2,920 research outputs found
Structural Invariance and the Energy Spectrum
We extend the application of the concept of structural invariance to bounded
time independent systems. This concept, previously introduced by two of us to
argue that the connection between random matrix theory and quantum systems with
a chaotic classical counterpart is in fact largely exact in the semiclassical
limit, is extended to the energy spectra of bounded time independent systems.
We proceed by showing that the results obtained previously for the
quasi-energies and eigenphases of the S-matrix can be extended to the
eigenphases of the quantum Poincare map which is unitary in the semiclassical
limit. We then show that its eigenphases in the chaotic case move rather
stiffly around the unit circle and thus their local statistical fluctuations
transfer to the energy spectrum via Bogomolny's prescription. We verify our
results by studying numerically the properties of the eigenphases of the
quantum Poincare map for billiards by using the boundary integral method.Comment: 10 pages, 5 figure
Urbanizaciones cerradas y transformaciones socioespaciales en Metepec, Estado de México
En los últimos tiempos, nuevas formas de urbanización específicamente,la urbanización cerrada están rompiendo con la manera tradicional de entender el crecimiento urbano, los modelos urbanísticos, la traza, el sentido del espacio público, entre otros factores. El propósito de este trabajo es explicar lo que se entiende por urbanización cerrada y, en un caso concreto, examinar cómo dicha modalidad ha transformado los componentes socioespaciales del municipio de Metepec (México). Dicha transformación se puede identificar por la extendida presencia de conjuntos urbanos que definen y redefinen la imagen urbana en Metepec. Las urbanizaciones cerradas modifican lo que tradicionalmente se había entendido como calle, rompen su continuidad y, por ende, su movilidad, además de instalar atmósferas de miedo en esos espacios sociales. Tales aspectos son analizados de manera detallada en las diferentes secciones del documento
Revan-degree indices on random graphs
Given a simple connected non-directed graph , we consider two
families of graph invariants:
(which has gained interest recently) and (that we introduce in this work); where denotes the edge of
connecting the vertices and , is the Revan degree of the
vertex , and is a function of the Revan vertex degrees. Here, with and the maximum and minimum
degrees among the vertices of and is the degree of the vertex .
Particularly, we apply both and R on two models of
random graphs: Erd\"os-R\'enyi graphs and random geometric graphs. By a
thorough computational study we show that \left and
\left, normalized to the order of the graph, scale
with the average Revan degree \left; here \left
denotes the average over an ensemble of random graphs. Moreover, we provide
analytical expressions for several graph invariants of both families in the
dense graph limit.Comment: 16 pages, 10 figure
In vitro Study of the Survival, Reproduction and Morphology of Daphnia pulicaria irradiated with a Low Energy Laser
Daphnia is a genus of crustaceans that is representative of freshwater communities. The species exhibit a high sensitivity to a wide range of toxic compounds so that they have been used internationally as biomonitors in toxicity tests to evaluate ecosystem conditions such as water quality. It is also a model genus in genetics, epigenetics and reproductive ecology. In this work, we used Daphnia pulicaria as a model to measure the effects of low-energy laser irradiation on survival, reproduction, and morphology variables of parental organisms and their offspring. We used (1) a single clone line of organisms to eliminate interindividual genetic variability; (2) individuals from more than 50 generations after the clone line was established, and offspring from the third brood onwards to dissipate maternal and epigenetic effects, and (3) neonates, those individuals of the species that have less than 48 hours of life, because they are the most sensitive stage to optical stimuli. We analyzed number of deaths, longevity, age at first reproduction, number of offspring per week, number of total offspring during all their life cycle, body size, size of the antennules, and length of the apical spine of the 4th and 5th brood of the irradiated individuals, who were exposed to a blue laser stimulus of 405 nm for 25 minutes with a power of 40 mW at a distance of 50 cm, compared to those of the control (non-irradiated) group
Imprints of galaxy evolution on H ii regions Memory of the past uncovered by the CALIFA survey
H ii regions in galaxies are the sites of star formation and thus particular
places to understand the build-up of stellar mass in the universe. The line
ratios of this ionized gas are frequently used to characterize the ionization
conditions. We use the Hii regions catalogue from the CALIFA survey (~5000 H ii
regions), to explore their distribution across the classical [OIII]/Hbeta vs.
[NII]/Halpha diagnostic diagram, and how it depends on the oxygen abundance,
ionization parameter, electron density, and dust attenuation. We compared the
line ratios with predictions from photoionization models. Finally, we explore
the dependences on the properties of the host galaxies, the location within
those galaxies and the properties of the underlying stellar population. We
found that the location within the BPT diagrams is not totally predicted by
photoionization models. Indeed, it depends on the properties of the host
galaxies, their galactocentric distances and the properties of the underlying
stellar population. These results indicate that although H ii regions are short
lived events, they are affected by the total underlying stellar population. One
may say that H ii regions keep a memory of the stellar evolution and chemical
enrichment that have left an imprint on the both the ionizing stellar
population and the ionized gasComment: 18 pages, 8 figures, accepted for publishing in A&
The effects of spatial resolution on Integral Field Spectrograph surveys at different redshifts. The CALIFA perspective
Over the past decade, 3D optical spectroscopy has become the preferred tool
for understanding the properties of galaxies and is now increasingly used to
carry out galaxy surveys. Low redshift surveys include SAURON, DiskMass,
ATLAS3D, PINGS and VENGA. At redshifts above 0.7, surveys such as MASSIV, SINS,
GLACE, and IMAGES have targeted the most luminous galaxies to study mainly
their kinematic properties. The on-going CALIFA survey () is the
first of a series of upcoming Integral Field Spectroscopy (IFS) surveys with
large samples representative of the entire population of galaxies. Others
include SAMI and MaNGA at lower redshift and the upcoming KMOS surveys at
higher redshift. Given the importance of spatial scales in IFS surveys, the
study of the effects of spatial resolution on the recovered parameters becomes
important. We explore the capability of the CALIFA survey and a hypothetical
higher redshift survey to reproduce the properties of a sample of objects
observed with better spatial resolution at lower redshift. Using a sample of
PINGS galaxies, we simulate observations at different redshifts. We then study
the behaviour of different parameters as the spatial resolution degrades with
increasing redshift.Comment: 20 pages, 16 figures. Accepted for publication in A&
Stellar Population gradients in galaxy discs from the CALIFA survey
While studies of gas-phase metallicity gradients in disc galaxies are common,
very little has been done in the acquisition of stellar abundance gradients in
the same regions. We present here a comparative study of the stellar
metallicity and age distributions in a sample of 62 nearly face-on, spiral
galaxies with and without bars, using data from the CALIFA survey. We measure
the slopes of the gradients and study their relation with other properties of
the galaxies. We find that the mean stellar age and metallicity gradients in
the disc are shallow and negative. Furthermore, when normalized to the
effective radius of the disc, the slope of the stellar population gradients
does not correlate with the mass or with the morphological type of the
galaxies. Contrary to this, the values of both age and metallicity at 2.5
scale-lengths correlate with the central velocity dispersion in a similar
manner to the central values of the bulges, although bulges show, on average,
older ages and higher metallicities than the discs. One of the goals of the
present paper is to test the theoretical prediction that non-linear coupling
between the bar and the spiral arms is an efficient mechanism for producing
radial migrations across significant distances within discs. The process of
radial migration should flatten the stellar metallicity gradient with time and,
therefore, we would expect flatter stellar metallicity gradients in barred
galaxies. However, we do not find any difference in the metallicity or age
gradients in galaxies with without bars. We discuss possible scenarios that can
lead to this absence of difference.Comment: 24 pages, 17 figures, accepted for publication in A&
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