Accurate analysis of smoothly modulated AC waveforms applied to the calibration of fluctuating harmonic analyzers

Calibrated harmonic analyzers are required to underpin international regulations regarding harmonic emissions for electrical appliances. A method to accurately analyze waveforms containing smoothly fluctuating harmonics is described. The response of an analyzer to the characterized waveform is considered and a method to calibrate an analyzer is presented.     

Accurate concentration measurements using surface-enhanced Raman and deuterium exchanged dye pairs

Quantitative applications of surface-enhanced resonance Raman scattering (SERRS) are often limited by the reproducibility of SERRS intensities, given the difficulty of controlling analyte-substrate interactions and the associated local field enhancement. As demonstrated here, SERRS from dye molecules even within the same structural class that compete with similar substrates display distinct spectral intensities that are not proportional to analyte concentrations, which limits their use as internal standardization probes and/or for multiplex analysis. Recently, we demonstrated that isotopic variants of rhodamine 6G (R6G), namely R6G-d0 and R6G-d4, can be used for internal standards in SERRS experiments with a linear optical response from picomolar to micromolar concentrations (of total analytes). Here we extend these results by describing a straightforward method for obtaining isotopomeric pairs of other Raman active dyes by hydrogen-deuterium exchange conditions for substitution at electron rich aromatic heterocycles. Most of the known SERRS active probes can be converted into the corresponding isotopomeric molecule by this exchange method, which significantly expands the scope of the isotopic edited internal standard (IEIS) approach. The relative quantification using IEIS enables accurate, reproducible (residual standard deviation +/-2.2%) concentration measurements over a range of 200 pM to 2 muM. These studies enable easy access to a variety of isotopically substituted Raman active dyes and establish the generality of the methodology for quantitative SERRS measurements. For the first time, three rhodamine 6G isotopomers have been created and show distinct Raman spectra, demonstrating the principle of the approach for application as a multiplex technique in biomolecular detection/quantification.     

Growth and characterization of III-N bulk crystals

Hexagonal BN crystals were grown from solution by application of a thermal gradient. The solvent used to dissolve the source was optimized by changing the ratio of components to have the lowest melting point. The investigation of adding a third component demonstrated further reduction of the melting point with BN as an additive. A solution was created with enhanced properties allowing the growth of BN. BN was grown on a PBN seed at T _g = 900 °C and P = 0.2 MPa for approximately 65 h. The BN crystals were found to be embedded in a solvent matrix, as determined by EDS. In addition, GaN crystals were grown in a modified solution at T _g = 800 °C and P = 0.2 MPa. Raman spectroscopy verified wurtzite GaN structure with good crystallinity. The successful growth of BN and GaN from solution suggests this to be a method of choice for growth of the III-Ns, and may prove to be a viable alternative to current costly wafer production techniques.     

Growth and mechanical properties of GeSi bulk crystals

Bulk crystals of Ge_1–xSi _x alloys were grown by the Czochralski technique. Full single crystals were obtained for the alloys of composition 0 < x < 0.15 and 0.9 < x < 1, while single crystal parts near the seeds of ingots provided alloys of intermediate composition. The dislocation velocity and mechanical strength of the GeSi alloys were investigated by the etch pit technique and compressive deformation tests, respectively. In the GeSi alloys of the composition range 0.004 < x < 0.080 the dislocation velocity decreases monotonically with increasing Si content in the temperature range 450–700°C and the stress range 3–24 MPa. In contrast, in the composition range 0.94 < x < 1 the dislocation velocity first increases and then decreases with decreasing Si content in the temperature range 750–850°C and the stress range 3–30 MPa. The velocity of dislocations was determined as functions of stress and temperature. The stress–strain behaviour in the yield region of the GeSi alloys of composition 0 < x < 0.4 is similar to that of Ge at temperatures lower than about 600°C. However, the yield stress becomes temperature-insensitive at high temperatures and increases with increasing Si content. The stress–strain curves of the GeSi alloys of composition 0.94 < x < 1 are similar to those of pure Si at temperatures of 800–1000°C and the yield stress increases with decreasing Si content down to x = 0.94. The yield stress of the GeSi alloys is dependent on the composition, being proportional to x(1 – x). The strengthening mechanism in alloy semiconductors is discussed.     

Comparison of the irreversible thermomagnetic behaviour of some ferro- and ferrimagnetic systems

The magnetic behaviour of two ferromagnetic oxides and two ferrimagnetic oxides (ferrites) are compared to study the effect of magnetocrystalline anisotropy on thermal-history-dependence of magnetization of these ordered magnetic systems. All four compounds show thermomagnetic irreversibility (M _FC >M _ZFC) below a certain temperature,T _irr. The highly anisotropic ferromagnetic oxide, SrRuO₃ and the hard ferrite, SrFe₁₂O₁₉ show sharp peaks belowT _c in theirM _ZFC(T) curves, whereas for the soft ferrite Ni_0.8Zn_0.2Fe₂O₄ and the low anisotropic ferromagnetic oxide La_0.7Ca_0.3MnO₃ only a broad maximum is observed inM _ZFC, when measured in small magnetic fields. The shapes of theM _ZFC(T) curves are inversely-related to the magnitude of the coercivities (H _c) of the compounds in relation to the applied field, and the temperature dependence of H_c.M _FC andM _ZFC are related through the coercivity for all four magnetic systems.     

Accurate measurements of the acoustical physical constants of LiNbO (3) and LiTaO(3) single crystals

The acoustical physical constants (elastic constant, piezoelectric constant, dielectric constant, and density) of commercial surface acoustic wave (SAW)-grade LiNbO(3) and LiTaO(3) single crystals were determined by measuring the bulk acoustic wave velocities, dielectric constants, and densities of many plate specimens prepared from the ingots. The maximum probable error in each constant was examined by considering the dependence of each constant on the measured acoustic velocities. By comparing the measured values of longitudinal velocities that were not used to determine the constants with the calculated values using the previously mentioned constants, we found that the differences between the measured and calculated values were 1 m/s or less for both LiNbO(3) and LiTaO(3) crystals. These results suggest that the acoustical physical constants determined in this paper can give the values of bulk acoustic wave velocities with four significant digits.     

Intensity and phase measurements of nondiffracting beams generated with a magneto-optic spatial light modulator

Nondiffracting beams are of interest for optical metrology applications because the size of the beam does not change as the beam propagates. However, accuracy can be increased if the diameter of the beam is smaller. One technique for accomplishing this is to use the dark axial intensity profile associated with a higher-order nondiffracting Bessel function beam. We generate these higher-order Bessel function beams with a programmable spatial light modulator. We study the intensity patterns and the phase dependence of these nondiffracting beams. In addition, we examine interference effects caused by recording these patterns onto a binary spatial light modulator.     

Magnetization plateaus and thermodynamic properties of a ferrimagnetic Kagome-like nanoparticle under an applied magnetic field

Journal of Materials Science - Magnetic properties of a Kagome-like nanoparticle with a ferromagnetic exchange coupling described by the mixed-spin (5/2, 3/2) Ising model were studied, and unique...     

Thermal diffusivity measurements of foil-shaped materials by vectorial analysis using an AC calorimeter

Measurements of thermal diffusivity of foil-shaped materials have been carried out using a photoirradiation-type AC calorimeter at room temperature. In this method the frequency effect, which is caused by heat loss from the sample to the environment, is readily detected in measurements of both amplitude and phase components of the AC temperature signal, Even though the chopping frequency is appropriate, the two diffusivities calculated from these two components differ from each other, Moreover, the difference between the two values increases when the chopping frequency increases. Simple vectorial calculation with the two components one from the amplitude and the other from the phase- permits the frequency ellect to be determined. The calculated result is the geometric average of the two diffusivities. This analytic method was tested with diamond film and SUS-304 foil. From these we confirmed that the vectorial analytic method gives similar diffusivity values for different frequencies indicating its reliability.Paper presented at the Twelfth Symposium on TherrmophysicaI Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Magnetic susceptibility measurements of LHP and LNP crystals

Ferroelectric single crystals such as lead hydrogen phosphate (LHP) and dihydrated lead nitrate phosphate (LNP) have been derived from the diffusion of lead nitrate into the set gel containing orthophosphoric acid. By employing Faraday’s Gouy balance technique, the magnetic susceptibilities of LHP and LNP have been determined. It has been observed that (i) the gram and molar susceptibilities are independent of magnetic field, (ii)χ _M of LNP materials are greater than that of LHP materials and (iii) the positive values of magnetic susceptibilities suggest that LHP and LNP are paramagnetic materials.     

AC loss measurements of twisted and untwisted BSCCO multifilamentary tapes

AC losses in twisted and untwisted BSCCO multifilamentary superconducting tapes with Ag matrix developed in DAPAS program were measured by an electrical method. Magnetization and transport losses were measured by a pick-up coil and by a voltage taps. Total AC loss during simultaneous application of AC transport current and an AC transverse magnetic field was given by the sum of the magnetization and transport losses measured during this simultaneous application. The magnetization loss without transport current of untwisted and twisted tapes was measured first to evaluate the effect of twisting to decouple filaments. Then, the total AC loss of the twisted tape was measured in transverse magnetic fields with various amplitudes and orientations, while the amplitude of the transport current was fixed. The measured total AC loss in a parallel transverse magnetic field was compared with some theoretical models to study the detailed characteristics of the measured total AC loss of the sample.     

Neutron transmission measurements of zinc and lead single crystals

Neutron transmission measurements of zinc and lead single crystals have been carried out in a neutron wavelength band from 0.03 to 0.55 nm at different orientations of the crystal with regard to the beam direction. The measurements were performed using both time-of-flight and fixed-angle scattering spectrometers installed in front of the ET-RR-1 reactor horizontal channels. It was found that the position of the observed dips in the neutron transmission measurements corresponded to the reflections from the (hkl) planes of the hexagonal zinc single crystal which was cut along the (002) plane, while in the case of lead, the single crystal was cut perpendicular to the (311) plane. The reflectivity from the (002) plane of zinc was determined using both transmission and reflection methods. The maximum reflectivity was found to be 55% when the zinc crystal was orientated at 45° to the beam direction. The wavelength spread of the observed reflectivity curve was found to be in agreement with the calculated one, taking into consideration the spectrometer's resolution and the crystal mosaic spread.     

Propagation of longitudinal and bulk waves in shock-loaded transversally isotropic single crystals

The paper is present 3D numerical simulation data on elastoplastic deformation in auxetic single crystals with account of anisotropic pressure. The use of anisotropic pressure allows us to demonstrate the absence of shock wave splitting into an elastic precursor and a plastic wave in a Zn single crystal in the loading direction [0001]. This effect in Zn single crystals is observed in full-scale experiments at any loading rate in the [0001] direction. It is shown that anisotropic pressure should be entered into mathematical models of materials whose elastic properties are characterised by five and more independent elastic constants and hence by bulk compression anisotropy. The use of isotropic pressure in simulating the deformation of such materials leads to nonphysical results.     

Measurement of diffusion in small 5A zeolite crystals using a wall-coated capillary column

A novel method of measuring diffusion in small (micron-sized) zeolite crystals has been developed based on measurement of the chromatographic response for a capillary column, the internal surface of which is coated with an incomplete monolayer of the zeolite crystals. Special techniques are needed to prepare such a column; in the commercially available wall-coated zeolite columns the surface coverage of the zeolite crystals is too low to permit reliable diffusion measurements. A theoretical expression giving the HETP (height equivalent to a theoretical plate) as a function of gas velocity, based on a modification of Golay's analysis for a liquid-coated capillary column, has been derived. As in conventional chromatography, the HETP is governed by the sum of the contributions from axial dispersion and mass transfer resistance, but, in contrast to conventional chromatography, the axial dispersion contribution for a wall-coated column can be confidently estimated a priori. The relative importance of intercrystalline and external diffusion resistances depends inter alia on the ratio of tube to particle diameters. The advantage of the technique arises because it is possible to make reliable measurements of the intracrystalline diffusivity, even for relatively fast systems, by using a sufficiently small tube diameter. The validity of the method is tested by measuring the diffusion of n-butane in small commercial 5A zeolite crystals. In contrast to other macroscopic techniques which, for this system, generally yield rather low apparent diffusivity values, the values we obtain are close to the self-diffusivities obtained from p.f.g. n.m.r. measurements and the macroscopically measured transport diffusivities for large laboratory synthesized crystals.     

Melt growth and characterization of Mg2Si bulk crystals

We have grown Mg₂Si bulk crystals by the vertical Bridgman method using a high-purity Mg (6N-up) source. The grown crystals were single-phase Mg₂Si and had well-developed grains (1-5 mm³). Laue observations and SEM-EDX observations confirmed that crystalline quality in the grains was single crystal with stoichiometric composition. Electron concentration of the single crystalline specimens grown from 6N-up-Mg was 4.0 × 10¹⁵ cm^− 3 at room temperature (RT). This value is more than one order of magnitude lower than that of specimens grown from 4N-Mg [(5-7) × 10¹⁶ cm^− 3]. The Hall mobility of 14,500 cm²/Vs was observed at 45 K in the crystals grown from 6N-up-Mg. We also found that Al impurity plays an important role in the crystals grown from a low-purity Mg source. From the optical absorption measurement, we estimated that the indirect energy gap was about 0.66 eV at 300 K and about 0.74 eV at 4 K.     

Numerical simulations of electromagnetic behavior and AC loss in rectangular bulk superconductor with an elliptical flaw under AC magnetic fields

This paper presents a finite element model based on the H-formulation to solve the electromagnetic behavior and AC loss in rectangular bulk superconductor with an elliptical flaw in AC external field condition. Both the interior flaw and the edge flaw are considered. A modified E–J power law which is valid for an arbitrary current density range is adopted in order to predict the strong local enhancement of the current density in the vicinity of the flaw tip. The results for the usual E–J power law are calculated for comparison as well. The simulation results show that the existence of the flaw significantly blocks the flow of the induced current and forces the current to redistribute around it. Meanwhile, the strong local enhancement of the current density is observed in the vicinity of the flaw tip. Furthermore, the influences of the size and position of the flaw on the local enhancement of the current density in the vicinity of the flaw tip are investigated. In addition, it is found that the influence of the flaw on the AC loss of the sample is slight for both cases of the interior flaw and the edge flaw.     

Frequency-domain sensitivity analysis for small imaging domains using the equation of radiative transfer

Optical tomography of small imaging domains holds great promise as the signal-to-noise ratio is usually high, and the achievable spatial resolution is much better than in large imaging domains. Emerging applications range from the imaging of joint diseases in human fingers to monitoring tumor growth or brain activity in small animals. In these cases, the diameter of the tissue under investigation is typically smaller than 3 cm, and the optical path length is only a few scattering mean-free paths. It is well known that under these conditions the widely applied diffusion approximation to the equation of radiative transfer (ERT) is of limited applicability. To accurately model light propagation in these small domains, the ERT has to be solved directly. We use the frequency-domain ERT to perform a sensitivity study for small imaging domains. We found optimal source-modulation frequencies for which variations in optical properties, size, and location of a tissue inhomogeneity lead to maximal changes in the amplitude and phase of the measured signal. These results will be useful in the design of experiments and optical tomographic imaging systems that probe small tissue volumes.     

AC susceptibilities of conducting cylinders and their applications in electromagnetic measurements

We present accurate calculations and tabulations of the volume and midplane-averaged complex ac susceptibilities of nonmagnetic conducting cylinders with aspect ratio ranging from 0.1 to 10 as functions of a dimensionless frequency. We discuss their features in terms of eddy-current demagnetizing effect. We explain their applications in high-sensitivity, low-temperature, and high-field ac susceptometers and contactless conductivity measurements.