Small Phase Differences Research Articles

蓄冷器の熱音響理論

Performance of regenerator used in refrigerator is discussed in terms of thermoacoustics. Thermoacoustic theory results in two types of heat flux. One is due to isothermal reversible process and it contributes to heat-pumping effect. The other is due to irreversible process and it corresponds to regenerator loss. Limiting lowest temperature is independent of heat capacity of regenerator matrix. Large amplitude of pressure and small phase-difference between oscillations of pressure and velocity decrease regenerator loss. Refrigeration power is maximized at some frequency, where the loss is 50% of ideal case. External work required for refrigerator is composed of isothermal reversible part and irreversible one corresponding to dissipation of energy. Ratio of irreversible work to reversible one increases as pressure amplitude increases, Local COP of regenerator is independent of heat capacity of regenerator matrix, Some methods of achieving higher efficiency are discussed.

Acoustic controlled rotation and orientation

Acoustic energy is applied to a pair of locations spaced about a chamber, to control rotation of an object levitated in the chamber. Two acoustic transducers applying energy of a single acoustic mode, one at each location, can (one or both) serve to levitate the object in three dimensions as well as control its rotation. Slow rotation is achieved by initially establishing a large phase difference and/or pressure ratio of the acoustic waves, which is sufficient to turn the object by more than 45°, which is immediately followed by reducing the phase difference and/or pressure ratio to maintain slow rotation. A small phase difference and/or pressure ratio enables control of the angular orientation of the object without rotating it. The sphericity of an object can be measured by its response to the acoustic energy.

Effects of geomagnetic pulsations on the Doppler shift of HF backscatter radar echoes

The effects of geomagnetic pulsations on the Doppler shifts of HF backscatter radar echoes are studied. Three mechanisms are considered: (1) variation of the phase refractive index under the influence of the varying magnetic component, (2) modulation of the plasma density, and (3) electrodynamic drift of the ionosphere. It is shown that the electrodynamic drift is probably the most efficient mechanism to account for the measured Doppler shifts. In this model the Doppler shift on F propagation modes is sensitive to the eastward electric field of the wave, while E propagation modes are sensitive to the northward and eastward components with weights depending on the reflection height. Pi 2 and Pc 3 effects on the Doppler shift of backscattered echoes are presented in the experimental part. In one example of continuous pulsations it is found that the coherence of ground magnetic variations and HF echo Doppler shifts is high near specific frequencies in the spectra. The coherence of radar measurements in resolution cells about 100 km apart is nearly unity and the cross‐phase spectra show very small phase differences. An example of the effects of Pi 2 pulsations on F and Es propagation modes is presented.

Far-field analytical model for laser arrays and fitting with experimental results

Coupled laser arrays emit far-field radiation which is not well described by the grating-like formulation. An exact diffraction theory solution for the far field of coupled laser arrays is derived. The model is used to obtain excellent fit with the far-field pattern of a twin coupled laser diode operated under pulse modulation and with that of a hybrid coupled diode laser device. The fitted results exhibit the existence of a small phase difference between the coupled stripes and this difference is increased up to 12° in the hybrid device.

Floating metal ring in an alternating magnetic field

The levitation of a metal ring in an alternating magnetic field, often used as a demonstration of induced current in introductory courses, is shown to be due entirely to some rather small phase differences. The fields and phases are directly measured and used to calculate the force, with the result agreeing with the weight of the ring. All theory and measurement are within the reach of students taking a first course in electromagnetism.

A multistation study of low latitude Pc3 geomagnetic pulsations

An array of four low latitude induction coil magnetometer stations has been used to study the spatial and temporal characteristics of Pc3 pulsations over a longitudinal range of 17° at L = 1.8−2.7 in Southeast Australia. Pc3 data over a period of about 6 months have been investigated. Interstation phase variations and polarization characteristics have been investigated in detail for 10 selected individual days common to all four stations. The East-West station chain shows generally highest coherency between X (North-South) components with relatively small interstation phase differences corresponding to low azimuthal wave numbers (| m x , y | ≲ 10). Wave spectra are generally the same at the azimuthai stations ( L = 1.8) but are often different at the higher latitude station ( L = 2.7) while wave polarization ellipticities and major axis azimuth directions at all four stations are generally similar. Diurnal variations in interstation phase indicate that Pc3 waves propagate away from local noon towards the night time with left-hand polarization and North-East major axis azimuth directions in the morning and right-hand polarization and North-West azimuth directions in the afternoon. Apparent meridional propagation is always away from the equator from North to South with | m x , y | < 12. These properties are all consistent with Pc3 wave generation by a field line resonance situated South of the network at L > 3. The resonance may be associated with the plasmapause region or field line resonances resulting from coupling with a global compressional wave mode of low wave number which is capable of propagating energy from the subsolar upstream or magnetosheath regions into the magnetosphere and down to lower latitudes near the noon meridian.

Precise measurement of phase difference and amplitude ratio with an interchange reference method

A simple but very precise method for the assessment of small phase difference θ and amplitude ratio R of two coherent sinusoidal signals is described. The method utilizes a lock‐in amplifier as a null detector, and a precision level decade ratio‐transformer provides attenuation for one of the test signals. When each of the test signals is used in turn as the reference, one can compute R and θ: R = [(α1/α2)(β2/β1)]1/2, cos θ = [(α1α2)/(β1β2)]1/2, where α and β are attenuator readings. It is estimated that for θ = 10°, the uncertainties in R and θ are less than 10 ppm and 0.01 degree, respectively.

Cellular autonomy of the Gonyaulax circadian clock.

Because of the long term persistence of free-running circadian rhythms in populations of unicells, several investigators have considered, but not demonstrated, a possible role for intercellular interaction in maintaining synchrony between individual cells. The experiments described here were designed to test more critically the possibility that there is interaction between cells, including those possessing only small phase differences. None was detected; the bioluminescent glow of the mixed cultures matched the algebraic sum of the independent control cultures.

Measurement of very small phase differences

A simple method is presented to measure very small phase differences in the range of microradians between two ac voltages. The voltages are combined linearly and one of them is adjusted in amplitude such that the output is a minimum. This minimum voltage is proportional to the phase shift to be measured. The method is applicable from power to radio frequencies.

Molecular resonance effects in heavy ion excitation functions

The inelastic and fusion excitation functions are analyzed using an interference mechanism between the barrier and internal waves of the heavy ion optical potential. The undamped overlapping molecular resonances are found to be the main dynamical mechanism for the gross oscillations in the excitation function. Our result suggests a rather interesting correlation between the total reaction excitation and the direct surface reaction excitation function. Its origin may be understood as follows: At the resonance, the wave function is pulled into the nuclear interior, and thus, the total reaction cross section is at maximum. The direct surface reaction is, however, shifted by a small phase difference near the surface region. This picture should be valid in the case of overlapping molecular resonance of the heavy ion systems. Good agreement between calculated and experimental inelastic and fusion excitation functions for $^{12}\mathrm{C}$+ $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$+ $^{16}\mathrm{O}$ is obtained.

Secondary mean motions arising in a buoyancy induced flow

The paper presents numerical calculations of the growth and non-linear interaction of two dimensional and transverse disturbances in a natural convection boundary layer flow adjacent to a vertical flat plate. We find that finite amplitude effects result in a double longitudinal mean secondary vortex system. At certain spanwise positions and, for particular phases of the primary wave, this highly organized longitudinal circulation causes an alternate spanwise thinning and thickening of the boundary region and resultant steepening and flattening of the base flow velocity profile. Measurements of the response of the flow to controlled two-dimensional streamwise disturbances, modulated by a transverse standing wave also show similar characteristics and that, in fact, the two disturbance features are and remain locked together at a small phase difference. Experimentally determined transition conditions thus correspond very closely to flows in which this analysis finds large vortex motions.

Analysis of the Spun Yarn Structure of Crimped Fiber Assemblies

This article concerns the structure of yarns composed of crimped fiber assemblies. A theory to derive the diameter of a yarn is presented if the yarn is composed of helical coils having the same lead length. The positions of fibers in a yarn cross section are determined as follows: When three helical coils having different phase lags gather together to come in touch with one another, then the positions of the axes of these three helicals can be detemined. This procedure is repeated many times until covering all fibers in the cross section. The theoretical analysis clarifies that, when the phase differences are uniformly distributed random variables, the yarn diameter takes the maximum and this model is adapted for a high crimped yarn; and that a model of exponentially distributed random variables with larger density at the side of small phase difference conforms to a middle or low crimped yarn.

Methods of Measuring Small Phase Difference Changes in Interference Devices

A review is presented of the present status of the technology of interference measurements of small changes of certain physical quantities. The capability limits of measurements with the aid of interference, imposed by diffraction and by noise in the radiation source and receiver, are analyzed. The most effective visual and photometric methods of measuring phase differences of interfering beams are described. The modulation method, in which a phase difference change of (10?5?10?6)?2? can be detected, and the phase method used in automatic interferometers are considered in greater detail.

Cerebral impedance with different kinds of anesthesia

Values of specific impedance of the cat's cerebral cortex were measured in the awake state and under various kinds of anesthesia (epontol, sodium thiopental, and ether). Measurements were taken at a frequency of 1 kHz using Ranck's four-electrode method. It was found that the development of general anesthesia was not accompanied by definite changes in impedance (±4%). The fact that substantial functional changes in cortical neurons such as these do not lead to changes in impedance can be explained by the relative independence of total cortical impedance from the membrane resistance of nerve cells. The quite small phase difference (5°) between the measuring current and the potential difference recorded in the cortex proves that the current passes virtually through the intercellular space only. The impedance of the cerebral cortex was assumed to be an entity essentially unrelated to the functional state of the cortex; the impedance cannot therefore determine the amplitude changes of the electrocorticogram (ECoG) recorded. The magnitude of cortical specific impedance was found to be 258 ±10Φ·cm.

Методы измерения малых изменений разности фаз в интерференционных устройствах

Методы измерения малых изменений разности фаз в интерференционных устройствах

Analysis of Yarn Structure of Crimped Fiber Assemblies

This article concerns the structure of yarns composed of crimped fiber assemblies. A theory to derive the diameter of a yarn is presented if the yarn is composed of helical coils having the same lead length. The positions of fibers in a yarn cross section are determined as follows: When three helical coils having different phase lags gather together to come in touch with one another, then the positions of the axes of these three helicals can be detemined. This procedure is repeated many times until covering all fibers in the cross section. The theoretical analysis clarifies that, when the phase differences are uniformly distributed random variables, the yarn diameter takes the maximum and this model is adapted for a high crimped yarn; and that a model of exponentially distributed random variables with larger density at the side of small phase difference conforms to a middle or low crimped yarn.

Small phase differences in holographic interferometry

Nonlinear development of hologram recordings is used for the amplification of small phase differences in holographic interferometry.

Cesium Beam Frequency Standard Cavity Design

A new technique of constructing resonant cavities for exciting the Ramsey resonance in cesium beam frequency standards is discussed. A centrally located E-plane tee is used as the feed system in a symmetric even-order mode cavity. The location of the tee is determined initially from measurements made on the cavity when operated in a symmetric odd-order mode. Both the theoretical conditions and construction methods required to obtain very small phase differences between the oscillating magnetic fields at the ends of the cavity are described. Experimental results indicate agreement with theory and that the method is effective and simple to apply.

Small phase differences in holographic interferometry

Abstract Nonlinear development of hologram recordings is used for the amplification of small phase differences in holographic interferometry.

Improvement to the National Physical Laboratory Atomic Clock

THE second of time is now defined in terms of the hyperfine line of caesium-133, and is that interval which makes the frequency of the spectral line 9192631770 Hz (ref. 1). The second model of the National Physical Laboratory (NPL) standard described briefly in 1959 (ref. 2) has operated since then at a value estimated to be within one part in 1011 of the spectral line frequency, or approximately 1 µs per day. It can be used with a precision ten times better than this, and the main limitation to the use of the full precision is the possibility of a frequency shift due to a small phase difference between the two ends of the cavity resonant structure. The symmetry of the resonance shows that an error due to this cause does not exceed one part in 1011. Another way of checking the phase error is to reverse the cavity physically, thus reversing the effect. This method was used with the first NPL standard3 and also at the National Bureau of Standards (NBS)4, the National Research Council of Canada5 and the Laboratoire Suisse de Recherches Horlogeres6. Its drawbacks are that it involves the physical handling, movement and refixing of the cavity structure, and it occupies a time of possibly several days, during which the comparison standard must remain constant. The NBS overcame the handling problem by reversing the positions of the oven and detector, but although they then obtained more consistent results they were left with a residual uncertainty of ±3 parts in 1012. The residual uncertainty at the Laboratoire Suisse de Recherches Horlogeres was ±5 parts in 1012, although at the National Research Council, Ottawa, a frequency difference of 5 parts in 1012 due to this effect was reproduced in two measurements to 4 parts in 1013, a hydrogen maser being used as the comparison standard.