145 research outputs found

    A Free-Algebraic Solution for the Planar Approximation

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    An explicit solution for the generating functional of n-point functions in the planar approximation is given in terms of two sets of free-algebraic annihilation and creation operators.Comment: 15 pages, added referenc

    Loop models, random matrices and planar algebras

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    We define matrix models that converge to the generating functions of a wide variety of loop models with fugacity taken in sets with an accumulation point. The latter can also be seen as moments of a non-commutative law on a subfactor planar algebra. We apply this construction to compute the generating functions of the Potts model on a random planar map

    Exact beta function from the holographic loop equation of large-N QCD_4

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    We construct and study a previously defined quantum holographic effective action whose critical equation implies the holographic loop equation of large-N QCD_4 for planar self-avoiding loops in a certain regularization scheme. We extract from the effective action the exact beta function in the given scheme. For the Wilsonean coupling constant the beta function is exacly one loop and the first coefficient agrees with its value in perturbation theory. For the canonical coupling constant the exact beta function has a NSVZ form and the first two coefficients agree with their value in perturbation theory.Comment: 42 pages, latex. The exponent of the Vandermonde determinant in the quantum effective action has been changed, because it has been employed a holomorphic rather than a hermitean resolution of identity in the functional integral. Beta function unchanged. New explanations and references added, typos correcte

    Strings in flat space and pp waves from N=4{\cal N}=4 Super Yang Mills

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    We explain how the string spectrum in flat space and pp-waves arises from the large NN limit, at fixed gYM2g^2_{YM}, of U(N) N=4{\cal N} =4 super Yang Mills. We reproduce the spectrum by summing a subset of the planar Feynman diagrams. We give a heuristic argument for why we can neglect other diagrams. We also discuss some other aspects of pp-waves and we present a matrix model associated to the DLCQ description of the maximally supersymmetric eleven dimensional pp-waves.Comment: 36 pages, 5 figures. v3: minor typos corrected, references adde

    A random cell motility gradient downstream of FGF controls elongation of amniote embryos

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    Vertebrate embryos are characterized by an elongated antero-posterior (AP) body axis, which forms by progressive cell deposition from a posterior growth zone in the embryo. Here, we used tissue ablation in the chicken embryo to demonstrate that the caudal presomitic mesoderm (PSM) has a key role in axis elongation. Using time-lapse microscopy, we analysed the movements of fluorescently labelled cells in the PSM during embryo elongation, which revealed a clear posterior-to-anterior gradient of cell motility and directionality in the PSM. We tracked the movement of the PSM extracellular matrix in parallel with the labelled cells and subtracted the extracellular matrix movement from the global motion of cells. After subtraction, cell motility remained graded but lacked directionality, indicating that the posterior cell movements associated with axis elongation in the PSM are not intrinsic but reflect tissue deformation. The gradient of cell motion along the PSM parallels the fibroblast growth factor (FGF)/mitogen-activated protein kinase (MAPK) gradient1, which has been implicated in the control of cell motility in this tissue2. Both FGF signalling gain- and loss-of-function experiments lead to disruption of the motility gradient and a slowing down of axis elongation. Furthermore, embryos treated with cell movement inhibitors (blebbistatin or RhoK inhibitor), but not cell cycle inhibitors, show a slower axis elongation rate. We propose that the gradient of random cell motility downstream of FGF signalling in the PSM controls posterior elongation in the amniote embryo. Our data indicate that tissue elongation is an emergent property that arises from the collective regulation of graded, random cell motion rather than by the regulation of directionality of individual cellular movements

    Progress in noncommutative function theory

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    In this expository paper we describe the study of certain non-self-adjoint operator algebras, the Hardy algebras, and their representation theory. We view these algebras as algebras of (operator valued) functions on their spaces of representations. We will show that these spaces of representations can be parameterized as unit balls of certain WÔłŚW^{*}-correspondences and the functions can be viewed as Schur class operator functions on these balls. We will provide evidence to show that the elements in these (non commutative) Hardy algebras behave very much like bounded analytic functions and the study of these algebras should be viewed as noncommutative function theory

    Nonhermitean Random Matrix Models : a Free Random Variable Approach

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    Using the standard concepts of free random variables, we show that for a large class of nonhermitean random matrix models, the support of the eigenvalue distribution follows from their hermitean analogs using a conformal transformation. We also extend the concepts of free random variables to the class of nonhermitean matrices, and apply them to the models discussed by Ginibre-Girko (elliptic ensemble) and Mahaux-Weidenm\"uller (chaotic resonance scattering).Comment: 7 pages LaTeX, 1 EPS figur

    Muscle flaps ÔÇô an alternative for decortication or resection to solve the residual space in impaired patients

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    Universitatea de Medicin─â ╚Öi Farmacie ÔÇ×Victor Babe╚ÖÔÇŁ, Clinica I Chirurgie, Spitalul Clinic Jude┼úean de Urgen┼ú─â ÔÇ×Pius BrinzeuÔÇŁ, Clinica de Chirurgie Toracic─â, Spitalul Clinic Municipal de Urgen┼ú─â, Timi╚Öoara, Rom├ónia, Al XIII-lea Congres al Asocia╚Ťiei Chirurgilor ÔÇ×Nicolae AnestiadiÔÇŁ ╚Öi al III-lea Congres al Societ─â╚Ťii de Endoscopie, Chirurgie miniminvaziv─â ╚Öi Ultrasonografie ÔÇŁV.M.Gu╚ŤuÔÇŁ din Republica MoldovaIntroducere: Decortic─ârile sau rezec╚Ťiile pulmonare reprezint─â tratamentul chirurgical obi┼čnuit ├«n cazul pacien╚Ťilor cu empiem sau abcese pulmonare cronice. Pentru un num─âr redus de pacien╚Ťi cu comorbidit─â╚Ťi severe asociate sau disfunc╚Ťii respiratorii aceste opera╚Ťii nu sunt indicate. Am analizat eficien╚Ťa lambourilor musculare pentru a corecta cavit─â╚Ťile reziduale. Material ╚Öi metode: Am studiat pacien╚Ťi cu scor de risc ASA >3, cu FEV si FVC<40, clasa NYHA mai mare sau egal─â cu II. Am inclus ├«n studiu pacien╚Ťi cu empiem (1caz), aspergiliom (8 cazuri), abces pulmonar cronic (1 caz) .Am folosit diverse lambouri musculare pentru a umple cavit─â╚Ťile. Pentru pacien╚Ťii cu aspergilom am practicat toracotomie, cavernotomie, excizia micetomului, sutura fistulei. Am folosit lambouri din pectoralul mare (2), mu┼čchii intercostali (4) ┼či dorsal mare (2). Pentru pacien╚Ťii cu supura╚Ťii cronice pulmonare am folosit dorsal mare, iar pentru empiem am asociat ┼či mu┼čchi pectoral mare, trapez ┼či intercostal cu toracoplastie. Rezultate: Evolu╚Ťia imediat─â a fost favorabil─â ├«n toate cazurile cu excep╚Ťia unuia care a necesitat reinterven╚Ťie pentru s├óngerare. Un pacient a dezvoltat serom. ├Än toate cazurile, viabilitatea lamboului nu a fost afectat─â. Nu s-au inregistrat decese. Concluzii: Scopul acestor interven╚Ťii a fost sa elimin─âm spa╚Ťiile libere din pleur─â sau pl─âm├ón. Pentru pacien╚Ťii tara╚Ťi, decortic─ârile ┼či rezec╚Ťiile sunt opera╚Ťii riscante, aceast─â nou─â abordare fiind benefic─â. Evolu╚Ťia favorabil─â, morbiditatea minim─â dup─â folosirea lambourilor musculare justific─â deplin acest procedeu. Chiar dac─â num─ârul mic de cazuri ├«n care am practicat acest tip de opera╚Ťie ne limiteaz─â pentru moment spectrul de experien╚Ť─â, rezultatele pozitive sunt ├«ncurajatoare.Introduction: The surgical treatment of residual space for patients with empyema or chronic lung abscess is in most cases decortication or lung resection. For a limited number of patients with severe comorbidities or respiratory dysfunction these procedures are prohibited. We analyzed the efficiency of muscle flaps to solve the residual cavities these patients. Material and methods: We studied patients with ASA risk > 3, with FEV and FVC < 40%, NYHA II or more. Patients with empyema (1 case), aspergilloma (8 cases), chronic lung abscess (1 case) were included in the study. Different types of muscle flaps were used to fill the cavities. For patients with aspergilloma we performed thoracotomy, cavernotomy, excision of the micetoma, fistulae suture; muscles used: pectoris major ÔÇô 2, intercostal ÔÇô 4 and latissimus dorsi ÔÇô 2. For the patient with chronic suppuration of the lung we used latissimus, and for the empyema we associated pectoris major, trapezius and intercostal muscle with thoracoplasty. Results: The immediate outcome was favorable in all cases except one who required exploration for bleeding. One patient developed wound seroma. In all cases the viability of the transposed muscle was not affected. We recorded no mortality. Conclusions: The aim of surgery is to eliminate all empty space in the pleura or lung. For impaired patients decortication or resection are very risky, thus new approach was needed. The good outcome, minimal morbidity after using muscle flaps, fully justify their use. The low number of patients limits our experience, but the good results are encouraging

    Twisted local systems solve the (holographic) loop equation of large-N QCD_4

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    We construct a holographic map from the loop equation of large-N QCD in d=2 and d=4, for planar self-avoiding loops, to the critical equation of an equivalent effective action. The holographic map is based on two ingredients: an already proposed holographic form of the loop equation, such that the quantum contribution is reduced to a regularized residue; a new conformal map from the region encircled by the based loop to a cuspidal fundamental domain in the upper half-plane, such that the regularized residue vanishes at the cusp. As a check, we study the first coefficient of the beta function and that part of the second coefficient which arises from the rescaling anomaly, in passing from the Wilsonian to the canonically normalised (holographic) effective action.Comment: 42 pages, latex; abstract shortened and a reference added as suggested by the referee; typos in Eq.(72,76,77,82,83,84) correcte
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