137 research outputs found
New cobalt(I) complexes derived from dicarbonyltricyanocobaltate(I)
The preparation and characterization of several series of mixed ligand cobalt(I) complexes of the types [Co(CN)_2(CO)_2(PR_3)]–, [Co(CN)_2(CO)(PR_3)_2]–, and [Co(CN)(CO)_2(PR_3)_2], prepared by the reactions of tertiary phosphines (PR_3) with [Co(CN)_3(CO)_2]^(2–), are described and some novel aspects of their chemistry are discussed
Conformal sigma models corresponding to gauged Wess-Zumino-Witten theories
We develop a field-theoretical approach to determination of the background
target space fields corresponding to general coset conformal theories
described by gauged WZW models. The basic idea is to identify the effective
action of a gauged WZW theory with the effective action of a sigma model. The
derivation of the quantum effective action in the gauged WZW theory is
presented in detail, both in the bosonic and in the supersymmetric cases. We
explain why and how one can truncate the effective action by omitting most of
the non-local terms (thus providing a justification for some previous
suggestions). The resulting metric, dilaton and the antisymmetric tensor are
non-trivial functions of (or ) and represent a large class of
conformal sigma models. The exact expressions for the fields in the
sypersymmetric case are equal to the leading order (`semiclassical') bosonic
expressions (with no shift of ). An explicit form in which we find the sigma
model couplings makes it possible to prove that the metric and the dilaton are
equivalent to the fields which are obtained in the operator approach, i.e. by
identifying the -operator of the conformal theory with a Klein-Gordon
operator in a background. The metric can be considered as a `deformation' of an
invariant metric on the coset space and the dilaton can be in general
represented in terms of the logarithm of the ratio of the determinants of the
`deformed' and `round' metrics.Comment: 56 pages, harvmac (b), CERN-TH.6804/93 (minor changes in sects.
2,4,6
機械翻訳用超大規模辞書データ資源
会議名: 言語資源活用ワークショップ2016, 開催地: 国立国語研究所, 会期: 2017年3月7日-8日, 主催: 国立国語研究所 コーパス開発センター情報交流の国際化に伴い多言語情報の充実は今や喫緊の課題である。特に固有名詞やPOI (points of interest)は膨大な数量に加え頻繁な名称変更にも対応する必要があるため,正確で充実した多言語辞書データ資源が必須だ。そこで,機械翻訳の作業効率と精度を格段に向上させる,超大規模辞書データ資源(Very Large Scale Lexica: VLSL)の構築例として,固有名詞・専門用語等を含む日中韓英辞書データベースや多言語固有名詞辞書データベースを紹介する。VLSLは情報検索・形態素解析・固有表現認識・用語抽出等,自然言語処理の幅広い分野に応用が可能で更なる展開が期待される
Asymptotic Safety of Gravity Coupled to Matter
Nonperturbative treatments of the UV limit of pure gravity suggest that it
admits a stable fixed point with positive Newton's constant and cosmological
constant. We prove that this result is stable under the addition of a scalar
field with a generic potential and nonminimal couplings to the scalar
curvature. There is a fixed point where the mass and all nonminimal scalar
interactions vanish while the gravitational couplings have values which are
almost identical to the pure gravity case. We discuss the linearized flow
around this fixed point and find that the critical surface is four-dimensional.
In the presence of other, arbitrary, massless minimally coupled matter fields,
the existence of the fixed point, the sign of the cosmological constant and the
dimension of the critical surface depend on the type and number of fields. In
particular, for some matter content, there exist polynomial asymptotically free
scalar potentials, thus providing a solution to the well-known problem of
triviality.Comment: 18 pages,typeset with revtex
Gauging a Non-Semi-Simple WZW Model
We consider gauged WZW models based on a four dimensional non-semi-simple
group. We obtain conformal \s-models in spacetime dimensions (with
exact central charge ) by axially and vectorially gauging a
one-dimensional subgroup. The model obtained in the axial gauging is related to
the black string after a correlated limit is taken in the latter model. By
identifying the CFT corresponding to these \s-models we compute the exact
expressions for the metric and dilaton fields. All of our models can be mapped
to flat spacetimes with zero antisymmetric tensor and dilaton fields via
duality transformations.Comment: 17 pages, harvmac, THU-93/30 (The discussion and reference sections
are expanded
Chiral gauged WZNW models and heterotic string backgrounds
We construct new heterotic string backgrounds which are analogous to
superstring solutions corresponding to coset models but are not simply the
`embeddings'of the latter. They are described by the (1,0) supersymmetric
extension of the chiral gauged WZNW models. The `chiral gauged' WZNW
action differs from the standard gauged WZNW action by the absence of the
-term (and thus is not gauge invariant in the usual sense) but can
still be expressed as a combination of WZNW actions and is conformal invariant.
We explain a close relation between gauged and chiral gauged WZNW models and
prove that in the case of the abelian the chiral gauged theory is
equivalent to a particular gauged WZNW theory. In contrast to
the gauged WZNW model, the chiral gauged one admits a (1,0) supersymmetric
extension which is consistent at the quantum level. Integrating out the
gauge field we determine the exact (in ) form of the couplings of the
corresponding heterotic sigma model. While in the bosonic (superstring) cases
all the fields depend (do not depend) non-trivially on here the
metric receives only one correction while the antisymmetric tensor
and the dilaton remain semiclassical. As a simplest example, we discuss the
basic solution which is the heterotic string counterpart of the `black
string' background.Comment: 41 pages, harvmac, CERN-TH.6962, USC-93/HEP-S
Heterotic string solutions and coset conformal field theories
We discuss solutions of the heterotic string theory which are analogous to
bosonic and superstring backgrounds related to coset conformal field theories.
A class of exact `left-right symmetric' solutions is obtained by supplementing
the metric, antisymmetric tensor and dilaton of the superstring solutions by
the gauge field background equal to the generalised Lorentz connection with
torsion. As in the superstring case, these backgrounds are \a'-independent,
i.e. have a `semiclassical' form. The corresponding heterotic string sigma
model is obtained from the combination of the (1,0) supersymmetric gauged WZNW
action with the action of internal fermions coupled to the target space gauge
field. The pure (1,0) supersymmetric gauged WZNW theory is anomalous and does
not describe a consistent heterotic string solution. We also find (to the order
) a two-dimensional perturbative heterotic string solution with the
trivial gauge field background. To the leading order in it coincides
with the known bosonic or superstring solutions. This solution
does not correspond to a `heterotic' combination of the left superstring and
right bosonic -operators at the conformal field theory level. Some duality
properties of the heterotic string solutions are studied.Comment: 28 pages, harvmac (b), CERN-TH.6872/93, RI-150-9
Organism-sediment interactions govern post-hypoxia recovery of ecosystem functioning
Hypoxia represents one of the major causes of biodiversity and ecosystem functioning loss for coastal waters. Since eutrophication-induced hypoxic events are becoming increasingly frequent and intense, understanding the response of ecosystems to hypoxia is of primary importance to understand and predict the stability of ecosystem functioning. Such ecological stability may greatly depend on the recovery patterns of communities and the return time of the system properties associated to these patterns. Here, we have examined how the reassembly of a benthic community contributed to the recovery of ecosystem functioning following experimentally-induced hypoxia in a tidal flat. We demonstrate that organism-sediment interactions that depend on organism size and relate to mobility traits and sediment reworking capacities are generally more important than recovering species richness to set the return time of the measured sediment processes and properties. Specifically, increasing macrofauna bioturbation potential during community reassembly significantly contributed to the recovery of sediment processes and properties such as denitrification, bedload sediment transport, primary production and deep pore water ammonium concentration. Such bioturbation potential was due to the replacement of the small-sized organisms that recolonised at early stages by large-sized bioturbating organisms, which had a disproportionately stronger influence on sediment. This study suggests that the complete recovery of organism-sediment interactions is a necessary condition for ecosystem functioning recovery, and that such process requires long periods after disturbance due to the slow growth of juveniles into adult stages involved in these interactions. Consequently, repeated episodes of disturbance at intervals smaller than the time needed for the system to fully recover organism-sediment interactions may greatly impair the resilience of ecosystem functioning.
Is the prevalence of psychiatric disorders associated with urbanization?
Objectives In many countries, the total rate of psychiatric disorders tends to be higher in urban areas than in rural areas. The relevance of this phenomenon is that it may help in identifying environmental factors that are important in the pathogenesis of mental disorders. Moreover, urban preponderance suggests that the allocation of funds and services should take urbanization levels into account. Method The Netherlands Mental Health Survey and Incidence Study (NEMESIS) used the Composite International Diagnostic Interview (CIDI) to determine the prevalence of DSM-III-R disorders in a sample of 7,076 people aged 18–64. The sample was representative of the population as a whole. The study population was assigned to five urbanization categories defined at the level of municipalities. The association between urbanization and 12-month prevalence rates of psychiatric disorders was studied using logistic regression taking several confounders into account. Results The prevalence of psychiatric disorders gradually increased over five levels of urbanization. This pattern remained after adjustment for a range of confounders. Comorbidity rates also increased with level of urbanization. Conclusion This study confirms that psychiatric disorders are more common and more complex in more urbanized areas. This should be reflected in service allocation and may help in identifying environmental factors of importance for the aetiology of mental disorders. j Key words population survey – psychiatric epidemiology – mental disorders – urbanizatio
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