Seasonal and spatial distribution of matrix-bound phosphine and its relationship with the environment in the Changjiang River Estuary, China

Sediment is commonly considered as a source of phosphine, which is a highly toxic and reactive atmospheric trace gas. This study aims to investigate the seasonal and spatial distribution of matrix-bound phosphine (MBP) and its relationship with the environment in the Changjiang River Estuary. A total of 43 surface sediments were collected in four seasons of 2006, and concentrations of MBP and relative environmental factors were analyzed. MBP ranged from 1.93 to 94.86 ng kg(-1) dry weight (dw) with an average concentration of 17.14 ng kg(-1) dw. The concentrations of MBP in the tipper estuary were, higher than those in the lower estuary, which could be attributed to greater pollutant inputs in the upper estuary. The concentrations of MBP also varied with season, with November > August > May > February. Significant correlations existed between MBP and total phosphorus (TP), organic phosphorus (OP), inorganic phosphorus (W), organic carbon (OC), total nitrogen (TN), the grain size, and redox potential (Eh), suggesting that these sedimentary environmental characteristics played an important role in controlling the MBP levels in the sediments. Notably, there were positive linear relationships between the concentrations of soluble reactive phosphorus (SRP), TP, and chlorophyll a (Chl a) in bottom water and MBP in sediments. These relationships might be very complicated and need further exploration. This work is the first comprehensive study of the seasonal and spatial distribution of MBP in sediments and its relationships with environmental factors in a typical estuary, and will lead to deeper understanding of the phosphorus (P) biogeochemical cycle. (C) 2008 Elsevier Ltd. All rights reserved.

Scaling approach to conical indentation in elastic-plastic solids with work hardening

We derive, using dimensional analysis and finite element calculations, several scaling relationships for conical indentation in elastic-plastic solids with work hardening. Using these scaling relationships, we examine the relationships between hardness, contact area, initial unloading slope, and mechanical properties of solids. The scaling relationships also provide new insights into the shape of indentation curves and form the basis for understanding indentation measurements, including nano- and micro-indentation techniques. They may also be helpful as a guide to numerical and finite element calculations of indentation problems.

The temporal and spatial distribution, composition and abundance of Protozoa in Chaohu Lake, China: Relationship with eutrophication

Systematic investigations into the temporal and spatial distribution, composition and abundance of protozoa in two regions with different trophic levels in Chaohu Lake, a large, shallow and highly eutrophic freshwater lake in China, were conducted during 2002-2003. A total of 114 species of protozoa, including phytomastigophorans, zoomastigophorans, amoebae and ciliates, were identified from 120 polyurethane foam unit (PFU) samples exposed at four stations and from various types of natural substrates. Of the 114 taxa, 36 core species were found on PFU substrates and 23 of these were found on natural ones. Protozoan abundance and chemical physical parameters at nine sampling stations, four in the western lake and five in the eastern part, indicate trophic gradient changes along the lake. Seasonal variations in the species composition of major groups at littoral PFU sampling stations illustrate the effect of a severe algal bloom on the protozoan community structure. Temporal and spatial distributions of individual abundance as functions of water temperature and trophic status were revealed. This study demonstrates again that the PFU artificial substrate method samples protozoan communities more effectively than routine natural substrate methods. (c) 2005 Elsevier GmbH. All rights reserved.

MECHANISM OF RADIATION CROSS-LINKING OF POLYMERS AND ITS RELATIONSHIP WITH STRUCTURAL MULTIPLICITY

In an attempt to explore the effect of structural multiplicity of polymers on the mechanism of radiation crosslinking, the adaptability of the Charlesby-Pinner's equation and its various modified versions are examined. It is recognized that both chemical and morphological multiplicity of polymer structure results in the multiplicity of crosslinking mechanism, and that any single equation can only be applicable to a certain step of the whole radiation process.

Phytoplankton distributions and their relationship with the environment in the Changjiang Estuary, China

This study was carried out in the Changjiang Estuary from 19 to 26 May 2003. Based on the data collected from 29 stations, including two anchor stations, phytoplankton taxonomic composition, abundance, diurnal variability and spatial distribution were examined. Eighty-seven species, including 54 species of diatoms and 16 red tide causative species, were identified. Average diversity index (H') and evenness (J) values were 1.04 and 0.40, respectively. A bloom in abundance of certain phytoplankton species, especially Prorocentrum dentatum and Skeletoneina costatum, was thought to be the cause of the low diversity index and evenness values. Total phytoplankton abundance averaged 6.75 x 10(5) cells 1(-1), and was much higher than previous investigation carried out in the same month in 1986. Abundance increased seaward showing a distinct spatial difference, and the dominant species varied with salinity. Correlation between phosphorus and abundance further supported the former conclusion that phosphorus is the controlling factor in phytoplankton growth in the Changjiang Estuary where light is not limiting. Based on the relationship between DO, pH and abundance, it is likely that the bloom was caused by rapid in situ growth of phytoplankton with high nutrients and sufficient light. The data also indicated that the duration of the bloom was not long and

Relationships between hardness, elastic modulus, and the work of indentation

The work done during indentation is examined using dimensional analysis and finite element calculations for conical indentation in elastic-plastic solids with work hardening. An approximate relationship between the ratio of hardness to elastic modulus and the ratio of irreversible work to total work in indentation is found. Consequently, the ratio of hardness to elastic modulus may be obtained directly from measuring the work of indentation. Together with a well-known relationship between elastic modulus, initial unloading slope, and contact area, a new method is then suggested for estimating the hardness and modulus of solids using instrumented indentation with conical or pyramidal indenters.

The relationship of SIF between plate and plane fracture problems and the effect of the plate thickness on SIF

In the present paper, it is shown that the zero series eigenfunctions of Reissner plate cracks/notches fracture problems are analogous to the eigenfunctions of anti-plane and in-plane. The singularity in the double series expression of plate problems only arises in zero series parts. In view of the relationship with eigen-values of anti-plane and in-plane problem, the solution of eigen-values for Reissner plates consists of two parts: anti-plane problem and in-plane problem. As a result the corresponding eigen-values or the corresponding eigen-value solving programs with respect to the anti-plane and in-plane problems can be employed and many aggressive SIF computed methods of plane problems can be employed in the plate. Based on those, the approximate relationship of SIFs between the plate and the plane fracture problems is figured out, and the effect relationship of the plate thickness on SIF is given.

An Energy-Based Method for Analyzing Instrumented Spherical Indentation Experiments

Using dimensional analysis and finite element calculation, we studied spherical indentation in elastic-plastic solids with work hardening. We report two previously unknown relationships between hardness, reduced modulus, indentation depth, indenter radius, and work of indentation. These relationships, together with the relationship between initial unloading stiffness and reduced modulus, provide an energy-based method for determining contact area, reduced modulus, and hardness of materials from instrumented spherical indentation measurements. This method also provides a means for calibrating the effective radius of imperfectly shaped spherical indenters. Finally, the method is applied to the analysis of instrumented spherical indentation experiments on copper, aluminum, tungsten, and fused silica.