1,418 research outputs found
Moderate Deviation Analysis for Classical Communication over Quantum Channels
© 2017, Springer-Verlag GmbH Germany. We analyse families of codes for classical data transmission over quantum channels that have both a vanishing probability of error and a code rate approaching capacity as the code length increases. To characterise the fundamental tradeoff between decoding error, code rate and code length for such codes we introduce a quantum generalisation of the moderate deviation analysis proposed by AltÅg and Wagner as well as Polyanskiy and Verdú. We derive such a tradeoff for classical-quantum (as well as image-additive) channels in terms of the channel capacity and the channel dispersion, giving further evidence that the latter quantity characterises the necessary backoff from capacity when transmitting finite blocks of classical data. To derive these results we also study asymmetric binary quantum hypothesis testing in the moderate deviations regime. Due to the central importance of the latter task, we expect that our techniques will find further applications in the analysis of other quantum information processing tasks
The Dynamic Brain: From Spiking Neurons to Neural Masses and Cortical Fields
The cortex is a complex system, characterized by its dynamics and architecture,
which underlie many functions such as action, perception, learning, language,
and cognition. Its structural architecture has been studied for more than a
hundred years; however, its dynamics have been addressed much less thoroughly.
In this paper, we review and integrate, in a unifying framework, a variety of
computational approaches that have been used to characterize the dynamics of the
cortex, as evidenced at different levels of measurement. Computational models at
different space–time scales help us understand the fundamental
mechanisms that underpin neural processes and relate these processes to
neuroscience data. Modeling at the single neuron level is necessary because this
is the level at which information is exchanged between the computing elements of
the brain; the neurons. Mesoscopic models tell us how neural elements interact
to yield emergent behavior at the level of microcolumns and cortical columns.
Macroscopic models can inform us about whole brain dynamics and interactions
between large-scale neural systems such as cortical regions, the thalamus, and
brain stem. Each level of description relates uniquely to neuroscience data,
from single-unit recordings, through local field potentials to functional
magnetic resonance imaging (fMRI), electroencephalogram (EEG), and
magnetoencephalogram (MEG). Models of the cortex can establish which types of
large-scale neuronal networks can perform computations and characterize their
emergent properties. Mean-field and related formulations of dynamics also play
an essential and complementary role as forward models that can be inverted given
empirical data. This makes dynamic models critical in integrating theory and
experiments. We argue that elaborating principled and informed models is a
prerequisite for grounding empirical neuroscience in a cogent theoretical
framework, commensurate with the achievements in the physical sciences
HARP/ACSIS: A submillimetre spectral imaging system on the James Clerk Maxwell Telescope
This paper describes a new Heterodyne Array Receiver Programme (HARP) and
Auto-Correlation Spectral Imaging System (ACSIS) that have recently been
installed and commissioned on the James Clerk Maxwell Telescope (JCMT). The
16-element focal-plane array receiver, operating in the submillimetre from 325
to 375 GHz, offers high (three-dimensional) mapping speeds, along with
significant improvements over single-detector counterparts in calibration and
image quality. Receiver temperatures are 120 K across the whole band and
system temperatures of 300K are reached routinely under good weather
conditions. The system includes a single-sideband filter so these are SSB
figures. Used in conjunction with ACSIS, the system can produce large-scale
maps rapidly, in one or more frequency settings, at high spatial and spectral
resolution. Fully-sampled maps of size 1 square degree can be observed in under
1 hour.
The scientific need for array receivers arises from the requirement for
programmes to study samples of objects of statistically significant size, in
large-scale unbiased surveys of galactic and extra-galactic regions. Along with
morphological information, the new spectral imaging system can be used to study
the physical and chemical properties of regions of interest. Its
three-dimensional imaging capabilities are critical for research into
turbulence and dynamics. In addition, HARP/ACSIS will provide highly
complementary science programmes to wide-field continuum studies, and produce
the essential preparatory work for submillimetre interferometers such as the
SMA and ALMA.Comment: MNRAS Accepted 2009 July 2. 18 pages, 25 figures and 6 table
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