4,216 research outputs found
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Children use one-to-one correspondence to establish equality after learning tocount
Humans make frequent and powerful use of external symbolsto express number exactly, leading some to question whetherexact number concepts are only available through the acqui-sition of symbolic number systems. Although prior work hasaddressed this longstanding debate on the relationship betweenlanguage and thought in innumerate populations and semi-numerate children, it has frequently produced conflicting re-sults, leaving the origin of exact number concepts unclear.Here, we return to this question by replicating methods pre-viously used to assess exact number knowledge in innumer-ate groups, such as the Pirah Ìa, with a large sample of semi-numerate US toddlers. We replicate previous findings fromboth innumerate cultures and developmental studies showingthat numeracy is linked to the concept of exact number. How-ever, we also find evidence that this knowledge is surprisinglyfragile even amongst numerate children, suggesting that nu-meracy alone does not guarantee a full understanding of exact-ness
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A speed-accuracy trade-off in childrenâs processing of scalar implicatures
Scalar implicaturesâinferences from a weak description (âIate some of the cookiesâ) that a stronger alternative is true(âI didnât eat allâ)âare paradigm cases of pragmatic infer-ence. Childrenâs trouble with scalar implicatures is thus animportant puzzle for theories of pragmatic development, giventheir communicative competence in other domains. Previousresearch has suggested that access to alternatives might be key.Here, we explore childrenâs reaction times in a new paradigmfor measuring scalar implicature processing. Alongside fail-ures on scalar implicatures with âsome,â we replicate previ-ous reports of failures with ânone,â and find evidence of aspeed-accuracy trade-off for both quantifiers. Motivated bythese findings, we explore the relationship between accuracyand reaction time with a Drift Diffusion Model. We find evi-dence consistent with the hypothesis that preschoolers lack ac-cess to the alternatives for scalar implicature computation, al-though this set of alternatives may be broader than previouslyassumed
Terahertz and Infrared Photodetection using p-i-n Multiple-Graphene-Layer Structures
We propose to utilize multiple-graphene-layer structures with lateral p-i-n
junctions for terahertz (THz) and infrared (IR) photodetection and substantiate
the operation of photodetectors based on these structures. Using the developed
device model, we calculate the detector dc responsivity and detectivity as
functions of the number of graphene layers and geometrical parameters and show
that the dc responsivity and detectivity can be fairly large, particularly, at
the lower end of the THz range at room temperatures. Due to relatively high
quantum efficiency and low thermogeneration rate, the photodetectors under
consideration can substantially surpass other THz and IR detectors.
Calculations of the detector responsivity as a function of modulation frequency
of THz and IR radiation demonstrate that the proposed photodetectors are very
fast and can operate at the modulation frequency of several tens of GHz.Comment: 7 pages, 4 figure
Advantageous GOES IR results for ash mapping at high latitudes: Cleveland eruptions 2001
The February 2001 eruption of Cleveland Volcano, Alaska allowed for comparisons of volcanic ash detection using two-band thermal infrared (10â12 ÎŒm) remote sensing from MODIS, AVHRR, and GOES 10. Results show that high latitude GOES volcanic cloud sensing the range of about 50 to 65°N is significantly enhanced. For the Cleveland volcanic clouds the MODIS and AVHRR data have zenith angles 6â65 degrees and the GOES has zenith angles that are around 70 degrees. The enhancements are explained by distortion in the satellite view of the cloud\u27s lateral extent because the satellite zenith angles result in a âside-lookingâ aspect and longer path lengths through the volcanic cloud. The shape of the cloud with respect to the GOES look angle also influences the results. The MODIS and AVHRR data give consistent retrievals of the ash cloud evolution over time and are good corrections for the GOES data
The Net Global Effects of Alternative U.S. Biofuel Mandates
One of the declared objectives of U.S. biofuel policy is the reduction of greenhouse gas (GHG) emissions from fossil fuel combustion, but many studies have questioned whether such a reduction would actually occur and, if so, how large it would be. This report describes the global market, land use, GHG emissions, and nitrogen use impacts of the U.S. Renewable Fuel Standard (RFS2) and several alternative biofuel policy designs, which differ in terms of mandate magnitude and feedstock composition, over the 2010-2030 period
Multiple Rabi rotations of trions in InGaAs quantum dots observed by photon echo spectroscopy with spatially shaped laser pulses
We study Rabi rotations arising in intensity-dependent photon echoes from an
ensemble of self-assembled InGaAs quantum dots. To achieve a uniform
distribution of intensities within the excited ensemble, we introduce flattop
intensity profiles of picosecond laser pulses. This allows us to overcome the
damping of Rabi rotations imposed by the spatial inhomogeneity of Rabi
frequencies by a Gaussian laser profile. Using photon echo polarimetry, we
distinguish between the coherent optical responses from exciton and trion
ensembles. Here, we demonstrate that a photo-induced charging of the quantum
dots leads to a significant reduction of the number of neutral quantum dots
under resonant excitation with intensive optical pulses with areas exceeding
. The trion ensemble shows robust Rabi rotations when the area
of the refocussing pulse is increased up to 5.5. We analyze the remaining
attenuation of Rabi rotations by theoretical modeling of excitation induced
dephasing, inhomogeneity of dipole moments, and coupling to acoustic phonons.
The latter is identified as the dominating mechanism resulting in a loss of
optical coherence during the action of the involved optical pulses
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Evaluating the structure and magnitude of the ash plume during the initial phase of the 2010 Eyjafjallajökull eruption using lidar observations and NAME simulations
The Eyjafjallajökull volcano in Iceland erupted explosively on 14 April 2010, emitting a plume of ash into the atmosphere. The ash was transported from Iceland toward Europe where mostly cloud-free skies allowed ground-based lidars at Chilbolton in England and Leipzig in Germany to estimate the mass concentration in the ash cloud as it passed overhead. The UK Met Office's Numerical Atmospheric-dispersion Modeling Environment (NAME) has been used to simulate the evolution of the ash cloud from the Eyjafjallajökull volcano during the initial phase of the ash emissions, 14â16 April 2010. NAME captures the timing and sloped structure of the ash layer observed over Leipzig, close to the central axis of the ash cloud. Relatively small errors in the ash cloud position, probably caused by the cumulative effect of errors in the driving meteorology en route, result in a timing error at distances far from the central axis of the ash cloud. Taking the timing error into account, NAME is able to capture the sloped ash layer over the UK. Comparison of the lidar observations and NAME simulations has allowed an estimation of the plume height time series to be made. It is necessary to include in the model input the large variations in plume height in order to accurately predict the ash cloud structure at long range. Quantitative comparison with the mass concentrations at Leipzig and Chilbolton suggest that around 3% of the total emitted mass is transported as far as these sites by small (<100 ÎŒm diameter) ash particles
Observations of volcanic clouds in their first few days of atmospheric residence: The 1992 eruptions of crater peak, Mount Spurr volcano, Alaska
Satellite SO2 and ash measurements of Mount Spurrâs three 1992 volcanic clouds are compared with groundâbased observations to develop an understanding of the physical and chemical evolution of volcanic clouds. Each of the three eruptions with ratings of volcanic explosivity index three reached the lower stratosphere (14 km asl), but the clouds were mainly dispersed at the tropopause by moderate to strong (20â40 m/s) tropospheric winds. Three stages of cloud evolution were identified. First, heavy fallout of large (\u3e500 ÎŒm) pyroclasts occurred close to the volcano (vent) during and immediately after the eruptions, and the cloud resembled an advected gravity current. Second, a much larger, highly elongated region marked by a secondaryâmass maximum occurred 150â350 km downwind in at least two of the three events. This was the result of aggregate fallout of a bimodal size distribution including fine (\u3c25 \u3eÎŒm) ash that quickly depleted the solid fraction of the volcanic cloud. For the first several hundred kilometers, the cloud spread laterally, first as an intrusive gravity current and then by wind shear and diffusion as downwind cloud transport occurred at the windspeed (during the first 18â24 h). Finally, the clouds continued to move through the upper troposphere but began decreasing in areal extent, eventually disappearing as ash and SO2 were removed by meteorological processes. Total SO2 in each eruption cloud increased by the second day of atmospheric residence, possibly because of oxidation of coerupted H2S or possibly because of the effects of sequestration by ice followed by subsequent SO2 release during fallout and desiccation of ashy hydrometeors. SO2 and volcanic ash travelled together in all the Spurr volcanic clouds. The initial (18â24 h) area expansion of the clouds and the subsequent several days of drifting were successfully mapped by both SO2 (ultraviolet) and ash (infrared) satellite imagery
Enabling quantitative data analysis through e-infrastructures
This paper discusses how quantitative data analysis in the social sciences can engage with and exploit an e-Infrastructure. We highlight how a number of activities which are central to quantitative data analysis, referred to as âdata managementâ, can benefit from e-infrastructure support. We conclude by discussing how these issues are relevant to the DAMES (Data Management through e-Social Science) research Node, an ongoing project that aims to develop e-Infrastructural resources for quantitative data analysis in the social sciences
Plasmas and Controlled Nuclear Fusion
Contains reports on two research projects.National Science Foundation (Grants GK-57)National Science Foundation (Grants GK-614
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