17,445 research outputs found
Pilot Power Allocation Through User Grouping in Multi-Cell Massive MIMO Systems
In this paper, we propose a relative channel estimation error (RCEE) metric,
and derive closed-form expressions for its expectation and
the achievable uplink rate holding for any number of base station antennas ,
with the least squares (LS) and minimum mean squared error (MMSE) estimation
methods. It is found that RCEE and converge to the same
constant value when , resulting in the pilot power
allocation (PPA) is substantially simplified and a PPA algorithm is proposed to
minimize the average per user with a total pilot power
budget in multi-cell massive multiple-input multiple-output systems.
Numerical results show that the PPA algorithm brings considerable gains for the
LS estimation compared with equal PPA (EPPA), while the gains are only
significant with large frequency reuse factor (FRF) for the MMSE estimation.
Moreover, for large FRF and large , the performance of the LS approaches to
the performance of the MMSE, which means that simple LS estimation method is a
very viable when co-channel interference is small. For the achievable uplink
rate, the PPA scheme delivers almost the same average achievable uplink rate
and improves the minimum achievable uplink rate compared with the EPPA scheme.Comment: 30 pages, 5 figures, submitted to IEEE Transactions on Communication
Carbon emission right as a new property right: rescue CDM developers in China from 2012
Clean development mechanism (CDM) is encountering many uncertainties due to the coming end of the commitment period and critically suggested reformation. As the largest participant in the CDM market, China shoulders the biggest proportion of market risk. Among the studies on CDM in China, few have focused upon the legal aspect of CDM, which is crucial in defending developers’ interests. To fill this research gap in making the transition from policy to law, this paper claims that carbon emission right, which is the basis of trade, should be attributed as a property right in Property Law of People’s Republic of China. The present study will discuss the characteristics of carbon emission, definition, and legal attribution of carbon emission right. The valid object of carbon emission right in the CDM market under Property Law should be certified emissions reductions (CERs). The usufructuary right could be specifically applied in practice to the owners’ property right on CERs in China. Although experience from the CDM is not fully applicable to the development of cap and trading, the success of CDM market provides a reasonable platform to study emission right in the view of legal science. Furthermore, the proposed research acts as the pioneer study that lay the theoretical foundations in legal science on emission right trading for other potential schemes, which in turn addresses international environmental issues.published_or_final_versio
Machine Learning for High-entropy Alloys: Progress, Challenges and Opportunities
High-entropy alloys (HEAs) have attracted extensive interest due to their
exceptional mechanical properties and the vast compositional space for new
HEAs. However, understanding their novel physical mechanisms and then using
these mechanisms to design new HEAs are confronted with their high-dimensional
chemical complexity, which presents unique challenges to (i) the theoretical
modeling that needs accurate atomic interactions for atomistic simulations and
(ii) constructing reliable macro-scale models for high-throughput screening of
vast amounts of candidate alloys. Machine learning (ML) sheds light on these
problems with its capability to represent extremely complex relations. This
review highlights the success and promising future of utilizing ML to overcome
these challenges. We first introduce the basics of ML algorithms and
application scenarios. We then summarize the state-of-the-art ML models
describing atomic interactions and atomistic simulations of thermodynamic and
mechanical properties. Special attention is paid to phase predictions,
planar-defect calculations, and plastic deformation simulations. Next, we
review ML models for macro-scale properties, such as lattice structures, phase
formations, and mechanical properties. Examples of machine-learned
phase-formation rules and order parameters are used to illustrate the workflow.
Finally, we discuss the remaining challenges and present an outlook of research
directions, including uncertainty quantification and ML-guided inverse
materials design.Comment: This review paper has been accepted by Progress in Materials Scienc
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