9,330 research outputs found
Scanner observations of selected cool stars
Photoelectric spectral scans at 30-A resolution of 9 dwarfs, 10 giants and 6 supergiants with spectral types GO to M5 were presented. All stars were observed every 4 A from wavelength 3300 to wavelength 7000. Absorption features at this resolution coincide with: strong atomic lines of Fe 1,11, Ca 1,11, Mg 1, and Na 1; vibrational bands of the electronic transitions of TiO, MgH, CaH, SiH, AlH, Cn, Ch, C2, OH, and NH. The dependence of the wavelength 3740 Fe 1 blend and the wavelength 3440 depression on temperature is discussed
Impact of disorder on unconventional superconductors with competing ground states
Non-magnetic impurities are known as strong pair breakers in superconductors
with pure d-wave pairing symmetry. Here we discuss d-wave states under the
combined influence of impurities and competing instabilities, such as pairing
in a secondary channel as well as lattice symmetry breaking. Using the
self-consistent T-matrix formalism, we show that disorder can strongly modify
the competition between different pairing states. For a d-wave superconductor
in the presence of a subdominant local attraction, Anderson's theorem implies
that disorder always generates an s-wave component in the gap at sufficiently
low temperature, even if a pure d_{x^2-y^2} order parameter characterizes the
clean system. In contrast, disorder is always detrimental to an additional
d_{xy} component. This qualitative difference suggests that disorder can be
used to discriminate among different mixed-gap structures in high-temperature
superconductors. We also investigate superconducting phases with lattice
symmetry breaking in the form of bond order, and show that the addition of
impurities quickly leads to the restoration of translation invariance. Our
results highlight the importance of controlling disorder for the observation of
competing order parameters in cuprates.Comment: 13 pages, 10 figure
Memory, learning and language in autism spectrum disorder
Background and aims: The ‘dual-systems’ model of language acquisition has been used by Ullman and colleagues to explain patterns of strength and weakness in the language of higher-functioning people with autism spectrum disorder (ASD). Specifically, intact declarative/explicit learning is argued to compensate for a deficit in non-declarative/implicit procedural learning, constituting an example of the so-called ‘see-saw’ effect. Ullman and Pullman (2015) extended their argument concerning a see-saw effect on language in ASD to cover other perceived anomalies of behaviour, including impaired acquisition of social skills. The aim of this paper is to present a critique of Ullman and colleagues’ claims, and to propose an alternative model of links between memory systems and language in ASD.
Main contribution: We argue that a 4-systems model of learning, in which intact semantic and procedural memory are used to compensate for weaknesses in episodic memory and perceptual learning, can better explain patterns of language ability across the autistic spectrum. We also argue that attempts to generalise the ‘impaired implicit learning/spared declarative learning’ theory to other behaviours in ASD are unsustainable.
Conclusions: Clinically significant language impairments in ASD are under-researched, despite their impact on everyday functioning and quality of life. The relative paucity of research findings in this area lays it open to speculative interpretation which may be misleading.
Implications: More research is need into links between memory/learning systems and language impairments across the spectrum. Improved understanding should inform therapeutic intervention, and contribute to investigation of the causes of language impairment in ASD with potential implications for prevention
On Charge-3 Cyclic Monopoles
We determine the spectral curve of charge 3 BPS su(2) monopoles with C_3
cyclic symmetry. The symmetry means that the genus 4 spectral curve covers a
(Toda) spectral curve of genus 2. A well adapted homology basis is presented
enabling the theta functions and monopole data of the genus 4 curve to be given
in terms of genus 2 data. The Richelot correspondence, a generalization of the
arithmetic mean, is used to solve for this genus 2 curve. Results of other
approaches are compared.Comment: 34 pages, 16 figures. Revision: Abstract added and a few small
change
The Struck-and-lost Factor in Alaskan Walrus Harvests, 1952-1972
Struck-and-lost rates during hunts for walruses, Odobenus rosmarus (Linnaeus), in Alaska from 1952 to 1972 did not vary from year to year. On average, 42% of the animals struck by bullets were lost (i.e., not retrieved). About 55% of the struck-and lost animals died immediately; the rest were wounded. Apparently, most of the wounded died soon after they were struck. The sex-age composition of the struck-and-lost animals was about the same as that in the harvest, and the proportion lost did not vary with the size of the group encountered. Claims of reduction in loss rates in recent years, based on improved firepower, are open to question. Considerable improvement in weapons took place also during the 21-year period of this study, but it merely increased the proportion of outright kills among the struck-and-lost animals. It did not reduce the proportion lost of the animals that were struck.Key words: walrus, Odobenus rosmarus, Alaska, harvests, struck-and-lostLe taux d'animaux frappés et perdus au cours de la chasse au morse, Odobenus rosmarus (Linnaeus) en Alaska de 1952 à 1972 n'a pas varié d'une année à l'autre. En moyenne, 42 p. cent des animaux frappés par les balles ont été perdus (c.-à-d. non récupérés). Environ 55 p. cent des animaux frappés et perdus sont morts sur le coup et 45 p. cent ont été blessés. Il semble que la plupart de ces derniers soient morts peu de temps après avoir été frappés. La composition selon le sexe et l'âge des animaux frappés et perdus était environ la même que celle des prises, et la proportion des animaux perdus ne variait pas avec la taille du groupe chassé. On peut remettre en question les affirmations des dernières années concernant une réduction du taux de perte causée par l'amélioration de la puissance de feu. Durant les 21 années de l'étude, les armes ont subi de grosses améliorations, mais celles-ci ont tout simplement fait augmenter la proportion des bêtes tuées sur le coup, parmi les animaux qui avaient été frappés et perdus. Les améliorations apportées aux armes n'ont pas réduit la proportion des animaux perdus parmi ceux qui avaient été frappés.Mots clés: morse, Odobenus rosmarus, Alaska, prises, frappés et perdu
Associations between Proprioceptive Neural Pathway Structural Connectivity and Balance in People with Multiple Sclerosis
Mobility and balance impairments are a hallmark of multiple sclerosis (MS), affecting nearly half of patients at presentation and resulting in decreased activity and participation, falls, injuries, and reduced quality of life. A growing body of work suggests that balance impairments in people with mild MS are primarily the result of deficits in proprioception, the ability to determine body position in space in the absence of vision. A better understanding of the pathophysiology of balance disturbances in MS is needed to develop evidence-based rehabilitation approaches. The purpose of the current study was to (1) map the cortical proprioceptive pathway in vivo using diffusion-weighted imaging and (2) assess associations between proprioceptive pathway white matter microstructural integrity and performance on clinical and behavioral balance tasks. We hypothesized that people with MS (PwMS) would have reduced integrity of cerebral proprioceptive pathways, and that reduced white matter microstructure within these tracts would be strongly related to proprioceptive-based balance deficits. We found poorer balance control on proprioceptive-based tasks and reduced white matter microstructural integrity of the cortical proprioceptive tracts in PwMS compared with age-matched healthy controls (HC). Microstructural integrity of this pathway in the right hemisphere was also strongly associated with proprioceptive-based balance control in PwMS and controls. Conversely, while white matter integrity of the right hemisphere’s proprioceptive pathway was significantly correlated with overall balance performance in HC, there was no such relationship in PwMS. These results augment existing literature suggesting that balance control in PwMS may become more dependent upon (1) cerebellar-regulated proprioceptive control, (2) the vestibular system, and/or (3) the visual system
Mg/Ti multilayers: structural, optical and hydrogen absorption properties
Mg-Ti alloys have uncommon optical and hydrogen absorbing properties,
originating from a "spinodal-like" microstructure with a small degree of
chemical short-range order in the atoms distribution. In the present study we
artificially engineer short-range order by depositing Pd-capped Mg/Ti
multilayers with different periodicities and characterize them both
structurally and optically. Notwithstanding the large lattice parameter
mismatch between Mg and Ti, the as-deposited metallic multilayers show good
structural coherence. Upon exposure to H2 gas a two-step hydrogenation process
occurs, with the Ti layers forming the hydride before Mg. From in-situ
measurements of the bilayer thickness L at different hydrogen pressures, we
observe large out-of-plane expansions of the Mg and Ti layers upon
hydrogenation, indicating strong plastic deformations in the films and a
consequent shortening of the coherence length. Upon unloading at room
temperature in air, hydrogen atoms remain trapped in the Ti layers due to
kinetic constraints. Such loading/unloading sequence can be explained in terms
of the different thermodynamic properties of hydrogen in Mg and Ti, as shown by
diffusion calculations on a model multilayered systems. Absorption isotherms
measured by hydrogenography can be interpreted as a result of the elastic
clamping arising from strongly bonded Mg/Pd and broken Mg/Ti interfaces
The Decay of Magnetic Fields in Kaluza-Klein Theory
Magnetic fields in five-dimensional Kaluza-Klein theory compactified on a
circle correspond to ``twisted'' identifications of five dimensional Minkowski
space. We show that a five dimensional generalisation of the Kerr solution can
be analytically continued to construct an instanton that gives rise to two
possible decay modes of a magnetic field. One decay mode is the generalisation
of the ``bubble decay" of the Kaluza-Klein vacuum described by Witten. The
other decay mode, rarer for weak fields, corresponds in four dimensions to the
creation of monopole-anti-monopole pairs. An instanton for the latter process
is already known and is given by the analytic continuation of the \KK\ Ernst
metric, which we show is identical to the five dimensional Kerr solution. We
use this fact to illuminate further properties of the decay process. It appears
that fundamental fermions can eliminate the bubble decay of the magnetic field,
while allowing the pair production of Kaluza-Klein monopoles.Comment: 25 pages, one figure. The discussion of fermions has been revised: We
show how fundamental fermions can eliminate the bubble-type instability but
still allow pair creation of monopole
Nonadiabatic Pauli susceptibility in fullerene compounds
Pauli paramagnetic susceptibility is unaffected by the electron-phonon
interaction in the Migdal-Eliashberg context. Fullerene compounds however do
not fulfill the adiabatic assumption of Migdal's theorem and nonadiabatic
effects are expected to be relevant in these materials. In this paper we
investigate the Pauli spin susceptibility in nonadiabatic regime by following a
conserving approach based on Ward's identity. We find that a sizable
renormalization of due to electron-phonon coupling appears when
nonadiabatic effects are taken into account. The intrinsic dependence of
on the electron-phonon interaction gives rise to a finite and negative isotope
effect which could be experimentally detected in fullerides. In addition, we
find an enhancement of the spin susceptibility with temperature increasing, in
agreement with the temperature dependence of observed in fullerene
compounds. The role of electronic correlation is also discussed.Comment: Revtex, 10 pages, 8 figures include
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