A nanostructure-based electrochemical sensor for square wave voltammetric determination of N-acetylcysteine in pharmaceutical and biological samples

Ionics - In this study, a carbon paste electrode (CPE) was chemically modified with Pt/carbon nanotubes (CNTs) nanocomposite and 8,9-dihydroxy-7-methyl-12H-benzothiazolo [2,3-b] quinazolin-12-one...     

Ionic liquid/multiwall carbon nanotubes paste electrode for square wave voltammetric determination of methyldopa

Ionic liquid/multiwall carbon nanotubes paste electrode has been used as a novel sensor for the efficient quantitative determination of methyldopa (MDOP) in pharmaceutical and biological samples by using square wave voltammetry. This new sensor shows a better electrochemical response with lower over-potential and high sensitivity for MDOP compared with unmodified carbon paste electrode in physiological condition. The electro-oxidation of MDOP occurred in a pH-dependent 2e^? and 2H⁺ process, and the electrode reaction followed a diffusion-controlled pathway. Under the optimum conditions, the voltammetric oxidation peak current of MDOP showed two linear dynamic ranges with a detection limit of 0.1 μM for MDOP. The novel sensor has been found selective and successfully implemented for the determination of MDOP in real samples such as tablet and patient urine.     

Voltammetric behavior and determination of antidepressant drug paroxetine at carbon-based electrodes

Ionics - Simple, rapid, sensitive, and reproducible methods were developed for the assay of paroxetine in tablets. The electrooxidative behavior and determination of paroxetine on boron-doped...     

Electrochemical behavior and voltammetric determination of dihydronicotinamide adenine dinucleotide using a glassy carbon electrode modified with single-walled carbon nanohorns

Ionics - We report a simple method for the direct and quantitative determination of dihydronicotinamide adenine dinucleotide (NADH) using a single-walled carbon nanohorn (SWCNH) modified glassy...     

与方波合成有关的李萨如图形的实验与理论研究

通过方波与方波、正弦波与方波合成的图形来研究李萨如图形,利用傅里叶级数理论把方波展开为正弦和余弦形式的傅里叶级数,然后利用Matlab软件来合成2列相互垂直的方波与正弦波以及2列方波的李萨如图形,并与实验上观察到的现象进行比较,并分析了两者之间的差异.     

半浮栅晶体管Marx方波脉冲电源设计

为得到工业需要的大电流高重频方波脉冲,分析并改进了半导体全控型Marx发生器,在充电的同时实现了截尾功能。设计采用新型半浮栅结构晶体管 (SFGT)作为主开关,可产生kV高压、百A大电流、高重频的方波脉冲。优化了电路结构,解决直流充电源受脉冲电源放电电压冲击问题。研制得到电流100 A、频率4 kHz、脉宽4 s、负高压6 kV、上升沿下降沿均在80 ns内的方波脉冲发生器。研究了相应的SFGT磁芯隔离驱动电路,结合了SFGT栅极并联自主电容隔离驱动和IR2110的半桥驱动电路,并对半桥上的MOS管的栅极等效电路进行了理论分析,驱动电路具有抗干扰能力强且脉宽调节范围大的特点。     

Phase behavior of unsymmetrical dimers on a square lattice

Monte Carlo simulations in the grand canonical ensemble have been carried out to study phase transitions in monolayers formed by heterogeneous dimers, composed of segments A and B, on a square lattice. The unsymmetrical segment-segment interactions are assumed (u_AA ≠ u_BB). The systems with u_AB = u_BB = −1 and different AA-interactions studied in our previous work [W. R?ysko, M. Borówko, Surf. Sci. 520 (2002) 151] are reconsidered. The structural phase transitions at high temperatures are investigated. It is shown that topology of a phase diagram depends on the energy u_AA. For repulsive AA-interactions a triple point is found and the system belongs to the universality class of a tricritical point. When u_AA < 0 the critical line of the order-disorder transition terminates at a critical end point and the system belongs to the universality class of the 2D Ising model.     

输入方波信号的过阻尼谐振子的随机共振

计算了在输入方波信号情况下过阻尼谐振子的输出功率谱和信噪比,详细讨论了相应的随机共振现象,并与输入余弦信号情况进行对比.研究发现:它们均出现随机共振现象,且均存在共振和抑制并存的现象.但这一并存现象,在两模型中分别出现于不同的共振曲线. 关键词： 过阻尼谐振子 随机共振 方波信号     

Sensitive voltammetric determination of diclofenac using room-temperature ionic liquid-modified carbon nanotubes paste electrode

An ionic liquid-modified carbon nanotubes paste electrode (IL/CNTPE) has been fabricated using hydrophilic ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) as a binder. This electrode showed enhanced electrochemical response and strong analytical activity towards the direct electrochemical oxidation of diclofenac (DCF). The electron transfer coefficient, α, and charge transfer resistance (R _ct) of DCF at the modified electrode were calculated. Under optimal conditions at pH 7.0, the anodic peak currents increased linearly with the concentration of DCF in the range of 0.5–300 μmol L^?1 with a detection limit of 0.2 μmol L^?1 (3σ). The interferences of foreign substances were investigated. Differential pulse voltammetry was used to check the applicability of the proposed sensor to the determination of DCF in real samples with satisfactory results.     

Simultaneous determination of amlodipine besylate and rosuvastatin calcium in binary mixtures by voltammetric and chromatographic techniques

Voltammetric and liquid chromatographic (LC) methods have been developed for the simultaneous determination of amlodipine besylate (AML) and rosuvastatin calcium (ROS) for the first time. Detailed electrochemical behavior and simultaneous voltammetric determination of AML and ROS were investigated in detail using glassy carbon electrode (GCE). High-performance liquid chromatography (HPLC) and ultra-performance liquid chromatography (UPLC) were also developed for the comparison. Voltammetric method exhibited linear dynamic responses for the simultaneous assay of AML and ROS in the concentration range between 0.006 and 2.85 μg/mL and between 0.01 and 5.00 μg/mL, with detection limits of 0.001 and 0.003 μg/mL, respectively. On the other hand, LC methods presented a wider linearity range than that of the SWV method between 0.5 and 100 μg/mL with the detection limits of 0.011 and 0.027 μg/mL for AML and 0.034 and 0.042 μg/mL for ROS by UPLC and HPLC techniques, respectively.     

ZnO nanoparticle-modified ionic liquid-carbon paste electrodefor voltammetric determination of folic acid in food and pharmaceutical samples

In this work, a ZnO/nanoparticles (NPs) modified carbon ionic liquid paste electrode (ZnO/NP/CILPE) was fabricated and used to investigate the electrochemical behavior of folic acid. ZnO/NP/CILPE was prepared by mixing hydrophilic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim]-[PF₆])), ZnO/NPs, graphite powder, and liquid paraffin together. The fabricated ZnO/NP/CILPE showed great electrocatalytic ability to the oxidation of folic acid, and an irreversible oxidation peak appeared at 0.75 V (vs. Ag/AgCl) with improved peak current. Under the optimized conditions of pH 9.0, the plot of peak current vs. folic acid concentration consisted of two linear segments with slopes of 1.776and 0.033 μA/μM in the concentration ranges of 0.05–1.5 μM and 1.5–550.0 μM, respectively. The detection limit was 0.01 μM (3σ). The proposed sensor was successfully applied for the determination of folic acid in fortified food and pharmaceutical samples.     

Theoretical investigation of planar square carbon allotrope and its hydrogenation

Using density functional theory we investigate a novel carbon allotrope 'SqC': a square planar material that can be more than tetracoordinated. Carbon atoms in this 2D square Bravais lattice form an unusual five-center four-electron bond with neighboring four carbon atoms (tetracoordination). Such an electron-deficient bonding leaves an empty orbital which enables penta- or hexa-coordinated carbon atom. Indeed, our simulations demonstrate such penta- and hexa-coordinated configurations upon partial and complete hydrogenation, respectively. Surprisingly, in all the forms SqC shows the metallic character. SqC has the binding energy of 6.7 eV and it also satisfies the Born stability criteria. Yet our phonon calculations show that it may only be considered as quasi-stable.     

Spontaneous localizations of the wave function and classical behavior

We investigate and develop further two models, the GRW model and the K model, in which the Schrödinger evolution of the wave function is spontaneously and repeatedly interrupted by random, approximate localizations, also called self-reductions below. In these models the center of mass of a macroscopic solid body is well localized even if one disregards the interactions with the environment. The motion of the body shows a small departure from the classical motion. We discuss the prospects and the difficulties of observing this anomaly. As far a the influence of the surroundings on submacroscopic objects (like dust particles) is concerned, we show that the estimates obtained recently in the theory of continuous measurements and in the K model are compatible. Also, we elaborate upon the relationship between the models. Firstly, borrowing a line of thought from the K model, we find the transition region between macroscopic and microscopic behaviors in the GRW model. Secondly, we refine the propagation rule of the wave function in the K model with the help of the time-evolution equation proposed in the GRW model.     

Numerical visualization of vortex flow behavior in square jets in cross-flow

Direct numerical simulations have been performed in this study to visualize the flow behavior of single and multiple square jets issuing normally into a cross-flow. Three configurations are considered, a single jet located in the centre of the domain, twin jets in side-by-side (SBS) arrangement in the spanwise direction and triple jets in tandem arrangement with twin jets at the front and a third jet in downstream along the centre line. Simulation uses a jet to cross-flow velocity ratio of 2.5 and the Reynolds number 225, based on the free-stream quantities and the jet width. While the vortical structures predicted from single jet case were in good qualitatively agreement with the findings of other researchers, our results show that the process of merging between two counter-rotating vortex pairs (CRVP) in twin jets configurations is strongly dependent on the jet-to-jet edge distance. Further downstream in the far-field, results from the SBS twin jets show a most dominating larger CRVP accompanied with a smaller inner vortex pair. The observations are in good qualitative agreement with the experimental findings in the literature. The resulting flow structures of triple jets in tandem configuration have revealed, for the first time, more complicated flow interactions between individual jets and cross-flow, providing further insights of complex flow physics and its potential engineering applications.     

Unifying the crystallization behavior of hexagonal and square crystals with the phase-field-crystal model

By employing the phase-field-crystal models, the atomic crystallization process of hexagonal and square crystals is investigated with the emphasis on the growth mechanism and morphological change. A unified regime describing the crystallization behavior of both crystals is obtained with the thermodynamic driving force varying. By increasing the driving force, both crystals(in the steady-state) transform from a faceted polygon to an apex-bulged polygon, and then into a symmetric dendrite. For the faceted polygon, the interface advances by a layer-by-layer(LL) mode while for the apex-bulged polygonal and the dendritic crystals, it first adopts the LL mode and then transits into the multi-layer(ML)mode in the later stage. In particular, a shift of the nucleation sites from the face center to the area around the crystal tips is detected in the early growth stage of both crystals and is rationalized in terms of the relation between the crystal size and the driving force distribution. Finally, a parameter characterizing the complex shape change of square crystal is introduced.     

Roughening behavior of a one-dimensional crystal surface with inverse square potential

The discrete Gaussian chain with inverse square potential—which models a one-dimensional crystal surface—is studied by Monte-Carlo methods. The system is found to undergo a roughening transition, and the temperature-dependent correlation function exponent η(T) is shown to be discontinous at the critical point. These results can be transposed to the metal-insulator transition of a one-dimensional plasma of logarithmically interacting charges.