292 research outputs found
Stable isotope compositions of a late Jurassic ammonite shell: a record of seasonal surface water temperatures in the southern hemisphere?
International audienceExceptional preservation of aragonite secreted by ammonites offers an opportunity to determine the seasonal temperature variations of Mesozoic surface waters. Ontogenetic profiles of carbon and oxygen isotope compositions have been obtained from the nacreous layer of a well-preserved Late Jurassic (Oxfordian) ammonite (Perisphinctes) from Madagascar. A similar range of oxygen isotope compositions was also obtained from an associated benthic bivalve (Astarte) which suggests the absence of sampling bias. Late Jurassic seasonal variations in the southern Hemisphere were close to 2.5°C and relatively weak when compared to the 2.5â6.5°C temperature range prevailing in the present-day Indian ocean at a paleolatitude of 40±1° S. According to the hypothesis of an ice cap-free Late Jurassic Earth, average sea surface temperatures may have been up to 7°C higher than now
BCI-Based Navigation in Virtual and Real Environments
A Brain-Computer Interface (BCI) is a system that enables people to control an external device with their brain activity, without the need of any muscular activity. Researchers in the BCI field aim to develop applications to improve the quality of life of severely disabled patients, for whom a BCI can be a useful channel for interaction with their environment. Some of these systems are intended to control a mobile device (e. g. a wheelchair). Virtual Reality is a powerful tool that can provide the subjects with an opportunity to train and to test different applications in a safe environment. This technical review will focus on systems aimed at navigation, both in virtual and real environments.This work was partially supported by the Innovation, Science and Enterprise Council of the Junta de AndalucĂa (Spain), project P07-TIC-03310, the Spanish Ministry of Science and Innovation, project TEC 2011-26395 and by the European fund ERDF
Stable isotope (ÎŽ18O and ÎŽ13C) sclerochronology of Callovian (Middle Jurassic) bivalves (Gryphaea (Bilobissa) dilobotes) and belemnites (Cylindroteuthis puzosiana) from the Peterborough Member of the Oxford Clay Formation (Cambridgeshire, England): Evidence of palaeoclimate, water depth and belemnite behaviour
Incremental ÎŽ18O and ÎŽ13C signals were obtained from three well-preserved specimens of Cylindroteuthis puzosiana and from three well-preserved specimens of Gryphaea (Bilobissa) dilobotes from the Peterborough Member of the Oxford Clay Formation (Cambridgeshire, England). Through-ontogeny (sclerochronological) ÎŽ18O data from G. (B.) dilobotes appear to faithfully record seasonal temperature variations in benthic Callovian waters of the study area, which range from c. 14 °C to c. 17 °C (arithmetic mean temperature c. 15 °C). Water depth is estimated to have been in the region of c. 50 m, based upon comparisons between these data, previously published non-incremental sea surface ÎŽ18O values, and a modern analogue situation. Productivity in Callovian waters was comparable with that in modern seas, based upon ÎŽ13C data from G. (B.)dilobotes, with 13C depletion occurring during warmer periods, possibly related to an interaction between plankton blooms and intra-annual variations in mixing across a thermocline. Incremental ÎŽ18O data from C.puzosiana provide temperature minima of c.11 °C for all specimens but with maxima varying between c.14 °C and c.16 °C for different individuals (arithmetic mean values c. 13 °C). Temperatures for late ontogeny, when the C. puzosiana individuals must have been living close to the study site and hence the analysed specimens of G. (B.) dilobotes, are closely comparable to those indicated by the latter. However, for signiïŹcant portions of ontogeny C. puzosiana experienced temperatures between c. 2 °C and c. 3 °C cooler than the winter minimum as recorded by co-occurring G. (B.) dilobotes. Comparisons with modern seas suggest that descent to a depth of c. 1000 m would be necessary to explain such cool minimum temperatures. This can be discounted due to the lack of deep waters locally and due to estimates of the depth tolerance of belemnites. The most likely cause of cool ÎŽ18O signals from C. puzosiana is a cosmopolitan lifestyle including migration to more northerly latitudes. Mean ÎŽ13C values from C. puzosiana are comparable with those from G.(B.)dilobotes. However, the incrementally acquired data are highly variable and probably inïŹuenced by metabolic effects.The probable identiïŹcation of migratory behaviour in C. puzosiana calls into question the reliability of some belemnite species as place-speciïŹc palaeoenvironmental archives and highlights the beneïŹts of adopting a sclerochronological approach
Multi-proxy assessment of brachiopod shell calcite as a potential archive of seawater temperature and oxygen isotope composition
Most of our knowledge of past seawater temperature history is based on
ÎŽ18O values of calcium carbonate fossil shells. However, the
determination of past temperatures using this proxy requires the knowledge
of past seawater ÎŽ18O values, which is generally poorly
constrained. Other paleothermometers using carbonate archives, such as Mg/Ca
ratios and clumped isotopes (Î47), have been developed to allow for paleotemperatures to be estimated independently and to allow past ocean ÎŽ18O values to be calculated using various groups of calcifying
organisms. Articulated brachiopod shells are some of the most commonly used
archives in studies of past oceanic geochemistry and temperature. They are
abundant in the fossil record since the Cambrian, and for decades, their low
Mgâcalcite mineralogy has been considered relatively resistant to diagenetic
alteration. Here, we investigate the potential of brachiopod shells as
recorders of seawater temperatures and seawater ÎŽ18O values
using new brachiopod shell geochemical data by testing multiple well-established or suggested paleothermometers applied to carbonate archives.
Modern articulated brachiopod shells covering a wide range of temperatures
(â1.9 to 25.5ââC), depths (5 to 3431âm) and salinities (33.4 to
37.0âPSU) were analysed for their stable isotope compositions (ÎŽ13C, ÎŽ18O and Î47) and their elemental ratios
(Mg/Ca, Sr/Ca, Na/Ca and Li/Ca). Our data allowed us to propose a revised
oxygen isotope fractionation equation between modern-brachiopod shell
calcite and seawater:
(1)
T
=
-
5.0
(
±
0.2
)
(
ÎŽ
18
O
c
-
ÎŽ
18
O
sw
)
+
19.4
(
±
0.4
)
,
where ÎŽ18Oc is in â° VPDB, ÎŽ18Osw is in â° VSMOW, and T is in âC. Our results strongly support the use of clumped isotopes as an
alternative temperature proxy but confirm significant offsets relative to
the canonical relationship established for other biogenic and abiogenic
calcium carbonate minerals. Brachiopod shell Mg/Ca ratios show no
relationship with seawater temperatures, indicating that this ratio is a
poor recorder of past changes in temperatures, an observation at variance
with several previous studies. Despite significant correlations with
brachiopod living temperature, brachiopod shell Sr/Ca, Na/Ca and Li/Ca
values indicate the influence of environmental and biological factors
unrelated to temperature, which undermines their potential as alternative
temperature proxies. Kinetic effects (growth rates) could explain most of the
deviation of brachiopod shell calcite from expected isotopic equilibrium
with seawater and part of the distribution of Sr/Ca, Na/Ca and Li/Ca ratios.</p
Predicting mental imagery based BCI performance from personality, cognitive profile and neurophysiological patterns
Mental-Imagery based Brain-Computer Interfaces (MI-BCIs) allow their users to send commands
to a computer using their brain-activity alone (typically measured by ElectroEncephaloGraphyâ
EEG), which is processed while they perform specific mental tasks. While very
promising, MI-BCIs remain barely used outside laboratories because of the difficulty
encountered by users to control them. Indeed, although some users obtain good control
performances after training, a substantial proportion remains unable to reliably control an
MI-BCI. This huge variability in user-performance led the community to look for predictors of
MI-BCI control ability. However, these predictors were only explored for motor-imagery
based BCIs, and mostly for a single training session per subject. In this study, 18 participants
were instructed to learn to control an EEG-based MI-BCI by performing 3 MI-tasks, 2
of which were non-motor tasks, across 6 training sessions, on 6 different days. Relationships
between the participantsâ BCI control performances and their personality, cognitive
profile and neurophysiological markers were explored. While no relevant relationships with
neurophysiological markers were found, strong correlations between MI-BCI performances
and mental-rotation scores (reflecting spatial abilities) were revealed. Also, a predictive
model of MI-BCI performance based on psychometric questionnaire scores was proposed.
A leave-one-subject-out cross validation process revealed the stability and reliability of this
model: it enabled to predict participantsâ performance with a mean error of less than 3
points. This study determined how usersâ profiles impact their MI-BCI control ability and
thus clears the way for designing novel MI-BCI training protocols, adapted to the profile of
each user
Bias in Online Freelance Marketplaces: Evidence from TaskRabbit and Fiverr
Online freelancing marketplaces have grown quickly in recent years. In theory, these sites offer workers the ability to earn money without the obligations and potential social biases associated with traditional employment frameworks. In this paper, we study whether two prominent online freelance marketplaces - TaskRabbit and Fiverr - are impacted by racial and gender bias. From these two platforms, we collect 13,500 worker profiles and gather information about workers' gender, race, customer reviews, ratings, and positions in search rankings. In both marketplaces, we find evidence of bias: we find that gender and race are significantly correlated with worker evaluations, which could harm the employment opportunities afforded to the workers. We hope that our study fuels more research on the presence and implications of discrimination in online environments
Some cultural consequences in Spain of the Spanish Invasion of Morocco 1859-60
This article argues is a contribution to the study of interrelationships between colonialism, art, and literature in the nineteenth century. The article argues that the Spanish invasion of Morocco in 1859 led to contradictions and tensions within liberal nationalism, not least because of concerns about the tensions between the need for military reassertion of Spain and the respect for the independence of nations. This led to some reconfiguration of Spanish intellectuals' already complex relationship with North Africa and Islam. A major, perhaps surprising consequence of this reconfiguration, was some equation of Moroccan identity with a monotonous surface that was resistant to the gaze. In consequence, the Catalan painter Fortuny's crucial experience of Morocco led him to value near blank surfaces, and thus to make a major contribution to the origins of modern art
Prospective analysis of circulating metabolites and endometrial cancer risk
Background: Endometrial cancer is strongly associated with obesity and dysregulation of metabolic factors such as estrogen and insulin signaling are causal risk factors for this malignancy. To identify additional novel metabolic pathways associated with endometrial cancer we performed metabolomic analyses on pre-diagnostic plasma samples from 853 case-control pairs from the European Prospective Investigation into Cancer and Nutrition (EPIC). Methods: A total of 129 metabolites (acylcarnitines, amino acids, biogenic amines, glycerophospholipids, hexoses, and sphingolipids) were measured by liquid chromatography-mass spectrometry. Conditional logistic regression estimated the associations of metabolites with endometrial cancer risk. An analysis focusing on clusters of metabolites using the bootstrap lasso method was also employed. Results: After adjustment for body mass index, sphingomyelin [SM] C18:0 was positively (OR1SD: 1.18, 95% CI: 1.05-1.33), and glycine, serine, and free carnitine (C0) were inversely (OR1SD: 0.89, 95% CI: 0.80-0.99; OR1SD: 0.89, 95% CI: 0.79-1.00 and OR1SD: 0.91, 95% CI: 0.81-1.00, respectively) associated with endometrial cancer risk. Serine, C0 and two sphingomyelins were selected by the lasso method in >90% of the bootstrap samples. The ratio of esterified to free carnitine (OR1SD: 1.14, 95% CI: 1.02-1.28) and that of short chain to free acylcarnitines (OR1SD: 1.12, 95% CI: 1.00-1.25) were positively associated with endometrial cancer risk. Further adjustment for C-peptide or other endometrial cancer risk factors only minimally altered the results. Conclusion: These findings suggest that variation in levels of glycine, serine, SM C18:0 and free carnitine may represent specific pathways linked to endometrial cancer development. If causal, these pathways may offer novel targets for endometrial cancer prevention
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