AC Phase Research Articles

A precision power amplifier for calibration systems

A simple design for a precision, high-voltage and high-current amplifier is given. A pair of such amplifiers is implemented in the ac voltage, current, power and phase angle calibration system in Federal Bureau for Measures and Precious Metals in Belgrade, Serbia. The measurement results of output stability, as the most important parameter in metrology applications, are presented.

RNA Interference-Mediated Inhibition of Erythropoietin Receptor Expression Suppresses Tumor Growth and Invasiveness in A2780 Human Ovarian Carcinoma Cells

Although recombinant human erythropoietin (rHuEpo) has revolutionized the treatment of anemia, recent clinical trials suggested that rHuEpo use may be associated with decreased survival in cancer patients. Although the expression of erythropoietin (Epo) receptor (EpoR) has been demonstrated in various human cancers, the effect of exogenous Epo on the growth and therapy resistance of EpoR-bearing tumor cells is unclear at present. In the current study, we examined the hypothesis that EpoR may contribute to tumor growth independent of Epo in A2780 human ovarian carcinoma cells. A2780 human ovarian carcinoma cells showed high levels of EpoR expression, but lacked expression of Epo mRNA and biologically active Epo protein under both normoxic and hypoxic conditions. Exogenous Epo did not stimulate EpoR-mediated signaling, proliferation, invasiveness, or resistance to cytotoxic drugs in A2780 cells. In contrast, specific inhibition of EpoR expression using a short hairpin RNA (shRNA) expression plasmid resulted in markedly reduced proliferation and invasiveness in vitro. In addition, inhibition of EpoR expression led to abrogated in vivo ovarian cancer cell growth in a tumor xenograft system and resulted in decreased EpoR signaling. Our findings suggest that EpoR may be constitutively active in some cancer cells in the absence of Epo and provide the first evidence for a potential role of an Epo-independent, EpoR-mediated pathway in the growth of some human cancers.

高電圧ダブルパルス電圧重畳位相制御交流試験装置とその応用

高電圧ダブルパルス電圧重畳位相制御交流試験装置とその応用

Modelling Power Law Dependencies of Frequency Dependent AC Conductivity and Permittivity of Conductor-Relaxor Composites

Porous lead magnesium niobate-lead titanate (PMN-PT 90:10) relaxors were impregnated with water to provide a model conductor-insulator mixture, to study their power law frequency dependency of ac conductivity, permittivity and phase angle. Relaxor materials with a range of open porosity filled with water created composites with conductor volume fractions ranging from 8.2% to 22.2%. The use of a high relative permittivity PMN-PT (∼ 8000) enabled the power law dispersion to be observed at relatively low frequencies (∼ 2 kHz). Good agreement was obtained between experimental data and predicted results based on a logarithmic mixing rule with a strong correlation between the power law exponent and conductor-insulator fraction. The model and numerical methods presented are considered a simple approach to interpret and predict and the frequency dependent properties of materials which similar heterogeneity.

Catalytic activity-surface structure correlation of molybdenum-based catalysts

Controlled reduction temperature of equivalent 5 monolayer of molybdenum trioxide deposited on TiO 2 enabled us to obtain two distinct, well-defined states of molybdenum surfaces. The reduction was performed using hydrogen. A stable bifunctional (metal–acid) MoO 2(H x ) ac phase is obtained at reduction temperature of 673 K. In this phase, the metallic function consists of delocalized π electrons over Mo atoms placed along the C-axis of the deformed rutile structure of MoO 2. The acidic function consists of Brönsted Mo-OH group(s). At reduction temperature of 873 K, a metallic Mo(0) state is obtained. The metallic function consists of large particle sizes (clusters) of Mo atoms. Hydroisomerization of n-hexane and 1-hexene to methyl pentanes and dimethyl butanes are obtained on the bifunctional phase. On the other hand, hydrogenation, hydrocracking and formation of benzene occur on the metallic Mo(0) state. Aromatization of cyclohexene and cyclohexane is performed by the bifunctional MoO 2(H x ) ac surface at 623–673 K reaction temperatures. The absence of such aromatization catalytic processes in the case of n-hexane and 1-hexene on MoO 2(H x ) ac is attributed to the fact that cyclization of 1-hexene to cyclohexene, the pathway for benzene formation, is structure-sensitive catalytic process. It occurs on the Mo(0) large particle size(s). Apparently, molybdenum Mo–Mo atoms placed along the C-axis (atomic wire) in MoO 2(H x ) ac phase do not favor this cyclization process. On the contrary, aromatization of cyclohexene and cyclohexane are structure-insensitive catalytic processes.

Surface electronic structure-catalytic activity correlation of partially reduced molybdenum oxide(s) for the isomerization of light alkenes and alkanes

Catalytic activity-surface electronic structure correlation was carried out using surface XPS-UPS techniques. In situ reduction by hydrogen, were carried out at similar experimental conditions to those employed for the catalytic reactions. In the case of MoO3 deposited on TiO2, the reduction to MoO2 state with the bifunctional MoO2(Hx)ac phase on its surface starts at 573 K and reaches a stable state at temperatures between 653–673 K. In the case of alumina support, a strong metal-support interaction takes place during the catalyst preparation, leading to Al2(MoO4)3 complex formation as characterized by XRD. The reduction process(s) of this complex by hydrogen as a function of temperature is different from what is observed in the case of titania support. The changes in the chemical structure of the sample surface in both systems were tested for the catalytic reactions of 1-pentene and n-pentane

Modeling of VSC-Based HVDC Systems for a Newton-Raphson OPF Algorithm

The paper presents the model of a voltage source converter -high voltage direct current (VSC-HVDC) suitable for optimal power flow (OPF) solutions using Newton's algorithm. The VSC-HVDC's ability to provide independent control of the converters ac voltage magnitudes and phase angles relative to the system voltage, which allows the use of separate active and reactive power control loops for system regulation, is well represented by the model. In this new development in Newton OPF, the VSC-HVDC system equations are incorporated directly into the matrix W for a unified optimal solution in a single frame-of-reference. The multipliers method is used to handle all inequality constraints of variables, leading to highly efficient OPF solutions of constrained power networks. The solution approach does not require structural changes in the linearised system of equations during the iterative process using Newton's method. The effectiveness of the VSC-HVDC model and its proposed implementation in Newton OPF is demonstrated by means of two sample systems.

A Measuring Method of the Single-Phase AC Frequency, Phase, and Reactive Power Based on the Hilbert Filtering

This paper presents a novel measuring method based on the Hilbert filtering for the digital monitoring of the single-phase ac frequency, phase, and reactive power. According to this method, the sampled voltage signal passes a pair of the Hilbert filters. Then, the ac frequency and phase can be obtained by the phase detection and the phase-locked loop algorithm. Additionally, the sampled current signal also makes its phase shift by the other Hilbert filter. The current output is multiplied by the one of the phase-shifted voltage signals, and the reactive power is acquired from the dc component of the product. Because a type of infinite impulse response (IIR) Hilbert filters with low-order and small phase-shift error is adopted, this measuring method cannot only obtain fast and accurate digital monitoring results but also be easily realized with the DSP or other microprocessor programming codes. This method has been successfully applied in the design of a digital multifunctional power instrument

Development of an AC Phase Controlled Testing Apparatus with an Impulse Voltage

Overvoltages as lightning surges and/or switching surges will affect power apparatuses and electric appliances, which make them of deterioration. However, recent AC testing apparatuses haven't been functions generating an impulse voltage. Moreover, the apparatuses with controlling an impulse voltage haven't been utilized except the low voltage function generator. Therefore, an AC phase controlled testing apparatus with an impulse voltage (0.8/6μs) has been developed in order to elucidate mechanism of the degradation in insulating materials with a AC power supply simulating the overvoltages.

The catalytic active sites in partially reduced MoO 3 for the hydroisomerization of 1-pentene and n-pentane

In situ characterization by XPS and UPS of bulk commercial MoO 3 and the equivalent five atomic layers of MoO 3 deposited on TiO 2 before and following the reduction by hydrogen at different temperatures led to the identification of the chemical species on the surface. These spectra reveal that MoO 3 is the only state present prior to reduction. However, a predominant Mo 5+ state on the sample surface is formed at reduction temperatures between 573 and 623 K. Continued reduction leads to the formation of MoO 2, which reaches a stable state at temperatures between 653 and 673 K. The metallic character of MoO 2 is observed as a density of states (DOS) at the Fermi level. This metallic function dissociates hydrogen molecules to atoms. Bonding of these active (H) atoms with surface oxygen leads to the formation of Brönsted acid (Mo-OH) group(s) as characterized by O 1s and catalytic properties. As a result, a bifunctional MoO 2(H x ) ac phase is formed on the outermost sample surface layer in these systems. More sensitive UPS measurements established the presence of MoO 2 in the upper four to five surface monoatomic layers during the reduction process. Combination of XPS–UPS provides valuable information on the chemical composition of the upper surface layers. Apparently, a stable sandwich-like structure is formed in which the composition from bulk to surface consists of MoO 3, Mo 2O 5 and MoO 2. The outermost surface layer in this structure is a bifunctional MoO 2(H x ) ac phase. The catalytic performances of the different Mo suboxides towards the hydroisomerization reactions of 1-pentene and n-pentane were studied. The MoO 3 phase has no catalytic activity due to its insulating properties. Double-bond and skeletal isomerization reactions of 1-pentene take place on the acid function(s) of Mo 5+ state, while n-pentane and isopentane are the only products observed in the case of MoO 2(H x ) ac. Both metallic and acid functions are required for the isomerization of n-pentane to isopentane. Consequently, it is concluded that the dehydrogenation process is the rate-determining step in the isomerization reaction of n-pentane. Hydrogenation of 1-pentene is the dominant reaction when the bifunctional MoO 2(H x ) ac phase is used.

Real space imaging of the microscopic origins of the ultrahigh dielectric constant in polycrystalline CaCu3Ti4O12

The origins of an ultrahigh dielectric constant in polycrystalline CaCu3Ti4O12 (CCTO) were studied using the combination of impedance spectroscopy, electron microscopy, and scanning probe microscopy (SPM). Impedance spectra indicate that the transport properties in the 0.1Hz–1MHz frequency range are dominated by a single parallel resistive-capacitive (RC) element with a characteristic relaxation frequency of 16Hz. dc potential distributions measurements by SPM illustrate that significant potential drops occur at the grain boundaries, which thus can be unambiguously identified as the dominant RC element. High frequency ac amplitude and phase distributions illustrate very weak grain boundary contrast in SPM, indicative of strong capacitive coupling across the interfaces. These results demonstrate that the ultrahigh dielectric constant reported for polycrystalline CCTO materials is related to grain-boundary behavior.

Novel Concept for Mains Voltage Proportional Input Current Shaping of a VIENNA Rectifier Eliminating Controller Multipliers

This paper proposes a novel mains voltage proportional input current control concept eliminating the multiplication of the output voltage controller output and the mains ac phase voltages for the derivation of mains phase current reference values of a three-phase/level/switch pulsewidth-modulated (VIENNA) rectifier system. Furthermore, the concept features low input current ripple amplitude as, e.g., achieved for space-vector modulation, a low amplitude of the third harmonic of the current flowing into the output voltage center point, and a wide range of modulation. The practical realization of the analog control concept as well as experimental results for application with a 5-kW prototype of the pulsewidth-modulated rectifier are presented. Furthermore, a control scheme which relies only on the absolute values of the input phase currents and a modified control scheme which does not require information about the mains phase voltages are presented.

High-Q Class E power amplifier analysis using energy conservation

Existing analytic treatments of the high-Q Class E power amplifier have provided expressions in terms of trigonometric functions of the load angle and AC phase. By using conservation of energy it is possible to derive simpler expressions involving just AC phase. It is then possible to express the carrier frequency response as low order rational functions in X, the normalised frequency offset. The effect of varying the shunt capacitor value is also explored. It is demonstrated that classic Class E is one member of a family of solutions, which includes series-tuned Class C. Good agreement with measured data is seen.

Simplified Models of Harmonics Produced by Twelve-Pulse AC/DC Converters under Unbalanced Supply Voltage

AC/DC converters generate current harmonics in power systems. Detailed analysis of current harmonics produced by twelve-pulse ac/dc converters under non-ideal operating conditions can be quite time consuming. A simple analytical model is proposed to evaluate current harmonics produced by twelve-pulse ac/dc thyristor converters under unbalanced supply voltage. Simplified models of ac current harmonics amplitudes and phase angles are derived as a function of the complex voltage unbalanced factor. Simulation results are presented in order to confirm the validity of the proposed analytical model.

Ac behaviour and phase transition in PLZT 6/80/20 ferroelectric ceramics

The Ac behaviour of PLZT 6/80/20 ferroelectric ceramics was analyzed around and above the phase transition. Two relaxation processes are identified, showing that the so-called ‘universal relaxation law’ holds for the ceramics. A critical point in the values of the Ac conductivity, around the temperature corresponding to the maximum of the dielectric losses, is observed below the transition temperature due to the relaxor behaviour. The frequency dependence of the Ac conductivity at various temperatures and the hysteresis loops show classical relaxor behaviour with a diffuse phase transition.

Catalytic reactions of methylcyclohexane (MCH) on partially reduced MoO 3

XPS and UPS characterization of partially reduced MoO 3 by hydrogen at different temperatures enabled us to define the metallic character of MoO 2. Hydrogen dissociation by this state results in the formation of Brönsted acidic group(s) Mo–OH as characterized by O 1s and catalytic properties. A bifunctional MoO 2(H x ) ac phase is formed on the outermost sample surface layer. Two hydrocarbons were studied: methylcyclohexane (MCH) and n-heptane ( nC7). The catalytic behavior of MCH on this system shows two different pathways depending on the reaction temperature. A selectivity close to 95% in dimethyl and ethyl-cyclopentanes (DMCP and EtCP) products were obtained at temperatures between 493 and 573 K. At higher temperatures up to 653 K, toluene is the major dehydrogenation product. The general tendency of this catalytic system seems to behave as a bifunctional; to confirm this hypothesis, an acid-supported catalyst, i.e. sulfated zirconia-supported Pt–Ir, was tested under the same experimental conditions. The possible formations of dimethyl or ethylcyclopentanes as intermediate products in the catalytic reaction of n-heptane have been explored using both catalysts.

Ab initiostudy of the phase diagram of epitaxialBaTiO3

Using a combination of first-principles and effective-Hamiltonian approaches, we map out the structure of BaTiO3 under epitaxial constraints applicable to growth on perovskite substrates. We obtain a phase diagram in temperature and misfit strain that is qualitatively different from that reported by Pertsev et al. [Phys. Rev. Lett. 80, 1988 (1998)], who based their results on an empirical thermodynamic potential with parameters fitted at temperatures in the vicinity of the bulk phase transitions. In particular, we find a region of `r phase' at low temperature where Pertsev et al. have reported an `ac phase'. We expect our results to be relevant to thin epitaxial films of BaTiO3 at low temperatures and experimentally-achievable strains.

The bifunctional catalytic properties of a partially H 2-reduced MoO 3

XPS–UPS techniques were employed in order to identify the different Mo suboxides produced by hydrogen reduction of bulk MoO 3 at different temperatures. A bifunctional MoO 2(H x ) ac phase is formed on the surface of MoO 2 produced by this reduction process at temperatures between 623 and 673 K. Dehydration of 2-propanol and the hydroisomerization of 1-hexene and n-hexane were interpreted using these dual (metal–acid) functions of MoO 2(H x ) ac.

Hydroisomerization of n-heptane and dehydration of 2-propanol on bulk and supported WO 2(H x) ac on TiO 2

Characterization by XPS–UPS and XRD of commercial bulk WO 2 enabled us to identify the presence of four to five layers of WO 3 on the sample surface with an equal amount of W 5+, possibly W 20O 58 in the interface. The presence of these WO 3 and W 20O 58 on the WO 2 surface were not detected by XRD. Exposure of commercial bulk WO 2 to hydrogen at temperatures higher than 673 K results in the reduction of surface WO 3 to WO 2 and the formation of the bifunctional WO 2(H x ) ac phase on its surface. A complete conversion of surface WO 3 to WO 2(H x ) ac has been obtained following the exposure of the sample to hydrogen for at least 6 h at 773 K. A conversion of 52% of n-heptane at 573 K reaction temperature and a selectivity of 90% in isomerization products, mainly 2,3-MH and multibranched molecules were obtained. The isomerization products distribution is in agreement with the statistical and thermodynamic equilibrium of the methyl-shift mechanism. The stability of the active WO 2(H x ) ac phase has been tested under prolonged exposure to hydrogen and the reaction mixture. Similar results were obtained in the case of bulk WO 3 and WO 3/TiO 2 systems. Dehydration and dehydrogenation of 2-propanol were studied on these systems at 393 K reaction temperature.

Po-topic IV-14: Imaging & localizing device using the barkhausen effect

We have been investigating the use of amorphous magnetic materials as locator tags for medical applications. Heinrich Barkhausen discovered in 1919 that a slow, smooth increase of magnetic field applied to a piece of ferromagnetic material, such as iron, causes the material to become magnetized not continuously, but in small steps. A large Barkhausen effect (large step change) was observed in 1931 because of domain reversal at a rapid velocity along the wire. In the late 1980s, an even larger Barkhausen effect was produced in amorphous wires giving rise to an even sharper magnetic pulse because of domain or flux reversal in the core of the wire. In an AC magnetic field, the reversal of the domains emits large, sharp magnetic pulses of the opposite sign. We are taking advantage of this pulsed response to tag and image the location and orientation of implanted devices. Several factors affect the feasibility of imaging and reconstruction of embedded tags. These include the strength of the detected signals; the ability to reconstruct locations and orientations of the tags; and signal sensitivity to tissue composition, inhomogeneities, and the presence of neighboring metals. We have obtained voltage signals from wires of several diameters with an iron-core pickup coil along a distance from the center of a wire with the coil as a function of angle for a 60–80 Hz driving field. At a distance of about 8 cm., we have obtained a strong signal of typically 2V (depending on length), more than 50 times the background noise (about 20 mV). At 30 cm separation, we detected a signal of 0.5 V, 25:1 above background noise. When the wire direction is mis-oriented relative to the driving AC magnetic field, the amplitude and phase of the resultant output signal changes. This is because only the portion of the magnetic field that is parallel to the wire axis contributes to the Barkhausen effect for that wire. By using multiple positions of the coil, we have been able to determine the changes of these two parameters for a more accurate localization. We have also determined that intervening tissues have little effect on the signals, as was expected theoretically. Our preliminary results indicate that in vivo 3D reconstruction is feasible.