Wall-layer Structures Research Articles

Effect of the crosslinking and drying method on the oxidative stability of lipid microcapsules obtained by complex coacervation.

The crosslinking and drying method of microcapsules prepared by complex coacervation has been investigated in order to achieve a better control of the oxidative stability of the final powder product. Methyl oleate was microencapsulated with gelatin and gum arabic as wall materials. For improving the oxidative stability of microcapsules, the crosslinking and drying method was optimized in order to obtain a product with a stable and dense wall layer structure. The wall layer crosslinked by transglutaminase was found to be more thermostable than other food-grade crosslinking agents. Combined uses of different crosslinking agents had been carried out for microcapsules obtained by freeze drying, and the product crosslinked in turn by transglutaminase and tannic acid exhibited the relatively best oxidative stability measured by oxidation induction time. However, a new method of organic solvent replacement drying was found to be more suitable for drying microcapsules, since this method could achieve better oxidative stability than freeze or spray drying even by using transglutaminase or tannic acid alone as the crosslinking agent. The SEM graphs showed that this new drying method could avoid ice crystal formation and reduce the external force during the drying process, thus effectively reducing the occurrence of micro-holes in the wall layer and inhibiting the adhesion between the microcapsules. From the analysis of the secondary structure measurement, this new drying method could convert irregular structures into α-helical structures, hence enhancing the compactness of the wall layer structure. The organic solvent replacement drying method is an economical and environmental method with promising application prospects.

How Can We Manage Gallbladder Lesions by Transabdominal Ultrasound?

The most important role of ultrasound (US) in the management of gallbladder (GB) lesions is to detect lesions earlier and differentiate them from GB carcinoma (GBC). To avoid overlooking lesions, postural changes and high-frequency transducers with magnified images should be employed. GB lesions are divided into polypoid lesions (GPLs) and wall thickening (GWT). For GPLs, classification into pedunculated and sessile types should be done first. This classification is useful not only for the differential diagnosis but also for the depth diagnosis, as pedunculated carcinomas are confined to the mucosa. Both rapid GB wall blood flow (GWBF) and the irregularity of color signal patterns on Doppler imaging, and heterogeneous enhancement in the venous phase on contrast-enhanced ultrasound (CEUS) suggest GBC. Since GWT occurs in various conditions, subdividing into diffuse and focal forms is important. Unlike diffuse GWT, focal GWT is specific for GB and has a higher incidence of GBC. The discontinuity and irregularity of the innermost hyperechoic layer and irregular or disrupted GB wall layer structure suggest GBC. Rapid GWBF is also useful for the diagnosis of wall-thickened type GBC and pancreaticobiliary maljunction. Detailed B-mode evaluation using high-frequency transducers, combined with Doppler imaging and CEUS, enables a more accurate diagnosis.

Incidentally detected focal fundal gallbladder wall thickening: Differentiation contrast enhanced ultrasound features with high-resolution linear transducers.

To investigate the value of contrast enhanced ultrasound with high resolution linear transducers (HF-CEUS) for differential diagnosis of focal fundal gallbladder (GB) wall thickening. A total of 32 patients with incidentally detected focal fundal GB wall thickening were included. After conventional B mode ultrasound (BMUS) examinations, HF-CEUS were performed with a 7.5-12 MHz 9L4 linear transducer (S2000 HELX OXANA unit, Siemens). Two radiologists independently reviewed the HF-CEUS enhancement patterns to determine the differential features between malignancy and benignity with a five-point confidence scale. The diagnostic accuracy of BMUS and HF-CEUS for GB wall thickening was compared. The final gold standard was surgery with histological examination. Final diagnoses included GB adenocarcinoma (n = 16), adenomyomatosis (n = 12), Xanthogranulomatous (n = 2) and cholecystitis (n = 2). HF-CEUS features associated with GB adenocarcinoma including arterial phase inhomogeneous hyperenhancement, venous phase hypoenhancement and disruption of GB wall layer structure (P < 0.05). Two small (5 mm) liver metastasis were confirmed by HF-CEUS during the late phase liver sweep as hypoenhanced lesions. Nonenhanced Rokitansky-Aschoff sinuses were clearly observed in 83.3% focal adenomyomatosis. Overall sensitivity, specificity and accuracy for differentiation between malignant and benign focal fundal GB wall thickening of HF-CEUS and BMUS were 84.3% vs 53.1%, 90.6% vs 59.3% and 87.5% vs 56.2% (P < 0.005). CEUS performed with high frequency linear transducers could be a useful alternative in the differential diagnosis of focal fundal GB wall thickening on conventional ultrasound.

Immune Checkpoint Inhibitor-Induced Colitis Successfully Followed up by Ultrasonography

Nivolumab is an immune checkpoint inhibitor (ICI), which is used for treatment of advanced malignancies. Diarrhea is a typical adverse effect of ICIs. Several endoscopic features of ICI-related colitis have been reported. Herein, we reported a case of ICI-related colitis, with successful follow-up using ultrasonography (US). A 54-year-old woman, diagnosed with renal cell carcinoma, underwent radical nephrectomy. Multiple liver and bone metastases appeared 6 months after surgery. She was prescribed sunitinib, which was discontinued, because of severe diarrhea. She was prescribed nivolumab after 1 week. However, she was hospitalized 9 days later, due to fever and diarrhea. US showed diffuse wall thickening from the cecum to the rectum. The wall layer structures were preserved, and thickening was observed mainly in the submucosa, but not in the mucosa, without a decrease in the echo level. Subsequently, sigmoidoscopy was performed. Severe edema was observed in the mucosa, without any erosion and granularity. She was clinically diagnosed with ICI-related colitis, and steroid therapy was administered. One week after steroid therapy, the diarrhea improved, and the earlier findings showed marked improvement on US. After another week of reduced steroid dose, US revealed further improvement, and she was discharged.

Ion energy distribution function in the wall layer at a negative wall potential with respect to the plasma

On the basis of the kinetic approach, the self-consistent problem of the gas discharge ion distribution function in the sheath near a surface at a negative potential with respect to the plasma is solved. For the first time, the solution takes into account the dependence of the ion charge exchange cross section from the atom on the ion energy, as well as the real ion distribution function in the unperturbed plasma. It is shown that the dependence of the charge exchange cross section on the ion energy significantly affects the shape of the ion distribution function. It is found that the mean energy of the ions near the wall depends on the electron mean energy in the unperturbed plasma. It was also found that, at the same electron mean energy, the form of the distribution function has practically no effect on the ion distribution function in the wall sheath. The calculations are in good agreement with the known mass spectrometric measurements of the ion distribution function. The obtained results give an opportunity to develop a self-consistent solution of the wall layer structure problem including the quasi-neutral presheath.

Drift and pseudomomentum in bounded turbulent shear flows.

This paper is concerned with the evaluation of two Lagrangian measures which arise in oscillatory or fluctuating shear flows when the fluctuating field is rotational and the spectrum of wave numbers which comprise it is continuous. The measures are the drift and pseudomomentum. Phillips [J. Fluid Mech. 430, 209 (2001)] has shown that the measures are, in such instances, succinctly expressed in terms of Lagrangian integrals of Eulerian space-time correlations. But they are difficult to interpret, and the present work begins by expressing them in a more insightful form. This is achieved by assuming the space-time correlations are separable as magnitude, determined by one-point velocity correlations, and spatial diminution. The measures then parse into terms comprised of the mean Eulerian velocity, one-point velocity correlations, and a family of integrals of spatial diminution, which in turn define a series of Lagrangian time and velocity scales. The pseudomomentum is seen to be strictly negative and related to the turbulence kinetic energy, while the drift is mixed and strongly influenced by the Reynolds stress. Both are calculated for turbulent channel flow for a range of Reynolds numbers and appear, as the Reynolds number increases, to approach a terminal form. At all Reynolds numbers studied, the pseudomomentum has a sole peak located in wall units in the low teens, while at the highest Reynolds number studied, Re(τ)=5200, the drift is negative in the vicinity of that peak, positive elsewhere, and largest near the rigid boundary. In contrast, the time and velocity scales grow almost logarithmically over much of the layer. Finally, the drift and pseudomomentum are discussed in the context of coherent wall layer structures with which they are intricately linked.

Use of Endoscopic Ultrasound to Evaluate Large Gastric Folds: Features Predictive of Malignancy

The aim of this study was to investigate with endoscopic ultrasound (EUS) the features of the gastric wall that can be used to predict malignant disease in patients with large gastric folds. We retrospectively reviewed the EUS findings of 65 patients (26 with benign and 39 with malignant disease) with large gastric folds on endoscopy and EUS and analyzed the predictors of malignant disease (e.g., gastric wall thickness, preservation of five-layered structure, thickened layers). Gastric wall thickness (≥9.8 mm), thickened deep layer, thickened muscularis propria and non-preserved wall layer structures were significantly more prevalent in patients with malignant disease on EUS. Among them, gastric wall thickness (≥9.8 mm) (odds ratio = 6.72, 95% confidence interval = 1.23–36.73, p = 0.028) and thickened muscularis propria (odds ratio = 37.14, 95% confidence interval = 7.02–196.49, p < 0.001) were significantly associated with malignant disease. Our data indicate that EUS is a useful tool for assessing large gastric folds and that gastric wall thickness (≥9.8 mm) and thickened muscularis propria are significant features predictive of malignant disease on EUS.

DNS and LES of turbulent flow in a closed channel featuring a pattern of hemispherical roughness elements

Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) were performed for fully-developed turbulent flow in channels with smooth walls and walls featuring hemispherical roughness elements at shear Reynolds numbers Reτ=180 and 400, with the goal of studying the effect of these roughness elements on the wall-layer structure and on the friction factor. The LES and DNS approaches were verified first by comparison with existing DNS databases for smooth walls. Then, a parametric study for the hemispherical roughness elements was conducted, including the effects of shear Reynolds number, normalized roughness height (k+=10–20) and relative roughness spacing (s+/k+=2–6). The sensitivity study also included the effect of distribution pattern (regular square lattice vs. random pattern) of the roughness elements on the walls. The hemispherical roughness elements generate turbulence, thus increasing the friction factor with respect to the smooth-wall case, and causing a downward shift in the mean velocity profiles. The simulations revealed that the friction factor decreases with increasing Reynolds number and roughness spacing, and increases strongly with increasing roughness height. The effect of random element distribution on friction factor and mean velocities is however weak. In all cases, there is a clear cut between the inner layer near the wall, which is affected by the presence of the roughness elements, and the outer layer, which remains relatively unaffected. The study reveals that the presence of roughness elements of this shape promotes locally the instantaneous flow motion in the lateral direction in the wall layer, causing a transfer of energy from the streamwise Reynolds stress to the lateral component. The study indicates also that the coherent structures developing in the wall layer are rather similar to the smooth case but are lifted up by almost a constant wall-unit shift y+ (∼10–15), which, interestingly, corresponds to the relative roughness k+=10.

Endoscopic Ultrasound for Differential Diagnosis of Duodenal Lesions

Duodenal tumors are rare and require a different management from that of esophagogastric neoplasia. The present study retrospectively analyses the endoscopic ultrasound (EUS) features of duodenal tumors of both epithelial and subepithelial origin. During a 12 year period, all duodenal tumors with histologic confirmation by surgery or biopsy were collected including endoscopic and endosonographic images. EUS images were analyzed for specific features (echogenicity, wall layer structure and relation, outer margins) to possibly distinguish epithelial (polyps and carcinoma versus lymphoma) and subepithelial (tumor type) tumors. 53/80 cases had histologic confirmation (mean age 53.1 ± 11.4 years, m:f = 33:20), 31 were epithelial (13 adenomas, 12 carcinomas, 6 lymphomas) and 22 subepithelial (11 GISTs, 7 Brunneromas, 1 lipoma, 3 NETs). EUS did not recognize carcinomas in 2/13 adenomas. EUS features suggesting carcinoma were loss of wall layers and irregular margins. 5/6 lymphomas showed inhomogeneous thickening with layers partially recognizable. Tumor type of subepithelial lesions correlated with echogenicity: GIST tumors were mostly (62.5 %) hypocheoic with the 3 malignant cases being characterized by heterogeneous echopattern with irregular outer margins. Of the hyperechoic lesions, lipomas had a homogeneous whitish appearance, while NET and Brunneromas were less hyperechoic. In the latter, the endoscopic aspect was also helpful for differential diagnosis. Accuracy of combined endoscopic/EUS imaging for all duodenal lesions was 84.9 % (45/53). No procedural complications occurred among all patients that received EUS examinations. EUS contributes to the differential diagnosis of epithelial lesions known to be malignant; in subepithelial tumors, tissue confirmation is still required.

Twofold interpenetration corrugated brick wall frameworks of 3d−4f heterometallic coordination polymers

Two 3d−4f heterometallic coordination polymers [EuCo(pydc) 3(H 2O) 3] n · 2 nH 2O ( 1) [YbCo(pydc) 3(H 2O) 3] n · nH 2O ( 2) have been hydrothermally synthesized from pyridine-2,4-dicarboxylic acid (H 2pydc). Compounds 1 and 2 possess isostructural twofold interpenetration corrugated brick wall layer structures with (6,3) topology.

Numerical simulation of the interactions of highly entangled polymers with coherent structure in a turbulent channel flow

Abstract Direct numerical simulations have been conducted with many cluster models of beads and connecting springs in a turbulent channel flow in order to investigate how the low-speed streaks and the small-scale flow related to the streaks are affected by the cluster models. The cluster model represents highly entangled polymers observed in the quiescent and flowing aqueous solution. The cluster models were introduced in the buffer region to simulate the experiments of Tiederman et al. (Tiederman, W.G., Luchik, T.S., Bogard, D.G., 1985. Wall-layer structure and drag reduction. J. Fluid Mech. 156, 419–437) in which the polymer solution was injected from a slot in the channel wall. An experiment has been carried out for visual observation of highly entangled polymers in a turbulent channel flow of the same Reynolds number in order to determine a parameter of the cluster model. The computational results show that the minor streaks and the small-scale eruptive flows associated with the streamwise vortices are attenuated selectively by the cluster models. The length scale and time scale of these structures are comparable to those of the cluster model. On the other hand, the dynamics of large-scale streaks are found to be basically unchanged. These results are consistent with the measurement of a suppression of low threshold Reynolds-stress producing motion by Harder and Tiederman (Harder, K.J., Tiederman, W.G., 1991. Drag reduction and turbulent structure in two-dimensional channel flows. Philos. Trans. R. Soc. Lond. 336, 19–34).

Characterization of the Local Layer Structure of a Broad Wall in a Surface Stabilized Ferroelectric Liquid Crystal Using Synchrotron X-Ray Micro-Diffraction

The local layer structure of the broad wall of a zig-zag defect in a thin-surface stabilized ferroelectric liquid crystal cell was characterized using a synchrotron X-ray microbeam of less than 5 µm spatial resolution. By using a rocking curve measurement at the broad wall, multiple or broad peaks were observed between a pair of peaks due to a chevron structure. These new peaks are clear evidence of a modified pseudo-bookshelf structure at the wall. For 1.5 µm thick cells, a bookshelf layer is relatively flat, but is accompanied by small areas of inclined layer connecting the bookshelf and the chevron structures. For 10 µm thick cells, the pseudo-bookshelf structure bends or undulates both perpendicular and parallel to the rubbing direction. No appreciable change in the layer spacing was observed in the modified pseudo-bookshelf structure. The temperature dependence of the broad wall layer structure was also measured.

Active turbulence control for drag reduction in wall-bounded flows

The objective of this study is to explore concepts for active control of turbulent boundary layers leading to skin-friction reduction using the direct numerical simulation technique. Significant drag reduction is achieved when the surface boundary condition is modified to suppress the dynamically significant coherent structures present in the wall region. The drag reduction is accompanied by significant reduction in the intensity of the wall-layer structures and reductions in the magnitude of Reynolds shear stress throughout the flow. The apparent outward shift of turbulence statistics in the controlled flows indicates a displaced virtual origin of the boundary layer and a thickened sublayer. Time sequences of the flow fields show that there are essentially two drag-reduction mechanisms. Firstly, within a short time after the control is applied, drag is reduced mainly by deterring the sweep motion without modifying the primary streamwise vortices above the wall. Consequently, the high-shear-rate regions on the wall are moved to the interior of the channel by the control schemes. Secondly, the active control changes the evolution of the wall vorticity layer by stabilizing and preventing lifting of the spanwise vorticity near the wall, which may suppress a source of new streamwise vortices above the wall.

An investigation of wall-layer dynamics using a combined temporal filtering and correlation

The relative role of outer- and wall-layer structures in the dynamics of the near-wall region of a turbulent boundary layer was explored by examining the scaling of the spanwise correlation coefficient between the wall shear stress and the streamwise velocity fluctuation, RTu(z), within narrow frequency bands spanning the entire turbulence spectrum. The scaling characteristics of RTu( z) within the individual frequency bands indicate that one can separate the contribution to the streamwise velocity fluctuations, in the buffer and logarithmic regions, due to outer-layer structures from those due to wall-layer events. Results provide insight into the lack of wall scaling for the conventional correlation coefficient, RTU(z), in the near-wall region. Moreover, the ‘negative dip’ in R,,(x+), which has often been associated with the low-speed streaks, was found to exist within certain frequency bands for all Reynolds numbers investigated (1579 < Re, < 5961). More interestingly, it is shown that, although the energy of the outer-layer structures increases with Reynolds number to overwhelm the streamwise velocity fluctuations in the near-wall region, the production of the Reynolds shear stress is dominated by wall-layer eddies. The findings of the current investigation provide strong support for Townsend’s hypothesis of ‘active’ and ‘inactive ’ motions.

Linear, hydrodynamic flow in a rotating saturated porous medium

Linear, steady, axisymmetric flow of a homogeneous fluid in a rigid, bounded, rotating, saturated porous medium is analyzed. The fluid motions are driven by differential rotation of horizontal boundaries. The dynamics of the interior region and vertical boundary layers are investigated as functions of the Ekman number E(=v/ΩL 2) and rotational Darcy 3 numberN(=kΩ/v) which measures the ratio between the Coriolis force and the Darcy frictional term. IfN≫E −1/2, the permeability is sufficiently high and the flow dynamics are the same as those of the conventional free flow problem with Stewartson'sE 1/3 andE 1/4 double layer structure. For values ofN≤E −1/2 the effect of porous medium is felt by the flow; the Taylor-Proudman constraint is no longer valid. ForN≪E −1/3 the porous medium strongly affects the flow; viscous side wall layer is absent to the lowest order and the fluid pumped by the Ekman layer, returns through a region of thicknessO(N −1). The intermediate rangeE −1/3≪N≪E −1/2 is characterized by double side wall layer structure: (1)E 1/3 layer to return the mass flux and (ii) (NE)1/2 layer to adjust the interior azimuthal velocity to that of the side wall. Spin-up problem is also discussed and it is shown that the steady state is reached quickly in a time scaleO(N).

Large eddy simulation of the flow in a transpired channel

The flow in a transpired channel has been computed by large eddy simulation. The numerical results compare very well with experimental data. Blowing decreases the wall shear stress and enhances turbulent fluctuations, while suction has the opposite effect. The wall layer thickness normalized by the local wall shear velocity and kinematic viscosity increases on the blowing side of the channel and decreases on the suction side. Suction causes more rapid decay of the spectra, larger mean streak spacing and higher two-point correlations. On the blowing side, the wall layer structures lie at a steeper angle to the wall, whereas on the suction side this angle is shallower.

Optimization of the injection process for drag-reducing additives

The primary objective of this experimental study was to determine the optimum combination of additive concentration, additive flowrate, injector angle and injector width for injecting a drag-reducing additive into a channel flow of water. The experiments were designed to keep an effective concentration of the additive in the buffer region where previous experiments have shown the additives directly affect the turbulent structures. Flow visualization of the wall-layer structures was conducted for the optimum combination of injection variables at the streamwise locations where the drag reduction peaked and where the additive became fully mixed with the channel flow of water.

Wall-layer structure and drag reduction

When drag-reducing additives are confined entirely to the linear sublayer of a turbulent channel flow of water, both the spanwise spacing and bursting rate of the wall-layer structure are the same as those for a water flow and there is no evidence of drag reduction. Drag reduction is measured downstream of the location where the additives injected into the sublayer begin to mix in significant quantities with the buffer region (10 &lt; y+ &lt; 100)The superscript + denotes a dimensionless quantity scaled with the kinematic viscosity ν and the wall shear velocity v* = (τw/ρ)½. of the channel flow. At streamwise locations where drag reduction does occur and where the injected fluid is not yet uniformly mixed with the channel flow, the dimensionless spanwise streak spacing increases and the average bursting rate decreases. The decrease in bursting rate is larger than the corresponding increase in streak spacing. The wall-layer structure is like the structure in the flow of a homogeneous, uniformly mixed, drag-reducing solution. Thus, the additives have a direct effect on the flow processes in the buffer region and the linear sublayer appears to have a passive role in the interaction of the inner and outer portions of a turbulent wall layer.