汽油机喷水提高缸内压力和NOx降低排放的研究

基于三维仿真软件,研究了缸内直喷(GDI)发动机在低负荷运行工况下通过喷水对缸内压力和排放的影CFD NOx响。在计算过程中,喷水设置在发动机压缩冲程中(℃A),汽油喷入缸内的时段为660~680℃。研究结果表640~650 A明,喷入一定量的水之后,发动机的热效率有所提高,缸内局部火焰温度降低,氮氧化合物排放也随之降低。     

Nanoscale Flexoelectricity

Electromechanical effects are ubiquitous in biological and materials systems. Understanding the fundamentals of these coupling phenomena is critical to devising next‐generation electromechanical transducers. Piezoelectricity has been studied in detail, in both the bulk and at mesoscopic scales. Recently, an increasing amount of attention has been paid to flexoelectricity: electrical polarization induced by a strain gradient. While piezoelectricity requires crystalline structures with no inversion symmetry, flexoelectricity does not carry this requirement, since the effect is caused by inhomogeneous strains. Flexoelectricity explains many interesting electromechanical behaviors in hard crystalline materials and underpins core mechanoelectric transduction phenomena in soft biomaterials. Most excitingly, flexoelectricity is a size‐dependent effect which becomes more significant in nanoscale systems. With increasing interest in nanoscale and nano‐bio hybrid materials, flexoelectricity will continue to gain prominence. This Review summarizes work in this area. First, methods to amplify or manipulate the flexoelectric effect to enhance material properties will be investigated, particularly at nanometer scales. Next, the nature and history of these effects in soft biomaterials will be explored. Finally, some theoretical interpretations for the effect will be presented. Overall, flexoelectricity represents an exciting phenomenon which is expected to become more considerable as materials continue to shrink.     

Procedural Justice, Not Absorptive Capacity, Matters in Multinational Enterprise ICT Transfers

• This paper empirically tests the effectiveness of information and communications technology (ICT) knowledge transfer and adoption in the multinational enterprise (MNE) as an issue of critical importance to contemporary MNE functioning. In contrast to mainstream thinking on absorptive capacity, but in line with prevailing international business theory, our research supports the proposition that perceptions of procedural justice, rather than absorptive capacity, determine effectiveness, especially in cases of high tacit knowledge transfers.
• Data was collected from senior ICT representatives in 86 Canadian subsidiaries of foreign owned MNEs. Each of these subsidiaries recently experienced a significant ICT transfer imposed by the parent organization.
• Support was found for the main propositions: Procedural justice significantly predicted successful ICT transfer and adoption, while absorptive capacity was not significant. These findings are consistent even when knowledge tacitness was high.
• The perceived success of the ICT transfer as well as its adoption varied widely across these firms. The potential reasons for this divergence in effectiveness are manifold, but our findings suggest that in situations of substantial knowledge tacitness, a higher level of procedural justice, rather than a higher level of absorptive capacity, is critical to effective transfer and adoption.

     

Stability of the ultrafine-grained microstructure in silver processed by ECAP and HPT

The high-temperature thermal stability of the ultrafine-grained (UFG) microstructures in low stacking fault energy silver was studied by differential scanning calorimetry (DSC). The UFG microstructures were achieved by equal-channel angular pressing (ECAP) and high-pressure torsion (HPT) at room temperature (RT). The defect structure in the as-processed samples was examined by electron microscopy and X-ray line profile analysis. The stored energy calculated from the defect densities was compared to the heat released during DSC. The sum of the energies stored in grain boundaries and dislocations in the ECAP-processed samples agreed with the heat released experimentally within the experimental error. The temperature of the DSC peak maximum decreased while the released heat increased with increasing numbers of ECAP passes. The released heat for the specimen processed by one revolution of HPT was much smaller than after 4–8 passes of ECAP despite the 2 times larger dislocation density measured by X-ray line profile analysis. This dichotomy was caused by the heterogeneous sandwich-like microstructure of the HPT-processed disk: about 175 μm wide surface layers on both sides of the disk exhibited a UFG microstructure while the internal part was recrystallized, thereby yielding a relatively small released heat.     

Improved fracture toughness and fatigue life of carbon fiber reinforced epoxy composite due to incorporation of rubber nanoparticles

In this study, core–shell rubber (CSR) nanoparticles with approximate particle size of 35 nm were used as a modifier for the epoxy polymer. The effects of various CSR contents in the epoxy matrix on mode I interlaminar fracture toughness, tensile strength, and fatigue life of the carbon fabric reinforced epoxy (CF/EP) composites were investigated. The experimental results showed that the mode I interlaminar fracture toughness at crack initiation and propagation significantly improved by 71.21 and 58.47 %, respectively, when 8.0 wt% CSR was dispersed in the epoxy matrix. The fatigue life of the modified CF/EP composites at all of CSR contents dramatically increased 75–100 times longer than that of the unmodified CF/EP composites at high cycle fatigue while tensile strength slightly increased by about 10 %. Field emission scanning electron microcopy (FESEM) observations of the fracture surfaces were conducted to explain failure mechanisms of CSR addition to the CF/EP composites. The evidences of the rubber nanoparticle debonding, plastic void growth, and microshear banding were credited for delaying the onset of matrix crack, and reducing the crack growth rate, as a result, attributed to increase in the mechanical properties of the CF/EP composites.     

In situ fabrication of platinum/graphene composite shell on polymer microspheres through reactive self-assembly and in situ reduction

We present a simple method to fabricate a uniform-sized graphene–metal–polymer composite microsphere of core–shell structure. On the surface of amine-functionalized polymer microsphere, graphene oxide (GO) sheets were affixed to give a core–shell structure by self-assembly process followed by the immobilization of platinum (Pt) ions to the assembled GO shell. Subsequently, they were chemically reduced in situ converting both GO and Pt ions to reduced GO (RGO) and Pt nanoparticles (NPs), respectively. As a result, a robust RGO-Pt composite shell, composed of RGO sheets and well-distributed Pt NPs, was fabricated on the microsphere surface. Meanwhile, the insulative GO shell was converted to the conductive RGO-Pt shell giving 24.0 S m^?1 of electrical conductivity. We demonstrated that the electrical property of the shell was significantly improved by the incorporation of Pt NPs.     

Nanoparticle Accumulation in Angiogenic Tissues: Towards Predictable Pharmacokinetics

Nanoparticles are increasingly used in medical applications such as drug delivery, imaging, and biodiagnostics, particularly for cancer. The design of nanoparticles for tumor delivery has been largely empirical, owing to a lack of quantitative data on angiogenic tissue sequestration. Using fluorescence correlation spectroscopy, the deposition rate constants of nanoparticles into angiogenic blood vessel tissue are determined. It is shown that deposition is dependent on surface charge. Moreover, the size dependency strongly suggests that nanoparticles are taken up by a passive mechanism that depends largely on geometry. These findings imply that it is possible to tune nanoparticle pharmacokinetics simply by adjusting nanoparticle size.     

Biodegradable Nanocapsules as siRNA Carriers for Mutant K‐Ras Gene Silencing of Human Pancreatic Carcinoma Cells

The application of small interfering RNA (siRNA)‐based RNA interference (RNAi) for cancer gene therapy has attracted great attention. Gene therapy is a promising strategy for cancer treatment because it is relatively non‐invasive and has a higher therapeutic specificity than chemotherapy. However, without the use of safe and efficient carriers, siRNAs cannot effectively penetrate the cell membranes and RNAi is impeded. In this work, cationic poly(lactic acid) (CPLA)‐based degradable nanocapsules (NCs) are utilized as novel carriers of siRNA for effective gene silencing of pancreatic cancer cells. These CPLA‐NCs can readily form nanoplexes with K‐Ras siRNA and over 90% transfection efficiency is achieved using the nanoplexes. Cell viability studies show that the nanoparticles are highly biocompatible and non‐toxic, indicating that CPLA‐NC is a promising potential candidate for gene therapy in a clinical setting.     

Heat Transfer and Exergy Analysis of a Spiral Heat Exchanger

The heat transfer effectiveness of a countercurrent spiral heat exchanger is expressed as a function of number of transfer units, ratio of flow capacity rates, number of spiral turns, and dimensionless start-point angle of spiral (dimensionless angular angle of the start point of a spiral curve constituting the solid wall of the heat exchanger). The heat transfer effectiveness is weakly dependent on the dimensionless start-point angle of spiral, but moderately increases with the number of spiral turns. As the number of spiral turns is larger than 20, the heat transfer effectiveness of the spiral heat exchanger approaches that of a counterflow heat exchanger. The heat transfer effectiveness of the spiral heat exchanger has a maximum. The optimum number of transfer units at the maximum heat transfer effectiveness increases with the number of spiral turns, whereas it increases with a decrease of the ratio of flow capacity rates. In the second-law analysis, an optimum hot flow-to-cold flow capacity-rate ratio is found. For obtaining a large net recovered exergy rate, the spiral heat exchanger needs to possess a large number of transfer units (greater than 2.0) and operate at a near balanced-flow condition. In addition, a small consumed mechanical power is demanded.