Suspended particulate matter in Jiaozhou Bay： Properties and variations in response to hydrodynamics and pollution

Based on water samples collected and observations of currents, tidal levels as well as turbidities taken, respectively over a period of 15 and 7 d, in southwestern Jiaozhou Bay on August, 2001, it was found that: ( i ) the average content of non mineral component amounted to 87% of the suspended sediment matter (SPM) in Jiaozhou Bay,much higher than in estuaries and bays where turbidity is high and mineral particulates dominates; (ii) in contrast to high turbid bays, SPM was generally coarser than bed deposits and in upper water column than in lower water column in Jiaozhou Bay; (iii) in fair weathers, suspended sediment concentration (SPC) varied regularly within tidal cycles and neap-spring cycles, but the regularity was deformed in storms; and (iv) SPC was controlled by settling/resuspension near the bed and by advection at the surface at the study site with a depth of 20 m, suggesting weak vertical exchanges. It was concluded that SPM property of a low turbid bay is sensitive to pollution, and that the maintenance of low turbidity in the bay depends on less SPM supply, low waves and currents, and controlling on discharge of particulate pollutants.     

Dynamics of sediment resuspension and the conceptual schema of nutrient release in the large shallow Lake Taihu,China

On the basis of investigations in situ, it was found that mass exchange on the water-sediment interface occurred chiefly on the superficial sediment within 5-10 cm. The spatial physicochemical character of sediment was distributed uniformly. The observation of lake currents and waves indicated that the dynamic sources, which act on the interface of water and sediment, came mainly from waves under strong wind forcing, while the critical shear stresses     

Effect of 6H-SiC crystal growth shapes on thermo-elastic stress in the growing crystal

The effect of 6H-SiC crystal growth shapes on the thermo-elastic stress distribution in the growing crystal was systematically investigated by using a finite element method. The thermo-elastic stress distribution in the crystal with a flat growth shape was more homogeneous than that in the crystals with concave and convex growth shapes, and the value of thermo-elasticity in the crystal with a flat growth shape was also smaller than that in the two other types of crystals. The maximum values of thermo-elastic stress appeared at interfaces between the crystal and the graphite lid. If the lid was of the same properties as 6H-SiC, the thermo-elastic stress would decrease in two orders of magnitude. Thus, to grow 6H-SiC single crystals of high quality, a transition layer of SiC formed by deposition or reaction is suggested; meanwhile the thermal field in the growth chamber should be adjusted to maintain the crystals with flat growth shapes.     

Three-dimensional FEM analysis of stress distribution in dynamic maxillary canine movement

An alteration in stress/strain distribution within periodontal ligament (PDL) occurs when the tooth is mechanical stimulated in orthodontic treatment. The majority of previous finite element studies were confined to a static evaluation on initial loading status, and a dynamic long-term analysis was rarely performed in orthodontics. The present study sought to analyze the stress distribution patterns within tooth root, PDL, and alveolar bone during dynamic canine tipping and bodily movement with three-dimensional finite element method in four consecutive therapeutic weeks. We observed that the highest stress was on root surface, secondly alveolar bone, and finally, PDL for either tipping or bodily movement. Throughout the PDL and root surface, the highest stress was always around the cervical area in both patterns of movement through four phases. Moreover, a lower and more uniform stress distribution was produced during bodily movement compared with tipping movement. These results indicated that canine translation might be healthier for periodontal tissue than tipping movement; the cervical region bore a greater load and might also be a susceptible area for tissue damage (except for the apex) regardless of movement pattern.     

Settling characteristics of ultrafine iron ore slimes

The slurry settling characteristics are the most important to design a thickener in process industries. In this work, the iron ore slurry from the screw classifier overflow was used for the settling study. It was observed that the original slurry exhibited a low settling velocity and a turbid supernatant during the settling process. Commercial flocculating agents with anionic, cationic, and nonionic characters were used to improve the settling behavior of suspensions, which were added into the slurry at different ranges of slurry pH values, respectively. The settling results show that the use of flocculants increase the settling rate by several times. Compared with the cationic and nonionic flocculants, the anionic flocculant is more effective in enhancing the slurry settling rate. The small dose of the anionic flocculant is found to be more effective, but the other flocculants are less effective even at higher dosages. The simulation of an industrial thickener was carried out based on the laboratory settling data, and the appropriate design and selection parameters of the industrial thickener were estimated.     

THE EFFECT OF, ABRASION ON LOW STRESS MECHANICAL PROPERTIES OF FABRIC

The low stress mechanical properties of a pure wool and a wool / polyester blend twill fab-rics which were abraded at various abrasion cycles were measured using the KES-F system andthe Instron tensile machine. The surface change of fabrics before and after abrasion was stu-died by means of scanning electron microscope. With the increasing number of cycles, the re-covery behavior of the fabrics studied in tensile, shear and bending deformation decrease, theantibuckling ability lowers, the friction coefficient increases. The geometric roughness de-creases during the first step of abrasion then enhances with further abrasion. The influence ofabrasion on mechanical properties of the pure wool fabric are larger than that of blend fabric.     

Rheological behavior and constitutive equations of heterogeneous titanium-bearing molten slag

Experimental studies on the rheological properties of a CaO–SiO₂–Al₂O₃–MgO–TiO₂–(TiC) blast furnace (BF) slag system were conducted using a high-temperature rheometer to reveal the non-Newtonian behavior of heterogeneous titanium-bearing molten slag. By measuring the relationships among the viscosity, the shear stress and the shear rate of molten slags with different TiC contents at different temperatures, the rheological constitutive equations were established along with the rheological parameters; in addition, the non-Newtonian fluid types of the molten slags were determined. The results indicated that, with increasing TiC content, the viscosity of the molten slag tended to increase. If the TiC content was less than 2wt%, the molten slag exhibited the Newtonian fluid behavior when the temperature was higher than the critical viscosity temperature of the molten slag. In contrast, the molten slag exhibited the non-Newtonian pseudoplastic fluid characteristic and the shear thinning behavior when the temperature was less than the critical viscosity temperature. However, if the TiC content exceeded 4wt%, the molten slag produced the yield stress and exhibited the Bingham and plastic pseudoplastic fluid behaviors when the temperature was higher and lower than the critical viscosity temperature, respectively. When the TiC content increased further, the yield stress of the molten slag increased and the shear thinning phenomenon became more obvious.     

Simulating a typhoon storm surge in the East Sea of China using a coupled model

A coupled numerical model with a 2’?2’ resolution grid has been developed and used to simulate five typical typhoon storm surges (5612, 7413, 7910, 8114, 9711) in the East Sea of China. Three main driving forces have been considered in this coupled model: wave radiation stress, combined wave-current bottom shear stress and wave-state dependent surface wind stress. This model has then been compared with in situ measurements of the storm set-up. The effect of different driving force components on the total storm surge has also been investigated. This study has found that the coupled model with high resolution is capable of simulating the five typical typhoons better than the uncoupled models, and that the wave-dependent surface wind stress plays an important role in typhoon storm surge-wave coupling in this area and can increase the storm set-up by 1m. The study of the five typhoon cases has shown that the general coupling effects could increase storm set-up by 20% to 32%. Thus, it is suggested that to predict typhoon storm surges in the East Sea of China, a storm surge-wave coupled model be adopted.     

The study of temperature effects on steel box girder for Taizhou Bridge

Using the temperature gradient which was proposed by continuously measuring on flat steel box girder of Runyang Bridge, temperature effects of flat steel box girder was studied for Taizhou Yangtze River Bridge. With three temperature gradient models (JTG D60-2004 specification, BS5400 specification and the temperature gradient which was proposed in this paper), the control sections stress was calculated by finite element program ANSYS. The calculated result indicates that the temperature gradient that was put forward in JTG D60-2004 specification and BS5400 specification for calculating stress of flat steel box girder was not suitable to apply to flat steel box girder. The temperature gradient on flat steel box girder which was proposed in this paper was reasonable.     

Scale dependence of direct shear tests

Direct shear test has been widely used to measure the shear strength of soils and other particulate materials in industry because of its simplicity. However, the results can be dependent on the specimen size. The ASTM （American Society for Testing and Materials） publications suggest that for testing soils the shear box should be at least ten times the diameter of the largest particle and the height of the box should be no more than half of its diameter. These guidelines are empirically based. A series of two-dimensional numerical direct shear tests are performed to investigate this scaling effect. By analyzing the bulk friction, particle translation and rotation, percentage of sliding, average volume （area） and shear strain and the evolution of the shear band, we find that the traditional guidelines for direct shear tests are questionable. Scaling dependency of bulk friction on the property of granular materials is clearly present. Our current analysis points out that the scaling effects can vary significantly depending on the particle properties other than their sizes. Of all the parameters we observed, particle rotation appears to have a decisive correlation with the bulk friction. Formation of a shear band is universal. As the shearing progresses, particle rotation begins to concentrate near the shear plane. By defining the width of a shear band as the standard deviation of the distribution of translational gradient or the standard deviation of the distribution of particle rotation, quantitative evolutions of shear band are presented. Both measures of the shear band width dropped rapidly during pre-failure stage. After peak stress both measures begin to approach steady state as the bulk friction stabilizes to the residual stage. These observations suggest that structure formation inside the shear band controls the scaling effect.     

Erosion and sediment delivery in rills on steep loess slope

Sediment delivery in rills on the loess slope was studied by inflow experiments. Relationships between sediment delivery rate in rills and flow shear stress, discharge and slope gradient, maximum sediment and unit runoff power, and discharge and slope gradient were analyzed. A relationship is presented for calculating the erosion rate in rills .     

Spatial variability and representation of seabed sediment grain sizes： An example from the Zhoushan-Jinshanwei transect, Hangzhou Bay,China

Grain size analysis was undertaken for the 2-cm interval sub-samples of eight short cores collected along the Zhoushan-Jinshanwei transect in Hangzhou Bay, using a Malvern Mastersizer 2000 laser particle size analyzer. The result indicates that there are different vertical distribution patterns of mean grain size for the short cores. In the study area, the thickness of the seabed moving layer on an annual temporal scale is much larger than that of the deposited layer,i.e. the sedimentary environment is highly dynamic. As a result, the vertical distributions of mean grain size within the short cores represent different types of sedimentary records formed in the same environment, rather than signals of long-term environmental evolution. The seabed sediment consists mainly of silts in the study area, and the vertically-averaged value of mean grain size has a tendency of convergence when the thickness over which the mean value is derived increases. Such patterns indicate that the grain size composition of the deposit is controlled mainly by the source of material supply; nevertheless, to some degree hydraulic sorting is effective, which has resulted in the differences in distribution patterns along the transect between the grainsize values of the surficial sediment and the vertically-averaged values. For long-term sediment transport modeling for an environment associated with strong tidal action and silty sediment, it may be more appropriate to use the vertically-averaged grain size than the value for thesurficial sediment, as the model input.     

Dynamic Investigation of Interface Stress on Below-Knee Residual Limb in a Prosthetic Socket

The dynamic effects of inertial loads on the interface stresses between a residual limb and the trans-tibial prosthetic socket were investigated. A 3-D nonlinear finite element model, based on the actual geometry of the residual limb, including internal bones and socket liner, was developed to study the mechanical interaction between the socket and the residual limb during walking. To simulate the friction/slip boundary conditions between the skin and liner, automated surface-to-surface contact was used. The results show that interface pressure and shear stress have a similar double-peaked waveform shape in the stance phase. The average difference in interface stresses between the cases with and without consideration of inertial forces is 8.4% in the stance phase and 20.1% in the swing phase. The results suggest that the dynamic effects of inertial loads on interface stress distribution during walking must be considered in prosthetic socket design.     

Hydrostatic settling velocity of sediments

The settling of sediments is an accelerative process in which the concentration of the main sediments zone will heavily influence settling velocity, but the explicit relationship between the concentration and settling velocity has not been reported in literature. Here a theoretical function was built for the time dependent concentration and time dependent settling velocity of sediments ; then the entire settling process reflecting concentration was shown on the basis of sediments instant-settlement theory and mathematical method. Agreement of computed results and experimental data was found. Several governing parameters, including particle size,particle density,inltial suspended sediments concentration and suspension height, were discussed with a series of calculated velocity curves. The research indicated that (1) the presented concentration-velocity time relationship is rational, (2) settling process of the sediments group with variation of concentration consists of acceleration stage, uniform motion stage and deceleration stage, and (3) particle size, particle density and initial suspended sediments concentration have more influence on the settling velocity than the suspension height and water temperature.     

Deformation and damage behaviors of as-cast TiAl-Nb alloy during creep

By means of creep properties measurement and microstructure observation,the deformation and damage behavior of an as-cast TiAl-Nb alloy during creep at temperature near 750°C were investigated.The results showed that the microstructure of the alloy consisted of lamellarγ/α_2 phase,and the boundaries consisted ofγphase located in between lamellarγ/α_2 phases with different orientations.In the latter stage of creep,the dislocation networks appeared in the interfaces of lamellarγ/α_2 phases due to the coarsening of them,which made the coherent interface transforming into the semi-coherent one for reducing its adhesive strength.The deformation mechanism of the alloy during creep was twinning and dislocations slipping within lamellarγ/α_2 phases.In the later period of creep,significant amount of dislocations plied up in the interfaces of lamellarγ/α_2 phases,which may cause the stress concentration to promote the initiation and propagation of the cracks along the lamellarγ/α_2interfaces perpendicular to the stress axis.Wherein,some cracks on the various cross-sections were connected by tearing edge along the direction of maximum shear stress,up to the creep fracture,which is considered to be the damage and fracture mechanism of alloy during creep at 750°C.     

An experiment study of quartz-coesite transition at differential stress

In order to study quartz-coesite transition under the conditions of differential stress, experiments of quartzite deformation were carried out using a triaxial testing system with a Griggs type solid medium pressure vessel. Analyses on the plastically-deformed samples under optical microscope and Raman spectra show that fine-grained coesite was present in the region of samples adjacent to the pistons at temperatures of 950--I000~C, confining pressure of 1.3 GPa, differential stress of 1.5--1.67 GPa, and total strain of 75%--81%. It is evident that the transition pressure of quartz-coesite at differential stress and intensely-strained conditions is far lower than the pressure for coesite stability at isostatic pressure. In other words, the stress condition of coesite occurrence is not unique. The decrease in confining pressure for quartz-coesite transition under differential stress conditions is controlled by a combined effect of the maximum principal stress that provides a high stress environment, and differential stress that causes sample deformation. Coesite was produced in the plastically-deformed samples in this study, but it can occur in both semi-brittle and plastic deformation regimes as seen in previous studies. Phase transition in semi-brittle deformation regime is caused by local mechanical instability induced by shear deformation, and phase transition in plastic flow regime is due to strain instability induced by the presence of a high dislocation density within intensely-deformed quartz crystals.     

AA2198-T34合金搅拌摩擦焊的应力腐蚀行为及其特征

To better understand the stress-corrosion behavior of friction stir welding (FSW), the effects of the microstructure on the stress-corrosion behavior of the FSW in a 2198-T34 aluminum alloy were investigated. The experimental results show that the low-angle grain boundary (LABs) of the stir zone (SZ) of FSW is significantly less than that of heated affected zone (HAZ), thermo-mechanically affected zone (TMAZ), and parent materials (PM), but the grain boundary precipitates (GBPs) T1 (Al₂CuLi) were less, which has a slight effect on the stress corrosion. The dislocation density in SZ was greater than that in other regions. The residual stress in SZ was +67 MPa, which is greater than that in the TMAZ. The residual stress in the HAZ and PM is ?8 MPa and ?32 MPa, respectively, and both compressive stresses. The corrosion potential in SZ is obviously less than that in other regions. However, micro-cracks were formed in the SZ at low strain rate, which indicates that the grain boundary characters and GBPs have no significant effect on the crack initiation in the stress-corrosion process of the AA2198-T34. Nevertheless, the residual tensile stress has significant effect on the crack initiation during the stress-corrosion process.     

Matrix-bound phosphine: A new form of phosphorus found in sediment of Jiaozhou Bay

Matrix-bound phosphine (PH3),a new form of phosphorus,was found in sediment of Jiaozhou Bay in December 2001,Concentration and distribution of PH3 in different layers of sediment with different stations were analyzed.The results show that PH3 concentrations are various with different layers and different stations.PH3 concentrations in the bottom layer of sediment (20-30 cm) are usually higher than those in the surface layer (0-4cm) ,The highest PH3 concentration in our investigation reaches 685 ng/kg (dry),which is much higher than those in terrestrial paddy soil ,marsh and landfill that have been reported up to now,The correlation analysis indicates that there is no apparent correlation between the concentrations of PH3 and inorganic phosphorus in sediment.However,the correlation between the concentrations of phosphine and organic phosphorus in the bottom layer of sediment is remarkable (R^2=0.83).It is considered that PH3 in sediment of Jiaozhou Bay is mainly produced from the decomposition of organic phosphorus in the anaerobic condition,and so PH3 concentrations are related to organic phosphorus concentration and anaerobic environment in sediment,The discovery of PH3 in sediment will give people some new ideas on the mechanisms of phosphorus supplement and biogeochemical cycle in Jiaozhou Bay.     

Can the climate background of western North Pacific typhoon activity be predicted by climate model?

Based on the observation and reanalysis data through 1948-2004, the vertical shear of zonal wind, outgoing Iongwave radiation, and divergence fields in the lower and upper troposphere during summer are revealed to correlate significantly with the concurrent western North Pacific （WNP） typhoon frequency, and they therefore can be regarded as predictors for the WNP typhoon activity anomaly. After that, the 34-year （1970-2003） ensemble hindcast experiments are performed by the nine-level atmospheric general circulation model developed at the Institute of Atmospheric Physics Under the Chinese Academy of Sciences （IAP9L-AGCM）, aiming to investigate the numerical predictability of the summer vertical shear of zonal wind and divergence field in the lower troposphere. It is found that the temporal correlation coefficients between the hindcast and observation are 0.70 and 0.62 for the vertical shear of zonal wind and divergence field, respectively. This suggests that the model possesses a large potential skill for predicting the large-scale climate background closely related to the WNP typhoon activity, and the model is therefore capable of performing the real-time numerical prediction of the WNP typhoon activity anomaly to some extent.     

A study on responses of soil erosion and sediment yield to closing cultivation on sloping land in a small catchment using ^137Cs technique in the Rolling Loess Plateau, China

By comparison of volumes and ^137Cs Contents of the deposited sediments before and after 1993,changes of specific sediment yields and relative sediment contributions from the gully area and from the inter gully area after closing cultivation on the later area on a small catchment of Zhaojia Gully,in the Rolling Loess Plateau,are analyzed in this paper.Closing cultivation in a large scale has not resulted in decrease but increase of specific sediment yield and the relative sediment contribution of the inter-gully area,and in increase of the sediment yield and the contribution of the gully area,for a short term.The mean specific sediment yield of 29650 t km^-2a^-1 of 1994-1996 in the catchment was 2.2 times the average value of 13413 t km^-2 a^-1 for a long term.The specific sediment yield of the inter-gully area decreased from the 14335t km^-2a^-1 in 1994 to 7034 t km^-2 a^-1 in 1995 and 3517 t km^-1a^-1 in 1996 which was much greater than the value of 21118 t km^-2 a^-1 before 1993.The relative sediment contribution from the inter-gully area decreased form 23% in 1994 to 15% in 1995 and 6% in 1996,while the contribution from the gully area increased form 77% in 1994 to 85% in 1995 and 94% in 1996.It is suggested that compacting of ploughed soils resulted in increasing of the erosion resistance but in decreasing of the precipitation infiltration,therefore,the soil erosion reduced but the runoff amount increased on the inter-gully area.Increase of delivering runoff from the inter-gully area to the gully area should result in activeness of gully erosion and mass movements,consequently,in increase of the total sediment yield from the catchment.