Joint Attention and Word Learning in Ngas-Speaking Toddlers in Nigeria

This study examines infants’ joint attention behavior and language development in a rural village in Nigeria. Participants included eight younger (1;0 to 1;5, M age=1;2) and eight older toddlers (1;7 to 2;7, M age=2; 1). Joint attention behaviors in social interaction contexts were recorded and coded at two time points six months apart. Analyses revealed that these toddlers were producing more high-level joint attention behaviors than less complex behaviors. In addition, the quality and quantity of behaviors produced by these Nigerian children was similar to those found in other cultures. In analyses of children’s noun and verb comprehension and production (in relation to the number of nouns or verbs on a parental checklist), parents reported proportionally more verbs than nouns, perhaps because Ngas has some linguistic characteristics that are similar to languages in which a noun bias is not seen (e.g. Mandarin Chinese). An examination of the interrelations of joint attention and language development revealed that joint attention behaviors were related to both noun and verb development at different times. The set of results is important for understanding the emergence of joint attention in traditional cultures, the comprehension and production of nouns and verbs given the specific linguistic properties of a language and the importance that early social contexts may have for language development

Ecosystem resistance in the face of climate change: a case study from the freshwater marshes of the Florida Everglades

Shaped by the hydrology of the Kissimmee-Okeechobee-Everglades watershed, the Florida Everglades is composed of a conglomerate of wetland ecosystems that have varying capacities to sequester and store carbon. Hydrology, which is a product of the region’s precipitation and temperature patterns combined with water management policy, drives community composition and productivity. As shifts in both precipitation and air temperature are expected over the next 100 years as a consequence of climate change, CO2 dynamics in the greater Everglades are expected to change. To reduce uncertainties associated with climate change and to explore how projected changes in atmospheric CO2 concentration and climate can alter current CO2 exchange rates in Everglades freshwater marsh ecosystems, we simulated fluxes of carbon among the atmosphere, vegetation, and soil using the DAYCENT model. We explored the effects of low, moderate, and high scenarios for atmospheric CO2 (550, 850, and 950 ppm), mean annual air temperature (þ1, þ2.5, and þ4.28C) and precipitation (2, þ7, and þ14%), as predicted by the IPCC for the year 2100 for the region, on CO2 exchange rates in short- and long-hydroperiod wetland ecosystems. Under 100 years of current climate and atmospheric CO2 concentration, Everglades freshwater marsh ecosystems were estimated to be CO2-neutral. As atmospheric CO2 concentration increased and under climate change projections, there were slight shifts in the start and length of the wet season (1 to þ7 days) and a small enhancement in the sink capacity (by 169 to 573 g C m2 century1 ) occurred at both short- and longhydroperiod ecosystems compared to CO2 dynamics under the current climate regime. Over 100 years, rising temperatures increased net CO2 exchange rates (þ1 to 13 g C m2 century1 ) and shifts in precipitation patterns altered cumulative net carbon uptake by þ13 to 46 g C m2 century1 . While changes in ecosystem structure, species composition, and disturbance regimes were beyond the scope of this research, results do indicate that climate change will produce small changes in CO2 dynamics in Everglades freshwater marsh ecosystems and suggest that the hydrologic regime and oligotrophic conditions of Everglades freshwater marshes lowers the ecosystem sensitivity to climate change. Key word

The Quantum Hall Effect in Drag: Inter-layer Friction in Strong Magnetic Fields

We study the Coulomb drag between two spatially separated electron systems in a strong magnetic field, one of which exhibits the quantum Hall effect. At a fixed temperature, the drag mimics the behavior of $\sigma_{xx}$ in the quantum Hall system, in that it is sharply peaked near the transitions between neighboring plateaux. We assess the impact of critical fluctuations near the transitions, and find that the low temperature behavior of the drag measures an exponent $\eta$ that characterizes anomalous low frequency dissipation; the latter is believed to be present following the work of Chalker.Comment: 13 pages, Revtex 2.0, 1 figure upon request, P-93-11-09

Elemental energy spectra of cosmic rays measured by CREAM-II

We present new measurements of the energy spectra of cosmic-ray (CR) nuclei from the second flight of the balloon-borne experiment CREAM (Cosmic Ray Energetics And Mass). The instrument (CREAM-II) was comprised of detectors based on different techniques (Cherenkov light, specific ionization in scintillators and silicon sensors) to provide a redundant charge identification and a thin ionization calorimeter capable of measuring the energy of cosmic rays up to several hundreds of TeV. The data analysis is described and the individual energy spectra of C, O, Ne, Mg, Si and Fe are reported up to ~ 10^14 eV. The spectral shape looks nearly the same for all the primary elements and can be expressed as a power law in energy E^{-2.66+/-0.04}. The nitrogen absolute intensity in the energy range 100-800 GeV/n is also measured.Comment: 4 pages, 3 figures, presented at ICRC 2009, Lodz, Polan

Measurements of cosmic-ray energy spectra with the 2nd CREAM flight

During its second Antarctic flight, the CREAM (Cosmic Ray Energetics And Mass) balloon experiment collected data for 28 days, measuring the charge and the energy of cosmic rays (CR) with a redundant system of particle identification and an imaging thin ionization calorimeter. Preliminary direct measurements of the absolute intensities of individual CR nuclei are reported in the elemental range from carbon to iron at very high energy.Comment: 4 pages, 3 figures, presented at XV International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI 2008

Heuristic Models of Two-Fermion Relativistic Systems with Field-Type Interaction

We use the chain of simple heuristic expedients to obtain perturbative and exactly solvable relativistic spectra for a family of two-fermionic bound systems with Coulomb-like interaction. In the case of electromagnetic interaction the spectrum coincides up to the second order in a coupling constant with that following from the quantum electrodynamics. Discrepancy occurs only for S-states which is the well-known difficulty in the bound-state problem. The confinement interaction is considered too. PACS number(s): 03.65.Pm, 03.65.Ge, 12.39.PnComment: 16 pages, LaTeX 2.0

Applications of Two-Body Dirac Equations to the Meson Spectrum with Three versus Two Covariant Interactions, SU(3) Mixing, and Comparison to a Quasipotential Approach

In a previous paper Crater and Van Alstine applied the Two Body Dirac equations of constraint dynamics to the meson quark-antiquark bound states using a relativistic extention of the Adler-Piran potential and compared their spectral results to those from other approaches, ones which also considered meson spectroscopy as a whole and not in parts. In this paper we explore in more detail the differences and similarities in an important subset of those approaches, the quasipotential approach. In the earlier paper, the transformation properties of the quark-antiquark potentials were limited to a scalar and an electromagnetic-like four vector, with the former accounting for the confining aspects of the overall potential, and the latter the short range portion. A part of that work consisted of developing a way in which the static Adler-Piran potential was apportioned between those two different types of potentials in addition to covariantization. Here we make a change in this apportionment that leads to a substantial improvement in the resultant spectroscopy by including a time-like confining vector potential over and above the scalar confining one and the electromagnetic-like vector potential. Our fit includes 19 more mesons than the earlier results and we modify the scalar portion of the potential in such a way that allows this formalism to account for the isoscalar mesons {\eta} and {\eta}' not included in the previous work. Continuing the comparisons made in the previous paper with other approaches to meson spectroscopy we examine in this paper the quasipotential approach of Ebert, Faustov, and Galkin for a comparison with our formalism and spectral results.Comment: Revisions of earlier versio