Shock transmission in a coupled beam system

This paper investigates the circumstances under which high peak acceleration can occur in the internal parts of a system when subjected to impulsive driving on the outside. Motivating examples include the design of packaging for transportation of fragile items. The system is modelled in an idealised form using two beams coupled with point connections. A Rayleigh-Ritz model of such coupled beams was validated against measurements on a particular beam system, then the model was used to explore the acceleration response to impulsive driving in the time, frequency and spatial domains. This study is restricted to linear vibration response and additional mechanisms for high internal acceleration due to nonlinear effects such as internal impacts are not considered. Using Monte Carlo simulation in which the indirectly driven beam was perturbed by randomly placed point masses a wide range of system behaviour was explored. This facilitates identification of vulnerable configurations that can lead to high internal acceleration. The results from the study indicate the possibility of curve veering influencing the peak acceleration amplification. The possibility of veering within an ensemble was found to be dependent on the relative coupling strength of the modes. Understanding of the mechanism may help to avoid vulnerable cases, either by design or by preparatory vibration testing. © 2013 Elsevier Ltd.

DNA加合物研究及在环境毒理学中的应用

致癌物在生物体内经解毒系统诱导与生物体内的DNA形成加合物,DNA加合物综合反映了生物体对致癌物的暴露、吸收、分布、代谢以及机体对DNA的修复能力,是致癌物有效作用的量度,与致癌作用直接相关。目前较多用于DNA加合物测定的方法是~(32)P后标记技术。DNA加合物作为一项反映人群暴露于致癌物的指标在肿瘤分子流行病学研究中得到了较好的应用,鱼与哺乳动物一样可活化致癌物形成DNA加合物,由于解毒系统不完善及DNA修复能力差而对致癌物特别敏感,因此鱼及其他水生动物的DNA加合物研究受到重视并且一直引人注目。

关于金钱鲃属分类的一些问题(鲤形目:鲤科:鲃亚科)

目的讨论金线属是否适宜作亚属划分和该属云南湖泊3亚种的分类地位。方法形态分类和系统发育分析相结合的方法。结果提出了属下划分亚属的参考标准；过去所分的两个亚属之间无明显的形态特征差异，也不能构成姐妹群关系；云南湖泊3亚种被分散在属内不同的支序中。结论无论在系统发育上，还是在分类上，过去所分亚属均不恰当，且该属不适宜划分亚属；云南湖泊3亚种应分别提升为独立的种。

凤眼莲组织培养的研究

将凤眼莲茎段培养在含６－ＢＡ１～１０ｍｇ／Ｌ的ＭＳ培养基上，光照培养，可直接分化出芽．６－ＢＡ浓度为３ｍｇ／Ｌ时，芽分化频率最高，达４６．７％．所分化的不定芽必须及时转移到低激素浓度的培养基上，才能进一步生长发育．凤眼莲幼叶和幼根外植体在上述相同培养条件下，仅能形成愈伤组织．凤眼莲再生植株必须生长在高湿度的培养环境中，液体培养明显优于固体培养．

The propagation of acoustic waves in a slowly varying duct with radially sheared axial mean flow

We consider the propagation of acoustic waves along a cylindrical duct carrying radially sheared axial mean flow, in which the duct radius is allowed to vary slowly along the axis. In previous work [A.J. Cooper & N. Peake, Journal of Fluid Mechanics 445 (2001) 207-234.] radially sheared axial mean flow with nonzero swirl in a slowly varying duct was considered, but in this paper we set the swirl to zero, thereby allowing simplification of the calculations of both the mean and unsteady flows. In this approach the acoustic wavenumber and corresponding eigenfunction are determined locally, while the wave amplitude is found by solving an evolution equation along the duct. Sample results are presented, including a case in which, perhaps surprisingly, the number of cut-on modes increases as the duct radius decreases. © 2013 Elsevier Ltd. All rights reserved.

鳜鱼的耗氧率及其池塘养殖

本文较详细地报道了鳜鱼的耗氧率和窒息点，并对鳜鱼和作其饲料的鱼同池饲养的可能性进行了探讨。结果表明，鳜鱼耗氧量和体重正相关（ｒ＝０．９９），耗氧率与体重反相关（ｒ＝－０．９７）；在水温２０℃，鱼种耗氧率约为０．１４ｍｇ／ｇ．ｈ．，成鱼约为０．１２ｍｇ／ｇ．ｈ．；耗氧量和耗氧率均与水温正相关（ｒ＝０．９０，ｒ＝０．９４），水温１３—３０℃时，体重２３０±１１．７ｇ的鳜鱼。耗氧量为１４．３１—４２．１３ｍｇ／尾。ｈ．，耗氧率为０．０５９—０．１７５ｍｇ／ｇ．ｈ．；鳜鱼耗氧率昼夜变化与家鱼相反，黄昏至凌晨是高峰

鲤斜管虫的形态及形态发生的研究

本文报道了鲤斜管虫的形态、纤毛下器、核器、银线系及形态发生过程。其腹面口区具二环围口纤毛列及一口前纤毛列；背面具一列背刚毛；腹面纤毛列的数目可发生较大变动。在其形态发生过程中，左纤毛列在右纤毛列发生断裂前同时断裂；短基粒列形成后仔虫的背刚毛；前仔虫保留原口管前端部分，后仔虫的口管重新形成。本文还对鲤斜管虫的形态学特征、口管形成机理及分类问题等进行了讨论。

Modelling the vibration of tyre sidewalls

The dynamical behaviour of the sidewall has an important influence on tyre vibration characteristics. Nonetheless, it remains crudely represented in many existing models. The current work considers a geometrically accurate, two-dimensional, sidewall description, with a view to identifying potential shortcomings in the approximate formulations and identifying the physical characteristics that must be accounted for. First, the mean stress state under pressurisation and centrifugal loading is investigated. Finite-Element calculations show that, while the loaded sidewall shape remains close to a toroid, its in-plane tensions differ appreciably from the associated analytical solution. This is largely due to the inability of the anisotropic sidewall material to sustain significant azimuthal stress. An approximate analysis, based on the meridional tension alone, is therefore developed, and shown to yield accurate predictions. In conjunction with a set of formulae for the 'engineering constants' of the sidewall material, the approximate solutions provide a straightforward and efficient means of determining the base state for the vibration analysis. The latter is implemented via a 'waveguide' discretisation of a variational formulation. Its results show that, while the full geometrical description is necessary for a complete and reliable characterisation of the sidewall's vibrational properties, a one-dimensional approximation will often be satisfactory in practice. Meridional thickness variations only become important at higher frequencies (above 500 Hz for the example considered here), and rotational inertia effects appear to be minor at practical vehicle speeds. © 2013 Elsevier Ltd. All rights reserved.

Friction-induced vibration: Model development and comparison with large-scale experimental tests

This paper presents a comparison between theoretical predictions and experimental results from a pin-on-disc test rig exploring friction-induced vibration. The model is based on a linear stability analysis of two systems coupled by sliding contact at a single point. Predictions are compared with a large volume of measured squeal initiations that have been post-processed to extract growth rates and frequencies at the onset of squeal. Initial tests reveal the importance of including both finite contact stiffness and a velocity-dependent dynamic model for friction, giving predictions that accounted for nearly all major clusters of squeal initiations from 0 to 5 kHz. However, a large number of initiations occurred at disc mode frequencies that were not predicted with the same parameters. These frequencies proved remarkably difficult to destabilise, requiring an implausibly high coefficient of friction. An attempt has been made to estimate the dynamic friction behaviour directly from the squeal initiation data, revealing complex-valued frequency-dependent parameters for a new model of linearised dynamic friction. These new parameters readily destabilised the disc modes and provided a consistent model that could account for virtually all initiations from 0 to 15 kHz. The results suggest that instability thresholds for a wide range of squeal-type behaviour can be predicted, but they highlight the central importance of a correct understanding and accurate description of dynamic friction at the sliding interface. © 2013 Elsevier Ltd. All rights reserved.

Transient response of structures with uncertain properties to nonlinear shock loading

A method is presented to predict the transient response of a structure at the driving point following an impact or a shock loading. The displacement and the contact force are calculated solving the discrete convolution between the impulse response and the contact force itself, expressed in terms of a nonlinear Hertzian contact stiffness. Application of random point process theory allows the calculation of the impulse response function from knowledge of the modal density and the geometric characteristics of the structure only. The theory is applied to a wide range of structures and results are experimentally verified for the case of a rigid object hitting a beam, a plate, a thin and a thick cylinder and for the impact between two cylinders. The modal density of the flexural modes for a thick slender cylinder is derived analytically. Good agreement is found between experimental, simulated and published results, showing the reliability of the method for a wide range of situations including impacts and pyroshock applications. © 2013 Elsevier Ltd. All rights reserved.

中华绒螯蟹人工授精的突破

<正> Schcank等(1967)曾报道用电刺激法采取马蹄蟹(Limulus polyphemus)的精荚和卵子,并声称由此获得的精、卵可以互相授精,但未见更详细的说明和证明授精的根据。有关中华绒螯蟹(Eriocheir sinensis)的人工授精,迄今未见任何报道。

直链烷基苯磺酸盐在模拟水生态系统中转化和归宿的研究

用~(14)C标记直链烷基苯磺酸盐,(~(14)C-LAS),研究了在由塘泥、水草、鱼、螺蛳和溞构成的室内模拟水生态系统中,LAS的降解规律、在水生生物体内的积累分布及其与在水中降解之间的相互关系.

鱼类的天然雌核发育

<正> 1.孤雌生殖,雌核发育和杂合发育单性型种群在脊椎动物中是罕见的。尽管如此,到目前为止几乎已在各类脊椎动物中发现了单性型种群。该种群通常涉及3种繁殖方式,即孤雌生殖(parthenogenesis)、雌核发育(gynogenesis)和杂合发育(hybridogenesis)。