Effect of liquid slip in electrokinetic parallel-plate microchannel flow

Liquid slip at hydrophobic surfaces in microchannels has frequently been observed. We present here an analytical solution for oscillating flow in parallel-plate microchannels by combining the electrokinetic transport phenomena with Navier's slip condition. Our parametric results suggest that electrokinetic transport phenomena and liquid slip at channel walls are both important and should be considered simultaneously. Their significance depends on channel wall material, electrolyte concentration, and pH. For pressure-driven-flow, liquid slip counteracts the effect by the electrical double layer and induces a larger flow rate. A higher apparent viscosity would be predicted if slip is neglected. For electroosmotic flow, liquid slip alters the flow rate by about 20% for a thick electrical double layer. Our results provide design guidelines to precisely control time-dependent microflow in hydrophobic microfluidic microelectromechanical system devices.     

Shah convolution Fourier transform detection: multiple-sample injection technique

For the direct measurement of electrophoretic mobility, multiple-point (Shah function) detected, time-domain detector signals were converted into frequency-domain plots by means of Fourier transformation. Multiple sample plugs (up to a maximum of three) were introduced into the separation channel and the resultant time-domain signals were then Fourier-transformed. The multiple-sample injection technique has been successfully demonstrated for a one-component system and a separation. Though the number of fluorescing zones flowing through the illuminated length of the channel is greater than the number of analytes in the solution, Shah convolution Fourier transform detection (SCOFT) is able to identify the number of fluorescent species in the solution based on their migration velocities. The height of the fundamental peak increases as the number of injected sample plugs is increased. More importantly, the signal-to-noise ratio (S/N) is found to be proportional to the number of injected sample plugs. With these findings, the multiple-sample injection technique certainly has got many potential applications in trace analysis. The technique would be equally applicable to other separation techniques (e.g., high-performance liquid chromatography) and detection methods (e.g., absorption, refractive index).     

Self-aggregated phosphorescent platinum(II) polymeric material from modified poly(4-vinylpyridine)

A solvochromic material made from incorporation of photoluminescent Pt(II)([formula: see text]) moieties into commercially available homopolymer poly(4-vinylpyridine) exhibits different emission energies, due to different degrees of self-aggregation in various solvents and as thin film upon exposure to vapour of different volatile organic compounds (VOC); self-aggregation enables intra- and intermolecular interactions arising from pi-stacking of the Pt([formula: see text]) moieties, which is affected by medium polarity.     

An investigation on the influence of a vinyl pyrrolidone/vinyl acetate copolymer on the moisture permeation, mechanical and adhesive properties of aqueous-based hydroxypropyl methylcellulose film coatings

Polymers for aqueous film coating, such as hydroxypropyl methylcellulose (HPMC), often require the inclusion of a plasticizer to reduce brittleness and increase flexibility and ductility. A vinyl pyrrolidone/vinyl acetate copolymer (S630) was investigated for its influence on HPMC film coating parameters, comparing the results with a commonly used plasticizer, polyethylene glycol and another copolymer, polyvinyl alcohol. The viscous properties of the solutions and the glass transition temperatures of the equivalent polymer films were evaluated. Its effect on the film properties, such as appearance, surface roughness, moisture permeation and mechanical properties, as well as its ability to promote better adhesion of the film coat to the core surface, was compared. S630 was able to reduce the viscosity of the polymer solution and glass transition temperature of HPMC, as well as, enhance the mechanical properties of the cast film. The moisture permeation was slightly reduced but not to the same extent as polyethylene glycol. A 10% concentration of S630 increased the adhesive strength and toughness of the HPMC film coat. In conclusion, S630 was effective as a film-former, substrate adhesive and plasticizer. It has the potential to be used to replace the more volatile plasticizers which have problems of loss or migration.     

Developments toward a complete micro-total analysis system for Duchenne muscular dystrophy diagnosis

The diagnosis of Duchenne muscular dystrophy (DMD) has historically utilized either PCR or requires Southern blot analysis, a southern blot analysis, however, is not amenable to incorporation in a microdevice format. A PCR amplification-based method has been developed, and we have previously coupled this amplification with microchip separation of the PCR fragments for DMD diagnosis. Diagnoses of affected patients were performed by comparing exon concentrations to those of control samples amplified at the same time. To accurately identify mutations in patient samples, this work established normal ranges for the concentration of each amplified exon fragment using control samples amplified over successive days. Our studies show that the number of cycles used in the amplification process affects this range. Affected patient samples were analyzed using these normal ranges and the mutations detected by Southern blot analysis were also diagnosed using the microchip separation method.

Employing the microchip separation method decreases the time required for the analysis, but the time required for DNA purification and PCR amplification must also be decreased for faster total analysis of patient samples. Development of microchip methods for these processing steps is one approach for reducing the individual times, while also providing the possibility of integrating these steps in a single device. Here we report on the microchip extraction of genomic DNA from whole blood using a novel sol–gel matrix that is easily formed in microdevices. IR-mediated PCR amplification of a β-globin fragment from genomic DNA followed by electrophoretic analysis on a single integrated microdevice is presented for the first time. Work towards the development of a micro-total analysis device for DMD diagnosis, through integration of all processing steps on a single device, is also discussed.     

Synthesis and properties of azo dye aligning layers for liquid crystal cells

The synthesis and properties of azo dyes that can be used for photoaligning liquid crystals (LCs) have been investigated. The structures and the synthetic procedure for the azo dyes are presented. The photoaligning of azo dyes takes place purely due to the reorientation of the molecular absorption oscillators perpendicular to the UV light polarization. The qualitative model for the phenomenon in terms of the rotational diffusion of the azo dye molecules in the field of the polarized light is discussed. The order parameters S = -0.4 (80% of the maximum absolute value S_m = -0.5) were measured from the polarized absorption spectra at the wavelength 372 nm. A temperature stable pretilt angle of 5.3° was obtained by a two-step exposure of the azo dye film using normally incident polarized light followed by oblique non-polarized light. The azimuthal anchoring energy of the photoaligned substrate was A_ϕ ≈10^-4 J m^-2, which is the same as the anchoring of the rubbed polyimide (PI) layer. The voltage holding ratio value of a photoaligned LC cell was found to be even higher than for a rubbed PI layer, which enables the applications of azo dyes as aligning layers in active matrix liquid crystal displays. The thermal stability of the photoaligned azo dye layers is sufficiently high, but UV stability has to be improved, e.g. by polymerization. A new LCD aligning technology based on polymerized azo dye layers is envisaged.     

一种基于种群熵估计的自适应遗传算法

为获得运行过程中对搜索空间勘探和开采的平衡 ,该文提出了一种基于种群熵估计的参数自适应遗传算法。该算法每一进化代的新种群由保留、繁殖和随机 3部分子种群组成 ,其数量则由相应的参数进行控制。通过引入种群熵的概念对种群内个体的多样性进行度量并使用一种简单的方法对其进行估计以确定各控制参数 ,该算法实现了参数的自适应调节。试验结果表明该算法能够有效协调勘探和开采 ,在处理复杂问题时表现出较高的性能