1,685 research outputs found
Beyond "the Relationship between the Individual and Society": broadening and deepening relational thinking in group analysis
The question of âthe relationship between the individual and societyâ has troubled group analysis since its inception. This paper offers a reading of Foulkes that highlights the emergent, yet evanescent, psychosocial ontology in his writings, and argues for the development of a truly psychosocial group analysis, which moves beyond the individual/society dualism. It argues for a shift towards a language of relationality, and proposes new theoretical resources for such a move from relational sociology, relational psychoanalysis and the âmatrixial thinkingâ of Bracha Ettinger which would broaden and deepen group analytic understandings of relationality
Structural order parameter and itinerant electron magnetism in Cd2Re2O7
We describe the low temperature behaviour of the magnetic susceptibility of
Cd2Re2O7 in terms of a Landau theory of structural phase transitions. We
calculate the zero temperature Pauli susceptibility using a tight-binding
approach to reveal the mechanism of coupling between the structural order
parameter and itinerant magnetism.Comment: Submitted to the Proceedings of ICM 2003, Rom
Impurity state in Haldane gap for S=1 Heisenberg antiferromagnetic chain with bond doping
Using a new impurity density matrix renormalization group scheme, we
establish a reliable picture of how the low lying energy levels of a
Heisenberg antiferromagnetic chain change {\it quantitatively} upon bond
doping. A new impurity state gradually occurs in the Haldane gap as ,
while it appears only if with as . The
system is non-perturbative as . This explains the
appearance of a new state in the Haldane gap in a recent experiment on
YCaBaNiO [J.F. DiTusa, et al., Phys. Rev. Lett. 73 1857(1994)].Comment: 4 pages of uuencoded gzip'd postscrip
Bowhead whales, and not right whales, were the primary target of 16th- to 17th-century Basque Whalers in the Western North Atlantic
During the 16th and 17th centuries, Basque whalers travelled annually to the Strait of Belle Isle and Gulf of St. Lawrence to hunt whales. The hunting that occurred during this period is of primary significance for the North Atlantic right whale, Eubalaena glacialis (MĂŒller, 1776), because it has been interpreted as the largest human-induced reduction of the western North Atlantic population, with ~12250â21 000 whales killed. It has been frequently reported that the Basques targeted two species in this region: the North Atlantic right whale and the bowhead whale, Balaena mysticetus L., 1758. To evaluate this hypothesis and the relative impact of this period of whaling on both species, we collected samples from 364 whale bones during a comprehensive search of Basque whaling ports from the 16th to the 17th century in the Strait of Belle Isle and Gulf of St. Lawrence. Bones were found and sampled at 10 of the 20 sites investigated. DNA was extracted from a subset (n = 218) of these samples. Analysis of the mitochondrial cytochrome b region identified five whale species. The identification of only a single right whale bone and 203 bowhead whale bones from at least 72 individuals indicates that the bowhead whale was likely the principal target of the hunt. These results imply that this whaling had a much greater impact (in terms of numbers of whales removed) on the bowhead whale population than on the western North Atlantic right whale population.Aux XVIe et XVIIe siĂšcles, les baleiniers basques se rendaient tous les ans au dĂ©troit de Belle Isle et au golfe du Saint- Laurent pour faire la chasse aux baleines. La chasse qui sâest effectuĂ©e pendant cette pĂ©riode revĂȘt une grande importance pour la baleine franche ou baleine noire de lâAtlantique Nord, Eubalaena glacialis (MĂŒller, 1776), car cette activitĂ© serait interprĂ©tĂ©e comme la plus grande rĂ©duction de la population de baleines franches de lâAtlantique Nord causĂ©e par lâĂȘtre humain, au rythme dâenviron 12 250 Ă 21 000 baleines tuĂ©es. On a souvent signalĂ© que les Basques visaient deux espĂšces dans cette rĂ©gion, soit la baleine franche de lâAtlantique Nord et la baleine borĂ©ale, Balaena mysticetus L., 1758. Pour Ă©valuer cette hypothĂšse et lâincidence relative de cette pĂ©riode de pĂȘche aux baleines sur ces deux espĂšces, nous avons recueilli des Ă©chantillons provenant de 364 ossements de baleines dans le cadre dâune recherche approfondie de ports basques de chasse Ă la baleine remontant aux XVIe et XVIIe siĂšcles dans le dĂ©troit de Belle Isle et le golfe du Saint-Laurent. Des ossements ont Ă©tĂ© trouvĂ©s et Ă©chantillonnĂ©s Ă 10 des 20 sites ayant fait lâobjet de notre recherche. De lâADN a Ă©tĂ© extrait dâun sous-ensemble (n = 218) de ces Ă©chantillons. Lâanalyse mitochondriale cytochrome b de la rĂ©gion a permis dâidentifier cinq espĂšces de baleines. Lâidentification dâun seul os de baleine franche et de 203 os de baleines borĂ©ales provenant dâau moins 72 individus laisse croire que la baleine borĂ©ale Ă©tait probablement la cible principale des chasseurs. Ces rĂ©sultats impliquent que la chasse Ă la baleine a eu des incidences beaucoup plus grandes (en termes de nombres de baleines Ă©liminĂ©es) sur la population de baleines borĂ©ales que sur la population de baleines franches de lâouest de lâAtlantique Nord
Effects of domain walls on hole motion in the two-dimensional t-J model at finite temperature
The t-J model on the square lattice, close to the t-J_z limit, is studied by
quantum Monte Carlo techniques at finite temperature and in the underdoped
regime. A variant of the Hoshen-Koppelman algorithm was implemented to identify
the antiferromagnetic domains on each Trotter slice. The results show that the
model presents at high enough temperature finite antiferromagnetic (AF) domains
which collapse at lower temperatures into a single ordered AF state. While
there are domains, holes would tend to preferentially move along the domain
walls. In this case, there are indications of hole pairing starting at a
relatively high temperature. At lower temperatures, when the whole system
becomes essentially fully AF ordered, at least in finite clusters, holes would
likely tend to move within phase separated regions. The crossover between both
states moves down in temperature as doping increases and/or as the off-diagonal
exchange increases. The possibility of hole motion along AF domain walls at
zero temperature in the fully isotropic t-J is discussed.Comment: final version, to appear in Physical Review
Edge states in Open Antiferromagnetic Heisenberg Chains
In this letter we report our results in investigating edge effects of open
antiferromagnetic Heisenberg spin chains with spin magnitudes
using the density-matrix renormalization group (DMRG) method initiated by
White. For integer spin chains, we find that edge states with spin magnitude
exist, in agreement with Valence-Bond-Solid model picture. For
half-integer spin chains, we find that no edge states exist for spin
chain, but edge state exists in spin chain with , in
agreement with previous conjecture by Ng. Strong finite size effects associated
with spin dimmerization in half-integer spin chains will also be discussed.Comment: 4 pages, RevTeX 3.0, 5 figures in a separate uuencoded postscript
file. Replaced once to enlarge the acknowlegement
Large-scale structural organization of social networks
The characterization of large-scale structural organization of social
networks is an important interdisciplinary problem. We show, by using scaling
analysis and numerical computation, that the following factors are relevant for
models of social networks: the correlation between friendship ties among people
and the position of their social groups, as well as the correlation between the
positions of different social groups to which a person belongs.Comment: 5 pages, 3 figures, Revte
The Haldane gap for the S=2 antiferromagnetic Heisenberg chain revisited
Using the density matrix renormalization group (DMRG) technique, we carry out
a large scale numerical calculation for the S=2 antiferromagnetic Heisenberg
chain. Performing systematic scaling analysis for both the chain length and
the number of optimal states kept in the iterations , the Haldane gap
is estimated accurately as . Our systematic
analysis for the S=2 chains not only ends the controversies arising from
various DMRG calculations and Monte Carlo simulations, but also sheds light on
how to obtain reliable results from the DMRG calculations for other complicated
systems.Comment: 4 pages and 1 figur
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