Out Of Phase Component Research Articles

The effect of cation disorder on magnetic properties of new double perovskites La2NixCo1-xMnO6 (x = 0.2–0.8)

Solid solutions of new double perovskite oxides La2NixCo1-xMnO6 (x = 0.2, 0.25, 0.5, 0.75, 0.8) were synthesized by solid-state reaction method. The X-ray powder diffraction data show that all the compounds crystallize in the monoclinic structure with space group P21/n at room temperature. The elementary composition of the powders was determined by the electron Probe Microanalysis. Raman and IR spectra show strong bands at (520, 650 cm−1) and (426, 600 cm−1) respectively, attributed to the stretching vibration of Ni/Co-O and Mn-O bonds in the structure. The magnetic studies for all the compounds have been performed in both DC and AC magnetic fields in the temperature range from 2 to 300 K. All samples exhibit a main paramagnetic to ferromagnetic (PM-FM) transition between 232 K and 260 K, and their Curie temperature increases rapidly with increasing x values. Three samples with x = 0.2, 0.25 and 0.5 respectively display also a secondary PM-FM transition between 200 K and 208 K. The thermal variation of out of phase component of AC susceptibility presents also frequency-dependent transitions between 65 K and 110 K unfolding the existence of super-paramagnetic mono-domains in all samples. The band gap energy has been calculated and revealing semiconductor behavior for all samples.

Geophysical and geochemical investigation for structures favorable to uranium mineralization in Dhofar region, Sultanate of Oman

The very low frequency electromagnetic (VLF-EM) method is a rapid and reliable geophysical method was used in the investigation for uranium bearing structures in the Proterozoic basement of the Dhofar region that may be a potential source and trap for uranium and associated minerals in Sultanate of Oman. Accordingly, the in-phase and out of phase components of VLF-EM field along 11 traverses were recorded at two different transmitter frequencies viz. 16 kHz and 16.4 kHz at an approximate line interval of 20 m with a measurement interval of 10 m. These measured components were subjected to Fraser and Karous-Hjelt filtering in order to decipher the nature and depth to the sub-surface conductor. The Fraser filtered in-phase VLF-EM components yield a strong amplitude almost over the top of the conductor. On the other hand, the Hjelt filtered responses yield the depth to the source in the range 10–80 m. Spectral analysis of selected a few traverses result the depth to source in the range 31–39 m. Analytical signal approach of total magnetic field of line-I substantiates this depth. The peaks of Fraser filtered stacked profiles delineate approximately the trend of the sub-surface fault which mimic the trend inferred from the combined interpretation of VLF-EM and magnetic anomalies. The results of Fraser and Karous-Hjelt filter output suggest a mineralized conductive sub-surface fault aligned along NW-SE. It may be noted that the random sampling of gamma ray spectrometer has recorded a maximum uranium concentration of up to 30–40 ppm prior to VLF-EM survey.

AC magnetic response of superconducting single crystals exhibiting a second peak on the DC magnetization curves

The strong modulation of the AC magnetic response in the magnetic field-temperature region of the DC magnetization peak effect (PE) occurring just below the DC irreversibility line (IL) of weakly pinned superconducting single crystals is well known. However, it is not yet clear if the AC magnetic signal registered at usual frequencies and amplitudes is significantly affected by the presence of the second magnetization peak (SMP) in the DC magnetic hysteresis curves, since the SMP appears in specimens with stronger pinning and is located well below the IL. We investigated the AC magnetic response of several La2−xSrxCuO4 and 122-type pnictide superconducting single crystals exhibiting a pronounced DC SMP. It was found that in the case of small demagnetization effects, the AC magnetic signal across the SMP remains in the linear regime, with no detectable distortions in the SMP range (within the high sensitivity of a Physical Property Measurement System). This indicates reduced values of the Campbell penetration depth compared with the London magnetic penetration depth. A clearly nonmonotonic, SMP-related variation has only been obtained for the DC field dependence of the out of phase component of the AC magnetic moment in the nonlinear regime. The nonlinear AC Bean regime far below the IL has been attained in the conditions of enhanced demagnetization effects (plate-like specimens in perpendicular magnetic fields).

Novel load emulation technique for performance evaluation of isolated solar PV system under varying load conditions

Solar Photo Voltaic (SPV) sources are widely used in present scenario of energy crisis for various applications including grid connected PV plants and grid isolated standalone applications. The performance of solar PV system is highly dependent upon the operating conditions of source and loads especially in standalone applications. The effect on various types of loads on standalone system can be easily analyzed at design stage and testing stage by using load emulation technique, where a virtual load is used to replace actual load, giving more flexibility and accuracy to loading conditions. Here a novel load emulator model is presented which can provide accurate variation in load power factor and THD compared to existing models. The converter decouples the current in to in phase and out of phase components and the in phase component can be regenerated. The model is simulated using MATLABTM simulation and the results are validated by comparing with experimental results obtained by loading SPV inverter with actual load. Hence the proposed load emulator is very useful in design and development of application specific solar PV systems and also for performance analysis of such systems based on various standards.

Dielectric and specific heat relaxations in vapor deposited glycerol.

Recently [S. Capponi, S. Napolitano, and M. Wübbenhorst, Nat. Commun. 3, 1233 (2012)], vapor deposited glasses of glycerol have been found to recover their super-cooled liquid state via a metastable, ordered liquid (MROL) state characterized by a tremendously enhanced dielectric strength along with a slow-down of the relaxation rate of the structural relaxation. To study the calorimetric signature of this phenomenon, we have implemented a chip-based, differential AC calorimeter in an organic molecular beam deposition setup, which allows the simultaneous measurement of dielectric relaxations via interdigitated comb electrodes and specific heat relaxation spectra during deposition and as function of the temperature. Heating of the as-deposited glass just above the bulk Tg and subsequent cooling/reheating revealed a step-wise increase in cp by in total 9%, indicating unambiguously that glycerol, through slow vapour deposition, forms a thermodynamically stable glass, which has a specific heat as low as that of crystalline glycerol. Moreover, these glasses were found to show excellent kinetic stability as well as evidenced by both a high onset-temperature and quasi-isothermal recovery measurements at -75 °C. The second goal of the study was to elucidate the impact of the MROL state on the specific heat and its relaxation to the super-cooled state. Conversion of "MROL glycerol" to its "normal" (ordinary liquid, OL) state revealed a second, small (∼2%) increase of the glassy cp, a little gain (<10%) in the relaxed specific heat, and no signs of deviations of τcal from that of normal "bulk" glycerol. These findings altogether suggest that the MROL state in glycerol comprises largely bulk-type glycerol that coexist with a minor volume fraction (<10%) of PVD-induced structural anomalies with a crystal-like calorimetric signature. Based on the new calorimetric findings, we have proposed a new physical picture that assumes the existence of rigid polar clusters (RPCs) and conclusively explains the extraordinary high kinetic stability of the MROL state, its specific calorimetric signature, the enhanced strength, and apparent slow-down of the dielectric α-relaxation. In this new picture, the incredibly slow and strengthened dielectric response is ascribed to driven rotational diffusion of whole RPCs, a mechanism that perfectly couples to the relaxation time of the "normal" glycerol fraction. First considerations based on the strength and the retardation of the dielectric RPCs' response yield independently a size estimate for the RPCs in the order of 4-5 nm. Finally, we have discussed possible crystallisation and reorganisation effects, which give rise to pronounced out-of phase components of the specific heat at higher temperatures.

Structural, magnetic and electronic properties on the Li-doped manganites

We present results of a comprehensive investigation of the structural, frequency dependent ac susceptibility, dc magnetization, magnetoresistance and thermoelectric power measurements on polycrystalline samples of La1−xLixMnO3 (0.05≤x≤0.30). All samples undergo ferromagnetic to paramagnetic transition and metal to semiconductor transition. A cusp in the zero field-cooled in dc magnetization and a frequency-dependent peak in the ac susceptibility reveal the glassy behaviors. The out of phase component of the ac susceptibility shows frequency-dependent peaks below the Curie temperature (indicative of glassy behavior) which have previously been interpreted in terms of freezing of clusters. The grain boundaries play a dominant role in the conduction process. The framework of the magnon and phonon drag concept analyzed thermoelectric power data at low temperature, while small polaron conduction mechanism explained thermoelectric power data at high temperature. It has been found that the percolation threshold sample is x=0.10, so the author’s point of view refers to make spot on this sample in the future works.

Design and Implementation Analysis of OSD based Audio Crosstalk Cancellation with Multi-Channel Inputs on DSP Processors

To overcome the basic system inversion problems in conventional crosstalk cancellation systems, the three channel Optimum Source Distribution (OSD) was developed by Takashi et al., that provides balance between in-phase and out of phase components. The main difficulty in this system is real-time implementation of cross talk cancellation filters on DSP platforms, particularly when filter lengths are very long with system operates on multichannel inputs. This paper discusses the implementation complexities and proposes an efficient approach to reduce the power consumption. It also discusses efficient usage of available processor memory. By utilizing the processor resources and existing frequency domain techniques, this approach would be one of best methods for long filters. The mathematical model, with efficient design for floating point DSP processors, clearly explains the optimization methods at algorithmic and instruction levels. The computational complexity of the proposed method was measured for various multi-channel input sources and the comparison was shown. The results indicate that the proposed method provides efficient computations than existing methods. Keywords: Convolution, Crosstalk Cancellation, Optimal Source Distribution, Overlap Save Method, Uniform Partitioned Convolution

Single and multi-walled carbon nanotubes doped (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors

Carbon nanotubes (CNTs) added polycrystalline (CNT)y(Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (y=0, 0.25%, 1.0% and 7%) superconductor samples have been synthesized at normal pressure. The X-ray diffraction (XRD) studies of these samples have shown an orthorhombic crystal structure following PMMM space group. The added CNTs have been found to diffuse at the inter-grain sites and act as cementing material. SEM images show that CNTs are forming an electrical-network between grains. These observations suggest that the CNT addition to the CuTl-1223 compounds improve the electrical connection between superconducting grains which in turn increase the Jc of the final compound. The room temperature resistivity of as-prepared samples decreases with the addition of CNT. The onset temperature of superconductivity [Tc(onset)] and zero resistivity critical temperature [Tc(R=0)] are found to decrease with the CNT additions. Except for the samples with CNT additions of 0.25%, the density [mass/volume] of final compound after CNT addition is decreased. Magnitude of diamagnetism is also suppressed with the addition of CNT which suggests that some of carbon atoms diffuse into the unit cells at the intra-grain sites. The Tc(R=0) becomes quite stable after post-annealing in oxygen atmosphere; the Tc(R=0) varies between 98 and 96K in polycrystalline (CNT)y(Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (y=0, 0.25%, 1.0% and 7%) samples. The out of phase component of magnetic susceptibility observed as a broad peak in the as-prepared samples, is transformed to a sharp peaks after post-annealing of the samples in oxygen atmosphere. This shows that oxygen diffusion converts the inter-grain material to respective oxides and carbonates that increase the surface areas of the current flow around inter-grain loops that reduce the hysteresis losses. The electron-microscopy of these samples has shown that inter-grain voids population is suppressed with the addition of CNTs. FTIR absorption measurements of (CNT)y(Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ (y=0, 0.25%, 1.0% and 7%) samples have shown apical and planar oxygen modes at their usual positions.

Magnetic and electrical transport properties of La 0.5A 0.5CoO 3 nanoparticles (A = Sr, Ca, and Ba)

We have investigated the effect of particle size on the electrical transport and magnetic properties of La 0.5A 0.5CoO 3 (A = Sr, Ca, and Ba) nanoparticles synthesized by sol–gel technique. A size-induced metal to insulator transition is observed in the resistivity behaviour of Sr- and Ba-doped samples as the dimension changes from higher to lower ones. The magnetoresistance exhibits almost linear behaviour throughout the studied field range. The zero-field-cooled (ZFC) and field-cooled (FC) magnetizations display a broad paramagnetic to ferromagnetic transition at T C with a large magnetic irreversibility. The magnetization results indicate that Co 3+ ions are in the intermediate spin state but Co 4+ ions stay in a mixture of intermediate and high spin states. The observed frequency dependent shoulder in the in-phase and the peak in the out of phase component of the ac susceptibility indicate the glassy nature of the samples. The analysis of the ac magnetization results suggests that the magnetic behaviour is consistent with the cluster glass model.

Properties of thermally activated flux motion in MTG-GdBCO measured by AC susceptibility

Thermally activated flux motion in melt texture growth Gd-Ba-Cu-O bulk has been studied by ac susceptibility measurements. The irreversibility line Birr(T) and the intrinsic pinning energy U(T, B) of the bulk have been extrapolated from the measurements, which can be written as Birr(T) = BO(1-T/Tc)n where 80T < BO < 98T and 1.4 < n < 1.48, and U(T,B)=U0(1−t)1.5B−0.8 where t is the reduced temperature T/Tc and B is magnetic field, respectively. Also experiments reveal that peak temperature Tp of the out of phase component χ′′ max(T) shifts towards low temperature region with the decreasing of the ac field. All these results suggest that the thermally activated flux motion process might be based on the Bean's critical state model, rather than thermally assisted flux-flow (TAFF) process.

On the numerical modelling of VLF chorus dynamical spectra

Abstract. This paper presents a study of the use of a one-dimensional Vlasov Hybrid Simulation (VHS) computer code to simulate the dynamical spectra (i.e. frequency versus time spectrograms) of ELF/VLF chorus signals (from ~a fraction to ~10 kHz). Recently excellent measurements of chorus have been made in the source region close to the geomagnetic equator aboard the four spacecraft Cluster mission. Using Cluster data for wave amplitude, which is up to 300 pT, local gyrofrequency, cold plasma density, and L-shell, observed chorus signals are reproduced with remarkable fidelity and, in particular, sweep rates in the range 1–10 kHz result as observed. Further, we find that the sweep rate is a falling function of increasing cold plasma density, again in accord with observations. Finally, we have satisfactorily simulated the rather rare falling frequency elements of chorus which are sometimes observed aboard Cluster in the generation region. For both rising and falling chorus we have presented detailed structural analyses of the generation regions. The main contributor to the frequency sweep rate is primarily the establishment of wave number/frequency gradients across the generation region by the out of phase component of the resonant particle current. The secondary contributor is the shortening of the wavelength of resonant particle current relative to that of the wave field. In view of the close agreement between observation and simulation, we conclude that nonlinear electron cyclotron resonance is indeed the mechanism underlying the generation of chorus signals just outside the plasmasphere.

The role of dipolar interaction in the quantitative determination of particulate magnetic carriers in biological tissues

The use of magnetic ac susceptibility measurements of biological tissues in the quantitative determination of their particulate magnetic carrier content has been investigated. In a first step, an ad hoc series of agar dilutions of the superparamagnetic contrast agent Endorem®, used as an example of magnetic carrier, has been characterized to determine the influence of the dipolar interaction. With this result in hand, the quantitative determination of the content of a magnetic carrier in the ex vivo liver and spleen tissues of rats, to which the same compound was previously administered, has been accomplished. It is shown that, by careful interpretation of the temperature dependent out-of-phase susceptibility profiles in the cryogenic range, it is possible to discern between the magnetic contribution of the carrier and that of biomineral iron, being able to detect magnetic carrier iron concentrations of the order of 1 µg Fe g−1 dry tissue. At the usual dosages in humans, necessarily small to avoid toxicity, the amount of magnetic carrier in terms of elemental iron is small compared to physiological iron. The choice of their most salient property, that is, the magnetic moment, therefore makes the quantification possible even in such a minority proportion. By analysing the magnetic dynamics, through a method that just considers the in-phase and the out-of phase components of the susceptibility at only one frequency, it has been possible to decouple the carrier concentration from eventual local aggregations, opening the possibility of investigating the degree of particle clustering at a larger observation scale compared with transmission electron microscopy, and independently of physiological iron.

The reduced weak links in Cu 0.5Tl 0.5Ba 2Ca 4− xMg xCu 5O 14− δ ( x = 1, 2 and 3) superconductors

The weak links in Cu 0.5Tl 0.5Ba 2Ca 4− x Mg x Cu 5O 14− δ ( x = 1, 2 and 3) superconductors have been reduced by carrying out post-annealing of samples in the air, oxygen and nitrogen atmospheres. The weak link behavior is studied from the width and peak temperature ( T P) of out of phase component of magnetic susceptibility ( χ″). A broad χ″ magnetic transition associated with a lower T P a finger print of the weak links in oxide superconductors, was observed in the as-prepared samples. After post-annealing the samples in the air, oxygen and nitrogen atmospheres this transition is changed to a sharp χ″ peak and the T P is shifted to higher temperatures; which is an evidence of strong intergrain coupling. These effects are most prominently observed in oxygen post-annealed samples. The post-annealing in oxygen possibly promotes oxygen intake to the intergrain sites resulting into oxides of respective elements appearing at the termination ends of the crystals, i.e. grain boundaries. The formation of these oxides at the grain boundaries possibly provides large surface area to the shielding currents, better intergrain coupling, a sharp out of phase component of magnetic susceptibility ( χ″) and higher quantity of diamagnetism.

Mimicking a squeezed-bath interaction: Quantum-reservoir engineering with atoms

The interaction of an atomic two-level system and a squeezed vacuum leads to interesting novel effects in atomic dynamics, including line narrowing in resonance fluorescence and absorption spectra, and a suppressed (enhanced) decay of the in-phase and out-of phase component of the atomic polarization. On the experimental side these predictions have so far eluded observation, essentially due to the difficulty of embedding atoms in a 4 pi squeezed vacuum. In this paper we show how to ``engineer'' a squeezed-bath-type interaction for an effective two-level system. In the simplest example, our two-level atom is represented by the two ground levels of an atom with angular momentum J=1/2 -> J=1/2 transition (a four level system) which is driven by (weak) laser fields and coupled to the vacuum reservoir of radiation modes. Interference between the spontaneous emission channels in optical pumping leads to a squeezed bath type coupling, and thus to symmetry breaking of decay on the Bloch sphere. With this system it should be possible to observe the effects predicted in the context of squeezed bath - atom interactions. The laser parameters allow one to choose properties of the squeezed bath interaction, such as the (effective) photon number expectation number N and the squeezing phase phi. We present results of a detailed analytical and numerical study.

Anodic Oxide Growth on Tantalum with AC + DC Fields: I . Experimental Procedures and Results

The small signal ac response of the ionic conductivity growth process was described using the ionic admittivity defined as the (complex) ratio of the ac components of ionic current density and field since, unlike the ratio of current and voltage (admittance), this gives results independent of film thickness. Ideally constant ac and dc components of field were approximated by applying a ramp plus an ac voltage increasing with the average film thickness. Growth due to the ac ionic current produces an out of phase component of thickness giving a series capacitance effect. The measured current density includes the electric displacement current density. When corrected for these effects, plots of the real vs. the imaginary part of the ionic admittivity at a given dc current density were well represented as arcs of circles with centers above the real axis. The ionic admittivity could thus be described using , where is the angular frequency (ω) corresponding to the maximum imaginary part and the central angle subtended by the arc. was not far from inversely proportional to the dc ionic current density independent of temperature.

Superconductivity in the series La 3Ba 3Ca xCu 6+xO y, 0≤ x≤3, an oxygen deficient tetragonal triple perovskite structure

The system La 3Ba 3Ca x Cu 6+ x O y was chosen for a study as a system on high temperature superconductors. The system retains its tetragonal triple layer perovskite structure over the range 0≤ x≤3. The transition temperature ( T c) defined by the onset of the transition in the out of phase component of the AC susceptibility rises with x to 80 K for x=1. T c remains fixed at approximately 80 K through x=3. The unit cell size is also strongly dependent on calcium content for x<1. For x > 1 it is fairly constant. There is a strong correlation between the size of the unit cell and T c.

Eddy current imaging

A laboratory eddy current imaging system has been assembled to scan a probe over a sample and to record digital eddy current images. The system is microprocessor controlled and it transmits images to a VAX 780 computer for image processing. These images have been used for probe characterization and to study the imaging process. The eddy current system has a vector response to a flaw; the signal has both magnitude and phase. Images of response magnitude, in-phase component, out-of phase component, and phase angle have been displayed. Image processing techniques have been applied to the images for data correction and to extract imformation. Two types of probes have been examined: cylindrical pot-core probes and recording head probes.

Harmonic mixing in the classical charge density wave model above threshold

The third order response properties of the classical model for charge transport by charge density waves above the conductivity threshold are investigated analytically. The model is isomorphic to that of a resistively shunted Josephson circuit (RSJ model) and thus exhibits an oscillating solution above a threshold electric driving field with a characteristic internal frequencyω ph . By a systematic perturbation expansion in powers of the perturbing field strengths thedc response of the time varying state to twoac fields of frequencies ω and 2ω is evaluated. This determines the harmonic mixing signal (HMS) as a third order response. The general formula is explicitly evaluated far above threshold giving a result similar to the Kanter-Vernon formula for the rectified signal in second order. In addition to the resonance atω ph =ω a second resonance is found atω ph =2ω. A characteristic feature for the HMS above threshold is the absence of an out of phase component, i.e. the internal phase shift is zero.

Consequences of thermorheological complexity in viscoelastic materials

An additive compliance model was used to simulate thermorheologically complex behavior of a linear viscoelastic material. Creep compliance isotherms were generated using the model and timetemperature shift factors were determined. Thea T shift factors depend upon both time and temperature in a transient experiment and can be unambiguously determined for all regions of time and temperature. The dynamic response was also obtained using the additive compliance model, and the frequency and temperature dependence of the shift factors were determined for both the in-phase and out-of-phase components of the complex compliance. Thea T shift factor of the in-phase component was a function of both frequency and temperature and was a well defined quantity. The shift factor for the out-ofphase component of the dynamic compliance was not identical to that of the in-phase component; furthermore, this shift factor was undefined for certain regions of frequency and temperature.

Dynamic X-ray diffraction technique for measuring rheo-optical properties of crystalline polymeric materials

A dynamic X-ray diffraction technique, which can follow the responses of polymer crystals (crystallization, orientation, and lattice deformation) to mechanical excitation of sinusoidal strain induced to bulk specimen, was described. The descriptions for such responses are qualitatively made by using a narrow sector technique, which can measure the X-ray diffraction intensity distribution at a particular phase angle of the sinusoidal strain as a function of static and dynamic strains, temperature, and angular frequency. A typical result is demonstrated in terms of the investigation of orientation crystallization phenomena of natural rubber vulcanizates. More quantitative descriptions can be made by using a half-circle sector technique, which can measure the in-phase and out-of phase components of the dynamic X-ray diffraction intensity distribution. From these, one can obtain the dynamic strain-induced crystallization and orientation coefficients and the dynamic response of lattice deformation of specific crystal plane both as function of temperature and frequency. After a brief survey of the principle of the half-circle sector technique, frequency dependence of the dynamic strain-induced crystallization coefficients of the (002) and (200) crystal planes of natural rubber vulcanizates is demonstrated in terms of the two frequency dispersion regions around 10−2 and 101 Hz at a room temperature. The former and latter dispersions must be correlated with the crystallization processes of the so-calledα- andγ-filaments, respectively. In addition, frequency and temperature dispersions of the dynamic strain-induced orientation coefficient and the dynamic response of lattice deformation of the (110) crystal plane of polyethylene are demonstrated in relation to the so-calledα 1 andα 2 dispersions of dynamic mechanical modulus function of this material.