1,074 research outputs found
Carbon and oxygen isotopic composition of the Middle Miocene Badenian gypsum-associated limestones of West Ukraine
The middle Miocene Badenian basin of the Carpathian Foredeep is characterized by complex sedimentary and diagenetic carbonate-evaporite transitions. Six locations have been selected to evaluate the controls on the carbon and oxygen isotopic composition of the Badenian gypsum-associated limestones of the Tyras Formation in West Ukraine. At three locations marine limestones overlie the gypsum, at one location (Anadoly) the gypsum-associated limestones are polygenic, and at two localities (Pyshchatyntsi and Lozyna) gypsum deposits are lacking. The studied limestones have originated as primary, mostly peloidal carbonates as well as secondary carbonates formed by hypogene sulphate calcitisation. They show a wide range of d13C (from from -0.9‰ to -39.8‰) and d18O values (from 0.9‰ to -12.2‰). The Badenian limestones formed in marine environments (either as deposits accumulated at the bottom of the sea or forming the infillings of solution cavities within gypsum) have less negative d18O values compared to predominantly diagenetic formations. Wide ranges and usually very negative d13C values and low d18O values of those limestones indicate that they suffered important meteoric diagenesis as supported by common sparitic fabrics. In addition, a large range of d13C values even in the group of samples characterized by less-negative d18O values shows that bacterial sulphate reduction and methane oxidation were active processes in the pore fluids of the Tyras Formation. Very low carbon isotopic compositions (d13C values from -22 to -40‰) of some sparitic limestones in the studied sections indicate the occurrence of oxidized methane within the diagenetic environment. Accordingly, the isotopic signatures of the studied limestones are a combination of both primary and secondary processes, the latter having a primordial importance. The common occurrence of similar negative d13C and d18O values in evaporite-related carbonates in other Miocene evaporite basins suggest that extensive dissolution- reprecipitation in diagenetic or vadose-phreatic environments were common in evaporite-related carbonates
Variaciones espaciales y temporales del registro del límite K/T en Haiti: implicaciones acerca del evento o eventos
El registro en la capa del límite K/T (KTB), en diferentes localidades de la Península Meridional de Haití, muestra claras evidencias de disrupciones físicas causadas por el impacto postulado de un bólico al final del Maastrichtiense. Tanto el registro bioestratigráfico como el litológico de la capa KTB, en diferentes localidades, muestra también diversos grados de mezcla, con componentes faunísticos de edades congruentes con los bioeventos característicos de la transición del límite, equivalentes a la parte terminal de la Zona de Abathomphalus mayaroensis y partes de las Zonas de Guembelitria cretacea y de Parvularugoglobigerina eugubina. La nanoflora calcárea también muestra taxones de la transición, concurrentes con los datos de foraminíferos, e indicativos de las Subzonas de Micula murus y Micula prinsii, así como de la Subzona de Cruciplacolithus primus (CP1a), del Paleoceno basal. La capa del límite tiene variaciones en su potencia, con un máximo de 75cm en el estratotipo de la Formación Beloc, y a techo de la capa principal tectítica hay un máximo de iridio. Los análisis geoquímicos y la datación radiométrica han demostrado también que las esférulas son tectitas (Premo e Izett, 1991) que pueden estar relacionadas cronológicamente con el evento de impacto registrado en Chicxulub, Yucatán, México, hace 65 Ma. Aún más, las delicadas estructuras sedimentarias primarias en la capa del límite son constantes en todos los afloramientos, aunque hay diferencias espaciales incluso a corta distancia. Además, en las áreas adyacentes al estratotipo (Platon Piton y Madame Toussaint) se encuentra una capa volcanogénica, bajo el nivel tectítico principal relacionado con el evento de Chicxulub, que muestra una laminación cruzada, tanto conspicua como críptica, indicativa de procesos de flujo complejos, multifásicos y subacuáticos que afectaron a la sedimentación de forma parecida a la del lecho KTB. Se conocen tales estructuras como características de la acción de ondas oscilantes sobre la cohesión de los sedimentos. El movimiento de las aguas asociado con un seiche es el único análogo actual conocido de un flujo subacuático que proporcione un mecanismo plausible para explicar el que varios niveles de la columna de agua, en una gran cuenca, pueden oscilar para desarrollar las estructuras observadas. Dada la magnitud del impacto del bólido, debieron desarrollarse ‘megaseiches’ en los océanos a escala mundial y, subsecuéntemente, se producirían otros ‘megaseiches’ más localizados durante los reajustes principales de la corteza. Esos fenómenos pueden así explicar la heterogeneidad de pautas y discrepancias faunísticas observadas en varias localidades del KTB, de distinta profundidad de depósito, en el mundo. Las estructuras representan un registro de los movimientos del agua y de la resuspensión de los sedimentos en momentos diferentes. Tal como se ha observado en seiches modernos a pequeña escala, la duración y atenuación de los movimientos del agua y la magnitud de la tracción y resuspensión estuvieron controlados por diversos modos oscilatorios que dieron lugar a complejas estructuras sedimentarias y al retrabajamiento de los microfósiles
The STAR Silicon Strip Detector (SSD)
The STAR Silicon Strip Detector (SSD) completes the three layers of the
Silicon Vertex Tracker (SVT) to make an inner tracking system located inside
the Time Projection Chamber (TPC). This additional fourth layer provides two
dimensional hit position and energy loss measurements for charged particles,
improving the extrapolation of TPC tracks through SVT hits. To match the high
multiplicity of central Au+Au collisions at RHIC the double sided silicon strip
technology was chosen which makes the SSD a half million channels detector.
Dedicated electronics have been designed for both readout and control. Also a
novel technique of bonding, the Tape Automated Bonding (TAB), was used to
fullfill the large number of bounds to be done. All aspects of the SSD are
shortly described here and test performances of produced detection modules as
well as simulated results on hit reconstruction are given.Comment: 11 pages, 8 figures, 1 tabl
Phase-space dependence of particle-ratio fluctuations in Pb+Pb collisions from 20A to 158A GeV beam energy
A novel approach, the identity method, was used for particle identification
and the study of fluctuations of particle yield ratios in Pb+Pb collisions at
the CERN Super Proton Synchrotron (SPS). This procedure allows to unfold the
moments of the unknown multiplicity distributions of protons (p), kaons (K),
pions () and electrons (e). Using these moments the excitation function of
the fluctuation measure [A,B] was measured, with A and
B denoting different particle types. The obtained energy dependence of
agrees with previously published NA49 results on the related
measure . Moreover, was found to depend
on the phase space coverage for [K,p] and [K,] pairs. This feature most
likely explains the reported differences between measurements of NA49 and those
of STAR in central Au+Au collisions
Centrality dependence of proton and antiproton spectra in Pb+Pb collisions at 40A GeV and 158A GeV measured at the CERN SPS
The yields of (anti-)protons were measured by the NA49 Collaboration in
centrality selected Pb+Pb collisions at 40A GeV and 158A GeV. Particle
identification was obtained in the laboratory momentum range from 5 to 63 GeV/c
by the measurement of the energy loss dE/dx in the TPC detector gas. The
corresponding rapidity coverage extends 1.6 units from mid-rapidity into the
forward hemisphere. Transverse mass spectra, the rapidity dependences of the
average transverse mass, and rapidity density distributions were studied as a
function of collision centrality. The values of the average transverse mass as
well as the midrapidity yields of protons when normalized to the number of
wounded nucleons show only modest centrality dependences. In contrast, the
shape of the rapidity distribution changes significantly with collision
centrality, especially at 40A GeV. The experimental results are compared to
calculations of the HSD and UrQMD transport models.Comment: 25 pages, 12 figures, submitted to PR
Energy dependence of kaon-to-proton ratio fluctuations in central Pb+Pb collisions from = 6.3 to 17.3 GeV
Kaons and protons carry large parts of two conserved quantities, strangeness
and baryon number. It is argued that their correlation and thus also
fluctuations are sensitive to conditions prevailing at the anticipated
parton-hadron phase boundary. Fluctuations of the and
ratios have been measured for the first time by NA49 in central Pb+Pb
collisions at 5 SPS energies between = 6.3 GeV and 17.3 GeV.
Both ratios exhibit a change of sign in , a measure of
non-statistical fluctuations, around = 8 GeV. Below this
energy, is positive, indicating higher fluctuation
compared to a mixed event background sample, while for higher energies,
is negative, indicating correlated emission of kaons
and protons. The results are compared to UrQMD calculations which which give a
good description at the higher SPS energies, but fail to reproduce the
transition to positive values.Comment: 5 pages, 4 figure
Measurement of Production Properties of Positively Charged Kaons in Proton-Carbon Interactions at 31 GeV/c
Spectra of positively charged kaons in p+C interactions at 31 GeV/c were
measured with the NA61/SHINE spectrometer at the CERN SPS. The analysis is
based on the full set of data collected in 2007 with a graphite target with a
thickness of 4% of a nuclear interaction length. Interaction cross sections and
charged pion spectra were already measured using the same set of data. These
new measurements in combination with the published ones are required to improve
predictions of the neutrino flux for the T2K long baseline neutrino oscillation
experiment in Japan. In particular, the knowledge of kaon production is crucial
for precisely predicting the intrinsic electron neutrino component and the high
energy tail of the T2K beam. The results are presented as a function of
laboratory momentum in 2 intervals of the laboratory polar angle covering the
range from 20 up to 240 mrad. The kaon spectra are compared with predictions of
several hadron production models. Using the published pion results and the new
kaon data, the K+/\pi+ ratios are computed.Comment: 10 pages, 11 figure
Proton -- Lambda Correlations in Central Pb+Pb Collisions at sqrt(s_{NN}) = 17.3 GeV
The momentum correlation between protons and lambda particles emitted from
central Pb+Pb collisions at sqrt(s_{NN}) = 17.3 GeV was studied by the NA49
experiment at the CERN SPS. A clear enhancement is observed for small relative
momenta (q_{inv} < 0.2 GeV). By fitting a theoretical model, which uses the
strong interaction between the proton and the lambda in a given pair, to the
measured data a value for the effective source size is deduced. Assuming a
static Gaussian source distribution we derive an effective radius parameter of
R_G = 3.02 \pm 0.20$(stat.)^{+0.44}_{-0.16}(syst.) fm.Comment: 14 pages, 9 figures, submitted to Phys. Rev.
System-size and centrality dependence of charged kaon and pion production in nucleus-nucleus collisions at 40A GeV and158A GeV beam energy
Measurements of charged pion and kaon production are presented in centrality
selected Pb+Pb collisions at 40A GeV and 158A GeV beam energy as well as in
semi-central C+C and Si+Si interactions at 40A GeV. Transverse mass spectra,
rapidity spectra and total yields are determined as a function of centrality.
The system-size and centrality dependence of relative strangeness production in
nucleus-nucleus collisions at 40A GeV and 158A GeV beam energy are derived from
the data presented here and published data for C+C and Si+Si collisions at 158A
GeV beam energy. At both energies a steep increase with centrality is observed
for small systems followed by a weak rise or even saturation for higher
centralities. This behavior is compared to calculations using transport models
(UrQMD and HSD), a percolation model and the core-corona approach.Comment: 32 pages, 14 figures, 4 tables, typo table II correcte
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