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The bifurcation of two-dimensional gravity–capillary waves into solitary waves when the phase velocity and group velocity are nearly equal is investigated in the presence of constant vorticity. We found that gravity–capillary solitary waves with decaying oscillatory tails exist in deep water in the presence of vorticity. Furthermore we found that the presence of vorticity influences strongly (i) the solitary wave properties and (ii) the growth rate of unstable transverse perturbations. The growth rate and bandwidth instability are given numerically and analytically as a function of the vorticity.
A nonlinear Schrödinger equation for the envelope of two-dimensional gravity–capillary waves propagating at the free surface of a vertically sheared current of constant vorticity is derived. In this paper we extend to gravity–capillary wave trains the results of Thomas et al. (Phys. Fluids, 2012, 127102) and complete the stability analysis and stability diagram of Djordjevic & Redekopp (J. Fluid Mech., vol. 79, 1977, pp. 703–714) in the presence of vorticity. The vorticity effect on the modulational instability of weakly nonlinear gravity–capillary wave packets is investigated. It is shown that the vorticity modifies significantly the modulational instability of gravity–capillary wave trains, namely the growth rate and instability bandwidth. It is found that the rate of growth of modulational instability of short gravity waves influenced by surface tension behaves like pure gravity waves: (i) in infinite depth, the growth rate is reduced in the presence of positive vorticity and amplified in the presence of negative vorticity; (ii) in finite depth, it is reduced when the vorticity is positive and amplified and finally reduced when the vorticity is negative. The combined effect of vorticity and surface tension is to increase the rate of growth of modulational instability of short gravity waves influenced by surface tension, namely when the vorticity is negative. The rate of growth of modulational instability of capillary waves is amplified by negative vorticity and attenuated by positive vorticity. Stability diagrams are plotted and it is shown that they are significantly modified by the introduction of the vorticity.
In the recent years, the development of wind turbines has been so hectic in Taiwan. The design of the turbine blades directly impacts power effectiveness. In this study, the effects of manufacturing parameters and environmental factors on the mechanical properties of carbon fiber/epoxy composites that are used in turbine blades are discussed. Parameters of the manufacturing process affect the mechanical properties. Carbon composites made by a different numbers of layers are tested on various aspects of performance such as mechanical strength and corrosion resistance.
M. M. Hedman, University of Idaho Moscow, Idaho, USA,
F. Postberg, University of Heidelberg Heidelberg, GERMANY,
D. P. Hamilton, University of Maryland College Park, Maryland, USA,
S. Renner, University of Lille Lille, FRANCE,
H.-W. Hsu, University of Colorado Boulder, Colorado, USA
All of the giant planets in the outer Solar System possess rings composed primarily of particles less than 100 microns across. Such small particles are conventionally referred to as “dust grains” regardless of their composition, and so these rings are considered “dusty rings” (as opposed to the more famous main rings of Saturn and Uranus, whose particles are more than a millimeter across). Dusty rings are often very tenuous and so can be much more difficult to observe than Saturn's broad, bright, and dense main rings. Nevertheless, dusty rings are extremely interesting because they have very rich dynamics and are extremely sensitive probes of their environment.
The high surface-area-to-volume ratio of dust-sized grains makes them much more responsive to non-gravitational forces like solar radiation pressure, plasma drag, and torques from the planet's electromagnetic field. Furthermore, sub-millimeter particles can be lost from the ring system on relatively short timescales due to erosion via charged-particle and micrometeoroid bombardment or through ejection by the non-gravitational forces listed above. This means that small particles need to be constantly supplied to these rings from larger bodies, and indeed all of the known dusty rings are associated with larger objects that are the likely sources of dusty debris. The most dramatic example of this is Saturn's E ring, which is clearly supplied by material erupting from beneath the surface of the geologically active moon Enceladus. However, this is a special case, and most dusty rings are instead associated with denser rings (which are composed primarily of millimeter-to-metersized particles) or small moons. These objects can serve as dust sources because they are constantly being bombarded by micrometeoroids, and these impacts release fine debris that can escape the weak gravitational fields of these small bodies and go into orbit around the planet. Note that the amount of dust released by this process depends on the size, mass, and regolith properties of the source object, and calculations of the dust production rate based on simple estimates of impact ejecta velocity distributions suggest that source moons that are several kilometers across are the most efficient at producing dusty rings (Burns et al., 1999).
As the consciousness of energy saving and carbon reduction and comfortable environment is paid increasing attention to, the common objective of various countries with decreasing energy is to develop and popularize high efficiency and low running noise blowers. This study uses CFD to calculate the flow field and performance of a blower and compare with the experimental measurement. The characteristic curve of blower shows that the simulated and experimental values are close to each other, the difference between the values is only 0.4%. This analysis result proofs the CFD package is a highly reliable tool for the future blower design improvement. In addition, this study discusses the noise distribution of blower flow field, the periodic pressure output value calculated by CFD is used in the sound source input of sound pressure field, so as to simulate and analyze the aerodynamic noise reading of the flow field around the blower. The result shows that the simulated value of flow field around the fan has as high as 80.5 dB(A) ∼ 81.5 dB(A) noise level and is agree with measurement (82 dB(A)). The noise level is low but has a sharp noise. According to the numerical results, designer of the blower modify the tongue geometry and remove the sharp noise.
Prior to integrated circuit (IC) packaging, die performance must be verified using probe cards to screen for defective products. With the decrease in IC line width, the dimensions of the pads used for performance verification and the spacing between adjacent pads have also decreased. However, when the pad pitch is reduced to less than 30 μm, commonly used probe cards will face manufacturing problems in miniaturization. To resolve probe card manufacturing problems caused by the miniaturization of IC components, the use of an anisotropic conductive film (ACF) in probe cards was proposed in this study. Theoretical calculations and experimental testing of this probe structure were conducted to demonstrate the feasibility of this concept.
In theoretical calculations, composite material and buckling theory were utilized to evaluate the buckling behavior of the ACF. In experimental testing, photolithography and electroplating techniques were used to control the line width and spacing intervals of the micron-scale metal wires in the ACF. After the ACF was fabricated, the mechanical properties of the ACF during wafer testing were assessed. Theoretical analyses and experimental testing verified that ACFs can potentially be applied to the performance verification of IC products. In the ACF structure, multiple probes came into contact with each pad. Therefore, ACFs can potentially be applied to the performance verification of IC components with pad diameters of less than 20 μm. The results of this study directly benefit the miniaturization of ICs.
The simulations of flow past a two-dimensional circular cylinder are conducted to investigate the feasibility of adaptive mesh refinement applied on curved spectral elements. The nonconforming spectral element method and adaptive meshes technique are used to the curve surfaces and observe whether any discontinuity of the solutions. The adaptive nonconforming spectral element method is implemented to compare with those obtained by conforming mesh method with respect to several existing numerical and experimental studies. Meanwhile, three kinds of estimated error base mesh adaptation are conducted to compare their accuracy and efficiency with conforming mesh method. The results show adaptive nonconforming mesh method is more efficient than the conforming method. Especially, the vorticity error based method performs highest accuracy and fastest convergence. The results show this mesh refinement technique is applicable on the curved elements with satisfactory accuracy. It releases this technique may be applied on the simulations of flow past objects with more general geometries.
Accurate estimation of food portion size is critical in dietary studies. Hands are potentially useful as portion size estimation aids; however, their accuracy has not been tested. The aim of the present study was to test the accuracy of a novel portion size estimation method using the width of the fingers as a ‘ruler’ to measure the dimensions of foods (‘finger width method’), as well as fists and thumb or finger tips. These hand measures were also compared with household measures (cups and spoons). A total of sixty-seven participants (70 % female; age 32·7 (sd 13·7) years; BMI 23·2 (sd 3·5) kg/m2) attended a 1·5 h session in which they estimated the portion sizes of forty-two pre-weighed foods and liquids. Hand measurements were used in conjunction with geometric formulas to convert estimations to volumes. Volumes determined with hand and household methods were converted to estimated weights using density factors. Estimated weights were compared with true weights, and the percentage difference from the true weight was used to compare accuracy between the hand and household methods. Of geometrically shaped foods and liquids estimated with the finger width method, 80 % were within ±25 % of the true weight of the food, and 13 % were within ±10 %, in contrast to 29 % of those estimated with the household method being within ±25 % of the true weight of the food, and 8 % being within ±10 %. For foods that closely resemble a geometric shape, the finger width method provides a novel and acceptably accurate method of estimating portion size.
With good combustion characteristics, hydrogen has been developing as a clean alternative fuel of engines. This study is to develop a diesel/hydrogen dual fuel engine. The hydrogen was added at inlet port in a 4-cylinder direct injection turbocharged diesel engine with an EGR (Exhaust Gas Recirculation) system to investigate engine performance and exhaust pollutant. The measured items are composed of the gas pressure of cylinder, crank angle, consumption rate of diesel, consumption rate of hydrogen, air flow rate, emissions (HC, CO2, NOX, and Smoke), and so on. The authors analyze how the addition of hydrogen with EGR system influences the engine performance and emissions. The diesel/hydrogen dual fuel turbocharged engine can increase the brake thermal efficiency with a greater decrease in emissions compared with the turbocharged diesel engine. Furthermore, the authors little altered the engine structure to get the positive effect of energy saving and pollutant decreasing.
Tornadoes are one type of violent flow phenomenon and occur in many places in the world. There are many research methods that aim to reduce the loss of human lives and material damage caused by tornadoes. One effective method is numerical simulation such as that in Ishihara et al. (J. Wind Engng Ind. Aerodyn., vol. 99, 2011, pp. 239–248). The swirling structure of the Navier–Stokes flow is significant for both the mathematical analysis and numerical simulations of tornadoes. In this paper, we try to clarify the swirling structure. More precisely, we performed numerical computations on axisymmetric Navier–Stokes flows with a no-slip flat boundary. We compared a hyperbolic flow with swirl and one without swirl, and observed that the following phenomenon occurs only in the swirl case: the distance between the point with the maximum magnitude of velocity
-axis changed drastically at a specific time (which we call the turning point). Besides, an ‘increasing velocity phenomenon’ occurred near the boundary, and the maximum value of
was obtained near the axis of symmetry and the boundary when the time was close to the turning point in the swirl case.
Recent meta-analyses of resting-state networks in major depressive disorder (MDD) implicate network disruptions underlying cognitive and affective features of illness. Heterogeneity of findings to date may stem from the relative lack of data parsing clinical features of MDD such as phase of illness and the burden of multiple episodes.
Resting-state functional magnetic resonance imaging data were collected from 17 active MDD and 34 remitted MDD patients, and 26 healthy controls (HCs) across two sites. Participants were medication-free and further subdivided into those with single v. multiple episodes to examine disease burden. Seed-based connectivity using the posterior cingulate cortex (PCC) seed to probe the default mode network as well as the amygdala and subgenual anterior cingulate cortex (sgACC) seeds to probe the salience network (SN) were conducted.
Young adults with remitted MDD demonstrated hyperconnectivity of the left PCC to the left inferior frontal gyrus and of the left sgACC to the right ventromedial prefrontal cortex (PFC) and left hippocampus compared with HCs. Episode-independent effects were observed between the left PCC and the right dorsolateral PFC, as well as between the left amygdala and right insula and caudate, whereas the burden of multiple episodes was associated with hypoconnectivity of the left PCC to multiple cognitive control regions as well as hypoconnectivity of the amygdala to large portions of the SN.
This is the first study of a homogeneous sample of unmedicated young adults with a history of adolescent-onset MDD illustrating brain-based episodic features of illness.
Several previous cross-sectional studies have shown that vegetarians have a better metabolic profile than non-vegetarians, suggesting that a vegetarian dietary pattern may help prevent chronic degenerative diseases. However, longitudinal studies on the impact of vegetarian diets on metabolic traits are scarce. We studied how several sub-types of vegetarian diets affect metabolic traits, including waist circumference, BMI, systolic blood pressure (SBP), diastolic blood pressure, fasting blood glucose, total cholesterol (TC), HDL, LDL, TAG and TC:HDL ratio, through both cross-sectional and longitudinal study designs. The study used the MJ Health Screening database, with data collected from 1994 to 2008 in Taiwan, which included 4415 lacto-ovo-vegetarians, 1855 lacto-vegetarians and 1913 vegans; each vegetarian was matched with five non-vegetarians based on age, sex and study site. In the longitudinal follow-up, each additional year of vegan diet lowered the risk of obesity by 7 % (95 % CI 0·88, 0·99), whereas each additional year of lacto-vegetarian diet lowered the risk of elevated SBP by 8 % (95 % CI 0·85, 0·99) and elevated glucose by 7 % (95 % CI 0·87, 0·99), and each additional year of ovo-lacto-vegetarian diet increased abnormal HDL by 7 % (95 % CI 1·03, 1·12), compared with non-vegetarians. In the cross-sectional comparisons, all sub-types of vegetarians had lower likelihoods of abnormalities compared with non-vegetarians on all metabolic traits (P<0·001 for all comparisons), except for HDL and TAG. The better metabolic profile in vegetarians is partially attributable to lower BMI. With proper management of TAG and HDL, along with caution about the intake of refined carbohydrates and fructose, a plant-based diet may benefit all aspects of the metabolic profile.
Since the end of the Warring States period (221 B.C.), the traditional history of China has always been said to have begun with the “Three August Sovereigns” and the “Five Emperors.” The stages in Chinese civilization were thus personified and ancient society was conceived of as having been ruled by an uninterrupted line of emperors. This early period of Chinese history may be divided into three periods, each of which may be typified by one oracle-graph.
The first period is the era of the legendary personages. This is before the period of the Yellow Emperor and may be represented by the oracle-bone graph for “sage.” The second period is the era of the emperors who created social institutions, an era which may be represented by the oracle-bone graph for “jade pendant.” The final period is the era of authentic dynastic history, covering the Hsia, Shang, and Chou dynasties. This period may be represented by the oracle-bone graph for “king.”
The oracle-bone character for “sage” is a pictograph of a man with extremely keen hearing. This implies exceptional physical or mental capabilities which would enable that person to bring great benefits to the community. This period of the sage saw the invention and development of a series of technological skills and tools which improved the standard of living of the community, but the stage had still not been reached when the social system necessary for political organization could come into being; that is to say, society had not yet reached the stage of true civilization.
In this study, the properties of surface acoustic wave (SAW) filters, including phase velocity and electromechanical coupling coefficient (K2) are investigated. The effective surface permittivity (ESP) method was employed to estimate the K2 of bulk materials (single layer) and multi-layer (double-layer and trilayer) structures. In the cases of bulk materials, the calculation results agree with the experimental data, and the errors are less than 7% for quartz. In the cases of double-layer materials, the phase velocity and K2 of various materials, such as ZnO/Diamond and LiNbO3/Diamond, were acquired, and the results demonstrate that LiNbO3/diamond is the optimal choice for high-frequency SAW devices. For the cases of trilayer, the structure of ZnO/PZT/diamond has relatively high K2 and phase velocity. Therefore, this structure is the optimal trilayer structure for high-frequency SAW devices. The study demonstrates that ESP method can be successfully used for estimating SAW properties in piezoelectric multi-layer structures even though the structures contain nonpiezoelectric film (diamond). The proposed numerical computation has the potential to shorten the developing time of SAW device.
The growth of the size of cache and the number of processor cores in modern CPUs is the major factor in advancing the computing performance of modern machines. The effect of CPU cache size in multicore computers on performance, however, has attracted little attention in lubrication and engineering analyses. In this study, the effect of cache size on the computational performance of two parallel iterative methods in solving two Reynolds equations is examined. Four computers, with CPU cache size from 4 to 40 MB and the number of processor cores from 4 to 16, were used. The sizes of the numerical grid were selected to simulate large gridwork (256 × 256) to small gridwork (2048 × 2048) tasks. It is found that the size of CPU cache is a major factor influencing the parallel efficiency in using the RBSOR method. On the other hand, the SPSOR method obtains much higher parallel efficiency than the RBSOR for medium-grained tasks, regardless of the size of CPU cache. The use of the SPSOR can, therefore, provide a much better parallel computing performance than the RBSOR in the cases of having a large number of grids or in a system with limited CPU cache.
Nanoparticles of ∼55 nm in diameter have been found to significantly increase the fracture toughness of nanocomposites with a ductile polymer matrix. This paper presents a comparative study of the effectiveness of micrometer-sized and nanosized elastomeric particles in improving the fracture toughness and strength of polymeric adhesives. Particular focuses are on the effects of particle size, matrix ductility, and adhesive thickness on the shear strength and fracture toughness. The results reveal that for an epoxy adhesive cured with a J400 hardener, nanosized particles can produce nearly 18 times more increase in fracture toughness than what can be achieved using micrometer-sized particles at the same volume fraction of 5.0 vol%. This huge improvement of adhesives' fracture toughness by nanosized particles is similar to that observed in bulk nanocomposites, indicating that the superior toughening mechanism of nanosized elastomeric particles is equally effective in thin adhesives constrained by stiff adherends.