1,971 research outputs found

### On Polynomial Relations in the Heisenberg Algebra

Polynomial relations between the generators of the classical and quantum
Heisenberg algebras are presented. Some of those relations can have a meaning
of the formulas of the normal ordering for the creation/annihilation operators
occurred in the method of the second quantization.Comment: 10 pages, Preprint CRN 94/08 and IFUNAM FT 94-41 (corrected), LaTeX
The title is changed, the paper is expanded, extra references are added,
typos are correcte

### On a graded q-differential algebra

Given a unital associatve graded algebra we construct the graded
q-differential algebra by means of a graded q-commutator, where q is a
primitive N-th root of unity. The N-th power (N>1) of the differential of this
graded q-differential algebra is equal to zero. We use our approach to
construct the graded q-differential algebra in the case of a reduced quantum
plane which can be endowed with a structure of a graded algebra. We consider
the differential d satisfying d to power N equals zero as an analog of an
exterior differential and study the first order differential calculus induced
by this differential.Comment: 6 pages, submitted to the Proceedings of the "International
Conference on High Energy and Mathematical Physics", Morocco, Marrakech,
April 200

### Dynamics of vascular branching morphogenesis: the effect of blood and tissue flow

Vascularization of embryonic organs or tumors starts from a primitive lattice of capillaries. Upon perfusion, this lattice is remodeled into branched arteries and veins. Adaptation to mechanical forces is implied to play a major role in arterial patterning. However, numerical simulations of vessel adaptation to haemodynamics has so far failed to predict any realistic vascular pattern. We present in this article a theoretical modeling of vascular development in the yolk sac based on three features of vascular morphogenesis: the disconnection of side branches from main branches, the reconnection of dangling sprouts ('dead ends'), and the plastic extension of interstitial tissue, which we have observed in vascular morphogenesis. We show that the effect of Poiseuille flow in the vessels can be modeled by aggregation of random walkers. Solid tissue expansion can be modeled by a Poiseuille (parabolic) deformation, hence by deformation under hits of random walkers. Incorporation of these features, which are of a mechanical nature, leads to realistic modeling of vessels, with important biological consequences. The model also predicts the outcome of simple mechanical actions, such as clamping of vessels or deformation of tissue by the presence of obstacles. This study offers an explanation for flow-driven control of vascular branching morphogenesis

### Physical Acoustics

Contains reports on two research projects.U. S. Navy (Office of Naval Research) under Contract Nonr-1841(42)National Aeronautics and Space Administratio

### Goldstone-Mode Phonon Dynamics in the Pyrochlore Cd2Re2O7

We have measured the polarized Raman scattering spectra of Cd2Re2O7, the
first superconducting pyrochlore, as a function of temperature. For
temperatures below the cubic-to-tetragonal structural phase transition (SPT) at
200K, a peak with B1 symmetry develops at zero frequency with divergent
intensity. We identify this peak as the first observation of the Goldstone
phonon in a crystalline solid. The Goldstone phonon is a collective excitation
that exists due to the breaking of the continuous symmetry with the SPT. Its
emergence coincides with that of a Raman-active soft mode. The order parameter
for both features derives from an unstable doubly-degenerate vibration (with Eu
symmetry) of the O1 atoms which drives the SPT.Comment: 4+ pages, 4 figures. Updated figures and text. Accepted to PR

### Biharmonic pattern selection

A new model to describe fractal growth is discussed which includes effects
due to long-range coupling between displacements $u$. The model is based on the
biharmonic equation $\nabla^{4}u =0$ in two-dimensional isotropic defect-free
media as follows from the Kuramoto-Sivashinsky equation for pattern formation
-or, alternatively, from the theory of elasticity. As a difference with
Laplacian and Poisson growth models, in the new model the Laplacian of $u$ is
neither zero nor proportional to $u$. Its discretization allows to reproduce a
transition from dense to multibranched growth at a point in which the growth
velocity exhibits a minimum similarly to what occurs within Poisson growth in
planar geometry. Furthermore, in circular geometry the transition point is
estimated for the simplest case from the relation $r_{\ell}\approx L/e^{1/2}$
such that the trajectories become stable at the growing surfaces in a
continuous limit. Hence, within the biharmonic growth model, this transition
depends only on the system size $L$ and occurs approximately at a distance $60
\%$ far from a central seed particle. The influence of biharmonic patterns on
the growth probability for each lattice site is also analysed.Comment: To appear in Phys. Rev. E. Copies upon request to
[email protected]

### Facebook, a nova arquibancada para o marketing de relacionamento

This paper aims to relate the marketing strategies adopted by football teams in social media networks with an increasing number of users and their interactions on the fanpage of each football club. Information was gathered from the top Brazilian football teams in the first and second divisions in 2013 on Facebook. The findings show that Authenticity, Disclosure and Information Dissemination are positively related to increasing the number of users. Authenticity impacts directly in the number of interactions, reinforcing the need for an active management of the fanpages. The findings show that the professional management of a Facebook page contributes positively to the increase in the number of fans on its pages. This allows clubs to model new relationship strategies with their fans and sponsors.Keywords: social media, social network sites, relationship marketing, marketing strategy, Facebook, sports management.Este artigo tem como objetivo relacionar as estratÃ©gias de marketing adotadas por equipes de futebol em redes sociais com o aumento no nÃºmero de usuÃ¡rios e de suas interaÃ§Ãµes na fanpage de cada clube. Para atingir esse objetivo, coletaram-se informaÃ§Ãµes das principais equipes da primeira e segunda divisÃ£o de futebol brasileiro em 2013 no Facebook. As descobertas mostram que a Autenticidade, a DivulgaÃ§Ã£o e a InformaÃ§Ã£o sÃ£o positivamente relacionadas com o aumento de usuÃ¡rios. A Autenticidade impacta diretamente no nÃºmero de interaÃ§Ãµes, reforÃ§ando a necessidade de uma gestÃ£o ativa das pÃ¡ginas. As descobertas mostram que o gerenciamento profissional de pÃ¡ginas do Facebook contribui positivamente para o aumento do nÃºmero de fÃ£s em suas pÃ¡ginas. Isso permite aos clubes modelar novas estratÃ©gias de relacionamento com seus fÃ£s e patrocinadores.Palavras-chave: mÃdia social, sites de redes sociais, marketing de relacionamento, estratÃ©gia de marketing, Facebook, marketing esportivo

### Strategy for Enhancing Ultrahigh-Molecular-Weight Block Copolymer Chain Mobility to Access Large Period Sizes (>100 nm)

Assembling ultrahigh-molecular-weight (UHMW) block copolymers (BCPs) in rapid time scales is perceived as a grand challenge in polymer science due to slow kinetics. Through surface engineering and identifying a nonvolatile solvent (propylene glycol methyl ether acetate, PGMEA), we showcase the impressive ability of a series of lamellar poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) BCPs to self-assemble directly after spin-coating. In particular, we show the formation of large-period (â‰ˆ111 nm) lamellar structures from a neat UHMW PS-b-P2VP BCP. The significant influence of solventâ€“polymer solubility parameters are explored to enhance the polymer chain mobility. After optimization using solvent vapor annealing, increased feature order of ultralarge-period PS-b-P2VP BCP patterns in 1 h is achieved. Isolated metallic and dielectric features are also demonstrated to exemplify the promise that large BCP periods offer for functional applications. The methods described in this article center on industry-compatible patterning schemes, solvents, and deposition techniques. Thus, our straightforward UHMW BCP strategy potentially paves a viable and practical path forward for large-scale integration in various sectors, e.g., photonic band gaps, polarizers, and membranes that demand ultralarge period sizes

### Theory of Non-Reciprocal Optical Effects in Antiferromagnets: The Case Cr_2O_3

A microscopic model of non-reciprocal optical effects in antiferromagnets is
developed by considering the case of Cr_2O_3 where such effects have been
observed. These effects are due to a direct coupling between light and the
antiferromagnetic order parameter. This coupling is mediated by the spin-orbit
interaction and involves an interplay between the breaking of inversion
symmetry due to the antiferromagnetic order parameter and the trigonal field
contribution to the ligand field at the magnetic ion. We evaluate the matrix
elements relevant for the non-reciprocal second harmonic generation and
gyrotropic birefringence.Comment: accepted for publication in Phys. Rev.

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