27,057 research outputs found
Geology of the Snap Lake kimberlite intrusion, Northwest Territories, Canada: field observations and their interpretation
The Cambrian (523 Ma) Snap Lake hypabyssal kimberlite intrusion, Northwest Territories, Canada, is a complex segmented diamond-bearing ore-body. Detailed geological investigations suggest that the kimberlite is a multi-phase intrusion with at least four magmatic lithofacies. In particular, olivine-rich (ORK) and olivine-poor (OPK) varieties of hypabyssal kimberlite have been identified. Key observations are that the olivine-rich lithofacieshas a strong tendency to be located where the intrusion is thickest and that there is a good correlation between intrusion thickness, olivine crystal size and crystal content. Heterogeneities in the lithofacies are attributed to variations in intrusion thickness and structural complexities. The geometry and distribution of lithofacies points to magmaticco-intrusion, and flow segregation driven by fundamental rheological differences between the two phases. We envisage that the low-viscosity OPK magma acted as a lubricant for the highly viscous ORK magma. The presenceof such low-viscosity, crystal-poor magmas may explain how crystal-laden kimberlite magmas (>60 vol.%) are able to reach the surface during kimberlite eruptions. We also document the absence of crystal settling and the development of an unusual subvertical fabric of elongate olivine crystals, which are explained by rapid degassing-induced quench crystallization of the magmas during and after intrusio
On the zero set of G-equivariant maps
Let be a finite group acting on vector spaces and and consider a
smooth -equivariant mapping . This paper addresses the question of
the zero set near a zero of with isotropy subgroup . It is known
from results of Bierstone and Field on -transversality theory that the zero
set in a neighborhood of is a stratified set. The purpose of this paper is
to partially determine the structure of the stratified set near using only
information from the representations and . We define an index
for isotropy subgroups of which is the difference of
the dimension of the fixed point subspace of in and . Our main
result states that if contains a subspace -isomorphic to , then for
every maximal isotropy subgroup satisfying , the zero
set of near contains a smooth manifold of zeros with isotropy subgroup
of dimension . We also present a systematic method to study
the zero sets for group representations and which do not satisfy the
conditions of our main theorem. The paper contains many examples and raises
several questions concerning the computation of zero sets of equivariant maps.
These results have application to the bifurcation theory of -reversible
equivariant vector fields
The Indirect Limit on the Standard Model Higgs Boson Mass from the Precision FERMILAB, LEP and SLD Data
Standard Model fits are performed on the most recent leptonic and b quark Z
decay data from LEP and SLD, and FERMILAB data on top quark production, to
obtain and . Poor fits are obtained, with confidence levels
2%. Removing the b quark data improves markedly the quality of the fits and
reduces the 95% CL upper limit on by 50 GeV.Comment: 6 pages 3 tables i figur
Bidirectional ventricular tachycardia in cardiac sarcoidosis.
A 73-year-old man with history of pulmonary sarcoidosis was found to have runs of non-sustained bidirectional ventricular tachycardia (BVT) with two different QRS morphologies on a Holter monitor. Cardiac magnetic resonance delayed gadolinium imaging revealed a region of patchy mid-myocardial enhancement within the left ventricular basal inferolateral myocardium. An 18-fluorodeoxyglucose positron emission tomography (FDG-PET) showed increased uptake in the same area, consistent with active sarcoid, with no septal involvement. Follow-up FDG-PET one year later showed disease progression with new septal involvement. Cardiac sarcoidosis, characterized by myocardial inflammation and interstitial fibrosis that can lead to conduction system disturbance and macro re-entrant arrhythmias, should be considered in differential diagnosis of BVT. BVT may indicate septal involvement with sarcoidosis before the lesions are large enough to be detected radiologically
What forms of evidence do novice teachers need?
The Teacher Training Resource Bank (TTRB) is a project, funded by the English Teacher Development Agency for Schools (TDA). It aims to articulate, represent and enhance the professional knowledge bases that underpin teacher education through the development of a knowledge portal. The TTRB seeks to link theory, debate and practice and raise the profile of teacher training research and knowledge creation.
Records of TTRB usage since its inception in 2006 demonstrate widespread use of the resource within English initial teacher education (ITE) and in schools. An independent evaluation (Chambers et al, 2009) indicated a positive impact on trainee teachers by making a large range of recent research resource material easily available. Trainee teachers were further enabled to make connections between theory and research, and the quality of their academic work was seen to be improved.
The paper draws on a spiral model of knowledge management developed by Nonaka, I & Konno, N. (1998) to discuss the ways in which the TTRB can support and democratise the construction of professional knowledge in ITE from the perspectives of novice teachers and their mentors and tutors.
This study has findings that illustrate successful mechanisms that bridge the perceived divide between theory and practice that can be seen to have potential across Europe
Determination of polarized parton distribution functions with recent data on polarization asymmetries
Global analysis has been performed within the next-to-leading order in
Quantum Chromodynamics (QCD) to determine polarized parton distributions with
new experimental data in spin asymmetries. The new data set includes JLab,
HERMES, and COMPASS measurements on spin asymmetry A_1 for the neutron and
deuteron in lepton scattering. Our new analysis also utilizes the double-spin
asymmetry for pi^0 production in polarized pp collisions, A_{LL}^{pi^0},
measured by the PHENIX collaboration. Because of these new data, uncertainties
of the polarized PDFs are reduced. In particular, the JLab, HERMES, and COMPASS
measurements are valuable for determining Delta d_v(x) at large x and Delta
qbar(x) at x~0.1. The PHENIX pi^0 data significantly reduce the uncertainty of
Delta g(x). Furthermore, we discuss a possible constraint on Delta g(x) at
large x by using the HERMES data on g_1^d in comparison with the COMPASS ones
at x~0.05.Comment: 11 pages, REVTeX, 13 eps files, Phys. Rev. D in pres
On the symmetry breaking phenomenon
We investigate the problem of symmetry breaking in the framework of dynamical
systems with symmetry on a smooth manifold. Two cases will be analyzed: general
and Hamiltonian dynamical systems. We give sufficient conditions for symmetry
breaking in both cases
Bunge’s Mathematical Structuralism Is Not a Fiction
In this paper, I explore Bunge’s fictionism in philosophy of mathematics. After an overview of Bunge’s views, in particular his mathematical structuralism, I argue that the comparison between mathematical objects and fictions ultimately fails. I then sketch a different ontology for mathematics, based on Thomasson’s metaphysical work. I conclude that mathematics deserves its own ontology, and that, in the end, much work remains to be done to clarify the various forms of dependence that are involved in mathematical knowledge, in particular its dependence on mental/brain states and material objects
Metrics for measuring distances in configuration spaces
In order to characterize molecular structures we introduce configurational
fingerprint vectors which are counterparts of quantities used experimentally to
identify structures. The Euclidean distance between the configurational
fingerprint vectors satisfies the properties of a metric and can therefore
safely be used to measure dissimilarities between configurations in the high
dimensional configuration space. We show that these metrics correlate well with
the RMSD between two configurations if this RMSD is obtained from a global
minimization over all translations, rotations and permutations of atomic
indices. We introduce a Monte Carlo approach to obtain this global minimum of
the RMSD between configurations
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