Improved external device for a mass‐carrying sliding system for shaking table testing

Shaking tables are suitable facilities to assess and validate the behavior of structures and nonstructural components under actual seismic actions. Because of the size and weight limitations of the tables, some approaches, like testing reduced‐scale models or testing only the main structural components, are deemed necessary. In these cases, to comply with modeling requirements, large amount of extra‐mass should be added to the specimen. Therefore, to avoid the risk of lateral instability of models, to maintain the weight of test specimens within table payload, while maintaining the amount of mass needed, an external device for transmitting the inertia forces to the models using an improved sliding system is proposed. Although friction devices for similar purposes have been developed using sliding bearings (Teflon pads or rollers), the measured coefficient of dynamic friction and the energy dissipated by friction have been very high. In order to drastically diminish the damping added to the specimen response when a friction device is used, the improved device employs a linear motion guide system (LMGS) with very low friction. Shaking table tests to collapse of reinforced concrete walls were used to evaluate the effectiveness of the proposed device. Measured dynamic friction coefficients, spectral accelerations and hysteresis loops show that friction developed in the LMGS did not add any significant amount of damping into the specimen response. Thus, the proposed device is a reliable and suitable mass‐carrying sliding system (MCSS) for dynamic testing using medium‐size shaking tables. Copyright © 2010 John Wiley & Sons, Ltd.     

下投式探空资料对数值预报初始场影响的个例分析

通过对2000年8月加勒比海地区飓风Debby活动期间,连续2个时次中使用下投式探空资料同化分析后,利用英国气象局全球数值预报系统的数值预报分析场和背景场的对比分析,阐明了由于下投式探空资料的引入,较好地描述了实际大气的情况,为数值预报提供了较为接近实际的初始场,从而提高了数值预报的精度。其中以湿度场和风场的贡献为最大。     

Secular resonances between bodies on close orbits II: prograde and retrograde orbits for irregular satellites

In extending the analysis of the four secular resonances between close orbits in Li and Christou (Celest Mech Dyn Astron 125:133–160, 2016) (Paper I), we generalise the semianalytical model so that it applies to both prograde and retrograde orbits with a one-to-one map between the resonances in the two regimes. We propose the general form of the critical angle to be a linear combination of apsidal and nodal differences between the two orbits \( b_1 \Delta \varpi + b_2 \Delta \varOmega \), forming a collection of secular resonances in which the ones studied in Paper I are among the strongest. Test of the model in the orbital vicinity of massive satellites with physical and orbital parameters similar to those of the irregular satellites Himalia at Jupiter and Phoebe at Saturn shows that \({>}20\) and \({>}40\%\) of phase space is affected by these resonances, respectively. The survivability of the resonances is confirmed using numerical integration of the full Newtonian equations of motion. We observe that the lowest order resonances with \(b_1+|b_2|\le 3\) persist, while even higher-order resonances, up to \(b_1+|b_2|\ge 7\), survive. Depending on the mass, between 10 and 60% of the integrated test particles are captured in these secular resonances, in agreement with the phase space analysis in the semianalytical model.     

International legal options for the control of biofouling on international vessels

Shipping represents a threat as a vector for the transfer of non-indigenous marine species through the discharge of ballast water and biofouling of vessels’ external structures and internal piping. While considerable attention has been given to the management of ballast water, there currently exists no international legal instrument with which to control biofouling.A number of existing legal mechanisms may be applicable in the context of coastal States’ rights under international law. However, existing mechanisms are insufficient to regulate all aspects of the biofouling problem to ensure comprehensive management of the issue. There is, therefore, a need for the development of a comprehensive international agreement to address this gap. The issue of biofouling on international vessels has now been included on the work programme of the International Maritime Organisation (IMO). As a contribution to discussions on how to address this particular issue at an international level, this article provides an analysis of the options available through the IMO to address this issue.Having defined the specific “threat scenario” with regard to hull fouling, the article will consider: (i) the international legal framework that has been established to regulate the harmful impacts of international shipping; (ii) the range of practical measures that are available to manage biofouling on vessels; and (iii) international legal options available to States to address the threat of biofouling posed by international shipping.     

小波变换及其在影像表示中的应用和其方向选择性算法的改进

小波理论是研究多分辨率信号处理的理论,目前被公认为有前途的新理论。金字塔结构的影像处理、影像理解,现代GIS处理多比例尺的要求以及地形、场论中的逼近均需有关这一理论的支持。本文利用小波变换分解原始影像以实现影像的小波表示,并发展为任意方向的小波变换、逆变换,利用它检测航片中建筑物及其阴影的公共边缘。这种表示方式可为某些影像特征或识别目标提供较为经济的分辨率,该表示方式使影像中具有一定层次的结构更易于发现和利用。实验结果证明了此方法是有效的。     

A new model for the structure of the DACs regions in the Oe and Be stellar atmospheres

As it is already known, the spectra of many Oe and Be stars present Discrete Absorption Components (DACs) which, because of their profiles' width as well as the values of the expansion / contraction velocities, they create a complicated profile of the main spectral lines. This fact is interpreted by the existence of two or more independent layers of matter, in the region where the main spectral lines are formed. Such a structure is responsible for the formation of a series of satellite components (DACs) for each main spectral line. In this paper we present a first approximation to a mathematical model reproducing the complex profile of the spectral lines of Oe and Be stars that present DACs. This model presupposes that the regions, where these spectral lines are formed, are not continuous but consist of a number of independent absorbing density layers of matter, followed by an emission region and an external general absorption region. When we fit the spectral lines that present DACs, with this model, we can calculate the values of the apparent rotation and expansion / contraction velocities of the regions where the DACs are formed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spatial variations in surface sediment structure in riffle–pool sequences: a preliminary test of the Differential Sediment Entrainment Hypothesis (DSEH)

Riffle–pool sequences are maintained through the preferential entrainment of sediment grains from pools rather than riffles. This preferential entrainment has been attributed to a reversal in the magnitude of velocity and shear stress under high flows; however the Differential Sediment Entrainment Hypothesis (DSEH) postulates that differential entrainment can instead result from spatial sedimentological contrasts. Here we use a novel suite of in situ grain‐scale field measurements from a riffle–pool sequence to parameterize a physically‐based model of grain entrainment. Field measurements include pivoting angles, lift forces and high resolution digital elevation models (DEMs) acquired using terrestrial laser scanning, from which particle exposure, protrusion and surface roughness were derived. The entrainment model results show that grains in pools have a lower critical entrainment shear stress than grains in either pool exits or riffles. This is because pool grains have looser packing, hence greater exposure and lower pivoting angles. Conversely, riffle and pool exit grains have denser packing, lower exposure and higher pivoting angles. A cohesive matrix further stabilizes pool exit grains. The resulting predictions of critical entrainment shear stress for grains in different subunits are compared with spatial patterns of bed shear stress derived from a two‐dimensional computational fluid dynamics (CFD) model of the reach. The CFD model predicts that, under bankfull conditions, pools experience lower shear stresses than riffles and pool exits. However, the difference in sediment entrainment shear stress is sufficiently large that sediment in pools is still more likely to be entrained than sediment in pool exits or riffles, resulting in differential entrainment under bankfull flows. Significantly, this differential entrainment does not require a reversal in flow velocities or shear stress, suggesting that sedimentological contrasts alone may be sufficient for the maintenance of riffle–pool sequences. This finding has implications for the prediction of sediment transport and the morphological evolution of gravel‐bed rivers. Copyright © 2012 John Wiley & Sons, Ltd.     

Vertical Carbon Flux of Biogenic Matter in a Coastal Area of the Aegean Sea: The Importance of Appendicularians

This work focuses on the direct measurement of the vertical flux of appendicularian houses in order to assess their importance as a component of vertical carbon flux in coastal areas. For this purpose, arrays of cylindrical sediment traps were deployed for 5 to 8 days at two depths in a coastal area of the northern Aegean Sea (inner Thermaikos Gulf) during spring. The data support the contention that resuspension was minimal. Fecal pellet (FP) production and grazing experiments with the dominant copepods (Acartia clausi) were conducted to provide additional information on the potential FP contribution to the total carbon flux. The magnitude of the vertical flux of particulate organic carbon (POC) ranged between 310 and 724 mg C m^?2 day^?1. The proportion of phytoplankton carbon in the POC vertical flux was up to 45 %. The contribution of zooplankton FPs to the total carbon never exceeded 5 %. On the contrary, appendicularian houses were an essential component of the biogenic carbon flux contributing up to 55.3 % of the total vertical carbon flux. Consequently, both phytoplankton and appendicularian houses contributed equally to the biogenic carbon flux exceeding 80 % of the total sinking POC. Taking into account the sinking speed of the particles and the environment in the area, all this carbon probably reaches the seafloor, thus indicating a strong pelagic–benthic coupling.     

Orbital observations of meteors in the Martian atmosphere using the SPOSH camera

We investigate the expected performance of a wide-angle camera in Martian orbit, which, unlike previous cameras that have flown to Mars, is capable of recording meteor activity in that planet's atmosphere. We show that, based on our current understanding of meteor physics and the interplanetary meteoroid population, several meteors will be detected by this instrument during a single nightside pass on a low Martian orbit. The instrument will also record the signatures of meteor showers expected to occur every Martian year (1.88 Earth years). The results of this investigation will test models of the flux of “large” (mm-cm) meteoroids at the orbit of Mars and their interaction with the Martian atmosphere.