The Mo−OH proton of the low-pH form of sulfite oxidase: Comparison of the hyperfine interactions obtained from pulsed ENDOR, CW-EPR and ESEEM measurements

Pulsed electron nuclear double resonance (ENDOR) spectra have been obtained for the exchangeable Mo-OH proton of the low-pH form of native chicken liver sulfite oxidase (SO) and recombinant human SO for the first time. The spectra of the two enzymes are very similar, indicating a similar binding geometry of the hydroxyl ligand to the Mo center. The isotropic hyperfine interaction (hfi) constant for the proton of the OH ligand in both enzymes is about 26 MHz. The anisotropic components of the hfi obtained from the pulsed ENDOR spectra are about 1.6–1.8 times larger than those obtained by continuous-wave electron paramagnetic resonance and electron spin echo envelope modulation. These hfi differences are explained by a rotational disorder of the Mo-OH group. A similar rotational disorder of the coordinated exchangeable ligand has been found previously for the high-pH and phosphate-inhibited forms of SO.     

Comparison of cell membrane water permeability in monolayers and suspensions

We previously measured the membrane water permeability of monolayers and suspensions of MIN6 mouse insulinoma cells at room temperature, and found that water transport was faster in monolayers. Here, we compare water transport kinetics in monolayers and suspensions over a range of temperatures for two different cell types, MIN6 cells and bovine pulmonary artery endothelial cells (BPAEC). At room temperature the results for BPAEC and MIN6 cells were similar, with approximately 2-fold faster water transport in monolayers than suspensions. The activation energy for water transport (Ea) was estimated from Arrhenius plots of the water permeability data. The values of Ea for monolayers and suspensions of MIN6 cells were not significantly different. However, the activation energy was significantly lower for BPAEC monolayers (Ea = 49 +/- 2 kJ per mol) than suspensions (Ea = 70 +/- 4 kJ per mol). Predictions of water transport during cryopreservation revealed substantial differences in supercooling between monolayers and suspensions.     

A CW-EPR and ESEEM spectroscopic study of the dithiadiazolyl radicals p-XC6F4CNSSN (X = CN, Br)

Two dithiadiazolyl radicals, p-NCC₆F₄CNSSN and p-BrC₆F₄CNSSN, have recently been found to be paramagnetic in the solid state. While the β-phase of the first one exhibits spontaneous magnetization below 36 K, the second one shows a paramagnetic character in the solid state. The spin density distribution in these radicals is examined through continuous-wave electron paramagnetic resonance and electron spin echo envelope modulation spectroscopies. Hyperfine correlation sublevel spectroscopy provides information about the interaction of the unpaired spin with F and N nuclei. A signal coming from the interaction with Br nucleus is also detected. The superhyperfme coupling constants of the unpaired electron with the magnetic nuclei are obtained and values of the corresponding spin densities, ?_s and ?_σ - ?_π, can be estimated in the isolated radicals. Spin density distribution has also been calculated in both molecules with density functional theory, being in excellent agreement with those determined from the spectra. The spin density is mainly concentrated in the dithiadiazolyl ring, but some spin density is observed on the fluorinated aromatic rings. They also provide a strong basis to understand the differences of the magnetic behavior of both molecules in terms of their respective packing in the solid state.     

Accurate determination of elastic parameters for multicomponent membranes

Heterogeneities in the cell membrane due to coexisting lipid phases have been conjectured to play a major functional role in cell signaling and membrane trafficking. Thereby the material properties of multiphase systems, such as the line tension and the bending moduli, are crucially involved in the kinetics and the asymptotic behavior of phase separation. In this Letter we present a combined analytical and experimental approach to determine the properties of phase-separated vesicle systems. First we develop an analytical model for the vesicle shape of weakly budded biphasic vesicles. Subsequently experimental data on vesicle shape and membrane fluctuations are taken and compared to the model. The parameters obtained set limits for the size and stability of nanodomains in the plasma membrane of living cells.     

A novel technique for measurement of core loss in low permeability materials

A survey of existing techniques for measuring core loss in magnetic materials is presented. It is shown that the most challenging combination is a low permeability material at low measurement frequency. Such materials have application in components of power converters, and thus are of considerable technological significance. Measurement difficulties stem from losses in the windings employed, which are difficult to disentangle from loss in the core, as well as the stringent requirements on phase accuracy of measurement instruments. Another practical problem is the large power capacity required of the drive source to achieve significant induction levels. A new resonant measurement setup, which we call the “virtual impedance” technique, is proposed as a solution to these problems. Its utility is demonstrated with measurements of a commercial composite core with permeability 14μ₀ whose low-core loss defeats conventional methods of measurement.     

Infrared technique for simultaneous determination of temperature and emissivity

This paper presents, in the context of materials dynamic behaviour study, a method for simultaneous measurement of the temperature and emissivity of a solid’s surface, by the use of infrared radiation. In contrast to existing methods, this method has no need for a pre-measurement of the surface emissivity. The emissivity and the temperature are measured simultaneously, by detecting the variations of emitted radiation and infrared radiation reflecting on the surface, at two different spectral zones. In this way, the accuracy of the measured temperature is greatly improved in cases were the surface optical properties vary during the measurement. Several experiments were carried out in order to complete the theoretical foundation of the method and to outline its accuracy and some of its limitations. There are various industrial applications of this method, for example the control of the temperature of the mechanical parts during work machining. One of them may be the measurement of the temperature of a sample during mechanical testing. An application of the method is proposed, that is easy to employ with non-sophisticated infrared and optical components. The results confirm the accuracy of the proposed method with an order of 3% of precision for temperature determination.     

Enhancement of hydrogen gas permeability in electrically aligned MWCNT-PMMA composite membranes

The multi-walled carbon nanotube (MWCNT) dispersed polymethylmethacrylate (PMMA) composite membranes have been prepared for hydrogen gas permeation application. Composite membranes are characterized by Raman spectroscopy, optical microscopy, X-ray diffraction, electrical measurements and gas permeability measurements. The effect of electric field alignment of MWCNT in PMMA matrix on gas permeation has been studied for hydrogen gas. The permeability measurements indicated that the electrically aligned MWCNT in PMMA has shown almost 2 times higher permeability for hydrogen gas as compare to randomly dispersed MWCNT in PMMA. The enhancement in permeability is explained on the basis of well aligned easy channel provided by MWCNT in electrically aligned sample. The effect of thickness of membrane on the gas permeability also studied and thickness of about 30 μm found to be optimum thickness for fast hydrogen gas permeates.     

Development and testing of a CW-EPR apparatus for imaging of short-lifetime nitroxyl radicals in mouse head

This article describes a method for reducing the acquisition time in three-dimensional (3D) continuous-wave electron paramagnetic resonance (CW-EPR) imaging. To visualize nitroxyl spin probes, which have a short lifetime in living organisms, the acquisition time for a data set of spectral projections should be shorter than the lifetime of the spin probes. To decrease the total time required for data acquisition, the duration of magnetic field scanning was reduced to 0.5 s. Moreover, the number of projections was decreased by using the concept of a uniform distribution. To demonstrate this faster data acquisition, two kinds of nitroxyl radicals with different decay rates were measured in mice. 3D EPR imaging of 4-hydroxy-2,2,6,6-tetramethylpiperidine-d₁₇-1-¹⁵N-1-oxyl in mouse head was successfully carried out. 3D EPR imaging of nitroxyl spin probes with a half-life of a few minutes was achieved for the first time in live animals.     

Study of couple stresses and wall permeability effects on the flow in permeable membranes

This study focused on investigating wall permeability, and couple stresses effects on the fluid flow between two permeable membranes. These flows are encountered in a variety of industrial and applied biological processes, particularly in the fluid filtration process through dialyzer membranes. Darcy’s law is employed to define the fluid suction and injection via surface of the membrane. Fluid motion is assumed to be steady and Stokesian, where the flow Reynolds number is low. The exact solution for the fluid flow field is obtained in conjunction with the lubrication approximation. Explicit expressions are derived for some useful quantities of flow interest. A significant change in the flow field is noticed for the presented non-Newtonian fluid model. Graphical results show that the flow field has prominent deviations when the inlet pressure, membrane permeability, and the couple stress parameters are changed. In order to validate results, numerical values of the filtration constant and the average pressure drop for a dialyzer membrane are computed. A comparison of the derived results with existing data reveals a good agreement with experimental and empirical results. The presented results are new and can be reduced to existing results in the literature for specified values of the couple stress parameters.     

Speed-dependent Voigt profile for water vapor in infrared remote sensing applications

The Voigt profile does not provide a sufficiently accurate representation of the line shape for air-broadened H₂O vapor over a significant range of conditions commonly encountered in atmospheric remote sensing. A speed-dependent Voigt profile yields much improved residuals in the analysis of water from infrared measurements collected by the atmospheric chemistry experiment (ACE), a satellite mission for remote sensing of the Earth's atmosphere. An analytical expression is presented for the rapid calculation of the speed-dependent Voigt profile.     

浅海声速剖面的匹配波束反演方法

为了快速反演获得浅海声速剖面,利用匹配波束构造了反演代价函数,在此基础上研究了浅海声速剖面的匹配波束反演方法(MBI)。并运用东中国海的实验数据进行实际反演,验证了MBI的可行性和鲁棒性。利用垂直线列阵接收的29个不同位置的爆炸声信号进行了声速剖面反演,MBI反演的结果与实验中直接测量的声速剖面一致,且反演声速剖面的均方根误差小于2 m/s。研究结果表明,MBI比常规匹配场反演(MFI)获得浅海声速剖面更快速、更准确,并且对底质参数的失配具有较高的鲁棒性。     

Experimental determination technique for magnetic anisotropy of individual nanowires

We present an experimental technique to determine the magnetic anisotropy of ferromagnetic nanowires. In the technique, the magnetization state is monitored by measuring the anisotropic magnetoresistance with rotating the external magnetic field. The measured magnetoresistance curves exhibit basically the same curves typically appeared in the torque magnetometric measurements, which are then readily analyzed based on the Stoner–Wohlfarth theory with a single fitting parameter – the magnetic anisotropy. By applying the present technique to Permalloy nanowires, it is shown that the shape anisotropy in real nanowires is significantly influenced by the edge roughness.     

Interferometric technique for the determination of thermal nonlinearities in semiconductor glasses

An experimental method for the determination of thermal nonlinearities of semiconductor doped glasses induced by cw laser radiation is presented. An estimation of the intensity dependent refractive index is given, at steady state conditions, which is in good agreement with experimental data reported in the literature for similar materials.     

Determination of the permittivity,permeability and conductivity profile for the ionosphere using an inverse scattering approach

A method for reconstructing the conductivity of the ionosphere together with the permittivity and conductivity as a function of altitude is discussed. This method is derived by solving the inverse scattering problem for an inhomogeneous dispersive plasma with a layered structure. Two ionospheric models are considered for this purpose, one at the equator and one at the polar caps. The experimental data required are clearly defined and methods of generating such data are discussed.     

Experimental determination of human erythrocyte membrane permeability coefficients for a series of amides

Erythrocyte membrane permeability coefficients have been determined for a series of amides by a method based on the physical and mathematical modelling of hypotonic haemolysis process. The results show that penetration of the substances occurs by two alternative ways through aqueous pores formed by proteins and by the direct dissolving of the molecules in membrane lipids. This conclusion can be confirmed by the correlation analysis between permeability coefficients of native erythrocytes and those pre-incubated with the monosodium salt of p-chloromercuribenzenesulfonic acid (pCMBS), and the partition coefficients of the substances in hydrophilic-hydrophobic phases. Penetration of substances through hydrophilic channels is limited by the sterical factor and diameter in particular. Permeability coefficients for erythrocytes pre-incubated with pCMBS increase in an accordance with the rise of the partition coefficients with correlation coefficient of 0.94, thereby indicating a lipid route of permeation of molecules through erythrocyte membranes.     

Application of fission track detection technique for determination of uranium in liquids

A high sensitive (10⁻⁴ ppm) fission track detection technique for determination of uranium in liquids was developed. The technique was applied for the measurement of uranium concentration in extraction phosphoric acid and phosphorus fertilizer, viz., ammophous.     

Alpha track profile study and range determination in PADC plastic detectors

An extensive study of alpha particle track profile has been carried out in PADC plastic detectors. Track profile geometry and its parameters have been studied. Various values of alpha energies were used, and the etch rate ratio (V) was measured as a function of the residual range (RR) along the alpha particle track. A mathematical formula between V and RR was established. Also in this work, alpha particle ranges in plastic foils have been measured at various energies using two methods; namely the track profile technique (TPT) and the over etched track diameter method. A comparison between the measured ranges and calculated ones is presented, and a good agreement has been found.