Differences between signal currents for both polarities of applied voltages on cavity ionization chambers

A difference between the surface potential of the charge collecting electrode and that of the guard electrode of an ionization chamber changes the charge collecting volume depending on the applied voltage. If the difference is large, the saturation curve of the signal current shows a maximum at a low applied voltage. Even when there is no electrical or mechanical defect, the signal current from a parallel plate ionization chamber irradiated with ⁶⁰Co γ-rays increases or decreases with the applied voltage beyond the recombination region depending on the polarity of the applied voltage. The variation in the signal current is explained as a result of the change in the stopping power of air due to the acceleration or deceleration of secondary electrons. These electrons are emitted from the polarizing electrode towards the collector as a result of Compton scattering. In a range of low applied voltages, the signal current from a cylindrical ionization chamber is expected to be smaller for a negative applied voltage than for a positive applied voltage. This is because epithermal electrons are expected to have a higher probability of being lost by back diffusion than positive ions which are originally produced in a thermal equilibrium condition. An experimental result, however, showed no difference in the polarities of the applied voltage. The result may be explained as a consequence of the fact that epithemal electrons do not drift for long distances and maintain their energies.     

The electric field as a novel switch for uptake/release of hydrogen for storage in nitrogen doped graphene

Nitrogen-doped graphene was recently synthesized and was reported to be a catalyst for hydrogen dissociative adsorption under a perpendicular applied electric field (F). In this work, the diffusion of H atoms on N-doped graphene, in the presence and absence of an applied perpendicular electric field, is studied using density functional theory. We demonstrate that the applied field can significantly facilitate the binding of hydrogen molecules on N-doped graphene through dissociative adsorption and diffusion on the surface. By removing the applied field the absorbed H atoms can be released efficiently. Our theoretical calculation indicates that N-doped graphene is a promising hydrogen storage material with reversible hydrogen adsorption/desorption where the applied electric field can act as a switch for the uptake/release processes.     

The effect of electric field strength,buffer type and concentration on separation parameters in capillary zone electrophoresis

Summary Probe solutes were used to investigate the effect of buffer type, concentration and applied voltage on solute mobility, column efficiency and resolution in capillary zone electrophoresis. With low conductivity buffers higher concentrations and/or higher voltages could be used to improve column efficiency and resolution. Doubling the concentration of the buffer doubles the amount of heat generated inside the column while doubling the applied voltage cause a 4-fold increase. Solute migration time is approximately an inverse function of the charge density of the buffer's cation. Analysis time is increased by about 30% if the buffer concentration is doubled while it is cut in half if the applied voltage is doubled. Column efficiency is improved (higher theoretical plate count) with increasing buffer concentration and/or applied voltage as long as the heat generated is efficiently dissipated. The separation factor is directly related to analysis time and, therefore, selectivity improves with increasing buffer concentration but decreases with increasing applied voltage. Hence, resolution is optimized by increasing buffer concentration at a moderate applied voltage.     

Externally applied electric fields on immiscible lipid monolayers: repulsion between condensed domains precludes domain migration

Lipid and protein molecules anisotropically oriented at a hydrocarbon-aqueous interface configure a dynamic array of self-organized molecular dipoles. Electrostatic fields applied to lipid monolayers have been shown to induce in-plane migration of domains or phase separation in a homogeneous system. In this work, we have investigated the effect of externally applied electrostatic fields on different lipid monolayers exhibiting surface immiscibility. In the monolayers studied, lipids in the condensed state segregate in discontinuous round-shaped domains, with the lipid in the liquid-expanded state forming the continuous phase. The use of fluorescent probes with selective phase partitioning allows analyzing by epifluorescence microscopy the migrations of the domains under the influence of inhomogeneous electric fields applied to the surface. Our observations indicate that a positive potential applied to an electrode placed over the monolayer promotes a repulsion of the domains until a steady state is reached, indicating the presence of a force opposed to the externally applied electric force. The experimental results were modeled by considering that the opposing force is generated by the dipole-dipole repulsion between the domains.     

Effects of Applied Electric Fields on Drop—Interface and Drop—Drop Coalescence*

In this work, coalescence of a single organic or aqueous drop with its homophase at a horizontal liquid interface was investigated under applied electric fields. The coalescence time was found to decrease for aqueous drops as the applied voltage was increased, regardless of the polarity of the voltage. For organic drops, the coalescence time increased with increasing applied voltage of positive polarity and decreased with increasing applied voltage of negative polarity. Under an electric field, the coalescence time of aqueous drops decreases due to polarization of both the drop and the flat interface. The dependency of organic drop-interface coalescence on the polarity of the electric field may be a result of the negatively charged organic surface in the aqueous phase. Due to the formation of a double layer, organic drops are subjected to an electrostatic force under an electric field, which, depending on the field polarity, can be attractive or repulsive. Pair-drop coalescence of aqueous drops in the organic phase was also studied. Aqueous drop-drop coalescence is facilitated by polarization and drop deformation under applied electric fields. Without applied electric fields, drop deformation increases the drainage time of the liquid film between two approaching drops. Therefore, a decrease in the interfacial tension, which causes drop deformation, accelerates drop-drop coalescence under an electric field and inhibits drop coalescence in the absence of an electric field.     

Interfacial constraints on water and proton transport across nafion membranes

Water and proton transport across a Nafion membrane are measured as functions of water activity and applied electric potential with a polymer electrolyte hydrogen pump. Water and proton transport across the membrane must match water and proton transport entering and leaving the electrode/membrane/vapor three phase interfaces at the anode and cathode. At low applied electric potential proton and water fluxes are correlated. At moderate to high applied electric potential the proton current is constant, independent of applied electric potential, while the water transport increases with increasing electric potential. At high applied electric potential water and proton transport become uncoupled at the membrane interfaces; water is transported across the membrane/vapor interface and protons are transported across the membrane/electrode interface. The applied electric potential drives electro‐osmosis to redistribute the water in the membrane. Water redistribution is limited by the interfacial transport of water across the membrane/vapor interface. © 2015 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2015 , 53, 1580–1589     

Start‐up of electrophoresis of an arbitrarily oriented dielectric cylinder

An analytical study is presented for the transient electrophoretic response of a circular cylindrical particle to the step application of an electric field. The electric double layer adjacent to the particle surface is thin but finite compared with the radius of the particle. The time‐evolving electroosmotic velocity at the outer boundary of the double layer is utilized as a slip condition so that the transient momentum conservation equation for the bulk fluid flow is solved. Explicit formulas for the unsteady electrophoretic velocity of the particle are obtained for both axially and transversely applied electric fields, and can be linearly superimposed for an arbitrarily‐oriented applied field. If the cylindrical particle is neutrally buoyant in the suspending fluid, the transient electrophoretic velocity is independent of the orientation of the particle relative to the applied electric field and will be in the direction of the applied field. If the particle is different in density from the fluid, then the direction of electrophoresis will not coincide with that of the applied field until the steady state is attained. The growth of the electrophoretic mobility with the elapsed time for a cylindrical particle is substantially slower than for a spherical particle.     

Integrated pulsed amperometry for the analysis of organic compounds

Integrated pulsed amperometric detection (IPAD) was applied for the detection of organic compounds for flow injection analysis. The pulse waveform used in the integrated pulsed amperometry consisted of three steps: detection potential, oxidation potential, and adsorption potential. The pulse waveform was applied to the working electrode as the analyte flowed through the electrochemical cell. Unlike ordinary pulsed amperometry, a faradaic current was integrated over the duration period of the detection potential in the IPAD. Therefore, the total charge was measured by integrating the current after the detection potential was applied. The current for the initial 10 ms, after applying the detection potential, was excluded from the integration due to a large charging current at the initial period. Compared with pulsed amperometry, integrated pulsed amperometry provides a better signal-to-noise ratio and a lower detection limit. This method was applied to the quantitative analysis of thiourea as a representative analyte of organosulfur compounds in a flow injection analysis.     

GC with LC-like packed capillary columns

Capillary columns of 0.3–0.35 mm internal diameter and 0.3–7.7 m length, packed with 3 to 30 μm octadecylsilica stationary phases as used for liquid chromatography, were applied to gas chromatographic separation of low boiling hydrocarbons. Van Deemter plots for these columns showed the optimum column efficiency to occur at linear velocities of 4–5 cm/s. A short column was applied to the rapid separation of components of a natural gas and impurities in standard gases, while a long column was applied to the separation of complex mixtures.     

30 years of research in thermal analysis and calorimetry

The research in thermal analysis and calorimetry, conducted by the author over the period 1964 to 1993, is summarised and concisely reviewed. The major investigations have focussed on thermal analysis studies of coordination compounds, particularly the metal dithiocarbamate complexes. A significant solution calorimetric study of some metal dithiocarbamate complexes has also been undertaken. DSC has been applied to determine the sublimation enthalpies of many metal dithiocarbamate and metal pentane-2,4-dionate complexes and solution calorimetry has been applied to study the thermochemistry of the latter group of complexes. Thermal analysis investigations of several inorganic molten salt systems have been initiated. Thermometric titrimetry has been applied to study metal-macrocyclic ligand systems in aqueous media and particularly those systems of environmental significance. Temperature calibration standards for TMA have been proposed and TMA has been applied to study the mechanical properties of several common inorganic compounds. DTA has been applied to study a wide variety of phenols and has subsequently been applied as an analytical technique to determine the components of solid state phenol mixtures. Thermometric titrimetry has been applied to determine the phenolic content of wines. A comprehensive thermal analysis study of Australian brown coal has been undertaken, involving the DSC determination of coal specific energy, a TG/DTA study of the coal pyrolysis and combustion processes and a TG/DTA and EGA study of the cation catalytic effect on the coal pyrolysis process. Thermal analysis and calorimetric techniques have been extensively publicised and promoted by the publication of specialist reviews, the presentation of symposia review papers and the oral presentation of short courses, particularly in the SE Asian region. This review essentially reveals the diversity of possible application of thermal analysis and calorimetric techniques and the primary significance of thermodynamic data in the fundamental rationalisation of chemical phenomena.     

Determining membrane capacitance by dynamic control of droplet interface bilayer area

By making dynamic changes to the area of a droplet interface bilayer (DIB), we are able to measure the specific capacitance of lipid bilayers with improved accuracy and precision over existing methods. The dependence of membrane specific capacitance on the chain-length of the alkane oil present in the bilayer is similar to that observed in black lipid membranes. In contrast to conventional artificial bilayers, DIBs are not confined by an aperture, which enables us to determine that the dependence of whole bilayer capacitance on applied potential is predominantly a result of a spontaneous increase in bilayer area. This area change arises from the creation of new bilayer at the three phase interface and is driven by changes in surface tension with applied potential that can be described by the Young-Lippmann equation. By accounting for this area change, we are able to determine the proportion of the capacitance dependence that arises from a change in specific capacitance with applied potential. This method provides a new tool with which to investigate the vertical compression of the bilayer and understand the changes in bilayer thickness with applied potential. We find that, for 1,2-diphytanoyl-sn-glycero-3-phosphocholine membranes in hexadecane, specific bilayer capacitance varies by 0.6-1.5% over an applied potential of ±100 mV.     

强外电场作用下二甲基硅酮的分子结构和激发态

The ground states of dimethyl siloxane under different intense electric fields ranging from - 0. 04 to 0. 04 a. u. are optimized using density functional theory DFT / B3P86 at 6-311 ++ G（d,p）level. The excitation energies and oscillator strengths under the same intense applied electric fields are calculated employing the revised hybrid CIS-DFT method. The result shows that the electronic state,molecular geometry,total energy,dipole moment and excitation energy are strongly dependent on the field strength and behave asymmetry to the direction of the applied electric field. As the electric field changes from - 0. 04 to 0. 04 a. u. ,the bond length of Si-O increases whereas the bond length of Si-C decreases because of the charge transfer induced by the applied electric field. The dipole moment of the ground state decreases linearly with the applied field strength. However,the dipole moment of molecule changes from positive to negative as the inverse electric field increase to - 0. 03 a. u. Further increase of the inverse electric field results in an increase of the total energy of the molecule. The dependence of the calculated excitation energies on the applied electric field strength is fitting well to the relationship proposed by Grozema. The excitation energies of the first five excited states of dimethyl siloxane decrease as the applied electric filed increases because the energy gap between the HOMO and LUMO become close with the field,which shows that the molecule is easy to be excited under electric field and hence can be easily dissociated.     

Magnetic sponge prepared with an alkanedithiol-bridged network of nanomagnets

The magnetic dipole-dipole interaction between nanomagnets having huge magnetic moments can have a strength comparable to that of the van der Waals interaction between them, and it can be manipulated by applying an external magnetic field of conventional strength. Therefore, the cooperation between the dipole-dipole interaction and the applied magnetic field allows the magnetic moments of nanomagnets to be aligned and organized in an ordered manner. In this work, a network of magnetic nanoparticles connected with flexible long-alkyl-chain linkers was designed to develop a "magnetic sponge" capable of absorbing and desorbing guest molecules with changes in the applied magnetic field. The magnetization of the sponge with long-alkyl-chain bridges (30 C atoms) exhibited a 500% increase after cooling in the presence of an applied field of 7 T relative to that in the absence of a magnetic field. Cooling in a magnetic field leads to anisotropic stretching in the sponge due to reorganization of the nanomagnets along the applied field, in contrast to the isotropic organization under zero-field conditions. Such magnetic-responsive organization and reorganization of the magnetic particle network significantly influences the gas absorption capacity of the nanopores inside the material. The absorption and desorption of guests in an applied magnetic field at low temperature can be regarded as a fascinating "breathing feature" of our magnetic sponge.     

Optimal separation times for electrical field flow fractionation with Couette flows

The prediction of optimal times of separation as a function of the applied electrical field and cation valence have been studied for the case of field flow fractionation [Martin M., Giddings J. C., J. Phys. Chem. 1981, 85, 727] with charged solutes. These predictions can be very useful to a priori design or identify optimal operating conditions for a Couette-based device for field flow fractionation when the orthogonal field is an electrical field. Mathematically friendly relationships are obtained by applying the method of spatial averaging to the solute species continuity equation; this is accomplished after the role of the capillary geometrical dimensions on the applied electrical field equations has been assessed [Oyanader M. A., Arce P., Electrophoresis 2005; 26, 2857]. Moreover, explicit analytical expressions are derived for the effective parameters, i.e. diffusivity and convective velocity as functions of the applied (orthogonal) electrical field. These effective transport parameters are used to study the effect of the cation valence of the solutes and of the magnitude of the applied orthogonal electrical field on the values of the optimal time of separation. These parameters play a significant role in controlling the optimal separation time, leading to a family of minimum values, for particular magnitudes of the applied orthogonal electrical field.     

外电场作用下甲基乙烯基硅酮分子结构和电子光谱

采用密度泛函B3P86方法在6-311++G(d, p)基组水平上优化得到了沿分子轴方向不同外电场(0-0.04 a.u.)作用下, 甲基乙烯基硅酮分子的基态电子状态、几何结构、电偶极矩和分子总能量. 在优化构型下利用杂化CIS-DFT方法(CIS-B3P86)研究了同样外电场条件下对甲基乙烯基硅酮的激发能和振子强度的影响. 计算结果表明, 分子几何构型与电场大小呈现强烈的依赖关系, 分子偶极矩μ随电场的增加先减小后急剧增大. 电场为零时, 分子总能量为-483.5532137 a.u., 随着电场增加, 能量升高, 在F=0.02 a.u.时达到最大值-483.5393952 a.u., 此后, 继续增大电场系统总能量则开始降低. 激发能随电场增加急剧减小, 表明在电场作用下, 分子易于激发和离解.     

X‐ray photoelectron spectroscopic study of Tencel treated with a cationic β‐cyclodextrin derivative

The interaction and the durability to laundering of a cationic β‐cyclodextrin derivative applied to Tencel were examined by x‐ray photoelectron spectroscopy (XPS). The N1(s) XPS spectra of the cationic β‐cyclodextrin treated substrates revealed the presence of the applied finish on the fibre surface and that the durability of the applied finish to hand‐wash was good. However, the cationic β‐cyclodextrin derivative showed poor durability to the ISO CO6/C2S wash protocol. Copyright © 2009 John Wiley & Sons, Ltd.     

Application of Hadamard transformation to MEKC

The Hadamard transform (HT) technique, which permits the S/N in CE to be improved, was applied to MEKC. Multiple sample injection of fluorescent analytes according to a Hadamard code sequence was performed using an optically gated sample injection technique, in which a sample plug was produced based on photodegradation by irradiation with an intense laser beam. The capillary and reservoirs were filled with a sample solution containing buffer components and SDS as a pseudostationary phase. A preliminary study confirmed that fluorescein ion could be photobleached in the presence of SDS. The optically gated sample injection technique was then applied to multiple sample injection, based on a Hadamard matrix. The S/N in the electropherogram obtained by HT-MEKC was improved substantially compared to that obtained by a single injection method. When the technique was applied to the separation of several amino acids labeled with FITC, the S/N ratio for each amino acid was enhanced, without any evidence of degradation in separation resolution. Moreover, HT-MEKC was applied to the analysis of amino acids contained in a Japanese beverage, resulting in improved S/Ns for the amino acids.     

Electroosmotic flow in channels with step changes in zeta potential and cross section

We consider the effects that step changes in zeta potential and cross section have on electroosmosis in long-and-narrow channels with arbitrary cross-sectional shapes. The Stokes equation of flow is solved analytically utilizing the thin Debye layer approximation to provide effective slip velocities on the channel walls. The effects of channel dimensions, surface potentials, applied pressure drop, and applied voltage are discussed. One anecdotal case, a two-region rectangular channel, is presented to illustrate the solution. The flow in each region is a combination of a uniform electroosmotic flow and a nonuniform pressure-driven flow. The electroosmotic pumping causes the pressure gradient in each region to adjust so that the flow rate is the same in each region and the overall applied pressure drop is met, resulting in convex velocity profiles in some regions and concave velocity profiles in other regions. By appropriate choice of the applied pressure drop, flat velocity profiles may be achieved in one or more regions.     

t,F显著性检验应用中的一个问题

文章就ｔ，Ｆ显著性检验在同一个问题上检验判断的不一致性，提出在对一种分析结果（或测试结果）实施鉴定时，有必要同时进行ｔ，Ｆ的联合检验，而只有当联合检验一同被接受之后，所作用出的判定结论才是完整和可信赖的。     

芯片自由流梯度电场电泳及其应用

尽管在垂直的电场和流体场作用下,采用芯片自由流电泳（μ-FFE）可实现样品的连续微分离和制备,但是由于在运行过程中,存在分析物的区带展宽问题,会直接影响样品的分离效果．在本文中,在施加固定电压的情况下,通过向和分离缓冲液相同的电极缓冲液中添加硫酸钠的方法,在分离腔内形成了梯度电场．通过对罗丹明B和甲基绿混合物的分离发现,在均一电场下,施加400V分离电压,混合物需2min才能完全分离：甲基绿的区带宽度为3．8mm,与罗丹明B的分辨率是3．2．在向电极缓冲液中添加5mmol／L硫酸钠形成的电场梯度下,施加300V的分离电压,两种染料可在10S内完成分离;在20S时,甲基绿的区带宽度被压缩到015mm,检测灵敏度提高了7倍以上;与罗丹明B的分辨率可达到16．2．此外,该方法还被用于牛血清白蛋白的富集．与施加均一电场相比,蛋白质的检测灵敏度得到了显著提高．上述结果表明,通过在μ-FFE中引入梯度电场,可有效提高样品的分辨率、检测灵敏度和分析速度．