Simplified Relationships for Particle-Size Distribution and Permeation Groutability Limits for Soils

The particle-size distribution of soil with mean particle size and fines content are used not only in soil classifications but also in a number of other soil property relationships. In this study, two simple relationships (hyperbolic [tan?h(x)] and S-curve) were investigated to represent the particle size distribution of soils. The parameters of the hyperbolic model were correlated to various soil parameters such as the mean particle size, particle size range, and fines content. There was no direct correlation between Fredlund (four-parameter model) and S-curve model parameters and the soil parameters. The predictions of the two (hyperbolic) and three (S-curve) parameter models were compared to the four-parameter model (unimodal) using limited soil data from the literature and the agreements were good. The hyperbolic model was used to map the Unified Soil Classification System. A recent study had quantified the relationship between the grouting pressure and the fines content in nonplastic soils. Also in the current practice, upper and lower particle-size distribution limits are used in determining the groutability of soils. In this study, the relationship between grouting pressure and fines contents of the soil was generalized using the hyperbolic particle-size distribution model and verified with a groutability study using an acrylamide grout. Based on limited data in the literature, the groutability of soils was defined using a new set of parameters, grouting pressure, fines content, and mean particle size diameter of the soil.     

Stress corrosion cracking behaviors of RE-containing ME21 magnesium alloy processed by equal-channel angular pressing

A commercial as-cast ME21 magnesium alloy containing rare-earth (RE) element was processed by equalchannel angular pressing to obtain fine-grained micro structure. Stress corrosion cracking (SCC) behaviors of the fine-grained samples were studied by slow-strain-rate testing in air, distilled water and Hanks’solution at the strain rate of 1×10~(-6) s~(-1). All samples show a relatively low SCC sensitivity in distilled water but a great SCC tendency in Hanks’ solution. The microscopic observations of the fracture surfaces and the side surfaces reveal obvious active anodic dissolution and hydrogen embrittlement cracks, which indicate the higher SCC susceptibility in Hanks'solution. The fine-grained microstructure with more crystal defects promotes the passivation process of the oxide film and restrains the hydrogen induced cracking of the ME21 magnesium alloy, leading to the higher general corrosion resistance as well as SCC resistance.     

Effects of oil contamination and bioremediation on geotechnical properties of highly plastic clayey soil

Leakage of oil and its derivatives into the soil can change the engineering behavior of soil as well as cause enviro nmental disasters.Also,recovering the contaminated sites into their natural condition and making contaminated materials as both environmentally and geotechnically suitable construction materials need the employment of remediation techniques.Bioremediation,as an efficient,low cost and environmentalfriendly approach,was used in the case of highly plastic clayey soils.To better understand the change in geotechnical properties of highly plastic fine-grained soil due to crude oil contamination and bioremediation,Atterberg limits,compaction,unconfined compression,direct shear,and consolidation tests were conducted on natural,contaminated,and bioremediated soil samples to investigate the effects of contamination and remediation on fine-grained soil properties.Oil contamination reduced maximum dry density(MDD),optimum moisture content(OMC),unconfined compressive strength(UCS),shear strength,swelling pressure,and coefficient of consolidation of soil.In addition,contamination increased the compression and swelling indices and compressibility of soil.Bioremediation reduced soil contamination by about 50%.Moreover,in comparison with contaminated soil,bio re mediation reduced the MDD,UCS,swelling index,free swelling and swelling pressure of soil,and also increased OMC,shear strength,cohesion,internal friction angle,failure strain,porosity,compression index,and settlement.Micro structural analyses showed that oil contamination does not alter the soil structure in terms of chemical compounds,elements,and constituent minerals.While it decreased the specific surface area of the soil,and the bio re mediation significantly increased the mentioned parameters.Bioremediation resulted in the formation of quasi-fibrous textures and porous and agglomerated structures.As a result,oil contamination affected the mechanical properties of soil negatively,but bioremediation improved these properties.     

P2HBT: Partially Policy Hidden E-Healthcare System with Black-Box Traceability

Electronic health record (EHR), as the core of the e-healthcare system, is an electronic version of patient medical history, which records personal health-related information. EHR embodies the value of disease monitoring through large-scale sharing via the Cloud service provider (CSP). However, the health data-centric feature makes EHR more preferable to the adversaries compared with other outsourcing data. Moreover, there may even be malicious users who deliberately leak their access privileges for benefits. An e-healthcare system with a black-box traceable and robust data security mechanism is presented for the first time. Specifically, we propose an effective P2HBT, which can perform fine-grained access control on encrypted EHRs, prevent the leakage of privacy contained in access policies, and support tracing of traitors. Under the standard model, the scheme is proved fully secure. Performance analysis demonstrates that P2HBT can achieve the design goals and outperform existing schemes in terms of storage and computation overhead.     

Fabrication of Y and Fe co-doped BaZr0.13Ti1.46O3 fine-grained ceramics for temperature-stable multilayer ceramic capacitors

Y³⁺ and Fe³⁺ co-doped BaZr_0.13Ti_1.46O₃ powders were synthesized by wet chemical method through a precipitation process, able to control uniformity and particle size of the BaZr_0.13Ti_1.46O₃-based particles. Fine-grained BaZr_0.13Ti_1.46O₃ ceramics co-doped with various amounts of Y³⁺ and Fe³⁺ were prepared at low sintering temperature to yield good dielectric properties and gentle temperature stability. The co-doping effect on the microstructure and dielectric properties of BaZr_0.13Ti_1.46O₃ ceramics were studied. Results showed the dielectric constants firstly to increase monotonically then decrease with the increase of Y³⁺ and Fe³⁺concentration. Overall, the resulting ceramics met the X8R specification when Y³⁺ and Fe³⁺ contents were 2 or 4 mol%. Moreover, the increase in Y³⁺ and Fe³⁺ doping concentration from 6 to 8 mol% satisfied the X7R specification.     

Spark plasma sintering of titanium nitride in nitrogen: Does it affect the sinterability and the mechanical properties?

Titanium nitride ceramics have an intrinsic interest due to its optical and structural applications. However, the conditions for sintering of dense pieces are not still clarified. This research work is focused on the spark plasma sintering (SPS) of near-fully dense fine-grained TiN. The main goal is giving a response to a longstanding debate: can the external atmosphere favor sintering? Different sintering atmospheres, either vacuum or a nitrogen flow, have been used during SPS heating to this purpose. X ray diffraction analysis has showed the presence of TiN as the main phase with traces of Ti₄O₇ in optimal SPS conditions (1600?°C, one minute dwell time). Our results show that the use of a nitrogen flow while heating can improve sinterability very slightly, but mechanical properties are essentially unaltered within the experimental uncertainty. The hardness reaches values as high as 20GPa whereas fracture toughness can be evaluated around 4?MPam^1/2.     

Microstructure and mechanical properties of fine-grained boron carbide ceramics fabricated by high-pressure hot pressing combined with high-energy ball milling

Dense and fine-grained boron carbide (B₄C) ceramics were fabricated via high-pressure hot pressing (100?MPa) using powders, which are prepared by high-energy ball milling. These powders were sintered at a low temperature (1800?°C) without any sintering aid. The dense and fine-grained B₄C ceramics demonstrate super high hardness, outstanding fracture toughness and modern flexure strength. The milled powders were characterised by disordered crystal structure and ultrafine particle size that ranges from a few nanometres to a few hundred nanometres. The combined contributions of high pressure and the characteristic of the milled powders guaranteed that the dense fine-grained microstructure was achieved at only 1800?°C. The grain size distribution of the ceramics was inhomogeneous and ranged from 70?nm to 1.6?µm. However, the average grain size was fine at only 430?nm, which partially contributed to the super high hardness of the B₄C ceramics. The locally concentrated areas of the small grains changed the fracture mode of the B₄C ceramics from the complete transgranular fracture to a mixture of transgranular and intergranular fractures, thereby enhancing the toughness of the B₄C ceramics. The relative density, Vickers hardness, flexure strength and fracture toughness of the obtained B₄C ceramics reached up to 99.5%, 41.3?GPa, 564?MPa and 4.41?MPa?m^1/2, respectively.     

Fine grained Nd3+:Lu2O3 transparent ceramic with enhanced photoluminescence

Fine-grained Nd³⁺:Lu₂O₃ transparent ceramic was developed by a two-step sintering method in flowing H₂ atmosphere at T₁ = 1720 °C for 15 min and T₂ = 1620 °C for 10 h. The initial nanopowders were synthesized by a wet chemical processing with a uniform particle size of about 40 nm. The average grain size of the obtained 3 at.% Nd³⁺:Lu₂O₃ ceramic was 406 nm, which is ∼150 times smaller than the coarse-grained ceramic by normal H₂ sintering. The emission intensity of the fine-grained transparent ceramic is 3 times of its coarse-grained counterpart, indicating higher Nd concentration without serious quenching in fine-grained transparent ceramic is possible, which agreed well with the prediction of an atomistic modeling work with YAG. EXAFS research demonstrated that with decreasing grain size, higher degree of disorder factor of the local environment of doped Nd atoms was discovered.     

含硫低品位细粒锡尾矿的回收试验研究

广西某细粒锡尾矿中锡、硫品位分别为0.27%和2.05%,具有一定的综合回收价值,但锡石的嵌布粒度较细且共生关系较复杂,回收难度较大。为提高该尾矿中锡的回收效果,基于矿石性质特点,采用脱硫—浮锡工艺对锡进行回收。试验以硫酸铜为活化剂、丁基黄药为捕收剂和松醇油为起泡剂,采用一粗一扫一精的浮选流程对尾矿中的硫化物进行脱除;以水玻璃和氟硅酸钠为抑制剂、苄基胂酸为捕收剂,采用一粗一扫一精的浮选流程对锡石进行回收,获得的锡精矿锡品位和回收率分别为2.95%和55.81%。此外,为进一步提高锡的回收率,在脱硫—浮锡试验基础上,添加了聚合氯化铝作为选择性絮凝剂,可获得锡品位3.05%、回收率为60.66%的锡精矿,结果表明,在选择性絮凝剂的作用下锡的回收效果得到了一定改善。     

大数模乘脉动阵列的FPGA细粒度映射实现

通过分析FPGA可配置逻辑块的细致结构,提出了一种基于FPGA的细粒度映射方法,并使用该方法高效实现了大数模乘脉动阵列.在保持高速计算特点的同时,将模乘脉动阵列的资源消耗降低为原来的三分之一.在低成本的20万门级FPGA器件中即可实现1024位模乘器.该实现每秒可进行20次RSA签名.如果换用高性能FPGA,签名速度更可提高至每秒40次.