Microstructure and Sliding Wear Behaviour of Ni(Cr)-TiB_2 Coatings Deposited by HVOF Spraying of SHS Powders

THERMAL SPRAYING provides a large range ofcoatings,which increase the wear resistance ofsubstrates[1].One of the major coating families is thecermet,composed of hard ceramic particles with ametallic binder.The most commonly used cermetcoatings in industrial applications are based on eitherthe WC-Co or the Cr3C2-Ni(Cr)systems with WC-17wt%Co and Cr3C2-25wt%Ni(Cr)being typicalcompositions[2,3].Although WC-Co deposits are hardand wear resistant at ambient temperatures their rangeof ap…     

Energy consumption minimization and throughput improvement in cognitive radio networks by joint optimization of detection threshold,sensing time and user selection

Wireless Networks - Cooperative spectrum sensing schemes proposed to solve the hidden terminal problem and mitigate multipath fading and shadowing effects, which enhance the sensing performance and...     

Study on the size dependent effective Young modulus by EPI method based on modified couple stress theory

Microsystem Technologies - Various experimental and theoretical researches have been shown the size-dependence behavior of the effective Young modulus (EYM) in the micron and sub-micron scales. One...     

A Novel Gas Sensor Based on Tunneling-Field-Ionization on Whisker-Covered Gold Nanowires

Typical gas ionization sensors (GISs) work by fingerprinting the ionization breakdown voltages of the gases to be identified. In this work, we developed a GIS that operates by field-ionizing the unknown gas at exceptionally low voltages. The resultant field-ion current-voltage (I-V) characteristic was then used to identify the gas. Freestanding gold nanowires (AuNW), terminated with nanoscale whisker-like features, were employed as field-amplifiers to reduce the field ionization threshold voltages. Synthesis of the AuNWs was carried out by the template-assisted technique accompanied by two alterations: 1) polystyrene (PS) microspheres were incorporated to reduce the compactness of the pores, thus prevent the nanostructures from collapse, and 2) the template was impregnated by HAuCl₄ to form gold nanowhiskers during the electrochemical nucleation of AuNWs. The sensor was tested in three elemental gases: Ar, N₂ and He, in a pressure range of 0.01 < P < 100 torr. Each gas demonstrated a distinctive I-V curve, particularly in the field-limited regime. The threshold ionization voltages ranged from 1 to 10 V, almost three orders of magnitude lower than the voltages used in field-ion-microscopy. The low-voltage field ionization was attributed to the field-amplifying nanoscale whiskers on the AuNW tips, as well as the presence of residual amorphous alumina with semiconducting characteristics, due to incomplete removal of the porous anodized alumina (PAA) template.     

Well Bore Stability Using a New Dynamic Model

Abstract

Well bore instability problems are difficult without actual geomechanical models. With advanced geomechanical problems such as dynamic well bore instabilities, an otherwise routine well bore instability problem escalates into a disastrous instability. It is common that, in areas where instabilities are infrequent, contractors and operators become complacent with poorly designed system. Consequently, when dynamic well bore instabilities do occur, the designed models are inadequate, mechanical problems compound the situation, and a disaster follows. Until now, not many researchers have taken into account the influences of dynamic instabilities in casing design while several situations reported in which the completed well subjected to failure due to the dynamic displacements. This study is intended to develop a new pragmatic geomechanical model to design casing based on ground motions around the drilled well. This model is applied and verified against field data and numerical model in the South Pars Gas Field (phases 6, 7, and 8 and well number SPDG-8) in Persian Gulf. The results indicate that dynamic displacements must be considered in design whenever the well is drilled in a zone where an earthquake is possible.     

N-methyl-D-aspartate receptor-dependent plasticity within a distributed corticostriatal network mediates appetitive instrumental learning.

The effect of microinfusion of the N-methyl-{d}-aspartate (NMDA) antagonist 2-amino-5-phosphonopentanoic acid (AP-5) into the amygdala, medial prefrontal cortex, and dorsal and ventral subiculum on acquisition of a lever-pressing task for food in rats was examined. Serial transmission between the basolateral amygdala and nucleus accumbens core was also examined in an asymmetric infusion design. AP-5 administered bilaterally into either the amygdala or medial prefrontal cortex markedly impaired learning, whereas administration into the dorsal or ventral subiculum had no effect. Unilateral infusion of AP-5 into either the nucleus accumbens core or amygdala was also sufficient to impair learning. These data provide novel evidence for NMDA receptor-dependent plasticity within corticostriatal networks in the acquisition of appetitive instrumental learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ultralow-voltage field-ionization discharge on whiskered silicon nanowires for gas-sensing applications

Several hundred million volts per centimetre of electric-field strength are required to field-ionize gas species. Such fields are produced on sharp metallic tips under a bias of a few kilovolts. Here, we show that field ionization is possible at dramatically lower fields on semiconductor nanomaterials containing surface states, particularly with metal-catalysed whiskers grown on silicon nanowires. The low-voltage field-ionization phenomena observed here cannot be explained solely on the basis of the large field-amplification effect of suspended gold nanoparticles present on the whisker tips. We postulate that field penetration causes upward band-bending at the surface of exposed silicon containing surface states in the vicinity of the catalyst. Band-bending enables the valence electron to tunnel into the surface states at reduced fields. This work provides a basis for development of low-voltage ionization sensors. Although demonstrated on silicon, low-voltage field ionization can be detected on any sharp semiconductor tip containing proper surface states.     

己烷低耗喷雾热解法大规模制备多壁碳纳米管

以己烷为碳源,二茂铁为催化剂前躯体,应用喷雾热解法,制备了多壁碳纳米管(MWCNTs).采用酸沥滤和空气氧化对MWCNTs进行纯化.利用SEM、TEM、XRD、EDS、TGA及Raman光谱分析等方法分别对原生和纯化MWCNTs进行表征.为制得优质、高产MWCNTs,对制备工艺参数作了优选,分别研讨了最佳制备参数,包括:二茂铁升华温度、己烷中二茂铁浓度、热解温度和时间,己烷与H2的流量比.MWCNTs具有典型的腊肠状(Sawsage-like)构型,长度大于数十微米,内、外管径分别为15nm～45nm及25nm～70nm,MWCNTs的纯度和产率的质量分数分别高于95%和70%.     

Equilibrium,kinetic and thermodynamic study of removal of reactive orange 12 on platinum nanoparticle loaded on activated carbon as novel adsorbent

The proposed research describes the synthesis and characterization of platinum nanoparticles loaded on activated carbon (Pt-NP-AC) and its efficient application as novel adsorbent for efficient removal of reactive orange 12 (RO-12). The influences of effective parameters following the optimization of variables on removal percentages, their value was set as 0.015 g Pt-NP-AC, pH 1, contact time of 13 min. At optimum values of all variables at 25 and 50 mgL⁻¹ of RO-12 enthalpy (ΔH⁰) and entropy (ΔS⁰) changes was found to be 59.89 and 225.076, respectively, which negative value of ΔG⁰ shows a spontaneous nature, and the positive values of ΔH⁰ and ΔS⁰ indicate the endothermic nature and adsorption organized of dye molecule on the adsorbent surface. Experimental data was fitted to different kinetic models including first-order, pseudo-second-order, Elovich and intra-particle diffusion models, and it was seen that the adsorption process follows pseudo-second-order model in consideration to intra-particle diffusion mechanism. At optimum values of all variables, the adsorption process follows the second-order kinetic and Langmuir isotherm model with adsorption capacity 285.143 mg g⁻¹ at room temperature.