The Supernova Remnant G11.2-0.3 and its central Pulsar

The plerion inside the composite Supernova Remnant G11.2-0.3 appears to be dominated by the magnetic field to an extent unprecedented among well known cases. We discuss its evolution as determined by a central pulsar and the interaction with the surrounding thermal remnant, which in turn interacts with the ambient medium. We find that a plausible scenario exists, where all the observations can be reproduced with rather typical values for the parameters of the system; we also obtain the most likely period for the still undetected pulsar.Comment: 10 pages, to be published on ApJ Letters. Formatted using AASTe

Improving The Performance Of Industrial-Technical Schools In Egypt In The Light Of Corporate Schools Model: A Qualitative Study

Corporate schools are no longer a new phenomenon since more organizations are currently moving towards this model for workplace learning. Therefore, the current study aimed at setting a suggested proposal to improve the performance of the industrial technical schools in Egypt in the light of the corporate schools model. This involves examining both the real goals and the problems encountered in the Egyptian industrial-technical education. Moreover, the study examines the corporate school phenomenon by analyzing one example of corporate schools. The current study used a qualitative-analytic method as it suits the nature of the study. The study came down to some results, most important of which are: (1) corporate schools can contribute to overcoming the problems which face the industrial schools; (2) corporate schools are educational entities that serve business strategy. Based on this, the paper concludes with a suggested proposal to improve the performance of the industrial-technical schools in Egypt

Effect of the nucleating agents Cr2O3 and LiF on crystallizing phases and microstructures of glass-ceramics prepared by using some industrial wastes

Glass-ceramics in the system diopside-anorthite-orthoclase were prepared using the waste known as the by-pass cement dust in the amount of 36 % of the batch constituents. The effects of addition of the nucleating agents Cr2O3, LiF, and mixtures of them on the crystallizability, phase assemblages, and the resultant microstructures were investigated. Low concentration of Cr2O3 (0.5 wt%) causes volume crystallization and formation of fine-grained microstructures of microcline, anorthite and aluminous pyroxene. Higher concentrations of Cr2O3 favor formation of leucite and aluminous pyroxene and inhibit crystallization of anorthite. LiF causes the formation of microcline and its transformation into orthoclase. It also increases the crystallizability with the formation of nonuniform coarse-grained texture. Α mixture of 0.5 % Cr2O3 and 1.5 % LiF causes a synergistic effect, where fine-grained microstructure is formed (due to Cr2O3) with orthoclase formation (due to LiF) in addition to aluminous pyroxene and anorthite. The effects of various Cr2O3 concentrations were discussed on the bases of the increased viscosity and separation of Cr2O3 and/or chromiumspinel phases. The effects of LiF were attributed to the role of fluorine ions in reducing the viscosity of the glasses, consequently facilitating crystallization of the structurally more complex silicate in addition to favoring reaching thermodynamic equilibrium

A Formal Object Model for Layered Networks to Support Verification and Simulation

This work presents an abstract formal model of the interconnection structure of the Open Systems Interconnection Reference Model (OSI-RM) developed using Object-Oriented modeling principles permitting it to serve as a re-usable platform in supporting the development of simulations and formal methods applied to layered network protocols. A simulation of the object model using MODSIM III was developed and Prototype Verification System (PVS) was used to show the applicability of the object model to formal methods by formally specifying and verifying a Global Systems for Mobile communications (GSM) protocol. This application has proved to be successful in two aspects. The first was showing the existence of discrepancies between informal standard protocol specifications, and the second was that communication over the layered GSM network was verified. Although formal methods is somewhat difficult and time consuming, this research shows the need for the formal specification of all communication protocols to support a clear understanding of these protocols and to provide consistency in their implementations. A domain for the application of this model is mobile cellular telecommunications systems. Mobile Communications is one of the most rapidly expanding sectors of telecommunications. Expectations of what a mobile cellular phone can do have vastly increased the complexity of cellular communication networks, which makes it imperative that protocol specifications be verified before implementation

The physics and kinematics of the evolved, interacting planetary nebula PN G342.0-01.7

Here we aim to study the physical and kinematical characteristics of the unstudied old planetary nebula (PN) PN G342.0-01.7, which shows evidence of interaction with its surrounding interstellar medium. We used Integral Field Spectra from the Wide Field Spectrograph on the ANU 2.3 m telescope to provide spectroscopy across the whole object covering the spectral range 3400-7000 {\AA}. We formed narrow-band images to investigate the excitation structure. The spectral analysis shows that the object is a distant Peimbert Type I PN of low excitation, formally of excitation class of 0.5. The low electron density, high dynamical age, and low surface brightness of the object confirm that it is observed fairly late in its evolution. It shows clear evidence for dredge-up of CN-processed material characteristic of its class. In addition, the low peculiar velocity of 7 km s$^{-1}$ shows it to be a member of the young disk component of our Galaxy. We built a self-consistent photoionisation model for the PNe matching the observed spectrum, the H$\beta$ luminosity, and the diameter. On the basis of this we derive an effective temperature $\log T_{\rm eff} \sim 5.05$ and luminosity $1.85 < \log L < 2.25$. The temperature is much higher than might have been expected using the excitation class, proving that this can be misleading in classifying evolved PNe. PN G342.0-01.7 is in interaction with its surrounding interstellar medium through which the object is moving in the south-west direction. This interaction drives a slow shock into the outer PN ejecta. A shock model suggests that it only accounts for about 10\% of the total luminosity, but has an important effect on the global spectrum of the PN.Comment: 15 pages, 6 figures, A&A accepted 201

CFD for the Design and Optimization of Slurry Bubble Column Reactors

Despite the notion that computational fluid dynamics (CFD) models are considered complicated, expensive, time-consuming and difficult to formulate, their implementation offers an advanced prospect to move beyond empirical models, which inherit severe limitations in terms of flexibility, scale-up, and optimization of slurry bubble column reactors (SBCRs). This is because complex hydrodynamics coupled with chemical reactions in such reactors increase the uncertainty in using empirical models, leading to significant startup delays and overruns. Recent work by Basha et al. has shown that properly validated CFD models provide an exceptional opportunity to gain detailed temporal and spatial information about the local hydrodynamics and overall behavior as well as performance of SBCRs. This chapter provides a comprehensive overview of different CFD frameworks which could be used to model SBCRs, namely the multi-Eulerian, direct numerical simulations (DNS) and large Eddy simulation (LES). The steps required in developing CFD models and the optimization of different sub-models, such as interphase interactions, solid-phase representation, bubble population balance, bubble-induced turbulence, mass transfer and reaction kinetics are highlighted. Different convergence criteria for meshing, solution stability and techniques for maximizing the CFD model scale without compromising accuracy are addressed. An example of using CFD multi-Eulerian frameworks to describe the local hydrodynamics in a pilot-scale SBCR (0.3-m ID, 3-m height) operating under the Fisher-Tropsch (F-T) synthesis process are also provided

Mass Transfer in Multiphase Systems

Mass transfer in reactive and non-reactive multiphase systems is of vital importance in chemical, petrochemical, and biological engineering applications. In this chapter, theories and models of mass transfer in gas-liquid, gas-solid and gas-liquid-solid systems with and without chemical reactions are briefly reviewed. Literature data on the mass transfer characteristics in multiphase reactors over the last two decades with applications to the Fischer-Tropsch (F-T) synthesis are summarized. Moreover, the F-T reactions are described and an overview of the use of Slurry Bubble Column Reactors (SBCRs) and Multitubular Fixed Bed Reactors (MTFBRs) for low temperature F-T (LTFT) synthesis are discussed. The important factors affecting the hydrodynamic (gas holdup, bubble size/distribution) and mass transfer parameters (volumetric mass transfer coefficients) in SBCRs for F-T synthesis, including operating conditions, gas-liquid-solid properties, reactor geometry and internals as well as gas distributors are also discussed. The discussion reveals that the performance of the LTFT SBCR operating in the churn-turbulent flow regime is controlled by the resistance in the liquid-side film and/or the F-T reaction kinetics depending on the operating conditions prevailing in the reactor. Also, there is a great need to understand the behavior and quantify the hydrodynamics and mass transfer in SBCRs operating with syngas (H2 + CO) and F-T reactor wax in the presence of active catalyst (iron or cobalt) under typical F-T synthesis conditions in a large SBCR with an inside diameter ≥0.15m