Effect of exposure on the erodibility of intertidal mudflats

Sediments on intertidal flats are exposed during low tides. Under the effect of exposure, the water content of sediments decreases because of the evaporation process, which alters the erosive behaviour of cohesive sediments, and therefore changes the patterns of erosion/accretion on intertidal flats. Consequently, exposure indirectly affects the intertidal morphology. An understanding of how exposure alters the erodibility of sediment on intertidal flats is critical to predicting the resilience of intertidal zones into the future during which sea-level rise is believed to exacerbate erosion in low-lying areas. Sediments were collected from an intertidal mudflat in the Firth of Thames, New Zealand in different seasons from 2017 to 2019 for laboratory experiments. Two experiments (Exp. 1 and Exp. 2) were set up in order to explore the effect of exposure including air temperature and exposure duration on erodibility of cohesive sediments. The EROMES device was used to measure the erosion potential of sediment (erosion threshold, Ƭᵣ N m⁻² and erosion rate, ER g m⁻² s⁻¹). Exp. 1 investigated erodibility of sediments exposed to a wide range of temperatures (controlled at 0, 8, 25 and 40°C) for 6 h. Meanwhile, Exp. 2 was designed to examine the effect of exposure duration on erodibility. In this experiment, a systematically-changed exposure duration (6 h, 1, 4 and 10 d) was used to mimic a wide range of exposure that might happen on an intertidal flat during a year (set to mimic the Firth of Thames field site). Experimental results indicated that erosion resistance of sediments significantly increased (increased Ƭᵣ, and decreased ER) corresponding to decreased water content after exposure. The higher the air temperature and the longer the exposure duration, the more stable the sediments were. For instance, the water content of exposed sediments decreased by 1.01 to 1.78 times, a rate which was a function of increasing temperature. The Ƭᵣ of exposed experiments was 1.2 to 2.2 times higher, whereas ER decreased 1.2 to 6.2 times. After 10 d, exposure increased Ƭᵣ by 1.7 to 4.4 times and decreased ER by 11.6 to 21.5 times compared with 6 h of exposure. Semi-empirical models fitted datasets from Exp.1 and Exp. 2 were used to predict the variations of Ƭᵣ and ER as functions of air temperature, T (°C) and exposure duration, D (h). These semi-empirical models were used to extend a Delft3D numerical model to test the effect of exposure on intertidal mudflat profiles and development of tidal channel networks. Model results indicated that exposure enhanced the more flat-topped shape of intertidal mudflats. Higher air temperature resulted in stronger effects on bed level change. For example, for the case of 40°C, bed level built up by 0.039m after one year of model time. Regarding the development of channel networks on intertidal mudflats, the exposure effect tended to create denser and deeper channel networks compared to model runs without the exposure effect. Our findings, therefore, contribute to the prediction of the intertidal morphology development, which will help to understanding the resilience of tidal flats and salt marshes in future under the effect of sea-level rise and global warming

Application of Path-integral for Studying EXAFS Cumulants

In this work, the path-integral effective potential (PIEP) method has been applied to re-study the temperature dependence of extended X-ray absorption fine structure (EXAFS) cumulants of materials. Using the trial density matrix and effective potential expression, we derived the analytical expressions of the first three EXAFS cumulants in the first shell of materials. The cumulant relation is also calculated to determine the temperature range in which the PIEP method could be applied. Our results are compared with available experimental data as well as with those calculated by the first-order perturbation approach in anharmonic Einstein model and the reasonable agreements are achieved

Choosing the best machine tool in mechanical manufacturing

Machine tools are indispensable components and play an important role in mechanical manufacturing. The equipment of machine tools has a huge effect on the operational efficiency of businesses. Each machine tool type is described by many different criteria, such as cost, technological capabilities, accuracy, energy consumption, convenience in operation, safety for workers, working noise, etc. If the selection of machine is only based on one or several criteria, it will be really easy to make mistakes, which means it is not possible to choose the real best machine. A machine is considered to be the best only when it is chosen based on all of its criteria. This work is called multi-criteria decision-making (MCDM). In this study, the selection of machine tools has been done using two different multi-criteria decision-making methods, including the FUCA method (Faire Un Choix Adéquat) and the CURLI method (Collaborative Unbiased Rank List Intergration). These are two methods with very different characteristics. When using the FUCA method, it is necessary to normalize the data and determine the weights for the criteria. Meanwhile, if using the CURLI method, these two things are not necessary. The selection of these two distinct methods is intended to produce the most generalizable conclusions. Three types of machine tool, which are considered in this study, include grinding machine, drilling machine and milling machine. The number of grinders that were offered for selection was twelve, the number of drills that were surveyed in this study was thirteen, while nine were the number of milling machines that were given for selection. The objective of this study is to determine the best solution in each type of machine. The results of ranking the machines are very similar when using the two mentioned methods. Specially, in all the surveyed cases, the two methods FUCA and CURLI always find the same best alternative. Accordingly, it is possible to firmly come to a conclusion that the FUCA method and the CURLI method are equally effective in machine tool selection. In addition, this study has determined the best three machines corresponding to the three different machine type

Design and performance analysis of a mechanically coupled spring compliant to out-of-plane oscillation

In this paper, a spring system symmetrically arranged around a circular plate compliant to out-of-plane oscillation is proposed. The spring system consists of single serpentine springs mutually coupled in a plane. Three theoretical mechanical models for evaluating the stiffness of the spring system are built, which are based on the flexural beam, Sigitta, and serpentine spring theories and equivalent mechanical spring structure models. The theoretically calculated results are in good agreement with numerical solutions using the finite element method, with errors less than 10% in the appropriate dimension ranges of the spring. Compared to similar spring structures without mechanical coupling, the proposed mechanically coupled spring shows advantage in suppressing the mode coupling

New primitives of controlled elements F2/4 for block ciphers

This paper develops the cipher design approach based on the use of data-dependent operations (DDOs). A new class of DDO based on the advanced controlled elements (CEs) is introduced, which is proven well suited to hardware implementations for FPGA devices. To increase the hardware implementation efficiency of block ciphers, while using contemporary FPGA devices there is proposed an approach to synthesis of fast block ciphers, which uses the substitution-permutation network constructed on the basis of the controlled elements F2/4 implementing the 2 x 2 substitutions under control of the four-bit vector. There are proposed criteria for selecting elements F2/4 and results on investigating their main cryptographic properties. It is designed a new fast 128-bit block cipher MM-128 that uses the elements F2/4 as elementary building block. The cipher possesses higher performance and requires less hardware resources for its implementation on the bases of FPGA devices than the known block ciphers. There are presented result on differential analysis of the cipher MM-12

Primary Cementless Bipolar Long Stem Hemiarthroplasty for Unstable Osteoporotic Intertrochanteric Fracture in the Elderly Patients

BACKGROUND: Intertrochanteric fracture (ITF) is a major part of fracture in femoral head fracture. 95% of ITF are found in elderly patients. Osteosynthese is the preferred method of choice. However, elderly patients had osteoporotic, combined with many of chronic disease conditions that increase the rate of osteosynthese failure. Hemiarthroplasty bipolar long-stem is a surgical method that helps patients relieve pain, facilitate early rehabilitation, limit long-term complications, and improve quality of life for patients. AIM: The aim of our study is to evaluate the clinical of result of primary cementless bipolar long stem hemiarthroplasty in treatment for unstable ITF in the elderly patients who have severe osteoporosis. METHODS: Between 01/2016 and 12/2017, 35 patients with ITF type A2.2 and A2.3 (AO) were included in our prospective study. These patients were over 70 years old and treatment by hemiarthroplasty cementless long stem at E hospital and Saint Paul hospital by one group surgeons. RESULTS: Mean age of studied subjects was 84.29 ± 6.17, the lowest was 71, the highest was 96; ratio male/female was 1/4. Follow-up of 35 patients for at least 6 months showed 88.6% caused by a low-energy injury; Average rehabilitation time was 4.63 ± 1.7 days. The average Harris point at the end was 90.4 ± 4.72. CONCLUSION: Primary cementless bipolar long stem hemiarthroplasty is one of good choices in treatment unstable ITF in elderly patients with severe osteoporosis helped patients improve the quality of life

Effect of Silica Nanoparticles on Properties of Coatings Based on Acrylic Emulsion Resin

Effect of nanosilica size on physic-mechanical properties, thermal stability and weathering durability of coating based on acrylic emulsion. Nanocomposite coating formulas were filled by 2 wt.% nanosilica particles which were used in this study, namely: nanosilica from Sigma (15-20nm), nansilica from rice husk (~70-200 nm) and nanosilica from Arosil – Belgium (7-12 nm). Obtained results showed that viscosity flow of coating formula containing nanosilica from Arosil saw the highest flow-time while coating formulas filled other nanosilica and unfilled nanosilica experienced similar flow-time. In presence of nanosilica, coating properties were improved in comparison with neat coating. However, coating filled by nanosilica from rice husk indicated the best properties in studied coating formula. It may explained that size of nanosilica from rice husk was the largest in studied nanosilica particles and thus easily dispersing into coating formula

On-chip ZnO nanofibers prepared by electrospinning method for NO2 gas detection

In the present study, on-chip ZnO nanofibers were fabricated by means of the electrospinning technique followed by a calcination process at 600 oC towards the gas sensor application. The morphology, composition, and crystalline structure of the as-spun and annealed ZnO nanofibers were investigated by field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD), respectively. The findings show that spider-net like ZnO nanofibers with a diameter of 60 – 100 nm were successfully synthesized without any incorporation of impurities into the nanofibers. The FESEM images also reveal that each nanofiber is composed of many nanograins. The combination of experimental and calculated X-ray diffraction data indicate that ZnO nanofibers were crystallized in hexagonal wurtzite structure. For the gas sensing device application, the ZnO nanofibers-based sensors were tested with the nitrogen dioxide gas in the temperature range of 200 oC to 350 oC and concentrations from 2.5 ppm to 10 ppm. The sensing property results indicate that at the optimal working temperature of 300 oC, the ZnO nanofibers-based sensors exhibited a maximum response of 30 and 166 times on exposure of 2.5 and 10 ppm NO2 gas, respectively. The presence of nanograins within nanofibers, which results in further intensification of the resistance modulation, is responsible for such high gas response

Current advances in seagrass research: A review from Viet Nam

Seagrass meadows provide valuable ecosystem services but are fragile and threatened ecosystems all over the world. This review highlights the current advances in seagrass research from Viet Nam. One goal is to support decision makers in developing science-based conservation strategies. In recent years, several techniques were applied to estimate the size of seagrass meadows. Independent from the method used, there is an alarming decline in the seagrass area in almost all parts of Viet Nam. Since 1990, a decline of 46.5% or 13,549 ha was found. Only in a few protected and difficult-to-reach areas was an increase observed. Conditions at those sites could be investigated in more detail to make suggestions for conservation and recovery of seagrass meadows. Due to their lifestyle and morphology, seagrasses take up compounds from their environment easily. Phytoremediation processes of Thalassia hemprichii and Enhalus acoroides are described exemplarily. High accumulation of heavy metals dependent on their concentration in the environment in different organs can be observed. On the one hand, seagrasses play a role in phytoremediation processes in polluted areas; on the other hand, they might suffer at high concentrations, and pollution will contribute to their overall decline. Compared with the neighboring countries, the total Corg stock from seagrass beds in Viet Nam was much lower than in the Philippines and Indonesia but higher than that of Malaysia and Myanmar. Due to an exceptionally long latitudinal coastline of 3,260 km covering cool to warm water environments, the seagrass species composition in Viet Nam shows a high diversity and a high plasticity within species boundaries. This leads to challenges in taxonomic issues, especially with the Halophila genus, which can be better deduced from genetic diversity/population structures of members of Hydrocharitaceae. Finally, the current seagrass conservation and management efforts in Viet Nam are presented and discussed. Only decisions based on the interdisciplinary cooperation of scientists from all disciplines mentioned will finally lead to conserve this valuable ecosystem for mankind and biodiversity