8,392 research outputs found
On coherent systems of type (n,d,n+1) on Petri curves
We study coherent systems of type on a Petri curve of genus
. We describe the geometry of the moduli space of such coherent systems
for large values of the parameter . We determine the top critical value
of and show that the corresponding ``flip'' has positive codimension.
We investigate also the non-emptiness of the moduli space for smaller values of
, proving in many cases that the condition for non-emptiness is the
same as for large . We give some detailed results for and
applications to higher rank Brill-Noether theory and the stability of kernels
of evaluation maps, thus proving Butler's conjecture in some cases in which it
was not previously known.Comment: 33 page
Shapes of clusters and groups of galaxies: Comparison of model predictions with observations
We study the properties of the 3-dimensional and projected shapes of haloes
using high resolution numerical simulations and observational data where the
latter comes from the 2PIGG (Eke et al. 2004) and SDSS-DR3GC group catalogues
(Merchan & Zandivarez 2005). We investigate the dependence of halo shape on
characteristics such as mass and number of members. In the 3-dimensional case,
we find a significant correlation between the mass and halo shape; massive
systems are more prolate than small haloes. We detect a source of strong
systematics in estimates of the triaxiality of a halo, which is found to be a
strong function of the number of members; LCDM haloes usually characterised by
triaxial shapes, slightly bent toward prolate forms, appear more oblate when
taking only a small subset of the halo particles. The ellipticities of observed
2PIGG and SDSS-DR3GC groups are found to be strongly dependent on the number of
group members, so that poor groups appear more elongated than rich ones.
However, this is again an artifact caused by poor statistics and not an
intrinsic property of the galaxy groups, nor an effect from observational
biases. We interpret these results with the aid of a GALFORM mock 2PIGG
catalogue. When comparing the group ellipticities in mock and real catalogues,
we find an excellent agreement between the trends of shapes with number of
group members. When carefully taking into account the effects of low number
statistics, we find that more massive groups are consistent with more elongated
shapes. Finally, our studies find no significant correlations between the shape
of observed 2PIGG or SDSS-DR3GC groups with the properties of galaxy members
such as colour or spectral type index.Comment: 9 pages, 10 figures, submitted to MNRA
Analysis Of The Cyclability Of Lithium-polymer Batteries
Comunicación y póster en congresoLithium ion batteries and similar energy storage devices have an increasing importance for the modern society as they are present in many portable electronic devices and have perspectives in the fields of electric vehicles and renewable energy accumulation.
Herein, we present results from charge and discharge cycles on batteries under controlled conditions. The cyclability of commercial lithium-polymer pouch batteries under different charge/discharge rates and temperatures was studied. Based on the results, the relationship between the state of charge and the cell voltage was obtained, as well as degradation of the cells, i.e., the decrease of the energy capacity after a number of cycles.
The experimental results were compared with simulations based on Newman's model for Lithium Ion Batteries, carried out using the COMSOL Multiphysics® software. The batteries and fuel cell and the heat transfer modules were use to couple between the temperature and the electrochemical interactions. The results show the correlation between temperature, C-rate and degradation in lithium ion batteries. It is specially remarkable the decrease of the apparent capacity of batteries at low temperatures, and the increase of the degradation at higher temperatures. These results are essential for the design of mechanisms that could prevent battery failure.The authors acknowledge the financial support from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 778045, and the "Plan Propio de Investigación y Transferencia de la Universidad de Málaga", code: PPIT.UMA.B5.2018/17
Square vortex solitons with a large angular momentum
We show the existence of square shaped optical vortices with a large value of
the angular momentum hosted in finite size laser beams which propagate in
nonlinear media with a cubic-quintic nonlinearity. The light profiles take the
form of rings with sharp boundaries and variable sizes depending on the power
carried. Our stability analysis shows that these light distributions remain
stable when propagate, probably for unlimited values of the angular momentum,
provided the hosting beam is wide enough. This happens if the peak amplitude
approaches a critical value which only depends on the nonlinear refractive
index of the material. A variational approach allows us to calculate the main
parameters involved. Our results add extra support to the concept of surface
tension of light beams that can be considered as a trace of the existence of a
liquid of light.Comment: 6 pages, 6 figures, submitted to Phys. Rev.
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Synthesis, structural characterisation and thermoelectric properties of Bi1−xPbxOCuSe
The effect of Pb2+ doping on the structure and thermoelectric properties of BiOCuSe (also known as BiCuSeO or BiCuOSe) is described. With increasing Pb2+ content, the expansion of the unit cell results in a weakening of the bonding between the [Bi2(1-x) Pb2xO2]2(1-x)+ and the [Cu2Se2]2(1-x)- layers. The electrical resistivity and Seebeck coefficient decrease in a systematic way with growing Pb2+ levels. The thermal conductivity rises due to the increase of the electronic contribution with doping. The power factor of materials with a 4-5% Pb2+ content takes values of ca. 8 W cm-1 K-2 over a wide temperature range. ZT at 673 K is enhanced by ca. 50% when compared to values found for other dopants, such as Sr2+ or Mg2+
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