10,154 research outputs found
Online Game with Time-Varying Coupled Inequality Constraints
In this paper, online game is studied, where at each time, a group of players
aim at selfishly minimizing their own time-varying cost function simultaneously
subject to time-varying coupled constraints and local feasible set constraints.
Only local cost functions and local constraints are available to individual
players, who can share limited information with their neighbors through a fixed
and connected graph. In addition, players have no prior knowledge of future
cost functions and future local constraint functions. In this setting, a novel
decentralized online learning algorithm is devised based on mirror descent and
a primal-dual strategy. The proposed algorithm can achieve sublinearly bounded
regrets and constraint violation by appropriately choosing decaying stepsizes.
Furthermore, it is shown that the generated sequence of play by the designed
algorithm can converge to the variational GNE of a strongly monotone game, to
which the online game converges. Additionally, a payoff-based case, i.e., in a
bandit feedback setting, is also considered and a new payoff-based learning
policy is devised to generate sublinear regrets and constraint violation.
Finally, the obtained theoretical results are corroborated by numerical
simulations.Comment: arXiv admin note: text overlap with arXiv:2105.0620
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
Binary Radiance Fields
In this paper, we propose binary radiance fields (BiRF), a storage-efficient
radiance field representation employing binary feature encoding that encodes
local features using binary encoding parameters in a format of either or
. This binarization strategy lets us represent the feature grid with highly
compact feature encoding and a dramatic reduction in storage size. Furthermore,
our 2D-3D hybrid feature grid design enhances the compactness of feature
encoding as the 3D grid includes main components while 2D grids capture
details. In our experiments, binary radiance field representation successfully
outperforms the reconstruction performance of state-of-the-art (SOTA) efficient
radiance field models with lower storage allocation. In particular, our model
achieves impressive results in static scene reconstruction, with a PSNR of
31.53 dB for Synthetic-NeRF scenes, 34.26 dB for Synthetic-NSVF scenes, 28.02
dB for Tanks and Temples scenes while only utilizing 0.7 MB, 0.8 MB, and 0.8 MB
of storage space, respectively. We hope the proposed binary radiance field
representation will make radiance fields more accessible without a storage
bottleneck.Comment: 21 pages, 12 Figures, and 11 Table
Spectral Normalized-Cut Graph Partitioning with Fairness Constraints
Normalized-cut graph partitioning aims to divide the set of nodes in a graph
into disjoint clusters to minimize the fraction of the total edges between
any cluster and all other clusters. In this paper, we consider a fair variant
of the partitioning problem wherein nodes are characterized by a categorical
sensitive attribute (e.g., gender or race) indicating membership to different
demographic groups. Our goal is to ensure that each group is approximately
proportionally represented in each cluster while minimizing the normalized cut
value. To resolve this problem, we propose a two-phase spectral algorithm
called FNM. In the first phase, we add an augmented Lagrangian term based on
our fairness criteria to the objective function for obtaining a fairer spectral
node embedding. Then, in the second phase, we design a rounding scheme to
produce clusters from the fair embedding that effectively trades off
fairness and partition quality. Through comprehensive experiments on nine
benchmark datasets, we demonstrate the superior performance of FNM compared
with three baseline methods.Comment: 17 pages, 7 figures, accepted to the 26th European Conference on
Artificial Intelligence (ECAI 2023
Reinforcement learning in large state action spaces
Reinforcement learning (RL) is a promising framework for training intelligent agents which learn to optimize long term utility by directly interacting with the environment. Creating RL methods which scale to large state-action spaces is a critical problem towards ensuring real world deployment of RL systems. However, several challenges limit the applicability of RL to large scale settings. These include difficulties with exploration, low sample efficiency, computational intractability, task constraints like decentralization and lack of guarantees about important properties like performance, generalization and robustness in potentially unseen scenarios.
This thesis is motivated towards bridging the aforementioned gap. We propose several principled algorithms and frameworks for studying and addressing the above challenges RL. The proposed methods cover a wide range of RL settings (single and multi-agent systems (MAS) with all the variations in the latter, prediction and control, model-based and model-free methods, value-based and policy-based methods). In this work we propose the first results on several different problems: e.g. tensorization of the Bellman equation which allows exponential sample efficiency gains (Chapter 4), provable suboptimality arising from structural constraints in MAS(Chapter 3), combinatorial generalization results in cooperative MAS(Chapter 5), generalization results on observation shifts(Chapter 7), learning deterministic policies in a probabilistic RL framework(Chapter 6). Our algorithms exhibit provably enhanced performance and sample efficiency along with better scalability. Additionally, we also shed light on generalization aspects of the agents under different frameworks. These properties have been been driven by the use of several advanced tools (e.g. statistical machine learning, state abstraction, variational inference, tensor theory).
In summary, the contributions in this thesis significantly advance progress towards making RL agents ready for large scale, real world applications
Integrating materials supply in strategic mine planning of underground coal mines
In July 2005 the Australian Coal Industryâs Research Program (ACARP) commissioned Gary Gibson to identify constraints that would prevent development production rates from achieving full capacity. A âTOP 5â constraint was âThe logistics of supply transport distribution and handling of roof support consumables is an issue at older extensive mines immediately while the achievement of higher development rates will compound this issue at most mines.â Then in 2020, Walker, Harvey, Baafi, Kiridena, and Porter were commissioned by ACARP to investigate Australian best practice and progress made since Gibsonâs 2005 report. This report was titled: - âBenchmarking study in underground coal mining logistics.â It found that even though logistics continue to be recognised as a critical constraint across many operations particularly at a tactical / day to day level, no strategic thought had been given to logistics in underground coal mines, rather it was always assumed that logistics could keep up with any future planned design and productivity. This subsequently meant that without estimating the impact of any logistical constraint in a life of mine plan, the risk of overvaluing a mining operation is high.
This thesis attempts to rectify this shortfall and has developed a system to strategically identify logistics bottlenecks and the impacts that mine planning parameters might have on these at any point in time throughout a life of mine plan. By identifying any logistics constraints as early as possible, the best opportunity to rectify the problem at the least expense is realised. At the very worst if a logistics constraint was unsolvable then it could be understood, planned for, and reflected in the mineâs ongoing financial valuations. The system developed in this thesis, using a suite of unique algorithms, is designed to âbolt ontoâ existing mine plans in the XPAC mine scheduling software package, and identify at a strategic level the number of material delivery loads required to maintain planned productivity for a mining operation. Once an event was identified the system then drills down using FlexSim discrete event simulation to a tactical level to confirm the predicted impact and understand if a solution can be transferred back as a long-term solution. Most importantly the system developed in this thesis was designed to communicate to multiple non-technical stakeholders through simple graphical outputs if there is a risk to planned production levels due to a logistics constraint
Atomistically-informed continuum modeling and isogeometric analysis of 2D materials over holey substrates
This work develops, discretizes, and validates a continuum model of a molybdenum disulfide (MoS2) monolayer interacting with a periodic holey silicon nitride (Si3N4) substrate via van der Waals (vdW) forces. The MoS2 layer is modeled as a geometrically nonlinear KirchhoffâLove shell, and vdW forces are modeled by a Lennard-Jones (LJ) potential, simplified using approximations for a smooth substrate topography. Both the shell model and LJ interactions include novel extensions informed by close comparison with fully-atomistic calculations. The material parameters of the shell model are calibrated by comparing small-strain tensile and bending tests with atomistic simulations. This model is efficiently discretized using isogeometric analysis (IGA) for the shell structure and a pseudo-time continuation method for energy minimization. The IGA shell model is validated against fully-atomistic calculations for several benchmark problems with different substrate geometries. Agreement with atomistic results depends on geometric nonlinearity in some cases, but a simple isotropic St.VenantâKirchhoff model is found to be sufficient to represent material behavior. We find that the IGA discretization of the continuum model has a much lower computational cost than atomistic simulations, and expect that it will enable efficient design space exploration in strain engineering applications. This is demonstrated by studying the dependence of strain and curvature in MoS2 over a holey substrate as a function of the hole spacing on scales inaccessible to atomistic calculations. The results show an unexpected qualitative change in the deformation pattern below a critical hole separation
Modelling, Monitoring, Control and Optimization for Complex Industrial Processes
This reprint includes 22 research papers and an editorial, collected from the Special Issue "Modelling, Monitoring, Control and Optimization for Complex Industrial Processes", highlighting recent research advances and emerging research directions in complex industrial processes. This reprint aims to promote the research field and benefit the readers from both academic communities and industrial sectors
EXAMINING PROTEIN CONFORMATIONAL DYNAMICS USING COMPUTATIONAL TECHNIQUES: STUDIES ON PHOSPHATIDYLINOSITOL-3-KINASE AND THE SODIUM-IODIDE SYMPORTER
Experimental biophysics techniques used to study proteins, polymers of amino acids that comprise most therapeutic targets of human disease, face limitations in their ability to interrogate the continual structural fluctuations exhibited by these macromolecules in the context of their myriad cellular functions. This dissertation aims to illustrate case studies that demonstrate how protein conformational dynamics can be characterized using computational methods, yielding novel insights into their functional regulation and activity. Towards this end, the work presented here describes two specific membrane proteins of therapeutic relevance: Phosphoinositide 3-kinase (PI3Kα), and the Na+/I- symporter (NIS).
The PI3KCA gene, encoding the catalytic subunit of the PI3Kα protein that phosphorylates phosphatidylinositol-4,5-bisphosphate (PIP2) to generate phosphatidylinositol-3,4,5-triphosphate (PIP3), is highly mutated in human cancer. As such, a deeper mechanistic understanding of PI3Kα could facilitate the development of novel chemotherapeutic approaches. The second chapter of this dissertation describes molecular dynamics (MD) simulations that were conducted to determine how PI3Kα conformations are influenced by physiological effectors and the nSH2 domain of a regulatory subunit, p85. The results reported here suggest that dynamic allostery plays a role in populating the catalytically competent conformation of PI3Kα.
NIS, a thirteen-helix transmembrane protein found in the thyroid and other tissues, transports iodide, a required constituent of thyroid hormones T3 and T4. Despite extensive experimental information and clinical data, many mechanistic details about NIS remain unresolved. The third chapter of this dissertation describes the results of unbiased and enhanced-sampling MD simulations of inwardly and outwardly open models of bound NIS under an enforced ion gradient. Simulations of NIS in the absence or presence of perchlorate are also described. The work presented in this dissertation aims to add to our mechanistic understanding of NIS ion transport and elucidate conformational states that occur between the inward and outward transitions of NIS in the absence and presence of bound Na+ and I- ions, which can provide valuable insight into its physiological activity and inform therapeutic interventions.
Taken together, these case studies demonstrate the ability of computational techniques to provide novel insights into the impact of structural dynamics on the functional regulation of therapeutically important biological macromolecules
Implicit Neural Head Synthesis via Controllable Local Deformation Fields
High-quality reconstruction of controllable 3D head avatars from 2D videos is
highly desirable for virtual human applications in movies, games, and
telepresence. Neural implicit fields provide a powerful representation to model
3D head avatars with personalized shape, expressions, and facial parts, e.g.,
hair and mouth interior, that go beyond the linear 3D morphable model (3DMM).
However, existing methods do not model faces with fine-scale facial features,
or local control of facial parts that extrapolate asymmetric expressions from
monocular videos. Further, most condition only on 3DMM parameters with poor(er)
locality, and resolve local features with a global neural field. We build on
part-based implicit shape models that decompose a global deformation field into
local ones. Our novel formulation models multiple implicit deformation fields
with local semantic rig-like control via 3DMM-based parameters, and
representative facial landmarks. Further, we propose a local control loss and
attention mask mechanism that promote sparsity of each learned deformation
field. Our formulation renders sharper locally controllable nonlinear
deformations than previous implicit monocular approaches, especially mouth
interior, asymmetric expressions, and facial details.Comment: Accepted at CVPR 202
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