基于微流控技术的蛋白质结晶及其筛选方法的研究进展

微流控技术以其高通量、 低消耗和集成化等优点成为蛋白质结晶微型化研究的重要手段. 本文综述了基于微流控技术的蛋白质结晶技术和方法, 主要包括微泵微阀、 液滴(Droplet)、 滑动芯片(SlipChip)以及液滴实验室(DropLab)等技术. 此外, 还针对当前膜蛋白在结构生物学研究中的重要地位, 综述了应用于膜蛋白结晶的微流控技术的研究进展.     

Exciton-phonon coupling channels in a ‘strain-free’ GaAs droplet epitaxy single quantum dot

We examine the temperature-dependent excitonic transition energy shift of strain-free GaAs droplet epitaxy (DE) quantum dots (QDs). Interestingly the statistical investigation of QD optical properties enables us to observe three distinct temperature dispersions for four series of DE QDs. We present comparative analyses of the exciton-phonon coupling mechanisms employing various empirical to multi-oscillator models associated with each QD-specific phonon dispersion spectrum. The systematic investigation of such QD exciton-phonon coupling is crucial for fine control of local defects in engineered quantum dot single-photon sources.     

Evaporation phenomenon past a rotating hydrocarbon droplet of ternary components

A numerical study of heat and mass transfer from an evaporating fuel droplet rotating around its vertical axis was performed in forced convection only on the side opposite to the flow. The flow was assumed to be laminar, and the droplet was assumed to maintain its spherical shape during its lifetime. Based on the abovementioned assumption, the conservation equations in a general curvilinear coordinate were solved numerically. The behavior of rotating droplet evaporation in the forced convection flow can be investigated by analyzing the effects of the rotation of the droplet on the evaporation process of multi-component hydrocarbons droplet. The droplet is simulated to behave as a hard sphere. The transfer equations are discretized using an implicit finite difference method. Thomas algorithm is used to solve the system of algebraic equations. Moreover, dimensionless parameters of heat and mass transfer phenomena around a rotating hydrocarbon droplet were determined. The thickness of the boundary layer is unknown for this model and therefore, it was determined in function of time. Additionally, the study concerns “Dgheim dimensionless number” which is the ratio of the rotation forces over the viscosity forces. Dgheim dimensionless number is correlated to Nusselt and Sherwood numbers for multi-component hydrocarbon droplets in evaporation by taking into account the effect of heat and mass Spalding, Prandtl and Schmidt numbers respectively. Also, correlations for Nusselt and Sherwood numbers in terms of Reynolds, Prandtl and Schmidt numbers are proposed. These correlations consider the rotation phenomenon and advance the variation of the thermophysical and transport properties in the vapor phase of multi-component blends.     

Heat and mass transfer of a fuel droplet evaporating in oscillatory flow

A numerical study of the heat and mass transfer from an evaporating fuel droplet in oscillatory flow was performed. The flow was assumed to be laminar and axisymmetric, and the droplet was assumed to maintain its spherical shape during its lifetime. Based on these assumptions, the conservation equations in a general curvilinear coordinate were solved numerically. The behaviors of droplet evaporation in the oscillatory flow were investigated by analyzing the effects of flow oscillation on the evaporation process of a n-heptane fuel droplet at high pressure.The response of the time history of the square of droplet diameter and space-averaged Nusselt numbers to the main flow oscillation were investigated in frequency band of 1–75 Hz with various oscillation amplitudes. Results showed that, depending on the frequency and amplitude of the oscillation, there are different modes of response of the evaporation process to the flow oscillation. One response mode is synchronous with the main flow oscillation, and thus the quasi-steady condition is attained. Another mode is asynchronous with the flow oscillation and is highly unsteady. As for the evaporation rate, however, in all conditions is more greatly enhanced in oscillatory flow than in quiescent air.To quantify the conditions of the transition from quasi-steady to unsteady, the response of the boundary layer around the droplet surface to the flow oscillation was investigated. The results led to including the oscillation Strouhal number as a criteria for the transition. The numerical results showed that at a low Strouhal number, a quasi-steady boundary layer is formed in response to the flow oscillation, whereas by increasing the oscillation Strouhal number, the phenomena become unsteady.     

Numerical study on the dynamics of droplet passing through a cylinder obstruction in confined microchannel flow

The droplet dynamics passing through a cylinder obstruction was investigated with direct numerical simulations with FE-FTM (Finite Element-Front Tracking Method). The effect of droplet size and capillary number (Ca) was studied for both Newtonian and viscoelastic fluids. In the case of Newtonian droplet immersed in Newtonian medium, the droplet breakup induced by the geometric hindrance depends on the droplet size. As Ca increases, the short droplets (1.3 times longer than the channel width) break up while passing through the obstruction. However, the breakup does not occur for longer droplets (1.8 times longer than the channel width). When the viscoelastic fluid characterized by the Oldroyd-B model is considered, the Newtonian droplet immersed in viscoelastic medium breaks up into two smaller droplets while passing through the cylinder obstruction with increasing De_m (Deborah number of the medium). We also show that the normal stress difference plays a key role on the droplet breakup and the droplet extension. The normal stress difference is enhanced in the negative wake region due to the droplet flow, which also promotes droplet extension in that region. This numerical study provides information not only on underlying physics of the droplet flows passing through a cylinder obstruction but also on the useful guidelines for microfluidic applications.     

Simulation of liquid jet primary breakup: Dynamics of ligament and droplet formation

Primary atomization of liquid injected at high speed into still air is investigated to elucidate physical processes by direct numerical simulation. With sufficient grid resolution, ligament and droplet formation can be captured in a physically sound way. Ligament formation is triggered by the liquid jet tip roll-up, and later ligaments are also produced from the disturbed liquid core surface in the upstream. Ligament production direction is affected by gas vortices. Disturbances are fed from the liquid jet tip toward upstream through vortices and droplet re-collision. When the local gas Weber number is O(1), ligaments are created, thus the ligament or droplet scale becomes smaller as the bulk Weber number increases. Observation of droplet formation from a ligament provides insights into the relevance between the actual droplet formation and pinch-off from a slow liquid jet in laboratory experiments. In the spray, the dominant mode is the short-wave mode driven by propagative capillary wave from the ligament tip. An injection nozzle that is necessary for a slow jet is absent for a ligament, thus the long-wave (Rayleigh) mode is basically not seen without the effect of stretch. By the present simulation, a series of physical processes have been revealed. The present result will be extended to LES modeling in the future.     

Measuring particle size distribution using LED-illumination

A particle/droplet image analysis (PDIA) system employing LED-illumination was designed. Freezing the moving droplets using high speed camera instead of stroboscopic illumination, the system had no requirement to synchronize the backlight and the camera. It featured low cost, low power consumption and simple optical configuration in comparison to laser-based systems. Only focused droplets in images were counted. Given the sample size of the system was relatively small, an upper-limit lognormal distribution was used to fit the actual data to represent the spray patterns. The accuracy of the diameter measurement was verified using precisely manufactured balls. Comparisons with two laser-based systems were given and the system’s capacity to distinct spray patterns were demonstrated in nozzle classification experiments.     

PyC的广义小滴沉积模式

通过偏光显微镜、扫描电镜(SEM)、X射线衍射(XDS)及X射线光电子能谱(XPS)考察了热解碳(Pyrocarbon,本文简写为PyC)的织构及生长特征等,提出了一个广义小滴沉积模式.PyC的光滑层(SL)、粗糙层(RL)及各向同性相(ISO)等三种主要织构的形成机制可由此模式得到满意的解释.     

Computer simulations of the growth of breath figures

We describe computer simulations of the growth of breath figures, the patterns formed when droplets condense on a cold surface. The focus is on the coalescence of droplets, which is an important growth mechanism, and the conditions for self-similar patterns, which are experimentally observed. It is assumed that individual droplets grow according to a power law; droplets that touch coalesce instantly and are replaced by a new droplet at the center of gravity of the coalescing pair. The average droplet radius, distribution of droplet sizes, surface coverage, and radial distribution function are determined as a function of the time for a variety of initial coverages and polydispersities. These quantities are compared to those determined by experiment, and our simple model is found to be in good accord with the observed behavior. It is observed that the process of coalescence induces spatial correlation between droplets.This paper is dedicated to Howard Reiss on his 66th birthday.     

A digital image analysis technique for quantitative characterisation of high-speed sprays

A digital image analysis technique developed as a particle or droplet sizing tool and capable of measuring non-spherical objects has been examined in terms of its suitability for quantitative measurements in moderately dense sprays and in particular the potential capability for the characterisation of small diameter, high-speed two-phase flows by employing high-intensity pulsed lasers for illumination. In order to evaluate robustness of the image analysis technique (PDIA), measurement certainty and also to assess whether measurement performance is sensitive to the optical set-up, the technique was applied to data obtained from a hollow cone spray via two independent optical configurations which employed firstly a diode laser and secondly an Nd:YAG laser. The calibration response of the two optical set-ups revealed significant differences in terms of the depth-of-field characteristics and thus effective measurement volume dimensions. Despite these differences, a comparison of PDIA spray data revealed excellent agreement between the two datasets for measured diameters in the range 10–90 μm in the number distributions which not only confirmed robustness of the technique but also the potential of PDIA for the measurement of fast, small diameter objects. Subsequent comparisons of the PDIA data were made with PDA data obtained within the same spray in space and time and showed excellent agreement between the two techniques for droplets larger than approximately 25 μm in diameter. Discrepancies between PDIA and PDA were observed in the volume size distributions for the larger droplets measured whose diameters were greater than approximately 40 μm. This discrepancy is due to the ability of PDIA to measure the diameter of non-spherical droplets which were shown to exist in significant numbers at this measurement location within the spray. In contrast, the well-established technique PDA, which relies on the assumption of droplet sphericity clearly does not detect the presence of these larger deformed droplets.