200 research outputs found
"The Role of Banks Where Service Replication Has Eroded Institutional Franchises"
Over the past decade forces of competition and adverse economic conditions--combined with regulatory forbearance and the moral hazards generated thereby-have contributed to severe erosion of bank profitability and a mounting number of insolvencies. At least three implications of this erosion may be identified. First, in response to pressures on capital and profits bank business strategies have begun emphasizing contraction and consolidation. Second, barring new elements of weakness afflicting other suppliers of financial services on which banks could capitalize, the role of banks in the future is likely to be reduced further. Third, the extent of this reduction will hinge to a considerable degree on whether new public policies applying to capital and deposit insurance are imposed. Life support policies will not restore the weak, but will impair the competitive viability of those remaining strong. The material is divided into four parts. The first consists of a brief summary of recent bank performance. The succeeding sections address the three implications introduced above.
Instantons, Quivers and Noncommutative Donaldson-Thomas Theory
We construct noncommutative Donaldson-Thomas invariants associated with
abelian orbifold singularities by analysing the instanton contributions to a
six-dimensional topological gauge theory. The noncommutative deformation of
this gauge theory localizes on noncommutative instantons which can be
classified in terms of three-dimensional Young diagrams with a colouring of
boxes according to the orbifold group. We construct a moduli space for these
gauge field configurations which allows us to compute its virtual numbers via
the counting of representations of a quiver with relations. The quiver encodes
the instanton dynamics of the noncommutative gauge theory, and is associated to
the geometry of the singularity via the generalized McKay correspondence. The
index of BPS states which compute the noncommutative Donaldson-Thomas
invariants is realized via topological quantum mechanics based on the quiver
data. We illustrate these constructions with several explicit examples,
involving also higher rank Coulomb branch invariants and geometries with
compact divisors, and connect our approach with other ones in the literature.Comment: 95 pages, 5 figures; v2: clarifying comments added, discussions using
tilting strengthened, references added and updated; v3: minor corrections,
final version to be published in Nuclear Physics
Mirror Maps in Chern-Simons Gauge Theory
We describe mirror symmetry in N=2 superconformal field theories in terms of
a dynamical topology changing process of the principal fiber bundle associated
with a topological membrane. We show that the topological symmetries of
Calabi-Yau sigma-models can be obtained from discrete geometric transformations
of compact Chern-Simons gauge theory coupled to charged matter fields. We
demonstrate that the appearence of magnetic monopole-instantons, which
interpolate between topologically inequivalent vacua of the gauge theory,
implies that the discrete symmetry group of the worldsheet theory is realized
kinematically in three dimensions as the magnetic flux symmetry group. From
this we construct the mirror map and show that it corresponds to the
interchange of topologically non-trivial matter field and gauge degrees of
freedom. We also apply the mirror transformation to the mean field theory of
the quantum Hall effect. We show that it maps the Jain hierarchy into a new
hierarchy of states in which the lowest composite fermions have the same
filling fractions.Comment: 40 pages LaTeX, 4 postscript files, uses psfig.sty; minor textual
changes, typos corrected, references adde
An N = 2 Supersymmetric Membrane Flow
We find M-theory solutions that are holographic duals of flows of the
maximally supersymmetric N=8 scalar-fermion theory in (2+1) dimensions. In
particular, we construct the M-theory solution dual to a flow in which a single
chiral multiplet is given a mass, and the theory goes to a new infra-red fixed
point. We also examine this new solution using M2-brane probes. The
(2+1)-dimensional field theory fixed-point is closely related to that of Leigh
and Strassler, while the M-theory solution is closely related to the
corresponding IIB flow solution. We recast the IIB flow solution in a more
geometric manner and use this to obtain an Ansatz for the M-theory flow. We are
able to generalize our solution further to obtain flows with del Pezzo
sub-manifolds, and we give an explicit solution with a conifold singularity.Comment: 28 pages; harvma
BAAD: a Biomass And Allometry Database for woody plants
Understanding how plants are constructedâi.e., how key size dimensions and the amount of mass invested in different tissues varies among individualsâis essential for modeling plant growth, carbon stocks, and energy fluxes in the terrestrial biosphere. Allocation patterns can differ through ontogeny, but also among coexisting species and among species adapted to different environments. While a variety of models dealing with biomass allocation exist, we lack a synthetic understanding of the underlying processes. This is partly due to the lack of suitable data sets for validating and parameterizing models. To that end, we present the Biomass And Allometry Database (BAAD) for woody plants. The BAAD contains 259â634 measurements collected in 176 different studies, from 21â084 individuals across 678 species. Most of these data come from existing publications. However, raw data were rarely made public at the time of publication. Thus, the BAAD contains data from different studies, transformed into standard units and variable names. The transformations were achieved using a common workflow for all raw data files. Other features that distinguish the BAAD are: (i) measurements were for individual plants rather than stand averages; (ii) individuals spanning a range of sizes were measured; (iii) plants from 0.01â100 m in height were included; and (iv) biomass was estimated directly, i.e., not indirectly via allometric equations (except in very large trees where biomass was estimated from detailed subâsampling). We included both wild and artificially grown plants. The data set contains the following size metrics: total leaf area; area of stem crossâsection including sapwood, heartwood, and bark; height of plant and crown base, crown area, and surface area; and the dry mass of leaf, stem, branches, sapwood, heartwood, bark, coarse roots, and fine root tissues. We also report other properties of individuals (age, leaf size, leaf mass per area, wood density, nitrogen content of leaves and wood), as well as information about the growing environment (location, light, experimental treatment, vegetation type) where available. It is our hope that making these data available will improve our ability to understand plant growth, ecosystem dynamics, and carbon cycling in the world\u27s vegetation
CO2 enrichment and soil type additively regulate grassland productivity
The development of a predictive understanding of how atmospheric CO2 enrichment is affecting the primary productivity of the terrestrial biosphere is among the most pressing of ecological challenges. The terrestrial biosphere absorbs c. 25% of anthropogenic carbon (C) emissions (Le Quere et al., 2018). Uncertainty in CO2 effects on ecosystem C uptake is a major constraint in the prediction of C cycling and the provisioning of productivity- related ecosystem services.
Grasslands cover c. 25% of the terrestrial area and are an important contributor to the global C balance (Sala et al., 1996). CO2 enrichment stimulates the aboveground net primary productivity (ANPP) of most water-limited grasslands by increasing plant water use efficiency (WUE; productivity per unit of transpiration; Morgan et al., 2004; Nowak et al., 2004; Fatichi et al., 2016), but grassland ANPP, as other ecosystem functions, is determined by drivers in addition to water availability which act simultaneously and often interactively with CO2 (Polley et al., 2011). CO2 enrichment usually shows greater stimulation of plant productivity when nitrogen (N) availability is relatively high (Owensby et al., 1994; Reich & Hobbie, 2013; Mueller et al., 2016), for example. Other drivers include precipitation timing (Hovenden et al., 2014), disturbance regimes (Newton et al., 2014), plant species composition (Langley & Megonigal, 2010; Fay et al., 2012; Polley et al., 2012) and soil properties (Epstein et al., 1997, 1998), including soil texture, which influences water availability to plants (Tor-Ngern et al., 2017)
CO2 enrichment and soil type additively regulate grassland productivity
The development of a predictive understanding of how atmospheric CO2 enrichment is affecting the primary productivity of the terrestrial biosphere is among the most pressing of ecological challenges. The terrestrial biosphere absorbs c. 25% of anthropogenic carbon (C) emissions (Le Quere et al., 2018). Uncertainty in CO2 effects on ecosystem C uptake is a major constraint in the prediction of C cycling and the provisioning of productivity- related ecosystem services.
Grasslands cover c. 25% of the terrestrial area and are an important contributor to the global C balance (Sala et al., 1996). CO2 enrichment stimulates the aboveground net primary productivity (ANPP) of most water-limited grasslands by increasing plant water use efficiency (WUE; productivity per unit of transpiration; Morgan et al., 2004; Nowak et al., 2004; Fatichi et al., 2016), but grassland ANPP, as other ecosystem functions, is determined by drivers in addition to water availability which act simultaneously and often interactively with CO2 (Polley et al., 2011). CO2 enrichment usually shows greater stimulation of plant productivity when nitrogen (N) availability is relatively high (Owensby et al., 1994; Reich & Hobbie, 2013; Mueller et al., 2016), for example. Other drivers include precipitation timing (Hovenden et al., 2014), disturbance regimes (Newton et al., 2014), plant species composition (Langley & Megonigal, 2010; Fay et al., 2012; Polley et al., 2012) and soil properties (Epstein et al., 1997, 1998), including soil texture, which influences water availability to plants (Tor-Ngern et al., 2017)
BAAD: A biomass and allometry database for woody plants.
Understanding how plants are constructedâi.e., how key size dimensions and the amount of mass invested in different tissues varies among individualsâis essential for modeling plant growth, carbon stocks, and energy fluxes in the terrestrial biosphere. Allocation patterns can differ through ontogeny, but also among coexisting species and among species adapted to different environments. While
a variety of models dealing with biomass allocation exist, we lack a synthetic understanding of the underlying processes. This is partly due to the lack of suitable data sets for validating and parameterizing models. To that end, we present the Biomass And Allometry Database (BAAD) for woody plants. The BAAD contains 259 634 measurements collected in 176 different studies, from 21 084 individuals across 678 species. Most of these data come from existing publications. However, raw data were rarely made public at the time of publication. Thus, the BAAD contains data from different studies, transformed into standard units and variable names. The transformations were achieved using a common workflow for all raw data files. Other features that distinguish the BAAD are: (i) measurements were for individual plants rather than stand averages; (ii) individuals spanning a range of sizes were measured; (iii) plants from 0.01â 100 m in height were included; and (iv) biomass was estimated directly, i.e., not indirectly via allometric
equations (except in very large trees where biomass was estimated from detailed sub-sampling). We included both wild and artificially grown plants. The data set contains the following size metrics: total leaf area; area of stem cross-section including sapwood, heartwood, and bark; height of plant and crown base, crown area, and surface area; and the dry mass of leaf, stem, branches, sapwood, heartwood, bark, coarse roots, and fine root tissues. We also report other properties of individuals (age, leaf size, leaf mass per area,
wood density, nitrogen content of leaves and wood), as well as information about the growing environment (location, light, experimental treatment, vegetation type) where available. It is our hope that making these data available will improve our ability to understand plant growth, ecosystem dynamics, and carbon cycling in the worldâs vegetation.EEA Santa CruzFil: Falster, Daniel S. Macquarie University. Biological Sciences; Australia.Fil: Duursma, Remko A. University of Western Sydney. Hawkesbury Insitute for the Environment; Australia.Fil: Ishihara, Masae I. Hiroshima University. Graduate School for International Development and Cooperation; JapĂłn.Fil: Barneche, Diego R. Macquarie University. Biological Sciences; Australia.Fil: FitzJohn, Richard G. Macquarie University. Biological Sciences; Australia.Fil: VĂ„rhammar, Angelica. University of Western Sydney. Hawkesbury Insitute for the Environment; Australia.Fil: Aiba, Masahiro. Tohoku University. Graduate School of Life Sciences; JapĂłn.Fil: Ando, Makoto. Kyoto University. Field Science Education and Research Center; JapĂłnFil: Anten, Niels. Centre for Crop Systems Analysis; PaĂses BajosFil: Aspinwall, Michael J. University of Western Sydney. Hawkesbury Insitute for the Environment; Australia.Fil: Gargaglione VerĂłnica Beatriz. Instituto Nacional de TecnologĂa Agropecuaria (INTA). EstaciĂłn Experimental Agropecuaria Santa Cruz; Argentina.Fil: Gargaglione VerĂłnica Beatriz. Universidad Nacional de la Patagonia Austral; Argentina.Fil: Peri, Pablo Luis. Instituto Nacional de TecnologĂa Agropecuaria (INTA). EstaciĂłn Experimental Agropecuaria Santa Cruz; Argentina.Fil: Peri, Pablo Luis. Universidad Nacional de la Patagonia Austral; Argentina.Fil: Peri, Pablo Luis. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina.Fil: York, Robert A. University of California Berkeley. Center for Forestry; Estados Unido
Aspects of ALE Matrix Models and Twisted Matrix Strings
We examine several aspects of the formulation of M(atrix)-Theory on ALE
spaces. We argue for the existence of massless vector multiplets in the
resolved spaces, as required by enhanced gauge symmetry in M-Theory,
and that these states might have the correct gravitational interactions. We
propose a matrix model which describes M-Theory on an ALE space in the presence
of wrapped membranes. We also consider orbifold descriptions of matrix string
theories, as well as more exotic orbifolds of these models, and present a
classification of twisted matrix string theories according to Reid's exact
sequences of surface quotient singularities.Comment: 27 pages LaTeX2e, 7 figures, using utarticle.cls (included),
array.sty, amsmath.sty, amsfonts.sty, cite.sty, epsf.sty. Bibtex style:
utphys.bst (.bbl file included). Section on wrapped membrane states revised
and expanded. We now argue for the existence of wrapped membranes and propose
a matrix model which describes M-Theory on an ALE space in the presence of
wrapped membrane
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