424 research outputs found
Annealed Flow Transport Monte Carlo
Annealed Importance Sampling (AIS) and its Sequential Monte Carlo (SMC)
extensions are state-of-the-art methods for estimating normalizing constants of
probability distributions. We propose here a novel Monte Carlo algorithm,
Annealed Flow Transport (AFT), that builds upon AIS and SMC and combines them
with normalizing flows (NFs) for improved performance. This method transports a
set of particles using not only importance sampling (IS), Markov chain Monte
Carlo (MCMC) and resampling steps - as in SMC, but also relies on NFs which are
learned sequentially to push particles towards the successive annealed targets.
We provide limit theorems for the resulting Monte Carlo estimates of the
normalizing constant and expectations with respect to the target distribution.
Additionally, we show that a continuous-time scaling limit of the population
version of AFT is given by a Feynman--Kac measure which simplifies to the law
of a controlled diffusion for expressive NFs. We demonstrate experimentally the
benefits and limitations of our methodology on a variety of applications
A Non-Asymptotic Analysis for Stein Variational Gradient Descent
We study the Stein Variational Gradient Descent (SVGD) algorithm, which optimises a set of particles to approximate a target probability distribution Ï â e
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on R
d. In the population limit, SVGD performs gradient descent in the space
of probability distributions on the KL divergence with respect to Ï, where the
gradient is smoothed through a kernel integral operator. In this paper, we provide a
novel finite time analysis for the SVGD algorithm. We provide a descent lemma
establishing that the algorithm decreases the objective at each iteration, and rates
of convergence for the averaged Stein Fisher divergence (also referred to as Kernel
Stein Discrepancy). We also provide a convergence result of the finite particle
system corresponding to the practical implementation of SVGD to its population
version
Talocalcaneal Coalition
CASE HISTORY: A 13-year-old male lacrosse athlete presented with gradual onset right ankle pain. Symptoms began at age ten, including multiple ankle sprains. The physician suspected plantar fasciitis and advised gel inserts, NSAID pain relievers, and physical therapy to no avail. The pain persisted as sports became more demanding. His performance continued to decrease, and gait became labored and disjointed, with an occasional limp. PHYSICAL EXAM: Lower extremity examination showed no varus or valgus deformities in the coronal plane. The symptomatic foot dorsiflexion was 20/35, with the knee flexed and extended. Manual strength test scores for plantarflexion, dorsiflexion, inversion, and eversion were 5/5. No hindfoot motion was observed. Lateral lunge test exhibited abduction of the foot with hip external rotation. Labored gait and a lack of coordination upon ground impact were observed during running. DIFFERENTIAL DIAGNOSES: Subtalar Joint Fracture, Calcaneal Stress Fracture, Achilles Tendonitis, Plantar Fasciitis. TESTS & RESULTS: A multiplanar MRI revealed a fibrous coalition of the talocalcaneal facet (TC). Medial facet was conjoined. Mild sprains were observed for both the anterior talofibular and calcaneofibular ligaments. Joint effusion from stress-related mild osseous edema was found at the calcaneus. FINAL DIAGNOSIS: Talocalcaneal coalition DISCUSSION: TC is a fibrous connection between the talus and calcaneal bone. The coalition locks the hindfoot in the valgus position. The deformity usually forms around 13-14 weeks of fetal development, and 75% of TC cases are asymptomatic until adolescence. TC accounts for 45% of all tarsal coalitions and is often bilateral. OUTCOME OF THE CASE: Surgical excision of fibrous coalition with autograft buttock fat was performed, followed by four months of physical therapy. Rehabilitation started with aquatic therapy. After four weeks, he had a normal gait and progressed to unilateral movements. Followed by reactive, plyometrics, and unpredictable loads training. RETURN TO ACTIVITY AND FURTHER FOLLOW-UP: After four months, the athlete returned to sport at a pre-operation performance level and continued to show improvement
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Multimedia delivery in the future internet
The term âNetworked Mediaâ implies that all kinds of media including text, image, 3D graphics, audio
and video are produced, distributed, shared, managed and consumed on-line through various networks,
like the Internet, Fiber, WiFi, WiMAX, GPRS, 3G and so on, in a convergent manner [1]. This white
paper is the contribution of the Media Delivery Platform (MDP) cluster and aims to cover the Networked
challenges of the Networked Media in the transition to the Future of the Internet.
Internet has evolved and changed the way we work and live. End users of the Internet have been confronted
with a bewildering range of media, services and applications and of technological innovations concerning
media formats, wireless networks, terminal types and capabilities. And there is little evidence that the pace
of this innovation is slowing. Today, over one billion of users access the Internet on regular basis, more
than 100 million users have downloaded at least one (multi)media file and over 47 millions of them do so
regularly, searching in more than 160 Exabytes1 of content. In the near future these numbers are expected
to exponentially rise. It is expected that the Internet content will be increased by at least a factor of 6, rising
to more than 990 Exabytes before 2012, fuelled mainly by the users themselves. Moreover, it is envisaged
that in a near- to mid-term future, the Internet will provide the means to share and distribute (new)
multimedia content and services with superior quality and striking flexibility, in a trusted and personalized
way, improving citizensâ quality of life, working conditions, edutainment and safety.
In this evolving environment, new transport protocols, new multimedia encoding schemes, cross-layer inthe
network adaptation, machine-to-machine communication (including RFIDs), rich 3D content as well as
community networks and the use of peer-to-peer (P2P) overlays are expected to generate new models of
interaction and cooperation, and be able to support enhanced perceived quality-of-experience (PQoE) and
innovative applications âon the moveâ, like virtual collaboration environments, personalised services/
media, virtual sport groups, on-line gaming, edutainment. In this context, the interaction with content
combined with interactive/multimedia search capabilities across distributed repositories, opportunistic P2P
networks and the dynamic adaptation to the characteristics of diverse mobile terminals are expected to
contribute towards such a vision.
Based on work that has taken place in a number of EC co-funded projects, in Framework Program 6 (FP6)
and Framework Program 7 (FP7), a group of experts and technology visionaries have voluntarily
contributed in this white paper aiming to describe the status, the state-of-the art, the challenges and the way
ahead in the area of Content Aware media delivery platforms
Exact closed form analytical solutions for vibrating cavities
For one-dimensional vibrating cavity systems appearing in the standard
illustration of the dynamical Casimir effect, we propose an approach to the
construction of exact closed-form solutions. As new results, we obtain
solutions that are given for arbitrary frequencies, amplitudes and time
regions. In a broad range of parameters, a vibrating cavity model exhibits the
general property of exponential instability. Marginal behavior of the system
manifests in a power-like growth of radiated energy.Comment: 17 pages, 7 figure
Electroconductive Hydrogel Based on Functional Poly(Ethylenedioxy Thiophene).
Poly(ethylene dioxythiophene) with functional pendant groups bearing double bonds is synthesized and employed for the fabrication of electroactive hydrogels with advantageous characteristics: covalently cross-linked porous 3D scaffolds with notable swelling ratio, appropriate mechanical properties, electroactivity in physiological conditions, and suitability for proliferation and differentiation of C2C12 cells. This is a new approach for the fabrication of conductive engineered constructs
On Correctness of Data Structures under Reads-Write Concurrency
Abstract. We study the correctness of shared data structures under reads-write concurrency. A popular approach to ensuring correctness of read-only operations in the presence of concurrent update, is read-set validation, which checks that all read variables have not changed since they were first read. In practice, this approach is often too conserva-tive, which adversely affects performance. In this paper, we introduce a new framework for reasoning about correctness of data structures under reads-write concurrency, which replaces validation of the entire read-set with more general criteria. Namely, instead of verifying that all read conditions over the shared variables, which we call base conditions. We show that reading values that satisfy some base condition at every point in time implies correctness of read-only operations executing in parallel with updates. Somewhat surprisingly, the resulting correctness guarantee is not equivalent to linearizability, and is instead captured through two new conditions: validity and regularity. Roughly speaking, the former re-quires that a read-only operation never reaches a state unreachable in a sequential execution; the latter generalizes Lamportâs notion of regular-ity for arbitrary data structures, and is weaker than linearizability. We further extend our framework to capture also linearizability. We illus-trate how our framework can be applied for reasoning about correctness of a variety of implementations of data structures such as linked lists.
A Computer-Aided Tool for the Simulation and Optimization of the Combined HDSâFCC Processes
Designing reliable cyber-physical systems overview associated to the special session at FDLâ16
CPS, that consist of a cyber part â a computing system â and a physical part â the system in the physical environment â as well as the respective interfaces between those parts, are omnipresent in our daily lives. The application in the physical environment drives the overall requirements that must be respected when designing the computing system. Here, reliability is a core aspect where some of the most pressing design challenges are: âą monitoring failures throughout the computing system, âą determining the impact of failures on the application constraints, and âą ensuring correctness of the computing system with respect to application-driven requirements rooted in the physical environment. This paper provides an overview of techniques discussed in the special session to tackle these challenges throughout the stack of layers of the computing system while tightly coupling the design methodology to the physical requirements.</p
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