587 research outputs found
Charged seven-dimensional spacetimes with spherically symmetric extra-dimensions
We derive exact solutions of the seven-dimensional Einstein-Maxwell equations
for a spacetime exhibiting Poincare invariance along four-dimensions and
spherical symmetry in the extra-dimensions. Such topology generically arises in
the context of braneworld models. Our solutions generalise previous results on
Ricci-flat spacetimes admitting the two-sphere and are shown to include
wormhole configurations. A regular coordinate system suitable to describe the
whole spacetime is singled-out and we discuss the physical relevance of the
derived solutions.Comment: 14 pages, 8 figures, uses RevTeX. Physical discussion clarified,
wormhole solutions added. References adde
Childrenâs comprehension monitoring of multiple situational dimensions of a narrative
Narratives typically consist of information on multiple aspects of a situation. In order to successfully create a coherent representation of the described situation, readers are required to monitor all these situational dimensions during reading. However, little is known about whether these dimensions differ in the ease with which they can be monitored. In the present study, we examined whether children in Grades 4 and 6 monitor four different dimensions (i.e., emotion, causation, time, and space) during reading, using a self-paced reading task containing inconsistencies. Furthermore, to explore what causes failure in inconsistency detection, we differentiated between monitoring processes related to availability and validation of information by manipulating the distance between two pieces of conflicting information. The results indicated that the monitoring processes varied as a function of dimension. Children were able to validate emotional and causal information when it was still active in working memory, but this was not the case for temporal and spatial information. When context and target information were more distant from each other, only emotionally charged information remained available for further monitoring processes. These findings show that the influence of different situational dimensions should be taken into account when studying childrenâs reading comprehension
Children's integration of information across texts: reading processes and knowledge representations.
Constructing a knowledge representation from multiple texts requires the integration of information across texts. The aim of the current study was to investigate how elementary school students integrate information across multiple text passages and, particularly, whether students use information from a prior text to improve understanding of a current text. A sample of 105 children in grades 4 and 6 participated in the experiment. The multiple-text integration paradigm was used to study integration processes across texts during reading. Recall and (application) questions were used to investigate the extent to which information from different text passages was integrated into knowledge representations after reading. Individual differences in reading comprehension ability and working memory were also considered. The results indicate that children in both grades spontaneously activate information from an earlier text to aid their understanding during reading, and that they integrate information across texts in their knowledge representations. This was the case regardless of grade or individual differences in reading-comprehension ability and working memory. These findings provide insight into the mechanisms that may be involved in the integration of information across texts.Development Psychopathology in context: schoo
Intrauterine exposure to chronic hypoxia in the rat leads to progressive diastolic function and increased aortic stiffness from early postnatal developmental stages
Aim We sought to explore whether fetal hypoxia exposure, an insult of placental insufficiency, is associated with left ventricular dysfunction and increased aortic stiffness at early postnatal ages. Methods Pregnant Sprague Dawley rats were exposed to hypoxic conditions (11.5% FiO2) from embryonic day E15â21 or normoxic conditions (controls). After delivery, left ventricular function and aortic pulse wave velocity (measure of aortic stiffness) were assessed longitudinally by echocardiography from day 1 through week 8. A mixed ANOVA with repeated measures was performed to compare findings between groups across time. Myocardial hematoxylin and eosin and picroâsirius staining were performed to evaluate myocyte nuclear shape and collagen fiber characteristics, respectively. Results Systolic function parameters transiently increased following hypoxia exposure primarily at week 2 (p \u3c .008). In contrast, diastolic dysfunction progressed following fetal hypoxia exposure beginning weeks 1â2 with lower early inflow Doppler velocities, and less of an increase in early to late inflow velocity ratios and annular and septal Eâ/Aâ tissue velocities compared to controls (p \u3c .008). As further evidence of altered diastolic function, isovolumetric relaxation time was significantly shorter relative to the cardiac cycle following hypoxia exposure from week 1 onward (p \u3c .008). Aortic stiffness was greater following hypoxia from day 1 through week 8 (p \u3c .008, except week 4). Hypoxia exposure was also associated with altered nuclear shape at week 2 and increased collagen fiber thickness at week 4. Conclusion Chronic fetal hypoxia is associated with progressive LV diastolic dysfunction, which corresponds with changes in nuclear shape and collagen fiber thickness, and increased aortic stiffness from early postnatal stages
Effects of social-cognitive processing demands and structural importance on narrative recall: Differences between children, adolescents, and adults
This study examined the contributions of developmental changes in social-cognitive ability throughout adolescence to the development of narrative comprehension. We measured the effects of sensitivity to the causal structure of narratives and of sensitivity to differences in social-cognitive processing demands on narrative recall by children (8â10 years old), adolescents (13â15 years old), and adults (19â21 years old). Generalized mixed-effects models for dichotomous variables revealed that social-cognitive processing demands of story elements predicted differences in narrative recall between the age groups, over and above the causal importance of story elements. Children's and adolescents' recall of the narrative differed from that of adults, and these differences were most apparent for social-cognitive aspects of the narrative. These findings suggest that immature social-cognitive abilities limit narrative comprehension in childhood and adolescence and, in doing so, contribute to our understanding of the interaction between reader characteristics and text characteristics in the development of narrative comprehension.Development Psychopathology in context: schoo
Two-Proton Correlations near Midrapidity in p+Pb and S+Pb Collisions at the CERN SPS
Correlations of two protons emitted near midrapidity in p+Pb collisions at
450 GeV/c and S+Pb collisions at 200A GeV/c are presented, as measured by the
NA44 Experiment. The correlation effect, which arises as a result of final
state interactions and Fermi-Dirac statistics, is related to the space-time
characteristics of proton emission. The measured source sizes are smaller than
the size of the target lead nucleus but larger than the sizes of the
projectiles. A dependence on the collision centrality is observed; the source
size increases with decreasing impact parameter. Proton source sizes near
midrapidity appear to be smaller than those of pions in the same interactions.
Quantitative agreement with the results of RQMD (v1.08) simulations is found
for p+Pb collisions. For S+Pb collisions the measured correlation effect is
somewhat weaker than that predicted by the model simulations, implying either a
larger source size or larger contribution of protons from long-lived particle
decays.Comment: 10 pages (LaTeX) text, 4 (EPS) figures; accepted for publication in
Phys. Lett.
Source Dimensions in Ultrarelativistic Heavy Ion Collisions
Recent experiments on pion correlations, interpreted as interferometric
measurements of the collision zone, are compared with models that distinguish a
prehadronic phase and a hadronic phase. The models include prehadronic
longitudinal expansion, conversion to hadrons in local kinetic equilibrium, and
rescattering of the produced hadrons. We find that the longitudinal and outward
radii are surprisingly sensitive to the algorithm used for two-body collisions.
The longitudinal radius measured in collisions of 200 GeV/u sulfur nuclei on a
heavy target requires the existence of a prehadronic phase which converts to
the hadronic phase at densities around 0.8-1.0 GeV/fm. The transverse radii
cannot be reproduced without introducing more complex dynamics into the
transverse expansion.Comment: RevTeX 3.0, 28 pages, 6 figures, not included, revised version, major
change is an additional discussion of the classical two-body collision
algorithm, a (compressed) postscript file of the complete paper including
figures can be obtained from Authors or via anonymous ftp at
ftp://ftp_int.phys.washington.edu/pub/herrmann/pisource.ps.
Pion interferometry with pion-source-medium interactions
An extended pion source, which can be temporarily created by a high energy
nuclear collision, will also absorb and distort the outgoing pions. We discuss
how this effect alters the interferometric pattern of the two-pion momentum
correlation function. In particular, we show that the two-pion correlation
function decreases rapidly when the opening angle between the pions increases.
The opening-angle dependence should serve as a new means of obtaining
information about the pion source in the analysis of experimental data.Comment: 14 pages (revtex) and 9 figures (uuencoded), Caltech preprint
MAP-175, Indiana Univ. preprint IU/NTC 914-1
Baryon phase-space density in heavy-ion collisions
The baryon phase-space density at mid-rapidity from central heavy-ion
collisions is estimated from proton spectra with interferometry and deuteron
coalescence measurements. It is found that the mid-rapidity phase-space density
of baryons is significantly lower at the SPS than the AGS, while those of total
particles (pion + baryon) are comparable. Thermal and chemical equilibrium
model calculations tend to over-estimate the phase-space densities at both
energies.Comment: 5 pages, 2 tables, no figure. RevTeX style. Accepted for publication
in Phys. Rev. C Rapid Communicatio
Lambda-proton correlations in relativistic heavy ion collisions
The prospect of using lambda-proton correlations to extract source sizes in
relativistic heavy ion collisions is investigated. It is found that the strong
interaction induces a large peak in the correlation function that provides more
sensitive source size measurements than two-proton correlations under some
circumstances. The prospect of using lambda-proton correlations to measure the
time lag between lambda and proton emissions is also studied.Comment: 4 pages, 3 figure, revtex style. Two short paragraphs are added at
referees' recommendations. Phys. Rev. Lett. in pres
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