386 research outputs found
Passive Reflection Codebook Design for IRS-Integrated Access Point
Intelligent reflecting surface (IRS) has emerged as a promising technique to
extend the wireless signal coverage of access point (AP) and improve the
communication performance cost-effectively. In order to reduce the path-loss of
the cascaded user-IRS-AP channels, the IRS-integrated AP architecture has been
proposed to deploy the IRSs and the antenna array of the AP within the same
antenna radome. To reduce the pilot overhead for estimating all IRS-involved
channels, in this paper, we propose a novel codebook-based IRS reflection
design for the IRS-integrated AP to enhance the coverage performance in a given
area. In particular, the codebook consisting of a small number of codewords is
designed offline by employing an efficient sector division strategy based on
the azimuth angle. To ensure the performance of each sector, we optimize its
corresponding codeword for IRS reflection pattern to maximize the
sector-min-average-effective-channel-power (SMAECP) by applying the alternating
optimization (AO) and semidefinite relaxation (SDR) methods. With the designed
codebook, the AP performs the IRS reflection training by sequentially applying
all codewords and selects the one achieving the best communication performance
for data transmission. Numerical results show that our proposed codebook design
can enhance the average channel power of the whole coverage area, as compared
to the system without IRS. Moreover, our proposed codebook-based IRS reflection
design is shown to achieve significant performance gain over other benchmark
schemes in both single-user and multi-user transmissions.Comment: 13 pages, 11 figure
Service selection strategic analysis for selfoperated e-commerce platforms under settlement
In order to study whether e-commerce platforms carry out service
cooperation after settlement in-depth, this paper focuses on service
selection strategic analysis for agent channels on some self-operated
e-commerce platforms settled in hybrid e-commerce platforms. We
present multi-leader-follower models in two different scenarios with
the platforms as leaders and the manufacturers as followers and give
some numerical experiments to analyze the impacts of service selection
strategies for self-operated platforms on all supply chain members.
Our finding shows that if the service cost efficiency is moderate
or low, the self-operated platform prefers to provide its service for
the agent; otherwise, its selection mainly depends on the unit product
service fee. In addition, fierce service competition and high unit
service fee are unfavorable to all members, while high service cost
efficiency may hurt both the platform and the manufacturer
A novel approach for bilevel programs based on Wolfe duality
This paper considers a bilevel program, which has many applications in
practice. To develop effective numerical algorithms, it is generally necessary
to transform the bilevel program into a single-level optimization problem. The
most popular approach is to replace the lower-level program by its KKT
conditions and then the bilevel program can be reformulated as a mathematical
program with equilibrium constraints (MPEC for short). However, since the MPEC
does not satisfy the Mangasarian-Fromovitz constraint qualification at any
feasible point, the well-developed nonlinear programming theory cannot be
applied to MPECs directly. In this paper, we apply the Wolfe duality to show
that, under very mild conditions, the bilevel program is equivalent to a new
single-level reformulation (WDP for short) in the globally and locally optimal
sense. We give an example to show that, unlike the MPEC reformulation, WDP may
satisfy the Mangasarian-Fromovitz constraint qualification at its feasible
points. We give some properties of the WDP reformulation and the relations
between the WDP and MPEC reformulations. We further propose a relaxation method
for solving WDP and investigate its limiting behavior. Comprehensive numerical
experiments indicate that, although solving WDP directly does not perform very
well in our tests, the relaxation method based on the WDP reformulation is
quite efficient
Effect of dynamic threshold pressure gradient on production performance in water-bearing tight gas reservoir
AbstractWater content and distribution have important impacts on gas production in water-bearing tight gas reservoirs. However, due to the structural and chemical heterogeneity of tight reservoirs, the water phase exists in various states, which has complicated the analyses of the effects of water characteristics on tight gas production performance. In this work, the water phase is distinguished from immobile to mobile states and the term of constrained water saturation is proposed. It is established that water can flow when the driving pressure difference is larger than the critical driving pressure difference. A new theoretical model of threshold pressure gradient is derived to incorporate the influences of constrained water saturation and permeability. On this basis, a new prediction model considering the varied threshold pressure gradient is obtained, and the result indicates that when threshold pressure gradient is constant, the real gas production capacity of the reservoir will be weakened. Meanwhile, a dynamic supply boundary model is presented, which indicates that the permeability has a strong influence on the dynamic supply boundary, whereas the impact of initial water saturation is negligible. These findings provide insights into the understanding of the effects of water state and saturation on the threshold pressure gradient and gas production rate in tight gas reservoirs. Furthermore, this study provides useful guidance on the prediction of field-scale gas production.Cited as: Zhu, W., Liu, Y., Shi, Y., Zou, G., Zhang, Q., Kong, D. Effect of dynamic threshold pressure gradient on production performance in water-bearing tight gas reservoir. Advances in Geo-Energy Research, 2022, 6(4): 286-295. https://doi.org/10.46690/ager.2022.04.0
VideoDreamer: Customized Multi-Subject Text-to-Video Generation with Disen-Mix Finetuning
Customized text-to-video generation aims to generate text-guided videos with
customized user-given subjects, which has gained increasing attention recently.
However, existing works are primarily limited to generating videos for a single
subject, leaving the more challenging problem of customized multi-subject
text-to-video generation largely unexplored. In this paper, we fill this gap
and propose a novel VideoDreamer framework. VideoDreamer can generate
temporally consistent text-guided videos that faithfully preserve the visual
features of the given multiple subjects. Specifically, VideoDreamer leverages
the pretrained Stable Diffusion with latent-code motion dynamics and temporal
cross-frame attention as the base video generator. The video generator is
further customized for the given multiple subjects by the proposed Disen-Mix
Finetuning and Human-in-the-Loop Re-finetuning strategy, which can tackle the
attribute binding problem of multi-subject generation. We also introduce
MultiStudioBench, a benchmark for evaluating customized multi-subject
text-to-video generation models. Extensive experiments demonstrate the
remarkable ability of VideoDreamer to generate videos with new content such as
new events and backgrounds, tailored to the customized multiple subjects. Our
project page is available at https://videodreamer23.github.io/
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