Difference-frequency ultrasound generation from microbubbles under dual-frequency excitation

The difference-frequency (DF) ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast agents infusion, the harmonic components scattered from the microbubbles, including DF, can be generated due to the nonlinear vibration. A theoretical study on the DF generation from microbubbles under the dual-frequency excitation is proposed in formula based on the solution of the RPNNP equation. The optimisation of the DF generation is discussed associated with the applied acoustic pressure, frequency, and the microbubble size. Experiments are performed to validate the theoretical predictions by using a dual-frequency signal to excite microbubbles. Both the numerical and experimental results demonstrate that the optimised DF ultrasound can be achieved as the difference frequency is close to the resonance frequency of the microbubble and improve the contrast-to-tissue ratio in imaging.     

Aequorea taiwanensis n. sp. (Hydrozoa, Leptomedusae) and mtCOI sequence analysis for the genus Aequorea

Aequorea taiwanensis, a new hydrozoan species from the Taiwan Strait was described using morphological and molecular characteristics. Both morphological and mitochondrial cytochrome oxidase subunit I (mtCOI) data supported A. taiwanensis n. sp. as a valid species. Sequence divergence and genetic distance of A. taiwanensis n. sp., A. papillata and A. conica were analysed based on the mtCOI gene sequences. The mtCOI sequences from these three species of the genus Aequorea showed high variation frequency, with sequence divergences ranging from 9.10% to 11.9%, and pairwise genetic distances ranging from 0.097 to 0.130. MtCOI sequence analysis provided diagnostic molecular systematic characteristics for accurate identification and discrimination of the species of Aequorea or their populations, and will be used to resolve evolutionary relationships among them.It was suggested that 10%—20% pairwise mtCOI sequence differences indicated the specieslevel divergence among congeneric species in the Hydromedusae.     

混合式全球网格划分方法及编码研究

根据基于多面体剖分的球面网格划分方案和基于地理坐标的等间隔网格划分方案的优缺点及地图投影的特点,提出了一种混合式全球网格划分方法。这种划分方法将全球分成了六个面片,每个面片的每一边都是90°,其中四个面片处于南北纬45°之间,以等距离圆柱投影为基础,采用矩形网格覆盖;两个面片处于高纬地区,以极地正方形变换为基础,采用不规则四边形网格覆盖。详细地阐述了网格的编码策略及存储方式,并给出了网格编码与地理坐标之间的相互转换方法。     

利用NOAA-AVHRR数据分析1982-2001年间中国植被的动态变化(英文)

The authors derived the normalized difference vegetation index (NDVI) from the NOAA/AVHRR Land dataset, at a spatial resolution of 8km and 15-day intervals, to investigate the vegetation variations in China during the period from 1982 to 2001. Then, GIS is used to examine the relationship between precipitation and the Normalized Difference Vegetation Index (NDVI) in China, and the value of NDVI is taken as a tool for drought monitoring. The results showed that in the study period, China’s vegetation cover h...     

岩溶在古地理研究中的作用——“关于古地理研究中若干原则问题的商榷”一文的补充及讨论

本文从现代、地史时期岩溶剥蚀速度及岩溶铝土矿的形成等方面探讨岩溶在古地理研究中的重大作用,从而提出稳定地区“缺失”某一时期地层,并非该时期为陆;而是前期仍有沉积,后期才真正上升为陆,遭受剥蚀。     

小尺度地形阻塞作用的数值试验

本文采用数值试验方法,讨论了一个高度只有200m的小尺度地形的阻塞作用,表明当大气低层的平均风速和温度层结使得Froude数小于1时,就有可能在地形的上风向形成阻塞。本文共试验了一般稳定层结、深厚逆温和浅薄逆温几种情况,讨论了数值结果和Froude数判别式之间的差异和原因,并计算了阻塞发生时的浓度分布。     

关于中国大陆五级以上地震的时间间隔问题

本文研究了我国大陆地区五级以上地震的时间间隔分布情况,发现我国大陆M_S≥5.0地震的时间间隔ΔT与其频次N_(ΔT)之间存在以下关系式:lgN_(ΔT)=2.14-0.15·ΔT本文还讨论了我国大陆出现长期无五级以上地震后,是否将有七级地震的问题。     

粉煤灰碎石混凝土灌注桩法加固软弱地基效果的分析与检验

对由深厚软弱土层组成的地基,采用粉煤灰碎石混凝土灌注桩法予以加固处理时,其施工机具相对简单,工期短,节约“三材”,投资省,具有显著的经济效益。由粉煤灰碎石混凝土灌注桩和深厚软弱土层共同构成的复合地基的工程特性,介于一般碎石桩复合地基与混凝土桩桩基之间,其基本特征是:承载力的提高,主要是置于深厚软弱土层中的粉煤灰碎石混凝土灌注桩的排水和垂直加筋作用的结果;其承载机理,部分具有一般碎石桩复合地基的特征;在结构物荷载作用下,其桩、土荷载分担特征,比较接近于普通混凝土桩桩基。     

Growth Dynamics of the Middle Devonian Jukoupu Bioherm,Xinshao, Hunan

The growth process, palaeoecological features and the function of organisms in reef-building of the Jukoupu bioherm in Hunan are discussed in detail. The bioherm is divided into 10 microfacies. Organisms are very abundant in the reef. Thirty-two genera Belonging to 7 phyla have been recognized. They make up 5 communities composed mainly of stromatopoids, Corals and algae, each of which has its own salient ecological features. An analysis of all communities shows that the organic functions are very complex. The same organisms may possess diverse functions simultaneously as the reef growth enters the late stage. The growth process of the reef may involve five stages' (l)biostrome stage, (2) stabilization stage, (3) frame-type reef-building stage, (4) binding and covering-type reef-building stage, and (5) baffle- type reef -building stage.     

玻璃钢作地面沉降监测标体的可行性研究

玻璃钢具有质量轻、强度高、耐腐蚀等特性,可作为达到特定工程目的的成型材料。本文通过论证,认为在地面沉降监测工程中为了更准确灵敏地反映地下岩土的变形,选用轻质高强度的玻璃钢作引测标体是可行的。此外,由于玻璃钢成本低,因此,还可使中小城市开展地面沉降监测时减少基础性投入。