10,951 research outputs found
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
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