800 research outputs found
Identity of electrons and ionization equilibrium
It is perhaps appropriate that, in a year marking the 90th anniversary of
Meghnad Saha seminal paper (1920), new developments should call fresh attention
to the problem of ionization equilibrium in gases. Ionization equilibrium is
considered in the simplest "physical" model for an electronic subsystem of
matter in a rarefied state, consisting of one localized electronic state in
each nucleus and delocalized electronic states considered as free ones. It is
shown that, despite the qualitative agreement, there is a significant
quantitative difference from the results of applying the Saha formula to the
degree of ionization. This is caused by the fact that the Saha formula
corresponds to the "chemical" model of matter.Comment: 9 pages, 2 figure
Combined approach of density functional theory and quantum Monte Carlo method to electron correlation in dilute magnetic semiconductors
We present a realistic study for electronic and magnetic properties in dilute
magnetic semiconductor (Ga,Mn)As. A multi-orbital Haldane-Anderson model
parameterized by density-functional calculations is presented and solved with
the Hirsch-Fye quantum Monte Carlo algorithm. Results well reproduce
experimental results in the dilute limit. When the chemical potential is
located between the top of the valence band and an impurity bound state, a
long-range ferromagnetic correlations between the impurities, mediated by
antiferromagnetic impurity-host couplings, are drastically developed. We
observe an anisotropic character in local density of states at the
impurity-bound-state energy, which is consistent with the STM measurements. The
presented combined approach thus offers a firm starting point for realistic
calculations of the various family of dilute magnetic semiconductors.Comment: 5 pages, 4 figure
Regularization of the Coulomb scattering problem
Exact solutions of the Schr\"odinger equation for the Coulomb potential are
used in the scope of both stationary and time-dependent scattering theories in
order to find the parameters which define regularization of the Rutherford
cross-section when the scattering angle tends to zero but the distance r from
the center remains fixed. Angular distribution of the particles scattered in
the Coulomb field is investigated on the rather large but finite distance r
from the center. It is shown that the standard asymptotic representation of the
wave functions is not available in the case when small scattering angles are
considered. Unitary property of the scattering matrix is analyzed and the
"optical" theorem for this case is discussed. The total and transport
cross-sections for scattering of the particle by the Coulomb center proved to
be finite values and are calculated in the analytical form. It is shown that
the considered effects can be essential for the observed characteristics of the
transport processes in semiconductors which are defined by the electron and
hole scattering in the fields of the charged impurity centers.Comment: 20 pages, 6 figure
Vocabulary intervention for adolescents with language disorder: a systematic review
Background: Language disorder and associated vocabulary difficulties can persist into adolescence, and can impact on long-term life outcomes. Previous reviews have shown that a variety of intervention techniques can successfully enhance students’ vocabulary skills; however, none has investigated vocabulary intervention specifically for adolescents with language disorder.
Aims: To carry out a systematic review of the literature on vocabulary interventions for adolescents with language disorder.
Methods & Procedures: A systematic search of 14 databases and other sources yielded 1320 studies, of which 13 met inclusion criteria. Inclusion criteria were: intervention effectiveness studies with a focus on enhancing oral receptive and/or expressive vocabulary skills in the study's aims; participants in the age range 11;0–16;11 with receptive and/or expressive language difficulties of any aetiology.
Main Contribution: There was a high degree of diversity between studies. Types of intervention included: semantic intervention (four studies); comparison of phonological versus semantic intervention (two); and combined phonological–semantic intervention (seven). The strongest evidence for effectiveness was found with a combined phonological–semantic approach. The evidence suggested a potential for all models of delivery to be helpful (individual, small group and whole class).
Conclusions & Implications: Tentative evidence is emerging for the effectiveness of a phonological–semantic approach in enhancing the vocabulary skills of adolescents who have language disorder. Future research needs to refine and develop the methodologies used in this diverse group of studies in order to replicate their findings and to build consensus
Spintronics: Fundamentals and applications
Spintronics, or spin electronics, involves the study of active control and
manipulation of spin degrees of freedom in solid-state systems. This article
reviews the current status of this subject, including both recent advances and
well-established results. The primary focus is on the basic physical principles
underlying the generation of carrier spin polarization, spin dynamics, and
spin-polarized transport in semiconductors and metals. Spin transport differs
from charge transport in that spin is a nonconserved quantity in solids due to
spin-orbit and hyperfine coupling. The authors discuss in detail spin
decoherence mechanisms in metals and semiconductors. Various theories of spin
injection and spin-polarized transport are applied to hybrid structures
relevant to spin-based devices and fundamental studies of materials properties.
Experimental work is reviewed with the emphasis on projected applications, in
which external electric and magnetic fields and illumination by light will be
used to control spin and charge dynamics to create new functionalities not
feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes
from the published versio
CaB_6: a new semiconducting material for spin electronics
Ferromagnetism was recently observed at unexpectedly high temperatures in
La-doped CaB_6. The starting point of all theoretical proposals to explain this
observation is a semimetallic electronic structure calculated for CaB_6 within
the local density approximation. Here we report the results of parameter-free
quasiparticle calculations of the single-particle excitation spectrum which
show that CaB_6 is not a semimetal but a semiconductor with a band gap of 0.8
eV. Magnetism in La_xCa_{1-x}B_6 occurs just on the metallic side of a Mott
transition in the La-induced impurity band.Comment: 4 pages, 1 postscript figur
You turn me cold: evidence for temperature contagion
Introduction
During social interactions, our own physiological responses influence those of others. Synchronization of physiological (and behavioural) responses can facilitate emotional understanding and group coherence through inter-subjectivity. Here we investigate if observing cues indicating a change in another's body temperature results in a corresponding temperature change in the observer.
Methods
Thirty-six healthy participants (age; 22.9±3.1 yrs) each observed, then rated, eight purpose-made videos (3 min duration) that depicted actors with either their right or left hand in visibly warm (warm videos) or cold water (cold videos). Four control videos with the actors' hand in front of the water were also shown. Temperature of participant observers' right and left hands was concurrently measured using a thermistor within a Wheatstone bridge with a theoretical temperature sensitivity of <0.0001°C. Temperature data were analysed in a repeated measures ANOVA (temperature × actor's hand × observer's hand).
Results
Participants rated the videos showing hands immersed in cold water as being significantly cooler than hands immersed in warm water, F(1,34) = 256.67, p0.1). There was however no evidence of left-right mirroring of these temperature effects p>0.1). Sensitivity to temperature contagion was also predicted by inter-individual differences in self-report empathy.
Conclusions
We illustrate physiological contagion of temperature in healthy individuals, suggesting that empathetic understanding for primary low-level physiological challenges (as well as more complex emotions) are grounded in somatic simulation
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The type and frequency of interactions that occur between staff and children outside in Early Years Foundation Stage settings during a fixed playtime period when there are tricycles available
This study reports on an investigation into adult and child interactions observed in the outdoor play environment in four Local Authority early years foundation stage settings in England. In this instance the common two features across the settings were the presence of tricycles and a timetabled outdoor play period. In total, across the four schools, there were 204 children. The study aimed to gain an understanding of the nature of the dialogues between staff and children, that is, the types of exchange that occurred when either the child approached an adult or the adult approached a child. The most frequent type of utterance was also analysed. The study concludes that adults in these settings spoke more than children and the greatest type of utterance was that of the adult about domestic matters. When the child initiated the conversation there were more extended child utterances than domestic utterances. This may suggest that children wish to be involved in conversations of depth and meaning and that staff need to become aware of how to develop this conversational language with children
Adaptive Filtering Enhances Information Transmission in Visual Cortex
Sensory neuroscience seeks to understand how the brain encodes natural
environments. However, neural coding has largely been studied using simplified
stimuli. In order to assess whether the brain's coding strategy depend on the
stimulus ensemble, we apply a new information-theoretic method that allows
unbiased calculation of neural filters (receptive fields) from responses to
natural scenes or other complex signals with strong multipoint correlations. In
the cat primary visual cortex we compare responses to natural inputs with those
to noise inputs matched for luminance and contrast. We find that neural filters
adaptively change with the input ensemble so as to increase the information
carried by the neural response about the filtered stimulus. Adaptation affects
the spatial frequency composition of the filter, enhancing sensitivity to
under-represented frequencies in agreement with optimal encoding arguments.
Adaptation occurs over 40 s to many minutes, longer than most previously
reported forms of adaptation.Comment: 20 pages, 11 figures, includes supplementary informatio
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