361,703 research outputs found
Beyond direct simulation Monte Carlo (DSMC) modelling of collision environments
Direct simulation Monte Carlo (DSMC) models have been successfully adopted and adapted to describe gas flows in a wide range of environments since the method was first introduced by Bird in the 1960s. We propose a new approach to modelling collisions between gas-phase particles in this work - operating in a similar way to the DSMC model, but with one key difference. Particles move in a mean field, generated by all previously propagated particles, which removes the requirement that all particles be propagated simultaneously. This yields a significant reduction in computation effort and lends itself to applications for which DSMC becomes intractable, such as when a species of interest is only a minor component of a large gas mixture
Efficient acoustic modelling of large acoustic spaces using finite difference methods.
Time domain methods for solving wave based acoustic models have been of continued interest and development since early work by key figures such as Bottledooren, as these methods can provide a simple and flexible approach for simulating a wide range of acoustic phenomena such as room modes. The nature of many time domain difference methods present significant computational resource requirements, as the size, sampling rate and inherent stability of the simulation has a distinct impact on the memory and execution time required for the simulation to give a satisfactory result. In this study the execution speed is analysed, for variations of the finite difference time domain method that may provide some increase in computation speed for large domains. It is suggested that leveraging a dynamic windowing method may reduce total computation time for some simulations, by decreasing the number of computations per time-step in the early stage of a simulation.N/
Research on Efficiency Analysis of Microservices
With the maturity of web services, containers, and cloud computing
technologies, large services in traditional systems (e.g. the computation
services of machine learning and artificial intelligence) are gradually being
broken down into many microservices to increase service reusability and
flexibility. Therefore, this study proposes an efficiency analysis framework
based on queuing models to analyze the efficiency difference of breaking down
traditional large services into n microservices. For generalization, this study
considers different service time distributions (e.g. exponential distribution
of service time and fixed service time) and explores the system efficiency in
the worst-case and best-case scenarios through queuing models (i.e. M/M/1
queuing model and M/D/1 queuing model). In each experiment, it was shown that
the total time required for the original large service was higher than that
required for breaking it down into multiple microservices, so breaking it down
into multiple microservices can improve system efficiency. It can also be
observed that in the best-case scenario, the improvement effect becomes more
significant with an increase in arrival rate. However, in the worst-case
scenario, only slight improvement was achieved. This study found that breaking
down into multiple microservices can effectively improve system efficiency and
proved that when the computation time of the large service is evenly
distributed among multiple microservices, the best improvement effect can be
achieved. Therefore, this study's findings can serve as a reference guide for
future development of microservice architecture.Comment: in Chinese languag
Ab initio Study of Luminescence in Ce-doped LuSiO: The Role of Oxygen Vacancies on Emission Color and Thermal Quenching Behavior
We study from first principles the luminescence of LuSiO:Ce
(LSO:Ce), a scintillator widely used in medical imaging applications, and
establish the crucial role of oxygen vacancies (V) in the generated
spectrum. The excitation energy, emission energy and Stokes shift of its
luminescent centers are simulated through a constrained density-functional
theory method coupled with a SCF analysis of total energies, and
compared with experimental spectra. We show that the high-energy emission band
comes from a single Ce-based luminescent center, while the large experimental
spread of the low-energy emission band originates from a whole set of different
Ce-V complexes together with the other Ce-based luminescent center.
Further, the luminescence thermal quenching behavior is analyzed. The
crossover mechanism is found to be very unlikely, with a large crossing energy
barrier (E) in the one-dimensional model. The alternative mechanism
usually considered, namely the electron auto-ionization, is also shown to be
unlikely. In this respect, we introduce a new methodology in which the
time-consuming accurate computation of the band gap for such models is
bypassed. We emphasize the usually overlooked role of the differing geometry
relaxation in the excited neutral electronic state Ce and in the
ionized electronic state Ce. The results indicate that such electron
auto-ionization cannot explain the thermal stability difference between the
high- and low-energy emission bands. Finally, a hole auto-ionization process is
proposed as a plausible alternative. With the already well-established excited
state characterization methodology, the approach to color center identification
and thermal quenching analysis proposed here can be applied to other
luminescent materials in the presence of intrinsic defects.Comment: 13 pages, 8 figures, accepted by Phys. Rev. Material
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