Interplay between spin-glass clusters and geometrical frustration

International audienceThe presence of spin-glass (SG) order in highly geometrically frustrated systems is analyzed in a cluster SG model. The model considers infinite-range disordered interactions among cluster magnetic moments and the J1−J2 model couplings between Ising spins of the same cluster. This model can introduce two sources of frustration: one coming from the disordered interactions and another coming from the J1−J2 intracluster interactions (intrinsic frustration). The framework of one-step replica symmetry breaking is adopted to obtain a one-cluster problem that is exactly solved. As a main result we create phase diagrams of the temperature T versus intensity of the disorder J, where the paramagnetic-SG phase transition occurs at Tf when T decreases for high-J values. For low-J values, the SG order is absent for antiferromagnetic clusters without intrinsic frustration. However, the SG order can be observed within the intracluster intrinsic frustration regime even for lower intensity of disorder. In particular, the results indicate that the presence of small clusters in geometrically frustrated antiferromagnetic systems can help stabilize the SG order within a weak disorder

Ising spin glass in a random network with a Gaussian random field

We investigate thermodynamic phase transitions of the joint presence of spin glass (SG) and random field (RF) using a random graph model that allows us to deal with the quenched disorder. Therefore, the connectivity becomes a controllable parameter in our theory, allowing us to answer what the differences are between this description and the mean-field theory i.e., the fully connected theory. We have considered the random network random field Ising model where the spin exchange interaction as well as the RF are random variables following a Gaussian distribution. The results were found within the replica symmetric (RS) approximation, whose stability is obtained using the two-replica method. This also puts our work in the context of a broader discussion, which is the RS stability as a function of the connectivity. In particular, our results show that for small connectivity there is a region at zero temperature where the RS solution remains stable above a given value of the magnetic field no matter the strength of RF. Consequently, our results show important differences with the crossover between the RF and SG regimes predicted by the fully connected theory

Osler-Weber-Rendu Syndrome - Dental Implications

Osler-Weber-Rendu syndrome (OWRS) is a rare hereditary, autosomal dominant disease characterized by a local angiodysplasia. Its clinical characteristics are vascular hamartomas of the skin and oral mucosa, arteriovenous malformations in the lungs, liver, kidney and brain, and episodes of epistaxis. The oral lesions, which become apparent through hemorrhagic telangiectasia, may be the first sign of the disease. This is a case report of a 74-year-old woman whose diagnosis of OWRS was established by her dentist based on the presence of telangiectasia in the skin and oral mucosa, reports of frequent nosebleeds of unknown etiology and a family history of telangiectasia. Amputation of a lower limb and comorbidities, such as cardiopathy, nephropathy and rheumatic disorders, completed the profile. OWRS causes major vascular changes that can be diagnosed initially by a dentist. In this article, we describe the skills and knowledge that dentists need to monitor patients with OWRS properly

Disco De Corte Dentado Passivo

Que diverge dos atuais discos disponíveis por ser concebido a partir de três linhas básicas, sendo que uma representa a superfície do solo, a outra apresenta a superfície da palhada e a terceira representa a profundidade de penetração do dente do disco no solo (FIGURA 02). Após a determinação dos contornos do disco e de seus dentes, torna-se possível a definição de alguns ângulos e dimensões para efeito construtivo. Sua construção física, após a definição de suas dimensões é realizada a partir de discos de bordas lisas (FIGURA 01 – A), com espessura de 4 a 6 mm., sem tratamento térmico e com diâmetro igual ao diâmetro externo do disco dentado projetado. Disco que apresenta ângulo oblíquo, formado entre a borda cortante do dente e do solo, durante o período efetivo de corte e que apresenta ângulo da ponta do dente (Epsílon), definido por expressão matemática, entre 25° a 30°.BR0300789 (A)A01B15/16A01B15/16BR20030300789A01B15/16A01B15/1

Specific heat and nonlinear susceptibility in spin glasses with random fields

We study magnetic properties of spin glass (SG) systems under a random field (RF), based on the suggestion that RFs can be induced by a weak transverse field in the compound LiHo x Y 1 − x F 4 .Weconsideracluster spin model that allows long-range disordered interactions among clusters and short-range interactions inside the clusters, besides a local RF for each spin following a Gaussian distribution with standard deviation Δ. We adopt the one-step replica symmetry breaking approach to get an exactly solvable single-cluster problem. We discuss the behavior of order parameters, specific heat C m , nonlinear susceptibility χ 3 , and phase diagrams for different disorder configurations. In the absence of RF, the χ 3 exhibits a divergence at T f , while the C m shows a broad maximum at a temperature T** around 30% above T f , as expected for conventional SG systems. The presence of RF changes this scenario. The C m still shows the maximum at T** that is weakly dependent on Δ. However,the T f is displaced to lower temperatures, enhancing considerably the ratio T** /T f . Furthermore, the divergence in χ 3 is replaced by a rounded maximum at a temperature T*, which becomes increasingly higher than T f as Δ is enhanced. As a consequence, the paramagnetic phase is unfolded in three regions: (i) a conventional paramagnetism ( T>T** ); (ii) a region with formation of short-range order with frozen spins ( T*<T <T** ); (iii) a region with slow growth of free-energy barriers slowing down the spin dynamics before the SG transition ( T f <T <T* ) suggesting an intermediate Griffiths phase before the SG state. Our results reproduce qualitatively some findings of LiHo x Y 1 − x F 4 as the rounded maximum of χ 3 behavior triggered by RF and the deviation of the conventional relationship between the T f and T**

Thermo‑magnetic signature of a superconducting multi‑band square with rough surface

In the present work, we will study the efect that the surface roughness of the sample has on the magnetic and thermodynamic properties in a mesoscopic superconducting meso-square under an external magnetic feld in a zero-feld cooling process. We will analyze the magnetization, superconducting electronic density, free Gibbs energy, specifc heat and entropy as a function of the roughness of the sample in a superconducting two-band square taking a Josephson type inter-band coupling. We show that the magnetic and thermodynamic properties depend on the roughness percentage of its surface. Our investigation was carried out by numerically solving the two-band time-dependent Ginzburg–Landau equations

Nonlinear susceptibility of a quantum spin glass under uniform transverse and random longitudinal magnetic fields

The interplay between quantum fluctuations and disorder is investigated in a quantum spin-glass model, in the presence of a uniform transverse field , as well as of a longitudinal random field hi , which follows a Gaussian distribution characterized by a width proportional to . The interactions are infinite-ranged, and the model is studied through the replica formalism, within a one-step replica-symmetry-breaking procedure; in addition, the dependence of the Almeida-Thouless eigenvalue λAT (replicon) on the applied fields is analyzed. This study is motivated by experimental investigations on the LiHoxY1−xF4 compound, where the application of a transverse magnetic field yields rather intriguing effects, particularly related to the behavior of the nonlinear magnetic susceptibility χ3, which have led to a considerable experimental and theoretical debate. We have analyzed two physically distinct situations, namely, and considered as independent, as well as these two quantities related, as proposed recently by some authors. In both cases, a spin-glass phase transition is found at a temperature Tf , with such phase being characterized by a nontrivial ergodicity breaking; moreover, Tf decreases by increasing towards a quantum critical point at zero temperature. The situationwhere and are related [ ≡ ( )] appears to reproduce better the experimental observations on the LiHoxY1−xF4 compound, with the theoretical results coinciding qualitatively with measurements of the nonlinear susceptibility χ3 In this later case, by increasing gradually, χ3 becomes progressively rounded, presenting a maximum at a temperature T ∗ (T ∗ > Tf ), with both the amplitude of the maximum and the value of T ∗ decreasing gradually. Moreover, we also show that the random field is the main responsible for the smearing of the nonlinear susceptibility, acting significantly inside the paramagnetic phase, leading to two regimes delimited by the temperature T ∗, one for Tf T ∗. It is argued that the conventional paramagnetic state corresponds to T >T ∗, whereas the temperature region Tf < T < T ∗ may be characterized by a rather unusual dynamics, possibly including Griffiths singularities

Nonlinear susceptibility of a quantum spin glass under uniform transverse and random longitudinal magnetic fields

The interplay between quantum fluctuations and disorder is investigated in a quantum spin-glass model, in the presence of a uniform transverse field , as well as of a longitudinal random field hi , which follows a Gaussian distribution characterized by a width proportional to . The interactions are infinite-ranged, and the model is studied through the replica formalism, within a one-step replica-symmetry-breaking procedure; in addition, the dependence of the Almeida-Thouless eigenvalue λAT (replicon) on the applied fields is analyzed. This study is motivated by experimental investigations on the LiHoxY1−xF4 compound, where the application of a transverse magnetic field yields rather intriguing effects, particularly related to the behavior of the nonlinear magnetic susceptibility χ3, which have led to a considerable experimental and theoretical debate. We have analyzed two physically distinct situations, namely, and considered as independent, as well as these two quantities related, as proposed recently by some authors. In both cases, a spin-glass phase transition is found at a temperature Tf , with such phase being characterized by a nontrivial ergodicity breaking; moreover, Tf decreases by increasing towards a quantum critical point at zero temperature. The situationwhere and are related [ ≡ ( )] appears to reproduce better the experimental observations on the LiHoxY1−xF4 compound, with the theoretical results coinciding qualitatively with measurements of the nonlinear susceptibility χ3 In this later case, by increasing gradually, χ3 becomes progressively rounded, presenting a maximum at a temperature T ∗ (T ∗ > Tf ), with both the amplitude of the maximum and the value of T ∗ decreasing gradually. Moreover, we also show that the random field is the main responsible for the smearing of the nonlinear susceptibility, acting significantly inside the paramagnetic phase, leading to two regimes delimited by the temperature T ∗, one for Tf T ∗. It is argued that the conventional paramagnetic state corresponds to T >T ∗, whereas the temperature region Tf < T < T ∗ may be characterized by a rather unusual dynamics, possibly including Griffiths singularities

Sistema E Processo De Monitoramento De Peso Em Esteiras De Transporte De Produtos Com Taliscas

A presente invenção refere-se a um Monitor de Produtividade de cana-de-açúcar, para elaboração de mapas de produtividade, requisito básico para a implementação da agricultura de precisão (AP), que permite a aplicação de um sistema de gerenciamento de produção eficiente. O sistema proposto não depende de sensores de pressão hidráulica que além de caros são mais complicados de serem instalados. A determinação do peso dos rebolos de cana-de-açúcar é obtida por medidas diretas e não por medidas indiretas. Sensores de inclinação do elevador garantem a correção destes valores para qualquer tipo de terreno que a colhedora estiver trabalhando. O programa computacional dedicado desenvolvido para gerenciar as informações obtidas das células de carga e dos sensores instalados na colhedora permite a obtenção da quantidade de cana-de-açúcar sendo colhida e de mapas de produtividade se um equipamento de GPS estiver acoplado a colhedora. O sistema de controle eletrônico recebe o sinal já tratado do sensor de peso, da velocidade da esteira transportadora, do sensor de velocidade de deslocamento da colhedora e do sensor instalado no sistema de corte de base. Essas informações juntamente com as coordenadas obtidas por um GPS instalado na colhedora, permitem a elaboração de um mapa digital que representa a superfície de produção da área colhida.BRPI0502658 (A)B65G1/02G06K11/00A01D45/10G06F17/60BR2005PI02658B65G1/02G06K11/00A01D45/10G06F17/6