Distribution and source apportionments of polychlorinated biphenyls (PCBs) in mariculture sediments from the Pearl River Delta, South China

Surface and core sediments collected from six mariculture farms in the Pearl River Delta (PRD) were analyzed to evaluate contamination levels of polychlorinated biphenyls (PCBs). The ∑PCBs (37 congeners) concentrations ranged from 5.10 to 11.0 ng g(-1) (mean 7.96 ng g(-1)) in surface and 3.19 to 22.1 ng g(-1) (mean 7.75 ng g(-1)) in core sediments, respectively. The concentrations were significantly higher than that measured in the sediments of their corresponding reference sites, whereby the average enrichment percentages were 62.0% and 42.7% in surface and core sediments, respectively. Significant correlations (R2=0.77, p<0.05) of PCB homologue group proportions between fish feeds and surface mariculture sediments suggested that fish feed input was probably the main source for the enrichment of PCBs. Due to the fact that PCBs could be transferred along food chains, PCB contamination in fish feeds and mariculture sediments should not be overlooked.     

UBV observations of short-period close binary V392 Orionis

The eclipsing binary V392 Ori was observed photoelectrically, from November 1984 to January 1985, inUBV bands using the P34B photometer attached to the 0.91 m reflector at the McDonald Observatory. Four-hundred eighty-six observations in each band were obtained. Six primary and 4 secondary minimum were observed during this period. The light curves show a typical Beta Lyrae-type variation instead of an Algol-type light curve reported earlier.     

《坤輿万国全图》与《利玛窦中国札记》中外译本考疑

金尼阁编译的《利玛窦中国札记》多种欧洲文字版本之间存在翻译差异,而300年后出版的英译本和中译本与原文存在严重错漏。600页的札记,利玛窦只用不到两页的篇幅叙述测绘《坤輿万国全图》一事,连实际比例尺的描述也不清楚。利玛窦承认没有见过其他的版本,"六幅版"地图出现在南京或北京,个别欧洲文字翻译版本不一,《坤輿万国全图》究竟是在南京还是北京完成的也有疑问。《利玛窦中国札记》用的是中国传统的测绘术语,指出地图的错误是针对西方地图而不是中国地图。《坤輿万国全图》中一半的中文地名,当时欧洲地图没有对应。1593年,利玛窦尚未制作《坤輿万国全图》,"六幅版"中文世界地图已出现在南京。因此,《坤輿万国全图》原本早已存在,《坤輿万国全图》应是郑和时代(1405—1433)大航海的成果,中国的地图学,不是西学东渐,甚至有可能是中国的世界地理与地图学流传到西方。世界地图史应该还原中国对地理大发现与地图学的贡献。     

Vibration isolation by trenches in continuously nonhomogeneous soil by the BEM

Vibration isolation of structures from ground-transmitted waves by open trenches in isotropic, linearly elastic or viscoelastic soil with a shear modulus varying continuously with depth is numerically studied. Both an exponential and a linear shear modulus variation with depth are used in this work. Waves produced by the harmonic motion of a rigid surface machine foundation are considered. The problem is solved by the frequency domain boundary element method employing the Green's function of Kausel-Peek-Hull for a thin layered half-space. Thus only the trench perimeter and the soil-foundation interface need essentially to be discretized. The proposed methodology is first tested for accuracy by solving two Rayleigh wave propagation problems in nonhomogeneous soil with known analytical solutions and/or for which experimental results are available. Then the method is applied to vibration isolation problems and the effect of the inhomogeneity on the wave screening effectiveness of trenches is studied.     

Non-linear steady state vibration and dynamic snap through of shallow arch beams

The non-linear steady state vibration of shallow arch beams is studied by a finite element method based on the principle of virtual work. Both the free and forced periodic vibrations are considered. The axial and flexural deformations are coupled by the induced axial force along the beam element. The spatial discretization is achieved by the usual finite element method and the steady state nodal displacements are expanded into a Fourier series. The harmonic balance method gives a set of non-linear algebraic equations in terms of the vibrating frequency and the Fourier coefficients of nodal displacements. The non-linear algebraic equations are solved by the Newtonian algorithm iteratively. The combined algorithm is called the incremental harmonic balance method. The importance of the conditions of completeness and balanceability is presented. Since the non-linearity is essentially softening, different orders of internal resonances between two modes can occur repeatedly. Isolated response curves are possible and are connected to the bifurcation of a particular excited mode.     

Photometric investigation of the short period eclipsing binary star V719 Her

The Behlen observatory 0.76 m telescope CCD photometer is used to obtain 347 observations of the short period (P0^d.4) eclipsing binary star V719 Her. The observations done withV andR bandpass filters were made on 6 nights in 1993. Previously published light elements and the present five timings of minimum provide a new epoch and a more accurate orbital period of 0.4009828 days. Our analyses show that the period of the system appears to decrease. We recommend future monitoring of the eclipse minima for this system. No published spectral classification for V719 Her exists. From the color,V-R=0.391, we estimate it to be about F5.The 1993 version of the Wilson Devinney model gave the photometric solutions. The adopted solution indicates that V719 Her is a W UMa type contact binary. The mass ratio,q=(m ₂/m ₁, where star 1 eclipse at the primary minimum)=0.296 suggests that V719 Her is a WUMa system with type-A (transit during primary eclipse) configuration. The secondary minimum shows a total eclipse. V719 Her with period less than 0.5 and spectral class F5, is probably a zero-age contact system. Since our photometric solution shows that the luminosity difference between the components is very large, we suspect that V719 Her is most likely a single line spectroscopic binary. We recommend spectroscopic study of this system.     

Centrifuge modelling of the effects of root geometry on transpiration-induced suction and stability of vegetated slopes

Shallow landslides (i.e. 1–2-m depth) on both man-made and natural slopes are of major concern worldwide that has led to huge amount of socio-economical losses. The use of vegetation has been considered as an environmentally friendly means of stabilising slopes. Existing studies have focused on the use of plant roots with different geometries to mechanically stabilise soil slopes, but there are little data available on the contribution of transpiration-induced suction to slope stability. This study was designed to quantify both the hydrological and mechanical effects of root geometry on the stability of shallow slopes. Centrifuge tests were conducted to measure soil suction in slope models supported by newly developed artificial roots. These artificial roots exhibit three different representative geometries (i.e. tap, heart and plate) and could simulate the effects of transpiration. The measured suction was then back-analysed through a series of finite element seepage-stability analyses to determine the factor of safety (FOS). It is revealed that after a rainfall event with a return period of 1000 years, the slope supported by heart-shaped roots retained the highest suction within the root depth, and thus, this type of root provided the greatest stabilisation effects. The FOS of the slope supported by the heart-shaped roots, through both mechanical reinforcement and transpiration-induced suction, is 16 and 28 % higher than that supported by the tap- and plate-shaped roots, respectively.     

Experimental investigation of the lift component of roll damping

The lift force and turning moment acting on a model towed obliquely to the direction of motion have been measured. Two models were used; one of them was tested fitted with and without a rudder. These measurements were used to determine the magnitude of the lift coefficient and the point of application of the transverse force acting on the model. The data were then used to determine the lift component of the roll damping moment. It has been found that the equivalent linear damping coefficient due to lift is a nonlinear function of the forward speed of the ship.