5,133 research outputs found
Foraminifera from the Eocene Variegated Shales near Barwinek (Magura Unit, Outer Carpathians), the type locality of Noth (1912) revisited
Early to middle Miocene foraminifera from the deep-sea Congo Fan, offshore Angola
Analysis of a 630m section of an exploration well penetrating the distal part of the Congo Fan (~2000m water depth)
yielded high abundance and diversity assemblages of agglutinated and calcareous benthic foraminifera. Planktonic foraminifera constrain
the age to Early – Middle Miocene, and \delta 18O records reveal the Mi1 (~16.3 Ma) isotopic shift. Relatively few taxonomic studies
of deep-water calcareous and agglutinated benthic foraminifera exist from this time period in this locality. All species encountered are
therefore taxonomically described and documented using SEM photography (over 170 species), along with 27 species of planktonic
foraminifera. Faunas show close affinities to those of the eastern Venezuela Basin, Gulf of Mexico and Central Paratethys.
Seven assemblages are defined and analysed using morphogroup analysis and Correspondence Analysis, documenting the response
of benthic foraminifera to three primary environmental-forcing factors; energy levels in the benthic boundary layer, oxygen levels
relating to changing surface water productivity, and fluctuations in the level of the CCD. Near the top and bottom of the studied
section both foraminiferal abundance and diversity decrease, corresponding with increased sand content implying greater energy levels
and environmental disturbance. The majority of the section consists of shales with very low percentage sand, high foraminiferal abundance
and diversity, and high sedimentation rates of ~10cm/kyr. Morphogroup analysis reveals a major switch in the fauna at around
oxygen isotope event Mi1, with the transition from an epifaunal-dominated Cibicidoides assemblage to shallow infaunal-dominated
Bulimina assemblage. We regard this as likely due to expansion of the oxygen minimum zone (paleobathymetric estimates are ~1000m)
related to increased surface-water productivity and global cooling. Shifts in calcareous foraminiferal percentage over the studied interval
overprint these signals and are believed to be related to a shoaling CCD, linked to reduced oceanic acidity and global atmospheric
CO2 levels during the early Middle Miocene Monterey Carbon Isotope Excursion
The tractability frontier of well-designed SPARQL queries
We study the complexity of query evaluation of SPARQL queries. We focus on
the fundamental fragment of well-designed SPARQL restricted to the AND,
OPTIONAL and UNION operators. Our main result is a structural characterisation
of the classes of well-designed queries that can be evaluated in polynomial
time. In particular, we introduce a new notion of width called domination
width, which relies on the well-known notion of treewidth. We show that, under
some complexity theoretic assumptions, the classes of well-designed queries
that can be evaluated in polynomial time are precisely those of bounded
domination width
Griffiths phase in diluted magnetic semiconductors
We study the effects of disorder in the vicinity of the ferromagnetic
transition in a diluted magnetic semiconductor in the strongly localized
regime. We derive an effective polaron Hamiltonian, which leads to the
Griffiths phase above the ferromagnetic transition point. The Griffiths-McCoy
effects yield non-perturbative contributions to the dynamic susceptibility. We
explicitly derive the long-time susceptibility, which has a pseudo-scaling
form, with the dynamic critical exponent being expressed through the
percolation indices.Comment: 4 pages, final version as publishe
Foraminifera from the Eocene variegated shales near Barwinek (Magura unit, Outer Carpathians), the type locality of Noth (1912) revisited
This is the final version of the article. Available from the Polish Geological Society via the URL in this record.A rich deep-water agglutinated foraminifera (DWAF) fauna (approximately 50 taxa) is documented from the lower to middle Eocene Variegated Shales of the Magura Unit, Outer Carpathians. Four localities have been sampled from the Barwinek region, which are thought to correspond to those studied by Rudolf Noth in 1912. A stream section of variegated red and green shales outcrop near Zyndranowa (Poland), was logged and extensively sampled. A further two outcrops of red shales were sampled in stream sections near Vyšny Komarnik (Slovakia), and a stream section close to Olchowiec (Poland). The DWAF recovered closely resemble assemblages of the same age in localities throughout the Carpathians. The material under study in this report has been correlated using the first appearance of Reticulophragmium amplectens, dating the samples early Middle Eocene. Two DWAF assemblages have been differentiated. The 'Rhabdammina Assemblage' is found mainly in green shales and is thought to be indicative of a high-energy slope or deep sea fan environment slightly reduced in oxygen; and the 'Paratrochamminoides Assemblage' is found mainly in red shales and is thought to be indicative of a well-oxygenated condensed sequence. The two faunas are otherwise very similar in composition. Of the seven new species described by Noth in 1912, one has been identified in this report and re-described as Paratrochamminoides deflexiformis (Noth).This study was originally carried out as an MSc project in Micropalaeontology at U.C.L. We would like to thank AAPG student Grants-in-Aid programme and the EEC-Socrates programme for the essential funding provided in support of this projec
Destroying coherence in high temperature superconductors with current flow
The loss of single-particle coherence going from the superconducting state to
the normal state in underdoped cuprates is a dramatic effect that has yet to be
understood. Here, we address this issue by performing angle resolved
photoemission spectroscopy (ARPES) measurements in the presence of a transport
current. We find that the loss of coherence is associated with the development
of an onset in the resistance, in that well before the midpoint of the
transition is reached, the sharp peaks in the ARPES spectra are completely
suppressed. Since the resistance onset is a signature of phase fluctuations,
this implies that the loss of single-particle coherence is connected with the
loss of long-range phase coherence.Comment: 7 pages, 7 figure
Coherency of the superconducting state: the muon spin rotation and ARPES studies of (BiPb)_2(SrLa)_2CuO_{6+\delta}
The superfluid density \rho_s in underdoped (T_c\simeq23K), optimally doped
(T_c\simeq35K) and overdoped (T_c\simeq29K) single crystalline
(BiPb)_2(SrLa)_2CuO_{6+\delta} samples was studied by means of muon-spin
rotation (\muSR). By combining the \muSR data with the results of ARPES
measurements on similar samples [Nature 457, 296 (2009)] good self-consistent
agreement is obtained between two techniques concerning the temperature and the
doping evolution of \rho_s.Comment: 4 pages, 3 figures
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