Direct observation of melting in a 2-D superconducting vortex lattice

Topological defects such as dislocations and disclinations are predicted to determine the twodimensional (2-D) melting transition. In 2-D superconducting vortex lattices, macroscopic measurements evidence melting close to the transition to the normal state. However, the direct observation at the scale of individual vortices of the melting sequence has never been performed. Here we provide step by step imaging through scanning tunneling spectroscopy of a 2-D system of vortices up to the melting transition in a focused-ion-beam nanodeposited W-based superconducting thin film. We show directly the transition into an isotropic liquid below the superconducting critical temperature. Before that, we find a hexatic phase, characterized by the appearance of free dislocations, and a smectic-like phase, possibly originated through partial disclination unbinding. These results represent a significant step in the understanding of melting of 2-D systems, with impact across several research fields, such as liquid crystal molecules, or lipids in membranes.Comment: Submitted to Nature Physic

Enhancement of long range correlations in a 2D vortex lattice by incommensurate 1D disorder potential

Long range correlations in two-dimensional (2D) systems are significantly altered by disorder potentials. Theory has predicted the existence of disorder induced phenomena such as Anderson localization and the emergence of novel glass and insulating phases as the Bose glass. More recently, it has been shown that disorder breaking the 2D continuous symmetry, such as a one dimensional (1D) modulation, can enhance long range correlations. Experimentally, developments in quantum gases have allowed the observation of a wealth of phenomena induced by the competition between interaction and disorder. However, there are no experiments exploring the effect of symmetry-breaking disorder. Here, we create a 2D vortex lattice at 0.1 K in a superconducting thin film with a well-defined 1D thickness modulation and track the field induced modification using scanning tunneling microscopy. We find that the 1D modulation becomes incommensurate to the vortex lattice and drives an order-disorder transition, behaving as a scale-invariant disorder potential. We show that the transition occurs in two steps and is mediated by the proliferation of topological defects. We find that critical exponents determining the loss of positional and orientational order are far above theoretical expectations for scale-invariant disorder and follow instead the critical behaviour which describes dislocation unbinding melting. Our data show for the first time that randomness disorders a 2D crystal, and evidence enhanced long range correlations in presence of a 1D modulation demonstrating the transformation induced by symmetry breaking disorder in interactions and the critical behaviour of the transition.Comment: 7 pages, 3 figures and supplementary information (11 pages, 9 figures

Thermal tool in the evaluation of the "pinhão'' (seed of Araucaria angustifolia) starch aimed agroindustrial process.

''Pinhão'' is an important source of food for inhabitants in the subtropical region of South America. Gelatinization temperatures for ''pinhão'' are smaller than for corn and cassava starches, bringing advantages in industrial processes. The ''pinhão'' starches of the 4 different provenances were subjected to dilutions of 1:4, 1:5 e 1:6, in water. The starches were evaluated using DSC to determine gelatinization characteristics of them. The results showed that the source and dilutions have influence in the gelation process of the starch.Edição dos Anais do 7º Simpósio de Análise Térmica, 2015, Bauru

Effect of treatment with hcl/alcoholic in the modification of corn starch.

Corn is the cereal most produced in the world. Corn starches were modified by HCl 0.1 mol L-1 in alcoholic and aqueous solutions. Three mass losses can be observed in the degradation process using TG-DTG curve. The native and treated starches samples don't show differences in the stability region. With DSC curves were observed lower values of the ΔH of gelatinization of the modified starch by HCl in the alcoholic solutions. The modifications using alcoholic solutions demonstrated a good alternative to obtain modifies starches.Edição dos Anais do 7º Simpósio de Análise Térmica, 2015, Bauru

Efeitos da oxidação induzida com permanganato de potássio na modificação do amigo de milho ceroso.

O amido milho ceroso ?waxy? possui apenas amilopectina, conferindo vantagens em processos industriais. Foram analisadas quatro amostras de amido milho ceroso, uma nativa e três modificadas com permanganato de potássio (KMnO4). As proporções amido/água (w/w) foram 1:4, 1:5 e 1:6. Para determinar as características de gelatinização dos amidos usou-se o DSC. Os resultados mostraram que a modificação e as diluições têm influência no processo de gelatinização do amido.Edição dos Anais do 7º Simpósio de Análise Térmica, 2015, Bauru

Disordered hyperuniformity in superconducting vortex lattices

The current carrying capability of type II superconductors under magnetic fields is determined to a large extent by the interaction of superconducting vortices with pinning centers. Vortices are arranged in lattices with varying degrees of disorder depending on the balance between the intervortex interactions and the pinning strength. We analyze here vortex arrangements in disordered vortex lattices of different superconducting systems, single crystals (Co-doped NbSe2, LiFeAs, and CaKFe4As4), and amorphous W- based thin films (with critical temperatures T-c from 4 K to 35 K and critical fields from 3.4 T to more than 90 T). We calculate for each case the structure factor and number variance and compare to calculations on an interacting set of partially pinned particles. We find that random density fluctuations appear when pinning overcomes interactions and show that the suppression of density fluctuations is correlated to the presence of interactions. We discuss the results within the framework of hyperuniform distributions and find that all studied lattices follow a similar increase of the number variance with the defect density

Dissipative continuous Euler flows

We show the existence of continuous periodic solutions of the 3D incompressible Euler equations which dissipate the total kinetic energy

Caracterização reológica e estrutural de amostras de amido de pinhão (Araucaria angustifolia) do banco de germoplasma da Embrapa.

A semente da Araucaria angustifolia, conhecida como pinhão, pode ser uma boa fonte de amido. Este amido apresenta estrutura diferenciada em relação às fontes convencionais. Apesar da importância comercial e cultural, a Araucaria angustifolia encontra-se em risco de extinção. A forma mais segura de garantir a preservação da Araucária é através do uso e exploração econômica de seus produtos não madeiráveis. É um produto originalmente brasileiro com poucos estudos e não apresenta padronização em suas características. Nesse estudo foram caracterizadas 4 amostras de amido de diferentes procedências do banco de germoplasma da EMBRAPA Florestas (Colombo, PR). Realizaram-se análises reológicas (Rápido viscoanálise - RVA) e estruturais (Microscopia eletrônica de varredura - MEV). Nas análises dos perfis reológicos demonstraram uma similaridade entre as amostras, diferenciando-as principalmente pela Viscosidade de pico e tendência a retrogradação. Através do MEV confirmou-se a forma característica do granulo de amido de pinhão e calculou-se seu diâmetro médio, que se apresentou entre 12-16μm. Com os resultados destas análises observou-se que os comportamentos foram similares, porém as diferenças genéticas influenciaram nestes resultados. Os resultados do MEV foram similares com a literatura

Theoretical aspects of the CEBAF 89-009 experiment on inclusive scattering of 4.05 GeV electrons from nuclei

We compare recent CEBAF data on inclusive electron scattering on nuclei with predictions, based on a relation between structure functions (SF) of a nucleus, a nucleon and a nucleus of point-nucleons. The latter contains nuclear dynamics, e.g. binary collision contributions in addition to the asymptotic limit. The agreement with the data is good, except in low-intensity regions. Computed ternary collsion contributions appear too small for an explanation. We perform scaling analyses in Gurvitz's scaling variable and found that for $y_G\gtrless 0$, ratios of scaling functions for pairs of nuclei differ by less than 15-20% from 1. Scaling functions for $0$ are, for increasing $Q^2$, shown to approach a plateau from above. We observe only weak $Q^2$-dependence in FSI, which in the relevant kinematic region is ascribed to the diffractive nature of the NN amplitudes appearing in FSI. This renders it difficult to separate asymptotic from FSI parts and seriously hampers the extraction of $n(p)$ from scaling analyses in a model-independnent fashion.Comment: 11 p. Latex file, 2 ps fig