21,179 research outputs found
Magnetocaloric effect in integrable spin-s chains
We study the magnetocaloric effect for the integrable antiferromagnetic
high-spin chain. We present an exact computation of the Gr\"uneisen parameter,
which is closely related to the magnetocaloric effect, for the quantum spin-s
chain on the thermodynamical limit by means of Bethe ansatz techniques and the
quantum transfer matrix approach. We have also calculated the entropy S and the
isentropes in the (H,T) plane. We have been able to identify the quantum
critical points H_c^{(s)}=2/(s+1/2) looking at the isentropes and/or the
characteristic behaviour of the Gr\"uneisen parameter.Comment: 6 pages, 3 figure
Theoretical investigation of moir\'e patterns in quantum images
Moir\'e patterns are produced when two periodic structures with different
spatial frequencies are superposed. The transmission of the resulting structure
gives rise to spatial beatings which are called moir\'e fringes. In classical
optics, the interest in moir\'e fringes comes from the fact that the spatial
beating given by the frequency difference gives information about details(high
spatial frequency) of a given spatial structure. We show that moir\'e fringes
can also arise in the spatial distribution of the coincidence count rate of
twin photons from the parametric down-conversion, when spatial structures with
different frequencies are placed in the path of each one of the twin beams. In
other words,we demonstrate how moir\'e fringes can arise from quantum images
Correction of artificial jumps in the historical geomagnetic measurements of Coimbra Observatory, Portugal
The Coimbra Magnetic Observatory (International Association of Geomagnetism and Aeronomy code COI) in Portugal has a long
history of observation of the geomagnetic field, spanning almost 150 yr
since the first geomagnetic measurements in 1866. These long instrumental
geomagnetic records provide very important information about variability of
geomagnetic elements and indices, their trends and cycles, and can be used
to improve our knowledge on the sources that drive variations of the
geomagnetic field: liquid core dynamics (internal) and solar forcing
(external).
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However, during the long life of the Coimbra Observatory, some inevitable
changes in station location, instrument's park and electromagnetic
environment have taken place. These changes affected the quality of the data
collected at COI causing breaks and jumps in the series of geomagnetic field
components and local K index. Clearly, these inhomogeneities, typically
shift-like (step-like) or trend-like, have to be corrected or, at least,
minimized in order for the data to be used in scientific studies or to be
submitted to international databases.
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In this study, the series of local K index and declination of the
geomagnetic field are analysed: the former because it allows direct
application of standard homogenization methods and the latter because it is
the longest continuous series produced at COI. For the homogenization,
visual and statistical tests (e.g. standard normal homogeneity test) have
been applied directly to the local geomagnetic K index series (from 1951 to
2012). The homogenization of the monthly averages of declination (from 1867
to 2012) has been done using visual analysis and statistical tests applied
to the time series of the first differences of declination values, as an
approximation to the first time derivative. This allowed not only
estimating the level of inhomogeneity of the studied series but also
detecting the highly probable homogeneity break points. These points have been
cross-checked with the metadata, and the COI series have been compared with
reference series from the nearest geomagnetic stations and, in the case of
declination series, from the recent geomagnetic field model COV-OBS to set
up the required correction factors. As a result, the homogenized series
measured in COI are considered to be essentially free of artificial shifts
starting from the second half of the 20th century, and ready to be used by
the scientific community
DNS of Laminar to Turbulent Transition on NACA 0012 Airfoil with Sand Grain Roughness
The Lattice-Boltzmann-based solver PowerFLOW is used to perform direct numerical simulations of the transitional flow over an airfoil at Reynolds number equal to 0.657 million. The leading edge of the airfoil is covered with sand particles, represented by polyhedra, to mimic the grit used in experiments. The sensitivity of the laminar to turbulent transition to the size of these particles, grid resolution, spanwise length is evaluated and rectangular trips are also tested
Spatial accessibility and social inclusion: The impact of Portugal's last health reform
Health policies seek to promote access to health care and should provide appropriate geographical accessibility to each demographical functional group. The dispersal demand of healthâcareservices and the provision for such services atfixed locations contribute to the growth of inequality intheir access. Therefore, the optimal distribution of health facilities over the space/area can lead toaccessibility improvements and to the mitigation of the social exclusion of the groups considered mostvulnerable. Requiring for such, the use of planning practices joined with accessibility measures. However,the capacities of Geographic Information Systems in determining and evaluating spatial accessibility inhealth system planning have not yet been fully exploited. This paper focuses on healthâcare services planningbased on accessibility measures grounded on the network analysis. The case study hinges on mainlandPortugal. Different scenarios were developed to measure and compare impact on the population'saccessibility. It distinguishes itself from other studies of accessibility measures by integrating network data ina spatial accessibility measure: the enhanced twoâstepfloating catchment area. The convenient location forhealthâcare facilities can increase the accessibility standards of the population and consequently reducethe economic and social costs incurred. Recently, the Portuguese government implemented a reform thataimed to improve, namely, the access and equity in meeting with the most urgent patients. It envisaged,in terms of equity, the allocation of 89 emergency network points that ensured more than 90% of thepopulation be within 30 min from any one point in the network. Consequently, several emergency serviceswere closed, namely, in rural areas. This reform highlighted the need to improve the quality of the emergencycare, accessibility to each care facility, and equity in their access. Hence, accessibility measures becomean efficient decisionâmaking tool, despite its absence in effective practice planning. According to anapplication of this type of measure, it was possible to verify which levels of accessibility were decreased,including the most disadvantaged people, with a larger time of dislocation of 12 min between 2001 and 2011
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