Performance of profiled single noise barriers covered with quadratic residue diffusers

The paper describes an investigation about the acoustic performance of noise barriers with quadratic residue diffuser (QRD) tops, and with T-, Arrow-, Cylindrical and Y-shape profiles. A 2D boundary element method (BEM) is used to calculate the barrier insertion loss. The results of rigid and with absorptive coverage are also calculated for comparisons. Using QRD on the top surface of almost all barrier models presented here is found to improve the efficiency of barriers compare with using absorptive coverage at the examined receiver positions. T-shape and Arrow-shape barriers are also found to provide better performance than other shapes of barriers. The best shape of barriers for utilising QRD among the tested models is the T-shape profile barrier. It is found that reducing the design frequency of QRD shifts the performance improvement towards lower frequency, and therefore the most efficient model for traffic noise is a barrier covered with a QRD tuned to around 400 Hz.     

Deriving correction functions to model the efficiency of noise barriers with complex shapes using boundary element simulations

The boundary element method (BEM) is a commonly used method to compute the insertion loss of noise barriers having arbitrary cross-sections. For large scale three-dimensional problems, however, the BEM is not feasible. On the other hand, standardized calculation methods for noise mapping are efficient, but shapes other than the straight barrier cannot be properly calculated. Attempts to merge these two approaches by using BEM to derive correction functions based on geometrical quantities such as source and target angle as well as the path length elongation between source and receiver caused by the barrier were usually focused on a small set of barrier types, dimensions, absorptive configurations, source or receiver positions. The main objective of this study is to investigate which functions based on the most common geometrical parameters are well suited for approximating the efficiency of different types of barriers, dimensions and absorptive configurations. To achieve this, numerous combinations of 7 different barrier types, different heights and widths as well as 3 different absorptive configurations were simulated using the 2D BEM for 8 different source positions. The octave-band-wise efficiency, i.e. the frequency-dependent gain in insertion loss compared to an equally high, fully reflective straight barrier was used as a basis for the correction functions. Linear as well as polynomial models were compared yielding a polynomial of third degree in the source and fourth degree in the target angle as the best model. Effects on the error using uniform sampling in the target angle instead of a uniform receiver grid as a basis for the correction functions are also investigated. Furthermore, wide-band efficiencies based on standardized traffic emission spectra are calculated showing small errors compared to single-band errors, in particular in the high-frequency range. A linear interpolation scheme is suggested to deal with barriers having dimensions not simulated in this work.     

一种基于碳纳米管场发射的发光二极管

制作了一个基于碳纳米管场发射的发光二极管,实验结果表明,这种发光二极管驱动场强低,亮度高,能够满足常用显示器和发光管的亮度要求,同时也用边界元法讨论了碳纳米管之间的场屏蔽效应.     

Integration of the efficiency of noise barrier caps in a 3D ray tracing method. Case of a T-shaped diffracting device

Road barrier diffracting caps have shown a renewed interest for several years since they give the opportunity of increasing the barrier efficiency without changing its overall height. First investigations on the efficiency of road barrier caps calculated with a boundary element method (BEM) have shown that the efficiency obtained with coherent line sources is underestimated compared to that with incoherent line sources, more representative of road traffic noise. The present work deals with the characterisation of the real performance of a T-shaped absorbing cap with road traffic noise conditions. Two different approaches are compared: on one hand calculations with the help of a BEM program able to achieve 2D and 2D simulations are made; on the other hand outdoor measurements on a test-wall using a maximum length sequence technique are carried out. The goal in the two approaches is to isolate the top edge diffracted sound field in order to determine an extrinsic value of octave band efficiency of the cap for many source-receiver pairs. These results integrated in a ray tracing prediction method enable the integration of air absorption along each ray path and give the real efficiency of such a device in the case of complex and realistic configurations for barriers of finite length.     

噪声对超导量子比特测量系统的影响

详细介绍了噪声对超导量子比特测量系统的影响。测量系统通过对时间的测量来获得单个约瑟夫森结跳变电流统计分布P(I)。在测量电路中采取了一系列的降噪措施,使得实验所能测到的约瑟夫森结的最低等效温度进一步的降低。     

Full-Energy peak efficiency of an NaI(Tl) detector with coincidence summing correction showing the effect of the source-to-detector distance

The coincidence summing effect is considered to be one of the most important problems in γ-ray spectrometry. It has played an important role in the detector calibration process, especially at low source-to-detector distances, which are the typical conditions when the environmental samples have to be measured. In this work, the γ–γ coincidence summing correction factors (CSCF) for a 3″×?3″ NaI(Tl) γ-ray detector have been calculated at different distances from the detector end cap. These factors with NaI(Tl) γ-ray detectors have rarely been discussed in the previous literature, due to the lack of the separation process of the close gamma energy lines in the scintillation detector spectrum. The γ–γ CSCF were calculated for ⁶⁰Co, ¹³³Ba and ¹⁵²Eu radioactive point sources, which show the simple and the complex decay scheme of several radionuclides. In order to obtain the CSCF, the following parameters must be estimated by the numerical simulation method (NSM): the total efficiency (ε_T), the full-energy peak efficiency (ε_P) and the effective solid angle (Ω_eff). These parameters were calculated numerically depending on the direct mathematical method and efficiency transfer method. The obtained CSCF was used to correct the measured efficiency curves, which were measured at different distances, then compared to the ETNA and EFFTRAN programs, as well as the CSCF. The results show a good agreement, especially at large source-to-detector distances.     

Thermal Ionization and Inductively Coupled Plasma Mass Spectrometry: Potential for Application to Studies on the Biokinetics of Molybdenum in Humans

Abstract

The use of stable isotopes as tracers in biokinetic investigations provides a means to obtain important metabolic data directly in humans without exposing the subjects to undue risks. In this work, three types of mass spectrometers are compared with regard to the determination of the abundances of stable isotopes of molybdenum in natural and enriched aqueous samples. The data show a good response of thermal ionization mass spectrometry (TIMS) and of high-resolution inductively coupled plasma mass spectrometry (ICPMS) to the isotopic enrichment of the samples, whereas conventional quadrupole ICPMS shows an unsatisfactory reproducibility of the results. Moreover, only TIMS can achieve an accuracy of better than 1% for the obtained isotopic ratios. Although a tedious procedure for the preparation of the biological samples is required and less sensitivity is achieved as compared to ICPMS, TIMS still seems to be method of choice for the accurate assessment of isotope ratios as required in multitracer studies on human biokinetics of trace metals.