1,199 research outputs found
El sistema deposicional del Golfo de León
El sistema deposicional del Golfo de León presenta una plataforma constituida por varios prismas epicontinentales, un talud y unascenso continental entallados por numerosos cañones, y dos cuerpos deposicionales profundos de gran importancia: el abanico del Ródano y el «Acúmulo de los Cañones Pirenaicos)). Las evaporitas messinienses han jugado un papel determinante en la evolución morfo-sedimentaria de este sistema durante el Plio-Cuaternario
Fine structure of the 0.7 MeV resonance in the 230Th neutron--induced cross section
The fine structure of the 0.7 MeV resonance in the 230Th neutron-induced
cross section is investigated within the hybrid model. A very good agreement
with experimental data is obtained. It is suggested that fine structure of the
cross section quantify the changes of the intrinsic states of the nucleus
during the disintegration process.Comment: 7 pages, 5 figure
Dénombrements directs des bactéries des milieux aquatiques par microscopie en épifluorescence : comparaison entre un système d'analyse d'images automatisé (Mudicam®) et l'observation visuelle
La technique de comptage par microscopie en épitluorescence est la méthode la plus performante pour dénombrer la totalité des bactéries présentes dans les milieux aquatiques. Cependant cette technique est longue, fastidieuse et subjective. Afin d'automatiser et de rendre objectif le dénombrement, le microscope à épifluorescence est couplé à un analyseur d'images. Si les systèmes d'analyse d'images sont utilisés pour les mesures de taille des bactéries aquatiques, très peu d'études font état de comparaison entre les dénombrements par analyse d'image et ceux réalisés de façon traditionnelle. Cet article présente les résultats des dénombrements de souches bactériennes de référence et de bactéries des milieux aquatiques, par la technique de microscopie en épifluorescence des cellules bactériennes marquées au DAPI, réalisés simultanément par observation microscopique visuelle (visuel) et par analyse d'images automatisée (automatique).Le système d'analyse d'images est composé d'une caméra vidéo (Lhesa LH40036) de sensibilité de 510-4 lux, d'une carte de numérisation (512 x 512 pixels, 8 bits, cyclope v 2.32, Digital vision) d'un micro-ordinateur 80-386 et d'un logiciel de dénombrement (Mudicam®. EAU). Le système est couplé à un microscope en épilluorescence Olympus BH2.Les dénombrements ont été réalisés d'une part sur des suspensions de souches bactériennes de référence (n = 30) à différents états physiologiques et sur des échantillons d'eaux (n = 50) d'origines diverses (fleuve, eaux saumâtre, marine et résiduaire). La comparaison des deux méthodes est réalisée par un modèle de régression linéaire et une analyse de variance. Les tests statistiques associés permettent de conclure à une bonne concordance entre les deux méthodes. A partir de l'ensemble des dénombrements réalisés, 18 d'entre eux pris au hasard ont été dénombrés de façon manuelle par deux opérateurs et par le système d'analyse d'image. Il apparaît que les différences de comptage les plus élevées correspondent aux dénombrements effectués par chacun des deux opérateurs. Ceci met en évidence que non seulement le système d'analyse d'image permet une quantification rapide des abondances bactériennes, mais en outre il supprime la subjectivité de l'opérateur tout en réalisant des dénombrements aussi précis.Direct counting by epifluorescence microscopy is the best method available to determine total counts of aquatic bacteria. However, microscopic observation is tedious and time-consuming. A more rapid and certainly less subjective way of counting bacteria is to combine epifluorescence microscopy with an image analysis system. Surprisingly, although image analysis is now a relatively common method to measure the size of aquatic bacteria, very few studies have been devoted to the validation of total counts by image-analysis systems. In this paper, we present data on simultaneous determination of total counts of 4'6-diamidino-2-phenylindole (DAPI) stained bacteria by visual means and by image-analysed (Mudicam® system) epifluorescence microscopy methods.The Olympus microscope BH2 is equipped for epifluorescence with a 100 W Hg lamp and a 100x oil immersion objective (Apo UVFL 160/1.3). The image analysis system consists et a high performance (5 x 10-4 lux) video camera (Lhesa LH40036) and an image processor which digitalizes the video image in a grey scale extending from 0 (black) to 255 (white) into a binary image with 512 x 512 pixels (8 bit, cyclope v 2.32, Digital Vision), and image analysis software (MUDICAM®. EAU). The samples were stained with DAPI (final concentration 2.5 µg/ml) and filtered through polycarbonate inters (0.22µm, Nuclepore Corporation). The surface area of the video image is 76 x 111 µm2.The analysed samples come from culture collections of different bacterial strains (n = 30) submitted to different conditions and incubation times to obtain various physiological states (Table 1). The nature water samples were collected from several aquatic ecosystems : Rhône river, Mediterranean sea, Thau lagoon and Montpellier sewage waters (n = 50). The bacterial abundances ranged from 105 to 108 cells/ml and the size range of the cells varied from 0.63 to 17 µm2. Comparisons between the image analysis and visual counts were made on the basic of thirty fields per filter. The image analysis counts are based on a two step procedure. The video image of each microscopie field is first numerised and stored on a hard disk (153 Mo). When all the fields have been stored, the digitized images are submitted to an automatic thresholding which allows background substraction. Automatic counting of bacterial cells is then performed on the basis of object specifications defined by the operator. These specifications concern the minima and maxima values of the area (expressed in pixel numbers) and the fluorescence (expressed in gray levels) of the objects. The MUDICAM®EAU software also provides the mean number of cells per millilitre and the associated variance.Average concentrations and confidence limits are shown in Table 2 for bacterial collection strain cultures and in Table 3 for water samples. When we compared visual and image analysis counts by- linear regression, the ability of the image analysis system to enumerate bacterial cells was clearly demonstrated. With bacterial culture (Fig. 2) and with water samples (Fig. 3), the coefficients of correlation were respectively r = 0.997 and r = 0.996 (p = 0.0001). The slopes of the models are not significantly different from unity and the Y-intercepts are not different from zero. Moreover we have compared the total visual counts of two experimenters and the image-analysed counts on eighteen random samples (Table 4). The variance analysis shows that there is no difference between the three methods, with mean value of 6.09, 6.08 and 6.11 for the image-analysed method, experimenter n° 1 and experimenter n° 2, respectively. While non significant, the greatest difference in counts was obtained between the two experimenters.If may be concluded that the image analyser tested for total counts by epifluorescence microscopy is a precise and rapid procedure for the determination of total bacterial counts. This method may be standardized and its automation allows the analysis of many samples, an important advantage in ecological studies. Storage of the samples also allows one to treat a posteriori some complementary aspects of the total count, such as the double staining of bacteria. The image analyser tested is appropriate for bacterial ecology studies which require epifluorescence microscopy
Utilisation du bouillon sélénite F modifié pour dénombrer Salmonella dans les milieux aquatiques
Ce travail a pour objet de présenter une nouvelle méthode de dénombrement des Salmonella dans différents types d'eaux (de rivière, saumâtre, eaux usées brutes et épurées) basée sur l'utilisation d'un milieu d'enrichissement au sélénite additionné de Novobiocine et de Pril et sur une adaptation de la technique du N.P.P. à l'ensemencement d'échantillons de grands volumes après filtration permettant de quantifier les très faibles concentrations de Salmonella. Les vérifications des performances de cette méthode d'isolement et de quantification sont basées sur l'étude des croissances de différentes souches de Salmonella et d'autres espèces bactériennes dans le milieu d'enrichissement modifié, ainsi que sur les résultats quantitatifs et qualitatifs fournis par cette méthode lorsqu'elle est appliquée à des échantillons d'eau en provenance de l'environnement aquatique. Ces résultats montrent notamment que la méthode proposée est suffisamment sensible pour détecter 1 à 2 Salmonella dans 10 litres d'eau analysée et qu'elle ne parait pas exclure de sérotypes, du moins parmi ceux les plus fréquemment isolés en France. L'efficacité de la méthode standardisée API Z pour l'identification enzymatique du genre Salmonella a été également testée en référence aux résultats de la sérotypie.This paper presents a new method for enumerating Salmonellae in environmental waters (freshwater, brackishwater, sewage and treated waters) using the F Selenite enrichment broth modified by the addition of Novobiocin and Pril, and an adaptation of the M.P.N. method for the inoculation of large amounts of water after filtration to improve the enumeration of low concentrations of Salmonellae. The verification of the performance of this detection and enumeration method are based on the study of the growth of different Salmonellae species and of others bacterial species in the modified enrichment broth, and on the quantitative and qualitative results obtained by the application of this methodology to aquatic environmental samples. These results show on one hand, that the sensitivity of the proposed method allows to enumerate 1 to 2 Salmonellae in 10 liter samples, and on the other hand that this method to net exclude any serovar from those which are the most frequently isolated in France. The efficiency of the API Z standardized method for the Salmonellae enzymatic identification versus serological identification was also verified
Threshold Resonant Structure of the 232Th Neutron-Induced Fission Cross Section
The structures observed in the sub-threshold neutron-induced fission of
^{232}Th were investigated employing a recent developed model. Theoretical
single-particle excitations of a phenomenological two-humped barrier are
determined by solving a system of coupled differential equations for the motion
along the optimal fission path. A rather good agreement with experimental data
was obtained using a small number of independent parameters. It is predicted
that the structure at 1.4 and 1.6 MeV is mainly dominated by spin 3/2 partial
cross-section with small admixture of spin 1/2, while the structure at 1.7 MeV
is given by a large partial cross section of spin 5/2.Comment: 17 pages 11 figure
Production of cold fragments in nucleus-nucleus collisions in the Fermi-energy domain
The reaction mechanism of nucleus-nucleus collisions at projectile energies
around the Fermi energy is investigated with emphasis on the production of
fragmentation-like residues. The results of simulations are compared to
experimental mass distributions of elements with Z = 21 - 29 observed in the
reactions 86Kr+124,112Sn at 25 AMeV. The model of incomplete fusion is modified
and a component of excitation energy of the cold fragment dependent on isospin
asymmetry is introduced. The modifications in the model of incomplete fusion
appear consistent with both overall model framework and available experimental
data. A prediction is provided for the production of very neutron-rich nuclei
using a secondary beam of 132Sn where e.g. the reaction 132Sn+238U at 28 AMeV
appears as a possible alternative to the use of fragmentation reactions at
higher energies.Comment: LaTeX, 15 pages, 5 figures, minor modifications, accepted for
publication in Nuclear Physics
Isotopic and velocity distributions of Bi produced in charge-pickup reactions of 208Pb at 1 A GeV
Isotopically resolved cross sections and velocity distributions have been
measured in charge-pickup reactions of 1 A GeV 208Pb with proton, deuterium and
titanium target. The total and partial charge-pickup cross sections in the
reactions 208Pb + 1H and 208Pb + 2H are measured to be the same in the limits
of the error bars. A weak increase in the total charge-pickup cross section is
seen in the reaction of 208Pb with the titanium target. The measured velocity
distributions show different contributions - quasi-elastic scattering and
Delta-resonance excitation - to the charge-pickup production. Data on total and
partial charge-pickup cross sections from these three reactions are compared
with other existing data and also with model calculations based on the coupling
of different intra-nuclear cascade codes and an evaporation code.Comment: 20 pages, 12 figures, background information on
http://www-w2k.gsi.de/kschmidt
Heavy Residue Isoscaling as a Probe of the Process of N/Z Equilibration
The isotopic and isobaric scaling behavior of the yield ratios of heavy
projectile residues from the collisions of 25 MeV/nucleon 86Kr projectiles on
124Sn and 112Sn targets is investigated and shown to provide information on the
process of N/Z equilibration occurring between the projectile and the target.
The logarithmic slopes and of the residue yield ratios
with respect to residue neutron number N and neutron excess N--Z are obtained
as a function of the atomic number Z and mass number A, respectively, whereas
excitation energies are deduced from velocities. The relation of the isoscaling
parameters and with the N/Z of the primary (excited)
projectile fragments is employed to gain access to the degree of N/Z
equilibration prior to fragmentation as a function of excitation energy. A
monotonic relation between the N/Z difference of fragmenting quasiprojectiles
and their excitation energy is obtained indicating that N/Z equilibrium is
approached at the highest observed excitation energies. Simulations with a
deep-inelastic transfer model are in overall agreement with the isoscaling
conclusions. The present residue isoscaling approach to N/Z equilibration
offers an attractive tool of isospin and reaction dynamics studies in
collisions involving beams of stable or rare isotopes.Comment: 15 pages, 4 figures, submitted to Phys. Lett.
Production mechanism of hot nuclei in violent collisions in the Fermi energy domain
A production mechanism of highly excited nuclei formed in violent collisions
in the Fermi energy domain is investigated. The collision of two nuclei is
decomposed into several stages which are treated separately. Simplified exciton
concept is used for the description of pre-equilibrium emission. A modified
spectator-participant scenario is used where motion along classical Coulomb
trajectories is assumed. The participant and one of the spectator zones undergo
incomplete fusion. Excitation energies of both cold and hot fragment are
determined. Results of the calculation are compared to recent experimental data
in the Fermi energy domain. Data on hot projectile-like, mid-velocity and
fusion-like sources are described consistently. Geometric aspects of
pre-equilibrium emission are revealed. Explanations to previously unexplained
experimental phenomena are given. Energy deposited into non-thermal degrees of
freedom is estimated.Comment: To appear in Nuclear Physics A, 27 pages, 19 figures, LaTe
Production of medium-mass neutron-rich nuclei in reactions induced by 136Xe projectiles at 1 A GeV on a beryllium target
Production cross sections of medium-mass neutron-rich nuclei obtained in the
fragmentation of 136Xe projectiles at 1 A GeV have been measured with the
FRagment Separator (FRS) at GSI. 125Pd was identified for the first time. The
measured cross sections are compared to 238U fission yields and model
calculations in order to determine the optimum reaction mechanism to extend the
limits of the chart of the nuclides around the r-process waiting point at N=82.Comment: 9 pages, 6 figure
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