584 research outputs found
Minority games, evolving capitals and replicator dynamics
We discuss a simple version of the Minority Game (MG) in which agents hold
only one strategy each, but in which their capitals evolve dynamically
according to their success and in which the total trading volume varies in time
accordingly. This feature is known to be crucial for MGs to reproduce stylised
facts of real market data. The stationary states and phase diagram of the model
can be computed, and we show that the ergodicity breaking phase transition
common for MGs, and marked by a divergence of the integrated response is
present also in this simplified model. An analogous majority game turns out to
be relatively void of interesting features, and the total capital is found to
diverge in time. Introducing a restraining force leads to a model akin to
replicator dynamics of evolutionary game theory, and we demonstrate that here a
different type of phase transition is observed. Finally we briefly discuss the
relation of this model with one strategy per player to more sophisticated
Minority Games with dynamical capitals and several trading strategies per
agent.Comment: 19 pages, 7 figure
Stationary states of a spherical Minority Game with ergodicity breaking
Using generating functional and replica techniques, respectively, we study
the dynamics and statics of a spherical Minority Game (MG), which in contrast
with a spherical MG previously presented in J.Phys A: Math. Gen. 36 11159
(2003) displays a phase with broken ergodicity and dependence of the
macroscopic stationary state on initial conditions. The model thus bears more
similarity with the original MG. Still, all order parameters including the
volatility can computed in the ergodic phases without making any
approximations. We also study the effects of market impact correction on the
phase diagram. Finally we discuss a continuous-time version of the model as
well as the differences between on-line and batch update rules. Our analytical
results are confirmed convincingly by comparison with numerical simulations. In
an appendix we extend the analysis of the earlier spherical MG to a model with
general time-step, and compare the dynamics and statics of the two spherical
models.Comment: 26 pages, 8 figures; typo correcte
Algebraic coarsening in voter models with intermediate states
The introduction of intermediate states in the dynamics of the voter model
modifies the ordering process and restores an effective surface tension. The
logarithmic coarsening of the conventional voter model in two dimensions is
eliminated in favour of an algebraic decay of the density of interfaces with
time, compatible with Model A dynamics at low temperatures. This phenomenon is
addressed by deriving Langevin equations for the dynamics of appropriately
defined continuous fields. These equations are analyzed using field theoretical
arguments and by means of a recently proposed numerical technique for the
integration of stochastic equations with multiplicative noise. We find good
agreement with lattice simulations of the microscopic model.Comment: 11 pages, 5 figures; minor typos correcte
Conservation of Sharp-Tailed Grouse (\u3cem\u3eTympanuchus phasianellus columbianus\u3c/em\u3e) Through Fecal DNA Extraction
Columbian Sharp-tailed Grouse (Tympanuchus phasianellus columbianus) are the rarest of the six extant Sharp-tailed Grouse subspecies. This subspecies experienced a 90% range contraction over the last century and have been extirpated from several states (Figure 1). In Washington alone, populations that once numbered hundreds of thousands of individuals now consist of fewer than 1,000 birds. Conservation effortsâincluding conservation translocations and habitat managementâare underway to help bolster this imperiled subspecies across their range. However, little is known about the ecology of this charismatic species and the factors that may be contributing towards higher rates of decline.
The collection of fecal pellets presents an opportunity to better understand Columbian Sharp-tailed Grouse across their range, by providing information on their diet and host ID. As a HERC Fellow in the Conservation Genetics Lab at Boise State University, I have been exploring the potential to use non-invasively collected fecal samples to understand how we can best capture different DNA types, which can be used to better inform the conservation and management of this charismatic grouse
Crater population and resurfacing of the Martian north polar layered deposits
Present-day accumulation in the north polar layered deposits (NPLD) is thought to occur via deposition on the north polar residual cap. Understanding current mass balance in relation to current climate would provide insight into the climatic record of the NPLD. To constrain processes and rates of NPLD resurfacing, a search for craters was conducted using images from the Mars Reconnaissance Orbiter Context Camera. One hundred thirty craters have been identified on the NPLD, 95 of which are located within a region defined to represent recent accumulation. High Resolution Imaging Science Experiment images of craters in this region reveal a morphological sequence of crater degradation that provides a qualitative understanding of processes involved in crater removal. A classification system for these craters was developed based on the amount of apparent degradation and infilling and where possible depth/diameter ratios were determined. The temporal and spatial distribution of crater degradation is interpreted to be close to uniform. Through comparison of the size-frequency distribution of these craters with the expected production function, the craters are interpreted to be an equilibrium population with a crater of diameter D meters having a lifetime of ~30.75D^(1.14) years. Accumulation rates within these craters are estimated at 7.2D^(â0.14) mm/yr, which corresponds to values of ~3â4 mm/yr and are much higher than rates thought to apply to the surrounding flat terrain. The current crater population is estimated to have accumulated in the last ~20 kyr or less
Effects of noise on convergent game learning dynamics
We study stochastic effects on the lagging anchor dynamics, a reinforcement
learning algorithm used to learn successful strategies in iterated games, which
is known to converge to Nash points in the absence of noise. The dynamics is
stochastic when players only have limited information about their opponents'
strategic propensities. The effects of this noise are studied analytically in
the case where it is small but finite, and we show that the statistics and
correlation properties of fluctuations can be computed to a high accuracy. We
find that the system can exhibit quasicycles, driven by intrinsic noise. If
players are asymmetric and use different parameters for their learning, a net
payoff advantage can be achieved due to these stochastic oscillations around
the deterministic equilibrium.Comment: 17 pages, 8 figure
Effects of noise and confidence thresholds in nominal and metric Axelrod dynamics of social influence
We study the effects of bounded confidence thresholds and of interaction and
external noise on Axelrod's model of social influence. Our study is based on a
combination of numerical simulations and an integration of the mean-field
Master equation describing the system in the thermodynamic limit. We find that
interaction thresholds affect the system only quantitatively, but that they do
not alter the basic phase structure. The known crossover between an ordered and
a disordered state in finite systems subject to external noise persists in
models with general confidence threshold. Interaction noise here facilitates
the dynamics and reduces relaxation times. We also study Axelrod systems with
metric features, and point out similarities and differences compared to models
with nominal features. Metric features are used to demonstrate that a small
group of extremists can have a significant impact on the opinion dynamics of a
population of Axelrod agents.Comment: 15 pages, 12 figure
PN_SCD1, VESICLE TRAFFICKING REGULATOR IS DEMETHYLATED AND OVEREXPRESSED IN FLORETS OF APOMICTIC PASPALUM NOTATUM GENOTYPES
Apomixis (asexual reproduction through seeds) is considered a deviation of the sexual
reproductive pathway leading to the formation of clonal progenies genetically identical to the
mother plant. It has been suggested that apomixis might be a consequence of epigenetic alterations,
such as interspecific hybridization and polyploidization, resulting in a wide deregulation of
reproductive development. Studies on epigenetic are transforming our actual idea of the structural
variation and diversity that prevails at key steps of plant female gametogenesis, with deep
implications for understanding the evolutionary trends that model innovation in reproductive
development and adaptation. Recent results have provided evidences indicating that epigenetic
mechanisms are crucial to control events that distinguish sexual from apomictic development.
Therefore, the epigenetic regulation of apomixis is an attractive theory as it potentially accounts for
the facultative nature of apomixis as well as the ability of apomictic to revert back to sexuality. In
this work we used the Methylation-Sensitive Amplification Polymorphism (MSAP) technique to
characterize floral genome cytosine methylation patterns occurring in sexual and aposporous
Paspalum notatum genotypes, in order to identify epigenetically-controlled genes putatively
involved in apomixis development. A partial and rather divergent methylation reprogramming was
detected in apomictic genotypes. From twelve polymorphic MSAP-derived sequences, one
(PN_6.6, renamed PN_SCD1) was selected due to its relevant annotation and differential
representation in 454 floral transcriptome libraries of sexual and apomictic P. notatum. PN_6.6
encodes the DENN domain/WD repeat-containing protein SCD1, which interacts with RAB
GTPases- and/or MAPKs to promote specialized cell division, functions in clathrin-mediated
membrane transport and was defined as potential substrate receptor of CUL4 E3 ubiquitin ligases.
Quantitative RT-PCR and comparative RNAseq analyses of laser microdissected nucellar cells
confirmed PN_SCD1 upregulation in florets of apomictic plants and revealed that overexpression
takes place just before the onset of apospory initials. Moreover, we found that several SCD1
molecular partners are upregulated in florets of P. notatum apomictic plants. Our results revealed a
specific vesicle trafficking molecular pathway epigenetically modulated during apomixis. Results
will be presented and critically discussed
Statistical Mechanics of Dilute Batch Minority Games with Random External Information
We study the dynamics and statics of a dilute batch minority game with random
external information. We focus on the case in which the number of connections
per agent is infinite in the thermodynamic limit. The dynamical scenario of
ergodicity breaking in this model is different from the phase transition in the
standard minority game and is characterised by the onset of long-term memory at
finite integrated response. We demonstrate that finite memory appears at the
AT-line obtained from the corresponding replica calculation, and compare the
behaviour of the dilute model with the minority game with market impact
correction, which is known to exhibit similar features.Comment: 22 pages, 6 figures, text modified, references updated and added,
figure added, typos correcte
Analysing multiparticle quantum states
The analysis of multiparticle quantum states is a central problem in quantum
information processing. This task poses several challenges for experimenters
and theoreticians. We give an overview over current problems and possible
solutions concerning systematic errors of quantum devices, the reconstruction
of quantum states, and the analysis of correlations and complexity in
multiparticle density matrices.Comment: 20 pages, 4 figures, prepared for proceedings of the "Quantum
[Un]speakables II" conference (Vienna, 2014
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