Directional wave separation in tubular acoustic systems – The development and evaluation of two industrially applicable techniques

An acoustic device is used to evaluate internal features and defects within tubes by determination of the acoustic impulse response. This paper concerns methods of separating the total pressure wave measured in the device into its forward and backward travelling components, which facilitates computation of the acoustic impulse response. The device comprises a tube that has a speaker at one end and is axially instrumented with microphones. Unlike similar works, the methods presented in this paper were designed to be applied in an industrial context, they allow simple calibration and implementation using readily transportable equipment. Two wave separation algorithms are presented; the first is a known method that has been improved to provide simplified calibration and the second is a computationally inexpensive technique that has been adapted to improve its operational bandwidth. The techniques are critically evaluated using a custom built test rig, designed to simulate realistic tube features and defects such as constrictions, holes and corrosion. It is demonstrated that, although inter-microphone attenuation is not accounted for in the second algorithm, both algorithms function well and give similar results. It is concluded that the added sophistication of the first method means that it is less affected by low frequency interference and is capable of yielding more accurate results. However, in practical use as an evaluation tool, the benefits of including inter-microphone attenuation are outweighed by the additional calibration and computational requirements. Finally the output of the wave separation techniques is validated by showing agreement between experimental impulse response measurements and those obtained from a theoretically derived acoustic tube simulator.     

Nonlinear dynamics of cantilevered pipes conveying fluid: Towards a further understanding of the effect of loose constraints

The nonlinear dynamics of a fluid-conveying cantilevered pipe with loose constraints placed somewhere along its length is investigated. The main objective of this study is to determine the effects of several geometrical and physical parameters of the loose constraints on the characteristics and behavior of pipes conveying fluid. Based on the full nonlinear equation of motion, the dynamical behavior of the pipe system is investigated. Phase portraits and bifurcation diagrams are constructed for a selected set of system parameters. Typical results are firstly compared to numerical ones reported previously and excellent agreement is obtained. Then, the threshold flow velocities for several key bifurcations including pitchfork, period doubling, chaos, and sticking behaviors are predicted, showing that in many cases, the gap size, stiffness, and asymmetry of the loose constraints have remarkable effects on the nonlinear responses of the cantilevered pipe conveying fluid. For a pipe system with small/large constraint gap sizes, small constraint stiffness, or large constraint offset, some of the complex dynamical behaviors including chaos and period-doubling bifurcations would disappear, at least in the flow velocity range of interest.     

μ介子转化电子装置超导磁体低温系统(英文)

μ介子转化为电子的试验装置(MECO)将安装在美国布鲁克海文国家实验室的交变磁场梯度同步加速器中。一台4.5K千瓦制冷量的氦制冷设备将为MECO试验中的四个大型的超导螺线管磁体提供冷量,针对MECO中超导磁体的性能特点及要求,主要讨论了该低温系统中每个超导磁体的冷却方法以及相应氦制冷机的流程设计方案。     

直线变压器驱动源磁芯能量传递效率

磁芯是直线变压器驱动源(LTD)的关键部件之一,起着初、次级能量传递和次级电压感应叠加的作用,磁芯的能量传递效率对LTD系统的效率、体积和重量影响显著。对LTD系统中影响磁芯能量传递效率的原因进行了初步的分析,并利用Pspice软件的非线性磁芯模型对磁芯的工作过程和损耗进行了模拟计算,最后对LTD磁芯的能量传递效率进行了初步的实验研究,在工作电压为20 kV时、脉宽约220 ns时,在2.8 Ω负载上获得了大于60%的能量传递效率。     

HIRFL-CSR电子冷却装置高精度螺线管线圈制作及磁场测量

采用特殊工艺制作了HIRFL-CSR电子冷却装置冷却段高精度螺线管线圈,两个产生反向磁场的线圈同轴、平行地放置在特制的测量装置上,高精度霍尔探头位于测量装置中心平面上,探头测量面与测量装置轴线重合,测量单个线圈磁场的横向分量,调节线圈几何轴相对于测量装置轴线的夹角,测得线圈磁轴的偏角小于1×10-3。     

Multipumping Nitrite Determination in Exhaled Breath Condensate

Abstract

A flow system based on multicommutation is proposed for the rapid, clean, and inexpensive determination of nitrites in small volumes of breath condensates. The procedure exploits the colorimetric detection of nitrite with the Griess reagent [0.03% naphthylethylene diamine dihydrochloride (NED), 0.5% sulpfhanilamide, and 3.0% phosphoric acid] in acidic medium at 540 nm correcting the variations of the baseline with measurements at 424 nm. The flow system was designed with a set of solenoid micropumps to minimize sample and reagent consumption and waste generation. The detection limit was estimated as 3.8 ng mL^?1 (99.7% confidence level) with a linear response ranging up to 500 ng mL^?1. The coefficient of variation was estimated as 0.7% for a solution containing 300 ng mL^?1 nitrite (n=9). Approximately 144 determinations can be carried out per hour, consuming only 678.4 µg Griess reagent and generating 1.184 mL of effluent per determination, thus providing an environmentally friendly alternative and a nonexpensive method. The procedure was successfully applied to determine nitrite in breath condensates.     

膜片电极支撑自组装双层脂膜中短杆菌肽离子通道的形成

通过一个两步程序在膜片电极尖端形成自组装双层脂膜：（1）膜片电极尖端沾取成膜液；（2）将吸附成膜液的尖端浸入电解液中，排除尖端多余的成膜液，通过电学方法监测双层脂膜的形成。将短杆菌肽通道蛋白分散在成膜液和电解质溶液中，在制备膜片电极支撑双层脂膜过程中，短杆菌肽重组到双层脂膜中形成离子通道，对通道的一般特性进行了研究，并观察到通道开放和关闭的现象。     

测量螺线管磁场的误差与修正

阐述实验验证螺线管磁场分布时理论与实验结果的差异原因及修正方法。     

Erosion of oil&gas industry choke valves using computational fluid dynamics and experiment

As part of several years research activity with erosion in chokes, Norsk Hydro ASA has developed a model to estimate erosion and lifetime of chokes by incorporating erosion models into particulate flow models. This model has been verified with the results from flow and erosion testing of two different types of chokes, Needle&Seat and External Sleeve. The erosion tests with both the modified Needle&Seat choke and the External Sleeve choke gave peak erosion rates only two or three times larger than calculated. This is assumed to be near the uncertainty of the erosion model alone. This is very satisfactory for such complex flow geometries. The model and the experiments demonstrated that the External Sleeve choke is much more prone to erosion attack, at the given low pressure conditions.     

Homogeneous continua in 2-manifolds

In 1960 R.H. Bing [2] proved that every homogeneous plane continuum that contains an arc is a simple closed curve. At that time Bing [2, p. 228] asked if every 1-dimensional homogeneous continuum that contains an arc and lies on a 2-manifold is a simple closed curve. We prove that no 2-manifold contains uncountably many disjoint triods. We use this theorem and decomposition theorems of F.B. Jones [10] and H.C. Wiser [19] to answer Bing's question in the affirmative. We also prove that every homogeneous indecomposable continuum in a 2-manifold can be embedded in the plane. It follows from this result and another theorem of Wiser [20] that every homogeneous continuum that is properly contained in an orientable 2-manifold is planar.