Laser Stabilisation for the Measurement of Thermal Noise

In order to measure the thermal noise of a mirror suspended in a vacuum it is necessary for the length measurement error due to intensity and frequency noise of the probe laser to be reduced below the thermal noise level. Here we report on an experiment to reduce the frequency and intensity noise of a 40mW Nd:YAG laser for this purpose. The frequency is stabilised using the standard reflection locking technique. To stabilise the laser intensity a technique which uses the properties of an in loop light field has been developed. This technique is capable of suppressing the intensity noise below the shot noise limit without reducing the useful laser power. A servo based on this technique has been designed and tested. The experimental results indicate that the laser noise can be reduced to a level which will allow a displacement sensitivity of 1.5 × 10^-19m/ Hz for the detection of thermal noise in a frequency band of 10 to 500Hz.     

Spectral noise analysis of Er3+:Ti:LiNbO3 curved waveguide amplifiers

We report simulations concerning optical amplification in Er:Ti:LiNbO₃ curved waveguides. The derivation and the evaluation of the spectral optical gain, the spectral noise figure, the amplified spontaneous emission photon number, and the signal to noise ratio are performed under the small gain approximation. The simulations show the evolution of these parameters under various pump regimes, Er concentration profiles and waveguide lengths. The results obtained are of significant interest for the design of complex, rare earth-doped integrated optics structures involving bent waveguides.     

Statistical equilibrium in simple exchange games I

This erratum corrects a mistake in reference [E. Scalas, U. Garibaldi, S. Donadio, Eur. Phys. J. B 53, 267 (2006)]. In that paper, we needed an aperiodic version of the BDY game, but, in formula (1), we incorrectly presented a periodic transition matrix of period 2 in the special case of g = 2 agents. Here, we present the right aperiodic version.     

Emergence of bimodality in noisy systems with single-well potential

We study the stationary probability density of a Brownian particle in a potential with a single-well subject to the purely additive thermal and dichotomous noise sources. We find situations where bimodality of stationary densities emerges due to presence of dichotomous noise. The solutions are constructed using stochastic dynamics (Langevin equation) or by discretization of the corresponding Fokker-Planck equations. We find that in models with both noises being additive the potential has to grow faster than |x| in order to obtain bimodality. For potentials ∝|x| stationary solutions are always of the double exponential form.     

Spontaneously generated coherence in a Doppler broadened atomic system

We investigate the spontaneously generated coherence (SGC) in a Doppler broadened four-level atomic system driven by two coherent fields. We plot the spontaneous emission spectra with different parameters and discuss how the initial atomic conditions and parameters of both fields change the number of peaks and dark lines of spontaneous emission spectra. Furthermore, we also show how the spontaneous emission spectrum is modified by Doppler effects in the viewed direction. Our results have important references to the experimental observation of SGC in hot atomic vapors.     

零排放燃气轮机的空气动力学特性

本文对采用二氧化碳作为基本工作流体的半闭环燃气轮机循环的空气动力学特性进行了详尽的分析.结果表明,不同工作流体的比热比值对压气机的压比、等熵效率及临界堵塞质量流量影响很大,并详细阐述了一种比热比对透平机械性能影响的修正方法,进而提出了一种零排放发动机的设计新思路,揭示了最初为空气工质而设计的压气机可以直接用于CO2零排放发动机中.     

An effective noise removal technique for recovering the shapes of diamond abrasive grains in SLM images degraded by clustered spike noise

A new noise-removal technique is applied to scanning laser microscopic (SLM) images to remove clustered spike noise in the images and to recover the shapes of diamond abrasive grains degraded by the noise. For achievement of this purpose, noise points in the SLM image are accurately detected by taking advantage of their properties in the space and spatial-frequency regions. The noise points are removed by a method of smoothing that is based on linear interpolation; that is, their pixel values are replaced by the interpolated values of their non-noise neighboring points. Noise-point information in the space region is acquired from image segmentation based on pixel classification, while noise-point information in the frequency region is derived from redundant wavelet decomposition for the SLM image. Fisher's linear discriminant method is used to yield the two noise-point images. The degraded grain shapes in the SLM images at different noise levels are satisfactorily recovered with a single iteration of smoothing without losses in sharp edges although a single smoothing needed four interpolations. Thus, the present noise-removal technique is shown to be effective for recovering the original shapes of the grains in every SLM image.     

A tuned damping device for reducing noise from railway track

A promising means to reduce the component of railway rolling noise radiated by the track is to increase the damping of the rail. This increases the attenuation with distance of vibrations transmitted along the rail and thereby reduces the noise radiated. To achieve this, a tuned, damped mass-spring absorber system has been designed. To cover a wide range of frequencies, multiple tuning frequencies are used along with a material with a high damping loss factor. Suitable materials have been found from extensive tests on samples and prototypes of the damper have been built and tested, both in the laboratory and in the field. Results are very promising with reductions of the track component of noise of around 6 dB being measured.     

The identification of tyre induced vehicle interior noise

Sound transmission into a vehicle is classified as either airborne or structure borne sound. From the point view of noise control, the reduction of noise transferred by different paths requires different solutions. Coherence function analysis is often used to identify transmission paths. However it can be difficult to separate the airborne from structure borne components. The principle of acoustic reciprocity offers a convenient method for overcoming this difficulty. The principal states that the transfer function between an acoustic volume velocity source and an acoustic receiver is independent of a reversal of the position of source and receiver. The work done on this study involves exciting a stationary tyre and measuring the surface velocity of the tyre at a number of discrete points. The acoustic transfer functions between each point on the tyre and a receiver point are measured reciprocally. Two sets of measurements are then combined to yield a measure of the sound pressure due to a point force on the tyre via the acoustic transmission path only. This technique also provides information on the relative contributions of various regions of the tyre wall to the resultant noise. Also the sound radiation characteristics, the horn effect, and resonance at the wheel housing are identified through the reciprocal measurement.     

Sound radiation and sound quality characteristics of refrigerator noise in real living environments

The characteristics of various types of refrigerator noise were investigated in an anechoic chamber and in a real living environment - a 100 m² apartment which is a common size in Korea. It was found that the sound pressure level of the refrigerator noise in the real living room was about 10 dB higher than the level in the anechoic chamber at the same position (1 m in front of refrigerator). In addition, a tolerance level for refrigerator noise was determined by subjective evaluation experiments. Refrigerator noise was presented by a loudspeaker placed in the kitchen where the refrigerator is normally located. Level 2 responses to the subjective evaluation (“hardly perceivable”) corresponded to a sound pressure level of about 26 dB(A), for which 90% of participants were satisfied with the level of refrigerator noise. A semantic differential test using various adjectives was also conducted to evaluate the sound quality of refrigerator noise. With the semantic differential and the factor analysis, adjectives used in this experiment were grouped into three factors. From the results of correlation and multiple regression analyses on the psychoacoustical parameters and subjective evaluations of 30 kinds of refrigerators, sound quality index which predict the subjective rating score were proposed.