Temperature variation of dielectric loss of silver-thermosetting polyester composites at audio frequencies

Dielectric loss of a metallopolymer system consisting of silver-coated glass spheres dispersed in unsaturated polyester is investigated at audio frequencies in the temperature range –180 to 45° C. The effect of the conductive filler is generally an enhancement of the dielectric loss due to the polymr matrix and no new loss peak is observed, and the activation energy for the -relaxation remains unaffected. It has also been found that dielectric dispersions corresponding to various filler concentrations appear to possess identical shapes in a pseudo Cole-Cole plot and that the loss maxima are collinear.[/p]     

Modern high precision bridges for measuring inductance and capacitance at audio frequencies

Summary Bridges of the type of 716-B and TM-351 and in general Schering type bridges can be considered as most suitable for measuring capacitance. The wide use of such bridges permits one to consider them as standard for the purpose.Attention should also be drawn to bridges with inductive ratio arms which possess very valuable properties: they require a small number of standard capacitors, they can measure the capacitance not only of two- but also of three-terminal capacitors, in this respect they are in no way inferior to the Schering circuit. Another property of these circuits should also be noted, they cannot be used at frequencies below 200 cps which rather limits their range of application as compared with some other circuit.Soviet industry has not as yet progressed very far in making capacitance bridges. Manufacture of bridges similar to type 716-B and TM-351 has begun.As far as the inductance bridges are concerned it is advisable to refrain, on the basis of the experience gained, from manufacturing bridges similar to TM-282 and completely reject the principle on which bridge 667-A is constructed, and which was criticized above. On the other hand improved types which are theoretically completely acceptable (such as the Sullivan AC-1100 or the Siemens Halske Rel-3R-114) will be too complicated for mass production. In addition the accuracy of the above-mentioned Siemens bridge may, despite many of its other advantages, prove to be in many cases inadequate.The difficulties thus arising in the choice of an inductance bridge circuit may perhaps be resolved by M. A. Bykov's proposal [5] of using a modified Anderson circuit for direct reading measurements. This modification opens up great possibilities in measuring small inductances with small Q factors, which is the great difficulty in bridge design; yet the Anderson circuit which gives a perfect balance, can, with the proposed modification, provide convenient measurements up to 0.01 h. At higher values it is advisable to use a Maxwell circuit in its usual form, as for instance in the TM-382 bridge. Work in one of the development departments, according to available information, is being conducted on these lines.     

Operational theory of eight-port homodyne detection

Abstract

The eight-port homodyne detection apparatus is analysed in the framework of the operational theory of quantum measurement. For an arbitrary quantum noise leaking through the unused port of the beam splitter, the positive operator valued measure and the corresponding operational homodyne observables are derived. It is shown that such an eight-port homodyne device can be used to construct the operational quantum trigonometry of an optical field. The quantum trigonometry and the corresponding phase space Wigner functions are derived for a signal field probed by a classical local oscillator and a squeezed vacuum in the unused port.     

Intercomparison of calibration systems for AC shunts up to audio frequencies

An intercomparison of calibration systems for AC shunts up to audio frequencies (10 kHz) between the National Research Council of Canada, Japan Electric Meters Inspection Corporation, and the National Institute of Standards and Technology, is presented. The comparison was implemented with a transfer standard of 10 A, 0.1 /spl Omega/ calculable AC/DC shunt, designed by Japan Electric Meters Inspection Corporation. The results indicate that there are no significant differences in the overall accuracy of calibration systems for AC shunts at frequencies up to 10 kHz in each laboratory.     

Piezoelectric two-layer stacks of cellular polypropylene ferroelectrets: transducer response at audio and ultrasound frequencies

Piezoelectric cellular polypropylene films, so-called ferroelectrets, are assembled in a stack with two active transducer layers. The stack is characterized with respect to its linear and quadratic response in a frequency range from 1 kHz to 80 kHz. A relatively smooth frequency response in the sound-pressure level is found for the individual layers as well as for both layers driven in phase. The piezoelectric response of the two-layer stack is twice the response of an individual layer over a rather broad frequency range. Furthermore, the influence of the preparation conditions on the resonance frequency and the effect of the quadratic distortion on the radiated sound are investigated both for the individual transducer films in the stack and for the stack system as a whole.     

Methods for measuring the Q-factor (or resistance) of induction coils at audio frequencies

Conclusions The above methods, especially those with the T-type circuits, may prove useful in studying coils, in testing, etc., for instance, in certifying coils used for checking the corresponding parameters of bridges (or Q-meters). They can also be used for evaluating losses in ferrites, ferromagnetic materials and other substances.     

Optical pattern recognition via adaptive spatial homodyne detection

We present an experimental demonstration of an optical pattern recognition scheme based on spatial homodyne detection. Our scheme is adaptive, all-optical, utilizes a single-element photo-detector, and provides a single parameter readout to quantify the efficacy of pattern recognition, thereby allowing very fast pattern recognition speeds. The spatial homodyne detector was applied to the identification of one- and two-dimensional phase profiles.     

Realistic eight-port homodyne detection and covariant phase space observables

We consider the quantum optical eight-port homodyne detection scheme in the case that each of the associated photon detectors is assigned with a different quantum efficiency. We give a mathematically rigorous and strictly quantum mechanical proof of the fact that the measured observable (positive operator measure) in the high-amplitude limit is a smearing of the covariant phase space observable related to the ideal measurement, that is, the measurement performed with fully efficient detectors. The result is proved for an arbitary parameter field. Furthermore, we investigate some properties of the measured observable. In particular, we show that detector inefficiencies do not affect the observable's ability to distinguish between different states.     

Robustness of homodyne tomography to phase-insensitive noise

Abstract

We study the effects of phase-insensitive noise on homodyne measurements of a radiation density matrix. We prove that this noise has an effect equivalent to a non-unit quantum efficiency at detectors. The overall effective quantum efficiency η_? of the measurement is evaluated in terms of the quantum efficiency at detectors and of the average number of noise photons added to the radiation field. For pure Gaussian-displacement noise, we show that half a photon of noise is enough to prevent the homodyne measurement of the density matrix.     

地铁FTGS音频信号检测系统设计

为准确检测地铁系统轨道电路中音频信号相关参数,利用脉冲捕获鉴频原理,设计一种基于MSP430单片机的地铁FTGS音频信号检测系统。该系统利用MSP430定时器的捕获功能与中断功能,对数字音频信号进行采集,求出其一系列周期,通过分析所得周期,直接在时域中求取上边频和下边频,得出音频信号的中心频率及位模式信息。以地铁实际FTGS音频信号作为分析对象进行测试,结果表明:该方法能够对地铁数字移频信号进行准确快速的测量,实现对音频信号的检测,有一定的应用价值。     

Wet mammals shake at tuned frequencies to dry

In cold wet weather, mammals face hypothermia if they cannot dry themselves. By rapidly oscillating their bodies, through a process similar to shivering, furry mammals can dry themselves within seconds. We use high-speed videography and fur particle tracking to characterize the shakes of 33 animals (16 animals species and five dog breeds), ranging over four orders of magnitude in mass from mice to bears. We here report the power law relationship between shaking frequency f and body mass M to be f ∼ M^−0.22, which is close to our prediction of f ∼ M^−0.19 based upon the balance of centrifugal and capillary forces. We also observe a novel role for loose mammalian dermal tissue: by whipping around the body, it increases the speed of drops leaving the animal and the ensuing dryness relative to tight dermal tissue.     

Determination of photon statistics and density matrix from double homodyne detection measurements

Abstract

We consider double balanced homodyne detection schemes with and without (local oscillator) phase-randomized detection. We discuss the reconstruction of the photon statistics from phase-randomized measurements. We show how the Wigner function of a photon-number state can be synthesized from phase-randomized double homodyne measurements of two properly prepared field states. Moreover we propose a new procedure to determine the whole density matrix from the Q function. Finally we express the Q function in terms of normally ordered moments and discuss their reconstruction.     

Ultrasonic detection of the anisotropy of protein cross linking in myocardium at diagnostic frequencies

Increased myocardial stiffness in aging and diabetes that may result in pathologies such as diastolic dysfunction has been attributed, in part, to an increase in cross linking of extracellular matrix proteins such as collagen. With the development of new approaches to cardiovascular therapy, it becomes increasingly important to develop noninvasive approaches for monitoring changes in myocardial cross linking. The objective of this study was to use ultrasound at frequencies used in clinical echocardiography to measure changes in myocardial attenuation resulting from increased cross linking as a function of angle of insonification over a complete rotation. Through-transmission radiofrequency-based measurements were performed on 36 specimens from 12 freshly excised ovine hearts at room temperature, which were then fixed in formalin to induce protein cross linking prior to repeated measurements. For angles near perpendicular to the myofiber direction, the measured slope of attenuation increased from 0.52 +/- 0.07 dB/(cm MHz) (mean +/- one standard deviation) for freshly excised to 0.85 +/- 0.08 dB/(cm MHz) for formalin-fixed myocardium. In contrast, results for parallel insonification exhibit considerable overlap (1.88 +/- 0.17 for freshly excised and 1.75 +/- 0.19 dB/(cm MHz) for formalin-fixed myocardium). Results of this study suggest that the response of the extracellular collagenous matrix to changes in cross linking is directionally dependent. The anisotropy of ultrasonic attenuation thus may provide an approach for noninvasive monitoring of the extent and progression of myocardial disease associated with changes in protein cross linking. Accounting for effects due to anisotropy may be essential for the future detection of such changes using ultrasonic attenuation in vivo.     

An inverse problem approach to optical homodyne tomography

Abstract

The problem of optical homodyne tomography is considered in the context of a Bayesian model-fitting or inverse problem approach. An algorithm is formulated, based on matrix computation rather than the numerical approximation of an analytic inverse transform. This automatically takes into account the effects of noise, detector inefficiencies and incomplete sampling of the data. The relationships with conventional reconstruction schemes, methods for including various forms of prior information and for calculating error estimates are discussed. The process of reconstructing the photon number distribution and the density matrix are illustrated using both simulated and experimental data.     

Energy transfer at optical frequencies to silicon-based waveguiding structures

For decades, crystalline silicon (Si) has been the semiconductor of choice for the majority of applications in microelectronics. Recent advances in material science have focused attention on the silicon-on-insulator (SOI) platform, a submicrometer-thick layer of single crystal Si resting on an insulating silicon dioxide (SiO2) layer. Here we calculate the lifetime of an electric dipole moment oscillating in the cover region of several canonical Si waveguiding structures. We show that the vicinity just above SOI produces the most dramatic changes to the radiative lifetime and thus the power spectrum of the emitting dipole. We demonstrate that SOI stands apart from other Si-based optoelectronic platforms in its ability to transport energy, in the form of light, away from an oscillating electric dipole via highly localized, optical- and IR-frequency guided waves.