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1.
This paper investigates the effects of a magnetic field on the free convective flow of a viscous, incompressible, dissipative fluid through a porous medium, occupying a semi-infinite region of the space bounded by an infinite vertical and porous plate. The plate is subjected to a normal suction velocity and the heat flux at the plate is constant. The magnetic field is of uniform strength and is applied perpendicular to the plate. An analytical solution to the problem is obtained. The influence of the magnetic parameter (M) and permeability parameter (K) is discussed for the case of air (P = 0.71) when the plate is subjected to a constant suction velocity and is being cooled by free convection currents.  相似文献   

2.
In this study, the homotopy analysis method (HAM) is used to obtain an approximate analytical solution for geometrically non-linear vibrations of thin laminated composite plates resting on non-linear elastic foundations. Geometric non-linearity is considered using von Karman’s strain-displacement relations. Then, the effects of the initial deflection, ply properties, aspect ratio of the plate and foundation parameters on the non-linear free vibration is studied. Comparison between the obtained results and those available in the literature demonstrates the potential of HAM for the analysis of such vibration problems, whose governing differential equations include the quadratic and cubic non-linear terms. This study shows that only a first-order approximation of the HAM leads to highly accurate solutions for this type of non-linear problems.  相似文献   

3.
Cheung P  Toda-Peters K  Shen AQ 《Biomicrofluidics》2012,6(2):26501-2650112
In this paper, we present a simple procedure to incorporate commercially available external pressure transducers into existing microfluidic devices, to monitor pressure-drop in real-time, with minimal design modifications to pre-existing channel designs. We focus on the detailed fabrication steps and assembly to make the process straightforward and robust. The work presented here will benefit those interested in adding pressure drop measurements in polydimethylsiloxane (PDMS) based microchannels without having to modify existing channel designs or requiring additional fabrication steps. By using three different devices with varying aspect ratio channels (wh0, width/depth), we demonstrate that our approach can easily be adapted into existing channel designs inexpensively. Furthermore, our approach can achieve steady state measurements within a matter of minutes (depending on the fluid) and can easily be used to investigate dynamic pressure drops. In order to validate the accuracy of the measured pressure drops within the three different aspect ratio devices, we compared measured pressure drops of de-ionized water and a 50 wt. % glycerol aqueous solution to four different theoretical expressions. Due to the deformability of PDMS, measured pressure drops were smaller than those predicted by the rigid channel theories (plate and rectangular). Modification of the rigid channel theories with a deformability parameter α provided better fits to the measured data. The elastic rectangular expression developed in this paper does not have a geometric restriction and is better suited for microchannels with a wider range of aspect ratios.  相似文献   

4.
In this research, linear and non-linear stability behaviour of a thin circular FGM plate subjected to the uniform temperature rise and the constant angular velocity loadings is analyzed. Properties of the FGM media are distributed across the thickness based on a power law form. Each property of the metal or ceramic constituents is considered to be the function of temperature based on the Touloukian model. General equilibrium equations for such conditions are obtained based on the classical plate theory. At first, the non-linear governing equations are established in a complete asymmetrical form. After that, two different analytical methods are presented to study the bifurcation behaviour. Existence of bifurcation phenomenon is examined. Pre-buckling analysis is performed for a plate with the immovable clamped edge. Stability equations are obtained based on the adjacent equilibrium criterion. The resulted equations are solved via the two distinct methodologies, i.e. the exact solution in terms of Coulomb wave functions and the power series method. A non-linear solution is also presented to detect the equilibrium path of the heated rotating FGM plate. It is found that the angular speed may stabilize the homogeneous circular plate which buckles during uniform heating. Furthermore, snapping may occur for FGM plates under the simultaneous action of heating and uniform rotation.  相似文献   

5.
The T-shaped microchannel system is used to mix similar or different fluids, and the laminar flow nature makes the mixing at the entrance junction region a challenging task. Acoustic streaming is a steady vortical flow phenomenon that can be produced in the microchannel by oscillating acoustic transducer around the sharp edge tip structure. In this study, the acoustic streaming is produced using a triangular structure with tip angles of 22.62°, 33.4°, and 61.91°, which is placed at the entrance junction region and mixes the inlets flow from two directions. The acoustic streaming flow patterns were investigated using micro-particle image velocimetry (μPIV) in various tip edge angles, flow rate, oscillation frequency, and amplitude. The velocity and vorticity profiles show that a pair of counter-rotating streaming vortices were created around the sharp triangle structure and raised the Z vorticity up to 10 times more than the case without acoustic streaming. The mixing experiments were performed by using fluorescent green dye solution and de-ionized water and evaluated its performance with the degree of mixing (M) at different amplitudes, flow rates, frequencies, and tip edge angles using the grayscale value of pixel intensity. The degree of mixing characterized was found significantly improved to 0.769 with acoustic streaming from 0.4017 without acoustic streaming, in the case of 0.008 μl/min flow rate and 38 V oscillation amplitude at y = 2.15 mm. The results suggested that the creation of acoustic streaming around the entrance junction region promotes the mixing of two fluids inside the microchannel, which is restricted by the laminar flow conditions.  相似文献   

6.
Cancer cell migration through tissue pores and tracks into the bloodstream is a critical biological step for cancer metastasis. Although in vivo studies have shown that expression of vimentin can induce invasive cell lines, its role in cell cytoskeleton reorganization and cell motility under in vitro physical confinement remains unknown. Here, a microfluidic device with cell culture chamber and collagen-coated microchannels was developed as an in vitro model for physiological confinement environments. Using this microchannel assay, we demonstrated that the knockdown of vimentin decreases 3T3 fibroblast cell directional migration speed in confined microchannels. Additionally, as cells form dynamic membranes that define the leading edge of motile cells, different leading edge morphologies of 3T3 fibroblast and 3T3 vimentin knockdown cells were observed. The leading edge morphology change under confinement can be explained by the effect of vimentin on cytoskeletal organization and focal adhesion. The microfluidic device integrated with a time-lapse microscope provided a new approach to study the effect of vimentin on cell adhesion, migration, and invasiveness.  相似文献   

7.
This paper presents a continuous delivery/continuous verifiability (CD/CV) method for IoT dataflows in edge–fog–cloud. A CD model based on extraction, transformation, and load (ETL) mechanism as well as a directed acyclic graph (DAG) construction, enable end-users to create efficient schemes for the continuous verification and validation of the execution of applications in edge–fog–cloud infrastructures. This scheme also verifies and validates established execution sequences and the integrity of digital assets. CV model converts ETL and DAG into business model, smart contracts in a private blockchain for the automatic and transparent registration of transactions performed by each application in workflows/pipelines created by CD model without altering applications nor edge–fog–cloud workflows. This model ensures that IoT dataflows delivers verifiable information for organizations to conduct critical decision-making processes with certainty. A containerized parallelism model solves portability issues and reduces/compensates the overhead produced by CD/CV operations. We developed and implemented a prototype to create CD/CV schemes, which were evaluated in a case study where user mobility information is used to identify interest points, patterns, and maps. The experimental evaluation revealed the efficiency of CD/CV to register the transactions performed in IoT dataflows through edge–fog–cloud in a private blockchain network in comparison with state-of-art solutions.  相似文献   

8.
Microfluidic spirals were used to successfully separate rare solid components from unpretreated human whole blood samples. The measured separation ratio of the spirals is the factor by which the concentration of the rare component is increased due to the Dean effect present in a flow profile in a curved duct. Different rates of dilution of the blood samples with a phosphate-buffered solution were investigated. The diameters of the spherical particles to separate ranged from 2 μm to 18 μm. It was found that diluting the blood to 20% is optimal leading to a separation ratio up to 1.97. Using two spirals continuously placed in a row led to an increase in separation efficacy in samples consisting of phosphate-buffered solution only from 1.86 to 3.79. Numerical investigations were carried out to display the flow profiles of Newtonian water samples and the shear-thinning blood samples in the cross-section of the experimentally handled channels. A macroscopic difference in velocity between the two rheologically different fluids could not be found. The macroscopic Dean flow is equally present and useful to help particles migrate to certain equilibrium positions in blood as well as lower viscous Newtonian fluids. The investigations highlight the potential for using highly concentrated, very heterogeneous, and non-Newtonian fluidic systems in known microsystems for screening applications.  相似文献   

9.
In this paper, an analytic solution of nonlinear H∞ robust controller is first proposed and used in a complete six degree-of-freedom nonlinear equations of motion of flight vehicle system with mass and moment inertia uncertainties. A special Lyapunov function with mass and moment inertia uncertainties is considered to solve the associated Hamilton-Jacobi partial differential inequality (HJPDI). The HJPDI is solved analytically, resulting in a nonlinear H∞ robust controller with simple proportional feedback structure. Next, the control surface inverse algorithm (CSIA) is introduced to determine the angles of control surface deflection from the nonlinear H∞ control command. The ranges of prefilter and loss ratio that guarantee stability and robustness of nonlinear H∞ flight control system implemented by CSIA are derived. Real aerodynamic data, engine data and actuator system of F-16 aircraft are carried out in numerical simulations to verify the proposed scheme. The results show that the responses still keep good convergence for large initial perturbation and the robust stability with mass and moment inertia uncertainties in the permissible ranges of the prefilter and loss ratio for which this design guarantees stability give same conclusion.  相似文献   

10.
Couple-stress solutions are obtained near the hole boundary of an infinite elastic plane subjected to a radial concentrated force at x = b, y = 0,under the restriction of r/b<-0.2 and b/l?;-10. Here r and l are the distance from the center of the hole to the point of interest and a characteristic length (couple-stress constant). At r = a, θ = ±π2, the stress ratio of the couple-stress solution to the classical one for the current problem is slightly lower than one of the Mindlin problem (1) for some values of v, except for v = 0.5 where they are equal. The dimensionless stress σ&#x0302;θθ is found along the hole boundary.  相似文献   

11.
杨艳刚  张彪  董敦义  王斌  张灿强 《资源科学》2011,33(7):1292-1297
为充分认识竹林生态系统在太湖流域水污染防治中的作用,于2009年7月-8月在浙江省安吉县对竹林土壤的硝态氮（NO-3-N）含量进行采样分析,并探讨了植被类型、地形条件等因素对土壤NO-3-N的影响。结果表明：①各采样点内,随土壤深度的增加,竹林土壤NO-3-N含量降低;②毛竹林0～30cm土壤层NO-3-N含量高于红笋竹林,而30～50cm土壤层则相反,但差异不显著;③林下植被为草灌结构的样点土壤NO-3-N含量高于林下植被为草丛结构的样点,这种差异在30～50cm上显著;④不同植被高度的土壤NO-3-N含量差异在0～10cm深度上达到显著水平;⑤土壤NO-3-N含量随海拔升高呈＂先下降后上升＂趋势,高海拔地区0～10cm土壤层的NO-3-N含量高于低海拔地区,10～30cm与低海拔地区相近,而30～50cm则小于低海拔地区;⑥位于陡坡的0～30cm土壤层NO-3-N含量均高于缓坡,而30～50cm土壤层则相反。综上分析,笔者认为竹林不同深度土壤NO-3-N的含量与植被状况、地形特点有密切关系。由于植被类型、覆盖度、枯落物以及地形条件的差异,影响了土壤水分获取及水分再分配进程,进而影响了土壤中NO-3-N的迁移和累积过程。  相似文献   

12.
This paper provides the closed form analytical solution to the problem of minimizing the material volume required to support a given set of bending loads with a given number of discrete structural members, subject to material yield constraints. The solution is expressed in terms of two variables, the aspect ratio, ρ-1, and complexity of the structure, q (the total number of members of the structure is equal to q(q+1)). The minimal material volume (normalized) is also given in closed form by a simple function of ρ and q, namely, V=q(ρ-1/q-ρ1/q). The forces for this nonlinear problem are shown to satisfy a linear recursive equation, from node-to-node of the structure. All member lengths are specified by a linear recursive equation, dependent only on the initial conditions involving a user specified length of the structure. The final optimal design is a class 2 tensegrity structure. Our results generate the 1904 results of Michell in the special case when the selected complexity q approaches infinity. Providing the optimum in terms of a given complexity has the obvious advantage of relating complexity q to other criteria, such as costs, fabrication issues, and control. If the structure is manufactured with perfect joints (no glue, welding material, etc.), the minimal mass complexity is infinite. But in the presence of any joint mass, the optimal structural complexity is finite, and indeed quite small. Hence, only simple structures (low complexity q) are needed for practical design.  相似文献   

13.
An analysis of the plastic enclaves developed around the end points of rigid fiber inclusions embedded in an elastic plate is undertaken. The plate is subjected to a uniform uniaxial stress at any angle of inclination with the axis of the fiber. It is assumed that the material of the plate is elastic-perfectly plastic and that the deformations are small. A singular solution of the stress field in the vicinity of the end points of the fiber is used in conjunction with the Mises yield criterion to obtain the radius of the plastic zone under conditions of plane strain and generalized plane stress. The dependence of the size and shape of the plastic deformation on the orientation of the fiber, the Poisson's ratio of the plate and the state of stress (plane strain or generalized plane stress) is established.  相似文献   

14.
Wang ZK  Zheng HY 《Biomicrofluidics》2012,6(1):12820-1282012
The study investigates the use of CO2 laser to induce glass strip peeling off to form microchannels on soda lime gass substrate. The strip peeling exhibits a strong dependence on the energy deposition rate on the glass surface. In spite of the vast difference in the combination of laser power and scanning speed, when the ratio of the two makes the energy deposition rate in the range 3.0-6.0 J/(cm2 s), the temperature rising inside glass will be above the strain point and reach the softening region of the glass. As a result, glass strip peeling is able to occur and form microchannels with dimensions of 20-40 μm in depth and 200-280 μm in width on the glass surface. Beyond this range, higher energy depsotion rate would lead to surface melting associated with solidification cracks and lower energy deposition rate causes the generation of fragment cracks.  相似文献   

15.
The essential content of a recent paper by the present writer comprises a comprehensive discussion of the physical bases underlying derivation of formulas for calculating the temperature distribution T, maximum temperature Tm and average temperature Ta in a toroidal electrical coil of rectangular cross section, internally generated heat and change of wire resistance with temperature being taken into account. Illustratively, the solution for the boundary value condition of constant surface temperature and uniform equivalent thermal conductivity was obtained.For the most part, however, problems that arise in practice are not encompassed in the comparatively simple boundary conditions of constant temperature. Experiment shows that in general the boundary condition is T ? T′ = ? K??n; whereof n denotes the outward drawn normal to the coil surface, K = (knh) the ratio of the equivalent thermal conductivity in the direction of n to the emissivity of the boundary surface, and T and T′ are the corresponding temperatures in the coil surface and the immediately adjacent ambient medium. Again, it frequently ensues in practice that the thermal conductivity is substantially different in the directions of the two principal axes of the cross section.In the present paper formulas for T, Tm, and Ta are obtained for electrical coils of ratio of external to internal radius greater than (roughly) two whereof (i) the thermal conductivity is different in the directions of the two principal axes of the cross section, (ii) K is different on but constant over each of the four faces of the coil, and (iii) no restriction is made as to T′ except that over each face it be expressible in a generalized Fourier series. Determination of T is posed as a boundary-value problem in the mathematical theory of heat; the formal solution of T effected by expansions in orthogonal functions; and Tm and Ta then determined through use of their known relationships with T. The resulting formulas are in the form of rapidly-converging singly-infinite trigonometric-hyperbolic series. Illustrative of application of these general formulas, the maximum temperatures in a coil of given dimensions subject to two different sets of surface conditions are calculated and found to be in excellent agreement with the known measured values.The just-mentioned formulas encompass practically all cases encountered in practice except those coils which do not satisfy the restriction as to ratio of radii. For these latter formulas for T, Tm, and Ta are obtained pursuant to conditions of (i) equivalent thermal conductivity different in the directions of the two principal axes of the cross section, (ii) K, and likewise T′, different on but constant over each of the four faces of the coil. These formulas are in the form of rapidly-converging singly-infinite trigonometric- Bessel function (of zero order) series: Illustratively, the maximum temperature in a coil of given dimensions is calculated and found to be in excellent agreement with the known measured value.  相似文献   

16.
We propose biofunctionalized nanofluidic slits (nanoslits) as an effective platform for real-time fluorescence-based biosensing in a reaction-limited regime with optimized target capture efficiency. This is achieved by the drastic reduction of the diffusion length, thereby a boosted collision frequency between the target analytes and the sensor, and the size reduction of the sensing element down to the channel height comparable to the depletion layer caused by the reaction. Hybridization experiments conducted in DNA-functionalized nanoslits demonstrate the analyte depletion and the wash-free detection ∼10 times faster compared to the best microfluidic sensing platforms. The signal to background fluorescence ratio is drastically increased at lower target concentrations, in favor of low-copy number analyte analysis. Experimental and simulation results further show that biofunctionalized nanoslits provide a simple means to study reaction kinetics at the single-pixel level using conventional fluorescence microscopy with reduced optical depth.  相似文献   

17.
The recycling of supracrustal materials, and in particular hydrated rocks, has a profound impact on mantle composition and thus on the formation of continental crust, because water modifies the physical properties of lithological systems and the mechanisms of partial melting and fractional fractionation. On the modern Earth, plate tectonics offers an efficient mechanism for mass transport from the Earth''s surface to its interior, but how far this mechanism dates back in the Earth''s history is still uncertain. Here, we use zircon oxygen (O) isotopes to track recycling of supracrustal materials into the magma sources of early Archean igneous suites from the Kaapvaal Craton, southern Africa. The mean δ18O values of zircon from TTG (tonalite–trondhjemite–granodiorite) rocks abruptly increase at the Paleo-Mesoarchean boundary (ca. 3230 million years ago; Ma), from mantle zircon values of 5‰–6‰ to approaching 7.1‰, and this increase occurs in ≤3230 Ma rocks with elevated Dy/Yb ratios. The 18O enrichment is a unique signature of low-temperature water–rock interaction on the Earth''s surface. Because the later phase was emplaced into the same crustal level as the older one and TTG magmas would derive from melting processes in the garnet stability field (>40 km depth), we suggest that this evident shift in TTG zircon O isotopic compositions records the onset of recycling of the mafic oceanic crust that underwent seawater hydrothermal alteration at low temperature. The onset of the enhanced recycling of supracrustal materials may also have developed elsewhere in other Archean cratons and reflects a significant change in the tectonic realm during craton formation and stabilization, which may be important processes for the operation of plate tectonics on early Earth.  相似文献   

18.
Exact solutions, based on couple-stresses plane strain theory of elasticity, are presented for the normal, shear and couple-stresses, displacements and rotations of an infinite-length (in z-axis) rectangular thin plate simply supported at two opposite edges (i.e.x=±L) and bent by a uniform load. Exact solutions reduce to classical values as l→0. Here l is defined as the new elastic material constant taking account of couple stresses.  相似文献   

19.
In a servomechanism using a two-phase alternating current control motor, a 90° difference is required in the phases of the carrier-frequency voltages applied to the fixed and control windings. This part describes and compares various methods of obtaining the phase difference.The question of the possibility of a phase-shifting proportional-derivative parallel “T” is answered in the negative, by the result that in any parallel “T” transfer characteristic, if the quadratic factor in the numerator is of the proportional-derivative form at the correct resonant frequency, the amount of phase shift which may be obtained from the remaining portion of the transfer characteristic is less than are tan (2n), where n is twice the carrier frequency divided by notch width. Thus for values of n high enough to have an appreciable stabilizing effect, the maximum obtainable intrinsic phase shift is negligible.In order to obtain a large phase shift it is necessary to add either a series input or a load impedance to the parallel “T,” or to use a phase-shifting network preceding or following the parallel “T.” Formulae and design charts are given for determination of the values of the components of phase lag networks.The method of calculation of tolerance requirements on the components, in terms of allowable deviation from the correct phase, is illustrated by an example of a phase lag network used in conjunction with a bridge “T” proportional-derivative network.  相似文献   

20.
Suppose that AXB=C is a consistent matrix equation and partition its solution X into a 2×2 block form. In this article we give some formulas for the maximal and minimal ranks of the submatrices in a solution X to AXB=C. From these formulas, we derive necessary and sufficient conditions for the submatrices to be zero and nonsingular, respectively. As applications, we give a group of formulas for the maximal and minimal ranks of submatrices in generalized inverses of matrices and their properties.  相似文献   

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