Titanium Foams Processed Through Powder Metallurgy Route Using Lubricant Acrawax as Space Holder Material

In the present work titanium foams have been synthesized using acrawax as the space holder material. Acrawax has generally been used as a lubricant for easier compaction of aluminium alloy powders. This study deals with the use of this space holder material in the form of beads for creating pores in titanium metal matrix. Acrawax facilitates the formation of continuous dense cell walls which is difficult to obtain using ordinary space holder materials. Moreover, acrawax is compressible in nature and it facilitates the formation of better and uniformly sized pores. Titanium foams have been synthesized utilizing acrawax in two different sizes. The effect of using differently sized acrawax on the cell walls and mechanical properties has also been carried out in this study.     

Which separation scenarios are advantageous for membranes or distillations?

We systematically analyze power requirements of membrane and distillation processes for binary mixtures where the desired product component is more permeable and also more volatile. We first derive a shortcut method to compare the efficiency of heat pump and steam-driven distillations. Then, power requirements of heat pump distillation and membrane separation are discussed. Distillation generally requires lower power when either high component recoveries are needed (at all tested product purities), or high purity product streams with modest recoveries are needed. For high purity products at modest recoveries, membranes have a potential to provide energy benefits for highly enriched feeds, especially those composed of close boiling components. Additionally, when feed concentration is moderate to high and product recovery and purity are modest, membranes are likely to show efficiency gain. For the advantageous distillation scenarios studied, the power was generally lower than the membranes by a factor of two to seven.     

Thermomechanical analysis of direct chill casting using finite element method

The transient nature of the start-up phase is the most critical phase in the direct chill (DC) casting during which the quality of the ingot is questioned. The hot crack and cold crack are the two major problems in the DC casting which originate during and after the solidification. In this work, the thermal, metallurgical, and the mechanical fields of DC casting are modeled. The attention is focused on the mushy state of alloy where the chances are high for the hot tearing. The heat conduction and metallurgical phase-change phenomenon are modeled together in a strongly coupled manner. An isothermal staggered approach is followed to couple the thermal and mechanical parts within a time step. Finite element method is used to discretize the thermal and mechanical field equations. A temperature-based fixed grid method is followed to incorporate the latent heat. The mushy state of alloy is characterized through the Norton-Hoff viscoplastic law and the solid phase is modeled through the Garafalo law. An axisymmetric round billet is simulated. The casting material is considered as AA1201 aluminum alloy. It is found that all the components of stress and viscoplastic strain are maximum at the billet center. Further, the start-up phase stresses and strains are always higher than the steady state phase. Therefore, the chances of hot crack formation are higher during the start-up phase and specifically at the billet center. It is proved that through the ramping procedure, the vulnerability of start-up phase can be lowered.     

了解嵌入系统的引导技术

引导是指在接通电源和装入应用之间,系统完成的一系列步骤,它在理论上简单,但实际上经常很复杂。引导加载器的主要任务是装入操作系统,但软硬件工程师对这个过程的看法并不相同。     

Towards elucidating the connection between epithelial–mesenchymal transitions and stemness

Epithelial cells undergoing epithelial-to-mesenchymal transitions have often been shown to behave as cancer stem cells, but the precise molecular connection remains elusive. At the genetic level, stemness is governed by LIN28/let-7 double inhibition switch, whereas EMT/MET is controlled by miR-200/ZEB double inhibition circuit and LIN28 is inhibited by miR-200, coupling the two modules. Here, using a specially devised theoretical framework to investigate the dynamics of the LIN28/let-7 system, we show that it can operate as a three-way switch (between low, high and intermediate LIN28 levels termed the D, U and hybrid D/U states) similar to the three-way operation of the miR-200/ZEB circuit that allows for the existence of a hybrid epithelial/mesenchymal (E/M) phenotype. We find significant correspondence between the existence of the three states of the two circuits: E–D, M–U and E/M–D/U. Incorporating the activation of OCT4 by LIN28, we find that the hybrid E/M phenotype has high likelihood (when compared with either the E or M states) to gain stemness. Combining the LIN28/let-7 regulation by NF-κB and c-MYC, we find that NF-κB, but not c-MYC, elevates the likelihood of E/M phenotype to gain stemness. Our results are consistent with emerging concept that partial EMT can lead to stemness.     

Switching in structural, optical, and magnetic properties of self-assembled Co-doped ZnO: effect of Co-concentration

Here, we report on the self-assembled Co-doped ZnO nanoparticles synthesized by using sol–gel technique. It has been observed that when Co is introduced in the solution, nanoparticles arrange themselves into a particular pattern. This self-assembly of Zn_1?xCo_xO, were found to be consistent with the change in Co-doping concentration. Using electron microscopy these systems were studied to confirm the assembly formation with doping. Optical study of these assemblies suggests the decrease in direct band gap of these systems with the increase in doping concentration. In addition to it, the Urbach energy was found to be increased, indicating the redistribution of states in between conduction and valence band with doping. Magnetic measurement shows the introduction of paramagnetic behavior with Co-doping in this self-assembled Co-doped ZnO.     

Measurement of Ambient Ammonia over the National Capital Region of Delhi,India

Mixing ratio of ambient ammonia (NH₃) was measured at various locations of the National Capital Region (NCR) of Delhi, India using a NH₃-analyzer during January 2010 to June 2012 in campaign mode. The present study has been carried out on campaign based measurement of mixing ratios of NH₃ and NO _x for short period of time over the NCR of Delhi represent the indicative values over the region. The average mixing ratio of ambient NH₃ was 20.9 ± 1.6 ppb during the period. The maximum average mixing ratio of ambient NH₃ (28.8 ± 3.0 ppb) was recorded in an industrial area surrounded by intensive vehicular traffic followed by an agricultural farm (27.5 ± 2.1 ppb), whereas the minimum (6.4 ± 1.2 ppb) was recorded in the semi-urban area. The diurnal trend of NH₃ depended on the ambient temperature at most of the sites and was affected by wind direction. Ambient NH₃ was correlated with the NO _x mixing ratio suggesting that the vehicular emission may be one of the sources of ambient NH₃ in the NCR of Delhi. However, long-term measurements of ambient NH₃ and their precursors will lead to seasonal variation of source apportionment over the NCR, Delhi, India.     

Stochastic analysis of an Erlangian arrival with linear cost structure

In this paper a control policy for an Erlangian arrival has been studied. Here, the server goes on vacation when the system becomes empty, returning to an operative state after a random idle period lapses, or the queue length becomes N, whichever is earlier. The expressions for various operational characteristics have been obtained. Numerical results have been computed and some of these are graphed. Graphical interpretation of linear cost structure has been discussed.