Fundamental consideration of wall heat partition of vertical subcooled boiling flows

Improved wall heat flux partitioning accounting sliding bubbles and a mechanistic model that incorporates the fundamental consideration of bubble frequency during low-pressure subcooled flow boiling is presented. A model considering the forces acting on departing bubbles at the heated surface is employed. Coupled with a three-dimensional two-fluid and population balance equations based on the modified MUSIG (MUltiple-SIze-Group) model, the behavior of an upward forced convective subcooled boiling flows in a vertical annular channel is simulated. Comparison of model predictions against local and axial measurements (heat fluxes ranged from 152.9 to 705.0 kW/m²) is made for the void fraction, Sauter mean bubble diameter and interfacial area concentration covering a range of different mass and heat fluxes and inlet subcoolings. Good agreement is achieved between the predicted and measured profiles. Reasonable agreement with recent experimental measurements is also attained for the predicted growth and waiting times of bubble frequency at particular local wall superheat and subcooling temperatures.     

Microarray with Micro‐ and Nano‐topographies Enables Identification of the Optimal Topography for Directing the Differentiation of Primary Murine Neural Progenitor Cells

During development and tissue repair, progenitor cells are guided by both biochemical and biophysical cues of their microenvironment, including topographical signals. The topographical cues have been shown to play an important role in controlling the fate of cells. Systematic investigation of topographical structures with different geometries and sizes under the identical experimental conditions on the same chip will enhance the understanding of the role of shape and size in cell–topography interactions. A simple customizable multi‐architecture chip (MARC) array is therefore developed to incorporate, on a single chip, distinct topographies of various architectural complexities, including both isotropic and anisotropic features, in nano‐ to micrometer dimensions, with different aspect ratios and hierarchical structures. Polydimethylsiloxane (PDMS) replicas of MARC are used to investigate the influence of different geometries and sizes in neural differentiation of primary murine neural progenitor cells (mNPCs). Anisotropic gratings (2 μm gratings, 250 nm gratings) and isotropic 1 μm pillars significantly promote differentiation of mNPCs into neurons, as indicated by expression of β‐III‐tubulin (59%, 58%, and 58%, respectively, compared to 30% on the control). In contrast, glial differentiation is enhanced on isotropic 2 μm holes and 1 μm pillars. These results illustrate that anisotropic topographies enhance neuronal differentiation while isotropic topographies enhance glial differentiation on the same chip under the same conditions. MARC enables simultaneous cost‐effective investigation of multiple topographies, allowing efficient optimization of topographical and biochemical cues to modulate cell differentiation.     

微胶囊化棕榈油的品质分析

以麦芽糊精与大豆分离蛋白为复配壁材、蔗糖脂肪酸酯和单硬脂酸甘油酯为乳化剂制备棕榈油微胶囊,检测其基本理化指标,探讨微胶囊的热稳定性、微粒微观结构及储藏稳定性。结果表明:自制微胶囊的含油量是38.21%,蛋白质含量是24.68%,自由下落堆积成锥体的休止角是36.1°,水溶解度是75.8%,所得微胶囊散落性良好,微观结构完整,表面结构光滑,形状呈球形或椭球形,微胶囊颗粒大小主要集中在0~40μm的范围内;热重分析表明,微胶囊热稳定性良好,高温对微胶囊品质影响较小;储藏实验表明,在贮藏过程中微胶囊化的棕榈油过氧化值增加量为6.5mmol/kg;红外谱图表明,在喷雾干燥过程中壁材与芯材未发生化学反应,因此制备的微胶囊成品具有良好的性能及品质。     

Effects of fractionated abdominal irradiation on small intestinal motility--studies in a novel in vitro animal model

Disordered small intestinal motility occurs frequently during acute radiation enteritis. However, the characteristics and time course of the motor dysfunction are poorly defined. These parameters were assessed in a novel animal model of radiation enteritis. Ileal pressures were recorded in vitro with perfused micromanometric catheter using an arterially perfused ileal loop in 22 ferrets following fractionated abdominal irradiation (9 doses 2.50 Gy thrice weekly for 3 weeks). Tissue damage was graded histologically. Studies were performed 3 to 29 days after irradiation. Tissue from 7 control animals was also studied. All treated animals developed diarrhoea. Histology showed changes consistent with mild to moderate radiation enteritis. Following irradiation, there was an initial increase in frequency followed by a non-significant reduction in the frequency, but not the amplitude of ileal pressure waves. The frequency of pressure waves showed an inverse relationship with time after radiation (r = -0.634, p < 0.002). There was no relationship between motility and histology. We conclude that abdominal irradiation is associated with a time-dependent reduction in ileal motility which does not correlate with light microscopic changes.     

Curved waveguides for spatial mode filters in semiconductor lasers

Curved waveguides are used as a lateral spatial mode filter to increase the threshold for the first-order mode in high-power narrow stripe semiconductor lasers. Beam propagation analysis is used to determine optimal waveguide geometries and radii of curvature to establish appropriate amounts of bend loss. Curved waveguide devices are fabricated and compared against conventional devices. Use of a curved waveguide increases the current level at which lateral beam instabilities occur from /spl sim/400 to /spl sim/700 mA with no decline in slope efficiency.     

Three-dimensional nonplanar fracture model using the surface integral method

A computer code based on the use of the surface integral method, which represents a crack as a distribution of force dipoles, has been developed for modeling 3D nonplanar fractures. The nonplanar geometry was approximated as piecewise linear by subdividing the fracture surface into triangular elements that assume constant crack opening in the interior, and a p ^1/2 variation of opening along the crack front. The resulting singular integral equations were integrated using a combination of numerical and analytical techniques.Convergence studies using the surface integral formulation have yielded accurate stress intensity factors and crack opening displacements for both planar and nonplanar cracks under a variety of mixed mode loading conditions. Elliptical meshes were mapped on to cylindrical and spherical surfaces to model nonplanar fractures that could be compared to published results. Also, a high aspect ratio rectangular mesh was used to model a nonplanar kinked crack under plane strain conditions.     

Nutritional situation of a Chinese community

AIM: To evaluate the anthropometric measurements and dietary intake of the free-living elderly in a Chinese community. METHOD: A survey was carried out on 48 male and female subjects aged 60 to 96 years using anthropometric, dietary intake and questionnaire techniques. RESULTS: The study indicated female subjects to have more health problems, like pain at the joints (33%), hypertension (17%) and diabetes (27%) as compared to the male subjects. Dietary intake analysis showed the Chinese male subjects to have a higher energy intake (1,623 kcal) compared to the females (1,197 kcal) even though they did not fulfill the recommended dietary intake. The intake for energy, fats and carbohydrates, was found to be significantly different (p < 0.05) between both sexes. Anthropometric measurements indicated male elderly subjects to be significantly heavier (p < 0.05, 55.4 kg) and taller (161.8 cm) than female elderly subjects (49.5 kg; 146.2 cm respectively). About half of the elderly were normal in their BMI (male 55.6%; female 50%) and only 6.6% of the female subjects were obese. More male subjects were found to be underweight (33%) compared to female subjects (17%). Waist hip ratio was 0.92 for male and 0.87 for female. CONCLUSION: Our study showed that female elderly subjects had more health problems compared to male elderly subjects. On the whole, the elderly did not fulfill the recommended amount for energy intake while the percentage for carbohydrates, fats and protein from the total calorie intake were not in accordance with the healthy diet guidelines. Anthropometrically, male subjects were heavier and taller than female subjects. Looking at body mass index, most of the male elderly subjects were in the normal to underweight range. With these results, more research is warranted to give a clearer picture of the Chinese elderly in the country.     

Characterization of acidic property of sulfo-group functionalized microporous and mesoporous silica by adsorption microcalorimetry

Sulfo-group functionalized microporous and mesoporous silica based-on a MCM-41 framework which showed solid acid property were synthesized and characterized by adsorption microcalorimetry. Both the sulfo-functionalized microporous and mesoporous silica (Micro-SO₃H and Meso-SO₃H) were prepared by the oxidation of thiol group (–SH) included mesoporous silica which was obtained through the hydrolysis and co-condensation of tetramethoxysilane (TMOS) and mercaptopropyl trimethoxysilane (MPTMS). The samples have an ordered two-dimensional hexagonal pore array similar to that of MCM-41 as depicted from the XRD patterns. Nitrogen adsorption also shows that both microporous and mesoporous silica have pore characteristics similar to MCM-41, i.e. high surface area and high pore volume. However, pore regularity, surface area and pore volume decreased as the MPTMS loading increased. Solid-state ²⁹Si NMR indicated that the sulfo groups were successfully incorporated into both microporous and mesoporous silica frameworks. This sulfo-functionalized porous silica have high NH₃ uptakes and high differential heats of NH₃ adsorption, suggesting the presence of strong acidic sulfo groups on the silica surface. Acid catalyses of the samples were characterized by the isomerization reaction of but-1-ene to cis, trans-but-2-ene.     

Effect of Interesterification of Palmitic Acid-rich Triacylglycerol on Postprandial Lipid and Factor VII Response

The process of interesterification results in changes in triacylglycerol (TAG) structure and is used to increase the melting point of dietary fats. The acute health effects of this process on palmitic acid-rich fats are uncertain with regard to postprandial lipemia, insulin and factor VII activated (FVIIa) concentrations. Two randomized crossover trials in healthy male subjects compared the effects of meals containing 50 g fat [interesterified palm oil (IPO) versus native palm oil (NPO); n = 20, and IPO versus high-oleic sunflower oil (HOS); n = 18], on postprandial changes in lipids, glucose, insulin, chylomicron composition and FVIIa. Compared with NPO, IPO decreased postprandial TAG and insulin concentrations. Both NPO and IPO increased FVIIa concentrations postprandially; mean increases at 6 h were 21 and 19%, respectively. Compared with HOS, IPO decreased postprandial TAG (47% lower incremental area under the curve) and reduced the postprandial increase in FVIIa concentration by 64% at 6 h; no significant differences in hepatic and total lipase activities or insulin concentrations were noted. All three test meals increased postprandial leukocyte counts (average 26% at 6 h). The fatty acid composition of the chylomicron TAG was similar to the test fats following all test meals. It is concluded that interesterification of palm oil does not result in adverse changes in postprandial lipids, insulin or FVIIa compared to high oleate and native palm oils. George J. Miller: Deceased August 2006.     

Electrical detection of fast reaction kinetics in nanochannels with an induced flow

Nanofluidic channels can be used to enhance surface binding reactions, since the target molecules are closely confined to the surfaces that are coated with specific binding partners. Moreover, diffusion-limited binding can be significantly enhanced if the molecules are steered into the nanochannels via either pressure-driven or electrokinetic flow. By monitoring the nanochannel impedance, which is sensitive to surface binding, low analyte concentrations have been detected electrically in nanofluidic channels within response times of 1-2 h. This represents a approximately 54 fold reduction in the response time using convective flow compared to diffusion-limited binding. At high-flow velocities, the presented method of reaction kinetics enhancement is potentially limited by force-induced dissociations of the receptor-ligand bonds. Optimization of this scheme could be useful for label-free, electrical detection of biomolecule binding reactions within nanochannels on a chip.