Matrix product representation of gauge invariant states in a Z_2 lattice gauge theory

The Gauss law needs to be imposed on quantum states to guarantee gauge invariance when one studies gauge theory in hamiltonian formalism. In this work, we propose an efficient variational method based on the matrix product ansatz for a Z_2 lattice gauge theory on a spatial ladder chain. Gauge invariant low-lying states are identified by evaluating expectation values of the Gauss law operator after numerical diagonalization of the gauge hamiltonian.Comment: 15 pages, 6 figures, minor corrections, accepted for publication in JHE

Cosmetic mastoidectomy for the combined supra/infratentorial transtemporal approach

Journal ArticleThe authors describe a cosmetic mastoidectomy technique for use when performing a combined supra/ infratentorial craniotomy and transtemporal exposure. The technique involves a single temporal suboccipital bone flap and cosmetic mastoidectomy, removing the outer table of bone for later replacement. Replacement of the outer table of mastoid bone enables tamponade of a fat graft against the dura to reduce the risk of postoperative cerebrospinal fluid leaks. The technique has been performed in eight patients treated for petrocliva[ meningiomas with excellent cosmetic results

Petroclival meningiomas: surgical experience in 109 cases

Journal ArticleThe surgical removal of petroclival meningiomas has historically been associated with a high incidence of morbidity and mortality. The 109 consecutive patients included in the present retrospective study represent a combined series of tumors operated on by the four authors during a period from 1980 to 1992. The series is composed of 40 men and 69 women ranging in age from 25 to 75 years (mean 51 years). Surgical approaches to tumors in this series included simple retromastoid (60 cases), combined supra- and infratentorial petrosal (22), transtemporal (primary transsigmoid retrolabyrinthine, translabyrinthine, or transcochlear (12), subtemporal (11), and frontotemporal transcavernous (eight). Grosstotal removal was achieved in 75 patients (69%). Recurrence or progression of disease occurred in 14 patients (13%) over a 6.1-year mean follow-up period, and it was found within the cavernous sinus in 12 of these cases. Four recurrent cases demonstrated histological compatibility with malignant meningioma. Perioperative death occurred in four patients, and there were 56 significant complications in 35 other patients. Review of this series, with the attendant complications, has facilitated the authors' decision-making when considering the risk of gross-total removal in selected patients with asymptomatic cavernous sinus invasion or tumor adherent to the brainstem

Axial anomaly with the overlap-Dirac operator in arbitrary dimensions

We evaluate for arbitrary even dimensions the classical continuum limit of the lattice axial anomaly defined by the overlap-Dirac operator. Our calculational scheme is simple and systematic. In particular, a powerful topological argument is utilized to determine the value of a lattice integral involved in the calculation. When the Dirac operator is free of species doubling, the classical continuum limit of the axial anomaly in various dimensions is combined into a form of the Chern character, as expected.Comment: 9 pages, uses JHEP.cls and amsfonts.sty, the final version to appear in JHE

Spectrum of the Hermitian Wilson-Dirac Operator for a Uniform Magnetic Field in Two Dimensions

It is shown that the eigenvalue problem for the hermitian Wilson-Dirac operator of for a uniform magnetic field in two dimensions can be reduced to one-dimensional problem described by a relativistic analog of the Harper equation. An explicit formula for the secular equations is given in term of a set of polynomials. The spectrum exhibits a fractal structure in the infinite volume limit. An exact result concerning the index theorem for the overlap Dirac operator is obtained.Comment: 8 pages, latex, 3 eps figures, minor correction

Neural networks for action representation: a functional magnetic-resonance imaging and dynamic causal modeling study

Automatic mimicry is based on the tight linkage between motor and perception action representations in which internal models play a key role. Based on the anatomical connection, we hypothesized that the direct effective connectivity from the posterior superior temporal sulcus (pSTS) to the ventral premotor area (PMv) formed an inverse internal model, converting visual representation into a motor plan, and that reverse connectivity formed a forward internal model, converting the motor plan into a sensory outcome of action. To test this hypothesis, we employed dynamic causal-modeling analysis with functional magnetic-resonance imaging (fMRI). Twenty-four normal participants underwent a change-detection task involving two visually-presented balls that were either manually rotated by the investigator's right hand (“Hand”) or automatically rotated. The effective connectivity from the pSTS to the PMv was enhanced by hand observation and suppressed by execution, corresponding to the inverse model. Opposite effects were observed from the PMv to the pSTS, suggesting the forward model. Additionally, both execution and hand observation commonly enhanced the effective connectivity from the pSTS to the inferior parietal lobule (IPL), the IPL to the primary sensorimotor cortex (S/M1), the PMv to the IPL, and the PMv to the S/M1. Representation of the hand action therefore was implemented in the motor system including the S/M1. During hand observation, effective connectivity toward the pSTS was suppressed whereas that toward the PMv and S/M1 was enhanced. Thus, the action-representation network acted as a dynamic feedback-control system during action observation

Dirac Operator Zero-modes on a Torus

We study Dirac operator zero-modes on a torus for gauge background with uniform field strengths. Under the basic translations of the torus coordinates the wave functions are subject to twisted periodic conditions. In a suitable torus coordinates the zero-mode wave functions can be related to holomorphic functions of the complex torus coordinates. We construct the zero-mode wave functions that satisfy the twisted periodic conditions. The chirality and the degeneracy of the zero-modes are uniquely determined by the gauge background and are consistent with the index theorem.Comment: 28 pages, 2 figure

Nonperturbative renormalization group in a light-front three-dimensional real scalar model

The three-dimensional real scalar model, in which the $Z_2$ symmetry spontaneously breaks, is renormalized in a nonperturbative manner based on the Tamm-Dancoff truncation of the Fock space. A critical line is calculated by diagonalizing the Hamiltonian regularized with basis functions. The marginal ($\phi^6$) coupling dependence of the critical line is weak. In the broken phase the canonical Hamiltonian is tachyonic, so the field is shifted as $\phi(x)\to\varphi(x)+v$. The shifted value $v$ is determined as a function of running mass and coupling so that the mass of the ground state vanishes.Comment: 23 pages, LaTeX, 6 Postscript figures, uses revTeX and epsbox.sty. A slight revision of statements made, some references added, typos correcte

Development of osteogenic cell sheets for bone tissue engineering applications

The use of scaffolds in combination with osteogenic cells has been the gold standard in bone tissue engineering strategies. These strategies have, however, in many cases failed to produce the desired results due to issues such as the immunogenicity of the biomaterials used and cell necrosis at the bulk of the scaffold related to deficient oxygen and nutrients diffusion. Here, we originally propose the use of cell sheet (CS) engineering as a possible way to overcome some of these obstacles. Osteogenic CSs were fabricated by culturing rat bone marrow stromal cells in thermoresponsive culture dishes. The CSs were recovered from the dishes using a low-temperature treatment and then were implanted subcutaneously in nude mice. New bone formation was verified from day 7 post-transplantation using X-ray, microcomputed tomography, and histological analysis. The presence of a vascularized marrow was also verified in the newly formed bone after 6 weeks of transplantation. Further, osteocytes were found in this newly formed tissue, supporting the conclusion that mature bone was formed after ectopically transplanting osteogenic CSs. These results therefore confirm the great potentiality of CS engineering to be used in bone tissue engineering applicationsThis study was partially supported by Formation of Innovation Center for Fusion of Advanced Technologies in the Special Coordination Funds for Promoting Science and Technology "Cell Sheet Tissue Engineering Center (CSTEC)" and the Global COE program, Multidisciplinary Education and Research Center for Regenerative Medicine (MER-CREM), from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.Financial support to R. P. Pirraco by the Portuguese Foundation for Science and Technology (FCT) through the PhD grant SFRH/BD/44893/2008 is also acknowledged