constituents glucose, galactose, mannose and arabinose. The potential heterogeneous properties of EPS as revealed in the present study may be explored in various biotechnological and industrial applications.

The hysteresis behavior of a linear stroke magnetorheologica l damper is characterized for several magnetic elds and sinusoidal excitations over a nominal operational frequency range of 1.0-3.0 Hz. The behavior of the damper is inadequately modeled using the equivalent viscous damping and the complex modulus. Therefore, four different nonlinear modeling perspectives are discussed for purposes of system identi cation procedures, including the 1) nonlinear Bingham plastic model, 2) nonlinear biviscous model, 3) nonlinear hysteretic biviscous model, and 4) nonlinear viscoelastic plastic model. The rst three nonlinear models are piecewise continuous in velocity. The fourth model is piecewise smooth in velocity. The parameters for each model are identi ed from an identi cation set of experimental data; these parameters are then used to reconstruct the force vs displacement and the force vs velocity hysteresis cycles for the respective model. Model performance is evaluated by calculating equivalent viscous damping and force time history errors between the model t and the experimental data. In addition to the identi cation study, a validation study was done. Model parameters were calculated for offset values of current and frequency. These intermediate parameters were used to calculate hysteresis cycles, which were compared with a second set of experimental data, a validation data set. Identi cation and validation study results including damping levels and force time history errors.

Microstructure formation in acidified mixed protein/polysaccharide gels is an important feature to control the mechanical properties of these gels. Previous work showed the relation between the charge density of the polysaccharide and the type of microstructure obtained. This manuscript deals with the mechanism behind the microstructure formation. This was studied with a combination of techniques, including light scattering, confocal microscopy (CLSM) and small deformation rheology. The microstructure obtained is a result of the competition between gelation of the protein aggregates and the phase separation between protein aggregates and polysaccharide molecules. The onset of gelation and microstructure formation occurs at a constant pH independent of the type and amount of polysaccharide added. The gelation of the protein aggregates induces the phase separation process that leads to the microstructure formation. The rate of gelation is controlled by the acidification rate, which can be used to modulate the microstructure of the mixed gels. A slower acidification rate results in a coarser microstructure because there is a longer time for the phase separation to occur.

This paper deals with thermal drying of wastewater sludges, whose management will become crucial in the forthcoming years. Sludges collected after mechanical dewatering in 5 different WWTPs are submitted to the same convective drying treatment in order to try finding some relations between the drying behaviours, the type of effluent and wastewater treatments. Results show clearly sludge drying remains a particularly complex operation because sludges may exhibit very different behaviours, both from kinetic and texture points of view. Initial moisture content and global composition are not sufficient to explain the different observed behaviours. It is too early to claim one or another type of water treatment has an influence on the drying behaviour. However, the drying rates can be classified in the inverse order of the organic content. Moreover for sludges at the same siccities, the harder the material (rheological properties), the higher the drying rate. Final textural properties can be related to the rheological properties and the internal diffusion limitations lowering the drying intensity.

In order to study the rheology of long chain branched polymers, branches have been added on linear polypropylene precursors in varying amounts using reactive modification with peroxydicarbonates. The branched polypropylene samples show distinct strain hardening, something absent from the linear melt; this considerably improves the melt strength of the modified polymer. The zero shear viscosity and the elasticity measured by the relaxation spectrum also increase with the number of branches per molecule. Two models are applied to describe strain hardening of the viscosity during the course of elongation. The model parameters were found to vary systematically with the degree of branching and, therefore, their values can be used as a measure of this. Consequently, fluidity, elasticity, strain hardening, and melt strength are all related to the degree of long chain branching.

The Pom-Pom model, recently introduced by McLeish and Larson ͓J. Rheol. 42, 81-110 ͑1998͔͒, is a breakthrough in the field of viscoelastic constitutive equations. With this model, a correct nonlinear behavior in both elongation and shear is accomplished. The original differential equations, improved with local branch-point displacement, are modified to overcome three drawbacks: solutions in steady state elongation show discontinuities, the equation for orientation is unbounded for high strain rates, the model does not have a second normal stress difference in shear. The modified extended Pom-Pom model does not show the three problems and is easy for implementation in finite element packages, because it is written as a single equation. Quantitative agreement is shown with experimental data in uniaxial, planar, equibiaxial elongation as well as shear, reversed flow and step-strain for two commercial low density polyethylene ͑LDPE͒ melts and one high density polyethylene ͑HDPE͒ melt. Such a good agreement over a full range of well defined rheometric experiments, i.e., shear, including reversed flow for one LDPE melt, and different elongational flows, is exceptional.

Clotrimazole is a wide spectrum local imidazolic antifungal agent used in several dermatological creams, having e.g. 1% (m/m) such as Canesten 1 and Fungizid-ratiopharm 1 cream. In the present work, a new system based on solid lipid nanoparticles (SLN TM) containing the identical concentration of drug has been developed. A comparative study between the rheological properties of the referred creams and the developed aqueous SLN dispersions was carried out. The influence of incorporation of SLN in a standard hydrophilic cream on its flow curves was also assessed. In addition, the release of clotrimazole from the two commercial creams, as well as from aqueous SLN dispersions was studied. Concerning the rheological investigations, all tested commercial creams revealed very low shear rates and no yield points. Lipid nanoparticles having a mean diameter of approx. 200 nm have been incorporated into a hydrophilic cream, in a concentration of 20%, 30% or 40% (m/m). The hydrophilic cream containing 20% of SLN showed a dilatant-like character; however, increasing the percentage of incorporated lipid nanoparticles to 30% and 40% the formulation changed to a more pseudoplastic character, showing yield values of 28 Pa and 39 Pa, respectively. For in vitro release studies, Franz diffusion cells with a cellulose acetate membrane were used to measure the release of clotrimazole from two different commercial formulations in comparison to the aqueous SLN dispersion. After 6 h the amount of drug released was higher than 48% when delivered from both investigated commercial formulations and not higher than 25% when delivered from the aqueous SLN dispersion. The percentage of drug released determined after 24 h was more than 50% for Canesten 1 cream and Fungizidratiopharm 1 cream and not higher than 30% for the developed SLN formulation showing its prolonged release character.

The development of small particles in ion chromatography (IC) is a recent phenomenon. Very few studies are available on packing polymeric particles bearing ionizable functional groups. This study explores the colloidal and rheological properties that govern slurry packing to form high efficiency IC columns. The polymeric substrate used was non-porous 4.4 m sulfonated ethylvinylbenzene-divinylbenzene (1.4 mequiv. SO 3 H/g resin) with 55% crosslink. We developed simple tests optical microscopy and sedimentation tests for predicting the quality of packed columns. The negatively charged particles (zeta potential: −52 mV in water) behave like colloids. The influence of counter-ion charge (Al 3+ , Mg 2+ , Na +) and ionic strength on column efficiency followed the Schulze-Hardy rule. Highly flocculating slurries give poorly packed columns with N ∼ 900 whereas under non-agglomerating slurry conditions efficiencies up to N > 10,000 can be achieved. A non-agglomerating slurry also shows non-Newtonian behaviour, specifically shear thickening. Packing at lower flow rate (<1 mL/min) or higher temperature (>50 • C) reduces the shear thickening and produces higher efficiency columns. The packed sulfonated resin column is coated with 72 nm quaternary ammonium bearing latex (AS4A) and used in the separation of F − , Cl − , NO 2 − , Br − , and NO 3 − yielding a reduced plate height of 1.9 under optimum conditions.

Numerical simulation can provide a useful tool for investigating the dynamics of phenomena like rock avalanches, within realistic geological contexts and in the framework of a better risk assessment and decision making. Difficulties in numerical modelling of a heterogeneous moving mass are mainly linked to the simulation of the complex behaviour assumed by the mass during propagation. The numerical code RASH3D, based on a continuum mechanics approach and on the long wave approximation, is used to back-analyse two cases of rock avalanches: Frank (1903, Canada) and Val Pola (1987, Italy). The two events are characterised by approximately the same volume (about 30 Â 10 6 m 3) while the run out area morphologies are widely different. Three alternative ''rheologies'' (Frictional, Voellmy and Pouliquen) are used. Comparison among obtained results underlines that the validation of a ''rheology'' requires not only a good agreement between the numerical simulation results and the run out area boundaries but also in term of depth distribution of the mass in the deposit. In case of a Frictional rheology, the obtained calibrated dynamic friction angle values are in a range of 15 AE 1 for both the cases; while assuming a Pouliquen or a Voellmy rheology it emerges a different behaviour of rheological parameters for each of the considered events. Besides the calibration of rheological parameters to better back-analyse each of the considered events, it is investigated how the behaviour due to the assumed rheology is influenced by the geometry of the run out area (e.g. narrow or broad valley).

This study presents an optimal design for magnetorheological (MR) valves for minimizing the control energy to be applied to coils to control the pressure drop of the valves. The optimization problem identifies parameters such as applied current, coil wire size and geometric dimensions of the valves which satisfy the specified pressure drop and inductive time constant requirements. After describing the configuration of MR valves, their pressure drops are obtained on the basis of the Bingham model of MR fluid. Then, the control energy which is an objective function and the inductive time constant are derived. Subsequently, an optimization procedure using a golden-section algorithm and a local quadratic fitting technique is constructed via a commercial finite element method parametric design language. Using the optimization tool developed in this study, optimal MR valve configurations are identified, which are constrained to a specific cylindrical volume defined by its radius and height. In addition, optimization results for MR valves with different required pressure drops and different constrained volumes are obtained and presented.