542 research outputs found
Network of social groups or Let's have a party
We present a simple model for growing up and depletion of parties due to the
permanent communication between the participants of the events. Because of the
rapid exchange of information, everybody is able to evaluate its own and and
all other parties by means of the list of its friends. Therefore the number of
participants at different parties can be changed incessantly. Depending on the
deepness of the social contacts, which will be characterized by a parameter
, a stable distribution of party members emerges. At a critical
an abrupt depletion of almost all parties is observed and as the
consequence all the peoples are assembled at a single party. The model is based
on a hierarchical social network. The probability that a certain person is
contacted to another one depends on the social distance introduced within the
network and homophily parameter .Comment: 15 pages, 6 figure
Absolute rate coefficients for photorecombination of berylliumlike and boronlike silicon ions
We report measured rate coefficients for electron-ion recombination for Si10+
forming Si9+ and for Si9+ forming Si8+, respectively. The measurements were
performed using the electron-ion merged-beams technique at a heavy-ion storage
ring. Electron-ion collision energies ranged from 0 to 50 eV for Si9+ and from
0 to 2000 eV for Si10+, thus, extending previous measurements for Si10+ [Orban
et al. 2010, Astrophys. J. 721, 1603] to much higher energies. Experimentally
derived rate coefficients for the recombination of Si9+ and Si10+ ions in a
plasma are presented along with simple parameterizations. These rate
coefficients are useful for the modeling of the charge balance of silicon in
photoionized plasmas (Si9+ and Si10+) and in collisionally ionized plasmas
(Si10+ only). In the corresponding temperature ranges, the experimentally
derived rate coefficients agree with the latest corresponding theoretical
results within the experimental uncertainties.Comment: 17 pages, 7 figures, 3 tables, 66 references, submitted to the J.
Phys. B special issue on atomic and molecular data for astrophysicist
Dielectronic Recombination of Fe XV forming Fe XIV: Laboratory Measurements and Theoretical Calculations
We have measured resonance strengths and energies for dielectronic
recombination (DR) of Mg-like Fe XV forming Al-like Fe XIV via N=3 -> N' = 3
core excitations in the electron-ion collision energy range 0-45 eV. All
measurements were carried out using the heavy-ion Test Storage Ring at the Max
Planck Institute for Nuclear Physics in Heidelberg, Germany. We have also
carried out new multiconfiguration Breit-Pauli (MCBP) calculations using the
AUTOSTRUCTURE code. For electron-ion collision energies < 25 eV we find poor
agreement between our experimental and theoretical resonance energies and
strengths. From 25 to 42 eV we find good agreement between the two for
resonance energies. But in this energy range the theoretical resonance
strengths are ~ 31% larger than the experimental results. This is larger than
our estimated total experimental uncertainty in this energy range of +/- 26%
(at a 90% confidence level). Above 42 eV the difference in the shape between
the calculated and measured 3s3p(^1P_1)nl DR series limit we attribute partly
to the nl dependence of the detection probabilities of high Rydberg states in
the experiment. We have used our measurements, supplemented by our
AUTOSTRUCTURE calculations, to produce a Maxwellian-averaged 3 -> 3 DR rate
coefficient for Fe XV forming Fe XIV. The resulting rate coefficient is
estimated to be accurate to better than +/- 29% (at a 90% confidence level) for
k_BT_e > 1 eV. At temperatures of k_BT_e ~ 2.5-15 eV, where Fe XV is predicted
to form in photoionized plasmas, significant discrepancies are found between
our experimentally-derived rate coefficient and previously published
theoretical results. Our new MCBP plasma rate coefficient is 19-28% smaller
than our experimental results over this temperature range
Dielectronic Recombination in Photoionized Gas. II. Laboratory Measurements for Fe XVIII and Fe XIX
In photoionized gases with cosmic abundances, dielectronic recombination (DR)
proceeds primarily via nlj --> nl'j' core excitations (Dn=0 DR). We have
measured the resonance strengths and energies for Fe XVIII to Fe XVII and Fe
XIX to Fe XVIII Dn=0 DR. Using our measurements, we have calculated the Fe
XVIII and Fe XIX Dn=0 DR DR rate coefficients. Significant discrepancies exist
between our inferred rates and those of published calculations. These
calculations overestimate the DR rates by factors of ~2 or underestimate it by
factors of ~2 to orders of magnitude, but none are in good agreement with our
results. Almost all published DR rates for modeling cosmic plasmas are computed
using the same theoretical techniques as the above-mentioned calculations.
Hence, our measurements call into question all theoretical Dn=0 DR rates used
for ionization balance calculations of cosmic plasmas. At temperatures where
the Fe XVIII and Fe XIX fractional abundances are predicted to peak in
photoionized gases of cosmic abundances, the theoretical rates underestimate
the Fe XVIII DR rate by a factor of ~2 and overestimate the Fe XIX DR rate by a
factor of ~1.6. We have carried out new multiconfiguration Dirac-Fock and
multiconfiguration Breit-Pauli calculations which agree with our measured
resonance strengths and rate coefficients to within typically better than
<~30%. We provide a fit to our inferred rate coefficients for use in plasma
modeling. Using our DR measurements, we infer a factor of ~2 error in the Fe XX
through Fe XXIV Dn=0 DR rates. We investigate the effects of this estimated
error for the well-known thermal instability of photoionized gas. We find that
errors in these rates cannot remove the instability, but they do dramatically
affect the range in parameter space over which it forms.Comment: To appear in ApJS, 44 pages with 13 figures, AASTeX with postsript
figure
Técnica microquirúrgica de anastomosis vascular sin sutura en el trasplante experimental de órganos
Las anastomosis vasculares para e! trasplante de órganos en pequeños animales se realizan habitualmente por sutura manual ya sea continua o discontinua, aunque en los últimos años se ha difundido una técnica sin sutura consistente en la utilización de «cuffs». En e! presente trabajo se describe la técnica de! cuff que nuestro equipo utilizó para la realización de las anastomosis vasculares en e! trasplante experimental de órganos. El cuff consta de un tubo o cuerpo, que se prolonga por una pestaña, y su tamaño es diferente según el calibre del vaso que se pretende anastornosar. Entre las ventajas que ofrece su utilización respecto de la sutura manual, destacan su sencillo aprendizaje, bajo coste y el reducido tiempo en que se realizan las anastomosis, que siempre son estancas. Se concluye que esta técnica constituye una alternativa a las ya clásicas técnicas de sutura manual y no aumenta al porcentaje de complicaciones, permitiendo además supervivencias a largo plazo en los modelos experimentales que fueron estudiados.Vascular anastornoses in organ transplants of small anirnals are usually performed with a manual suture using interrupted or continuous stitcbes, although over the last few years a suturefree technique has been deueloped consisting of the use of cuffs. In this paper, the cuff technique which our team used to perform vascular anastomoses in experimental organ transplants, is described. The cuff is made up oi a tube or body wich has a prolongation or up, tbe size varying according to the calibre of the blood vessel to be anastomosed. The advantages of this method in cornparison with manual sutures, is the ease with which the tecbnique is learnt, its low cost, and the speed with which the anastomoses are carried out, all of which are watertight. In conclusion, this technique constitutes an alternative to the classical manual suture techniques without increasing the percentage of cornplications, and allowing long-term suruiual rates in the experimental models studied
Necropulpectomía : tratamiento conservador en necrosis pulpar de un canino en un pastor alemán
En este trabajo se pone en práctica la endodoncia en la especie canina, aplicada a una lesión traumática dental a nivel de un canino en un perro de adiestramiento. La terapéutica se realiza en dos fases: provisional y definitiva; en ambos casos encaminadas hacia el tratamiento conservador de la pieza. Se describe la técnica utilizada para la necropulpectomía y posterior obturación con amalgama de plata de la cavidad pulpar.An endodoncy was practiced to trained dog that had had a traumatic injury affecting a canine tooth. The therapy was carried out in two phases: provisional and definitive. In both cases the purpose was to preserve the tooth. The applied technique for necropulpectomy and following filling of the pulp cavity whit silver amalgam is described
Electron-ion recombination measurements motivated by AGN X-ray absorption features: Fe XIV forming Fe XIII
Recent spectroscopic models of active galactic nuclei (AGN) have indicated
that the recommended electron-ion recombination rate coefficients for iron ions
with partially filled M-shells are incorrect in the temperature range where
these ions form in photoionized plasmas. We have investigated this
experimentally for Fe XIV forming Fe XIII. The recombination rate coefficient
was measured employing the electron-ion merged beams method at the Heidelberg
heavy-ion storage-ring TSR. The measured energy range of 0-260 eV encompassed
all dielectronic recombination (DR) 1s2 2s2 2p6 3l 3l' 3l'' nl''' resonances
associated with the 3p1/2 -> 3p3/2, 3s -> 3p, 3p -> 3d and 3s -> 3d core
excitations within the M-shell of the Fe XIV 1s2 2s2 2p6 3s2 3p parent ion.
This range also includes the 1s2 2s2 2p6 3l 3l' 4l'' nl''' resonances
associated with 3s -> 4l'' and 3p -> 4l'' core excitations. We find that in the
temperature range 2--14 eV, where Fe XIV is expected to form in a photoionized
plasma, the Fe XIV recombination rate coefficient is orders of magnitude larger
than previously calculated values.Comment: 4 pages, 4 figures, 1 table submitted to Ap
Isotope shift in the dielectronic recombination of three-electron ^{A}Nd^{57+}
Isotope shifts in dielectronic recombination spectra were studied for Li-like
^{A}Nd^{57+} ions with A=142 and A=150. From the displacement of resonance
positions energy shifts \delta E^{142,150}(2s-2p_1/2)= 40.2(3)(6) meV
(stat)(sys)) and \delta E^{142,150}(2s-2p_3/2) = 42.3(12)(20) meV of 2s-2p_j
transitions were deduced. An evaluation of these values within a full QED
treatment yields a change in the mean-square charge radius of ^{142,150}\delta
= -1.36(1)(3) fm^2. The approach is conceptually new and combines the
advantage of a simple atomic structure with high sensitivity to nuclear size.Comment: 10 pages, 3 figures, accepted for publication in Physical Review
Letter
Recommended from our members
Electron-ion recombination measurements of Fe7+, Fe8+, Fe13+ motivated by active galactic nuclei x-ray absorption features
Recent spectroscopic models of active galactic nuclei have indicated that the recommended electron-ion recombination rate coefficients for iron ions with partially filled Mshells are incorrect in the temperature range where these ions form in photoionized plasmas. We have investigated this experimentally for Fe7+ forming Fe6+, Fe8+ forming Fe7+, and Fe13+ forming Fe12+. The recombination rate coefficient was measured employing the electron-ion merged beams method at the Heidelberg heavy-ion storage-ring TSR. The measured energy range encompassed at least all dielectronic recombination (DR) resonances associated with core excitations within the M-shell of the parent ions. Already in our first measurement, that is for Fe13+, we find unusually strong DR resonances at low electron-ion collision energies leading to low temperature plasma DR rate coefficients orders of magnitude larger than the recommended rate coefficien
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