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1.
The accurate viscosity measurement of complex fluids is essential for characterizing fluidic behaviors in blood vessels and in microfluidic channels of lab-on-a-chip devices. A microfluidic platform that accurately identifies biophysical properties of blood can be used as a promising tool for the early detections of cardiovascular and microcirculation diseases. In this study, a flow-switching phenomenon depending on hydrodynamic balancing in a microfluidic channel was adopted to conduct viscosity measurement of complex fluids with label-free operation. A microfluidic device for demonstrating this proposed method was designed to have two inlets for supplying the test and reference fluids, two side channels in parallel, and a junction channel connected to the midpoint of the two side channels. According to this proposed method, viscosities of various fluids with different phases (aqueous, oil, and blood) in relation to that of reference fluid were accurately determined by measuring the switching flow-rate ratio between the test and reference fluids, when a reverse flow of the test or reference fluid occurs in the junction channel. An analytical viscosity formula was derived to measure the viscosity of a test fluid in relation to that of the corresponding reference fluid using a discrete circuit model for the microfluidic device. The experimental analysis for evaluating the effects of various parameters on the performance of the proposed method revealed that the fluidic resistance ratio (RJL/RL, fluidic resistance in the junction channel (RJL) to fluidic resistance in the side channel (RL)) strongly affects the measurement accuracy. The microfluidic device with smaller RJL/RL values is helpful to measure accurately the viscosity of the test fluid. The proposed method accurately measured the viscosities of various fluids, including single-phase (Glycerin and plasma) and oil-water phase (oil vs. deionized water) fluids, compared with conventional methods. The proposed method was also successfully applied to measure viscosities of blood with varying hematocrits, chemically fixed RBCS, and channel sizes. Based on these experimental results, the proposed method can be effectively used to measure the viscosities of various fluids easily, without any fluorescent labeling and tedious calibration procedures.  相似文献   

2.
Micromixers with floor-grooved microfluidic channels have been successfully demonstrated in experiment. In this work, we numerically simulated the mixing within the devices and used the obtained concentration versus channel length profiles to quantitatively characterize the process. It was found that the concentration at any given cross-section location of the microfluidic channel periodically oscillates along the channel length, in coordination with the groove-caused helical flow during the mixing, and eventually converges to the neutral concentration value of two the mixing fluids. With these data, the specific channel length required for each helical flow to complete, the mixing efficiency of the devices, and the total channel length required to complete a mixing were easily defined and quantified, and were used to directly and comprehensively characterize the micromixing. This concentration versus channel length profile-based characterization method was also demonstrated in quantitatively analyzing the micromixing within a classic T mixer. It has clear advantages over the traditional concentration image-based characterization method that is only able to provide qualitative or semiquantitative information about a micromixing, and is expected to find an increasing use in studying mixing and optimizing device structure through numerical simulations.  相似文献   

3.
In this paper, the event-triggered non-fragile H∞ fault detection filter is designed for a class of discrete-time nonlinear systems subject to time-varying delays and channel fadings. The Lth Rice fading model is utilized to reflect the actual received measurement signals, and its channel coefficients own arbitrary probability density functions on interval [0,1]. The event-based filter is constructed to reduce unnecessary data transmissions in the communication channel, which only updates the measurement signal to the filter when the prespecified “event” is triggered. Multiplicative gain variations are utilized to describe the phenomenon of parameter variations in actual implementation of the filter. Based on Lyapunov stability theory, stochastic analysis technology along with linear matrix inequalities (LMIs) skills, sufficient conditions for the existence of the non-fragile fault detection filter are obtained which make the filtering error system stochastically stable and satisfy the H∞ constraint. The gains of the filter can be calculated out by solving the feasible solution to a certain LMI. A simulation example is given to show the effectiveness of the proposed method.  相似文献   

4.
This paper is concerned with the event-based weighted residual generator design via non-parallel distribution compensation (PDC) scheme for fault diagnosis in discrete-time T–S fuzzy systems, under consideration of the imperfect premise matching membership functions. An event-triggered mechanism is firstly introduced to save communication resources, which leads to the premise variables of the system and observer to be asynchronous. Then, a fuzzy diagnostic observer with mismatched premise variables is designed to estimate the unmeasurable states of the system. Moreover, by using non-PDC method, a diagnostic observer-based weighted residual generator is established to improve the fault detection (FD) performance by using the information provided by each local system, in which the membership functions structure of the diagnostic observer and residual generator need not to be the same as the systems, and the L∞/L2 and L∞ FD scheme is used to optimize the FD performance. Finally, two simulation results are provided to show the efficiency of the proposed non-PDC method.  相似文献   

5.
For the diagnosis of biochemical reactions, the investigation of microflow behavior, and the confirmation of simulation results in microfluidics, experimentally quantitative measurements are indispensable. To characterize the mixing and reaction of fluids in microchannel devices, we propose a mixing quality index (Mqi) to quantify the cross-sectional patterns (also called mixing patterns) of fluids, captured with a confocal-fluorescence microscope (CFM). The operating parameters of the CFM for quantification were carefully tested. We analyzed mixing patterns, flow advection, and mass exchange of fluids in the devices with overlapping channels of two kinds. The mixing length of the two devices derived from the analysis of Mqi is demonstrated to be more precise than that estimated with a commonly applied method of blending dye liquors. By means of fluorescence resonance-energy transfer (FRET), we monitored the hybridization of two complementary oligonucleotides (a FRET pair) in the devices. The captured patterns reveal that hybridization is a progressive process along the downstream channel. The FRET reaction and the hybridization period were characterized through quantification of the reaction patterns. This analytical approach is a promising diagnostic tool that is applicable to the real-time analysis of biochemical and chemical reactions such as polymerase chain reaction (PCR), catalytic, or synthetic processes in microfluidic devices.  相似文献   

6.
This paper investigates L1-gain analysis and control of impulsive positive systems (IPSs) with interval uncertainty and time delay. For different types of impulsive effect, by means of the Razumikhin techniques and Lyapunov function theory, conditions are developed for guaranteeing the robust exponential stability with L1-gain performance. Then the positive stabilization with L1-gain performance is also addressed for IPSs with interval uncertainty and time delay through the state feedback control. In addition, the way to explore the minimum L1-gain is discussed. All the obtained conditions can be easily inspected by the linear programming (LP) method when some parameters are preset. Finally, simulations are provided to demonstrate the validity of the theoretical results.  相似文献   

7.
Studying enzymatic bioreactions in a millisecond microfluidic flow mixer   总被引：1，自引：0，他引：1  
In this study, the pre-steady state development of enzymatic bioreactions using a microfluidic mixer is presented. To follow such reactions fast mixing of reagents (enzyme and substrate) is crucial. By using a highly efficient passive micromixer based on multilaminar flow, mixing times in the low millisecond range are reached. Four lamination layers in a shallow channel reduce the diffusion lengths to a few micrometers only, enabling very fast mixing. This was proven by confocal fluorescence measurements in the channel’s cross sectional area. Adjusting the overall flow rate in the 200 μm wide and 900 μm long mixing and observation channel makes it possible to investigate enzyme reactions over several seconds. Further, the device enables changing the enzyme/substrate ratio from 1:1 up to 3:1, while still providing high mixing efficiency, as shown for the enzymatic hydrolysis using β-galactosidase. This way, the early kinetics of the enzyme reaction at multiple enzyme/substrate concentrations can be collected in a very short time (minutes). The fast and easy handling of the mixing device makes it a very powerful and convenient instrument for millisecond temporal analysis of bioreactions.  相似文献   

8.
This paper is concerned with the stability analysis of linear continuous-time delay-difference systems with multiple delays. Firstly, a new method for testing the L2-exponential stability of the considered system is proposed, which is easier to use than the one in the existing literature. In view of the conservatism and the complexity of the obtained stability conditions in the existing literature, a complete Lyapunov–Krasovskii functional (LKF) is constructed by analyzing the relationship among the multiple delays. Sufficient conditions for both L2-exponential stability and exponential stability are then derived based on the constructed LKFs, which are delay-independent. Exponential convergence rate for the considered system is also investigated by a new method, which is shown to be equivalent to the existing approach by using weighted LKFs. Robust stability under parameter uncertainties is also investigated. Numerical examples are provided to demonstrate the effectiveness and less conservativeness of the proposed method.  相似文献   

9.
Ordered statistics is applied in this paper to analyze the performance of ordered selection combining schemes with different modulation receptions operating in Nakagami-m fading environments. The ordered selection combining will be adapted to include the conventional selection combining (SC), the second-order diversity combining (SC-2), and the third-order diversity combining (SC-3). All the results are validated by comparing the special case Rayleigh distribution with the fading figure m=1 in the Nakagami-m distribution. The results show that SC is in performance the worst in both coherent and non-coherent schemes, as expected. The performance differences between SC-2 and MRC, and SC-3 and EGC are not significant when the diversity order L?3, but the differences will increase when L?5.  相似文献   

10.
Multiple-prespecified-dictionary sparse representation (MSR) has shown powerful potential in compressive sensing (CS) image reconstruction, which can exploit more sparse structure and prior knowledge of images for minimization. Due to the popular L1 regularization can only achieve the suboptimal solution of L0 regularization, using the nonconvex regularization can often obtain better results in CS reconstruction. This paper proposes a nonconvex adaptive weighted Lp regularization CS framework via MSR strategy. We first proposed a nonconvex MSR based Lp regularization model, then we propose two algorithms for minimizing the resulting nonconvex Lp optimization problem. According to the fact that the sparsity levels of each regularizers are varying with these prespecified-dictionaries, an adaptive scheme is proposed to weight each regularizer for optimization by exploiting the difference of sparsity levels as prior knowledge. Simulated results show that the proposed nonconvex framework can make a significant improvement in CS reconstruction than convex L1 regularization, and the proposed MSR strategy can also outperforms the traditional nonconvex Lp regularization methodology.  相似文献   

11.
In recent works several authors have considered the L1 fidelity term, the L2 fidelity term and the combined L1 and L2 fidelity term for denoising models, and they used the fast Fourier transform (FFT) algorithm which can only use periodic boundary conditions (BCs). In this paper, we combine the augmented Lagrangian method (ALM) and the symmetric Red–Black Gauss–Seidel (SRBGS) method to propose three algorithms that are suitable for different BCs. Experimental results show that the proposed algorithms are effective and the model with the combined L1 and L2 fidelity term demonstrates more advantages in efficiency and accuracy than other models with the L1 fidelity term or the L2 fidelity term.  相似文献   

12.
This paper studies vector incremental L2-gain and incremental stability for switched nonlinear systems using individual incremental gains and multiple storage functions. Firstly, a vector incremental L2-gain concept for switched nonlinear systems is proposed. Each subsystem is not required to have incremental L2-gain, but it has its own incremental L2-gain and the related storage function, when it is active. The transformation of “energy” from the active subsystem to each inactive subsystem is characterized by cross-supply rates. Then, we show that a switched nonlinear system who has vector incremental L2-gain can be incrementally stabilized under some constraints on the energy change of inactive subsystems. Secondly, a state-dependent switching law is designed to achieve vector incremental L2-gain, even if each subsystem does not have incremental L2-gain in the classic sense. Thirdly, each switched system is not required to have vector incremental L2-gain, but the feedback interconnection of switched nonlinear systems is incrementally stabilized by the design of a composite switching law. The switching law allows the two switched systems switch asynchronously. Two examples are provided to verify the effectiveness of the proposed method.  相似文献   

13.
Accurate measurement of blood viscoelasticity including viscosity and elasticity is essential in estimating blood flows in arteries, arterials, and capillaries and in investigating sub-lethal damage of RBCs. Furthermore, the blood viscoelasticity could be clinically used as key indices in monitoring patients with cardiovascular diseases. In this study, we propose a new method to simultaneously measure the viscosity and elasticity of blood by simply controlling the steady and transient blood flows in a microfluidic analogue of Wheastone-bridge channel, without fully integrated sensors and labelling operations. The microfluidic device is designed to have two inlets and outlets, two side channels, and one bridge channel connecting the two side channels. Blood and PBS solution are simultaneously delivered into the microfluidic device as test fluid and reference fluid, respectively. Using a fluidic-circuit model for the microfluidic device, the analytical formula is derived by applying the linear viscoelasticity model for rheological representation of blood. First, in the steady blood flow, the relationship between the viscosity of blood and that of PBS solution (μBlood/μPBS) is obtained by monitoring the reverse flows in the bridge channel at a specific flow-rate rate (QPBSSS/QBloodL). Next, in the transient blood flow, a sudden increase in the blood flow-rate induces the transient behaviors of the blood flow in the bridge channel. Here, the elasticity (or characteristic time) of blood can be quantitatively measured by analyzing the dynamic movement of blood in the bridge channel. The regression formula (ABlood (t) = Aα + Aβ exp [−(t − t0)/λBlood]) is selected based on the pressure difference (ΔP = PA − PB) at each junction (A, B) of both side channels. The characteristic time of blood (λBlood) is measured by analyzing the area (ABlood) filled with blood in the bridge channel by selecting an appropriate detection window in the microscopic images captured by a high-speed camera (frame rate = 200 Hz, total measurement time = 7 s). The elasticity of blood (GBlood) is identified using the relationship between the characteristic time and the viscosity of blood. For practical demonstrations, the proposed method is successfully applied to evaluate the variations in viscosity and elasticity of various blood samples: (a) various hematocrits form 20% to 50%, (b) thermal-induced treatment (50 °C for 30 min), (c) flow-induced shear stress (53 ± 0.5 mL/h for 120 min), and (d) normal rat versus spontaneously hypertensive rat. Based on these experimental demonstrations, the proposed method can be effectively used to monitor variations in viscosity and elasticity of bloods, even with the absence of fully integrated sensors, tedious labeling and calibrations.  相似文献   

14.
This paper is concerned with the exponential stability and L1-gain analysis problem for switched positive T–S fuzzy systems under both time-varying delays and asynchronous switching. By permitting the increase of the designed multiple Lyapunov functionals during the running time of the activated subsystem, solvable conditions for the stability and L1-gain are developed by adopting the mode-dependent average dwell time (MDADT) technique. The desired controllers guaranteeing the stability and the L1-gain performance are designed based on the obtained solvable conditions. An example is given to demonstrate the effectiveness of the proposed methods.  相似文献   

15.
The resistance coefficient of a body moving in a fluid depends on Reynolds Number R, Mach Number M and the parameter gLU2, which is customarily neglected in view of small weight of the air. Here L denotes a characteristic length; U denotes the body's speed of translation. The author points that dimensional deduction of this parameter does not limit it to the acceleration of gravity, and that the resistance coefficient is affected by the general acceleration to which the air is subjected. Evaluation of the acceleration of the air flowing about spheres puts this parameter in the form LR, where the characteristic length L is interpreted as the mean free molecular path. Large and small spheres were found to have widely different values of the pressure coefficient Δpq for the same Reynolds Number or Mach Number. Here Δp denotes the difference in pressure between front stagnation point and the rear portion of the sphere, and q denotes the dynamic pressure. The plot of Δpq against the parameter LR removes this confusion. The low values of Δpq are found to be associated with LR below a certain critical value, and high values of Δpq with LR above the critical value, which apparently indicates the condition under which the flow separation takes place. Attention is called to the effect of air pressure on the separation as shown by the parameter LR, and its possible bearing on the drag in high altitude flying.  相似文献   

16.
Wei Hou H  Gan HY  Bhagat AA  Li LD  Lim CT  Han J 《Biomicrofluidics》2012,6(2):24115-2411513
Sepsis is an adverse systemic inflammatory response caused by microbial infection in blood. This paper reports a simple microfluidic approach for intrinsic, non-specific removal of both microbes and inflammatory cellular components (platelets and leukocytes) from whole blood, inspired by the invivo phenomenon of leukocyte margination. As blood flows through a narrow microchannel (20 × 20 µm), deformable red blood cells (RBCs) migrate axially to the channel centre, resulting in margination of other cell types (bacteria, platelets, and leukocytes) towards the channel sides. By using a simple cascaded channel design, the blood samples undergo a 2-stage bacteria removal in a single pass through the device, thereby allowing higher bacterial removal efficiency. As an application for sepsis treatment, we demonstrated separation of Escherichia coli and Saccharomyces cerevisiae spiked into whole blood, achieving high removal efficiencies of ∼80% and ∼90%, respectively. Inflammatory cellular components were also depleted by >80% in the filtered blood samples which could help to modulate the host inflammatory response and potentially serve as a blood cleansing method for sepsis treatment. The developed technique offers significant advantages including high throughput (∼1 ml/h per channel) and label-free separation which allows non-specific removal of any blood-borne pathogens (bacteria and fungi). The continuous processing and collection mode could potentially enable the return of filtered blood back to the patient directly, similar to a simple and complete dialysis circuit setup. Lastly, we designed and tested a larger filtration device consisting of 6 channels in parallel (∼6 ml/h) and obtained similar filtration performances. Further multiplexing is possible by increasing channel parallelization or device stacking to achieve higher throughput comparable to convectional blood dialysis systems used in clinical settings.  相似文献   

17.
The present work describes the operation and simulation of a microfluidic laminar-flow mixer. Diffusive mixing takes place between a core solution containing lipids in ethanol and a sheath solution containing aqueous buffer, leading to self assembly of liposomes. Present device architecture hydrodynamically focuses the lipid solution into a cylindrical core positioned at the center of a microfluidic channel of 125 × 125-μm2 cross-section. Use of the device produces liposomes in the size range of 100–300 nm, with larger liposomes forming at greater ionic strength in the sheath solution and at lower lipid concentration in the core solution. Finite element simulations compute the concentration distributions of solutes at axial distances of greater than 100 channel widths. These simulations reduce computation time and enable computation at long axial distances by utilizing long hexahedral elements in the axial flow region and fine tetrahedral elements in the hydrodynamic focusing region. Present meshing technique is generally useful for simulation of long microfluidic channels and is fully implementable using comsol Multiphysics. Confocal microscopy provides experimental validation of the simulations using fluorescent solutions containing fluorescein or enhanced green fluorescent protein.  相似文献   

18.
Using data generated by progressive nucleation mechanism on the cumulative fraction of citations of individual papers published successively by a hypothetical author, an expression for the time dependence of the cumulative number Lsum(t) of citations of progressively published papers is proposed. It was found that, for all nonzero values of constant publication rate ΔN, the cumulative citations Lsum(t) of the cumulative N papers published by an author in his/her entire publication career spanning over T years may be represented in distinct regions: (1) in the region 0 < t < Θ0 (where Θ0 ≈ T/3), Lsum(t) slowly increases proportionally to the square of the citation time t, and (2) in the region t > Θ0, Lsum(t) approaches a constant Lsum(max) at T. In the former region, the time dependence of Lsum(t) of an author is associated with three parameters, viz. the citability parameter λ0, the publication rate ΔN and his/her publication career t. Based on the predicted dependence of Lsum(t) on t, a useful scientometric age-independent measure, defined as citation acceleration a = Lsum(t)/t2, is suggested to analyze and compare the scientific activities of different authors. Confrontation of the time dependence of cumulative number Lsum(t) of citations of papers with the theoretical equation reveals one or more citation periods during the publication careers of different authors.  相似文献   

19.
Let χm+1=T(χm) or even χm+1=T(χm,χm?1, …, χm?q), m=1,2,3 … be an iteration method for solving the nonlinear problem F(χ)=0, where F(χ) and its derivatives possess all of the properties required by T(χm). Then if it can be established that for the problem at hand ∥F(χm+1)∥?βm∥F(χm)∥, ? m > M0 (M0<∞) and 0?βm<1 , definitions are established and theorems proven concerning convergence, uniqueness and bounds on the error after ‘m’ successive iterations of a new approach to convergence properties T(χm). These charateristics are referred to as “alternate” (local, global) convergence properties and none of the proofs given are restricted to any specific type of method such as, e.g. contraction mapping types. Application of results obtained are illustrated using Newton's method as well as the general concept of Newton-like methods.  相似文献   

20.
This paper considers the stability and L2-gain for a class of switched neutral systems with time-varying discrete and neutral delays. Some new delay-dependent sufficient conditions for exponential stability and weighted L2-gain are developed for a class of switching signals with average dwell time. These conditions are formulated in terms of linear matrix inequalities (LMIs) and are derived by employing free weighting matrices method. As a special case of such switching signals, we can obtain exponential stability and normal L2-gain under arbitrary switching signals. Finally, two numerical examples are given to illustrate the effectiveness of the theoretical results.  相似文献   

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