Unsteady three-dimensional sources for a two-layer fluid of finite depth and their applications

To our friend Ernie Tuck, in celebration of his multi-faceted talents. The velocity potentials of various unsteady point sources are derived in this paper for a two-layer fluid of finite depth. Two-layer fluids are often used to study effects of density stratification on hydrodynamics of marine systems. The sources here are restricted to the upper fluid layer and the potentials of the induced flows are given for the whole fluid domain. The velocity potentials of a transient source of arbitrary strength and in arbitrary three-dimensional motion are derived first. The potentials of a time-harmonic source without forward speed, and then with forward speed, are obtained from the transient source by specifying the appropriate source strength and motion. These potentials are fundamental to the analyses of various types of body motion in finite water depths under the influence of surface and interfacial waves. As a sample application, a numerical solution of the radiation and diffraction problem for a floating rectangular barge is presented. The results indicate that internal waves can have a strong effect on the motions of the floating barge over a wide range of incident-wave frequencies.     

Effects of osmotic pretreatment and frying conditions on quality and storage stability of vacuum-fried pumpkin chips

The effects of osmotic (OP), ultrasound-assisted osmotic pretreatment (UAOP) and frying conditions on quality and storage stability of vacuum fried pumpkin chips were investigated. The pumpkin samples were pretreated in maltodextrin solution and subsequently fried at different temperatures (90–110 °C) and time periods (10–30 min). The results demonstrated that the moisture content, water activity, lightness, yellowness and carotenoid content of the fried chips decreased, while oil content, hardness and a* (dark brown colour) value increased with increasing frying temperature and time. UAOP reduced about 16.0% of oil absorption and enhanced approximately 70% of carotenoid retention in the fried chips. UAOP samples were also more stable during storage than the untreated ones, indicated by lower degradation kinetics constants of key quality parameters. The proposed pretreatment could be an effective method for food industries to develop vacuum fried pumpkin chips with improved quality and stability.     

论企业资产结构

就资产结构对企业经营的影响进行了分析，并针对不同类型的资产结构，提出了优化的主要途径.     

XRD and FTIR crystallinity indices in sound human tooth enamel and synthetic hydroxyapatite

The crystallinity index (CI) is a measure of the percentage of crystalline material in a given sample and it is also correlated to the degree of order within the crystals. In the literature two ways are reported to measure the CI: X-ray diffraction and infrared spectroscopy. Although the CI determined by these techniques has been adopted in the field of archeology as a structural order measure in the bone with the idea that it can help e.g. in the sequencing of the bones in chronological and/or stratigraphic order, some debate remains about the reliability of the CI values. To investigate similarities and differences between the two techniques, the CI of sound human tooth enamel and synthetic hydroxyapatite (HAP) was measured in this work by X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR), at room temperature and after heat treatment. Although the (CI)_XRD index is related to the crystal structure of the samples and the (CI)_FTIR index is related to the vibration modes of the molecular bonds, both indices showed similar qualitative behavior for heat-treated samples. At room temperature, the (CI)_XRD value indicated that enamel is more crystalline than synthetic HAP, while (CI)_FTIR indicated the opposite. Scanning (SEM) and transmission (TEM) images were also used to corroborate the measured CI values.     

Mechanisms and causes of wear in tooth enamel: implications for hominin diets

The wear of teeth is a major factor limiting mammalian lifespans in the wild. One method of describing worn surfaces, dental microwear texture analysis, has proved powerful for reconstructing the diets of extinct vertebrates, but has yielded unexpected results in early hominins. In particular, although australopiths exhibit derived craniodental features interpreted as adaptations for eating hard foods, most do not exhibit microwear signals indicative of this diet. However, no experiments have yet demonstrated the fundamental mechanisms and causes of this wear. Here, we report nanowear experiments where individual dust particles, phytoliths and enamel chips were slid across a flat enamel surface. Microwear features produced were influenced strongly by interacting mechanical properties and particle geometry. Quartz dust was a rigid abrasive, capable of fracturing and removing enamel pieces. By contrast, phytoliths and enamel chips deformed during sliding, forming U-shaped grooves or flat troughs in enamel, without tissue loss. Other plant tissues seem too soft to mark enamel, acting as particle transporters. We conclude that dust has overwhelming importance as a wear agent and that dietary signals preserved in dental microwear are indirect. Nanowear studies should resolve controversies over adaptive trends in mammals like enamel thickening or hypsodonty that delay functional dental loss.     

The cavitation behavior with short length blades in centrifugal pump

A CFD code with 2-D cascade model was developed to predict the cavitation behavior around the impeller blades of impeller in a centrifugal pump. The governing equations are the two-phase Reynolds Averaged Navier-Stokes equations in a homogeneous form in which both liquid and vapor phases are treated as incompressible fluid. To close the model, a standard k-ɛ turbulence model is introduced. And the mass transfer rates between liquid and vapor phases are implemented as well. The validations are carried out by comparing with reference data in impeller of a centrifugal pump impeller. The cavitation characteristics of current centrifugal pumps is tested at an ondesign point (V=8 m/s) and two off-design points (V=20 m/s and V=30 m/s), respectively. The criteria of cavitation and flow instability around blades are presented. The results show that the current centrifugal pump can safely operate without cavitation at on-design point. Also, the simulation shows cavitation develops inhomogeneously among the blades at off-design points. Moreover, the effects of additional blades in the impeller are studied as well. From the numerical results, it is expected that a half-length blade is the optimum configuration as additional blades in cavitation point of view.     

Synthesis of Aryl‐Substituted Pyrimidines by Site‐Selective Suzuki–Miyura Cross‐Coupling Reactions of 2,4,5,6‐Tetrachloropyrimidine

Suzuki–Miyaura reactions of 2,4,5,6‐tetrachloropyrimidine allow a convenient synthesis of mono‐, di‐, tri‐ and tetraarylpyrimidines which are not readily available by other methods. All reactions proceed with excellent site‐selectivity.     

Improvement in Texture of Pressure-Assisted Thermally Processed Carrots by Combined Pretreatment using Response Surface Methodology

The effect of pretreatment pressure (0.1 to 400 MPa), temperature (25 to 75 °C), and calcium chloride concentration (0 to 1.5%) and their complex interaction on hardness, residual pectinmethylesterase (PME) activity, and diffused calcium content of pressure-assisted thermal processed (PATP, 700 MPa, 105 °C for 15 min) carrot have been studied using response surface methodology. Predicted values of carrot hardness, calcium content, and residual PME activity were found to be in good agreement with experimental values as indicated by the high R ² values of 0.98, 0.96 and 0.96, respectively. The optimum processing conditions, namely, calcium chloride concentration 1.0%; pretreatment pressure ranging from 286 to 314 MPa; pretreatment temperature varying from 53.8 to 58.3 °C, fulfill the conditions to obtain the PATP carrot with hardness ≥145 N, calcium content ≥ 2.5 mg/g, and residual PME activity ≥ 70%. These conditions resulted in more than tenfold increase in the hardness of PATP carrot (14.08 to 145 N) as compared to PATP carrot without any pretreatment. The study demonstrated that response surface methodology can be used for modeling carrot quality parameters of PATP.     

Inlaying nanoscale surface recess patterns with nanoscale objects

A simple and versatile approach to constructing patterns on a solid surface using nanoscale objects is demonstrated. The approach is essentially an inlaying process, in which recess patterns fabricated on a surface are selectively filled with nanoscale objects. The objects are anchored firmly on the surface due to the spatial confinement provided by the recess structures. Protein molecules and inorganic nanoparticles are used in this demonstration. Cyclic voltammetry is used to detect electron transfer signals from patterns of protein molecules. The approach suggests a potentially fast, high-throughput and versatile technique for constructing architectural structures on a solid surface using nanoscale objects.     

Monofluorinated analogues of polybrominated diphenyl ethers as analytical standards: synthesis, NMR, and GC-MS characterization and molecular orbital studies

Polybrominated diphenyl ethers (PBDEs), a group of 209 individual congeners distinguishable by the number and position of bromines, are produced for use as flame retardants in consumer goods. PBDEs have become ubiquitous environmental contaminants, present in increasing levels in the environment and humans. In the present study, 10 individual monofluorinated analogues of PBDEs (F-PBDEs) and one difluorinated PBDE (FF-PBDE) were synthesized and characterized, and their gas chromatographic (GC) and mass spectrometric (MS) characteristics determined. The synthesis method utilized a nucleophilic reaction of bromophenols with diphenyliodonium salts and the perbromination of fluorosubstituted diphenyl ethers. Reaction yields were between 10% and 59% with > or = 98% purity. Apart from the aromatic ring carrying the fluorine atom, only minor chemical nuclear magnetic resonance (NMR) shift changes were observed in comparison to the corresponding parent PBDEs, with the exception that the J(F,H) coupling was stronger. Our preliminary data show that F-PBDEs and PBDEs have comparable retention times in gas chromatography with F-PBDEs demonstrating in general shorter or identical retention times, depending on the pattern of fluorine substitution. We also calculated the torsion angles and the dipole moments for both and report that there is a good correlation between GC retention times and the torsion angles but not with dipole moments. In MS, the difference of the ion peaks of the F-PBDE/ PBDE pairs is m/z 19 (F), which allows a simultaneous MS detection without separation. On the basis of GC separation, simultaneous MS detection, and the stability of fluorine due to its generally resistance to nucleophilic displacement, we propose that F-PBDEs may function as valuable potential standards, markers, and tracers in environmental analysis.