1,326 research outputs found
A note on a third order curvature invariant in static spacetimes
We consider here the third order curvature invariant
in static spacetimes
for which is conformally flat. We evaluate
explicitly the invariant for the -dimensional Majumdar-Papapetrou multi
black-holes solution, confirming that does indeed vanish on the event
horizons of such black-holes. Our calculations show, however, that solely the
vanishing of is not sufficient to locate an event horizon in
non-spherically symmetric spacetimes. We discuss also some tidal effects
associated to the invariant .Comment: 5 pages, 3 figures. Extra material available at
http://vigo.ime.unicamp.br/in
Tunable dipolar magnetism in high-spin molecular clusters
We report on the Fe17 high-spin molecular cluster and show that this system
is an exemplification of nanostructured dipolar magnetism. Each Fe17 molecule,
with spin S=35/2 and axial anisotropy as small as D=-0.02K, is the magnetic
unit that can be chemically arranged in different packing crystals whilst
preserving both spin ground-state and anisotropy. For every configuration,
molecular spins are correlated only by dipolar interactions. The ensuing
interplay between dipolar energy and anisotropy gives rise to macroscopic
behaviors ranging from superparamagnetism to long-range magnetic order at
temperatures below 1K.Comment: Replaced with version accepted for publication in Physical Review
Letter
The iridium double perovskite Sr2YIrO6 revisited: A combined structural and specific heat study
Recently, the iridate double perovskite SrYIrO has attracted
considerable attention due to the report of unexpected magnetism in this
Ir (5d) material, in which according to the J model, a
non-magnetic ground state is expected. However, in recent works on
polycrystalline samples of the series BaSrYIrO no indication of
magnetic transitions have been found. We present a structural, magnetic and
thermodynamic characterization of SrYIrO single crystals, with emphasis
on the temperature and magnetic field dependence of the specific heat. Here, we
demonstrate the clue role of single crystal X-ray diffraction on the structural
characterization of the SrYIrO double perovskite crystals by reporting
the detection of a supercell, where ,
and are the unit cell dimensions of the reported monoclinic subcell. In
agreement with the expected non-magnetic ground state of Ir (5d) in
SrYIrO, no magnetic transition is observed down to 430~mK. Moreover,
our results suggest that the low temperature anomaly observed in the specific
heat is not related to the onset of long-range magnetic order. Instead, it is
identified as a Schottky anomaly caused by paramagnetic impurities present in
the sample, of the order of \%. These impurities lead to
non-negligible spin correlations, which nonetheless, are not associated with
long-range magnetic ordering.Comment: 20 pages, 10 figure
Analysis of pairwise comparison matrices: an empirical research
Pairwise comparison (PC) matrices are used in multi-attribute decision problems (MADM) in order to express the preferences of the decision maker. Our research focused on testing various characteristics of PC matrices. In a controlled experiment with university students (N = 227) we have obtained 454 PC matrices. The cases have been divided into 18 subgroups according to the key factors to be analyzed. Our team conducted experiments with matrices of different size given from different types of MADM problems. Additionally, the matrix elements have been obtained by different questioning procedures differing in the order of the questions. Results are organized to answer five research questions. Three of them are directly connected to the inconsistency of a PC matrix. Various types of inconsistency indices have been applied. We have found that the type of the problem and the size of the matrix had impact on the inconsistency of the PC matrix. However, we have not found any impact of the questioning order. Incomplete PC matrices played an important role in our research. The decision makers behavioral consistency was as well analyzed in case of incomplete matrices using indicators measuring the deviation from the final order of alternatives and from the final score vector
Chronic Mechanical Circulatory Support for Inotrope-Dependent Heart Failure Patients Who Are Not Transplant Candidates Results of the INTrEPID Trial
ObjectivesThis study evaluated the impact of left ventricular assist device (LVAD) support on survival and quality of life in inotrope-dependent heart failure patients ineligible for cardiac transplantation.BackgroundThe role for LVADs as a bridge to cardiac transplantation has been established, but data supporting their role as permanent therapy in nontransplant candidates are limited.MethodsThe INTrEPID (Investigation of Nontransplant-Eligible Patients Who Are Inotrope Dependent) trial was a prospective, nonrandomized clinical trial comparing LVAD with optimal medical therapy (OMT). Fifty-five patients with New York Heart Association functional class IV symptoms who failed weaning from inotropic support were offered a Novacor LVAD. Eighteen of these patients did not receive an LVAD owing to patient preference (n = 14) or unavailability of the device (n = 4) but consented to follow-up and constitute a contemporaneous control group.ResultsThe LVAD and OMT patients were well matched for demographic and disease severity measures, except OMT patients had a lower mean serum sodium (128 mg/dl vs. 134 mg/dl; p = 0.001) and a higher mean blood urea nitrogen concentration (59 vs. 40; p = 0.02). The LVAD-treated patients had superior survival rates at 6 months (46% vs. 22%; p = 0.03) and 12 months (27% vs. 11%; p = 0.02). Adverse event rates were higher in the OMT group. Eighty-five percent of the LVAD-treated patients had minimal or no heart failure symptoms. Five LVAD patients and 1 OMT patient improved sufficiently while on therapy to qualify for cardiac transplantation.ConclusionsInotrope-dependent heart failure patients who are ineligible for transplantation have a high short-term mortality rate and derive a significant survival advantage from “destination” mechanical circulatory support
Self-gravitating domain walls and the thin-wall limit
We analyse the distributional thin wall limit of self gravitating scalar
field configurations representing thick domain wall geometries. We show that
thick wall solutions can be generated by appropiate scaling of the thin wall
ones, and obtain an exact solution for a domain wall that interpolates between
AdS_4 asymptotic vacua and has a well-defined thin wall limit.Solutions
representing scalar field configurations obtained via the same scaling but that
do not have a thin wall limit are also presented.Comment: 10 pages, revte
Submerged in the mainstream? A case study of an immigrant learner in a New Zealand primary classroom
Immigrant children from diverse language backgrounds face not only linguistic challenges when enrolled in mainstream English-medium classrooms, but also difficulties adjusting to an unfamiliar learning community. The culture of primary school classrooms in New Zealand typically reflects conventions across three dimensions: interactional, instructional task performance and cognitive-academic development. All three dimensions are underpinned by the culturally specific discourse conventions involved in language socialisation. New learners may be helped by classmates or their teacher to understand and successfully use these conventions, but left on their own they may sink rather than swim. This is a case study of one Taiwanese 11-year old boy, 'John', who entered a New Zealand primary classroom midway through the school year. John's basic conversational ability was sound, but he did not possess the interactive classroom skills needed to operate in the new culture of learning. Selected from a wider study of the classroom, transcript data from audio-recorded excerpts of John's interactions over several months with his teacher and classmates are interpreted from perspectives derived from sociocultural and language socialisation theories. The article concludes with a brief consideration of the extent to which John constructed, or was constrained from constructing meaningful learning experiences, and suggestions for further research and reflection
Soft systems methodology: a context within a 50-year retrospective of OR/MS
Soft systems methodology (SSM) has been used in the practice of operations research and management science OR/MS) since the early 1970s. In the 1990s, it emerged as a viable academic discipline. Unfortunately, its proponents consider SSM and traditional systems thinking to be mutually exclusive. Despite the differences claimed by SSM proponents between the two, they have been complementary. An extensive sampling of the OR/MS literature over its entire lifetime demonstrates the richness with which the non-SSM literature has been addressing the very same issues as does SSM
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