Robust supergain beamforming for circular array via second-order cone programming

The phenomenon of supergain for a circular array and its robust beamforming are presented. The coplanar superdirective array gain of the circular array, although it is not so extreme as an endfire line array, outperforms a lot over that of a conventional delay-and-sum beamformer in isotropic noise fields when the inter-element spacings are much smaller than one-half wavelength. However, optimum beamforming algorithms can be extremely sensitive to slight errors in array characteristics. The performance are known to degrade significantly if some of underlying assumptions on the sensor array is violated. Therefore, white noise gain constraint is used to improve the robustness of the supergain beamformer against random errors. We show that the design of the weight vector of robust supergain beamformer can be reformulated as a form of second-order cone programming and resolved efficiently via the well-established interior point method. Results of computer simulation for a 24-element circular array confirm satisfactory performance of the approach proposed in this paper.     

Sensitive detection of hydrogen peroxide in foodstuff using an organic�Cinorganic hybrid multilayer-functionalized graphene biosensing platform

We report on a new electrochemical biosensing strategy for the sensitive detection of hydrogen peroxide (H₂O₂) in foodstuff samples. It is based on a gold electrode modified with layer of graphene patterned with a multilayer made from an organic?Cinorganic hybrid nanomaterial. Initially, a layer of thionine (Th) was assembled on the surface of the graphene nanosheets, and these were then cast on the surface of the electrode for the alternate assembly of gold nanoparticles and horseradish peroxidase. The large surface-to-volume ratio and high conductivity of the nanosheets provides a benign microenvironment for the construction of the biosensor. The use of such a multilayer not only shortens the electron transfer pathway of the active center of the enzyme due to the presence of gold nanoparticles, but also enhances the electrocatalytic efficiency of the biosensor toward the reduction of H₂O₂. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The number of layers, the operating potential, and the pH of the supporting electrolyte were optimized. Linear response is obtained for the range from 0.5???M to 1.8?mM of H₂O₂, the detection limit is 10 nM (at S/N?=?3), and 95% of the steady-state current is reached within 2?s. The method was applied to sense H₂O₂ in spiked sterilized milk and correlated excellently with the permanganate titration method.

Bioanalytical applications of isothermal nucleic acid amplification techniques

The most popular in vitro nucleic acid amplification techniques like polymerase chain reaction (PCR) including real-time PCR are costly and require thermocycling, rendering them unsuitable for uses at point-of-care. Highly efficient in vitro nucleic acid amplification techniques using simple, portable and low-cost instruments are crucial in disease diagnosis, mutation detection and biodefense. Toward this goal, isothermal amplification techniques that represent a group of attractive in vitro nucleic acid amplification techniques for bioanalysis have been developed. Unlike PCR where polymerases are easily deactivated by thermally labile constituents in a sample, some of the isothermal nucleic acid amplification techniques, such as helicase-dependent amplification and nucleic acid sequence-based amplification, enable the detection of bioanalytes with much simplified protocols and with minimal sample preparations since the entire amplification processes are performed isothermally. This review focuses on the isothermal nucleic acid amplification techniques and their applications in bioanalytical chemistry. Starting off from their amplification mechanisms and significant properties, the adoption of isothermal amplification techniques in bioanalytical chemistry and their future perspectives are discussed. Representative examples illustrating the performance and advantages of each isothermal amplification technique are discussed along with some discussion on the advantages and disadvantages of each technique.     

气相色谱法测定人体血液中乙醇含量的测量不确定度评定

对气相色谱法测定人体血液中乙醇含量的测量不确定度进行评定。人体血液中乙醇含量测量结果的测量不确定度主要来源于相对定量校正因子、检材量、检材中添加内标物叔丁醇的体积、检材中乙醇峰面积的平均值与添加内标物叔丁醇峰面积的平均值之比、无水乙醇的纯度及密度等参数引起的不确定度。当检材中乙醇的含量为0．915mg／mL时,扩展不确定度为O．030mg/mL(k=2)。