纳米黏土与再生聚酯纤维混合处理黏土砂的抗剪强度

近年来,以纳米尺度和纳米颗粒以及定向或随机分布的离散单元(如纤维)来加固土体的材料已被广泛应用于岩土工程中.本研究的主要目的是研究纳米黏土与再生聚酯纤维混合作为一种新的稳定材料对土壤力学行为的影响.对于未强化和三种纤维含量介于0.1％和0.5％的强化土壤标本,以及三种纳米黏土含量介于0.5％和1.5％的土壤进行排干剪切...     

The effect of electrospinning parameters on the morphology of glass nanofibers

Abstract

Electrospinning of glass nanofibers, as one of the most important techniques for producing nanofibers, was the focus of the present research. This process was done using a carrying polymer in order to modify all important parameters of the process including the solution parameters, the electrospinning voltage, the electrospinning distance and feeding rate of the solution to achieve a desired nanofiber morphology. The produced nanofibers were pyrolyzed at a high temperature to remove the carrying polymer and the FTIR test approved that it was completely removed. The diameter of nanofibers and other details were investigated using SEM images and it was shown that the produced nanofibers have a finer diameter with an average of 228?nm and standard deviation of 46?nm in comparison to other works that reported 500?nm for these characteristics.     

Force and position control of grasp in multiple robotic mechanisms

One of the approaches to increase the dexterity of a robot manipulating system is a design philosophy that consists of multiple robotic mechanisms. Applications of such a collection of manipulators can be in the design of a dextrous end-effector, a reconfigurable fixture to locate and grip various sized objects, or cooperative robotic arms which through their coordinated motions are able to accomplish a given task. Although the applications of such a design philosophy are endless, many problems still remain to be addressed. One of these problems is the control of the contact forces (grasping forces) between the mechanisms and the position of the grasped object. This article addresses this problem. First, a model of the mechanisms in contact with the grasped object is postulated; second, the problem of controlling the grasping forces and the position of the grasped object is formulated in the linear multi-input/multi-output system, and, finally, a centralized optimal controller is proposed for controlling the desired variables. The results of this article are demonstrated using two examples. One of the main advantages of the proposed controller is that it also shapes the transient response of the grasping force, which is an important consideration in cases when grasping fragile objects. © 1996 John Wiley & Sons, Inc.     

Antiproliferative and antioxidative activities of cuttlefish (<Emphasis Type="Italic">Sepia pharaonis</Emphasis>) protein hydrolysates as affected by degree of hydrolysis

Bioactivities (including antioxidative and antiproliferative properties) of cuttlefish mantle protein hydrolysates (CPH) with the degree of hydrolysis (DH) of 20.9, 25.5, 30.6, 35.3 and 40.6% (shortened as 20, 25, 30, 35 and 40%, respectively) prepared using alcalase were evaluated. The results indicated that the CPH with 20, 30 and 40% DH showed the greatest activity against DPPH radical scavenging [5.2 µmol TE (torolox equivalent)/g sample], reducing power (0.4 absorbance at 700 nm) and total antioxidant capacity (0.6 mg ascorbic acid equivalent/g sample), which were 2.5, 6.5 and 13.8 times higher than the cuttlefish mantle protein isolate (CPI), respectively. The CPH with the DH of 20% had the highest effect against MDA-231 and T47D cancer cell lines with growth inhibition of 78.2 and 66.2%, which were 6.5 and 6 times higher activities compared to the CPI, respectively. The amino acid profile of CPH indicated that glutamine (15.7%) and asparagine (10.9%) were predominant.     

Investigation of sediment transport pattern and beach morphology in the vicinity of submerged groyne (case study: Dahane Sar Sefidrood)

Marine structures, such as Groynes, Sea walls and Detached Breakwaters, are constructed in coast of area to improve coast stability against bed erosions due to changing wave and current pattern. Marine mechanisms and interaction with the hydraulic structures need to be intensively studied. Groynes are one of the most prominent structures that are used in shore protection and littoral sediment. The main hydraulic function of the groyne is to control the long shore current and littoral sediment transport. This structure can be submerged and provide the necessary beach protection without negative aesthetic impact. However, for submerged structures adopted for beach protection, the shoreline response to these structures is not well understood. The objective of this study is to predict sediment transport in the vicinity of submerged groyne and comparison with non-submerged groyne focusing on a part of the coast at Dahane Sar Sefidrood, Guilan Province, Iran, where serious coast erosion has been occurred. The simulations were designed using a one-line model which can be used as a first approximation of shoreline prediction in the vicinity of groyne. The results of the proposed model are compared with experimental data to determine the shape of the coast. The results of predicted beach deformation show that when submerged groyne construct in the beach, sediment accumulation will be slightly less than the non-submerged groyne; because transfer coefficient for the submerged groyne is more than non-submerged groyne. This result will cause more sediment passing on submerged groyne. Finally, the result of the present study show that using submerged groyne is an efficient way to control the sediment and beach erosion without causing severe environmental effect on the coast.     

Hybrid intelligent water drop bundled wavelet neural network to solve the islanding detection by inverter-based DG

In this paper, a passive neuro-wavelet based islanding detection technique for grid-connected inverter-based distributed generation was developed. The weight parameters of the neural network were optimized by intelligent water drop (IWD) to improve the capability of the proposed technique in the proposed problem. The proposed method utilizes and combines wavelet analysis and artificial neural network (ANN) to detect islanding. Connecting distributed generator to the distribution network has many benefits such as increasing the capacity of the grid and enhancing the power quality. However, it gives rise to many problems. This is mainly due to the fact that distribution networks are designed without any generation units at that level. Hence, integrating distributed generators into the existing distribution network is not problem-free. Unintentional islanding is one of the encountered problems. Discrete wavelet transform (DWT) is capable of decomposing the signals into different frequency bands. It can be utilized in extracting discriminative features from the acquired voltage signals. In passive schemes with a large non-detection zone (NDZ), concern has been raised on active method due to its degrading power quality effect. The main emphasis of the proposed scheme is to reduce the NDZ to as close as possible and to keep the output power quality unchanged. The simulation results from Matlab/Simulink shows that the proposed method has a small non-detection zone, and is capable of detecting islanding accurately within the minimum standard time.     

A novel algorithm for frequency dependent modeling of ferrite ring and its optimum design to study VFTO behaviors within GIS

One of the fundamental issues in gas insulated substations (GIS) which has destructive effects on GIS equipment is the very fast transient over-voltages (VFTOs). This paper models a 400/230 kV substation in order to study the effects of VFTO extensively implemented on EMTP-RV. In addition, the application of ferrite rings for suppressing VFTOs is assessed thoroughly. The main advantage of this paper is its new proposed algorithm according to the ferrite ring frequency dependent modeling that is validated with experimental results. This paper examines the effects of three compositions of the ferrite ring on VFTO suppression. Moreover, it estimates the dimension of the ferrite ring based on the SF6 gas insulation withstand and the maximum effect of ferrite rings on VFTO suppression constraint with the COMSOL multiphysics software. Furthermore, it gains VFTO attenuated percentages due to the installation of the ferrite ring in different GIS nodes. Finally, it analyzes the offered VFTO amendment technique in various GIS switching scenarios.     

Multifunctional composites using reinforced laminae with carbon-nanotube forests

Traditional fibre-reinforced composite materials with excellent in-plane properties fare poorly when out-of-plane through-thickness properties are important. Composite architectures with fibres designed orthogonal to the two-dimensional (2D) layout in traditional composites could alleviate this weakness in the transverse direction, but all of the efforts so far have only produced limited success. Here, we unveil an approach to the 3D composite challenge, without altering the 2D stack design, on the basis of the concept of interlaminar carbon-nanotube forests that would provide enhanced multifunctional properties along the thickness direction. The carbon-nanotube forests allow the fastening of adjacent plies in the 3D composite. We grow multiwalled carbon nanotubes on the surface of micro-fibre fabric cloth layouts, normal to the fibre lengths, resulting in a 3D effect between plies under loading. These nanotube-coated fabric cloths serve as building blocks for the multilayered 3D composites, with the nanotube forests providing much-needed interlaminar strength and toughness under various loading conditions. For the fabricated 3D composites with nanotube forests, we demonstrate remarkable improvements in the interlaminar fracture toughness, hardness, delamination resistance, in-plane mechanical properties, damping, thermoelastic behaviour, and thermal and electrical conductivities making these structures truly multifunctional.     

Controlling electron overflow in phosphor-free InGaN/GaN nanowire white light-emitting diodes

We have investigated for the first time the impact of electron overflow on the performance of nanowire light-emitting diodes (LEDs) operating in the entire visible spectral range, wherein intrinsic white light emission is achieved from self-organized InGaN quantum dots embedded in defect-free GaN nanowires on a single chip. Through detailed temperature-dependent electroluminescence and simulation studies, it is revealed that electron leakage out of the device active region is primarily responsible for efficiency degradation in such nanowire devices, which in conjunction with the presence of nonradiative surface recombination largely determines the unique emission characteristics of nanowire light-emitting diodes. We have further demonstrated that electron overflow in nanowire LEDs can be effectively prevented with the incorporation of a p-doped AlGaN electron blocking layer, leading to the achievement of phosphor-free white light-emitting diodes that can exhibit for the first time virtually zero efficiency droop for injection currents up to ~2200 A/cm(2). This study also provides unambiguous evidence that Auger recombination is not the primary mechanism responsible for efficiency droop in GaN-based nanowire light-emitting diodes.     

Numerical Modeling for Hydraulic Resonance in Hydropower Systems Using Impulse Response

An effective numerical method to compute hydraulic resonance in pressurized piping of hydropower systems is presented. For this purpose, the impulse response method is used, i.e., a unit pressure impulse is introduced at the downstream waterway as an exciter. The method of characteristics is used to solve the governing equations for the hydraulic transient and to get the pressure response of the system in the time domain. The discrete Fourier transform is used to compute the frequency response of the system which gives the resonance frequencies in the hydropower plant system. To increase the accuracy of the results, unsteady friction is incorporated into the methodology. The influence of the unsteady friction, wave speed, and power on the pressure response diagram is investigated for the waterway of a multiunit hydropower plant which has been recently installed. Computed results agree very well with those obtained from the standard method of the characteristics.