Advanced ceramic material for high temperature turbine tip seals

Ceramic material systems are being considered for potential use as turbine blade tip gas path seals at temperatures up to 1370 1/4 C. Silicon carbide and silicon nitride structures were selected for study since an initial analysis of the problem gave these materials the greatest potential for development into a successful materials system. Segments of silicon nitride and silicon carbide materials over a range of densities, processed by various methods, a honeycomb structure of silicon nitride and ceramic blade tip inserts fabricated from both materials by hot pressing were tested singly and in combination. The evaluations included wear under simulated engine blade tip rub conditions, thermal stability, impact resistance, machinability, hot gas erosion and feasibility of fabrication into engine components. The silicon nitride honeycomb and low-density silicon carbide using a selected grain size distribution gave the most promising results as rub-tolerant shroud liners. Ceramic blade tip inserts made from hot-pressed silicon nitride gave excellent test results. Their behavior closely simulated metal tips. Wear was similar to that of metals but reduced by a factor of six

Advanced ceramic material for high temperature turbine tip seals

Forty-one material systems were evaluated for potential use in turbine blade tip seal applications at 1370 C. Both ceramic blade tip inserts and abradable ceramic tip shoes were tested. Hot gas erosion, impact resistance, thermal stability, and dynamic rub performance were the criteria used in rating the various materials. Silicon carbide and silicon nitride were used, both as blade tips and abradables. The blade tip inserts were fabricated by hot pressing while low density and honeycomb abradables were sintered or reaction bonded

Performance Evaluation Of Quality Of Service Of A 4g Network In A Tropical Environment

The Nigerian Communications Commission (NCC), which is a communication regulatory Authority sets some key Performance Indications (KPIs) that the GSM network providers need to adhere to in order to deliver an efficient and quality network services in the country [1]. In this paper, Transverse Electromagnetic Wave Simulator (TEMS) was used in collecting data (Drive Tests) related to – call setup success rate (CSSR), call drop rate (CDR), paging success rate (PSR), grade of service (GOS), handover success rate (HOSR) etc; from 30 Base transceiver stations (BTS or BS) within Enugu metropolis during a specified period of fifteen working days. The Path Loss Exponent of the Test-Bed was verified to ascertain if it is in agreement with the environment of interest and the Operation and Maintenance Centre Resources (OMCR) statistics and drive test data gathered were analyzed using different graphs. The results of the Investigation of performance of Quality of Service offered by the network provider, Mobile Telecommunications Nigeria (MTN) in Enugu metropolis showed high performance as the network was deployed in the appropriate environment – Shadowed Urban Environment with Path Loss Exponent of 3.12

Complete controllability of finite-level quantum systems

Complete controllability is a fundamental issue in the field of control of quantum systems, not least because of its implications for dynamical realizability of the kinematical bounds on the optimization of observables. In this paper we investigate the question of complete controllability for finite-level quantum systems subject to a single control field, for which the interaction is of dipole form. Sufficient criteria for complete controllability of a wide range of finite-level quantum systems are established and the question of limits of complete controllability is addressed. Finally, the results are applied to give a classification of complete controllability for four-level systems.Comment: 14 pages, IoP-LaTe

Entanglement and nonclassicality for multi-mode radiation field states

Nonclassicality in the sense of quantum optics is a prerequisite for entanglement in multi-mode radiation states. In this work we bring out the possibilities of passing from the former to the latter, via action of classicality preserving systems like beamsplitters, in a transparent manner. For single mode states, a complete description of nonclassicality is available via the classical theory of moments, as a set of necessary and sufficient conditions on the photon number distribution. We show that when the mode is coupled to an ancilla in any coherent state, and the system is then acted upon by a beamsplitter, these conditions turn exactly into signatures of NPT entanglement of the output state. Since the classical moment problem does not generalize to two or more modes, we turn in these cases to other familiar sufficient but not necessary conditions for nonclassicality, namely the Mandel parameter criterion and its extensions. We generalize the Mandel matrix from one-mode states to the two-mode situation, leading to a natural classification of states with varying levels of nonclassicality. For two--mode states we present a single test that can, if successful, simultaneously show nonclassicality as well as NPT entanglement. We also develop a test for NPT entanglement after beamsplitter action on a nonclassical state, tracing carefully the way in which it goes beyond the Mandel nonclassicality test. The result of three--mode beamsplitter action after coupling to an ancilla in the ground state is treated in the same spirit. The concept of genuine tripartite entanglement, and scalar measures of nonclassicality at the Mandel level for two-mode systems, are discussed. Numerous examples illustrating all these concepts are presented.Comment: Latex, 46 page

Hopf algebras: motivations and examples

This paper provides motivation as well as a method of construction for Hopf algebras, starting from an associative algebra. The dualization technique involved relies heavily on the use of Sweedler's dual

Repellent properties of Rotheca glabrum plant extracts against adults of Rhipicephalus appendiculatus

Abstract Background Rotheca glabrum (formerly known as Clerodendrum glabrum [Verbenaceae]) is used by local communities in the Limpopo Province of South Africa to control ticks on livestock and was selected from the database of the ARC-Onderstepoort Veterinary Institute. Its leaves were extracted using organic solvents ranging from polar to non-polar solvents (methanol, acetone and dichloromethane (DCM)). In addition, the traditional soap-water (infusion) and water-based (decoction) methods were used. The tick repelling activity was determined against the adult stage of the livestock tick Rhipicephalus appendiculatus. Results In the tick-climbing repellency bioassay a 30% acetone extract had a significant (p ≤ 0.05) repellent effect against adults of R. appendiculatus. The extract was still active at a lower concentration of 10%. The hexane fraction from the R. glabrum acetone extract had a higher tick repellency activity than the positive controls Amitix and Bayticol at the same concentrations. Unfortunately, the activity decreased after 2.5 h, probably due to volatility of the biologically active compound(s) within the extract. Conclusion Attempts were made to isolate the repellent compound from the acetone extract of R. glabrum. The process produced very good results up to a late stage in the bioassay-guided fractionation process. At that point, the repellent activity was lost. When two fractions were combined, the repellent activity was regained. These results provide strong evidence for the existence of a synergisticactivity of different compounds. It may be better to concentrate on extracts that would kill ticks rather than on extracts that would repel ticks

A Computational Approach in Estimating the Amount of Pond Pollution and Determining the Long Time Behavioural Representation of Pond Pollution Model

This paper specifically develops a computational approach in estimating the amount of pond pollution and determining the long time(every 48 hours) behavioural representation of the pond pollution model.This approach, which can be considered as an extension of the block predictor-corrector methods in form of implicit block multistep method has many computational advantages usingvariable step size technique. Moreover, it possesses some important advantages of designing a suitable step size, stopping criteria(prescribed tolerance level) and error control/minimization as well. This makes the new approach specifically efficient for solving systems of first-order ordinary differentialequations. Analysis of some theoretical properties of the method is carried out to ascertain the extent of performance of the method. Again, numerical results are given to display the performance and efficiency of this new method on system first-order ordinary differential equations

Cluster Dynamics for Randomly Frustrated Systems with Finite Connectivity

In simulations of some infinite range spin glass systems with finite connectivity, it is found that for any resonable computational time, the saturatedenergy per spin that is achieved by a cluster algorithm is lowered in comparison to that achieved by Metropolis dynamics.The gap between the average energies obtained from these two dynamics is robust with respect to variations of the annealing schedule. For some probability distribution of the interactions the ground state energy is calculated analytically within the replica symmetry assumptionand is found to be saturated by a cluster algorithm.Comment: Revtex, 4 pages with 3 figure