43,621 research outputs found
Multimedia information technology and the annotation of video
The state of the art in multimedia information technology has not progressed to the point where a single solution is available to meet all reasonable needs of documentalists and users of video archives. In general, we do not have an optimistic view of the usability of new technology in this domain, but digitization and digital power can be expected to cause a small revolution in the area of video archiving. The volume of data leads to two views of the future: on the pessimistic side, overload of data will cause lack of annotation capacity, and on the optimistic side, there will be enough data from which to learn selected concepts that can be deployed to support automatic annotation. At the threshold of this interesting era, we make an attempt to describe the state of the art in technology. We sample the progress in text, sound, and image processing, as well as in machine learning
Sub-Nyquist Sampling: Bridging Theory and Practice
Sampling theory encompasses all aspects related to the conversion of
continuous-time signals to discrete streams of numbers. The famous
Shannon-Nyquist theorem has become a landmark in the development of digital
signal processing. In modern applications, an increasingly number of functions
is being pushed forward to sophisticated software algorithms, leaving only
those delicate finely-tuned tasks for the circuit level.
In this paper, we review sampling strategies which target reduction of the
ADC rate below Nyquist. Our survey covers classic works from the early 50's of
the previous century through recent publications from the past several years.
The prime focus is bridging theory and practice, that is to pinpoint the
potential of sub-Nyquist strategies to emerge from the math to the hardware. In
that spirit, we integrate contemporary theoretical viewpoints, which study
signal modeling in a union of subspaces, together with a taste of practical
aspects, namely how the avant-garde modalities boil down to concrete signal
processing systems. Our hope is that this presentation style will attract the
interest of both researchers and engineers in the hope of promoting the
sub-Nyquist premise into practical applications, and encouraging further
research into this exciting new frontier.Comment: 48 pages, 18 figures, to appear in IEEE Signal Processing Magazin
Multiple Transition States and Roaming in Ion-Molecule Reactions: a Phase Space Perspective
We provide a dynamical interpretation of the recently identified `roaming'
mechanism for molecular dissociation reactions in terms of geometrical
structures in phase space. These are NHIMs (Normally Hyperbolic Invariant
Manifolds) and their stable/unstable manifolds that define transition states
for ion-molecule association or dissociation reactions. The associated dividing
surfaces rigorously define a roaming region of phase space, in which both
reactive and nonreactive trajectories can be trapped for arbitrarily long
times.Comment: 20 pages, 6 figure
Signal Reconstruction via H-infinity Sampled-Data Control Theory: Beyond the Shannon Paradigm
This paper presents a new method for signal reconstruction by leveraging
sampled-data control theory. We formulate the signal reconstruction problem in
terms of an analog performance optimization problem using a stable
discrete-time filter. The proposed H-infinity performance criterion naturally
takes intersample behavior into account, reflecting the energy distributions of
the signal. We present methods for computing optimal solutions which are
guaranteed to be stable and causal. Detailed comparisons to alternative methods
are provided. We discuss some applications in sound and image reconstruction
The resource theory of informational nonequilibrium in thermodynamics
We review recent work on the foundations of thermodynamics in the light of
quantum information theory. We adopt a resource-theoretic perspective, wherein
thermodynamics is formulated as a theory of what agents can achieve under a
particular restriction, namely, that the only state preparations and
transformations that they can implement for free are those that are thermal at
some fixed temperature. States that are out of thermal equilibrium are the
resources. We consider the special case of this theory wherein all systems have
trivial Hamiltonians (that is, all of their energy levels are degenerate). In
this case, the only free operations are those that add noise to the system (or
implement a reversible evolution) and the only nonequilibrium states are states
of informational nonequilibrium, that is, states that deviate from the
maximally mixed state. The degree of this deviation we call the state's
nonuniformity; it is the resource of interest here, the fuel that is consumed,
for instance, in an erasure operation. We consider the different types of state
conversion: exact and approximate, single-shot and asymptotic, catalytic and
noncatalytic. In each case, we present the necessary and sufficient conditions
for the conversion to be possible for any pair of states, emphasizing a
geometrical representation of the conditions in terms of Lorenz curves. We also
review the problem of quantifying the nonuniformity of a state, in particular
through the use of generalized entropies. Quantum state conversion problems in
this resource theory can be shown to be always reducible to their classical
counterparts, so that there are no inherently quantum-mechanical features
arising in such problems. This body of work also demonstrates that the standard
formulation of the second law of thermodynamics is inadequate as a criterion
for deciding whether or not a given state transition is possible.Comment: 51 pages, 9 figures, Revised Versio
Geography vs. Institutions at the Village Level
There is a well-known debate about the roles of geography versus institutions in explaining the long-term development of countries. These debates have usually been based on cross-country regressions where questions about parameter heterogeneity, unobserved heterogeneity, and endogeneity cannot easily be controlled for. The innovation of Acemoglu, Johnson and Robinson (2001) was to address this last point by using settler mortality as an instrument for geography-induced endogenous institutions and found that this supported their line of reasoning. We believe there is value-added to consider this debate at the micro level within a country as particularly questions of parameter heterogeneity and unobserved heterogeneity are likely to be smaller than between countries. Moreover, at the micro level it is possible to identify more precise transmission mechanisms from geography via institutions to economic development outcomes. In particular, we examine the determinants of economic development across villages on the Indonesian Island of Sulawesi and find that geography-induced endogenous emergence of land rights is the critical institutional link between geographic conditions and technological change. We therefore highlight and empirically validate a new transmission channel from endogenously generated institutions on economic development.geography, migration, land rights, institutions, technology adoption, agricultural development, Indonesia
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