3,564 research outputs found
Inventory and new records of Polychaete species from the Cap Bon peninsula , North East coast of Tunisia, Western Mediterranean Sea
An inventory of polychaete species is presented from the north-east coast of Tunisia with an historic review of the previous literature from Tunisian coasts. Altogether 40 families, 146 genera, and 238 species are currently known from the area, of which 86 taxa, 4 families (Chrysopetalidae, Pilargidae, Protodrilidae and Saccocirridae) and 40 genera (Saccocirrus, Protodrilus, Parathelepus, Thelepus, Petta, Isolda, Brada, Tharyx, Paraprionospio, Jasmineira, Hypsicomus, Euchone, Pseudobranchiomma, Laonome, Galathowenia, Lugia, Pseudomystides, Protomystides, Pirakia, Mysta, Eurysyllis, Parapionosyllis, Streptosyllis, Paraehlersia, Sigambra,
Ancistrosyllis, Kefersteinia, Chrysopetalum, Bhawania, Fimbriosthenelais, Subadyte, Panthalis, Dorvillea, Scalibregma, Paradoneis, Cirrophorus, Metasychis, Websterinereis, Euniphysa and Mastobranchus) are new additions to the polychaete fauna of Tunisia. The list, which provides a synthesis of the regional taxonomic work, including coastal areas from Sidi Daoud to the area of Menzel Hurr (Cap Bon Peninsula, Western Mediterranean Sea), can serve as a baseline for future studies
Tunneling, self-trapping and manipulation of higher modes of a BEC in a double well
We consider an atomic Bose-Einstein condensate trapped in a symmetric
one-dimensional double well potential in the four-mode approximation and show
that the semiclassical dynamics of the two ground state modes can be strongly
influenced by a macroscopic occupation of the two excited modes. In particular,
the addition of the two excited modes already unveils features related to the
effect of dissipation on the condensate. In general, we find a rich dynamics
that includes Rabi oscillations, a mixed Josephson-Rabi regime, self-trapping,
chaotic behavior, and the existence of fixed points. We investigate how the
dynamics of the atoms in the excited modes can be manipulated by controlling
the atomic populations of the ground states.Comment: 12 pages, 5 figure
The deformation complex is a homotopy invariant of a homotopy algebra
To a homotopy algebra one may associate its deformation complex, which is
naturally a differential graded Lie algebra. We show that infinity
quasi-isomorphic homotopy algebras have L-infinity quasi-isomorphic deformation
complexes by an explicit construction.Comment: A revised version. The final version will appear in the volume
"Current Developments and Retrospectives in Lie Theory
Structure and orientation of small particles of platinum deposited on NaCl and mica
The structure of small platinum particles condensed in vacuum onto NaCl (001), NaCl (111) and mica substrates was studied by electron diffraction and electron microscopy. Results show that above a certain substrate temperature decahedral or icosahedral particles are formed. These particles are practically absent with substrates cleaved in high vacuum. They are always much less numerous than in gold films prepared under the same conditions. Assumptions made to explain this phenomenon are: (1) the initial growth of an abnormal structure of the nuclei as opposed by the substrate; (2) the particles disappear before they attain a size which corresponds to the observations; and (3) the particles result from a coalescence mechanism leading to multiple twinned particles
Quicksort with unreliable comparisons: a probabilistic analysis
We provide a probabilistic analysis of the output of Quicksort when
comparisons can err.Comment: 29 pages, 3 figure
Irradiation du petit bassin et fonction ano-rectale.
peer reviewedLe traitement adjuvant des cancers du rectum a pour buts
de stériliser la maladie résiduelle infra-clinique et
d’améliorer le contrôle local. Depuis plus de 20 ans, des
milliers de malades ont été inclus dans des études randomisées,
visant d’abord à mettre en évidence un gain de survie et une
réduction des récidives loco-régionales, en relation avec la
radiothérapie pré- ou postopératoire, combinée ou non à la
chimiothérapie. Les conséquences en termes de qualité de vie de
ces traitements ont pourtant été peu étudiées, et la tolérance
fonctionnelle du néo-rectum et de l’appareil sphinctérien à la
radiothérapie restent mal connues [1]. Les difficultés liées à
l’étude des effets de l’irradiation sur les tissus normaux, ainsi que
la variabilité inter-individuelle de la réponse à la radiothérapie,
s’ajoutent et rendent le sujet plus complexe encore.
Les radiothérapeutes adaptent leur technique afin de réduire
autant que possible la dose administrée aux tissus normaux
avoisinant la tumeur. Dans le cas de l’irradiation du petit bassin,
c’est l’intestin grêle qui a longtemps été considéré comme la
structure à risque de complications, alors que l’atteinte du
sphincter anal était rarement mentionnée [2]. Malgré les répercussions
importantes de la dysfonction ano-rectale sur la qualité
de vie des malades, l’atteinte du sphincter anal par la radiothérapie
est restée un aspect négligé du traitement adjuvant des
cancers du petit bassin [3]. Cet article a pour but, à travers une
revue de la littérature, de mettre en évidence les effets qualitatifs
et quantitatifs de la radiothérapie sur la fonction du sphincter
anal, ainsi que de proposer une modification de la technique
actuelle d’irradiation des cancers du bas rectum
Search for surface magnetic fields in Mira stars. First detection in chi Cyg
In order to complete the knowledge of the magnetic field and of its influence
during the transition from Asymptotic Giant Branch to Planetary Nebulae stages,
we have undertaken a search for magnetic fields at the surface of Mira stars.
We used spectropolarimetric observations, collected with the Narval instrument
at TBL, in order to detect - with Least Squares Deconvolution method - a Zeeman
signature in the visible part of the spectrum. We present the first
spectropolarimetric observations of the S-type Mira star chi Cyg, performed
around its maximum light. We have detected a polarimetric signal in the Stokes
V spectra and we have established its Zeeman origin. We claim that it is likely
to be related to a weak magnetic field present at the photospheric level and in
the lower part of the stellar atmosphere. We have estimated the strength of its
longitudinal component to about 2-3 Gauss. This result favors a 1/r law for the
variation of the magnetic field strength across the circumstellar envelope of
chi Cyg. This is the first detection of a weak magnetic field at the stellar
surface of a Mira star and we discuss its origin in the framework of shock
waves periodically propagating throughout the atmosphere of these radially
pulsating stars. At the date of our observations of chi Cyg, the shock wave
reaches its maximum intensity, and it is likely that the shock amplifies a weak
stellar magnetic field during its passage through the atmosphere. Without such
an amplification by the shock, the magnetic field strength would have been too
low to be detected. For the first time, we also report strong Stokes Q and U
signatures (linear polarization) centered onto the zero velocity (i.e., at the
shock front position). They seem to indicate that the radial direction would be
favored by the shock during its propagation throughout the atmosphere.Comment: 9 pages, 4 figures accepted by Astronomy and Astrophysics (21
November 2013
Investigating changes in basal conditions of Variegated Glacier prior to and during its 1982–1983 surge
Variegated Glacier (Alaska) is known to surge periodically after a sufficient amount of cumulative mass balance is reached, but this observation is difficult to link with changes in the basal conditions. Here, using a 10-yr dataset, consisting of surface topography and surface velocity observations along a flow line for 25 dates, we have reconstructed the evolution of the basal conditions prior to and during the 1982–1983 surge. The model solves the full-Stokes problem along the central flow line using the finite element method. For the 25 dates of the dataset, the basal friction parameter distribution is inferred using the inverse method proposed by Arthern and Gudmundsson (2010). This method is here slightly modified by incorporating a regularisation term in the cost function to avoid short wavelength changes in the friction parameter. Our results indicate that dramatic changes in the basal conditions occurred between 1973 to 1983. Prior to the surge, periodic changes can be observed between winter and summer, with a regular increase of the sliding from 1973 to 1982. During the surge, the basal friction decreased dramatically and an area of very low friction moved from the upper part of the glacier to its terminus. Using a more complex friction law, these changes in basal sliding are then interpreted in terms of basal water pressure. Our results support that dramatic changes took place in the subglacial drainage system of Variegated Glacier, moving from a relatively efficient drainage system prior to the surge to an inefficient one during the surge. By reconstructing the water pressure evolution at the base of the glacier it is possible to propose a scenario for the hydrological history leading to the occurrence of a surge
Pressure-induced amorphization, crystal-crystal transformations and the memory glass effect in interacting particles in two dimensions
We study a model of interacting particles in two dimensions to address the
relation between crystal-crystal transformations and pressure-induced
amorphization. On increasing pressure at very low temperature, our model
undergoes a martensitic crystal-crystal transformation. The characteristics of
the resulting polycrystalline structure depend on defect density, compression
rate, and nucleation and growth barriers. We find two different limiting cases.
In one of them the martensite crystals, once nucleated, grow easily
perpendicularly to the invariant interface, and the final structure contains
large crystals of the different martensite variants. Upon decompression almost
every atom returns to its original position, and the original crystal is fully
recovered. In the second limiting case, after nucleation the growth of
martensite crystals is inhibited by energetic barriers. The final morphology in
this case is that of a polycrystal with a very small crystal size. This may be
taken to be amorphous if we have only access (as experimentally may be the
case) to the angularly averaged structure factor. However, this `X-ray
amorphous' material is anisotropic, and this shows up upon decompression, when
it recovers the original crystalline structure with an orientation correlated
with the one it had prior to compression. The memory effect of this X-ray
amorphous material is a natural consequence of the memory effect associated to
the underlying martensitic transformation. We suggest that this kind of
mechanism is present in many of the experimental observations of the memory
glass effect, in which a crystal with the original orientation is recovered
from an apparently amorphous sample when pressure is released.Comment: 13 pages, 13 figures, to be published in Phys. Rev.
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