225 research outputs found
Inverse cascades and resonant triads in rotating and stratified turbulence
Kraichnanâs seminal ideas on inverse cascades yielded new tools to study common phenomena in geophysical turbulent flows. In the atmosphere and the oceans, rotation and stratification result in a flow that can be approximated as two-dimensional at very large scales but which requires considering three-dimensional effects to fully describe turbulent transport processes and non-linear phenomena. Motions can thus be classified into two classes: fast modes consisting of inertia-gravity waves and slow quasi-geostrophic modes for which the Coriolis force and horizontal pressure gradients are close to balance. In this paper, we review previous results on the strength of the inverse cascade in rotating and stratified flows and then present new results on the effect of varying the strength of rotation and stratification (measured by the inverse Prandtl ratio N/f, of the Coriolis frequency to the Brunt-VĂ€isĂ€la frequency) on the amplitude of the waves and on the flow quasi-geostrophic behavior. We show that the inverse cascade is more efficient in the range of N/f for which resonant triads do not exist, /2â€N/fâ€21/2â€N/fâ€2. We then use the spatio-temporal spectrum to show that in this range slow modes dominate the dynamics, while the strength of the waves (and their relevance in the flow dynamics) is weaker.Fil: Oks, D.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FĂsica; ArgentinaFil: Mininni, Pablo Daniel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FĂsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FĂsica de Buenos Aires; ArgentinaFil: Marino, R.. Universite Lyon 2; FranciaFil: Pouquet, A.. State University of Colorado Boulder; Estados Unido
Strangeness Physics with CLAS at JLab
A brief overview of strangeness physics with the CLAS detector at JLab is
given, mainly covering the domain of nucleon resonances. Several excited states
predicted by the symmetric constituent quark model may have significant
couplings to the K-Lambda or K-Sigma channels. I will discuss data that are
relevant in the search for such states in the strangeness channel, and give an
outlook on the future prospects of the N* program at JLab with electromagnetic
probes.Comment: 9 pages, 7 figures, Conference on Strangeness in Nuclei, SENDAI 200
Anthropogenic Harvesting Pressure and Changes in Life History: Insights from a Rocky Intertidal Limpet
The importance of large breeding individuals for maintaining the health of marine fish and invertebrate populations has long been recognized. Unfortunately, decades of human harvesting that preferentially remove larger individuals have led to drastic reductions in body sizes of many of these species. Such size-selective harvesting is particularly worrisome for sequentially hermaphroditic species where the larger size classes are composed primarily of one sex. Whether these species can maintain stable sex ratios under sustained harvesting pressure depends on the level of plasticity of their life-history traits. Here, we show that populations of a marine limpet (Lottia gigantea) can adjust a fundamental aspect of their life history (the timing of sex change) when subjected to size-selective harvesting. As predicted by theoretical models, individuals from harvested populations change sex at smaller sizes and grow at slower rates compared to individuals from protected populations. In addition, the relative size at which the change from male to female occurs remains constant (?0.75; size at sex change/maximum size) across populations, regardless of harvesting pressure. Our results show that population-level demographic and life-history data, in conjunction with existing theory, can be sufficient to predict the responses of sequential hermaphrodites to harvesting pressure. Furthermore, they suggest such species can potentially adapt to size-selective harvesting
Effects of network topology, transmission delays, and refractoriness on the response of coupled excitable systems to a stochastic stimulus
We study the effects of network topology on the response of networks of
coupled discrete excitable systems to an external stochastic stimulus. We
extend recent results that characterize the response in terms of spectral
properties of the adjacency matrix by allowing distributions in the
transmission delays and in the number of refractory states, and by developing a
nonperturbative approximation to the steady state network response. We confirm
our theoretical results with numerical simulations. We find that the steady
state response amplitude is inversely proportional to the duration of
refractoriness, which reduces the maximum attainable dynamic range. We also
find that transmission delays alter the time required to reach steady state.
Importantly, neither delays nor refractoriness impact the general prediction
that criticality and maximum dynamic range occur when the largest eigenvalue of
the adjacency matrix is unity
Systems Theory and Cascades in Developmental Psychopathology
In the wake of prominent theoreticians in developmental science, whose contributions we review in this article, many developmental psychologists came to endorse a systems approach to understanding how the individual, as it develops, establishes functional relationships to social ecological contexts that from birth to school entry rapidly increase in complexity. The concept of developmental cascade has been introduced in this context to describe lawful processes by which antecedent conditions may be related with varying probabilities to specified outcomes. These are understood as processes by which function at one level or in one domain of behavior affect the organization of competency in later developing domains of general adaptation. Here we propose a developmental sequence by which the developing child acquires regulative capacities that are key to adjustment to a society that demands considerable control of emotional and cognitive functions early in life. We report empirical evidence showing that the acquisition of regulative capacities may be understood as a cascade of shifts in control parameters induced by the progressive integration of biological, transactional, and socioaffective systems over development. We conclude by suggesting how the developmental process may be accessed for effective intervention in populations deemed âat riskâ for later problems of psychosocial adjustment
South Korea's automotive labour regime, Hyundai Motorsâ global production network and tradeâbased integration with the European Union
This article explores the interrelationship between global production networks(GPNs) and free trade agreements (FTAs) in the South Korean auto industry and its employment relations. It focuses on the production network of the Hyundai Motor Group (HMG) â the third biggest automobile manufacturer in the world â and the FTA between the EU and South Korea. This was the first of the EUâs ânew generationâ FTAs, which among other things contained provisions designed to protect and promote labour standards. The articleâs argument is twofold. First, that HMGâs production network and Koreaâs political economy (of which HMG is a crucial part) limited the possibilities for the FTAâs labour provisions to take effect. Second, that the commercial provisions in this same FTA simultaneously eroded HMGâs domestic market and corporate profitability, leading to adverse consequences for auto workers in the more
insecure and low-paid jobs. In making this argument, the article advances a multiscalar conceptualization of the labour regime as an analytical intermediary between GPNs and FTAs. It also provides one of the first empirical studies of the EUâSouth Korea FTA in terms of employment relations, drawing on 105 interviews with trade unions, employer associations, automobile companies and state officials across both parties
Computer simulations of cosmic ray extensive air showers
This thesis describes the results of computer simulations of cosmic ray extensive air showers with primary energy in the range 10 (^14) â 10 (^19) eV. A brief review of simulations made by other authors is presented after which models for high energy nuclear interactions are discussed. The parameters chosen for the preferred model employed here are stated and some more recent data from accelerator experiments are mentioned. The predictions from the preferred model for proton initiated air showers are compared with experimental data and the results of previous simulations; the consequences of including trends seen from recent accelerator experiments in the model for interactions are also discussed. The break-up of energetic particles with atomic mass number as high as 56 as they traverse the atmosphere is discussed and a model to reconstruct this process at cosmic ray energies is described. The predictions from the preferred model for interactions assuming iron primary particles are given. It is concluded that a study of the average shower characteristics will not lead to a reliable determination of the mass composition of the primary radiation. Predictions for the fluctuations of measurable parameters in air showers are presented; it is shown that on the basis of these studies it is likely that comment may be made upon the primary composition. The results of these simulations are particularly relevant to the Haverah Park Extensive Air Shower Array; the improvements to the array presently being implemented should, according to the present results, enable an estimation of the primary composition IV at energies > 10 (^17) eV to be made. In particular the presence or otherwise of protons in the primary beam should be estimated. The feasibility of the cluster analysis of experimental data is investigated and it is shown on the basis of the clustering of simulation data that to a limited extent the separation of air showers into groups according to the atomic mass number of the primary particle is possible
New measurement of via neutron capture on hydrogen at Daya Bay
This article reports an improved independent measurement of neutrino mixing
angle at the Daya Bay Reactor Neutrino Experiment. Electron
antineutrinos were identified by inverse -decays with the emitted
neutron captured by hydrogen, yielding a data-set with principally distinct
uncertainties from that with neutrons captured by gadolinium. With the final
two of eight antineutrino detectors installed, this study used 621 days of data
including the previously reported 217-day data set with six detectors. The
dominant statistical uncertainty was reduced by 49%. Intensive studies of the
cosmogenic muon-induced Li and fast neutron backgrounds and the
neutron-capture energy selection efficiency, resulted in a reduction of the
systematic uncertainty by 26%. The deficit in the detected number of
antineutrinos at the far detectors relative to the expected number based on the
near detectors yielded in the
three-neutrino-oscillation framework. The combination of this result with the
gadolinium-capture result is also reported.Comment: 26 pages, 23 figure
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