138 research outputs found
Geometrical Construction of Heterogeneous Loop Amplitudes in 2D Gravity
We study a disk amplitude which has a complicated heterogeneous matter
configuration on the boundary in a system of the (3,4) conformal matter coupled
to two-dimensional gravity. It is analyzed using the two-matrix chain model in
the large N limit. We show that the disk amplitude calculated by
Schwinger-Dyson equations can completely be reproduced through purely
geometrical consideration. From this result, we speculate that all
heterogeneous loop amplitudes can be derived from the geometrical consideration
and the consistency among relevant amplitudes.Comment: 13 pages, 11 figure
Macroscopic -Loop Amplitude for Minimal Models Coupled to Two-Dimensional Gravity: Fusion Rules and Interactions
We investigate the structure of the macroscopic -loop amplitude obtained
from the two-matrix model at the unitary minimal critical point . We
derive a general formula for the -resolvent correlator at the continuum
planar limit whose inverse Laplace transform provides the amplitude in terms of
the boundary lengths and the renormalized cosmological constant .
The amplitude is found to contain a term consisting of multiplied by the product of modified Bessel
functions summed over their degrees which conform to the fusion rules and the
crossing symmetry. This is found to be supplemented by an increasing number of
other terms with which represent residual interactions of loops. We reveal
the nature of these interactions by explicitly determining them as the
convolution of modified Bessel functions and their derivatives for the case
and the case . We derive a set of recursion relations which relate
the terms in the -resolvents to those in the -resolvents.Comment: 30 pages, Latex, figures: figures have been introduced to represent
our results on the resolvents. A better formula for the resolvents has been
put and the section on residual interactions has been expanded to a large
exten
Macroscopoic Three-Loop Amplitudes and the Fusion Rules from the Two-Matrix Model
From the computation of three-point singlet correlators in the two-matrix
model, we obtain an explicit expression for the macroscopic three-loop
amplitudes having boundary lengths in the case of
the unitary series coupled to two-dimensional gravity. The sum
appearing in this expression is found to conform to the structure of the CFT
fusion rules while the summand factorizes through a product of three modified
Bessel functions. We briefly discuss a possible generalization of these
features to macroscopic -loop amplitudes.Comment: 9 pages, no figure, late
Continuum Annulus Amplitude from the Two-Matrix Model
An explicit expression for continuum annulus amplitudes having boundary
lengths and is obtained from the two-matrix model for the
case of the unitary series; . In the limit of vanishing
cosmological constant, we find an integral representation of these amplitudes
which is reproduced, for the cases of the and the , by a continuum approach consisting of quantum mechanics of loops
and a matter system integrated over the modular parameter of the annulus. We
comment on a possible relation to the unconventional branch of the Liouville
gravity.Comment: 9 pages, OU-HET 190, revised version. A part of the conclusions has
been corrected. A new result on integral representation of the annulus
amplitudes has been adde
Boundary operators in minimal Liouville gravity and matrix models
We interpret the matrix boundaries of the one matrix model (1MM) recently
constructed by two of the authors as an outcome of a relation among FZZT
branes. In the double scaling limit, the 1MM is described by the (2,2p+1)
minimal Liouville gravity. These matrix operators are shown to create a
boundary with matter boundary conditions given by the Cardy states. We also
demonstrate a recursion relation among the matrix disc correlator with two
different boundaries. This construction is then extended to the two matrix
model and the disc correlator with two boundaries is compared with the
Liouville boundary two point functions. In addition, the realization within the
matrix model of several symmetries among FZZT branes is discussed.Comment: 26 page
Loop Equations for + and - Loops in c = 1/2 Non-Critical String Theory
New loop equations for all genera in non-critical string
theory are constructed. Our loop equations include two types of loops, loops
with all Ising spins up (+ loops) and those with all spins down ( loops).
The loop equations generate an algebra which is a certain extension of
algebra and are equivalent to the constraints derived before in the
matrix-model formulation of 2d gravity. Application of these loop equations to
construction of Hamiltonian for string field theory is
considered.Comment: 21 pages, LaTex file, no figure
Evaluation of the aquatic macroinvertebrate community as a tool for monitoring a reservoir in the Pitangui river basin, Paraná, Brazil
Os macroinvertebrados bentônicos e nectônicos representam elementos importantes na estrutura e funcionamento dos ecossistemas aquáticos e sua distribuição é influenciada pela natureza química do substrato, composição da vegetação e profundidade da lâmina d'água. O conhecimento desta fauna contribui para a avaliação da qualidade da água e a elaboração de ações visando à conservação da biodiversidade. No presente estudo foram avaliadas diferentes medidas bióticas da comunidade de invertebrados da represa de Alagados, importante manancial da cidade de Ponta Grossa, no Paraná. Em cinco diferentes pontos de amostragem, foram coletados 18.473 exemplares de macroinvertebrados aquáticos ou semi-aquáticos, pertencentes a 46 táxons dos filos Annelida (Hirudinea e Oligochaeta), Mollusca (Gastropoda), Platyhelminthes (Turbellaria), Nematoda e Arthropoda (Arachnida, Crustacea e Insecta). Esta comunidade foi constituída predominantemente por organismos predadores (45,7% dos táxons amostrados), seguidos de coletores e/ou filtradores (23,9%); raspadores (15,2%), fragmentadores (13%) e detritívoros (2,2%). De modo geral, os índices de diversidade (H') e equitabilidade (J) foram significativamente baixos para os cinco locais investigados, com H' variando de 0,3301 a 1,0396. Quanto à tolerância dos organismos à poluição orgânica, alguns táxons mais sensíveis foram muito raros (Plecoptera) ou em baixa frequência (Trichoptera e Ephemeroptera). Entre os grupos mais resistentes a ambientes poluídos estão os Chironomidae e os Hirudinea, ambos bastante comuns nas amostras de Alagados. Este estudo reforça a importância da análise de bioindicadores na avaliação da qualidade de água para consumo humano e também para a conservação de ecossistemas, considerando que um programa de monitoramento ambiental deve integrar medidas físicas, químicas e biológicas.Benthic and nektonic macroinvertebrates play an important role in the structure and function of aquatic ecosystems and their distribution is influenced by chemical features of the substrate, vegetation composition, and water depth. Knowledge on the fauna contributes to the assessment of water quality and development of biodiversity conservation activities. Different biotic factors affecting the invertebrate community were evaluated in the Alagados reservoir, the main water source of the city of Ponta Grossa, Paraná. In five different sampling points, 18,473 specimens of aquatic or semiaquatic macroinvertebrates were collected, belonging to 46 taxa of the phylla Annelida (Hirudinea and Oligochaeta), Mollusca (Gastropoda), Platyhelminthes (Turbellaria), Nematoda and Arthropoda (Arachnida, Crustacea and Insecta). This community was composed mainly of predators (45.7% of the taxa sampled), collectors and/or filterers (23.9%), scrapers (15.2%), shredders (13.0%) and detritivores (2.2%). Diversity (H') and evenness (J) indices were significantly low for the sites examined, and H' ranged between 0.3301 and 1.0396. Regarding tolerance of organisms to organic pollution, more sensitive taxa were very rare (Plecoptera) or unusual (Trichoptera and Ephemeroptera). Among the more resistant groups are Chironomidae and Hirudinea, both fairly common in the samples. This study corroborates the importance of bioindicators as a tool to assess water quality for human consumption and for the conservation of aquatic environments, integrating physical, chemical and biological factors in monitoring programs
Instabilities and Oscillations in Isotropic Active Gels
We present a generic formulation of the continuum elasticity of an isotropic
crosslinked active gel. The gel is described by a two-component model
consisting of an elastic network coupled frictionally to a permeating fluid.
Activity is induced by active crosslinkers that undergo an ATP-activated cycle
and transmit forces to the network. The on/off dynamics of the active
crosslinkers is described via rate equations for unbound and bound motors. For
large activity motors yield a contractile instability of the network. At
smaller values of activity, the on/off motor dynamics provides an effective
inertial drag on the network that opposes elastic restoring forces, resulting
in spontaneous oscillations. Our work provides a continuum formulation that
unifies earlier microscopic models of oscillations in muscle sarcomeres and a
generic framework for the description of the large scale properties of
isotropic active solids.Comment: 13 pages, 5 figure
Robot-assisted pancreatoduodenectomy with preservation of the vascular supply for autologous islet cell isolation and transplantation: a case report
<p>Abstract</p> <p>Introduction</p> <p>For patients with chronic pancreatitis presenting with medically intractable abdominal pain, surgical intervention may be the only treatment option. However, extensive pancreatic resections are typically performed open and are associated with a substantial amount of postoperative pain, wound complications and long recovery time. Minimally invasive surgery offers an avenue to improve results; however, current limitations of laparoscopic surgery render its application in the setting of chronic pancreatitis technically demanding. Additionally, pancreatic resections are associated with a high incidence of diabetes. Transplantation of islets isolated from the resected pancreas portion offers a way to prevent post-surgical diabetes; however, preservation of the vascular supply during pancreatic resection, which determines islet cell viability, is technically difficult using current laparoscopic approaches. With recent advances in the surgical field, robotic surgery now provides a means to overcome these obstacles to achieve the end goals of pain relief and preserved endocrine function. We present the first report of a novel, minimally invasive robotic approach for resection of the pancreatic head that preserves vascular supply and enables the isolation of a high yield of viable islets for transplantation.</p> <p>Case presentation</p> <p>A 35-year old Caucasian woman presented with intractable chronic abdominal pain secondary to chronic pancreatitis, with a stricture of her main pancreatic duct at the level of the ampulla of Vater and distal dilatation. She was offered a robotic-assisted pylorus-preserving pancreatoduodenectomy and subsequent islet transplantation, to both provide pain relief and preserve insulin-secretory reserves.</p> <p>Conclusion</p> <p>We present a novel, minimally invasive robotic approach for resection of the pancreatic head with complete preservation of the vascular supply, minimal warm ischemia time (less than three minutes) and excellent islet recovery (134,727 islet equivalent). Our patient is currently pain-free with normal glycemic control. Robot-assisted pylorus-preserving pancreatoduodenectomy and autologous islet transplantation can be safely performed and has the potential to minimize operative traumas as well as to partially preserve endocrine function. Results from this case report suggest that this dual procedure should be considered as a treatment option for patients with chronic pancreatitis at earlier stages of the disease, before irreversible islet loss occurs.</p
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