524 research outputs found
Evanescent straight tapered-fiber coupling of ultra-high Q optomechanical micro-resonators in a low-vibration helium-4 exchange-gas cryostat
We developed an apparatus to couple a 50-micrometer diameter
whispering-gallery silica microtoroidal resonator in a helium-4 cryostat using
a straight optical tapered-fiber at 1550nm wavelength. On a top-loading probe
specifically adapted for increased mechanical stability, we use a
specifically-developed "cryotaper" to optically probe the cavity, allowing thus
to record the calibrated mechanical spectrum of the optomechanical system at
low temperatures. We then demonstrate excellent thermalization of a 63-MHz
mechanical mode of a toroidal resonator down to the cryostat's base temperature
of 1.65K, thereby proving the viability of the cryogenic refrigeration via heat
conduction through static low-pressure exchange gas. In the context of
optomechanics, we therefore provide a versatile and powerful tool with
state-of-the-art performances in optical coupling efficiency, mechanical
stability and cryogenic cooling.Comment: 8 pages, 6 figure
High-sensitivity monitoring of micromechanical vibration using optical whispering gallery mode resonators
The inherent coupling of optical and mechanical modes in high finesse optical
microresonators provide a natural, highly sensitive transduction mechanism for
micromechanical vibrations. Using homodyne and polarization spectroscopy
techniques, we achieve shot-noise limited displacement sensitivities of
10^(-19) m Hz^(-1/2). In an unprecedented manner, this enables the detection
and study of a variety of mechanical modes, which are identified as radial
breathing, flexural and torsional modes using 3-dimensional finite element
modelling. Furthermore, a broadband equivalent displacement noise is measured
and found to agree well with models for thermorefractive noise in silica
dielectric cavities. Implications for ground-state cooling, displacement
sensing and Kerr squeezing are discussed.Comment: 25 pages, 8 figure
Cryogenic properties of optomechanical silica microcavities
We present the optical and mechanical properties of high-Q fused silica
microtoroidal resonators at cryogenic temperatures (down to 1.6 K). A thermally
induced optical multistability is observed and theoretically described; it
serves to characterize quantitatively the static heating induced by light
absorption. Moreover the influence of structural defect states in glass on the
toroid mechanical properties is observed and the resulting implications of
cavity optomechanical systems on the study of mechanical dissipation discussed.Comment: 4 pages, 3 figure
Shard scheduler: object placement and migration in sharded account-based blockchains
We propose Shard Scheduler, a system for object placement and migration in account-based sharded blockchains. Our system calculates optimal placement and decides on object migrations across shards. It supports complex multi-account transactions caused by smart contracts. Placement and migration decisions made by Shard Scheduler are fully deterministic, verifiable, and can be made part of the consensus protocol. Shard Scheduler reduces the number of costly cross-shard transactions, ensures balanced load distribution and maximizes the number of processed transactions for the blockchain as a whole. To this end, it leverages a novel incentive model motivating miners to maximize the global throughput of the entire blockchain rather than the throughput of a specific shard. In our simulations, Shard Scheduler can reduce the number of costly cross-shard transactions by half while ensuring equal load and increasing throughput more than 2 fold when using 60 shards. We also implement and evaluate Shard Scheduler on Chainspace, more than doubling its throughput and reducing user-perceived latency by 70% when using 10 shards
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Content Censorship in the InterPlanetary File System
The InterPlanetary File System (IPFS) is currently the largest decentralized storage solution in operation, with thousands of active participants and millions of daily content transfers. IPFS is used as remote data storage for numerous blockchain-based smart contracts, Non-Fungible Tokens (NFT), and decentralized applications.
We present a content censorship attack that can be executed with minimal effort and cost, and that prevents the retrieval of any chosen content in the IPFS network. The attack exploits a conceptual issue in a core component of IPFS, the Kademlia Distributed Hash Table (DHT), which is used to resolve content IDs to peer addresses. We provide efficient detection and mitigation mechanisms for this vulnerability. Our mechanisms achieve a 99.6% detection rate and mitigate 100% of the detected attacks with minimal signaling and computational overhead. We followed responsible disclosure procedures, and our countermeasures are scheduled for deployment in the future versions of IPFS
Évolution de l’histoire naturelle et du pronostic des métastases des cancers du sein sur quatre décennies. Étude de 4 110 cancers du sein métastasés
Morel_Moreau_Morella. The Metamorphoses of Adolfo Bioy Casares Invention in a (Re) Animating Universe
Adolfo Bioy Casares short novel The Invention of Morel (La invención de Morel, 1940) envisioned the wish of human beings to define themselves through technology, indeed to reanimate the human as a technological double in an environment that gradually becomes virtual. This article develops the relationships connecting The Invention of Morel with three animating forms: the phantasmagoria, the automaton, and the machine-environment, to stress the privileged association they make between invention and (re)animation. With this purpose, the paper examines key contributions to our understanding of simulation and automata in the field of animation theory, such as Alan Cholodenko s Speculations on the Animation Automaton , but also Joubert-Laurencin s La lettre volante. Quatre essais sur le cinema d animation, which directly addresses Bioy Casares story as a metaphor of animated cinema. Sigmund Freud s psychoanalytical approach to the field of aesthetics in The Uncanny , and subsequent theories like Masahiro Mori s The Uncanny Valley , are also taken into consideration.Lorenzo Hernández, MC. (2013). Morel_Moreau_Morella. The Metamorphoses of Adolfo Bioy Casares Invention in a (Re) Animating Universe. Animation: An interdisciplinary journal. 8(2):185-202. doi:10.1177/1746847713485535S18520282Buchan, S. (2011). The Quay Brothers. doi:10.5749/minnesota/9780816646586.001.0001Cholodenko, A. (2013). The Crypt, the Haunted House, of Cinema. Cultural Studies Review, 10(2), 99-113. doi:10.5130/csr.v10i2.3474Crafton, D. (1993). Before Mickey. doi:10.7208/chicago/9780226231020.001.000
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