Canaletto’s paintings open a new window on the relative sea-level rise in Venice

The paintings by Canaletto (1697–1768), made with the help of a camera obscura, are just like real photographs, documenting as they do the Venice of the XVIII century with an accurate reproduction of all the details. The brown–green front left by the Laminaria, an alga living between the high and low tide, constitutes a precise biological indication of the average level of the high tide. By comparing the level of this front at Canaletto’s time with the present level, we can calculate/discover the relative sea level rise which has occurred in the last two and a half centuries.     

A color image segmentation method as used in the study of ancient monument decay

In the cultural heritage area, it is of fundamental importance to characterize and classify the conservation state of the materials constituting ancient monuments, in order to study and monitor their decay. Generally, the decay diagnosis is provided by “naked eye” analysis done by expert scientists “walking around” the artifact and recording the conservation state of each individual element they observe. In this paper, a color image segmentation approach, based on histogram threshold and edge detection techniques is presented, to extract degradation regions, characterized by holes or cavities, from color images of stone-materials. The goal is to provide an aid to the decay diagnosis by segmenting degraded regions from color images, computing quantitative data, such as the area and perimeter of the extracted zones, and processing qualitative information, such as various levels of depth detected into the same zones. Since color is a powerful tool in the distinction between objects, a segmentation technique based on color, instead of intensity only, has been used to provide a clearer discrimination between regions. The study case concerns the impressive remains of the Roman Theatre in the city of Aosta (Italy). In particular, we have processed and analyzed some color images of the theatre puddingstones, acquired by a camera.     

Environmentally-induced stone decay: the cumulative effects of crystallization–hydration cycles on a Lincolnshire oopelsparite limestone

An investigation has been undertaken at St Andrew’s church, Walpole St Andrew, Norfolk, to establish the underlying causes of the observed stone decay to the upper parts of the six stone piers. The stone decay was first recorded in the early 1930s. The salt-contaminated masonry within the church has been shown to undergo severe salt decay during the summer, with little damage occurring over the winter months. The south aisle piers have been shown to decay 2.5 times faster than the north aisle piers. Although crystallization–hydration cycles have been identified, the rate of decay is at its greatest when the cycling is relatively infrequent. This was not the expected trend. Furthermore, it has been shown that during extended periods where the ambient relative humidity is less than 75%, the rate of decay reaches a maximum. It is the length of this ‘drying’ period that apparently has the greatest influence on the rate of decay and could explain the significant difference in the rate of decay between the south and north aisle piers. The results have serious implications for passive conservation, where it is often recommended to lower the ambient relative humidity to well below the equilibrium relative humidity of the salt contaminant, to avoid crystallization–hydration cycles. Since, at the time of building, the church was situated on the coast, it is possible that the sodium chloride contamination occurred during the building process (1440–1520), particularly since the area was prone to sea-flooding at this time. Alternatively, the salt could have been applied as a treatment during the general restoration of 1897. Whatever the source of the salt, it seems likely that the ambient environment was changed by the insertion of a sealed floor in 1897, which could account for the onset of the salt decay.     

利用相干经典场操控激子间的纠缠度和混合度

借助于共生纠缠度和线性熵,研究了两个受驱动的量子点与单模腔场系统中激子纠缠度和混合度的演化动力学行为.结果表明:当无外加驱动场,激子的纠缠度和混合度呈现周期性的振荡.当激子受外经典场驱动时,其纠缠度和混合度都将减少.但Ω/g调节合适,我们能有效的抑制态的混合度而制备出一个纯净的激子纠缠态.     

Flat-top and low-dispersion optical interleavers based on nested prism pair structure

A novel flat-top and low-dispersion optical interleaver using ring cavities (RCs) in a Mach-Zehnder interferometer (MZI) is proposed. It is composed of eight mirrors and two nested prism pairs. Each prism and the two mirrors behave as a RC. Phase shift of RC is a periodic function of the frequency of the input light which acts as a phase dispersive mirror. The two phase shifts needed to achieve a flat-top spectral passband are provided by Fresnel reffectivities at the prism-air interface of the two RCs. The...     

中国档案文献近代散佚述论

档案文献是历史研究的第一手资料。由于自然和人为的原因，近百年来，中国档案文献蒙受了重大损失，教训深刻，发人深思。     

浅析惠州地区墙体材料的选择

本文通过对惠州地区建筑工程所用墙体材料的调查与分析, 并通过对烧结普通砖与新型墙体材料各项物理力学性能及经济指标的比较, 着重阐述了在实际工程当中惠州地区应广泛采用新型墙体材料的重要性, 以及大力推广墙体改革的必要性.     

圆形镜平面腔数值迭代计算

从菲涅尔-基尔霍夫积分衍射方程出发,推导了圆形镜平面腔所满足的自再现模迭代方程,给出了数值迭代方程的具体形式和TEM00、TEM01、TEM10 3个模式的具体迭代方法。分析计算了3个自再现模的形成过程、单程损耗及相位等特性,并比较了不同菲涅尔数时各模式的本征值和衍射损耗。该方法为研究圆形平面镜谐振腔的激光模式、损耗特性及相位提供了可靠的理论方法,具体的数值迭代方法也可推广应用到其他类型的谐振腔。     

Generation of four-photon entangled states based on interaction between a three-level atom and two bimodal cavities

A simple scheme is presented for generating four-photon entangled states with interaction between a three-level atom and two bimodal cavities.In the proposed protocol,the quantum information is encoded on Fock states of the cavity fields.The detection of the atom can collapse the cavity made/wave function to the desired state.The experimental feasibility of our proposal is also discussed.     

卡多话衰变现状研究

卡多话是哈尼族卡多支系人所说的一种语言,属于哈尼语碧卡方言,其使用人口约有18万。近20年来,随着社会的发展,卡多话呈现出一种衰退的趋势。围绕卡多话的衰退现象,从语言使用的现状、词汇能力以及语言本体的衰退表现三个方面来论证和揭示卡多话衰退的现状,并探究其衰退的原因。