2,496 research outputs found
Chaos and unpredictability in evolutionary dynamics in discrete time
A discrete-time version of the replicator equation for two-strategy games is
studied. The stationary properties differ from that of continuous time for
sufficiently large values of the parameters, where periodic and chaotic
behavior replace the usual fixed-point population solutions. We observe the
familiar period-doubling and chaotic-band-splitting attractor cascades of
unimodal maps but in some cases more elaborate variations appear due to
bimodality. Also unphysical stationary solutions have unusual physical
implications, such as uncertainty of final population caused by sensitivity to
initial conditions and fractality of attractor preimage manifolds.Comment: 4 pages, 4 figure
The computational complexity of Kauffman nets and the P versus NP problem
Complexity theory as practiced by physicists and computational complexity
theory as practiced by computer scientists both characterize how difficult it
is to solve complex problems. Here it is shown that the parameters of a
specific model can be adjusted so that the problem of finding its global energy
minimum is extremely sensitive to small changes in the problem statement. This
result has implications not only for studies of the physics of random systems
but may also lead to new strategies for resolving the well-known P versus NP
question in computational complexity theory.Comment: 4 pages, no figure
Adaptation and enslavement in endosymbiont-host associations
The evolutionary persistence of symbiotic associations is a puzzle.
Adaptation should eliminate cooperative traits if it is possible to enjoy the
advantages of cooperation without reciprocating - a facet of cooperation known
in game theory as the Prisoner's Dilemma. Despite this barrier, symbioses are
widespread, and may have been necessary for the evolution of complex life. The
discovery of strategies such as tit-for-tat has been presented as a general
solution to the problem of cooperation. However, this only holds for
within-species cooperation, where a single strategy will come to dominate the
population. In a symbiotic association each species may have a different
strategy, and the theoretical analysis of the single species problem is no
guide to the outcome. We present basic analysis of two-species cooperation and
show that a species with a fast adaptation rate is enslaved by a slowly
evolving one. Paradoxically, the rapidly evolving species becomes highly
cooperative, whereas the slowly evolving one gives little in return. This helps
understand the occurrence of endosymbioses where the host benefits, but the
symbionts appear to gain little from the association.Comment: v2: Correction made to equations 5 & 6 v3: Revised version accepted
in Phys. Rev. E; New figure adde
Quantum Games and Quantum Strategies
We investigate the quantization of non-zero sum games. For the particular
case of the Prisoners' Dilemma we show that this game ceases to pose a dilemma
if quantum strategies are allowed for. We also construct a particular quantum
strategy which always gives reward if played against any classical strategy.Comment: 4 pages, 4 figures, typographic sign error in the definition of the
operator J correcte
Hereditary sensory and autonomic neuropathies: types II, III, and IV
The hereditary sensory and autonomic neuropathies (HSAN) encompass a number of inherited disorders that are associated with sensory dysfunction (depressed reflexes, altered pain and temperature perception) and varying degrees of autonomic dysfunction (gastroesophageal reflux, postural hypotention, excessive sweating). Subsequent to the numerical classification of four distinct forms of HSAN that was proposed by Dyck and Ohta, additional entities continue to be described, so that identification and classification are ongoing. As a group, the HSAN are rare diseases that affect both sexes. HSAN III is almost exclusive to individuals of Eastern European Jewish extraction, with incidence of 1 per 3600 live births. Several hundred cases with HSAN IV have been reported. The worldwide prevalence of HSAN type II is very low. This review focuses on the description of three of the disorders, HSAN II through IV, that are characterized by autosomal recessive inheritance and onset at birth. These three forms of HSAN have been the most intensively studied, especially familial dysautonomia (Riley-Day syndrome or HSAN III), which is often used as a prototype for comparison to the other HSAN. Each HSAN disorder is likely caused by different genetic errors that affect specific aspects of small fiber neurodevelopment, which result in variable phenotypic expression. As genetic tests are routinely used for diagnostic confirmation of HSAN III only, other means of differentiating between the disorders is necessary. Diagnosis is based on the clinical features, the degree of both sensory and autonomic dysfunction, and biochemical evaluations, with pathologic examinations serving to further confirm differences. Treatments for all these disorders are supportive
Physical phase space of lattice Yang-Mills theory and the moduli space of flat connections on a Riemann surface
It is shown that the physical phase space of \g-deformed Hamiltonian
lattice Yang-Mills theory, which was recently proposed in refs.[1,2], coincides
as a Poisson manifold with the moduli space of flat connections on a Riemann
surface with handles and therefore with the physical phase space of
the corresponding -dimensional Chern-Simons model, where and are
correspondingly a total number of links and vertices of the lattice. The
deformation parameter \g is identified with and is an
integer entering the Chern-Simons action.Comment: 12 pages, latex, no figure
Recommended from our members
Evaluation of critical congenital heart defects screening using pulse oximetry in the neonatal intensive care unit.
ObjectiveTo evaluate the implementation of early screening for critical congenital heart defects (CCHDs) in the neonatal intensive care unit (NICU) and potential exclusion of sub-populations from universal screening.Study designProspective evaluation of CCHD screening at multiple time intervals was conducted in 21 NICUs across five states (n=4556 infants).ResultsOf the 4120 infants with complete screens, 92% did not have prenatal CHD diagnosis or echocardiography before screening, 72% were not receiving oxygen at 24 to 48âh and 56% were born â©Ÿ2500âg. Thirty-seven infants failed screening (0.9%); none with an unsuspected CCHD. False positive rates were low for infants not receiving oxygen (0.5%) and those screened after weaning (0.6%), yet higher among infants born at <28 weeks (3.8%). Unnecessary echocardiograms were minimal (0.2%).ConclusionGiven the majority of NICU infants were â©Ÿ2500âg, not on oxygen and not preidentified for CCHD, systematic screening at 24 to 48âh may be of benefit for early detection of CCHD with minimal burden
Optimal Self-Organization
We present computational and analytical results indicating that systems of
driven entities with repulsive interactions tend to reach an optimal state
associated with minimal interaction and minimal dissipation. Using concepts
from non-equilibrium thermodynamics and game theoretical ideas, we generalize
this finding to an even wider class of self-organizing systems which have the
ability to reach a state of maximal overall ``success''. This principle is
expected to be relevant for driven systems in physics like sheared granular
media, but it is also applicable to biological, social, and economic systems,
for which only a limited number of quantitative principles are available yet.Comment: This is the detailled revised version of a preprint on
``Self-Organised Optimality'' (cond-mat/9903319). For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.html and
http://angel.elte.hu/~vicsek
The TAOS Project Stellar Variability I. Detection of Low-Amplitude delta Scuti Stars
We analyzed data accumulated during 2005 and 2006 by the Taiwan-American
Occultation Survey (TAOS) in order to detect short-period variable stars
(periods of <~ 1 hour) such as delta Scuti. TAOS is designed for the detection
of stellar occultation by small-size Kuiper Belt Objects (KBOs) and is
operating four 50cm telescopes at an effective cadence of 5Hz. The four
telescopes simultaneously monitor the same patch of the sky in order to reduce
false positives. To detect short-period variables, we used the Fast Fourier
Transform algorithm (FFT) inasmuch as the data points in TAOS light-curves are
evenly spaced. Using FFT, we found 41 short-period variables with amplitudes
smaller than a few hundredths of a magnitude and periods of about an hour,
which suggest that they are low-amplitude delta Scuti stars (LADS). The
light-curves of TAOS delta Scuti stars are accessible online at the Time Series
Center website (http://timemachine.iic.harvard.edu)Comment: Accepted for publication in A
Incentive and dopamine sensitization produced by intermittent but not long access cocaine selfâadministration
The temporal pattern of drug use (pharmacokinetics) has a profound effect on the ability of selfâadministered cocaine to produce addictionâlike behavior in rodents, and to change the brain. To further address this issue, we compared the effects of long access (LgA) cocaine selfâadministration, which is widely used to model the transition to addiction, with intermittent access (IntA), which is thought to better reflect the pattern of drug use in humans, on the ability of a single, selfâadministered injection of cocaine to increase dopamine (DA) overflow in the core of the nucleus accumbens (using in vivo microdialysis), and to produce addictionâlike behavior. IntA experience was more effective than LgA in producing addictionâlike behaviorâa drug experienceâdependent increase in motivation for cocaine assessed using behavioral economic procedures, and cueâinduced reinstatementâdespite much less total drug consumption. There were no group differences in basal levels of DA in dialysate [DA], but a single selfâadministered IV injection of cocaine increased [DA] in the core of the nucleus accumbens to a greater extent in rats with prior IntA experience than those with LgA or limited access experience, and the latter two groups did not differ. Furthermore, high motivation for cocaine was associated with a high [DA] response. Thus, IntA, but not LgA, produced both incentive and DA sensitization. This is consistent with the notion that a hyperâresponsive dopaminergic system may contribute to the transition from casual patterns of drug use to the problematic patterns that define addiction.We compared the effects of long access cocaine selfâadministration with intermittent access on the ability of selfâadministered cocaine to increase dopamine overflow in the core of the nucleus accumbens and to produce addictionâlike behavior. Intermittent access (IntA) was more effective than long access (LgA) in producing addictionâlike behavior despite much less total drug consumption and cocaine increased dopamine to a greater extent in rats with prior IntA experience than those with LgA.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151906/1/ejn14418_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151906/2/ejn14418.pd
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