A voltammetric sensor based on graphene-modified electrode for the determination of trace amounts of l-dopa in mouse brain extract and pharmaceuticals

l-Dopa is the intermediate precursor of the neurotransmitter dopamine. Unlike dopamine, l-dopa easily enters the central nervous system. l-Dopa, as one of the catecholamines, is widely used as a source of dopamine in the treatment of most patients with Parkinson’s disease and epilepsy. Graphene (GR) is ideally suited for implementation in electrochemical applications due to its reported large electrical conductivity, large surface area, unique heterogeneous electron transfer rate, and low production costs. This work reports the synthesis of GR using a modified Brodie method and its application for the electrochemical determination of l-dopa in real samples. Electrochemical measurements were performed at glassy carbon electrode modified with graphene (GR/GCE) via drop casting method. Cyclic voltammograms of l-dopa at GR/GCE showed an increased current intensity compared with GCE. All the measurements were done in phosphate buffer solution 0.1 M (pH 6.2) and the oxidation peak was observed at 0.27 V vs. Ag/AgCl. The effect of scan rate showed that oxidation of l-dopa on GR/GCE was surface controlled. The oxidation peak current of l-dopa gradually increased with increasing accumulation time from 0 to 300 s and accumulation potential from 0.0 to 0.3 V and reached the maximum current response at 240 s and 0.2 V for the accumulation time and accumulation potential, respectively. Voltammetric peak currents showed a linear response for l-dopa concentration in the range of 0.04 to 79 μM and a detection limit of 0.022 μM (22 nM). The relative standard deviation for five determinations of 50 μM l-dopa was 0.52 %.     

Design and preparation of poly(lactic acid) hydroxyapatite nanocomposites reinforced with phosphorus‐based organic additive: Thermal,combustion, and mechanical properties studies

A new phosphorus‐based organic additive (PDA) was designed and successfully synthesized using a three‐component reaction for improvement of the thermal and combustion resistance of polylactic acid (PLA). For compensate for mechanical properties of PLA, hydroxyapatite nanoparticles was modified via in situ surface modification with PDA and was used for preparation of PLA nanocomposites. The structure and morphology as well as thermal, combustion, and mechanical properties of the all PLA systems were investigated. The X‐ray diffraction (XRD) and field‐emission scanning electron microscopy (FE‐SEM) results indicated that the presence of PDA as surface modifier has been necessary for a desirable dispersion of hydroxyapatite (HA) nanoparticles in the PLA matrix. The thermal, combustion, and mechanical properties of the PLA system films were investigated using thermogravimetric analysis (TGA), microscale combustion calorimeter (MCC), and tensile test, respectively. The initial decomposition temperature and char residue of PLA containing 6 mass% of PDA along with 2 mass% HA nanoparticles were increased 20°C and 12% respectively, compared with that of the neat PLA. The peak of heat release rate was decreased from 566 W/g for the neat PLA to 412 W/g for PLA containing 2 mass% of PDA along with 6 mass% HA nanoparticles. By incorporation of only 2 mass% HA nanoparticles and 6 mass% of PDA, the tensile strength was obtained 51 MPa higher than that of the neat PLA.     

Topology Management for Improving Routing and Network Performances in Mobile Ad Hoc Networks

A distributed topology management algorithm based on the construction of a forest from the topology of the network is proposed. In this algorithm, each tree of the forest forms a zone, and each zone is maintained proactively. As a result, the network can be seen as a set of non-overlapping zones. We introduce the concept of quality of connectivity for extracting the links connecting the pair of best nodes, and use this quality to construct the forest. We characterize the behaviors of the proposed topology management algorithm under various network density. We study the effect of the topology management on the performance of an ad hoc routing protocol. The results demonstrate that the performance of routing can be significantly improved with the help of topology management.     

为升压转换器提供关断功能的外接元件

图1是升压开关转换器电路,它有一个众所周知的问题：如果将升压转换器IC,的输入拉低来关断升压转换器,外接电感L,和正向偏置肖特基二极管D,就可以让负载继续引出电流。对于电池供电的设备来说,这是一个沉重的负载     

Modal analysis of silicon carbide nanotubes using structural mechanics

This article discusses the vibrational properties of silicon carbide nanotubes with various dimensions, chiralities and boundary conditions. The molecular mechanics-based finite element method is applied to study the mode shapes and natural frequencies of the silicon carbide nanotubes. The results reveal that the natural frequencies of the nanotubes increase with decreasing length, but they do not show monotone behaviors vs. diameter changes. The reasons are discussed in detail.     

Joint consideration of energy‐efficiency and coverage‐preservation in microsensor networks

This paper presents an energy‐efficient and coverage‐preserving communication protocol which distributes a uniform energy load to the sensors in a wireless microsensor network. This protocol, called Distance‐based Segmentation (DBS), is a cluster‐based protocol that divides the entire network into equal‐area segments and applies different clustering policies to each segment to (1) reduce total energy dissipation and (2) balance the energy load among the sensors. Therefore, it prolongs the lifetime of the network and improves the sensing coverage. Moreover, the proposed routing protocol does not need any centralized support from a certain node which is at odds with aiming to establish a scalable communication protocol. Results from extensive simulations on two different network configurations show that by lowering the number of wasteful transmissions in the network, the DBS can achieve as much as a 20% reduction in total dissipated energy as compared with current cluster‐based protocols. In addition, this protocol is able to distribute energy load more evenly among the sensors in the network. Hence, it yields up to a 66% increase in the useful network lifetime. According to the simulation results, the sensing coverage degradation of the DBS is considerably slower than that of the other cluster‐based protocols. Copyright © 2009 John Wiley & Sons, Ltd.     

Eccentricity effect of micropatterned surface on contact angle

This article experimentally shows that the wetting property of a micropatterned surface is a function of the center-to-center offset distance between successive pillars in a column, referred to here as eccentricity. Studies were conducted on square micropatterns which were fabricated on a silicon wafer with pillar eccentricity ranging from 0 to 6 μm for two different pillar diameters and spacing. Measurement results of the static as well as the dynamic contact angles on these surfaces revealed that the contact angle decreases with increasing eccentricity and increasing relative spacing between the pillars. Furthermore, quantification of the contact angle hysteresis (CAH) shows that, for the case of lower pillar spacing, CAH could increase up to 41%, whereas for the case of higher pillar spacing, this increment was up to 35%, both corresponding to the maximum eccentricity of 6 μm. In general, the maximum obtainable hydrophobicity corresponds to micropillars with zero eccentricity. As the pillar relative spacing decreases, the effect of eccentricity on hydrophobicity becomes more pronounced. The dependence of the wettability conditions of the micropatterned surface on the pillar eccentricity is attributed to the contact line deformation resulting from the changed orientation of the pillars. This finding provides additional insights in design and fabrication of efficient micropatterned surfaces with controlled wetting properties.     

Evaluating Performance of Honey Bee Mating Optimization

The honey bee mating optimization (HBMO) algorithm is presented and tested with various test functions, and its performance is compared with the genetic algorithm (GA). It is shown that the HBMO algorithm can overcome the weaknesses of the GA. The HBMO converges faster than the GA. Even when the HMBO starts from a more improper initial condition than the GA, it can reach a better solution in a smaller number of function evaluations. Furthermore, in some cases, the GA was not able to reach the global minimum.