119 research outputs found
Dynamic Hybrid Beamforming Design for Dual-Function Radar-Communication Systems
This paper investigates dynamic hybrid beamforming (HBF) for a dual-function
radar-communication (DFRC) system, where the DFRC base station (BS)
simultaneously serves multiple single-antenna users and senses a target in the
presence of multiple clutters. Particularly, we apply a HBF architecture with
dynamic subarrays and double phase shifters in the DFRC BS. Aiming at
maximizing the radar mutual information, we consider jointly designing the
dynamic HBF of the DFRC system, subject to the constraints of communication
quality of service (QoS), transmit power, and analog beamformer. To solve the
complicated non-convex optimization, an efficient alternating optimization
algorithm based on the majorization-minimization methods is developed.
Simulation results verify the advancement of the considered HBF architecture
and the effectiveness of the proposed design method
Benzyl alcohol oxidation using in situ generated hydrogen peroxide from hydrogen and oxygen
This thesis sets out an introduction to catalysis, particularly heterogeneous gold catalysis, the development of direct synthesis of hydrogen peroxide and benzyl alcohol oxidation by supported bimetallic gold-palladium catalysts. In addition the possibility of combining those two processes together to carry out the benzyl alcohol oxidation using in situ generated hydrogen peroxide.
The experimental chapter shows the detailed operation of preparing and testing of catalysts in particular for the reactions studied(H2O2formation, CO oxidation and benzyl alcohol oxidation).
In the results and discussion section, some basic knowledge of gold and palladium catalysis is reviewed including some popular preparation methods, the operation of the reactors, and testing in both direct synthesis of hydrogen peroxide and low-temperature CO oxidation. Afterwards, results of gold-palladium catalysis in the oxidation of benzyl alcohol using a mixture of hydrogen and oxygen are shown. In detail, some improvements for the reaction conditions, including temperature and duration, and catalysts, including gold and palladium ratios in alloys and the effect of preparation methods are discussed. In conclusion, higher reaction temperature (75oC) and longer reaction time (2 hours) seemed to be beneficial to converting benzyl alcohol to benzaldehyde by in situ generatedH2O2. Moreover, sol-immobilized1 wt% Au-Pd/TiO2with gold palladium ratio of 1:1 achieved the highest benzyl alcohol conversion and benzaldehyde selectivity among all samples with different metal ratios by different preparation methods
GREASE: A Generative Model for Relevance Search over Knowledge Graphs
Relevance search is to find top-ranked entities in a knowledge graph (KG)
that are relevant to a query entity. Relevance is ambiguous, particularly over
a schema-rich KG like DBpedia which supports a wide range of different
semantics of relevance based on numerous types of relations and attributes. As
users may lack the expertise to formalize the desired semantics, supervised
methods have emerged to learn the hidden user-defined relevance from
user-provided examples. Along this line, in this paper we propose a novel
generative model over KGs for relevance search, named GREASE. The model applies
to meta-path based relevance where a meta-path characterizes a particular type
of semantics of relating the query entity to answer entities. It is also
extended to support properties that constrain answer entities. Extensive
experiments on two large-scale KGs demonstrate that GREASE has advanced the
state of the art in effectiveness, expressiveness, and efficiency.Comment: 9 pages, accepted to WSDM 202
Double-Phase-Shifter based Hybrid Beamforming for mmWave DFRC in the Presence of Extended Target and Clutters
In millimeter-wave (mmWave) dual-function radar-communication (DFRC) systems,
hybrid beamforming (HBF) is recognized as a promising technique utilizing a
limited number of radio frequency chains. In this work, in the presence of
extended target and clutters, a HBF design based on the subarray connection
architecture is proposed for a multiple-input multiple-output (MIMO) DFRC
system. In this HBF, the double-phase-shifter (DPS) structure is embedded to
further increase the design flexibility. We derive the communication spectral
efficiency (SE) and radar signal-to-interference-plus-noise-ratio (SINR) with
respect to the transmit HBF and radar receiver, and formulate the HBF design
problem as the SE maximization subjecting to the radar SINR and power
constraints. To solve the formulated nonconvex problem, the joinT Hybrid
bRamforming and Radar rEceiver OptimizatioN (THEREON) is proposed, in which the
radar receiver is optimized via the generalized eigenvalue decomposition, and
the transmit HBF is updated with low complexity in a parallel manner using the
consensus alternating direction method of multipliers (consensus-ADMM).
Furthermore, we extend the proposed method to the multi-user multiple-input
single-output (MU-MISO) scenario. Numerical simulations demonstrate the
efficacy of the proposed algorithm and show that the solution provides a good
trade-off between number of phase shifters and performance gain of the DPS HBF
Evolution from quantum anomalous Hall insulator to heavy-fermion semimetal in magic-angle twisted bilayer graphene
The ground states of twisted bilayer graphene (TBG) at chiral and flat-band
limit with integer fillings are known from exact solutions, while their
dynamical and thermodynamical properties are revealed by unbiased quantum Monte
Carlo (QMC) simulations. However, to elucidate experimental observations of
correlated metallic, insulating and superconducting states and their
transitions, investigations on realistic, or non-chiral cases are vital. Here
we employ momentum-space QMC method to investigate the evolution of correlated
states in magic-angle TBG away from chiral limit at charge neutrality with
polarized spin/valley, which approximates to an experimental case with filling
factor . We find that the ground state evolves from quatum anomalous
Hall insulator into an intriguing correlated semi-metallic state as AA hopping
strength reaches experimental values. Such a state resembles the recently
proposed heavy-fermion representations with localized electrons residing at AA
stacking regions and delocalized electrons itinerating via AB/BA stacking
regions. The spectral signatures of the localized and itinerant electrons in
the heavy-fermion semimetal phase are revealed, with the connection to
experimental results being discussed.Comment: 6 pages, 4 figures with supplementary material (6 pages, 11 figures
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