988 research outputs found
Instability due to long range Coulomb interaction in a liquid of polarizable particles (polarons, etc.)
The interaction Hamiltonian for a system of polarons a la Feynman in the
presence of long range Coulomb interaction is derived and the dielectric
function is computed in mean field. For large enough concentration a liquid of
such particles becomes unstable. The onset of the instability is signaled by
the softening of a collective optical mode in which all electrons oscillate in
phase in their respective self-trapping potential. We associate the instability
with a metallization of the system. Optical experiments in slightly doped
cuprates and doped nickelates are analyzed within this theory.
We discuss why doped cuprates matallize whereas nickelates do not.Comment: 5 pages,1 figur
SDGs, Inclusive Health and the path to Universal Health Coverage. Disability and The Global South
The Sustainable Development Goals (SDGs) are a set of goals designed to improve
the social, economic and well-being of all, while maintaining global and
environmental sustainability. Health is one of the 17 goals, and focuses not only on
addressing morbidity and mortality, but also on improving access to healthcare
services for all through Universal Health Coverage (UHC). While disability is not
specifically mentioned in this goal, a focus on people with disabilities is important
given the inclusive nature of the SDGs and the fact that people with disabilities make
up the largest minority group in the world. This paper aims to critically consider what
the health goal could mean for people with disabilities and advocates for inclusive
health. It discusses the complex relationship between disability and health, and why
people with disabilities are more vulnerable to poor health are discussed, and then
considers factors that impact access to quality healthcare for people with disabilities
and how these impact on the achievement of the targets in SDG Health Goal and the
main principles of UHC. The paper argues that developing an inclusive approach to
healthcare will not only improve achieving good health for all, but is also important
since experiencing poor health may reduce quality of life and participation (e.g. in
education, employment or community activities). Poor quality of life and participation
can exacerbate disability, poverty and exclusion in addition to increasing suffering,
morbidity and early mortality. The paper concludes that an inclusive UHC will not
only fulfil the fundamental rights of people with disabilities to health and
rehabilitation, as emphasized within the UN Convention on the Rights of Persons with
Disabilities, but also contribute to the achievement of the SDGs
Endocrine correlates of male breast cancer risk: a case-control study in Athens, Greece
We studied the relation of certain endocrine-related variables among 23 cases of male breast cancer and 76 apparently healthy male controls. There were significant inverse associations with smoking (P = 0.03), birth order (P = 0.02) and reported frequency of orgasms in later life (P = 0.0004). The study provides strong indirect evidence that endocrine factors are important in the aetiology of male breast cancer. © 2000 Cancer Research Campaig
Tilting instability and other anomalies in the flux-lattice in some magnetic superconductors
The flux-line lattice in the compound , which has a tendency to
ferromagnetic order in the a-b plane is studied with external magnetic field
direction close to the c-axis. We show the existence of an instability where
the direction of flux-lines spontaneously tilts away from that of the applied
field near the onset of ferromagnetic order. The enhanced fluctuations in the
flux lattice and the square flux lattice recently observed are explained and
further experiments suggested.Comment: 12 pages, Latex file, no figur
Quantum Simulations of Extended Hubbard Models with Dipolar Crystals
In this paper we study the realization of lattice models in mixtures of
atomic and dipolar molecular quantum gases. We consider a situation where polar
molecules form a self-assembled dipolar lattice, in which atoms or molecules of
a second species can move and scatter. We describe the system dynamics in a
master equation approach in the Brownian motion limit of slow particles and
fast phonons, which we find appropriate for our system. In a wide regime of
parameters, the reduced dynamics of the particles leads to physical
realizations of extended Hubbard models with tuneable long-range interactions
mediated by crystal phonons. This extends the notion of quantum simulation of
strongly correlated systems with cold atoms and molecules to include
phonon-dynamics, where all coupling parameters can be controlled by external
fields.Comment: 44 pages, 14 figure
Absence of Meissner State and Robust Ferromagnetism in the Superconducting State of UCoGe: Possible Evidence of Spontaneous Vortex State
We report ac magnetic susceptibility and dc magnetization measurements on the
superconducting ferromagnet UCoGe (with superconducting and Curie temperatures
of ~K and ~K, respectively).
In the normal, ferromagnetic state (), the
magnetization curve exhibits a hysteresis loop similar to that of a regular
itinerant ferromagnet. Upon lowering the temperature below , the
spontaneous magnetization is unchanged, but the hysteresis is markedly
enhanced. Even deeply inside the superconducting state, ferromagnetism is not
completely shielded, and there is no Meissner region, a magnetic field region
of (a lower critical field). From these results, we suggest
that UCoGe is the first material in which ferromagnetism robustly survives in
the superconducting state and a spontaneous vortex state without the Meissner
state is realized.Comment: 5 pages, 4 figures, to be published in J. Phys. Soc. Jp
LOFAR tied-array imaging and spectroscopy of solar S bursts
Context. The Sun is an active source of radio emission that is often associated with energetic phenomena ranging from nanoflares to coronal mass ejections (CMEs). At low radio frequencies (<100 MHz), numerous millisecond duration radio bursts have been reported, such as radio spikes or solar S bursts (where S stands for short). To date, these have neither been studied extensively nor imaged because of the instrumental limitations of previous radio telescopes.
Aims. Here, LOw Frequency ARray (LOFAR) observations were used to study the spectral and spatial characteristics of a multitude of S bursts, as well as their origin and possible emission mechanisms.
Methods. We used 170 simultaneous tied-array beams for spectroscopy and imaging of S bursts. Since S bursts have short timescales and fine frequency structures, high cadence (~50 ms) tied-array images were used instead of standard interferometric imaging, that is currently limited to one image per second.
Results. On 9 July 2013, over 3000 S bursts were observed over a time period of ~8 h. S bursts were found to appear as groups of short-lived (<1 s) and narrow-bandwidth (~2.5 MHz) features, the majority drifting at ~3.5 MHzâs-1 and a wide range of circular polarisation degrees (2â8 times more polarised than the accompanying Type III bursts). Extrapolation of the photospheric magnetic field using the potential field source surface (PFSS) model suggests that S bursts are associated with a trans-equatorial loop system that connects an active region in the southern hemisphere to a bipolar region of plage in the northern hemisphere.
Conclusions. We have identified polarised, short-lived solar radio bursts that have never been imaged before. They are observed at a height and frequency range where plasma emission is the dominant emission mechanism, however, they possess some of the characteristics of electron-cyclotron maser emission
Prevalence, Causes and Socio-Economic Determinants of Vision Loss in Cape Town, South Africa
PURPOSE: To estimate the prevalence and causes of blindness and visual impairment in Cape Town, South Africa and to explore socio-economic and demographic predictors of vision loss in this setting. METHODS: A cross sectional population-based survey was conducted in Cape Town. Eighty-two clusters were selected using probability proportionate to size sampling. Within each cluster 35 or 40 people aged 50 years and above were selected using compact segment sampling. Visual acuity of participants was assessed and eyes with a visual acuity less than 6/18 were examined by an ophthalmologist to determine the cause of vision loss. Demographic data (age, gender and education) were collected and a socio-economic status (SES) index was created using principal components analysis. RESULTS: Out of 3100 eligible people, 2750 (89%) were examined. The sample prevalence of bilateral blindness (presenting visual acuity <3/60) was 1.4% (95% CI 0.9-1.8). Posterior segment diseases accounted for 65% of blindness and cataract was responsible for 27%. The prevalence of vision loss was highest among people over 80 years (odds ratio (OR) 6.9 95% CI 4.6-10.6), those in the poorest SES group (OR 3.9 95% CI 2.2-6.7) and people with no formal education (OR 5.4 95% CI 1.7-16.6). Cataract surgical coverage was 68% in the poorest SES tertile (68%) compared to 93% in the medium and 100% in the highest tertile. CONCLUSIONS: The prevalence of blindness among people â„50 years in Cape Town was lower than expected and the contribution of posterior segment diseases higher than previously reported in South Africa and Sub Saharan Africa. There were clear socio-economic disparities in prevalence of vision loss and cataract surgical coverage in this setting which need to be addressed in blindness prevention programs
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