Impulse duration: A new instrument for its measurement

An instrument is described which, when used with a ‘peak hold’ reading sound level meter, will measure the durations of acoustic impulses in accordance with the Atherley and Martin and CHABA criteria for hearing damage risk to impulsive noise. The instrument is small, lightweight, can be battery powered and is designed for field use.Comparison tests show that the impulse duration meter gives more accurate and repeatable results than the oscilloscope trace photograph method or the digital waveform recorder method of impulse duration assessment.By using the instrument with a suitable impulse source reverberation time, measurements may be conducted.     

A high aperture beamline for vacuum ultraviolet circular dichroism on the srs

The three-day international workshop Actinide-XAS-2006 was held at Forschungszentrum Karlsruhe (FZK), Germany, from September 18–20, 2006. Actinide-XAS-2006 was the fourth workshop on speciation, techniques, and facilities for radioactive materials at synchrotron light sources. The Actinide-XAS series addresses the specialized field of the application of synchrotron techniques for investigating radioactive materials and is a forum for teaching and scientific discussion in this field, thereby strengthening existing and establishing new transnational cooperative scientific networks. The first and second workshops, Actinide-XAS-1998 and Actinide-XAS-2000, were held in Grenoble at the ESRF. The third and last workshop, Actinide-XAS-2004, was held at Lawrence Berkeley National Laboratory.     

新型钕铁硼电磁阻尼演示仪

利用稀土永磁材料钕铁硼（Ｎｄ－Ｆｅ－Ｂ）设计制作出一种新型电关演示仪,可演示阻尼振动的三种状态（欠阻尼状态、临界阻尼状态、过阻尼状态）,配合投影仪使用,演示效果显著。     

一种新的角动量守恒演示实验仪

介绍了新研制成功的一种物理演示实验仪,它是以进动过程中突然除去进动的原因而使进动中止的方式来演示角动量守恒的．实验仪结构简单,操作方便,反映的物理原理深刻．     

A new method and instrument for accurately measuring interval between ultrashort pulses

Using second-order autocorrelation conception, a novel method and instrument for accurately measuring interval between two linearly polarized ultrashort pulses with real time were presented. The experiment demonstrated that the measuring method and instrument were simple and accurate (the measurement error ＜ 5 fs). During measuring, there was no moving element resulting in dynamic measurement error.     

A new low-power, open-path instrument for measuring methane flux by eddy covariance

This paper describes a new low-power instrument for measuring methane flux by eddy covariance method at sites without grid power. Design and field performance of the LI-7700 Methane Analyzer (LI-COR Biosciences) are examined in this study. The instrument uses 8?W of power in steady-state operation and employs a tunable diode laser in an open Herriott cell configuration with 0.47?m base path and 30?m optical path length. Methane number density is measured using wavelength modulation spectroscopy (WMS) with 2f detection. Typical signal noise is <5?ppb rms at 10?Hz. Corrections for variations in temperature, pressure and water vapor are described. Data losses due to mirror contamination and condensation are minimized by a radiation shield and automatic mirror cleaning system and are shown to be small. Measured spectra and co-spectra are shown to follow the Kaimal model at deployment sites meeting classical criteria, and to follow sensible heat flux co-spectra from the sonic anemometer in most other cases, including difficult ones. Measured fluxes are similar in magnitude to those expected from the literature, and zero flux was measured during both summer and winter at a site known to have fluxes at or very near zero.     

A new look at the PPAC

The Parallel Plate Avalanche Counter (PPAC) has been used mostly for measuring the energy loss of single, heavily ionizing particles. A PPAC is even more effective with high-energy showers for which a single event causes hundreds of electrons to pass through it. For operation at reduced pressures, the alkanes such as isobutane, C₄H₁₀ are excellent PPAC gasses with the quality of performance increasing with the size of the molecule. Under some circumstances the perfluoroalkanes such as perfluoropropane, C₃F₈, may be preferred. For operation at atmospheric pressure, CF₄ and mixtures containing Ar and CO₂ work well.     

望远镜：一件开拓知识疆域的利器

文章探讨了望远镜作为一件科学仪器,从其在400年前被发明以来,在扩展人类的宇宙视野、开拓人类的知识疆域方面发挥了极其重要的作用.文章首先论述了伽利略利用其亲手改进的望远镜作出了全新的天文发现,对哥白尼学说给予了决定性的支持;其次阐述了随着望远镜的不断改进,人类获得越来越多的关于天空的新奇知识,这些知识帮助和推动人类掌握最基本的自然规律;最后论述了望远镜在帮助人类探索宇宙尺度之大小的过程中发挥的重要作用,并进而让人类认识到其自身在宇宙中的真实位置.     

A new detector for laser induced recombination at the ESR

For laser induced recombination of heavy ions a new detector was developed that in comparison to a multiwire proportional counter provides better time resolution. It is able to cope with very high rates and gives the possibility for very easy online monitoring of the detected beam. This revised version was published online in August 2006 with corrections to the Cover Date.     

A instrument for measuring solution concentration

Optical Review - In this paper, a set of devices, including hardware and software systems, is designed based on the basic principle of Michelson interferometry to measure solution concentration,...     

A new look at the accelerating universe

We show that the cosmological model having zero cosmological constant, but containing the vacuum energy of a simple quantized free scalar field of low mass (VCDM model), agrees with the cosmic microwave background radiation (CMBR) and supernova (SNe-Ia) data at least as well as the classical cosmological model with a small nonzero cosmological constant. We also show that in the VCDM model the ratio of vacuum pressure to vacuum energy density is less than -1. We display the VCDM results for a set of parameters that give a very good fit to the CMBR power spectrum, and show that the same parameters also give a good fit to the SNe-Ia data.     

A new search for the doubly charmed baryon ■ at the LHC

The standard quark model is capable of predicting the existence of doubly heavy baryons.Similar to doubly heavy mesons,doubly heavy baryons may allow the QCD-inspired potential model,the nonrelativistic QCD(NRQCD)factorization theory[1],etc.,to work on them well,while serving as a fruitful“laboratory”for testing these theories when a greatly enough collection of relevant data is available.Many attempts have been made to observe doubly heavy baryons,yet none of them succeeded due to the difficulties in producing such baryons either at the e^+e^- colliders or at the hadronic colliders.Noticeably,the running of the large hadronic collider(LHC)with a large centre-of-mass protonproton collision energy and a much higher luminosity provides a good opportunity for experimentalists to realize the aforementioned observation.     

A quantile-based Time at Risk: A new approach for assessing risk in financial markets

In this paper, we provide a new measure for evaluation of risk in financial markets. This measure is based on the return interval of critical events in financial markets or other investment situations. Our main goal was to devise a model like Value at Risk (VaR). As VaR, for a given financial asset, probability level and time horizon, gives a critical value such that the likelihood of loss on the asset over the time horizon exceeds this value is equal to the given probability level, our concept of Time at Risk (TaR), using a probability distribution function of return intervals, provides a critical time such that the probability that the return interval of a critical event exceeds this time equals the given probability level. As an empirical application, we applied our model to data from the Tehran Stock Exchange Price Index (TEPIX) as a financial asset (market portfolio) and reported the results.     

Gas filter correlation instrument for air monitoring at submillimeter wavelengths

A gas filter correlation (GFC) instrument for air monitoring at submillimeter wavelengths has been developed. We used a high-power terahertz radiation source in combination with a specific gas filter cell to obtain a highly selective instrument to differentiate species present in an unknown mixture. This approach provides a new method for survey measurements in the spectrum from 100 to 1000 GHz, in which many molecular rotational lines appear. Basic operational considerations and preliminary experiments with hydrogen sulfide are described.     

A simple instrument for relative microhardness measurement

The design of a simple inexpensive instrument which can be used along with a simple laboratory microscope to measure microhardness of crystals is described. The design is based on the fact that the lengths of arms of indentation dislocation rosette (idr) are related to the hardness. By controlled indentation and subsequent etching of two similar crystals, the microhardness of one can be estimated in terms of that of the other from measurements of the arms ofidr.     

New techniques for new sources: A fresh look at energy-dispersive diffraction for high-pressure studies

Abstract

Energy-dispersive diffraction is the most frequently used technique for high-pressure studies with synchrotron radiation. For optimum performance it requires high-energy radiation and few existing sources are able to meet this requirement. This is also important with large volume devices which demand even higher energies in order to obtain sufficient transmission. When working with diamond-anvil cells, the main experimental difficulties arise from the very small sample sizes. The use of a conical diffraction geometry increases the diffracted intensities, improves the signal-to-noise ratio and largely overcomes the crystallite statistics problem. This technique can also be used to greatly simplify high-pressure single-crystal studies. Combining these developments with recent progress in detectors and electronics will open up the field of high-pressure kinetics, but it is only with the operation of third generation synchrotron sources such as the ESRF that the present experimental limitations will be overcome.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for High Pressure Crystallography’. Daresbury Laboratory 20-21 July 1991