Shear Wave Speed Dispersion Characteristics of Seafloor Sediments in the Northern South China Sea

To accurately characterize the shear wave speed dispersion of seafloor sediments in the northern South China Sea,five types of sediments including silty clay,clayey silt,sandy silt,silty sand,and clayey sand were selected,on which the measurements of the shear wave speed at 0.5-2.0 kHz and related physical properties were performed.Results reveal that the shear wave speed of sediments increases as the frequency increases,and the dispersion enhanced in the sediments in the order of silty clay,clayey silt,sandy silt,silty sand,and clayey sand,at a linear change rate of 0.727,0.787,3.32,4.893,and 6.967 m s−1 kHz−1,respectively.Through regression analysis,linear and logarithmic regression equations for the correlation between shear wave speed and frequency were established for each sediment type and the determination coefficients of regression equations indicate that the correlation is closer to a logarithmic relationship.The Grain-Shearing(GS)and Biot-Stoll models were used to calculate the shear wave speed dispersion of the five sediment types,and the comparison between theoretical prediction and measured results of shear wave speeds shows that the GS model can more accurately describe the shear wave speed dispersion characteristics of these sediments in the frequency band of 0.5-2.0 kHz.In the same band,the predictions obtained by using the Biot-Stoll model are significantly different from the measured data.

Discrete dislocation plasticity analysis of dispersion strengthening in oxide dispersion strengthened(ODS) steels

A discrete dislocation plasticity analysis of dispersion strengthening in oxide dispersion strengthened(ODS) steels was described. Parametric dislocation dynamics(PDD) simulation of the interaction between an edge dislocation and randomly distributed spherical dispersoids(Y2O3) in bcc iron was performed for measuring the influence of the dispersoid distribution on the critical resolved shear stress(CRSS). The dispersoid distribution was made using a method mimicking the Ostwald growth mechanism. Then, an edge dislocation was introduced, and was moved under a constant shear stress condition. The CRSS was extracted from the result of dislocation velocity under constant shear stress using the mobility(linear) relationship between the shear stress and the dislocation velocity. The results suggest that the dispersoid distribution gives a significant influence to the CRSS, and the influence of dislocation dipole, which forms just before finishing up the Orowan looping mechanism, is substantial in determining the CRSS, especially for the interaction with small dispersoids. Therefore, the well-known Orowan equation for determining the CRSS cannot give an accurate estimation, because the influence of the dislocation dipole in the process of the Orowan looping mechanism is not accounted for in the equation.

A CLOSED SYSTEM OF EQUATIONS FOR DENSE TWO-PHASE FLOW AND EXPRESSIONS OF SHEARING STRESS OF DISPERSED PHA’E AT A WALL

Inthis paper, each of the two phases in dense two-phase flow is considered as continuous medium and the fundamental equations for two-phase flow arc described in Eulerian form. The generalized constitutive relation of the Bingham fluid is applied to the dispersed phase with the analysis oj physical mechanism of dense two-phase flow. The shearing stress of dispersed phase at a wall is used to give a boundary condition. Then a mathematical model for dense two-phase flow is obtained. In addition, the expressions of shearing stress of dispersed phase at a wall is derived according to the fundamental model of the friclional collision between dispersed-plutse particles and the wall.

Novel multi-parametric diagnosis of non-alcoholic fatty liver disease using ultrasonography,body mass index,and Fib-4 index

BACKGROUND Shear wave speed(SWS),shear wave dispersion(SWD),and attenuation imaging(ATI)are new diagnostic parameters for non-alcoholic fatty liver disease.To differentiate between non-alcoholic steatohepatitis(NASH)and non-alcoholic fatty liver(NAFL),we developed a clinical index we refer to as the“NASH pentagon”consisting of the 3 abovementioned parameters,body mass index(BMI),and Fib-4 index.AIM To investigate whether the area of the NASH pentagon we propose is useful in discriminating between NASH and NAFL.METHODS This non-invasive,prospective,observational study included patients diagnosed with fatty liver by abdominal ultrasound between September 2021 and August 2022 in whom shear wave elastography,SWD,and ATI were measured.Histological diagnosis based on liver biopsy was performed in 31 patients.The large pentagon group(LP group)and the small pentagon group(SP group),using an area of 100 as the cutoff,were compared;the NASH diagnosis rate was also investigated.In patients with a histologically confirmed diagnosis,receiveroperating characteristic(ROC)curve analyses were performed.RESULTS One hundred-seven patients(61 men,46 women;mean age 55.1 years;mean BMI 26.8 kg/m2)were assessed.The LP group was significantly older(mean age:60.8±15.2 years vs 46.4±13.2 years;P<0.0001).Twenty-five patients who underwent liver biopsies were diagnosed with NASH,and 6 were diagnosed with NAFL.On ROC curve analyses,the areas under the ROC curves for SWS,dispersion slope,ATI value,BMI,Fib-4 index,and the area of the NASH pentagon were 0.88000,0.82000,0.58730,0.63000,0.59333,and 0.93651,respectively;the largest was that for the area of the NASH pentagon.CONCLUSION The NASH pentagon area appears useful for discriminating between patients with NASH and those with NAFL.

Mechanisms of shelf-break frontogenesis

The shelf-break front is an omnipresent phenomenon in coastal oceans all over the world, but there is still no definitive explanation for the genesis of such a front. It is possible that different mechanisms are operative at different times and locations, but all of them should have something to do with the sharp change of bottom topography near the shelf-break. A couple of recently proposed mechanisms of shelf-break frontogenesis are dicussed. One of them invokes a flow convergence produced by local air-sea interaction over sloping topography, whereas the other relies on the depth dependence of wind-induced shear dispersion. These novel ideas are based on new observational evidences and previous theoretical studies, and they are demonstrated here using an idealized ocean-atmosphere coupled model and a stand-alone ocean model. The air-sea interaction mechanism seems plausible for the shelf-break front in the East China Sea, and the shear dispersion mechanism is likely to be applicable to the shelf-break front off the northeastern United States.

A DELAY-DIFFUSION DESCRIPTION FOR TWO-DIMENSIONAL CONTAMINANT DISPERSION

In the earlier stage of dispersion process,the rate of dispersion associated with earlier discharge is relatively large because the memory term extends further back in time.In or- der to investigate the early properties of two-dimensional dispersion,we propose the delay-diffu- sion equation as follows: (?)integral from o to ∞(?) (x-integral from n=1 to τ (?),y-integral from n=1 to τ (?),t-τ)dτ=(?) which is based on the equation derived by Smith (1981).The D_(xz),D_(yz),D_(zy),D_(yy) and (?),(?) had been obtained.