Object Wave Determination by Single-Sideband Methods

The increased usage of the phase shifting transformers in various fields within power systems has introduced new challenges in performing on-site maintenance testing. These special transformers were used as converter transformers, rectifier transformers, harmonic mitigating transformers, zigzag transformers and quadrature boosters with unconventional vector groups, having an additional phase shift such as +/-7.50, +/-150 combined with normal `Delta and Star' configurations. The challenges now faced by the increased use of these transformers are testing them for accuracy on the voltage ratio and phase shift at site during commissioning and maintenance. Different test methods were performed / studied and were compared. A prototype of a three-phase converter transformer with variable ratio taps and vector groups was constructed and tested. The prototype transformer is constructed to have variable parameters for test trials on different vector groups and ratios. The three phase converter transformer prototype will have options to regulate the output voltage on varying input voltage using the tap changer and also can vary the phase shift by varying the vector group combinations. On-site testing of ratio and phase shift will be done on different types of traction rectifier transformers. The approach for factory testing and onsite testing of the special transformers will be different. The effect on the phase shift values when the ratio taps are changed will be the focus and the results compared. The study on the importance of phase shift on these special transformers is presented. The test results of different test methods using modern portable test equipment and conventional classical methods were compared and presented. The results of the ratio testing and the phase shift measurement variation during vector group variation and tap change were presented. (6 pages)

Pulses of a fluorinated analog of leucine, 5',5',5'-trifluoroleucine, reset the phase of the circadian rhythm of K(+) uptake in Lemna gibba G3 under continuous light conditions. The trifluoroleucine pulse caused the largest delay phase-shifts during the early subjective phase but it caused only small phase advances. The action of trifluoroleucine was investigated and the following results were obtained. (a) The uptake of trifluoroleucine was essentially the same at all circadian phases, even though phase shifting was dramatically different at different phases. At effective phases, the magnitude of phase shifting was well correlated with the amount of trifluoroleucine taken up by the duckweed. (b) The trifluoroleucine pulse lowered the endogenous content of valine and leucine but these decreases did not correlate with phase shifting. (c) Protein synthesis was not affected by trifluoroleucine pulses which caused large phase shifts. (d) Pulses of 4-azaleucine, a different structural analog of leucine, also caused phase shifting. However, neither the direction nor the effective times of phase shifting were similar to those of trifluoroleucine. Taken together, these results negate the proposition that trifluoroleucine and azaleucine caused phase shift by disturbing amino acid metabolism and/or inhibiting protein synthesis, but they suggest instead that these analogs are incorporated into some protein(s) which are necessary for normal clock operation.

Generalization of the Matsumoto–Tonomura approximation for the phase shift within an open aperture

The efficiency of regenerative refrigerators is generally maximized when the pressure and flow are in phase near the midpoint of the regenerator. Such a phase relationship minimizes the amplitude of the mass flow for a given acoustic power flow through the regenerator. To achieve this phase relationship in a pulse tube refrigerator requires that the flow at the warm end of the pulse tube lag the pressure by about 60 degrees. The inertance tube allows for the flow to lag the pressure, but such a large phase shift is only possible with relatively large acoustic power flows. In small pulse tube cryocoolers the efficiency is improved by maximizing the phase shift in the inertance tube. This paper describes a simple transmission line model of the inertance tube, which is used to find the maximum phase shift and the corresponding diameter and length of the optimized inertance tube. Acoustic power flows between 1 and 100 W are considered in this study, though the model may be valid for larger systems as well. For large systems the model can be used to find the minimum reservoir volume that in combination with the inertance tube provides a phase shift of 60 degrees. This transmission line model is compared with some experimental results on a small‐diameter inertance tube and found to agree quite well provided some heat transfer is taken into account. Design graphs for a frequency of 60 Hz and an average pressure of 2.5 MPa are presented for different pressure ratios and for both adiabatic and isothermal conditions.

We demonstrate a new full range complex spectral domain optical coherence tomography (FRC SD-OCT) method. Other than FRC SD-OCT systems reported in literature, which employed devices such as electro-/acousto optic modulators or piezo-driven mirrors providing the phase modulations necessary for retrieval of the complex-valued signal, the system presented works without any additional phase shifting device. The required phase shift is introduced by the galvanometer scanner used for transversally scanning the sample beam. By means of a slight displacement of the probe beam with respect to the scanning mirror's pivot axis, the sample arm length and thus the phase is continuously modulated as the beam is scanned in lateral direction. From such modulated spectral data, the complex-valued data yielding a twofold increase of accessible depth range can be calculated using an algorithm based on the Hilbert transform. To demonstrate the performance of our method quantitative measurements of the suppression of mirror images as a function of induced phase shift were performed. In order to validate the FRC SD-OCT technique for high-speed imaging of biological tissue, we present full-range images of the human anterior chamber in vivo.

Optimizing phase contrast in transmission electron microscopy with an electrostatic (Boersch) phase plate

When phase-shifting digital holography with a continuous fringe-scanning scheme is implemented using a PC-based measurement system without any synchronous circuit, nonuniform phase-shifted interference fringes are captured because of the fluctuation in the image-capturing interval. To cope with the nonuniform phase shifts, a statistical generalized phase-shifting approach is employed. Because the algorithm is designed to use an arbitrary phase shift, the nonuniform phase shifts do not obstruct object-wave retrieval. Moreover, multiple interference fringes can be obtained in a short time owing to the continuous fringe-scanning scheme. However, the wavefront calculation method is not designed for sequentially recorded interference fringes. To use multiple interference fringes appropriately, we develop a least-squares wavefront calculation method combined with corrections for the initial phase and the direction of phase rotation. We verify the proposed method by numerical simulations and optical experiments. The results show that the object wave with the same initial phase can be correctly reconstructed by using both phase correction methods simultaneously.

A direct phase shift extraction and wavefront reconstruction method in two-step generalized phase-shifting interferometry (GPSI) with arbitrary unknown phase shift is proposed. In this method the unknown phase shift α can be extracted by a determinate formula directly without iteration or additional judgment of its correct value from two or more phase shift solutions as necessary before. By an appropriate formula of GPSI the complex object field in the recording plane can be calculated and then the object wavefront in the original object plane obtained. This method is applicable for GPSI of any frame number K≥2 and for both the amplitude and phase objects. Computer simulations have shown that the phase shift extraction errors are below 0.01 rad in a wide range of 0.4 rad<α<2.6 rad and the computation time is greatly reduced by a factor of about 20 compared with the previous method. The effectiveness and accuracy of this method are also verified by optical experiments.

Silicon photonics enables the development of optical components on a chip with the potential for large-scale optical integrated circuits that can be fabricated at the wafer-scale using foundries similar to those used in the electronics industry. Although silicon is a passive optical material with an indirect bandgap, reconfigurable devices have been demonstrated using thermo-optic effects (large phase shifts, but relatively slow with large power consumption) and carrier plasma dispersion effects (high-speed, but small phase shifts). We recently demonstrated a low-power approach for inducing large phase shifts (>2π) using a technique that we call micro-opto-electro-mechanical index perturbation (MOEM-IP). In this initial work we characterized silicon nitride waveguides in which the propagating optical mode’s evanescent field is vertically coupled to silicon nitride microbridges. This interaction leads to an effective index tuning that is a strong function of the waveguide-microbridge separation. We now extend our MOEM-IP approach to different configurations (i.e. in-plane coupling) and material systems (i.e. silicon-oninsulator). Mode perturbation simulations indicate that the MOEM-IP approach is widely applicable to many configurations and material systems enabling large effective index tuning (Δneffective>0.1) requiring microbridge displacements of only a few hundred nanometers. We also examine several device applications that take advantage of MOEM-IP. These include tunable optical filters using high-Q microring cavities and optical phased arrays that enable chip-scale beam steering in two-dimensions using low-power phase shifting enabled by MOEM-IP.

For a modern aerodynamically unstable fighter, like the JAS 39 Gripen, the flight control system typically provides 45/spl deg/ phase margin. Therefore rate limiting of control surfaces, which may cause large phase shifts, is an important issue. Software rate limiters are placed on the control servo commands in order to prevent the hydraulic servos from rate limiting. When a rate limiter is saturated, the phase shift drastically reduces the stability margins of the closed loop and increases the risk for pilot-induced oscillation (PIO). This paper describes a novel method for compensating the phase shift of a rate limiter. In contrast to earlier phase compensation methods, this method uses feedback instead of logic or feedforward. Open loop and closed loop properties of the method are discussed. The method gives a drastic improvement on stability margins and reduces PIO tendencies.

Phase Shifts to Refeeding in the Syrian Hamster Mediated by Running Activity

A scheme of an all-optical nonlinear phase-shifting element is proposed, based on a reflective vertical cavity semiconductor (quantum-well) saturable absorber (R-VCSSA). The nonlinear round-trip phase shift in a low-intensity resonant VCSSA is obtained at an input intensity due to the saturating nonlinearity in index change and optically induced thermal effects. An enhanced large nonlinear positive or negative phase shift incurred in a reflected signal is investigated analytically with the wavelength tuning of the probe signal around the low-intensity resonant wavelength of a Fabry–Perot cavity. The device may be useful in compensating the phase of an input signal, either positive or negative, in long-haul fiber communications. A representative InGaAs/InP quantum-well-based VCSSA is considered to demonstrate the phase shift in the pump–probe configuration. With a device speed of 10 GHz, maximum phase shifts of −0.24 and +0.14 rad at pump power of 19.2 mW are observed for the operations at probe wavelengths of 1555.6 and 1557.8 nm, respectively.

Shoaling of bound infragravity waves on plane slopes for bichromatic wave conditions

Enhanced nearfield resolution of small phase objects using a priori knowledge

Islanding detection is a mandatory function for grid-connected converters. The popular slip mode frequency shift (SMS) and auto phase shift active islanding detection methods are investigated and an improved (IM)-SMS strategy is proposed in this study. In the proposed method, additional phase shift is introduced to help in stimulating the action of the islanding detection and the algorithm is simplified as well. When the utility grid is disconnected, the algorithm keeps the frequency of the converter output voltage deviating until the frequency protection relay is triggered. The working principle of the method is introduced and the guidance of parameters selection and optimisation is also provided. The islanding detection performance is evaluated through theoretical analysis and verified by digital simulation and experimental results. The IM-SMS method exhibits features of simplicity, easy implementation and high reliability.