1,058 research outputs found
Some gamma-ray shielding measurements made at altitudes greater than 115000 feet using large Ge(Li) detectors
A series of balloon-flight experiments at altitudes greater than 115,000 feet were conducted to gain information relative to the use of composite shields (passive and/or active) for shielding large-volume, lithium-drifted, germanium (Ge(Li)) detectors used in gamma-ray spectrometers. Data showing the pulse-height spectra of the environmental gamma radiation as measured at 5.3 and 3.8 gms sq cm residual atmosphere with an unshielded diode detector are also presented
Re-evaluating phoneme frequencies
Causal processes can give rise to distinctive distributions in the linguistic
variables that they affect. Consequently, a secure understanding of a
variable's distribution can hold a key to understanding the forces that have
causally shaped it. A storied distribution in linguistics has been Zipf's law,
a kind of power law. In the wake of a major debate in the sciences around
power-law hypotheses and the unreliability of earlier methods of evaluating
them, here we re-evaluate the distributions claimed to characterize phoneme
frequencies. We infer the fit of power laws and three alternative distributions
to 166 Australian languages, using a maximum likelihood framework. We find
evidence supporting earlier results, but also nuancing them and increasing our
understanding of them. Most notably, phonemic inventories appear to have a
Zipfian-like frequency structure among their most-frequent members (though
perhaps also a lognormal structure) but a geometric (or exponential) structure
among the least-frequent. We compare these new insights the kinds of causal
processes that affect the evolution of phonemic inventories over time, and
identify a potential account for why, despite there being an important role for
phonetic substance in phonemic change, we could still expect inventories with
highly diverse phonetic content to share similar distributions of phoneme
frequencies. We conclude with priorities for future work in this promising
program of research.Comment: 29pp (3 figures, 3 tables). This article has been provisionally
accepted for publication (Frontiers in Psychology, Language Sciences).
Supplementary information, data and code available at
http://doi.org/10.5281/zenodo.388621
Phylogenetic signal in phonotactics
Phylogenetic methods have broad potential in linguistics beyond tree
inference. Here, we show how a phylogenetic approach opens the possibility of
gaining historical insights from entirely new kinds of linguistic data--in this
instance, statistical phonotactics. We extract phonotactic data from 111
Pama-Nyungan vocabularies and apply tests for phylogenetic signal, quantifying
the degree to which the data reflect phylogenetic history. We test three
datasets: (1) binary variables recording the presence or absence of biphones
(two-segment sequences) in a lexicon (2) frequencies of transitions between
segments, and (3) frequencies of transitions between natural sound classes.
Australian languages have been characterized as having a high degree of
phonotactic homogeneity. Nevertheless, we detect phylogenetic signal in all
datasets. Phylogenetic signal is greater in finer-grained frequency data than
in binary data, and greatest in natural-class-based data. These results
demonstrate the viability of employing a new source of readily extractable data
in historical and comparative linguistics.Comment: Main text: 32 pages, 17 figures, 1 table. Supplementary Information:
17 pages, 1 figure. Code and data available at
http://doi.org/10.5281/zenodo.3936353. This article is in review but not yet
accepted for publication in a journa
The s Process: Nuclear Physics, Stellar Models, Observations
Nucleosynthesis in the s process takes place in the He burning layers of low
mass AGB stars and during the He and C burning phases of massive stars. The s
process contributes about half of the element abundances between Cu and Bi in
solar system material. Depending on stellar mass and metallicity the resulting
s-abundance patterns exhibit characteristic features, which provide
comprehensive information for our understanding of the stellar life cycle and
for the chemical evolution of galaxies. The rapidly growing body of detailed
abundance observations, in particular for AGB and post-AGB stars, for objects
in binary systems, and for the very faint metal-poor population represents
exciting challenges and constraints for stellar model calculations. Based on
updated and improved nuclear physics data for the s-process reaction network,
current models are aiming at ab initio solution for the stellar physics related
to convection and mixing processes. Progress in the intimately related areas of
observations, nuclear and atomic physics, and stellar modeling is reviewed and
the corresponding interplay is illustrated by the general abundance patterns of
the elements beyond iron and by the effect of sensitive branching points along
the s-process path. The strong variations of the s-process efficiency with
metallicity bear also interesting consequences for Galactic chemical evolution.Comment: 53 pages, 20 figures, 3 tables; Reviews of Modern Physics, accepte
Measuring the quantum efficiency of single radiating dipoles using a scanning mirror
Using scanning probe techniques, we show the controlled manipulation of the
radiation from single dipoles. In one experiment we study the modification of
the fluorescence lifetime of a single molecular dipole in front of a movable
silver mirror. A second experiment demonstrates the changing plasmon spectrum
of a gold nanoparticle in front of a dielectric mirror. Comparison of our data
with theoretical models allows determination of the quantum efficiency of each
radiating dipole.Comment: 4 pages, 4 figure
High-Definition Phonotactics Reflect Linguistic Pasts
Typological datasets for quantitative historicallinguistic
inquiry are growing in breadth, but a challenge is also
to increase their depth, since advanced methods often ideally
require many hundreds of traits per language. Using biphone
transition probabilities from phonemicized vocabulary data, we
extract several hundred high-definition phonotactic traits per
language, for 17 languages in the Ngumpin-Yapa and Yolngu
subgroups of the Pama-Nyungan family, Australia. We detect
phylogenetic signal at a significant level (p < 0.001 for both
subgroups), measured against a reference phylogeny inferred
from basic vocabulary cognacy data. This contrasts with simpler,
binary coding of biphones’ occurrence, which provides
insufficient detail for the detection of phylogenetic signal. Thus,
we demonstrate the viability of a new method in quantitative
historical linguistics, and emphasize the inferential power to be
harnessed from high-definition, trait-rich datasets for
comparative research
s-Process Studies In the Light of New Experimental Cross Sections: Distribution of Neutron Fluences and r-Process Residuals
A best set of neutron-capture cross sections has been evaluated for the most important s-process isotopes. With this data base, s-process studies have been carried out using the traditional model which assumes a steady neutron flux and an exponential distribution of neutron irradiations. The calculated sigma-N curve is in excellent agreement with the empirical sigma-N-values of pure s-process nuclei. Simultaneously, good agreement is found between the difference of solar and s-process abundances and the abundances of pure r-process nuclei. The abundance pattern of the iron group elements where s-process results complement the abundances obtained from explosive nuclear burning is discussed. The results obtained from the traditional s-process model such as seed abundances, mean neutron irradiations, or neutron densities are compared to recent stellar model calculations which assume the He-burning shells of red giant stars as the site for the s-process
Non-resonant direct p- and d-wave neutron capture by 12C
Discrete gamma-rays from the neutron capture state of 13C to its low-lying
bound states have been measured using pulsed neutrons at En = 550 keV. The
partial capture cross sections have been determined to be 1.7+/-0.5,
24.2+/-1.0, 2.0+/-0.4 and 1.0+/-0.4 microb for the ground (1/2-), first (1/2+),
second (3/2-) and third (5/2+) excited states, respectively. From a comparison
with theoretical predictions based on the non-resonant direct radiative capture
mechanism, we could determine the spectroscopic factor for the 1/2+ state to be
0.80 +/- 0.04, free from neutron-nucleus interaction ambiguities in the
continuum. In addition we have detected the contribution of the non-resonant
d-wave capture component in the partial cross sections for transitions leading
to the 1/2- and 3/2- states. While the s-wave capture dominates at En < 100
keV, the d-wave component turns out to be very important at higher energies.
From the present investigation the 12C(n,gamma)13C reaction rate is obtained
for temperatures in the range 10E+7 - 10E+10 K.Comment: Accepted for publication in Phys. Rev. C. - 16 pages + 8 figure
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