The simplified neutral transport routine in the guiding center ion-electron-neutral neoclassical PIC code XGC0 has been replaced by one that calls the Monte Carlo neutral transport code DEGAS2. This provides a more re...
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The simplified neutral transport routine in the guiding center ion-electron-neutral neoclassical PIC code XGC0 has been replaced by one that calls the Monte Carlo neutral transport code DEGAS2. This provides a more realistic treatment of neutral atoms in the tokamak edge plasma and allows detailed atomic physics and plasma-material interaction processes to be incorporated into the simulations. The spatial profile of the neutral particle source used in DEGAS2 is determined from the fluxes of XGC0 ions to the material surfaces, and DEGAS2 is run in a time dependent manner synchronized with XGC0. The kinetic plasma-kinetic neutral transport capability is demonstrated with example pedestal fueling simulations. (C) 2013 Elsevier B. V. All rights reserved.
Quantum secret-sharing and quantum error-correction schemes rely on multipartite decoding protocols, yet the nonlocal operations involved are challenging and sometimes infeasible. Here we construct a quantum secret-sh...
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Quantum secret-sharing and quantum error-correction schemes rely on multipartite decoding protocols, yet the nonlocal operations involved are challenging and sometimes infeasible. Here we construct a quantum secret-sharing protocol with a reduced number of quantum communication channels between the players. We introduce a scheme based on embedding a classical linear code into a quantum error-correcting code and then mapping the latter to a quantum secret-sharing protocol. In contrast to the Calderbank-Shor-Steane construction, we do not impose any restriction on the classical code; our protocol works with any arbitrary linear code. Our work paves the way towards the more general problem of simplifying the decoding of quantum error-correcting codes.
作者：
C. CastelnovoTCM Group
Cavendish Laboratory University of Cambridge Cambridge CB3 0HE United Kingdom
In this paper we study the behavior of the entanglement measure dubbed negativity in the context of the toric code model. Using a replica method introduced recently by Calabrese, Cardy, and Tonni [Phys. Rev. Lett. 109...
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In this paper we study the behavior of the entanglement measure dubbed negativity in the context of the toric code model. Using a replica method introduced recently by Calabrese, Cardy, and Tonni [Phys. Rev. Lett. 109, 130502 (2012)], we obtain an exact expression which illustrates how the nonlocal correlations present in a topologically ordered state reflect in the behavior of the negativity of the system. We find that the negativity has a leading area-law contribution if the subsystems are in direct contact with one another (as expected in a zero-range correlated model). We also find a topological contribution directly related to the topological entropy, provided that the partitions are topologically nontrivial in both directions on a torus. We further confirm by explicit calculation that the negativity captures only quantum contributions to the entanglement. Indeed, we show that the negativity vanishes identically for the classical topologically ordered eight-vertex model, which on the contrary exhibits a finite von Neumann entropy, inclusive of topological correction.
Evaluators of scientific research programs have several tools to document and analyze products of scientific research, but few tools exist for exploring and capturing the impacts of such research. Understanding impact...
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Evaluators of scientific research programs have several tools to document and analyze products of scientific research, but few tools exist for exploring and capturing the impacts of such research. Understanding impacts is beneficial because it fosters a greater sense of accountability and stewardship for federal research dollars. This article presents the High Impacts Tracking System (HITS), a new approach to documenting research impacts that is in development at the National Institute of Environmental Health Sciences (NIEHS). HITS is designed to help identify scientific advances in the NIEHS research portfolio as they emerge, and provide a robust data structure to capture those advances. We have downloaded previously un-searchable data from the central NIH grants database and developed a robust coding schema to help us track research products (going beyond publication counts to the content of publications) as well as research impacts. We describe the coding schema and key system features as well as several development challenges, including data integration, development of a final data structure from three separate ontologies, and ways to develop consensus about codes among program staff.
Listeners exploit small interindividual variations around a generic acoustical structure to discriminate and identify individuals from their voice-a key requirement for social interactions. The human brain contains te...
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Listeners exploit small interindividual variations around a generic acoustical structure to discriminate and identify individuals from their voice-a key requirement for social interactions. The human brain contains temporal voice areas (TVA) [1] involved in an acoustic-based representation of voice identity [2-6], but the underlying coding mechanisms remain unknown. Indirect evidence suggests that identity representation in these areas could rely on a norm-based coding mechanism [4, 7-11]. Here, we show by using fMRI that voice identity is coded in the TVA as a function of acoustical distance to two internal voice prototypes (one male, one female)-approximated here by averaging a large number of same-gender voices by using morphing [12]. Voices more distant from their prototype are perceived as more distinctive and elicit greater neuronal activity in voice-sensitive cortex than closer voices-a phenomenon not merely explained by neuronal adaptation [13, 14]. Moreover, explicit manipulations of distance-to-mean by morphing voices toward (or away from) their prototype elicit reduced (or enhanced) neuronal activity. These results indicate that voice-sensitive cortex integrates relevant acoustical features into a complex representation referenced to idealized male and female voice prototypes. More generally, they shed light on remarkable similarities in cerebral representations of facial and vocal identity.
There is little doubt that predictive coding is an important mechanism in language processing - indeed, in information processing generally. However, it is less clear whether the action system is the source of such pr...
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There is little doubt that predictive coding is an important mechanism in language processing - indeed, in information processing generally. However, it is less clear whether the action system is the source of such predictions during perception. Here I summarize the computational problem with motor prediction for perceptual processes and argue instead for a dual-stream model of predictive coding.
Some everyday objects are associated with a particular color, such as bananas, which are typically yellow. Behavioral studies show that perception of these so-called color-diagnostic objects is influenced by our knowl...
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Some everyday objects are associated with a particular color, such as bananas, which are typically yellow. Behavioral studies show that perception of these so-called color-diagnostic objects is influenced by our knowledge of their typical color, referred to as memory color [1, 2]. However, neural representations of memory colors are unknown. Here we investigated whether memory color can be decoded from visual cortex activity when color-diagnostic objects are viewed as grayscale images. We trained linear classifiers to distinguish patterns of fMRI responses to four different hues. We found that activity in V1 allowed predicting the memory color of color-diagnostic objects presented in grayscale in naive participants performing a motion task. The results imply that higher areas feed back memory-color signals to Vi. When classifiers were trained on neural responses to some exemplars of color-diagnostic objects and tested on others, areas V4 and LOC also predicted memory colors. Representational similarity analysis showed that memory-color representations in V1 were correlated specifically with patterns in V4 but not LOC. Our findings suggest that prior knowledge is projected from midlevel visual regions onto primary visual cortex, consistent with predictive coding theory [3].
The sensory cortex has been interpreted as coding information rather than stimulus properties since Sokolov in 1960 showed increased response to an unexpected stimulus decrement. The motor cortex is also organized aro...
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The sensory cortex has been interpreted as coding information rather than stimulus properties since Sokolov in 1960 showed increased response to an unexpected stimulus decrement. The motor cortex is also organized around expectation, coding the goal of an act rather than a set of muscle movements. Expectation drives not only immediate responses but also the very structure of the cortex, as demonstrated by development of receptive fields that mirror the structure of the visual world.
Fault-tolerant quantum computation with quantum error-correcting codes has been considerably developed over the past decade. However, there are still difficult issues, particularly on the resource requirement. For fur...
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Fault-tolerant quantum computation with quantum error-correcting codes has been considerably developed over the past decade. However, there are still difficult issues, particularly on the resource requirement. For further improvement of fault-tolerant quantum computation, here we propose a soft-decision decoder for quantum error correction and detection by teleportation. This decoder can achieve almost optimal performance for the depolarizing channel. Applying this decoder to Knill's C-4/C-6 scheme for fault-tolerant quantum computation, which is one of the best schemes so far and relies heavily on error correction and detection by teleportation, we dramatically improve its performance. This leads to substantial reduction of resources.
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