ESMRMB 2017, 34th Annual Scientific Meeting,Barcelona, ES,October 19–October 21: Abstracts,Thursday

Objective

Current magnetic resonance imaging (MRI) axon diameter measurements rely on the pulsed gradient spin-echo sequence, which is unable to provide diffusion times short enough to measure small axon diameters. This study combines the AxCaliber axon diameter fitting method with data generated from Monte Carlo simulations of oscillating gradient spin-echo sequences (OGSE) to infer micron-sized axon diameters, in order to determine the feasibility of using MRI to infer smaller axon diameters in brain tissue.

Materials and methods

Monte Carlo computer simulation data were synthesized from tissue geometries of cylinders of different diameters using a range of gradient frequencies in the cosine OGSE sequence . Data were fitted to the AxCaliber method modified to allow the new pulse sequence. Intra- and extra-axonal water were studied separately and together.

Results

The simulations revealed the extra-axonal model to be problematic. Rather than change the model, we found that restricting the range of gradient frequencies such that the measured apparent diffusion coefficient was constant over that range resulted in more accurate fitted diameters. Thus a careful selection of frequency ranges is needed for the AxCaliber method to correctly model extra-axonal water, or adaptations to the method are needed. This restriction helped reduce the necessary gradient strengths for measurements that could be performed with parameters feasible for a Bruker BG6 gradient set. For these experiments, the simulations inferred diameters as small as 0.5 μm on square-packed and randomly packed cylinders. The accuracy of the inferred diameters was found to be dependent on the signal-to-noise ratio (SNR), with smaller diameters more affected by noise, although all diameter distributions were distinguishable from one another for all SNRs tested.

Conclusion

The results of this study indicate the feasibility of using MRI with OGSE on preclinical scanners to infer small axon diameters.

     

Energy-efficient algorithms for assessment of the rail-circuit operation

The voltage in a rail circuit is determined for reliable detection of the mobile unit or a train on the section of the railway track. It is proposed to use the structures of the automatic block system based on the time-division channels of status scanning of the rail circuits with subsequent signal processing by two parameters. The first parameter includes the assessment of correspondence of the code signals transmitted to the rail circuit and received from the rail circuit. The second parameter is obtained based on the analysis of the voltage at the rail-circuit output within the current and previous measurements considering the voltagechange rate. This latter parameter makes it possible to distinguish reliably the state when the rail track is occupied by the train from the random changes of the rail-circuit parameters from the influence of the external factors. The proposed algorithms permit one to reduce significantly consumption of electric energy providing operation of rail circuits.     

Peat swamps at Giral lignite field of Barmer basin,Rajasthan, Western India: understanding the evolution through petrological modelling

International Journal of Coal Science & Technology - The lignite samples collected from Giral lignite field of Barmer basin have been subjected to petrological investigation. The data generated...     

Distribution of mineral species in different coal seams of Talcher coalfield and its transformation behavior at varying temperatures

International Journal of Coal Science & Technology - Mineral phase characterization and thorough understanding of its transformation behavior during combustion are imperative to know the...     

Correlations Among Signatures for Detection of Different Types of Fires

One way of overcoming the problem of false alarms encountered in a single parameter detection system due to non-fire stimulii is the simultaneous use of multiple signatures. Researchers have found significant benefits of multi-sensor detection in reducing false triggering. Appreciable interest has been expressed in using carbon monoxide (CO) or carbon dioxide (CO₂) gas sensors in combination with smoke sensors. The present study has been carried out to determine the correlation and inter-dependence between two different fire signatures like CO–OD (optical density), CO–CO₂, CO₂–OD. The signatures have been investigated using experimental measurements of a fire inside a closed compartment measuring 7 x 7 x 4.2 m. A range of fuels are used, and both smouldering and flaming combustion are examined. Attempts have been made to examine whether correlation coefficients between two signatures can form a basis of detection and be exploited as one of the components in multi- criteria fire detection algorithm. The CO/CO₂ ratio as a criterion for detector operation has also been examined and discussed in the light of existing literature and codal provisions.     

Knowledge formation and learning in the management of projects: A problem solving perspective

In contrast to traditional projects, which are assumed to be fully specified and then executed with little learning anticipated, complex projects cannot be fully specified at the outset and require continuous learning over their life cycles. Nevertheless, the key role of knowledge formation and learning in managing complex projects is under-developed for expanding project capability boundaries to include knowledge uncertainty and indeterminacy.     

Intensification of nonlinearity by dispersed events in media with structure and generation of various dominant frequencies in P- and S-waves

A model of a continuum with a structure described by infinite order equations of motion is proposed. In case that a wave is very long as compared with the size of the structure, equations are reduced to the fourth-order equations. A closed equation of motion, including nonlinear, dispersed and wave members, is derived. It is shown that solutions in the form of soliton waves exist only in media where wave velocity grows with pressure. In the media, where soliton waves do not exist, quasi-stationary solutions with multiple frequencies prevail. It is found that the nonlinear effect of multiple frequencies is unexpectedly high even for small deformation as dispersion violently intensifies nonlinear events. Moreover, in the domain of small deformation, there exist solutions for longitudinal and transversal waves with the same length and different frequencies. The solutions for the same length waves with different frequencies most often occur in seismology and seismic explorations.     

Microstructure-Based Estimation of Strength and Ductility Distributions for $$\alpha +\beta $$ Titanium Alloys

Titanium alloys are processed to develop a wide range of microstructure configurations and therefore material properties. While these properties are typically measured experimentally, a framework for property prediction could greatly enhance alloy design and manufacturing. Here a microstructure-sensitive framework is presented for the prediction of strength and ductility as well as estimates of the bounds in variability for these properties. The framework explicitly considers distributions of microstructure via new approaches for instantiation of structure in synthetic samples. The parametric evaluation strategy, including the finite element simulation package FEpX, is used to create and test virtual polycrystalline samples to evaluate the variability bounds of mechanical properties in Ti-6Al-4V. Critical parameters for the property evaluation framework are provided by measurements of single crystal properties and advanced characterization of microstructure and slip system strengths in 2D and 3D. Property distributions for yield strength and ductility are presented, along with the validation and verification steps undertaken. Comparisons between strain localization and slip activity in virtual samples and in experimental grain-scale strain measurements are also discussed.

     

Microstructural Features of Low-Alloy Pipeline Steels that Determine Impact Strength of Welded Joint Heat-Affected Zone

Metallurgist - Microstructural mechanisms reducing the impact strength values of a coarse grained heat-affected zone are studied for two K60 microalloyed steels. Research is conducted on specimens...     

Power Supply at Metallurgical Iron-and-Steel Works: Features and Development Prospects

Metallurgist - The article provides a brief assessment of the current state of power supply units at metallurgical plants and prospects for their future development. The principal power-supply...