反射率对入射角扫描测定单轴晶体的折射率

通过分析波矢沿任意方向的单轴晶体的折射率,在光轴位于入射面内时,给出了入射光分别为s光和p光的反射率拟合函数。利用改进的反射率扫描仪,测量了CaCO3晶体的s光和p光反射率随入射角变化情况,由理论拟合获得单轴晶体的两个主折射率,分别为no=1.6559和ne=1.4851。这种方法不需要对样品进行加工,其精度达到0.0001。另外,对于晶体光轴未知的情况,采用改进的布儒斯特技术分别测出三个晶体表面的布儒斯特角,由此可以确定光轴的方向。

River Ribble sheep dip incident September 1997. Electric-fishing survey report

This report summarises the findings of a series of electric-fishing surveys carried out at four sites on the River Ribble from September 1997 to September 1998. The aims of these surveys were to assess the impact on juvenile salmonids of a pollution incident involving Synthetic Pyrethrin (SP) that occurred near High Birkwith I (SD 802 767) in September 1997.One of these sites was 2.65km upstream of the pollution whilst the remaining three were at varying distances downstream. Data was collected during surveys of the River Ribble in 1992, 97 and 98. The 1997 and 1998 surveys were carried out specifically to monitor for any possible effects of the SP discharge. Data are shown as grades derived from the National Fisheries Classification scheme (NFC). Results are given for the four salmonid life stages; 0+ trout, >0+ trout, 0+ salmon, >0+ salmon and also Total Salmonids.

A model for the erosive wear of rubber at oblique impact angles

A model has been developed to predict the erosive wear behaviour of elastomers under conditions of glancing impact by small hard particles. Previous work has shown the erosive wear mechanism of elastomers under these conditions to be similar in nature to that of abrasive wear by a sharp blade. The model presented here was developed from the model of Southern and Thomas for sliding abrasion, by combining their treatment of the growth of surface cracks with a model for particle impact in which the force - displacement relationship for an idealized flat-ended punch on a semi-infinite elastic solid was assumed. In this way an expression for the erosive wear rate was developed, and compared with experimental measurements of wear rate for natural rubber, styrene - butadiene rubber and a highly crosslinked polybutadiene rubber. Good qualitative agreement was found between the predictions of the model and the experimental measurements. The variation of erosion rate with impact velocity, impact angle, particle size, elastic modulus of the material, coefficient of friction and fatigue properties were all well accounted for. Quantitative agreement was less good, and the effects of erosive particle shape could not be accounted for. The reasons for these discrepancies are discussed. © 1992 IOP Publishing Ltd.

Run-up of solitary waves on twin conical islands using a boussinesq model

This paper investigates the interaction of solitary waves (representative of tsunamis) with idealized flat-topped conical islands. The investigation is based on simulations produced by a numerical model that solves the two-dimensional Boussinesq-type equations of Madsen and Sørensen using a total variation diminishing Lax-Wendroff scheme. After verification against published laboratory data on solitary wave run-up at a single island, the numerical model is applied to study the maximum run-up at a pair of identical conical islands located at different spacings apart for various angles of wave attack. The predicted results indicate that the maximum run-up can be attenuated or enhanced according to the position of the second island because of wave refraction, diffraction, and reflection. It is also observed that the local wave height and hence run-up can be amplified at certain gap spacing between the islands, owing to the interference between the incident waves and the reflected waves between islands. © 2012 American Society of Mechanical Engineers.

Additional angles to calculate the deformation of RNA helices induced by bulge loops

Bulges are common features of folded RNA structures. The RNA axial kinking caused by bulges has been confirmed by many experiments. Usually, a kinking angle zeta and a bending angle theta are used to describe the kinking and twisting of RNA molecules containing bulges. Here, we present two additional angles (twist angle zeta(1), twist angle zeta(2)) to describe the deformation of RNA helices induced by bulge loops because only two angles (a kinking angle zeta and a bending angle theta) are not enough to define the deformation of RNA induced by bulges. (C) 2002 Elsevier Science B.V. All rights reserved.

Influence of film cooling hole angles and geometries on aerodynamic loss and net heat flux reduction

Turbine design engineers have to ensure that film cooling can provide sufficient protection to turbine blades from the hot mainstream gas, while keeping the losses low. Film cooling hole design parameters include inclination angle (α), compound angle (β ), hole inlet geometry and hole exit geometry. The influence of these parameters on aerodynamic loss and net heat flux reduction is investigated, with loss being the primary focus. Low-speed flat plate experiments have been conducted at momentum flux ratios of IR = 0.16, 0.64 and 1.44. The film cooling aerodynamic mixing loss, generated by the mixing of mainstream and coolant, can be quantified using a three-dimensional analytical model that has been previously reported by the authors. The model suggests that for the same flow conditions, the aerodynamic mixing loss is the same for holes with different α and β but with the same angle between the mainstream and coolant flow directions (angle κ). This relationship is assessed through experiments by testing two sets of cylindrical holes with different α and β : one set with κ = 35°, another set with κ = 60°. The data confirm the stated relationship between α, β, κ and the aerodynamic mixing loss. The results show that the designer should minimise κ to obtain the lowest loss, but maximise β to achieve the best heat transfer performance. A suggestion on improving the loss model is also given. Five different hole geometries (α =35.0°, β =0°) were also tested: cylindrical hole, trenched hole, fan-shaped hole, D-Fan and SD-Fan. The D-Fan and the SD-Fan have similar hole exits to the fan-shaped hole but their hole inlets are laterally expanded. The external mixing loss and the loss generated inside the hole are compared. It was found that the D-Fan and the SD-Fan have the lowest loss. This is attributed to their laterally expanded hole inlets, which lead to significant reduction in the loss generated inside the holes. As a result, the loss of these geometries is ≈ 50 % of the loss of the fan-shaped hole at IR = 0.64 and 1.44. Copyright © 2011 by ASME.

Direction and polarisation estimation using polarised cylindrical conformal arrays

In this study, the authors describe two-dimensional direction finding and signal polarisation estimation from a cylindrical conformal array consisting of directional and polarised antenna elements. Firstly, a simple and general transformation procedure, based on the mathematical framework of geometric algebra, is presented for arbitrary conformal arrays with polarised and directional antennas. Subsequently, the authors utilise the symmetry of cylindrical arrays to estimate signal parameters via rotational invariance techniques. The authors show how to iteratively estimate the azimuth and elevation angles of the incident signal, as well as its polarisation. To illustrate the versatility of this method, the results of simulations on a 3×4 cylindrical conformal array are shown and discussed. © 2012 The Institution of Engineering and Technology.

The effect of wind tunnel size on incident shock boundary layer in-teraction experiments

We examine the effects of varying the tunnel width to height ratio on the shock boundary layer interac-tion of an incident oblique shock with a turbulent boundary layer. The computational domain is a simpli-fied representation of typical wind tunnel experiments; the top wall of the tunnel is not modeled; only the flow conditions imposed by the shock are modeled on the top of the computational domain. A hy-pothesis of the expected effect of width to height ratio is presented and tested computationally. All flows are found to be three dimensional for the single shock strength range of width to height ratios considered. The effect of tunnel width is a function of the boundary layer thickness which decreases the effective width.