Analysis of the thickness of a fresh water lens and of the transition zone between this lens and upwelling saline water

In regions with saline groundwater, fresh water lenses may develop due to rainwater infiltration. The amount of fresh water that is available for e.g. agricultural crops depends on the thickness of the lens and the extent of mixing between fresh and saline water. In this paper, we consider the mixing of fresh water and upward moving saline ground water in low-lying deltaic areas. The parameters that dominate the flow and transport problem are investigated using dimensionless groups and scaled sensitivities. We characterize the numerically simulated thicknesses of the lens and of the mixing zone by spatial moments. Rayleigh number and mass flux ratio, which is the ratio of the salt water seepage and the precipitation, determine the thickness of the fresh water lens. The local thickness of the mixing zone is mainly influenced by the dispersive/diffusive groups and the mass flux ratio. In addition, convergence of streamlines towards an outflow boundary affects the thickness, particularly in the vicinity of this boundary.Analytical and numerical steady state solutions for lens thickness are compared, taking into account upward seepage, for the two cases with and without a density difference between lens and underlying groundwater. Agreement between the numerical and analytical solutions for the lens thickness is good except when the mass flux ratio becomes small. For zero mass flux ratio, it is implicitly assumed in the analytical solution that salt water is stagnant, and that is unrealistic. Relative contributions of longitudinal and transversal hydrodynamic dispersion and diffusion to the thickness of the mixing zone are quantified numerically for different phases of lens formation. Longitudinal dispersion dominates in the early stages of lens formation, while diffusion and transversal dispersion dominate at steady state.     

Tracking the shadows through GMRT

The structures of faint high redshift galaxies cannot be observed directly. But if a luminous quasar is located farther along their line of sight, high resolution absorption lines offer a valuable and reliable probe to their structure. GMRT is suited to monitor the absorption spectra, if the redshifted neutral hydrogen or OH doublet fall in one of the windows of the telescope. We present the OH doublet absorption spectra for the system B0218+357, taken at GMRT this year at resolution of approx. 9.5 km/sec with an rms noise of the order of 1 mJy. Based on our study of the OH doublet and 21cm neutral hydrogen line we infer that, in the lensing spiral galaxy of B0218 + 357, neutral hydrogen and OH coexist in tenous clouds and there is possibly a hole in the central part of the galaxy. In contrast, the gas is seen in high density clouds in the lens in an otherwise similar system PKS1830-211.     

Optical properties of Laue lenses for hard X-rays (>60 keV)

We report on preliminary results obtained with a Monte Carlo (MC) code developed to study the optical properties of Laue lenses for astro-physical observations. The MC code is written in the Python programming language and uses open source libraries. Among the physical quantities which can be investigated with the MC code, we paid our attention mainly to the estimation of the effective area, field of view (FOV) and point spread function (PSF) of the lens for observation of sources on-axis and off-axis.     

激光热透镜法测定水中痕量磷的研究

本文采用激光热透镜分析法测定水中痕量磷．研究并讨论了测定磷的各种影响因素，并与分光光度法进行比较．结果表明，热透镜分析方法比分光光度法具有较高的灵敏度．其线性范围为２～６０ｎｇＰ／ｍＬ，方法检出限为０．４ｎｇＰ／ｍＬ．用于雨水及地下水中痕量磷测定，结果满意．     

用相关分析方法检测引力透镜效应

本文建议用相关分析方法去检测引力透镜效应。对于多重类星体,通过测量各个类星体辐射的强度和相位,用相关函数方法来决定它们是否为同一类星体的各个像。     

Development of a new photon diffraction imaging system for diagnostic nuclear medicine

The objective of this project is to develop and construct an innovative imaging system for nuclear medicine and molecular imaging that uses photon diffraction and is capable of generating 1–2 mm spatial resolution images in two or three dimensions. The proposed imaging system would be capable of detecting radiopharmaceuticals that emit 100–200 keV gamma rays which are typically used in diagnostic nuclear medicine and in molecular imaging. The system is expected to be optimized for the 140.6 keV gamma ray from a Tc-99m source, which is frequently used in nuclear medicine. This new system will focus the incoming gamma rays in a manner analogous to a magnifying glass focusing sunlight into a small focal point on a detector's sensitive area. Focusing gamma rays through photon diffraction has already been demonstrated with the construction of a diffraction lens telescope for astrophysics and a scaled-down lens for medical imaging, both developed at Argonne National Laboratory (ANL). In addition, spatial resolutions of 3 mm have been achieved with a prototype medical lens. The proposed imaging system would be comprised of an array of photon diffraction lenses tuned to diffract a specific gamma ray energy (within 100–200 keV) emitted by a common source. The properties of photon diffraction make it possible to diffract only one specific gamma ray energy at a time, which significantly reduces scattering background. The system should be sufficiently sensitive to the detection of small concentrations of radioactivity that can reveal potential tumor sites at their initial stages of development. Moreover, the system's sensitivity would eliminate the need for re-injecting a patient with more radiopharmaceutical if this patient underwent a prior nuclear imaging scan. Detection of a tumor site at its inception could allow for an earlier initiation of treatment and wider treatment options, which can potentially improve the chances for cure.     

南海诸岛灰沙岛淡水透镜体研究述评

南海诸岛部分珊瑚礁上发育有灰沙岛,这些灰沙岛的面积多较小,其中一些灰沙岛地下形成淡水透镜体。以西沙群岛永兴岛为例,介绍了已有的永兴岛地下淡水透镜体的研究成果,包括灰沙岛淡水透镜体的形成和发育,其与地质、地形、气候和植被等因素的关系,以及淡水透镜体开发利用等问题,并提出进一步研究和管理的建议。     

沉积型矿产预测工作中预测要素变量的优选——以贵州省铝土矿为例

矿产预测是矿产资源潜力评价的最终目标和最重要环节。预测要素选取是矿产预测的重中之重,其主要是在典型矿床预测模型的基础上,初步拟选预测要素变量,通过分析已知矿床(点)与预测要素之间的关系,通过定性和定量分析,从而优选出对成矿有利、贡献较大的因素作为预测要素。     

Monte Carlo study of detector concepts for the MAX Laue lens gamma-ray telescope

MAX is a proposed Laue lens gamma-ray telescope taking advantage of Bragg diffraction in crystals to concentrate incident photons onto a distant detector. The Laue lens and the detector are carried by two separate satellites flying in formation. Significant effort is being devoted to studying different types of crystals that may be suitable for focusing gamma rays in two 100 keV wide energy bands centered on two lines which constitute the prime astrophysical interest of the MAX mission: the 511 keV positron annihilation line, and the broadened 847 keV line from the decay of ⁵⁶Co copiously produced in Type Ia supernovae. However, to optimize the performance of MAX, it is also necessary to optimize the detector used to collect the source photons concentrated by the lens. We address this need by applying proven Monte Carlo and event reconstruction packages to predict the performance of MAX for three different Ge detector concepts: a standard coaxial detector, a stack of segmented detectors, and a Compton camera consisting of a stack of strip detectors. Each of these exhibits distinct advantages and disadvantages regarding fundamental instrumental characteristics such as detection efficiency or background rejection, which ultimately determine achievable sensitivities. We conclude that the Compton camera is the most promising detector for MAX in particular, and for Laue lens gamma-ray telecopes in general.     

基于DLT模型的一种数码相机检校方法

直接线性模型法是相机检校中常用的一种方法，在其基础上提出了一种适合计算机处理的数码相机检校方法，其通过改变像方元素的单位，就可使用现有的摄影测量程序直接处理数字影像。文中进一步讨论了像素尺寸大小对系统误差的影响，并对像素大小的必要测定精度进行了公式推导。最后的实验结果表明，该方法可以获得较好的校准结果。