Effects of sediment physical properties on the phosphorus release in aquatic environment

Particle size, porosity, and the initial phosphorus concentration in sediments are the main factors affecting phosphorus release flux through the sediment-water interface. Sediments can be physically divided to muddy and sandy matters, and the adsorption-desorption capacity of sediment with phosphorus depends on particle size. According to phosphorus adsorption-desorption experiments, phosphorus sorption capacity of the sediment decreases with the increase of particle dimension. But among the size-similar particles, sediment with a bigger particle size has the larger initial phosphorus release rate. In terms of muddy and sandy sediments, there are inversely proportional relationships between the release rate and the flux. Due to the contact of surface sediment and the overlying water, the release flux from the sediment is either from direct desorption of surface sediment layer or from the diffusion of pore water in the sediment layer, which is mainly determined by sediment particle size and porosity. Generally, static phosphorus release process may include two stages: the first is the initial release. As for coarse particles, phosphorus is desorbed from surface sediment. And for fine particles, phosphorus concentration in water often decreases, mainly from pore water by the molecular diffusion. During the second stage, pore water flows faster in coarse sediment, and phosphorus is easy to desorb from the surface of the particles as diffusion dominates. For the smaller liquid-solid ratio of fine particles and the larger amount of phosphorus adsorption, the release flux from pore water due to diffusion is very small with longer sorption duration.     

Compressional and shear wave properties of marine sediments: comparisons between theory and data

According to a recently developed theory of wave propagation in marine sediments, the dispersion relationships for the phase speed and attenuation of the compressional and the shear wave depend on only three macroscopic physical variables: porosity, grain size, and depth in the sediment. The dispersion relations also involve three (real) parameters, assigned fixed values, representing microscopic processes occurring at grain contacts. The dispersion relationships are compared with extensive data sets, taken from the literature, covering the four wave properties as functions of all three physical variables. With no adjustable parameters available, the theory matches accurately the trends of all the data sets. This agreement extends to the compressional and shear attenuations, in that the theory accurately traces out the lower bound to the widely distributed measured attenuations: the theory predicts the intrinsic attenuation, arising from the irreversible conversion of wave energy into heat, whereas the measurements return the effective attenuation, which includes the intrinsic attenuation plus additional sources of loss such as scattering from shell fragments and other inhomogeneities in the medium. Provided one wave or physical property is known, say the compressional speed or the porosity, all the remaining sediment properties may be reliably estimated from the theory.     

海底沉积物压缩波声速比与物理特性的关系

海底沉积物因组成结构复杂导致声学特性复杂多样,多种理论解释模型存在参数较多且各具适用性现象·通过运用体积平均和等效参数的方法对海底沉积物声波传播机理进行研究,提出一种少参数的海底沉积物与底层海水的压缩波声速比通用模型(General Model of Sound Speed Ratio,GMSSR).GMSSR模型包含弹性结构分布因子、孔隙度、等效密度比、等效弹性模量比4个物理特性参数。分析海底沉积物两相介质结构的串联和并联两种极限情况分析,基于弹性结构分布因子和串并联结构的体积平均分布建立一般情况下海底沉积物的等效弹性模量表达式·应用GMSSR合理地分析各海域测量的海底沉积物声速比经验模型的共性和解释南海实测数据分散的范围,表明:(1)表层海底沉积物主要是以串联结构为主,接近于悬浮液状态或者体积分量很少的并联堆积状态;(2)等效弹性模量比的影响因素大于等效密度比,结构变化往往通过影响弹性结构分布因子而影响等效弹性模量比,从而引起声速比的变化;(3)不同研究海域的声速比-孔隙度经验关系具有相似性,可以通过GMSSR模型分析得出;(4)基于弹性结构分布因子的差异,可以合理解释南海海域测量表层海底沉积物声速比较大的分散性。      

Porosity and effective mechanical properties of plasma-sprayed Ni-based alloy coatings

The aim of this paper was to address the relationship between the porosity and micro-mechanical properties of the Ni-based alloy coatings which were prepared by a novel plasma-spraying system. The porosity and the mechanical properties of the coatings varied through changing the spraying parameters. Experimental results showed that the measured data of porosity, Young’s modulus and micro-hardness of the coating exhibited high scattering and followed the Weibull distribution. From statistic trend, the micro-hardness and Young’s modulus of the coating decreased with increasing the porosity of the coating. Moreover, generally, with increasing the micro-hardness of the coating, Young’s modulus of the coating increased.     

Spatially resolved measurement of rock core porosity

Density weighted, centric scan, Conical SPRITE MRI techniques are applied in the current work for local porosity measurements in fluid saturated porous media. The methodology is tested on a series of sandstone core samples. These samples vary in both porosity and degree of local heterogeneity due to bedding plane structure. The MRI porosity measurement is in good agreement with traditional gravimetric measurements of porosity. Spatially resolved porosity measurements reveal significant porosity variation in some samples. This novel MRI technique should have applications to the characterization of local porosity in a wide variety of porous media.     

Theoretical relationship between sound velocity and the physical properties of submarine sediment

Density and elastic modulus change ratios are introduced to describe the sound velocity of submarine sediment.The density change ratio is a composite parameter describing the sound velocity.It is expressed by three physical parameters:porosity,solid phase density and seawater density.The elastic modulus change ratio is also a composite parameter of sound velocity.It is expressed by three physical parameters,including porosity,solid phase modulus and seawater bulk modulus.The sound velocity formula can be developed into a Taylor polynomial formula of these two composite parameters.The change in the two composite parameters constitutes the sound velocity surface,which contains the complete information regarding velocity properties and sediment characteristics.The one-parameter velocity formula is a curve on the velocity surface.Each porosity-velocity empirical formula,which represents various sea locations and conditions,is transformed to a standard form.This result is the product of a reference velocity and a modulation function.Comparisons of the numerical calculation and measurements show that the derived modulation functions yield similar results.The difference between the velocity formula derived in this paper and the Wood velocity formula is due to the elastic modulus models.     

Rugate filter with multi-channel grown by glancing angle deposition

Glancing angle deposition (GLAD) is an effective technique to fabricate thin films with desired nanoscale porosity variations in three dimensions. GLAD can be used to grow rugate filters characterized by a sinusoidal refractive index profile from one single source material through control of film porosity. A multi-stopband rugate filter can be achieved either by introducing a layer of constant index into the center of sinusoidal refractive index profile or by embedding discrete layers of constant refractive index to sinusoidal index profile with the GLAD technique. Transmittance measurements of the one channel filter, formed with titanium dioxide, revealed this method is one of the most valid technologies to fabricate multi-band filters.     

Acoustic inversions for measuring boundary layer suspended sediment processes

Although sound has been applied to the study of sediment transport processes for a number of years, it is acknowledged that there are still problems in using the backscattered signal to measure suspended sediment parameters. In particular, when the attenuation due to the suspension becomes significant, the uncertainty associated with the variability in the scattering characteristics of the sediments in suspension can lead to inversion errors which accumulate as the sound propagates through the suspension. To study this attenuation propagation problem, numerical simulations and laboratory experiments have been used to assess the impact unpredictability in the scattering properties of the suspension has on the acoustically derived suspended sediments parameters. The results clearly show the commonly applied iterative implicit inversion can lead to calculated sediment parameters, which become increasingly erroneous with range, as the sound propagates through the suspension. To address this problem an alternative approach to the iterative implicit formulation is investigated using a recently described dual frequency inversion. This approach is not subject to the accumulation of errors and has an explicit solution. Here the dual frequency inversion is assessed and calculated suspended sediment parameters are compared with those obtained from the iterative implicit inversion.     

Geoacoustic inversion for fine-grained sediments

Fine-grained water saturated sediments like silty clays have the curious property that the speed of sound through its bulk medium is lower than that of the interstitial pore fluid. When a fine-grained sediment is at the water-sediment interface, classical theory predicts that there is an angle at which the reflection coefficient is zero, and there is total transmission of sound into the seabed. This angle is called the angle of intromission and has been directly observed at the seafloor only rarely. Data from a new measurement technique show this phenomenon with remarkable clarity. The presence of the angle of intromission creates an opportunity for a direct (i.e., without search) inversion for the sediment sound speed and density. Though acoustic techniques generally do not estimate sediment density very precisely, this technique is quite sensitive to density. Geoacoustic inversion results from reflection measurements in the Straits of Sicily compare very favorably with independent "ground truth" data indicating that the method is robust.     

Resonant ultrasound spectroscopy measurement of Young's modulus,shear modulus and Poisson's ratio as a function of porosity for alumina and hydroxyapatite

Modulus–porosity relationships are critical for engineered bone tissue scaffold materials such as hydroxyapatite (HA), where porosity is essential to biological function. Resonant ultrasound spectroscopy (RUS) measurements revealed that the Young's modulus, E, and shear modulus, G, of both alumina and HA decrease monotonically with increasing volume fraction porosity, P, for 0.06 < P < 0.39 (alumina) and 0.05 < P < 0.51 (HA). Although the elastic moduli of porous materials have been measured by a number of different ultrasonic resonance techniques (of which the RUS technique is one example) and over the last decade the elastic moduli of many solids have been measured by the RUS technique, this study is the first systematic RUS study of porous materials. Comparison of E versus P data for alumina (which has been studied extensively) with literature data from several measurement techniques indicates the RUS technique is effective for modulus–porosity measurements. Another key result is that although the HA specimens included in this study have a unimodal pore size distribution, the details of the decrease in E and G with increasing P agree well with literature data for HA with both unimodal and bimodal pore size distributions. In addition, Poisson's ratio exhibits a local minimum in the porosity range of 0.2 < P < 0.25 for both HA and alumina, which may be related to the pore morphology evolution during sintering.     

海底沉积物声速与物理性质的理论关系

为建立海底沉积物声速与物理性质的关系,引入密度变化比和弹性模量变化比为参数描述海底沉积物声速。密度变化比是描述声速的一个复合参数,由孔隙率、固相密度和海水密度三个物理参数表示;弹性模量变化比是描述声速的另一个复合参数,由孔隙率、固相体积模量和海水体积模量三个物理参数表示;声速公式可展开为这两个复合参数的泰勒多项式。两个复合参数的变化构成声速曲面,声速曲面包含了声速特性与沉积物性质的完整信息;而单参数声速公式是声速曲面上的一条曲线。数值计算与测试结果对比表明:把孔隙率-声速经验公式变换为参考声速乘以一个调制函数的标准形式,各个海区的孔隙率-声速经验公式的调制函数是相当接近的。论文导出的声速公式与Wood声速公式的区别在于弹性模量的模型不同。      

Accuracy evaluation of an X-ray microtomography system

Microstructural parameter evaluation of reservoir rocks is of great importance to petroleum production companies. In this connection, X-ray computed microtomography (μ-CT) has proven to be a quite useful method for the assessment of rocks, as it provides important microstructural parameters, such as porosity, permeability, pore size distribution and porous phase of the sample. X-ray computed microtomography is a non-destructive technique that enables the reuse of samples already measured and also yields 2-D cross-sectional images of the sample as well as volume rendering. This technique offers an additional advantage, as it does not require sample preparation, of reducing the measurement time, which is approximately one to three hours, depending on the spatial resolution used. Although this technique is extensively used, accuracy verification of measurements is hard to obtain because the existing calibrated samples (phantoms) have large volumes and are assessed in medical CT scanners with millimeter spatial resolution. Accordingly, this study aims to determine the accuracy of an X-ray computed microtomography system using a Skyscan 1172 X-ray microtomograph. To accomplish this investigation, it was used a nylon thread set with known appropriate diameter inserted into a glass tube. The results for porosity size and phase distribution by X-ray microtomography were very close to the geometrically calculated values. The geometrically calculated porosity and the porosity determined by the methodology using the μ-CT was 33.4 ± 3.4% and 31.0 ± 0.3%, respectively. The outcome of this investigation was excellent. It was also observed a small variability in the results along all 401 sections of the analyzed image. Minimum and maximum porosity values between the cross sections were 30.9% and 31.1%, respectively. A 3-D image representing the actual structure of the sample was also rendered from the 2-D images.     

利用超声测量水中含沙量垂线分布的方法

本文根据超声反射式测沙的原理，跟踪超声波在水中的传播，实时采集并获沙量沿垂线的分布规律，测量发射的一次超声脉冲，可得沙量分的瞬时特性；多次发射并取平均法。     

A Modified Biot/Squirt Model of Sound Propagation in Water-Saturated Sedment

A modified Biot/Squirt flow model was developed. The difference between MBISQ and BISQ models is the expression for the porosity differential. Numerical analysis shows that the acoustic dispersion predicted by MBISQ is much higher than by BISQ. Investigations of the effects of permeability, viscosity, and squirt flow length on velocity and attenuation indicate that the behavior of MBISQ agrees with that of the BISQ model. The result of sediment acoustic inversion based on MBISQ was more reasonable than the result of BISQ model.     

Selective-area doping of porous solgel films for integrated optics

A technique for doping of porous films by surface adsorption of ions from aqueous solution is demonstrated. Fabrication of the films by use of the solgel technique gives a nanometer-scale porosity, which provides high doping levels and homogeneity. Doping through a masking layer patterned by photolithography is thus possible. With Pb as a dopant, lead silicate films with refractive indices of 1.46 to 1.55 were obtained, with submicrometer patterning resolution. Linear control of the refractive index is achieved through variation of the solution pH. Applications of this technique in integrated optics and optical elements are proposed.     

Porosity engineering in glancing angle deposition thin films

We present a new technique for the fabrication of thin films at highly oblique flux incidence angles, in which the direction of film growth and the direction of incoming deposition flux are decoupled. The technique offers a high level of control over the porosity of thin films, and has been used to make thin films with a uniform and highly porous microstructure of tightly interwoven nanoscale fibres. The nanofibrous films have been analysed using scanning and transmission electron microscopy, and will be useful for thin film applications relying on high porosity, such as humidity sensors and super-capacitors. PACS 68.55.Jk; 68.55.Ac; 81.05.Rm; 61.46.+w; 81.15.Ef     

Thermographic measurement of the effect of humidity in mortar porosity

The objective of this analysis is to examine the influence of the moisture in the porosity measurement by means of thermal non-destructive test and ultrasound techniques. It is possible to determine the concrete durability by the calculation of its porosity. Porosity is determined in an indirect way, measuring mortar diffusivity by means of active thermography. Using ultrasound techniques, the porosity is related with the ultrasonic propagation of velocity. The diffusivity has been calculated using the W.J. Parker equation. In the ultrasound technique, using the pulse transmission method, ultrasonic propagation velocity was measured as a function of the water content. The conclusions express the correlation between both methods.     

Measuring nitrification in sediments--comparison of two techniques and three 15NO(-)3 measurement methods

Nitrification is a crucial process in sediment nitrogen cycling. We compared two (15)N tracer-based nitrification measurement techniques (isotope pairing technique (IPT) combined with (15)N nitrate pool dilution and (15)N ammonium oxidation) and three different (15)N analyses from bottom water nitrate (ammonia diffusion, denitrifier and SPINMAS) in a sediment mesocosm. The (15)N nitrate pool dilution technique combined with IPT can be used to quantify the in situ nitrification, but the minimum detection limit for the total nitrification is higher than that in the (15)N ammonium oxidation technique. The (15)N ammonium oxidation technique, however, is not applicable for sediments that have high ammonium content. If nitrate concentration and the amount of (15)N label in the sample are low, the (15)N nitrate analysis should be done with the denitrifier method. In higher (15)N concentrations, the less sensitive SPINMAS method can also be applied. The ammonia diffusion method is not suitable for bottom water (15)N nitrate analyses.     

Structural study of nanoporous ultra low-k dielectrics using complementary techniques: Ellipsometric porosimetry, X-ray reflectivity and grazing incidence small-angle X-ray scattering

This paper is focused on nanoporous methylsilsesquioxane deposited using a polymer approach and shows the complementarities of three experimental techniques: ellipsometric porosimetry (EP), X-ray reflectivity (XRR), and grazing incidence small-angle X-ray scattering (GISAXS). XRR and EP confirm that the pore volume fraction is larger for smaller dielectric constants. EP and GISAXS find mean pore sizes independent of the porosity, in the range 3-4 nm as diameter. GISAXS is the only technique that can estimate the porosity isotropy. Finally, the impact of integration processes such as surface plasma treatment, etching or stripping on the porosity is evaluated: the porosity remains unchanged except in the superficial layer where an increase of the pore size (or of the roughness) is observed.     

On the morphology of stain-etched porous silicon films

Morphology of stain-etched porous silicon films was investigated by a non-destructive technique, based on reflectance spectrometry: dielectric function profiles were computed by spectral reflectance via a finite difference model, and porosity was deduced by the effective medium approximation. Theoretical calculations were supported by high-resolution electron microscopy observations. The relations among oxidising species concentration in the etching solution, porosity profile and surface reflectance of the films were investigated.