2,764 research outputs found
Infinite Excess Entropy Processes with Countable-State Generators
We present two examples of finite-alphabet, infinite excess entropy processes
generated by invariant hidden Markov models (HMMs) with countable state sets.
The first, simpler example is not ergodic, but the second is. It appears these
are the first constructions of processes of this type. Previous examples of
infinite excess entropy processes over finite alphabets admit only invariant
HMM presentations with uncountable state sets.Comment: 13 pages, 3 figures;
http://csc.ucdavis.edu/~cmg/compmech/pubs/ieepcsg.ht
Nonlinear optics in Xe-filled hollow-core PCF in high pressure and supercritical regimes
Supercritical Xe at 293 K offers a Kerr nonlinearity that can exceed that of
fused silica while being free of Raman scattering. It also has a much higher
optical damage threshold and a transparency window that extends from the UV to
the infrared. We report the observation of nonlinear phenomena, such as
self-phase modulation, in hollow-core photonic crystal fiber filled with
supercritical Xe. In the subcritical regime, intermodal four-wave-mixing
resulted in the generation of UV light in the HE12 mode. The normal dispersion
of the fiber at high pressures means that spectral broadening can clearly
obtained without influence from soliton effects or material damage
Novel mid-infrared dispersive wave generation in gas-filled PCF by transient ionization-driven changes in dispersion
Gas-filled hollow-core photonic crystal fibre (PCF) is being used to generate
ever wider supercontinuum spectra, in particular via dispersive wave (DW)
emission in the deep and vacuum ultraviolet, with a multitude of applications.
DWs are the result of the resonant transfer of energy from a self-compressed
soliton, a process which relies crucially on phase matching. It was recently
predicted that, in the strong-field regime, the additional transient anomalous
dispersion introduced by gas ionization would allow phase-matched DW generation
in the mid-infrared (MIR)-something that is forbidden in the absence of free
electrons. Here we report for the first time the experimental observation of
such MIR DWs, embedded in a 4.7-octave-wide supercontinuum that uniquely
reaches simultaneously to the vacuum ultraviolet, with up to 1.7 W of total
average power
Proposal for a Council Regulation (EEC) derogating from Article 21 of Regulation (EEC) No 1035/72 on the common organization of the market in fruit and vegetables
We present the results of an experimental and numerical investigation into temporally nonlocal coherent interactions between ultrashort pulses, mediated by Raman coherence, in a gas-filled kagome-style hollow-core photonic-crystal fiber. A pump pulse first sets up the Raman coherence, creating a refractive index spatiotemporal grating in the gas that travels at the group velocity of the pump pulse. Varying the arrival time of a second, probe, pulse allows a high degree of control over its evolution as it propagates along the fiber through the grating. Of particular interest are soliton-driven effects such as self-compression and dispersive wave (DW) emission. In the experiments reported, a DW is emitted at ∼300 nm and exhibits a wiggling effect, with its central frequency oscillating periodically with pump-probe delay. The results demonstrate that a strong Raman coherence, created in a broadband guiding gas-filled kagome photonic-crystal fiber, can be used to control the nonlinear dynamics of ultrashort probe pulses, even in difficult-to-access spectral regions such as the deep and vacuum ultraviolet
Detection of HC11N in the Cold Dust Cloud TMC-1
Two consecutive rotational transitions of the long cyanopolyyne HC11N,
J=39-38, and J=38-37, have been detected in the cold dust cloud TMC-1 at the
frequencies expected from recent laboratory measurements by Travers et al.
(1996), and at about the expected intensities. The astronomical lines have a
mean radial velocity of 5.8(1) km/s, in good agreement with the shorter
cyanopolyynes HC7N and HC9N observed in this very sharp-lined source [5.82(5)
and 5.83(5) km/s, respectively]. The column density of HC11N is calculated to
be 2.8x10^(11) cm^(-2). The abundance of the cyanopolyynes decreases smoothly
with length to HC11N, the decrement from one to the next being about 6 for the
longer carbon chains.Comment: plain tex 10 pages plus 3 ps fig file
How social contexts affect cognition: mentalizing interferes with sense of agency during voluntary action
Living in complex social structures, humans have evolved a unique aptitude for mentalizing: trying to understand and predict the behaviour of others. To date, little is known about how mentalizing interacts with other cognitive processes. “Sense of agency” refers to the feeling of control over the outcomes of one's actions, providing a precursor of responsibility. Here, we test a model of how social context influences this key feature of human action, even when action outcomes are not specifically social. We propose that in social contexts, sense of agency is affected by the requirement to mentalize, increasing the complexity of individual decision-making. We test this hypothesis by comparing two situations, in which participants could either consider potential actions of another person (another participant acting to influence the task), or potential failures of a causal mechanism (a mechanical device breaking down and thereby influencing the task). For relatively good outcomes, we find an agency-reducing effect of external influence only in the social condition, suggesting that the presence of another intentional agent has a unique influence on the cognitive processes underlying one's own voluntary action. In a second experiment, we show that the presence of another potential agent reduces sense of agency both in a context of varying financial gains or of losses. This clearly dissociates social modulation of sense of agency from classical self-serving bias. Previous work primarily focused on social facilitation of human cognition. However, when people must incorporate potential actions of others into their decision-making, we show that the resulting socio-cognitive processes reduce the individuals' feelings of control
Scale-free networks with tunable degree distribution exponents
We propose and study a model of scale-free growing networks that gives a
degree distribution dominated by a power-law behavior with a model-dependent,
hence tunable, exponent. The model represents a hybrid of the growing networks
based on popularity-driven and fitness-driven preferential attachments. As the
network grows, a newly added node establishes new links to existing nodes
with a probability based on popularity of the existing nodes and a
probability based on fitness of the existing nodes. An explicit form of
the degree distribution is derived within a mean field approach. For
reasonably large , , where the
function is dominated by the behavior of for small
values of and becomes -independent as , and is a
model-dependent exponent. The degree distribution and the exponent
are found to be in good agreement with results obtained by extensive numerical
simulations.Comment: 12 pages, 2 figures, submitted to PR
How social contexts affect cognition: Mentalizing interferes with sense of agency during voluntary action
Living in complex social structures, humans have evolved a unique aptitude for mentalizing: trying to understand and predict the behaviour of others. To date, little is known about how mentalizing interacts with other cognitive processes. “Sense of agency” refers to the feeling of control over the outcomes of one's actions, providing a precursor of responsibility. Here, we test a model of how social context influences this key feature of human action, even when action outcomes are not specifically social. We propose that in social contexts, sense of agency is affected by the requirement to mentalize, increasing the complexity of individual decision-making. We test this hypothesis by comparing two situations, in which participants could either consider potential actions of another person (another participant acting to influence the task), or potential failures of a causal mechanism (a mechanical device breaking down and thereby influencing the task). For relatively good outcomes, we find an agency-reducing effect of external influence only in the social condition, suggesting that the presence of another intentional agent has a unique influence on the cognitive processes underlying one's own voluntary action. In a second experiment, we show that the presence of another potential agent reduces sense of agency both in a context of varying financial gains or of losses. This clearly dissociates social modulation of sense of agency from classical self-serving bias. Previous work primarily focused on social facilitation of human cognition. However, when people must incorporate potential actions of others into their decision-making, we show that the resulting socio-cognitive processes reduce the individuals' feelings of control
Combined soliton pulse compression and plasma-related frequency upconversion in gas-filled photonic crystal fiber
We numerically investigate self-frequency blueshifting of a fundamental soliton in a gas-filled hollow-core photonic crystal fiber. Because of the changing underlying soliton parameters, the blueshift gives rise to adiabatic soliton compression. Based on these features, we propose a device that enables frequency shifting over an octave and pulse compression from 30 fs down to 2.3 fs.W. Chang is supported by the Australian Research
Council (DE130101432)
Occupational lead neurotoxicity: Improvement in behavioural effects after reduction of exposure.
To evaluate critical exposure levels and the reversibility of lead neurotoxicity a group of lead exposed foundry workers and an unexposed reference population were followed up for three years. During this period, tests designed to monitor neurobehavioural function and lead dose were administered. Evaluations of 160 workers during the first year showed dose dependent decrements in mood, visual/motor performance, memory, and verbal concept formation. Subsequently, an improvement in the hygienic conditions at the plant resulted in striking reductions in blood lead concentrations over the following two years. Attendant improvement in indices of tension (20% reduction), anger (18%), depression (26%), fatigue (27%), and confusion (13%) was observed. Performance on neurobehavioural testing generally correlated best with integrated dose estimates derived from blood lead concentrations measured periodically over the study period; zinc protoporphyrin levels were less well correlated with function. This investigation confirms the importance of compliance with workplace standards designed to lower exposures to ensure that individual blood lead concentrations remain below 50 micrograms/dl
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