Lab-on-a-display: a new microparticle manipulation platform using a liquid crystal display (LCD)

This paper reports a new portable microfluidic platform, “lab-on-a-display,” that microparticles are manipulated by optoelectronic tweezers (OET) on a liquid crystal display (LCD). The OET has been constructed by assembling a ground layer, a liquid chamber, and a photoconductive layer. Without lens or optical alignments, the LCD image directly forms virtual electrodes on the photoconductive layer for dielectrophoretic manipulation. The lab-on-a-display was first realized by a conventional monochromatic LCD module and a light source brighter than 5,000 lux. It was successfully applied to the programmable manipulation of 45 μm polystyrene beads; more than 100 particles were transported with an optical image-driven control, following the moving edge of the image at every moment. The effects of bead size and bias voltage on the manipulation speed were also investigated. Due to the portability and compatibility for disposable applications, this new platform has potential for programmable particle manipulation or chip-based bioprocessing including cell separation and bead-based analysis.     

Precisely sized separation of multiple particles based on the dielectrophoresis gradient in the z-direction

We present a new 3D dielectrophoresis-field-flow fraction (DEP-FFF) concept to achieve precise separation of multiple particles by using AC DEP force gradient in the z-direction. The interlaced electrode array was placed at the upstream of the microchannel, which not only focused the particles into a single particle stream to be at the same starting position for further separation, but also increased the spacing between each particle by the retard effect to reduce particle–particle aggregation. An inclined electrode was also designed in back of the focusing component to continuously and precisely separate different sizes of microparticles. Different magnitudes of DEP force are induced at different positions in the z-direction of the DEP gate, which causes different penetration times and positions of particles along the inclined DEP gate. 2, 3, 4, and 6?μm polystyrene beads were precisely sized fractionation to be four particle streams based on their different threshold DEP velocities that were induced by the field gradient in the z-direction when a voltage of 6.5?V_p–p was applied at a flow rate of 0.6?μl/min. Finally, Candida albicans were also sized separated to be three populations for demonstrating the feasibility of this platform in biological applications. The results showed that a high resolution sized fractionation (only 25% size difference) of multiple particles can be achieved in this DEP-based microfluidic device by applying a single AC electrical signal.     

Study on the assembly and separation of biological cell by optically induced dielectrophoretic technology

Optically induced dielectrophoretic (ODEP) chip is to combine their own advantages of optical tweezers and electrodynamics manipulation technologies, which can trap single particles in high resolution as well as enrich much of micro-/nanoparticles in high throughput. The paper analyzed the structure of optoelectronic tweezers (OET) chip, moreover, the frequency response of multi-membrane eukaryotic cells about 10³–10⁹ Hz. The Clausius–Mositti (CM) frequency factor in terms of cell membrane, cell cytoplasm, nuclear envelope thickness changes, and volume ratio was illustrated. In the end, the paper presented 3D numeric model of cells in OET chip. The dielectrophoresis force acting on the dipole of 11.8-μm cells subjected to a non-uniform electric field under 60-μm Gaussian-distributed beam spot could be simulated in the enrichment process. The separation of cells that were two different types of CM values was calculated. Furthermore, it was proved to be feasible to achieve the efficient separation of cells using ODEP technology in the biological numerical model. Comparing with the literature of experiment, the results in cell dielectric spectroscopy and numeric model findings were in general agreement. The simplified structure and numeric model of nucleated cell provide a theoretical basis for research of biosensor and complex life.     

SPheno, a program for calculating supersymmetric spectra, SUSY particle decays and SUSY particle production at ee colliders

SPheno is a program that accurately calculates the supersymmetric particle spectrum within a high scale theory, such as minimal supergravity, gauge mediated supersymmetry breaking, anomaly mediated supersymmetry breaking, or string effective field theories. An interface exists for an easy implementation of other models. The program solves the renormalization group equations numerically to two-loop order with user-specified boundary conditions. The complete one-loop formulas for the masses are used which are supplemented by two-loop contributions in case of the neutral Higgs bosons and the μ parameter. The obtained masses and mixing matrices are used to calculate decay widths and branching ratios of supersymmetric particles as well as of Higgs bosons, b→sγ, Δρ and (g−2)_μ. Moreover, the production cross sections of all supersymmetric particle as well as Higgs bosons at e⁺e⁻ colliders can be calculated including initial state radiation and longitudinal polarization of the incoming electrons/positrons. The program is structured such that it can easily be extend to include non-minimal models and/or complex parameters.     

Highly efficient dual-channel cytometric-detection of micron-sized particles in microfluidic device

To demonstrate the ability to efficiently count and identify suspended micron-sized particles by simultaneously detecting their fluorescence emission and light scattering in microfabricated channel, a compact configuration that used a polydimethylsiloxane (PDMS) microfabricated channel as interrogation component, hydrodynamic focusing for particle control, and a simple free-space optical setup for signal detection, was accordingly developed. Subsequently, a quantitative count of 1.013 μm diameter fluorescently labeled beads in suspension was implemented in a microfluidic device employing both fluorescence emission and light scattering at average particle throughput ranging from 83 to 416 particles/s. As a result, the detection efficiencies above 88% for both signals and correlation percentages above 97% between them were routinely achieved. In addition, it was shown that effective differentiation of 1.013 μm fluorescently labeled beads from various unlabeled beads in mixed populations of high mixing ratios had been successfully realized in this microfluidic-device-based instrumentation. Finally, the demonstrated system was used to detect fluorescein isothiocyanate (FITC) labeled nonpathogenic bacteria of Escherichia coli (E. coli) DH5α. The results showed the detection efficiencies above 89.7% for fluorescence emission and 94.5% for light scattering signals, and a correlation of 94.9% between the two signals at an average throughput of 350 cells/s have been obtained. As a comparison, the detection accuracies of the dual-channel cytometric detection of the FITC-labeled E. coli DH5α cells in the microfluidic device are approximately 84.3% and 88.8% for fluorescence emission and light scattering respectively when compared against a manual cell count using a haemocytometer as a standard.     

Quantitative characterization of the focusing process and dynamic behavior of differently sized microparticles in a spiral microchannel

In this paper, a spiral microchannel was fabricated to systematically investigate particle dynamics. The focusing process or migration behavior of different-sized particles in the outlet region was presented. Specifically, for focused microparticles, quantitative characterization and analysis of how particles migrate towards the equilibrium positions with the increase in flow rate (De = 0.31–3.36) were performed. For unfocused microparticles, the particle migration behavior and the particle-free region’s formation process were characterized over a wide range of flow rates (De = 0.31–4.58), and the emergence of double particle-free regions was observed at De ≥ 3.36. These results provide insights into the design and operation of high-throughput particle/cell filtration and separation. Furthermore, using the location markers pre-fabricated along with the microchannel structures, the focusing or migration dynamics of different-sized particles along the spiral microchannel was systematically explored. The particle migration length effects on focusing degree and particle-free region width were analyzed. These analyses may be valuable for the optimization of microchannel structures. In addition, this device was successfully used to efficiently filter rare particles from a large-volume sample and separate particles of two different sizes according to their focusing states.     

Operational Regimes and Physics Present in Optoelectronic Tweezers

Optoelectronic tweezers (OET) are a powerful light-based technique for the manipulation of micro- and nanoscopic particles. In addition to an optically patterned dielectrophoresis (DEP) force, other light-induced electrokinetic and thermal effects occur in the OET device. In this paper, we present a comprehensive theoretical and experimental investigation of various fluidic, optical, and electrical effects present during OET operation. These effects include DEP, light-induced ac electroosmosis, electrothermal flow, and buoyancy-driven flow. We present finite-element modeling of these effects to establish the dominant mode for a given set of device parameters and bias conditions. These results are confirmed experimentally and present a comprehensive outline of the operational regimes of the OET device.     

Faster neighbour list generation using a novel lattice vector representation

In any many-body simulation where particles are coupled using short-range potentials, a key part of the simulation is to find which particles {j} interact with particle i. The set of such particles is known as the neighbour list of particle i. A novel algorithm is developed here which efficiently returns a neighbour list. A partially occupied reference lattice may be constructed for any simulation, with the position of particles defined as being a short vector separation from a node. A lattice vector which preserves translational symmetry in a periodic supercell under addition and subtraction operations can then be constructed from a single 32-bit integer number. A novel neighbour list algorithm is then developed which uses a single set of lattice vectors to return all nodes, and therefore all particles associated with the nodes, within a fixed radius sphere of particle i. This new algorithm preserves translational symmetry in a periodic supercell, requires a small memory overhead, and is shown to be faster than the well-known Linked-Cell method in all cases considered here.     

Oedometric test, Bauer's law and the micro-macro connection for a dry sand

What is the relationship between the macroscopic parameters of the constitutive equation for a granular soil and the microscopic forces between grains? In order to investigate this connection, we have simulated by molecular dynamics the oedometric compression of a granular soil (a dry and bad-graded sand) and computed the hypoplastic parameters hs (the granular skeleton hardness) and η (the exponent in the compression law) by following the same procedure than in experiments, that is by fitting the Bauer's law e/e₀=exp(−n(3p/hs)), where p is the pressure and e₀ and e are the initial and present void ratios. The micro-mechanical simulation includes elastic and dissipative normal forces plus slip, rolling and static friction between grains. By this way we have explored how the macroscopic parameters change by modifying the grains stiffness, V; the dissipation coefficient, γn; the static friction coefficient, μs; and the dynamic friction coefficient, μk. Cumulating all simulations, we obtained an unexpected result: the two macroscopic parameters seems to be related by a power law, hs=0.068(4)η9.88(3). Moreover, the experimental result for a Guamo sand with the same granulometry fits perfectly into this power law. Is this relation real? What is the final ground of the Bauer's Law? We conclude by exploring some hypothesis.     

Viscosity-difference-induced asymmetric selective focusing for large stroke particle separation

We developed a new approach for particle separation by introducing viscosity difference of the sheath flows to form an asymmetric focusing of sample particle flow. This approach relies on the high-velocity gradient in the asymmetric focusing of the particle flow to generate a lift force, which plays a dominated role in the particle separation. The larger particles migrate away from the original streamline to the side of the higher relative velocity, while the smaller particles remain close to the streamline. Under high-viscosity (glycerol–water solution) and low-viscosity (PBS) sheath flows, a significant large stroke separation between the smaller (1.0 μm) and larger (9.9 μm) particles was achieved in a sample microfluidic device. We demonstrate that the flow rate and the viscosity difference of the sheath flows have an impact on the interval distance of the particle separation that affects the collected purity and on the focusing distribution of the smaller particles that affects the collected concentration. The interval distance of 293 μm (relative to the channel width: 0.281) and the focusing distribution of 112 μm (relative to the channel width: 0.107) were obtained in the 1042-μm-width separation area of the device. This separation method proposed in our work can potentially be applied to biological and medical applications due to the wide interval distance and the narrow focusing distribution of the particle separation, by easy manufacturing in a simple device.     

Wafer mapping of the transverse piezoelectric coefficient, e31,f, using the wafer flexure technique with sputter deposited Pt strain gauges

Measurement of the transverse piezoelectric coefficient (e_31,f) in thin films is crucial for the development of microfabricated sensors, actuators, and transducers. Here, a method is described such that lithographically defined strain gauges enable non-destructive, position-dependent characterization of e_31,f in conjunction with the wafer flexure technique. Measurements of 100 nm thick Pt gauges deposited on 1 μm thick PbZr_0.52Ti_0.48O₃ thin films yield gauge factors of 6.24, with a gauge-to-gauge variation that is 5% of this value. The system allows for simultaneous measurement of the charge and strain, improving the overall accuracy of measurement. The small footprint of the combined strain gauge array/electrode pattern used for determining e_31,f, allows for a non-destructive mapping of the transverse piezoelectric coefficient across large-area wafers. Due to the clamping configuration used in wafer flexure experiments, e_31,f values can accurately be obtained within the central ∼2/3 of a full wafer. Measurements performed on a 1.3 μm thick randomly oriented polycrystalline PbZr_0.52Ti_0.48O₃ film made deposited on a 4 in. platinized silicon wafer by the sol-gel process show a high degree of uniformity, with e_31,f of −6.37 ± 0.60 C/m² for points measured within r = 3 cm.     

Cloud parameter retrievals from Meteosat and their effects on the shortwave radiation at the surface

A method based on Spinning Enhanced Visible and Infrared Imager (SEVIRI) measured reflectance at 0.6 and 3.9 µm is used to retrieve the cloud optical thickness (COT) and cloud effective radius (r_e) over the Iberian Peninsula. A sensitivity analysis of simulated retrievals to the input parameters demonstrates that the cloud top height is an important factor in satellite retrievals of COT and r_e with uncertainties around 10% for small values of COT and r_e; for water clouds these uncertainties can be greater than 10% for small values of r_e. The uncertainties found related with geometries are around 3%. The COT and r_e are assessed using well-known satellite cloud products, showing that the method used characterize the cloud field with more than 80% (82%) of the absolute differences between COT (r_e) mean values of all clouds (water plus ice clouds) centred in the range from ±10 (±10 µm), with absolute bias lower than 2 (2 μm) for COT (r_e) and root mean square error values lower than 10 (8 μm) for COT (r_e). The cloud water path (CWP), derived from satellite retrievals, and the shortwave cloud radiative effect at the surface (CRE_SW) are related for high fractional sky covers (F_sc >0.8), showing that water clouds produce more negative CRE_SW than ice clouds. The COT retrieved was also related to the cloud modification factor, which exhibits reductions and enhancements of the surface SW radiation of the order of 80% and 30%, respectively, for COT values lower than 10. A selected case study shows, using a ground-based sky camera that some situations classified by the satellite with high F_sc values correspond to situations of broken clouds where the enhancements actually occur. For this case study, a closure between the liquid water path (LWP) obtained from the satellite retrievals and the same cloud quantity obtained from ground-based microwave measurements was performed showing a good agreement between both LWP data set values.     

基于偏振控制的硅基颗粒导向系统设计

光学微操控技术已从颗粒的捕获和传输拓展到颗粒的分选和导向等更高级的逻辑操控,硅基光镊技术因能突破衍射极限并操控亚微米量级的颗粒而成为了微操控领域中最重要的手段之一。传统的硅基光镊技术一般采用微环、定向耦合器和多模干涉仪等器件,通过调节波长实现颗粒导向操作。文章提出了一种通过偏振调控的硅基颗粒导向操作方法,通过时域有限差分设计和优化了系统结构参数,并验证了该结构在颗粒导向操作中的可行性。实验装置结构简单、体积小巧,且操控更加方便。     

Numerical simulation of cloud droplet formation in a tank

Using the computational fluid dynamics (CFD) code FLUENT 6 together with the fine particle model (FPM), numerical simulations of droplet dynamics in a 12.4 m³ cloud tank were conducted. The coupled fields of water vapor, temperature, flow velocity, particle number concentration, and particle mass concentration inside the cloud tank were computed.The system responses to changes of the wall's temperature and mass fraction of water vapor, respectively, were investigated. Typical times for mixing the cloud tank's contents are in the range of some tens of seconds. The maximum volume-averaged deviations from the mean of temperature and mass fraction of water vapor are around 5% of the respective parameter changes applied to the wall.Time-dependent simulations were performed in order to study the growth of ammonium-sulfate particles in humid air at around room temperature. Supersaturation up to (S_w–1)=8.2×10⁻³ was achieved by the expansion of the gas. The particles were activated and grew rapidly to a maximum diameter of 5.2×10⁻⁶ m after critical supersaturation was reached. After S_w fell again below the equilibrium value, the particles shrank quickly and deactivated roughly 60 s after activation.The spatial inhomogeneities of temperature and water-vapor concentration cause volume-averaged deviations of the particle number N and diameter d_g of up to 2.3% and 36%, respectively.     

基于超导量子干涉仪的磁性颗粒检测单元分析

带有磁化退磁样品处理单元的扫描超导量子干涉仪（SQUID）显微镜系统,配合样品移动定位平台,可以实现生物样品内源磁性颗粒磁学特性和磁场分布的测量。基于SQUID的磁场检测单元为系统重要组成部分,介绍检测单元基本结构、检测原理,推导磁通、磁场和电压间的转换公式,建立磁性颗粒模型。通过仿真分析线圈参数对系统磁场灵敏度和空间分辨率的影响,设计绕制了直径500μm,30匝的超导接收线圈,系统磁场灵敏度为1.46×10-13 T/（Hz）^1/2,空间分辨率为500μm。磁性颗粒模型和仿真分析为系统设计、实验数据分析提供了理论依据。     

Second-order, exact charge conservation for electromagnetic particle-in-cell simulation in complex geometry

A second-order, exact charge-conserving algorithm for accumulating charge and current on the spatial grid for electromagnetic particle-in-cell (EM-PIC) simulation in bounded geometry is presented. The algorithm supports standard EM-PIC exterior boundary conditions and complex internal conductors on non-uniform grids. Boundary surfaces are handled by smoothly transitioning from second to first-order weighting within half a cell of the boundary. When a particle is exactly on the boundary surface (either about to be killed, or just created), the weighting is fully first-order. This means that particle creation and particle/surface interaction models developed for first-order weighting do not need to be modified. An additional feature is the use of an energy-conserving interpolation scheme from the electric field on the grid to the particles. Results show that high-density, cold plasmas with ωpeΔt∼1, and Δx/λD?1, can be modeled with reasonable accuracy and good energy conservation. This opens up a significant new capability for explicit simulation of high-density plasmas in high-power devices.     

Dynamic Cell and Microparticle Control via Optoelectronic Tweezers

This paper reports on cell and microparticle manipulation using optically induced dielectrophoresis. Our novel optoelectronic tweezers (OET) device enables optically controlled trapping, transportation, and sorting via dielectrophoretic forces. By integrating a spatial light modulator and using direct imaging, arbitrary dynamic manipulation patterns are obtained. Here, we demonstrate manipulation functions, including particle collectors, single-particle traps, individually addressable single-particle arrays, light-defined particle channels, and size-based particle sorting. OET-induced particle manipulation velocities are analyzed as a function of the applied voltage, optical pattern linewidth, and single-particle trap dimensions.     

On the stability of the information state system

The purpose of this paper is to present some preliminary results on the stability of the information state system. The information state system underlies the (infinite dimensional) dynamics of an H_∞ controller for a nonlinear system. Thus it is important to understand its stability and the structure of its equilibrium points. We analyse the important case corresponding to the mixed sensitivity problem. We prove the existence of an equilibrium information state, convergence under very general conditions to such an equilibrium state p_e and uniqueness of this state (up to an irrelevant constant). In this case the equilibrium p_e is usually singular in the sense that it takes on the value − ∞ except on a low dimensional subset of its domain.This meshes with the article [9] which analysed the effect of using p_e to initialize the information state controller and gave explicit formulas which in many cases produce a dramatic reduction in the amount of computation required to implement the controller. What this article suggests is that indeed p_e is the only equilibrium initialization possible.     

Linguistic fuzzy model identification based on PSO with different length of particles

To generate the structure and parameters of fuzzy rule base automatically, a particle swarm optimization algorithm with different length of particles (DLPPSO) is proposed in the paper. The main finding of the proposed approach is that the structure and parameters of a fuzzy rule base can be generated automatically by the proposed PSO. In this method, the best fitness (f_gbest) and the number (N_gbest) of active rules of the best particle in current generation, the best fitness (f_pbesti) which ith particle has achieved so far and the number (N_pbesti) of active rules of it when the best position emerged are utilized to determine the active rules of ith particle in each generation. To increase the diversity of structure, mutation operator is used to change the number of active rules for particles. Compared with some other PSOs with different length of particles, the algorithm has good adaptive performance. To indicate the effectiveness of the give algorithm, a nonlinear function and two time series are used in the simulation experiments. Simulation results demonstrate that the proposed method can approximate the nonlinear function and forecast the time series efficiently.     

Inertial migration of single particle in a square microchannel over wide ranges of <Emphasis Type="Italic">Re</Emphasis> and particle sizes

Inertial migration of particles has been widely used in inertial microfluidic systems to passively manipulate cells/particles. However, the migration behaviors and the underlying mechanisms, especially in a square microchannel, are still not very clear. In this paper, the immersed boundary-lattice Boltzmann method (IB-LBM) was introduced and validated to explore the migration characteristics and the underlying mechanisms of an inertial focusing single particle in a square microchannel. The grid-independence analysis was made first to highlight that the grid number across the thin liquid film (between a particle and its neighboring channel wall) was of significant importance in accurately capturing the migrating particle’s dynamics. Then, the inertial migration of a single particle was numerically investigated over wide ranges of Reynolds number (Re, from 10 to 500) and particle sizes (diameter-to-height ratio a/H, from 0.16 to 0.5). It was interesting to find that as Re increased, the channel face equilibrium (CFE) position moved outward to channel walls at first, and then inflected inwards to the channel center at high Re (Re?>?200). To account for the physical mechanisms behind this behavior, the secondary flow induced by the inertial focusing single particle was further investigated. It was found that as Re increased, two vortices appeared around the particle and grew gradually, which pushed the particle away from the channel wall at high Re. Finally, a correlation was proposed based on the numerical data to predict the critical length L_c (defined to describe the size of fluid domain that was strongly influenced by the particle) according to the particle size a/H and Re.