Power laws of natural swarms as fingerprints of an extended critical region.

Collective biological systems display power laws for macroscopic quantities and are fertile probing grounds for statistical physics. Besides power laws, natural insect swarms present strong scale-free correlations, suggesting closeness to phase transitions. Swarms exhibit imperfect dynamic scaling: their dynamical correlation functions collapse into single curves when written as functions of the scaled time tξ^{-z} (ξ: correlation length, z: dynamic exponent), but only for short times. Triggered by markers, natural swarms are not invariant under space translations. Measured static and dynamic critical exponents differ from those of equilibrium and many nonequilibrium phase transitions. Here we show the following: (i) The recently discovered scale-free-chaos phase transition of the harmonically confined Vicsek model has a novel extended critical region for N (finite) insects that contains several critical lines. (ii) As alignment noise vanishes, there are power laws connecting critical confinement and noise that allow calculating static critical exponents for fixed N. These power laws imply that the unmeasurable confinement strength is proportional to the perception range measured in natural swarms. (iii) Observations of natural swarms occur at different times and under different atmospheric conditions, which we mimic by considering mixtures of data on different critical lines and N. Unlike results of other theoretical approaches, our numerical simulations reproduce the previously described features of natural swarms and yield static and dynamic critical exponents that agree with observations.

Soliton approximation in continuum models of leader-follower behavior.

Complex biological processes involve collective behavior of entities (bacteria, cells, animals) over many length and time scales and can be described by discrete models that track individuals or by continuum models involving densities and fields. We consider hybrid stochastic agent-based models of branching morphogenesis and angiogenesis (new blood vessel creation from preexisting vasculature), which treat cells as individuals that are guided by underlying continuous chemical and/or mechanical fields. In these descriptions, leader (tip) cells emerge from existing branches and follower (stalk) cells build the new sprout in their wake. Vessel branching and fusion (anastomosis) occur as a result of tip and stalk cell dynamics. Coarse graining these hybrid models in appropriate limits produces continuum partial differential equations (PDEs) for endothelial cell densities that are more analytically tractable. While these models differ in nonlinearity, they produce similar equations at leading order when chemotaxis is dominant. We analyze this leading order system in a simple quasi-one-dimensional geometry and show that the numerical solution of the leading order PDE is well described by a soliton wave that evolves from vessel to source. This wave is an attractor for intermediate times until it arrives at the hypoxic region releasing the growth factor. The mathematical techniques used here thus identify common features of discrete and continuum approaches and provide insight into general biological mechanisms governing their collective dynamics.

Charging capacitors from thermal fluctuations using diodes.

We theoretically consider a graphene ripple as a Brownian particle coupled to an energy storage circuit. When circuit and particle are at the same temperature, the second law forbids harvesting energy from the thermal motion of the Brownian particle, even if the circuit contains a rectifying diode. However, when the circuit contains a junction followed by two diodes wired in opposition, the approach to equilibrium may become ultraslow. Detailed balance is temporarily broken as current flows between the two diodes and charges storage capacitors. The energy harvested by each capacitor comes from the thermal bath of the diodes while the system obeys the first and second laws of thermodynamics.

Mean-field theory of chaotic insect swarms.

The harmonically confined Vicsek model displays qualitative and quantitative features observed in natural insect swarms. It exhibits a scale-free transition between single and multicluster chaotic phases. Finite-size scaling indicates that this unusual phase transition occurs at zero confinement [Phys. Rev. E 107, 014209 (2023)2470-004510.1103/PhysRevE.107.014209]. While the evidence of the scale-free-chaos phase transition comes from numerical simulations, here we present its mean-field theory. Analytically determined critical exponents are those of the Landau theory of equilibrium phase transitions plus dynamical critical exponent z=1 and a new critical exponent φ=0.5 for the largest Lyapunov exponent. The phase transition occurs at zero confinement and noise in the mean-field theory. The noise line of zero largest Lyapunov exponents informs observed behavior: (i) the qualitative shape of the swarm (on average, the center of mass rotates slowly at the rate marked by the winding number and its trajectory fills compactly the space, similarly to the observed condensed nucleus surrounded by vapor) and (ii) the critical exponents resemble those observed in natural swarms. Our predictions include power laws for the frequency of the maximal spectral amplitude and the winding number.

Scale-free chaos in the confined Vicsek flocking model.

The Vicsek model encompasses the paradigm of active dry matter. Motivated by collective behavior of insects in swarms, we have studied finite-size effects and criticality in the three-dimensional, harmonically confined Vicsek model. We have discovered a phase transition that exists for appropriate noise and small confinement strength. On the critical line of confinement versus noise, swarms are in a state of scale-free chaos characterized by minimal correlation time, correlation length proportional to swarm size and topological data analysis. The critical line separates dispersed single clusters from confined multicluster swarms. Scale-free chaotic swarms occupy a compact region of space and comprise a recognizable "condensed" nucleus and particles leaving and entering it. Susceptibility, correlation length, dynamic correlation function, and largest Lyapunov exponent obey power laws. The critical line and a narrow criticality region close to it move simultaneously to zero confinement strength for infinitely many particles. At the end of the first chaotic window of confinement, there is another phase transition to infinitely dense clusters of finite size that may be termed flocking black holes.

Seasonal trends of Cyclospora cayetanensis infections in a community of Falcon State, Northwestern Venezuela.

BACKGROUND: Cyclosporiasis has a marked seasonality. Few community-based studies have addressed this issue and there are no reports from Venezuela. A study was conducted to determine the seasonal variation of infection in a community from Falcon State, Venezuela. METHODS: A sample of 732 individuals was collected for 1 y. Stools were examined with modified Ziehl-Neelsen carbolfuchsin staining of ethyl acetate-formalin concentrates and ultraviolet epiflorescence of wet mounts. RESULTS: Cyclospora prevalence was 9.9% (73/732) with monthly variation from 0% to 35.3%. A trend of increased infections coinciding with the rainy time was observed (p<0.001). CONCLUSIONS: Cyclosporiasis is common in this area with high endemicity during the rainy periods.

Uncovering spatiotemporal patterns in semiconductor superlattices by efficient data processing tools.

Time periodic patterns in a semiconductor superlattice, relevant to microwave generation, are obtained upon numerical integration of a known set of drift-diffusion equations. The associated spatiotemporal transport mechanisms are uncovered by applying (to the computed data) two recent data processing tools, known as the higher order dynamic mode decomposition and the spatiotemporal Koopman decomposition. Outcomes include a clear identification of the asymptotic self-sustained oscillations of the current density (isolated from the transient dynamics) and an accurate description of the electric field traveling pulse in terms of its dispersion diagram. In addition, a preliminary version of a data-driven reduced order model is constructed, which allows for extremely fast online simulations of the system response over a range of different configurations.

Designing Hyperchaos and Intermittency in Semiconductor Superlattices.

Weakly coupled semiconductor superlattices under dc voltage bias are excitable systems with many degrees of freedom that may exhibit spontaneous chaos at room temperature and act as fast physical random number generator devices. Superlattices with identical periods exhibit current self-oscillations due to the dynamics of charge dipole waves but chaotic oscillations exist on narrow voltage intervals. They disappear easily due to variation in structural growth parameters. Based on numerical simulations, we predict that inserting two identical sufficiently separated wider wells increases superlattice excitability by allowing wave nucleation at the modified wells and more complex dynamics. This system exhibits hyperchaos and varieties of intermittent chaos in extended dc voltage ranges. Unlike in ideal superlattices, our chaotic attractors are robust and resilient against noises and against controlled random disorder due to growth fluctuations.

Fluctuation-induced current from freestanding graphene.

At room temperature, micron-sized sheets of freestanding graphene are in constant motion, even in the presence of an applied bias voltage. We quantify the out-of-plane movement by collecting the displacement current using a nearby small-area metal electrode and present an Ito-Langevin model for the motion coupled to a circuit containing diodes. Numerical simulations show that the system reaches thermal equilibrium and the average rates of heat and work provided by stochastic thermodynamics tend quickly to zero. However, there is power dissipated by the load resistor, and its time average is exactly equal to the power supplied by the thermal bath. The exact power formula is similar to Nyquist's noise power formula, except that the rate of change of diode resistance significantly boosts the output power, and the movement of the graphene shifts the power spectrum to lower frequencies. We have calculated the equilibrium average of the power by asymptotic and numerical methods. Excellent agreement is found between experiment and theory.

Situación de los cuidados intensivos en España / Intensive care in Spain

No disponible

Active Ornstein-Uhlenbeck particles.

Active Ornstein-Uhlenbeck particles (AOUPs) are overdamped particles in an interaction potential subject to external Ornstein-Uhlenbeck noises. They can be transformed into a system of underdamped particles under additional velocity dependent forces and subject to white noise forces. There has been some discussion in the literature on whether AOUPs can be in equilibrium for particular interaction potentials and how far from equilibrium they are in the limit of small persistence time. By using a theorem on the time reversed form of the AOUP Langevin-Ito equations, I prove that they have an equilibrium probability density invariant under time reversal if and only if their smooth interaction potential has zero third derivatives. In the limit of small persistence Ornstein-Uhlenbeck time τ, a Chapman-Enskog expansion of the Fokker-Planck equation shows that the probability density has a local equilibrium solution in the particle momenta modulated by a reduced probability density that varies slowly with the position. The reduced probability density satisfies a continuity equation in which the probability current has an asymptotic expansion in powers of τ. Keeping up to O(τ) terms, this equation is a diffusion equation, which has an equilibrium stationary solution with zero current. However, O(τ^{2}) terms contain fifth- and sixth-order spatial derivatives and the continuity equation no longer has a zero current stationary solution. The expansion of the overall stationary solution now contains odd terms in the momenta, which clearly shows that it is not an equilibrium.

Fatal myocarditis and rhabdomyositis in a patient with stage IV melanoma treated with combined ipilimumab and nivolumab.

Combination immune checkpoint blockade with concurrent administration of the anti-ctla4 antibody ipilimumab and the anti-PD-1 antibody nivolumab has demonstrated impressive responses in patients with advanced melanoma and other diseases. That combination has also been associated with increased toxicity, including rare immune-related adverse events. Here we describe a case of fatal steroid-refractory myocarditis and panmyositis associated with the use of this combination in a patient with metastatic melanoma. Correlative studies indicated increased levels of serum interleukin 6 in this patient at the onset of toxicity, suggesting a possible role for anti-interleukin 6 receptor antibodies in the treatment of subsequent cases of this rare, but fatal, toxicity.

Contrarian compulsions produce exotic time-dependent flocking of active particles.

Animals having a tendency to align their velocities to an average of those of their neighbors may flock as illustrated by the Vicsek model and its variants. If, in addition, they feel a systematic contrarian trend, the result may be a time periodic adjustment of the flock or period doubling in time. These exotic phases are predicted from kinetic theory and numerically found in a modified two-dimensional Vicsek model of self-propelled particles. Numerical simulations demonstrate striking effects of alignment noise on the polarization order parameter measuring particle flocking: maximum polarization length is achieved at an optimal nonzero noise level. When contrarian compulsions are more likely than conformist ones, nonuniform polarized phases appear as the noise surpasses threshold.

Genetic diversity and cultivar variants in the NCGR cranberry (Vaccinium macrocarpon Aiton) collection.

The American cranberry (Vaccinium macrocarpon) is an endemic domesticated species that has become an economically important commercial fruit crop. The USDA-ARS National Clonal Germplasm Repository (NCGR) houses the national Vaccinium collection, which includes representatives of historical cranberry cultivars and wild-selected germplasm. The objective of this study wasto examine the genotypes of 271 cranberry plants from 77 accessions representing 66 named cultivars using 12 simple-sequence repeats to assess clonal purity and cultivar relatedness. Using principal components analysis and neighbour-joining based on estimated genetic distances between individuals, we identified 64 unique genotypes and observed that intracultivar variants (i.e. subclones) existed in the germplasm collection and in the commercial bogs where some accessions originated. Finally, through a comparison of the genotypes of this study with the previous studies, pedigree analysis and the study of the geographic distribution of cranberry diversity, we identified consensus genotypes for many accessions and cultivars. We highlight the important role that the NCGR collection playsfor ex situ conservation of cranberry germplasm for future breeders and researchers. The NCGR continues to search for historically relevant cultivars absent from the collection in an effort to preserve these genotypes before they are lost and no longer commercially grown.

[School assistance for attention deficit hyperactivity disorder in the Spanish autonomous regions]. / Atencion escolar al trastorno por deficit de atencion/hiperactividad en las comunidades españolas.

INTRODUCTION: In recent years different Spanish autonomous regions have presented policies on school assistance for attention deficit hyperactivity disorder (ADHD) or coordination between the educational and healthcare services, which result in protocols, instructions or guidelines of action. AIM: To determine and compare the proposals put forward by the different Spanish regions with respect to school assistance for ADHD. SUBJECTS AND METHODS: After searching for the documents that contain these policies, the information therein was analysed with the aim of being able to compare them in several different areas: document, scope of application, detection of ADHD, diagnosis, school measures, follow-up of the proposals of the Guidelines on clinical practice in attention deficit hyperactivity disorder, grounds and resources offered. RESULTS: The Valencian Region is the only one for which no documents were found. The document for the Balearic Islands was not analysed because it is not public, and in the other regions differences were found in the degree of compliance with the criteria assessed in each area. The policies in Extremadura, Galicia, Catalonia and Navarra are the ones that meet the largest number of criteria. All the regions with policies on ADHD propose some kind of school measures and resources such as bibliographical references, contacts or models of documents or screening tools. All of them, except Madrid, offer information about the detection and diagnosis of ADHD. CONCLUSION: There are differences among the proposals for school assistance for ADHD in Spain, and those of Extremadura, Galicia, Catalonia and Navarra are found to be the most complete.

TITLE: Atencion escolar al trastorno por deficit de atencion/hiperactividad en las comunidades españolas.Introduccion. En los ultimos años, distintas comunidades autonomas españolas han presentado politicas de atencion escolar al trastorno por deficit de atencion/hiperactividad (TDAH) o de coordinacion entre los servicios de educacion y sanidad, que se concretan en protocolos, instrucciones o guias de actuacion. Objetivo. Conocer y comparar las propuestas de las distintas comunidades españolas para la atencion escolar al TDAH. Sujetos y metodos. Tras una busqueda de los documentos que recogen estas politicas, se analizo su informacion para poder compararlos en varias areas: documento, ambito de aplicacion, deteccion del TDAH, diagnostico, medidas escolares, seguimiento de las propuestas de la Guia de practica clinica sobre el trastorno por deficit de atencion/hiperactividad, fundamentacion y recursos ofrecidos. Resultados. La Comunidad Valenciana es la unica de la que no se ha encontrado documento alguno. No se analizo el de Baleares, por no ser publico, y en las comunidades restantes se encuentran diferencias en el cumplimiento de los criterios valorados en cada area. Las politicas de Extremadura, Galicia, Cataluña y Navarra son las que cumplen el mayor numero de criterios. Todas las comunidades con politicas sobre el TDAH proponen algun tipo de medida escolar y recursos como bibliografia, contactos o modelos de documentos o herramientas de deteccion. Todas, menos Madrid, ofrecen informacion sobre la deteccion y el diagnostico del TDAH. Conclusion. Se constatan diferencias entre las propuestas de atencion escolar al TDAH en España, y se identifican las de Extremadura, Galicia, Cataluña y Navarra como las mas completas.

Two-dimensional collective electron magnetotransport, oscillations, and chaos in a semiconductor superlattice.

When quantized, traces of classically chaotic single-particle systems include eigenvalue statistics and scars in eigenfuntions. Since 2001, many theoretical and experimental works have argued that classically chaotic single-electron dynamics influences and controls collective electron transport. For transport in semiconductor superlattices under tilted magnetic and electric fields, these theories rely on a reduction to a one-dimensional self-consistent drift model. A two-dimensional theory based on self-consistent Boltzmann transport does not support that single-electron chaos influences collective transport. This theory agrees with existing experimental evidence of current self-oscillations, predicts spontaneous collective chaos via a period doubling scenario, and could be tested unambiguously by measuring the electric potential inside the superlattice under a tilted magnetic field.

Bifurcation analysis and phase diagram of a spin-string model with buckled states.

We analyze a one-dimensional spin-string model, in which string oscillators are linearly coupled to their two nearest neighbors and to Ising spins representing internal degrees of freedom. String-spin coupling induces a long-range ferromagnetic interaction among spins that competes with a spin-spin antiferromagnetic coupling. As a consequence, the complex phase diagram of the system exhibits different flat rippled and buckled states, with first or second order transition lines between states. This complexity translates to the two-dimensional version of the model, whose numerical solution has been recently used to explain qualitatively the rippled to buckled transition observed in scanning tunneling microscopy experiments with suspended graphene sheets. Here we describe in detail the phase diagram of the simpler one-dimensional model and phase stability using bifurcation theory. This gives additional insight into the physical mechanisms underlying the different phases and the behavior observed in experiments.

Soliton driven angiogenesis.

Angiogenesis is a multiscale process by which blood vessels grow from existing ones and carry oxygen to distant organs. Angiogenesis is essential for normal organ growth and wounded tissue repair but it may also be induced by tumours to amplify their own growth. Mathematical and computational models contribute to understanding angiogenesis and developing anti-angiogenic drugs, but most work only involves numerical simulations and analysis has lagged. A recent stochastic model of tumour-induced angiogenesis including blood vessel branching, elongation, and anastomosis captures some of its intrinsic multiscale structures, yet allows one to extract a deterministic integropartial differential description of the vessel tip density. Here we find that the latter advances chemotactically towards the tumour driven by a soliton (similar to the famous Korteweg-de Vries soliton) whose shape and velocity change slowly. Analysing these collective coordinates paves the way for controlling angiogenesis through the soliton, the engine that drives this process.

Stochastic model of tumor-induced angiogenesis: Ensemble averages and deterministic equations.

A recent conceptual model of tumor-driven angiogenesis including branching, elongation, and anastomosis of blood vessels captures some of the intrinsic multiscale structures of this complex system, yet allowing one to extract a deterministic integro-partial-differential description of the vessel tip density [Phys. Rev. E 90, 062716 (2014)]. Here we solve the stochastic model, show that ensemble averages over many realizations correspond to the deterministic equations, and fit the anastomosis rate coefficient so that the total number of vessel tips evolves similarly in the deterministic and ensemble-averaged stochastic descriptions.