Crystalline instability of Bi-2212 superconducting whiskers near room temperature

We report new evidences for the thermodynamic instability of whisker crystals in the Bi–Sr–Ca–Cu–O (BSCCO) system. Annealing treatments at 90°C have been performed on two sets of samples, which were monitored by means of X-Rays Diffraction (XRD) and Atomic Force Microscopy (AFM) measurements, respectively. Two main crystalline domains of Bi₂Sr₂CuCa₂O_8+x (Bi-2212) were identified in the samples by the XRD data, which underwent an evident crystalline segregation after about 60 hours. Very fast dynamics of the surface modifications was also described by the AFM monitoring. Two typologies of surface structures formed after about 3 annealing hours: continuous arrays of dome shaped bodies were observed along the edges of the whiskers, while in the central regions a dense texture of flat bodies was found. These modifications are described in terms of the formation of simple oxide clusters involving a degradation of the internal layers.     

Random Packing of Small Blocks: Pressure Effects,Orientational Correlations and Application to Polymer‐Based Composites

Packing is a complex phenomenon of prominence in many natural and industrial processes (liquid crystals, granular materials, infiltration, melting, flow, sintering, segregation, sedimentation, compaction, etc.). A variety of computational methods is available in particular for spheroid particles. Our aim is to apply the principle of the random sequential addition algorithm but with small blocks of varying size and orientation. Here the main purpose is to reproduce the observed arrangement of graphitic assemblies in polymeric matrices. Random packing is improved by applying an external pressure implemented with a drifted diffusive motion of the fillers. Attention is also paid to the emergence of structural and orientational order. Interestingly, mixtures of fillers of irregular shapes can be dealt with efficiently using the proposed algorithm.     

An NMR Phantom Mimicking Intramyocellular (IMCL) and Extramyocellular Lipids (EMCL)

Intramyocellular lipids (IMCL) play an important role in muscle metabolism. ¹H magnetic resonance spectroscopy is the method of choice for non-invasive assessment of IMCL. However, IMCL quantitation is hampered by the larger overlapping resonances of extramyocellular lipids (EMCL). A phantom that mimics EMCL and IMCL, i.e., the 0.2-ppm resonance splitting, would be useful for testing acquisition strategies and post-processing algorithms. Here, we propose a phantom that consists of a cylindrical bottle filled with dairy cream and sunflower oil. Similar to EMCL, the oil (CH₂) _n protons resonate at 1.5?ppm; similar to IMCL, the spherical shape of droplets in cream results in (CH₂) _n protons resonating at 1.3?ppm. The relative amount of IMCL versus EMCL can be easily controlled in a systematic and exact fashion by displacing the voxel of interest across the cream–oil interface. This phantom is of simple construction and made of inexpensive and readily available materials, and should be of value in testing both acquisition and spectral analysis strategies in the context of ICML/ECML studies.     

Multidimensional Secure Multilevel Polarization Shift Keying

We investigate a technique to improve the information confidentiality in optical fiber telecommunications. Starting from a basic scheme of unconventional coding technique [1] applied to a three-dimensional polarization shift keying, we extend the method to a four-dimensional physical space [2] to demonstrate the general applicability of the cryptographic method and to achieve better performance in terms of transmission throughput. Bit error rate (BER) is calculated for hypercube constellation modulation in two, three, and four dimensions, and an interesting relation among BER, transmission power, and space dimension is derived.