How background noise shifts eigenvectors and increases eigenvalues in DTI

Indroduction  The signal-to-noise ratio of in vivo diffusion tensor imaging (DTI) is usually very limited, especially if high resolution data is acquired. In a variety of settings, the signal of diffusion weighted images can drop below the background noise level yielding an underestimated diffusion constant. In this work, we report two new artefacts in DTI that are important in this regime. Methods  Both artifacts are described analytically and numerically and are demonstrated in DTI phantoms and in subjects in vivo. Results  First, eigenvectors are systematically shifted towards distinct ‘attractive’ orientations of the gradient scheme. Second, certain eigenvalues can be overestimated due to the underestimation of the measured diffusion, which can result in the misordering of eigenvalues Discussion  We show that these effects are relevant for current clinical settings of DTI.     

Thermoset IM-LSI-based C/C-SiC: Influence of flow direction and weld lines on microstructure and mechanical properties

The production of ceramic matrix composites (CMC) based on C/C-SiC is still very cost-intensive and therefore only economical for a few applications. The fabrication of the preforms involves many costs that need to be reduced. In this work, the shaping of the CFRP-preforms is realized by thermoset injection molding, which enables large-scale production. The polymeric matrix used is a multi-component matrix consisting of novolak resin, curing agent and lubricant. Six millimeter chopped carbon fiber with a proportion of 50 wt.% were used as a reinforcement. These ingredients are processed by an industrial equipment for compounding and injection molding in order to manufacture a CFRP demonstrator representing a brake disc. Test specimens are cut out of the demonstrator in different directions in order to investigate influences of flow direction and weld lines on microstructural and mechanical properties. Afterward, the CFRP samples were converted to C/C-SiC composites by the liquid silicon infiltration process. The article addresses the flow behavior of the compound during the injection molding and the building of the weld lines in the demonstrator. In addition, results of the directional dependence of the microstructural and mechanical properties within the fabricated disc in the different production steps are presented.     

Work-hardening stages of AA1070 and AA6060 after severe plastic deformation

Based on the concept of work-hardening for fcc metals, the commercially pure aluminum AA1070 (soft annealed) and the aluminum alloy AA6060 (peak-aged) were investigated. Equal-channel angular pressing (ECAP) was used to introduce very high strains and an ultrafine-grained microstructure. Compression tests were performed in a wide range of strain rates between 10⁻⁴ and 10³ s⁻¹ subsequently. The results show that strain path and the corresponding dislocation structure are important for the post-ECAP yielding and the following hardening response. Furthermore, the precipitates of the alloy clearly constrain the interactions of dislocations in work-hardening stage III—causing lower strain rate sensitivity and retarding the process of grain refinement as well. If compared to the pure aluminum, the precipitates avoid hardening in stage V where an additional rate and temperature-dependent effect contributes—supposedly caused by the interaction of deformation-induced vacancies and dislocations.     

Anomalous Dispersion of LO Phonons inLa.1.85Sr0.15CuO4

The dispersion of the highest energy LO phonon branch in La. _1.85 Sr _0.15 CuO ₄ in the (100) direction has been reinvestigated by high resolution inelastic neutron scattering. In contrast to what has been recently reported by McQueeney et al. (Phys. Rev. Lett. 82. , 628 (1999)), we find that the dispersion is continuous throughout the Brillouin zone. These results are in conflict with the idea of charge stripe order existing on a time scale which is long compared to that of the LO frequencies. On the other hand, the strong softening and boradening of LO phonons observed on doping might be taken as a precursor phenomenon to a stripe order phase with a periodicity of about 4 lattice constants. also at     

Interfacial Energy in Phase-Separated Glasses from Emulsion Rheology

Classical theories of emulsion rheology yield information on the deformation of a liquid drop dispersed into another liquid matrix phase. By connecting the deformation and relaxation, respectively, and the capillary number of the dispersed phase, interfacial energy can be estimated. This was applied to demixing borosilicate and lead borate glasses, which are known to exhibit significant form anisotropy after elongation. Interfacial energies in these two systems were calculated based on graphical data of prior isothermal elongation experiments. The method is discussed in terms of experimental difficulties. It might provide an alternative way to overcome the obvious lack of information on interfacial energies in glasses.     

Approximate syllogisms – on the logic of everyday life

Since Aristotle it is recognised that a valid syllogism cannot have two particular premises. However, that is not how a lay person sees it; at least as long as the premises read many, most etc, instead of a plain some. The lay people are right if one considers that these syllogisms do not have strict but approximate (Zadeh) validity. Typically there are only particular premises available in everyday life and one is dependent on such syllogisms. – Some rules on the usage of particular premises are given below.     

Gemini Surfactants Foam Formation Ability and Foam Stability Depends on Spacer Length

A series of cationic gemini surfactants containing different spacer length were synthesized and analyzed structurally. It was shown that the surface tension (σ) and critical micelle concentration (CMC), which had a maximum for the n-C₄H₈ spacer depended on the spacer length. The foaming ability and foam stability are high for the gemini surfactants with short spacers (C₂H₄ to n-C₄H₈), while longer spacers lead to a distinct decrease of these foam parameters. Foaming properties are discussed in terms of configuration and conformation of a surfactant molecule and in relation to micellization state kinetic.     

Observation of breathing-like modes in an individual multiwalled carbon nanotube

We study collective vibrational breathing modes in the Raman spectrum of a multiwalled carbon nanotube. In correlation with high-resolution transmission electron microscopy, we find that these modes have energies differing by more than 23% from the radial breathing modes of the corresponding single-walled nanotubes. This shift in energy is explained with intershell interactions using a model of coupled harmonic oscillators. The strength of this interaction is related to the coupling strength expected for few-layer graphene.