484 research outputs found
What does it take to learn a word?
Vocabulary learning is deceptively hard, but toddlers often make it look easy. Prior theories proposed that childrenâs rapid acquisition of words is based on language-specific knowledge and constraints. In contrast, more recent work converges on the view that word learning proceeds via domain-general processes that are tuned to richly structuredânot impoverishedâinput. We argue that new theoretical insights, coupled with methodological tools, have pushed the field toward an appreciation of simple, content-free processes working together as a system to support the acquisition of words. We illustrate this by considering three central phenomena of early language development: referential ambiguity, fast-mapping, and the vocabulary spurt
Preface: Unsolved problems of magnetospheric physics
The Unsolved Problems of Magnetospheric Physics Workshop was held in September 2015 in Scarborough, UK. In contrast to most other meetings, people were specifically asked not to present and discuss their recent results. Rather, they were asked to bring their opinions and thoughts on unsolved problems to the meeting. Short presentations were encouraged after which the audience would debate and discuss definitions of the problems and how they could be overcome. Were new observations required? New missions? Or simply did the community need to work better together to resolve pertinent and outstanding science questions? Around 50% of the meeting schedule was devoted to discussion sessions on these topics.Key PointsMany unsolved problems exist in magnetospheric physicsThe UPMP workshop discussed these problems and suggested possible solutionsFor some problems, the community already have the data and the tools to make rapid progressPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135163/1/jgra53053_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135163/2/jgra53053.pd
Kinetic-scale magnetic turbulence and finite Larmor radius effects at Mercury
We use a nonstationary generalization of the higher-order structure function
technique to investigate statistical properties of the magnetic field
fluctuations recorded by MESSENGER spacecraft during its first flyby
(01/14/2008) through the near Mercury's space environment, with the emphasis on
key boundary regions participating in the solar wind -- magnetosphere
interaction. Our analysis shows, for the first time, that kinetic-scale
fluctuations play a significant role in the Mercury's magnetosphere up to the
largest resolvable time scale ~20 s imposed by the signal nonstationarity,
suggesting that turbulence at this planet is largely controlled by finite
Larmor radius effects. In particular, we report the presence of a highly
turbulent and extended foreshock system filled with packets of ULF
oscillations, broad-band intermittent fluctuations in the magnetosheath,
ion-kinetic turbulence in the central plasma sheet of Mercury's magnetotail,
and kinetic-scale fluctuations in the inner current sheet encountered at the
outbound (dawn-side) magnetopause. Overall, our measurements indicate that the
Hermean magnetosphere, as well as the surrounding region, are strongly affected
by non-MHD effects introduced by finite sizes of cyclotron orbits of the
constituting ion species. Physical mechanisms of these effects and their
potentially critical impact on the structure and dynamics of Mercury's magnetic
field remain to be understood.Comment: 46 pages, 5 figures, 2 table
Minimization of Fungicidal Applications Against Potato Late Blight in the North Caucasian Region: Use of the âAgrodozorâ System
Late blight is considered to be the most devastating potato disease, which control requires application of fungicides able to significantly contaminate the environment and accumulate in agricultural products. Pesticide load on potato fields can be reduced via optimization of the scheme of protective treatments. Such optimization can be performed using a mathematical simulator describing the dependence of late blight-caused yield losses on the weather data and an âAgrodozorâ decision support system (DSS). The performed analysis of a situation in the regions of the North Caucasus allowed us to determine three zones differing in the disease harmfulness and characterized by potential yield losses at the level of <10, 10-20, and >20 % and the probability of disease appearance in field during 30, 77, and 90 % of seasons, respectively. Using the âAgrodozorâ DSS, we calculated the optimum dates of fungicidal treatments for these zones and showed that, comparing to the commonly used routine scheme of treatments, the use of this DSS provides a significant reduction of the number of such treatments and, therefore, the corresponding costs for their arrangement, as well as reduction of the total toxicity index of the required protective measures
Future beam experiments in the magnetosphere with plasma contactors: How do we get the charge off the spacecraft?
The idea of using a highâvoltage electron beam with substantial current to actively probe magnetic field line connectivity in space has been discussed since the 1970s. However, its experimental realization onboard a magnetospheric spacecraft has never been accomplished because the tenuous magnetospheric plasma cannot provide the return current necessary to keep spacecraft charging under control. In this work, we perform ParticleâInâCell simulations to investigate the conditions under which a highâvoltage electron beam can be emitted from a spacecraft and explore solutions that can mitigate spacecraft charging. The electron beam cannot simply be compensated for by an ion beam of equal current, because the ChildâLangmuir space charge limit is violated under conditions of interest. On the other hand, releasing a highâdensity neutral contactor plasma prior and during beam emission is critical in aiding beam emission. We show that after an initial transient controlled by the size of the contactor cloud where the spacecraft potential rises, the spacecraft potential can settle into conditions that allow for electron beam emission. A physical explanation of this result in terms of ion emission into spherical geometry from the surface of the plasma cloud is presented, together with scaling laws of the peak spacecraft potential varying the ion mass and beam current. These results suggest that a strategy where the contactor plasma and the electron beam operate simultaneously might offer a pathway to perform beam experiments in the magnetosphere.Key PointsThe contactor plasma mitigates spacecraft charging from electron beam emissionThe contactor allows ion emission over a larger, quasiâspherical areaThe peak of the spacecraft potential is lower for larger contactor cloudsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112002/1/jgra51731.pd
The proton and electron radiation belts at geosynchronous orbit: Statistics and behavior during highâspeed streamâdriven storms
The outer proton radiation belt (OPRB) and outer electron radiation belt (OERB) at geosynchronous orbit are investigated using a reanalysis of the LANL CPA (Charged Particle Analyzer) 8âsatellite 2âsolar cycle energetic particle data set from 1976 to 1995. Statistics of the OPRB and the OERB are calculated, including local time and solar cycle trends. The number density of the OPRB is about 10 times higher than the OERB, but the 1âMeV proton flux is about 1000 times less than the 1âMeV electron flux because the proton energy spectrum is softer than the electron spectrum. Using a collection of 94 highâspeed streamâdriven storms in 1976â1995, the storm time evolutions of the OPRB and OERB are studied via superposed epoch analysis. The evolution of the OERB shows the familiar sequence (1) prestorm decay of density and flux, (2) earlyâstorm dropout of density and flux, (3) sudden recovery of density, and (4) steady storm time heating to high fluxes. The evolution of the OPRB shows a sudden enhancement of density and flux early in the storm. The absence of a proton dropout when there is an electron dropout is noted. The sudden recovery of the density of the OERB and the sudden density enhancement of the OPRB are both associated with the occurrence of a substorm during the early stage of the storm when the superdense plasma sheet produces a âstrong stretching phaseâ of the storm. These storm time substorms are seen to inject electrons to 1âMeV and protons to beyond 1âMeV into geosynchronous orbit, directly producing a suddenly enhanced radiation belt population.Key PointsDuring highâspeed streamâdriven storms, the electron and proton radiation belts are directly enhanced by a single substormThe enhancing substorm occurs during the âstrong stretchingâ phase of the storm caused by the superdense plasma sheetProton and electron injection to 1 MeV is seen for these strong stretching phase substormsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/133567/1/jgra52702.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/133567/2/jgra52702_am.pd
Nonequilibrium Phenomena in the Magnetosphere: Phase Transition, Self-organized Criticality and Turbulence
The magnetosphere is a large scale natural system powered by the solar wind that exhibits many nonequilibrium phenomena. A wide range of these phenomena are driven directly by the solar wind or arise from the storage-release processes internal to the magnetosphere. Under the influnce by the turbulent solar wind, the magnetosphere during geomagnetically active periods is far from equilibrium and storms and substorms are essentially non-equilibrium phenomena. In spite of the distributed nature of the physical processes and the apparent irregular behavior, there is a remarkable coherence in the magnetospheric response during substorms and the entire magnetosphere behaves as a global dynamical system. Alongwith the global features, the magnetosphere exhibits many multi-scale and intermittent characteristics. These features of the magnetosphere have been studied in terms of phase transitions, self-organized criticality and turbulence. In the phase transition scenario the global features are modeled as first-order transitions and the multi-scale behavior is interpreted as a manifestation of the scale-free nature of criticality in second order phase transitions. In the self-organized criticality framework substorms are considered as avalanches in the system when criticality is reached. Many features of the magnetosphere, in particular the power law dependence of scale sizes, can be viewed as a feature of a turbulent system.The common theme underlying these approaches is the recognition that the nonequilibrium phenomena in the magnetosphere could be understood in terms of processes generic to such systems. In many cases the power-law behavior of the magnetosphere seen in many observations is the starting point for these studies. This chapter is an overview of the recent understanding achieved using these different approaches, and identifies the common issues and differences.National Science Foundation: ATM-0119196, ATM-0318629, DMS-0417800
National Aeronautics and Space Administration: NNG04E37
Exploration geophysics methods assist in hydrogeological and ecological survey of oilfield regions
The paper describes the procedure of hydrogeological and ecological survey In the regions adjacent to oilfield facilities. Results of Integrated geophysical survey, including high-precision gravity measurement, electrical prospecting methods. In that number, symmetrical electrical profiling, vertical electric sounding, and spontaneous potentials, were used to decide on the site and type of specialized hydrogeological and ecological works. The first priorities are the zones with Intense tectonic fracturing determined first by space geological Investigations and confirmed later by gravity measurement
REGIONAL EXPERIENCE OF ORGANIZING OF ANTIEPIDEMIC MEASURES DIRECTED TO THE PREVENTING OF DELIVERY AND SPREADING OF SEVERE ACUTE RESPIRATORY SYNDROME IN OMSK REGION
Characteristics of factors, defining the possibility of severe acute respiratory syndrome delivery into the territory of Omsk region are given. The data of complex approach for organization and anti-epidemic measures at the region level for preventing of SARS delivery and spreading are presented. Problems of scientific and practical character, that need to be solved for effective counteraction with epidemic spreading of «atypical pneumonia» are discussed
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