241 research outputs found
Tight Bounds for The Price of Fairness
A central decision maker (CDM), who seeks an efficient allocation of scarce
resources among a finite number of players, often has to incorporate fairness
criteria to avoid unfair outcomes. Indeed, the Price of Fairness (POF), a term
coined in Bertsimas et al. (2011), refers to the efficiency loss due to the
incorporation of fairness criteria into the allocation method. Quantifying the
POF would help the CDM strike an appropriate balance between efficiency and
fairness. In this paper we improve upon existing results in the literature, by
providing tight bounds for the POF for the proportional fairness criterion for
any , when the maximum achievable utilities of the players are equal or are
not equal. Further, while Bertsimas et al. (2011) have already derived a tight
bound for the max-min fairness criterion for the case that all players have
equal maximum achievable utilities, we also provide a tight bound in scenarios
where these utilities are not equal. Finally, we investigate the sensitivity of
our bounds and Bertsimas et al. (2011) bounds for the POF to the variability of
the maximum achievable utilities
Consideraciones jurídico-sociales sobre el arrendamiento de tierras rústicas en España y en la República Popular China
Study of comparative law on the legislations of rural leases in Spain and the PRC. Currently the PRC is facing a process of thorough review of its civil system and the laws governing private relationships between citizens. It is an inescapable requirement stemming from its new status as a world economic power. The reforms aim to modernize legal structures, their homologation and compatibility with international standards. Hence the importance of seeking models and the Spanish is a magnificent example in many fields. These include legislation on rural land leases because Spain has a solid and very rehearsed legal system whose roots go back to Roman law.Estudio de derecho comparado sobre las legislaciones de arrendamientos rústicos en España y en la República Popular China. En la actualidad la República Popular China se enfrenta a un proceso de profunda revisión de su sistema civil y de las leyes reguladoras de las relaciones privadas entre ciudadanos. Es una exigencia ineludible derivada de su nueva condición de potencia económica mundial. Las reformas pretenden la modernización de las estructuras jurídicas, su homologación y compatibilidad con los estándares internacionales. De ahí la importancia de buscar modelos y el español es un magnífico ejemplo en numerosas materias. Entre ellas se encuentra la legislación sobre arrendamientos de tierras rústicas, pues España cuenta con un sistema jurídico sólido y muy ensayado cuyas raíces se remontan al Derecho Romano.Study of comparative law on the legislations of rural leases in Spain and the PRC. Currently the PRC is facing a process of thorough review of its civil system and the laws governing private relationships between citizens. It is an inescapable requirement stemming from its new status as a world economic power. The reforms aim to modernize legal structures, their homologation and compatibility with international standards. Hence the importance of seeking models and the Spanish is a magnificent example in many fields. These include legislation on rural land leases because Spain has a solid and very rehearsed legal system whose roots go back to Roman law
Object Segmentation and Reconstruction Using Infrastructure Sensor Nodes for Autonomous Mobility
This thesis focuses on the Lidar point cloud processing for the infrastructure sensor node that serves as the perception system for autonomous robots with general mobility in indoor applications. Compared with typical schemes mounting sensors on the robots, the method acquires data from infrastructure sensor nodes, providing a more comprehensive view of the environment, which benefits the robot's navigation. The number of sensors would not need to be increased even for multiple robots, significantly reducing costs. In addition, with a central perception system using the infrastructure sensor nodes navigating every robot, a more comprehensive understanding of the current environment and all the robots' locations can be obtained for the control and operation of the autonomous robots.
For a robot in the detection range of the sensor node, the sensor node can detect and segment obstacles in its driveable area and reconstruct the incomplete, sparse point cloud of objects upon their movement. The complete shape by the reconstruction benefits the localization and path planning which follows the perception part of the robot's system.
Considering the sparse Lidar data and the variety of object categories in the environment, a model-free scheme is selected for object segmentation. Point segmentation starts with background filtering. Considering the complexity of the indoor environment, a depth-matching-based background removal approach is first proposed. However, later tests imply that the method is adequate but not time-efficient. Therefore, based on the depth matching-based method, a process that only focuses on the drive-able area of the robot is proposed, and the computational complexity is significantly reduced. With optimization, the computation time for processing one frame of data can be greatly increased, from 0.2 second by the first approach to 0.01 second by the second approach. After background filtering, the remaining points for occurring objects are segmented as separate clusters using an object clustering algorithm.
With independent clusters of objects, an object tracking algorithm is followed to allocate the point clusters with IDs and arrange the clusters in a time sequence. With a stream of clusters for a specific object in a time sequence, point registration is deployed to aggregate the clusters into a complete shape. And as noticed during the experiment, one of the differences between indoor and outdoor environments is that contact between objects in the indoor environment is much more common. The objects in contact are likely to be segmented as a single cluster by the model-free clustering algorithm, which needs to be avoided in the reconstruction process. Therefore an improvement is made in the tracking algorithm when contact happens. The algorithms in this thesis have been experimentally evaluated and presented
Tri-Attention: Explicit Context-Aware Attention Mechanism for Natural Language Processing
In natural language processing (NLP), the context of a word or sentence plays
an essential role. Contextual information such as the semantic representation
of a passage or historical dialogue forms an essential part of a conversation
and a precise understanding of the present phrase or sentence. However, the
standard attention mechanisms typically generate weights using query and key
but ignore context, forming a Bi-Attention framework, despite their great
success in modeling sequence alignment. This Bi-Attention mechanism does not
explicitly model the interactions between the contexts, queries and keys of
target sequences, missing important contextual information and resulting in
poor attention performance. Accordingly, a novel and general triple-attention
(Tri-Attention) framework expands the standard Bi-Attention mechanism and
explicitly interacts query, key, and context by incorporating context as the
third dimension in calculating relevance scores. Four variants of Tri-Attention
are generated by expanding the two-dimensional vector-based additive,
dot-product, scaled dot-product, and bilinear operations in Bi-Attention to the
tensor operations for Tri-Attention. Extensive experiments on three NLP tasks
demonstrate that Tri-Attention outperforms about 30 state-of-the-art
non-attention, standard Bi-Attention, contextual Bi-Attention approaches and
pretrained neural language models1
Multi-lipid synergy in synovial lubrication: natural redundancy vs. natural selection
The very low sliding friction of articular cartilage in the major synovial
joints such as hips and knees is crucial for their well-being, and has been
attributed to lubrication by phospholipid boundary layers. While
single-component lipid layers have demonstrated efficient lubricity in model
studies, in living joints there is a large number of different lipids, raising
the question of whether this is natural redundancy, or whether this
multiplicity confers any benefits. Here we examine lubrication by progressively
more complex mixtures of lipids representative of those in joints, using a
surface forces balance at physiologically-relevant salt concentrations and
pressures. We find that different lipid combinations differ very significantly
in their lubricating ability, as manifested by their robustness to hemifusion
under physiological loads, pointing to a clear lubrication synergy arising from
multiple lipid types in the lubricating layers. Insight into the origins of
this synergy is provided by molecular dynamics (MD) simulations of the
different lipid mixtures used in the experiments, which directly reveal how
hemifusion - associated with greatly increased friction - depends on the
detailed lipid composition. Our results provide insight into the role of lipid
type proliferation in healthy synovial joints, and point to new treatment
modalities for osteoarthritis
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