358,575 research outputs found
Quantum cryptography: key distribution and beyond
Uniquely among the sciences, quantum cryptography has driven both
foundational research as well as practical real-life applications. We review
the progress of quantum cryptography in the last decade, covering quantum key
distribution and other applications.Comment: It's a review on quantum cryptography and it is not restricted to QK
Stochastic accumulation of feature information in perception and memory
It is now well established that the time course of perceptual processing influences the first second or so of performance in a wide variety of cognitive tasks. Over the last20 years, there has been a shift from modeling the speed at which a display is processed, to modeling the speed at which different features of the display are perceived and formalizing how this perceptual information is used in decision making. The first of these models(Lamberts, 1995) was implemented to fit the time course of performance in a speeded perceptual categorization task and assumed a simple stochastic accumulation of feature information. Subsequently, similar approaches have been used to model performance in a range of cognitive tasks including identification, absolute identification, perceptual matching, recognition, visual search, and word processing, again assuming a simple stochastic accumulation of feature information from both the stimulus and representations held in memory. These models are typically fit to data from signal-to-respond experiments whereby the effects of stimulus exposure duration on performance are examined, but response times (RTs) and RT distributions have also been modeled. In this article, we review this approach and explore the insights it has provided about the interplay between perceptual processing, memory retrieval, and decision making in a variety of tasks. In so doing, we highlight how such approaches can continue to usefully contribute to our understanding of cognition
Controlling phonons and photons at the wavelength-scale: silicon photonics meets silicon phononics
Radio-frequency communication systems have long used bulk- and
surface-acoustic-wave devices supporting ultrasonic mechanical waves to
manipulate and sense signals. These devices have greatly improved our ability
to process microwaves by interfacing them to orders-of-magnitude slower and
lower loss mechanical fields. In parallel, long-distance communications have
been dominated by low-loss infrared optical photons. As electrical signal
processing and transmission approaches physical limits imposed by energy
dissipation, optical links are now being actively considered for mobile and
cloud technologies. Thus there is a strong driver for wavelength-scale
mechanical wave or "phononic" circuitry fabricated by scalable semiconductor
processes. With the advent of these circuits, new micro- and nanostructures
that combine electrical, optical and mechanical elements have emerged. In these
devices, such as optomechanical waveguides and resonators, optical photons and
gigahertz phonons are ideally matched to one another as both have wavelengths
on the order of micrometers. The development of phononic circuits has thus
emerged as a vibrant field of research pursued for optical signal processing
and sensing applications as well as emerging quantum technologies. In this
review, we discuss the key physics and figures of merit underpinning this
field. We also summarize the state of the art in nanoscale electro- and
optomechanical systems with a focus on scalable platforms such as silicon.
Finally, we give perspectives on what these new systems may bring and what
challenges they face in the coming years. In particular, we believe hybrid
electro- and optomechanical devices incorporating highly coherent and compact
mechanical elements on a chip have significant untapped potential for
electro-optic modulation, quantum microwave-to-optical photon conversion,
sensing and microwave signal processing.Comment: 26 pages, 5 figure
Generation and manipulation of nonclassical light using photonic crystals
Photonic crystal cavities can localize light into nanoscale volumes with high
quality factors. This permits a strong interaction between light and matter,
which is important for the construction of classical light sources with
improved properties (e.g., low threshold lasers) and of nonclassical light
sources (such as single and entangled photon sources) that are crucial pieces
of hardware of quantum information processing systems. This article will review
some of our recent experimental and theoretical results on the interaction
between single quantum dots and photonic crystal cavity fields, and on the
integration of multiple photonic crystal devices into functional circuits for
quantum information processing.Comment: 6 pages, 6 figures; replaced with revised versio
Tracing the Ingredients for a Habitable Earth from Interstellar Space through Planet Formation
We use the C/N ratio as a monitor of the delivery of key ingredients of life
to nascent terrestrial worlds. Total elemental C and N contents, and their
ratio, are examined for the interstellar medium, comets, chondritic meteorites
and terrestrial planets; we include an updated estimate for the Bulk Silicate
Earth (C/N = 49.0 +/- 9.3). Using a kinetic model of disk chemistry, and the
sublimation/condensation temperatures of primitive molecules, we suggest that
organic ices and macro-molecular (refractory or carbonaceous dust) organic
material are the likely initial C and N carriers. Chemical reactions in the
disk can produce nebular C/N ratios of ~1-12, comparable to those of comets and
the low end estimated for planetesimals. An increase of the C/N ratio is traced
between volatile-rich pristine bodies and larger volatile-depleted objects
subjected to thermal/accretional metamorphism. The C/N ratios of the dominant
materials accreted to terrestrial planets should therefore be higher than those
seen in carbonaceous chondrites or comets. During planetary formation, we
explore scenarios leading to further volatile loss and associated C/N
variations owing to core formation and atmospheric escape. Key processes
include relative enrichment of nitrogen in the atmosphere and preferential
sequestration of carbon by the core. The high C/N BSE ratio therefore is best
satisfied by accretion of thermally processed objects followed by large-scale
atmospheric loss. These two effects must be more profound if volatile
sequestration in the core is effective. The stochastic nature of these
processes hints that the surface/atmospheric abundances of biosphere-essential
materials will likely be variable.Comment: Accepted by PNAS per
http://www.pnas.org/content/early/2015/07/01/1500954112.abstract?sid=9fd8abea-9d33-46d8-b755-217d10b1c24
Recent advances on recursive filtering and sliding mode design for networked nonlinear stochastic systems: A survey
Copyright © 2013 Jun Hu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Some recent advances on the recursive filtering and sliding mode design problems for nonlinear stochastic systems with network-induced phenomena are surveyed. The network-induced phenomena under consideration mainly include missing measurements, fading measurements, signal quantization, probabilistic sensor delays, sensor saturations, randomly occurring nonlinearities, and randomly occurring uncertainties. With respect to these network-induced phenomena, the developments on filtering and sliding mode design problems are systematically reviewed. In particular, concerning the network-induced phenomena, some recent results on the recursive filtering for time-varying nonlinear stochastic systems and sliding mode design for time-invariant nonlinear stochastic systems are given, respectively. Finally, conclusions are proposed and some potential future research works are pointed out.This work was supported in part by the National Natural Science Foundation of China under Grant nos. 61134009, 61329301, 61333012, 61374127 and 11301118, the Engineering and Physical Sciences Research Council (EPSRC) of the UK under Grant no. GR/S27658/01, the Royal Society of the UK, and the Alexander von Humboldt Foundation of Germany
Structural brain complexity and cognitive decline in late life : A longitudinal study in the Aberdeen 1936 Birth Cohort
Copyright © 2014 Elsevier Inc. All rights reserved.Peer reviewedPostprin
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