Acquisition of Demonstratives in English and Spanish

The present work re-evaluates the long-standing claim that demonstratives are among infants’ earliest and most common words. Although demonstratives are deictic words important for joint attention, deictic gestures and non-word vocalizations could serve this function in early language development; the role of demonstratives may have been overestimated. Using extensive data from the CHILDES corpora (Study 1, N = 66, 265 transcripts) and McArthur-Bates CDI database (Study 2, N = 950), the language production of 18- to 24-month-old Spanish- and English-speaking children was analyzed to determine the age and order of acquisition, and frequency of demonstratives. Results indicate that demonstratives do not typically appear before the 50th word and only become frequent from the two-word utterance stage. Corpus data show few differences between Spanish and English, whereas parental report data suggest much later acquisition for demonstratives in English. These findings expand our knowledge of the foundations of deictic communication, and of the methodological challenges of assessing early production of function words

High-pT Signatures in Vector-Leptoquark Models

We present a detailed analysis of the collider signatures of TeV-scale massive vector bosons motivated by the hints of lepton flavour non-universality observed in $B$-meson decays. We analyse three representations that necessarily appear together in a large class of ultraviolet-complete models: a colour-singlet ($Z'$), a colour-triplet (the $U_1$ leptoquark), and a colour octet ($G'$). Under general assumptions for the interactions of these exotic states with Standard Model fields, including in particular possible right-handed and flavour off-diagonal couplings for the $U_1$, we derive a series of stringent bounds on masses and couplings that constrain a wide range of explicit new-physics models.Comment: 23 pages, 11 figures. v2: Minor modifications and references added. v3: Matching the journal version. The Feynrules and UFO files used for this work can be found at https://feynrules.irmp.ucl.ac.be/wiki/LeptoQuar

The Anisotropic Spatial Distribution of Hypervelocity Stars

We study the distribution of angular positions and angular separations of unbound hypervelocity stars (HVSs). HVSs are spatially anisotropic at the 3-sigma level. The spatial anisotropy is significant in Galactic longitude, not in latitude, and the inclusion of lower velocity, possibly bound HVSs reduces the significance of the anisotropy. We discuss how the observed distribution of HVSs may be linked to their origin. In the future, measuring the distribution of HVSs in the southern sky will provide additional constraints on the spatial anisotropy and the origin of HVSs.Comment: 4 pages, accepted to ApJ Letter

The TAOS Project: Upper Bounds on the Population of Small KBOs and Tests of Models of Formation and Evolution of the Outer Solar System

We have analyzed the first 3.75 years of data from TAOS, the Taiwanese American Occultation Survey. TAOS monitors bright stars to search for occultations by Kuiper Belt Objects (KBOs). This dataset comprises 5e5 star-hours of multi-telescope photometric data taken at 4 or 5 Hz. No events consistent with KBO occultations were found in this dataset. We compute the number of events expected for the Kuiper Belt formation and evolution models of Pan & Sari (2005), Kenyon & Bromley (2004), Benavidez & Campo Bagatin (2009), and Fraser (2009). A comparison with the upper limits we derive from our data constrains the parameter space of these models. This is the first detailed comparison of models of the KBO size distribution with data from an occultation survey. Our results suggest that the KBO population is comprised of objects with low internal strength and that planetary migration played a role in the shaping of the size distribution.Comment: 18 pages, 16 figures, Aj submitte

A Spectral Diagnostic for Density-Bounded HII Regions

The existence of density-bounded HII regions in spiral galaxies is supported by means of a spectral indicator based on the intensity of the [OI]6300A forbidden line. A grid of photoionization models providing spectral information of density-bounded nebulae is presented in order to test the validity of our indicator. The indicator is applicable to typical observed HII regions with solar or higher metallicities, and for the range of ages observed in normal HII regions. When applying the diagnostic to a large sample of HII regions of spiral galaxies taken from the literature, we find that a fraction of the selected HII regions with emission detected in the [OI]6300A line turn out to be consistent with the predictions of density-bounded photoionization models. Preliminary estimates of the fraction of Lyman continuum photons escaping ranges from 20% to 40%. The number of density-bounded HII regions could be even larger after confirmation of those regions for which the [OI] line was not detected, provided they are good density-bounded candidates. We stress the importance of having combined information on both good measurements or reliable upper limits for the intensity of this line, and good determinations of the Halpha luminosity for complete samples of HII regions in galaxies in order to make proper estimations as to whether UV photons escaping from HII regions are the main source of ionization of the diffuse ionized medium in galaxies.Comment: 15 pages, 5 figures, LaTeX, accepted for publication in M.N.R.A.

Interactions Between the Amazonian Rainforest and Cumuli Clouds: A Large‐Eddy Simulation, High‐Resolution ECMWF, and Observational Intercomparison Study

The explicit coupling at meter and second scales of vegetation's responses to the atmospheric‐boundary layer dynamics drives a dynamic heterogeneity that influences canopy‐top fluxes and cloud formation. Focusing on a representative day during the Amazonian dry season, we investigate the diurnal cycle of energy, moisture and carbon dioxide at the canopy top, and the transition from clear to cloudy conditions. To this end, we compare results from a large‐eddy simulation technique, a high‐resolution global weather model, and a complete observational data set collected during the GoAmazon14/15 campaign. The overall model‐observation comparisons of radiation and canopy‐top fluxes, turbulence, and cloud dynamics are very satisfactory, with all the modeled variables lying within the standard deviation of the monthly aggregated observations. Our analysis indicates that the timing of the change in the daylight carbon exchange, from a sink to a source, remains uncertain and is probably related to the stomata closure caused by the increase in vapor pressure deficit during the afternoon. We demonstrate quantitatively that heat and moisture transport from the subcloud layer into the cloud layer are misrepresented by the global model, yielding low values of specific humidity and thermal instability above the cloud base. Finally, the numerical simulations and observational data are adequate settings for benchmarking more comprehensive studies of plant responses, microphysics, and radiation