2,293 research outputs found
Map4rdf - Faceted Browser for Geospatial Datasets
Recently we have seen a large increase in the amount of geospatial data that is being published using RDF and Linked Data principles. Eorts such as the W3C Geo XG, and most recently the GeoSPARQL initiative are providing the necessary vocabularies to pub- lish this kind of information on the Web of Data. In this context it is necessary to develop applications that consume and take advantage of these geospatial datasets. In this paper we present map4rdf, a faceted browsing tool for exploring and visualizing RDF datasets enhanced with geospatial information
Latent solitons, black strings, black branes, and equations of state in Kaluza-Klein models
In Kaluza-Klein models with an arbitrary number of toroidal internal spaces,
we investigate soliton solutions which describe the gravitational field of a
massive compact object. We single out the physically interesting solution
corresponding to a point-like mass. For the general solution we obtain
equations of state in the external and internal spaces. These equations
demonstrate that the point-like mass soliton has dust-like equations of state
in all spaces. We also obtain the PPN parameters, which give the possibility to
obtain the formulas for perihelion shift, deflection of light and time delay of
radar echoes. Additionally, the gravitational experiments lead to a strong
restriction on the parameter of the model: . The point-like mass solution contradicts this restriction. The
condition satisfies the experimental limitation and defines a new
class of solutions which are indistinguishable from general relativity. We call
such solutions latent solitons. Black strings and black branes belong to this
class. Moreover, the condition of stability of the internal spaces singles out
black strings/branes from the latent solitons and leads uniquely to the black
string/brane equations of state , in the internal spaces and
to the number of the external dimensions . The investigation of
multidimensional static spherically symmetric perfect fluid with dust-like
equation of state in the external space confirms the above results.Comment: 8 pages, Revtex4, no figures, minor changes adde
Kaluza-Klein models: can we construct a viable example?
In Kaluza-Klein models, we investigate soliton solutions of Einstein
equation. We obtain the formulas for perihelion shift, deflection of light,
time delay of radar echoes and PPN parameters. We find that the solitonic
parameter k should be very big: |k|\geq 2.3\times10^4. We define a soliton
solution which corresponds to a point-like mass source. In this case the
soliton parameter k=2, which is clearly contrary to this restriction. Similar
problem with the observations takes place for static spherically symmetric
perfect fluid with the dust-like equation of state in all dimensions. The
common for both of these models is the same equations of state in our three
dimensions and in the extra dimensions. All dimensions are treated at equal
footing. To be in agreement with observations, it is necessary to break the
symmetry between the external/our and internal spaces. It takes place for black
strings which are particular examples of solitons with k\to \infty. For such k,
black strings are in concordance with the observations. Moreover, we show that
they are the only solitons which are at the same level of agreement with the
observations as in general relativity. Black strings can be treated as perfect
fluid with dust-like equation of state p_0=0 in the external/our space and very
specific equation of state p_1=-(1/2)\epsilon in the internal space. The latter
equation is due to negative tension in the extra dimension. We also demonstrate
that dimension 3 for the external space is a special one. Only in this case we
get the latter equation of state. We show that the black string equations of
state satisfy the necessary condition of the internal space stabilization.
Therefore, black strings are good candidates for a viable model of
astrophysical objects (e.g., Sun) if we can provide a satisfactory explanation
of negative tension for particles constituting these objects.Comment: 11 pages, Revtex4, no figures, appendix and references adde
Orientational properties of nematic disclinations
Topological defects play a pivotal role in the physics of liquid crystals and
represent one of the most prominent and well studied aspects of mesophases.
While in two-dimensional nematics, disclinations are traditionally treated as
point-like objects, recent experimental studies on active nematics have
suggested that half-strength disclinations might in fact possess a polar
structure. In this article, we provide a precise definition of polarity for
half-strength nematic disclinations, we introduce a simple and robust method to
calculate this quantity from experimental and numerical data and we investigate
how the orientational properties of half-strength disclinations affect their
relaxational dynamics.Comment: 6 pages, 5 figures, supplementary movies at
http://wwwhome.lorentz.leidenuniv.nl/~giomi/sup_mat/20150720
Multiphoton Discrete Fractional Fourier Dynamics in Waveguide Beam Splitters
We demonstrate that when a waveguide beam splitter (BS) is excited by N
indistinguishable photons, the arising multiphoton states evolve in a way as if
they were coupled to each other with coupling strengths that are identical to
the ones exhibited by a discrete fractional Fourier system. Based on the
properties of the discrete fractional Fourier transform, we then derive a
multiphoton suppression law for 50/50 BSs, thereby generalizing the
Hong-Ou-Mandel effect. Furthermore, we examine the possibility of performing
simultaneous multiphoton quantum random walks by using a single waveguide BS in
combination with photon number resolving detectors. We anticipate that the
multiphoton lattice-like structures unveiled in this work will be useful to
identify new effects and applications of high-dimensional multiphoton states.Comment: Accepted for publication in JOSA B on June 26, 201
Parallel model exploration for tumor treatment simulations
Abstract Computational systems and methods are often being used in biological research, including the understanding of cancer and the development of treatments. Simulations of tumor growth and its response to different drugs are of particular importance, but also challenging complexity. The main challenges are first to calibrate the simulators so as to reproduce real-world cases, and second, to search for specific values of the parameter space concerning effective drug treatments. In this work, we combine a multi-scale simulator for tumor cell growth and a genetic algorithm (GA) as a heuristic search method for finding good parameter configurations in reasonable time. The two modules are integrated into a single workflow that can be executed in parallel on high performance computing infrastructures. In effect, the GA is used to calibrate the simulator, and then to explore different drug delivery schemes. Among these schemes, we aim to find those that minimize tumor cell size and the probability of emergence of drug resistant cells in the future. Experimental results illustrate the effectiveness and computational efficiency of the approach.This work has received funding from the EU Horizon 2020 RIA program INFORE under grant agreement No
825070Peer ReviewedPostprint (author's final draft
Volumetric analysis of the piriform cortex in temporal lobe epilepsy
The piriform cortex, at the confluence of the temporal and frontal lobes, generates seizures in response to chemical convulsants and electrical stimulation. Resection of more than 50% of the piriform cortex in anterior temporal lobe resection for refractory temporal lobe epilepsy (TLE) was associated with a 16-fold higher chance of seizure freedom. The objectives of the current study were to implement a robust protocol to measure piriform cortex volumes and to quantify the correlation of these volumes with clinical characteristics of TLE. Sixty individuals with unilateral TLE (33 left) and 20 healthy controls had volumetric analysis of left and right piriform cortex and hippocampi. A protocol for segmenting and measuring the volumes of the piriform cortices was implemented, with good inter-rater and test-retest reliability. The right piriform cortex volume was consistently larger than the left piriform cortex in both healthy controls and patients with TLE. In controls, the mean volume of the right piriform cortex was 17.7% larger than the left, and the right piriform cortex extended a mean of 6 mm (Range: -4 to 12) more anteriorly than the left. This asymmetry was also seen in left and right TLE. In TLE patients overall, the piriform cortices were not significantly smaller than in controls. Hippocampal sclerosis was associated with decreased ipsilateral and contralateral piriform cortex volumes. The piriform cortex volumes, both ipsilateral and contralateral to the epileptic temporal lobe, were smaller with a longer duration of epilepsy. There was no significant association between piriform cortex volumes and the frequency of focal seizures with impaired awareness or the number of anti-seizure medications taken. Implementation of robust segmentation will enable consistent neurosurgical resection in anterior temporal lobe surgery for refractory TLE.
Molecular Gas in Infrared Ultraluminous QSO Hosts
We report CO detections in 17 out of 19 infrared ultraluminous QSO (IR QSO)
hosts observed with the IRAM 30m telescope. The cold molecular gas reservoir in
these objects is in a range of 0.2--2.1 (adopting a
CO-to- conversion factor ). We find that the molecular gas properties of IR QSOs,
such as the molecular gas mass, star formation efficiency () and the CO (1-0) line widths, are indistinguishable
from those of local ultraluminous infrared galaxies (ULIRGs). A comparison of
low- and high-redshift CO detected QSOs reveals a tight correlation between
L and for all QSOs. This suggests that,
similar to ULIRGs, the far-infrared emissions of all QSOs are mainly from dust
heated by star formation rather than by active galactic nuclei (AGNs),
confirming similar findings from mid-infrared spectroscopic observations by
{\it Spitzer}. A correlation between the AGN-associated bolometric luminosities
and the CO line luminosities suggests that star formation and AGNs draw from
the same reservoir of gas and there is a link between star formation on
kpc scale and the central black hole accretion process on much smaller scales.Comment: 30 pages, 9 figures, accepted for publication in The Astrophysical
Journa
Bounce and cyclic cosmology in extended nonlinear massive gravity
We investigate non-singular bounce and cyclic cosmological evolutions in a
universe governed by the extended nonlinear massive gravity, in which the
graviton mass is promoted to a scalar-field potential. The extra freedom of the
theory can lead to certain energy conditions violations and drive cyclicity
with two different mechanisms: either with a suitably chosen scalar-field
potential under a given Stuckelberg-scalar function, or with a suitably chosen
Stuckelberg-scalar function under a given scalar-field potential. Our analysis
shows that extended nonlinear massive gravity can alter significantly the
evolution of the universe at both early and late times.Comment: 20 pages, 5 figures, version published at JCA
Current Challenges for the Early Detection of Alzheimer's Disease: Brain Imaging and CSF Studies
The development of prevention therapies for Alzheimer's disease (AD) would greatly benefit from biomarkers that are sensitive to the subtle brain changes that occur in the preclinical stage of the disease. Reductions in the cerebral metabolic rate of glucose (CMRglc), a measure of neuronal function, have proven to be a promising tool in the early diagnosis of AD. In vivo brain 2-[18F]fluoro-2-Deoxy-D-glucose-positron emission tomography (FDG-PET) imaging demonstrates consistent and progressive CMRglc reductions in AD patients, the extent and topography of which correlate with symptom severity. There is increasing evidence that hypometabolism appears during the preclinical stages of AD and can predict decline years before the onset of symptoms. This review will give an overview of FDG-PET results in individuals at risk for developing dementia, including: presymptomatic individuals carrying mutations responsible for early-onset familial AD; patients with Mild Cognitive Impairment (MCI), often a prodrome to late-onset sporadic AD; non-demented carriers of the Apolipoprotein E (ApoE) ε4 allele, a strong genetic risk factor for late-onset AD; cognitively normal subjects with a family history of AD; subjects with subjective memory complaints; and normal elderly followed longitudinally until they expressed the clinical symptoms and received post-mortem confirmation of AD. Finally, we will discuss the potential to combine different PET tracers and CSF markers of pathology to improve the early detection of AD
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