Application of Finite Strain Landau Theory To High Pressure Phase Transitions

In this paper we explain how to set up what is in fact the only possible consistent construction scheme for a Landau theory of high pressure phase transitions that systematically allows to take into account elastic nonlinearities. We also show how to incorporate available information on the pressure dependence of elastic constants taken from experiment or simulation. We apply our new theory to the example of the high pressure cubic-tetragonal phase transition in Strontium Titanate, a model perovskite that has played a central role in the development of the theory of structural phase transitions. Armed with pressure dependent elastic constants calculated by density functional theory, we give a both qualitatively as well as quantitatively satisfying description of recent high precision experimental data. Our nonlinear theory also allows to predict a number of additional elastic transition anomalies that are accessible to experiment.Comment: submitted to Phys. Rev. Let

Robot graphic simulation testbed

The objective of this research was twofold. First, the basic capabilities of ROBOSIM (graphical simulation system) were improved and extended by taking advantage of advanced graphic workstation technology and artificial intelligence programming techniques. Second, the scope of the graphic simulation testbed was extended to include general problems of Space Station automation. Hardware support for 3-D graphics and high processing performance make high resolution solid modeling, collision detection, and simulation of structural dynamics computationally feasible. The Space Station is a complex system with many interacting subsystems. Design and testing of automation concepts demand modeling of the affected processes, their interactions, and that of the proposed control systems. The automation testbed was designed to facilitate studies in Space Station automation concepts

Modelling and analyzing adaptive self-assembling strategies with Maude

Building adaptive systems with predictable emergent behavior is a challenging task and it is becoming a critical need. The research community has accepted the challenge by introducing approaches of various nature: from software architectures, to programming paradigms, to analysis techniques. We recently proposed a conceptual framework for adaptation centered around the role of control data. In this paper we show that it can be naturally realized in a reflective logical language like Maude by using the Reflective Russian Dolls model. Moreover, we exploit this model to specify and analyse a prominent example of adaptive system: robot swarms equipped with obstacle-avoidance self-assembly strategies. The analysis exploits the statistical model checker PVesta

Rounding of first-order phase transitions and optimal cooperation in scale-free networks

We consider the ferromagnetic large-$q$ state Potts model in complex evolving networks, which is equivalent to an optimal cooperation problem, in which the agents try to optimize the total sum of pair cooperation benefits and the supports of independent projects. The agents are found to be typically of two kinds: a fraction of $m$ (being the magnetization of the Potts model) belongs to a large cooperating cluster, whereas the others are isolated one man's projects. It is shown rigorously that the homogeneous model has a strongly first-order phase transition, which turns to second-order for random interactions (benefits), the properties of which are studied numerically on the Barab\'asi-Albert network. The distribution of finite-size transition points is characterized by a shift exponent, $1/\tilde{\nu}'=.26(1)$, and by a different width exponent, $1/\nu'=.18(1)$, whereas the magnetization at the transition point scales with the size of the network, $N$, as: $m\sim N^{-x}$, with $x=.66(1)$.Comment: 8 pages, 6 figure

Density of critical clusters in strips of strongly disordered systems

We consider two models with disorder dominated critical points and study the distribution of clusters which are confined in strips and touch one or both boundaries. For the classical random bond Potts model in the large-q limit we study optimal Fortuin-Kasteleyn clusters by combinatorial optimization algorithm. For the random transverse-field Ising chain clusters are defined and calculated through the strong disorder renormalization group method. The numerically calculated density profiles close to the boundaries are shown to follow scaling predictions. For the random bond Potts model we have obtained accurate numerical estimates for the critical exponents and demonstrated that the density profiles are well described by conformal formulae.Comment: 9 pages, 9 figure

Interface mapping in two-dimensional random lattice models

We consider two disordered lattice models on the square lattice: on the medial lattice the random field Ising model at T=0 and on the direct lattice the random bond Potts model in the large-q limit at its transition point. The interface properties of the two models are known to be related by a mapping which is valid in the continuum approximation. Here we consider finite random samples with the same form of disorder for both models and calculate the respective equilibrium states exactly by combinatorial optimization algorithms. We study the evolution of the interfaces with the strength of disorder and analyse and compare the interfaces of the two models in finite lattices.Comment: 7 pages, 6 figure

Nonequilibrium dynamics of fully frustrated Ising models at T=0

We consider two fully frustrated Ising models: the antiferromagnetic triangular model in a field of strength, $h=H T k_B$, as well as the Villain model on the square lattice. After a quench from a disordered initial state to T=0 we study the nonequilibrium dynamics of both models by Monte Carlo simulations. In a finite system of linear size, $L$, we define and measure sample dependent "first passage time", $t_r$, which is the number of Monte Carlo steps until the energy is relaxed to the ground-state value. The distribution of $t_r$, in particular its mean value, $$, is shown to obey the scaling relation, $\sim L^2 \ln(L/L_0)$, for both models. Scaling of the autocorrelation function of the antiferromagnetic triangular model is shown to involve logarithmic corrections, both at H=0 and at the field-induced Kosterlitz-Thouless transition, however the autocorrelation exponent is found to be $H$ dependent.Comment: 7 pages, 8 figure

Adult Laryngeal Rhabdomyosarcoma: Report of a Case and Literature Review

Rhabdomyosarcoma is relatively seen in the pediatric age group with the head and neck region as the commonest site. To the best of our knowledge, few cases of laryngeal involvement in adult have been described in the literature. Biologically, rhabdomyosarcoma is different from squamous cell carcinoma, which is the commonest tumor of the larynx. A previously healthy non-smoker 77-year-old lady presented to the ENT outpatient with a six weeks history of intermittent alteration of voice quality. She had no history of sore throat, or any symptoms suggesting laryngo-pharyngeal reflux. Examination showed asymmetry of the left arytenoid cartilage and aryepiglottic fold. She subsequently had a direct laryngoscopy and biopsy. Histology and immunohistochemistry examination suggested the diagnosis of mesenchymal neoplasm. Following discussion at MDT she subsequently had a total laryngectomy. Histology confirmed a completely excised laryngeal rhabdomyosarcoma. Rhabdomyosarcoma of larynx in adult is a rare disease. Surgical treatment with or without adjuvant radiotherapy is currently the treatment of choice for this disease.Le Rhabdomyosarcome est relativement connu dans le groupe d'\ue2ge p\ue9diatrique et les r\ue9gions les plus touch\ue9es sont la t\ueate et le cou. A notre connaissance, peu de cas de l'implication du larynx chez des adultes ont \ue9t\ue9 cit\ue9s dans la litt\ue9rature. Biologiquement, rhabdomyosarcome est diff\ue9rent de la cellule squameuse carcinome, qui est la tumeur de larynx la plus ordinaire. Une femme non-fumeuse, \ue2g\ue9e de 77 ans d'une tr\ue8s bonne sant\ue9 au d\ue9part, s'est pr\ue9sent\ue9e \ue0 l'ORL ambulatoire avec une p\ue9riode de six semaines histoires de l'alt\ue9ration r\ue9p\ue9t\ue9e de la qualit\ue9 de la voix. Elle n'avait pas d'ant\ue9c\ue9dente de maux de gorge ou aucun sympt\uf4mes suggestifs le reflux laryngo-pharyngien. L'examen a montr\ue9 l'asym\ue9trie de la gauche aryt\ue9no\uefde cartilage aryepiglottique pli. Elle a par la suite eu une laryngoscopie directe et la biopsie. L'examen histologique et immunohistochimie a sugg\ue9r\ue9 le diagnostique des tumeurs mesenchymteuses, n\ue9oplasme. A la suite d'une discussion au MDT elle a ensuite eu une laryngectomie totale. L'histologie a confirm\ue9 une excis\ue9e larynx chez des adultes qui est une maladie rare. Le traitement chirurgical avec ou sans radioth\ue9rapie adjuvante est actuellement le traitement du choix pour cette maladie