Sustainable fisheries in shallow lakes: an independent empirical test of the Chinese mitten crab yield model

Next to excessive nutrient loading, intensive aquaculture is one of the major anthropogenic impacts threatening lake ecosystems. In China, particularly in the shallow lakes of mid-lower Changjiang (Yangtze) River, continuous overstocking of the Chinese mitten crab (Eriocheir sinensis) could deteriorate water quality and exhaust natural resources. A series of crab yield models and a general optimum-stocking rate model have been established, which seek to benefit both crab culture and the environment. In this research, independent investigations were carried out to evaluate the crab yield models and modify the optimum-stocking model. Low percentage errors (average 47%, median 36%) between observed and calculated crab yields were obtained. Specific values were defined for adult crab body mass (135 g/ind.) and recapture rate (18% and 30% in lakes with submerged macrophyte biomass above and below 1 000 g/m(2)) to modify the optimum-stocking model. Analysis based on the modified optimum-stocking model indicated that the actual stocking rates in most lakes were much higher than the calculated optimum-stocking rates. This implies that, for most lakes, the current stocking rates should be greatly reduced to maintain healthy lake ecosystems.</p

An Approximate Cone Beam Reconstruction Algorithm for Gantry-Tilted CT Using Tangential Filtering

FDK algorithm is a well-known 3D (three-dimensional) approximate algorithm for CT (computed tomography) image reconstruction and is also known to suffer from considerable artifacts when the scanning cone angle is large. Recently, it has been improved by performing the ramp filtering along the tangential direction of the X-ray source helix for dealing with the large cone angle problem. In this paper, we present an FDK-type approximate reconstruction algorithm for gantry-tilted CT imaging. The proposed method improves the image reconstruction by filtering the projection data along a proper direction which is determined by CT parameters and gantry-tilted angle. As a result, the proposed algorithm for gantry-tilted CT reconstruction can provide more scanning flexibilities in clinical CT scanning and is efficient in computation. The performance of the proposed algorithm is evaluated with turbell clock phantom and thorax phantom and compared with FDK algorithm and a popular 2D (two-dimensional) approximate algorithm. The results show that the proposed algorithm can achieve better image quality for gantry-tilted CT image reconstruction

Evaluation of Slag Reaction Efficiency in Slag-Cement Mortars under Different Curing Temperature

At present, not many studies have considered methods to quantitatively evaluate the reaction efficiency of granulated blast furnace slag (GBFS) at different curing temperatures. For high volume slag concrete, when the replacement ratio exceeds a certain &rsquo;threshold&rsquo; value, the superfluous and ineffective slag will no longer react in concrete but simply behave as a fine aggregate, which may cause the decrement of strength. The &rsquo;threshold&rsquo; value depends on the reaction efficiency of slag. In this study, experiments on mortars with different replacement ratios by slag were conducted at different curing temperatures (20, 30, and 50 &deg;C, respectively), the threshold values of effective replacement ratio by slag were comprehensively analyzed through the reaction efficiency of slag mortar. The results showed that the turning point of the strength curve with replacement ratio can be considered as the threshold value of the effective replacement ratio by slag in mortar. Along with the curing temperature enhancement, the threshold value of the effective replacement ratio by slag in concrete decreased, whereas the reaction efficiency of slag increased. Meanwhile, the analysis of cement effective coefficient (k value) and basicity was also calculated. Based on the obtained threshold values of effective replacement ratio at different curing temperatures, the formula for the determination of reaction efficiency coefficient of slag in the mortar can be established. Therefore, the reaction efficiency coefficient and upper limit of the effective replacement ratio of slag at different temperatures can be calculated more intuitively and quantitatively, providing a theoretical basis and reference for practical engineering applications

An approximate cone beam reconstruction algorithm for gantry-tilted CT

Abstract not reproduced here by request of the publisher. The text is available from: http://dx.doi.org/10.1117/12.653121

Data correction for gantry-tilted local CT

The gantry-tilted helical cone-beam computed tomography (CT) has an inherent problem that the relative shift of the region of interest (ROI) blurs the reconstructed image. This problem becomes more serious in the gantry-tilted local CT imaging due to the nature of local scanning. This paper proposes a new method to improve the gantry-tilted local imaging by correcting the local scanning data. Computer simulations show that the proposed method can enhance the local imaging performance to a certain extent in terms of the image sharpening and artifacts reduction

A reconstruction algorithm for helical CT imaging on PI-planes

In this paper, a Feldkamp type approximate reconstruction algorithm is presented for helical cone-beam Computed Tomography. To effectively suppress artifacts due to large cone angle scanning, it is proposed to reconstruct the object pointwisely on unique customized tilted PI-planes which are close to the data collecting helices of the corresponding points. Such a reconstruction scheme can considerably suppress the artifacts in the cone-angle scanning. Computer simulations show that the proposed algorithm can provide improved imaging performance compared with the existing approximate cone-beam reconstruction algorithms

An extended half-scan Feldkamp-type CT reconstruction

Abstract not reproduced here by request of the publisher. The text is available from: http://dx.doi.org/10.1117/12.653126

A new scheme and reconstruction algorithm for dual source circular CT

Circular cone beam scanning has been a most popular scheme for computed tomography (CT) imaging, which is simple and can achieve symmetric projection data of the interested object. Many algorithms have been developed for circular cone beam CT. Many of these are FDK type algorithms, which can achieve good reconstruction quality when cone angle is small but may cause image deformation and density reduction at off plane when the cone angle is large. With the recently introduced dual source circular cone beam CT, we can deal with this problem under a new dual source geometry. In this paper, we propose a novel reconstruction scheme dual source circular cone beam CT by placing X-ray sources on two circular planes perpendicular to the rotating axis. We propose a reconstruction algorithm for this scanning scheme and evaluate the scanning scheme and the reconstruction algorithm with a 3D Shepp Logan phantom and a disk phantom. Simulation results show that the proposed method can provide improved reconstruction image quality for both in plane and off plane of the object