Smoothed particle hydrodynamic modelling of the cerebrospinal fluid for brain biomechanics: accuracy and stability

The Cerebrospinal Fluid (CSF) can undergo shear deformations under head motions. Finite Element (FE) models, which are commonly used to simulate biomechanics of the brain, including traumatic brain injury, employ solid elements to represent the CSF. However, the limited number of elements paired with shear deformations in CSF can decrease the accuracy of their predictions. Large deformation problems can be accurately modelled using the mesh-free Smoothed Particle Hydrodynamics (SPH) method, but there is limited previous work on using this method for modelling the CSF. Here we explored the stability and accuracy of key modelling parameters of an SPH model of the CSF when predicting relative brain/skull displacements in a simulation of an in vivo mild head impact in human. The Moving Least Squares (MLS) SPH formulation and Ogden rubber material model were found to be the most accurate and stable. The strain and strain rate in the brain differed across the SPH and FE models of CSF. The FE mesh anchored the gyri, preventing them from experiencing the level of strains seen in the in vivo brain experiments and predicted by the SPH model. Additionally, SPH showed higher levels of strains in the sulci compared to the FE model. However, tensile instability was found to be a key challenge of the SPH method, which needs to be addressed in future. Our study provides a detailed investigation of the use of SPH and shows its potential for improving the accuracy of computational models of brain biomechanics

Evaluation of nonmetallic thermal protection materials for the manned space shuttle. Volume 1, task 1: Assessment of technical risks associated with utilization of nonmetallic thermal protection system

Technical problems of design and flight qualification of the proposed classes of surface insulation materials and leading edge materials were reviewed. A screening test plan, a preliminary design data test plan and a design data test plan were outlined. This program defined the apparent critical differences between the surface insulators and the leading edge materials, structuring specialized screening test plans for each of these two classes of materials. Unique testing techniques were shown to be important in evaluating the structural interaction aspects of the surface insulators and a separate task was defined to validate the test plan. In addition, a compilation was made of available information on proposed material (including metallic TPS), previous shuttle programs, pertinent test procedures, and other national programs of merit. This material was collected and summarized in an informally structured workbook

Estimating Phase Velocity and Attenuation of Guided Waves in Acoustic Logging Data

Phase velocity and attenuation of guided waves have been estimated from multireceiver, full waveform, acoustic logging data using the extended Prony's method. Since a formation affects velocity and attenuation, estimating these quantities is important in evaluating the formation properties. The estimation is performed using an array processing technique which requires two steps: (1) the traces for all receivers are transformed into the frequency domain, and (2) for each frequency the extended Prony's method is used to determine the presence of a guided wave propagating past the array of receivers. The guided wave properties estimated by the Prony's method include amplitude, attenuation, and phase change which is related to phase velocity. An important assumption in this array processing technique is that the formation, borehole fluid, and tool are homogeneous along the receiving array. For synthetic data, the phase velocities and attenuation of the tube wave and two modes of the pseudo-Rayleigh wave are accurately estimated over many frequencies, with the exception that the low amplitude of the second mode causes its attenuation estimate to be somewhat less accurate. For laboratory data, very good estimates of the phase velocities of the tube wave and three modes of the pseudo-Rayleigh wave are obtained. Since the materials used in the laboratory experiment had very large quality factors, the attenuation could not be estimated. For field data, the dispersion of the tube wave and the velocity of the pseudo-Rayleigh wave at its cutoff are very close to those predicted by another, independent method. Accurate attenuation estimates could not be made because the data are noisy and consist of only eight traces.Massachusetts Institute of Technology. Full Waveform Acoustic Logging Consortiu

Velocity Analysis of Multi-Receiver Full Waveform Acoustic Logging Data In Open and Cased Holes

Average semblance and maximum-likelihood spectral analyses are applied to synthetic and field full waveform acoustic logging data to determine formation velocities. Of particular interest is the ability of these methods to resolve the P and shear/pseudo Rayleigh arrivals in data from poorly-bonded cased boreholes. In synthetic open-hole data the velocity analyses yield results within 4% of the true velocities. Results from synthetic well-bonded cased hole data are generally as good as those from the open hole data. However, if the formation P-wave velocity is within roughly 10% of the plate velocity of the steel pipe (about 5.3-5.5 km/s), then there may be a resonance effect that appears to slow down the P wave slightly (on the order of 6%). For cased-hole models with no steel/cement bonding (the free-pipe situation), the measured P-wave velocities are typically 6 to 8% less than the actual formation velocities. If the formation S-wave velocity is greater than about 2.5 km/s, the S-wave velocity estimate may also be 6 to 8% low. Furthermore, increasing the thickness of either the cement layer or the fluid layer between the pipe and the cement further decreases the formation velocity estimates. Also, if the P-wave velocity is within roughly 15% of the velocity of the steel arrival, the P wave may not be resolved by the semblance method unless the data is first low-pass filtered. Initial tests show that this filtering process may adversely affect the final P-wave velocity estimate, but the details of this type of approach have not been studied. The P wave is resolved. by spectral analysis of the original, unfiltered data. For cased-hole models with no cement/formation bonding (the unbonded-casing situation), formation S-wave velocities are estimated to within 3% relative error, and the formation P-wave velocity is estimated to within 2% error in a slow formation. However, for P-wave velocities between 3.4 km/s and 5.94 km/a, the P wave cannot be resolved by spectral analysis, and it is resolved by the semblance method only in the model with the low velocity (3.4 km/s).Massachusetts Institute of Technology. Full Waveform Acoustic Logging ConsortiumPhillips Petroleum Fellowshi

Preserving Natural Science Collections: Chronicle of Our Environmental Heritage

This report recommends action in the areas outlined below. Strategies for implementation of each recommendation are presented in chapter three, Meeting the Challenge: Recommendations and Strategies. Stewardship of collections Public awareness Staffing, education, and training Technology transfer Conservation research Guidelines and standards of practic

User experience of mixed reality applications for healthy ageing : A systematic review

Mixed reality (MR) technologies are being used increasingly to support healthy ageing, but past reviews have concentrated on the efficacy of the technology. This systematic review provides a synthesis of recent experimental studies on the instrumental, emotional and non-instrumental aspects of user experience of healthy older adults in relation to MR-related applications. The review was listed on PROSPERO, utilised a modified PICOS framework, and canvassed all published work between January 2010 to July 2021 that appeared in major databases (Scopus, PubMed, CINAHL, Web of Science, and the Cochrane Library). The literature search revealed 15 eligible studies. Results indicated that all included studies measured the instrumental quality of their applications, all but two studies measured the emotional reactions triggered by gameplay, and only six studies examined participants’ perception of non-instrumental quality of the applications. All included studies focused on improving a health domain such as cognitive or physical training. This suggests that the instrumental quality of the MR applications remains the focus of user experience studies, with far fewer studies examining the non-instrumental quality of the applications. Implications for game design and future research are discussed

Dispersion strengthening in vanadium microalloyed steels processed by simulated thin slab casting and direct charging. Part 2 - chemical characterisation of dispersion strengthening precipitates

The composition of the sub-15 nm particles in six related vanadium high strength low alloy steels, made by simulated thin slab direct charged casting, has been determined using electron energy loss spectroscopy (EELS). Such particles are considered to be responsible for dispersion hardening. For the first time, particles down to 4 nm in size have had their composition fully determined. In all the steels, the particles were nitrogen and vanadium rich and possibly slightly sub-stoichiometric carbonitrides. Equilibrium thermodynamics predicted much higher carbon to metal atomic ratios than observed in all cases so that kinetics and mechanical deformation clearly control the precipitation process. Thus it is important to formulate the steel with this in mind