Comparison of data-driven analysis methods for identification of functional connectivity in fMRI

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 97-103).Data-driven analysis methods, such as independent component analysis (ICA) and clustering, have found a fruitful application in the analysis of functional magnetic resonance imaging (fMRI) data for identifying functionally connected brain networks. Unlike the traditional regression-based hypothesis-driven analysis methods, the principal advantage of data-driven methods is their applicability to experimental paradigms in the absence of a priori model of brain activity. Although ICA and clustering rely on very different assumptions on the underlying distributions, they produce surprisingly similar results for signals with large variation. The main goal of this thesis is to understand the factors that contribute to the differences in the identification of functional connectivity based on ICA and a more general version of clustering, Gaussian mixture model (GMM), and their relations. We provide a detailed empirical comparison of ICA and clustering based on GMM. We introduce a component-wise matching and comparison scheme of resulting ICA and GMM components based on their correlations. We apply this scheme to the synthetic fMRI data and investigate the influence of noise and length of time course on the performance of ICA and GMM, comparing with ground truth and with each other. For the real fMRI data, we propose a method of choosing a threshold to determine which of resulting components are meaningful to compare using the cumulative distribution function of their empirical correlations. In addition, we present an alternate method to model selection for selecting the optimal total number of components for ICA and GMM using the task-related and contrast functions. For extracting task-related components, we find that GMM outperforms ICA when the total number of components are less then ten and the performance between ICA and GMM is almost identical for larger numbers of the total components. Furthermore, we observe that about a third of the components of each model are meaningful to be compared to the components of the other.by Yongwook Bryce Kim.S.M

Study of the ecological gas for MRPCs

The Multigap Resistive Plate Chamber (MRPC) is a gaseous detector; the performance depends very much on the gas mixture as well as the design. MRPCs are used as a timing device in several collider experiments and cosmic ray experiments thanks to the excellent timing performance. The typical gas mixtures of RPC-type detectors at current experiments are based on the gases $\rm C_2F_4H_2$ and $\rm SF_6$. These gases have very high Global Warming Potential (GWP) values of 1430 and 23900 respectively. The present contribution has been performed as a part of efforts to reduce the amount of greenhouse gases used in high energy experiments. The performance of MRPC has been measured with two different gas mixtures; $\rm C_2F_4H_2$ based gas mixtures and the ecological $\rm C_3F_4H_2$ (HFO-1234ze). A small MRPC was used for the tests. It has an sensitive area of 20 $\times$ 20 $\rm cm^2$; it was been built with 6 gaps of 220 $\mu$m. In normal operation, the strong space charge created within the gas avalanche limits the avalanche's growth. $\rm SF_6$ plays an important part in the process due to its high attachment coefficient at low electric fields. It is thus necessary to find another gas that has a similar attachment coefficient. $\rm CF_{3}I$ is a possible candidate. Tests were performed with this gas added to $\rm C_3F_4H_2$

Storing unitary operators in quantum states

We present a scheme to store unitary operators with self-inverse generators in quantum states and a general circuit to retrieve them with definite success probability. The continuous variable of the operator is stored in a single-qubit state and the information about the kind of the operator is stored in classical states with finite dimension. The probability of successful retrieval is always 1/2 irrespective of the kind of the operator, which is proved to be maximum. In case of failure, the result can be corrected with additional quantum states. The retrieving circuit is almost as simple as that which handles only the single-qubit rotations and CNOT as the basic operations. An interactive way to transfer quantum dynamics, that is, to distribute naturally copy-protected programs for quantum computers is also presented using this scheme.Comment: 4 pages, 3 figures, errors in Eq. (8) and Fig. 3 are fixed, to appear in Phys. Rev.

Measuring effective diffusivity in porous media with a gasket-free, radial arrangement

The final publication is available at Elsevier via https://dx.doi.org/10.1016/j.ijheatmasstransfer.2018.10.054 © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/A simple technique for measuring the effective diffusivity, and ultimately tortuosity, in porous media is presented. The method uses a custom-built apparatus, based on a radial geometry, which eliminates the need for any gaskets to seal the edge of the sample. This makes it particularly well suited for thin media such as films and layers. The experiment is based on the transient response of the oxygen concentration at the center of the sample as oxygen diffuses into an initially nitrogen filled domain from the sample perimeter. The analytical solution of Fick’s law for transient diffusion in cylindrical coordinates is fitted to the measured oxygen concentration profile to obtain the effective diffusivity. To validate the method, binary diffusion coefficients of N2-Air system were measured and the results show a close match and are consistent for a range of experimental parameters like flow rate and domain thickness. The classical study of diffusion in porous media based on sphere packing is revisited for further validation of the technique. The results show good agreement to the well-known Bruggeman correlation as well as to the experimental values reported in the literature. The new technique is further applied to other types of thin porous materials and the results indicate that the Bruggeman correlation generally underestimates the effective diffusivity of non-sphere packing.Natural Science and Engineering Research CouncilCanada and the Automotive Fuel Cell Corporatio

The effects of functional instability of the ankle joint on balance

BACKGROUND: Individuals who suffer from ankle instability may experience restricted movement and a weakening of the muscles that support the ankle. PURPOSE: The aim of this study was to investigate the effects of functional instability of the ankle joint on static and dynamic balance performances. METHODS: Twenty-five participants (8 male, 17 female) were recruited for this study. The subjects were divided into two groups: an ankle instability and a normal ankle stability group. The static and dynamic limits of stability performance were assessed in single leg standing using the BioRescue device. In addition, the Functional Reach Test (FRT) and the Modified Functional Reach Test (MFRT) were also recorded. RESULTS: Significant differences between the two groups were found in the moving distance and the mean velocity of the center of pressure during the single leg standing test, the pendular limits of stability test, and the MFRT. However, the FRTshowed no significant difference between the two groups. The results showed that the static and dynamic balance performances were reduced in the ankle instability group compared with the control group. CONCLUSION: Both the MFRT and BioRescue were sensitive and appropriate to identify clinically important differences between the two groups. The MFRT is a quick and inexpensive clinical measure of postural instability relevant to individuals with ankle instability. Further studies should use the MFRT to determine the effectiveness of clinical interventions for ankle instability that target improvements in balance

Characteristics of clinical measurements between biomechanical responders and non-responders to a shoe designed for knee osteoarthritis

The purpose of this study was to investigate the characteristics of biomechanical and clinical measurements in relation to the knee adduction moment when wearing a standard shoe and a shoe design for individuals with knee osteoarthritis (Flex-OA). Kinematic and kinetic data were collected from thirty-two healthy individuals (64 knees) using a ten camera motion analysis system and four force plates. Subjects performed 5 walking trials under the two conditions and the magnitude of individuals' biomechanical responses where explored in relation to the clinical assessment of the Foot Posture Index, hip rotation range, strength of hip rotators, and active ankle-foot motion, all of which have been described as possible compensation mechanisms in knee osteoarthritis. Significant reductions in the first peak of the knee adduction moment (KAM) during stance phase (9.3%) were recorded (p<0.0001). However, despite this difference, 22 of 64 knees showed either no change or an increased KAM, indicating a non-response or negative-response to the Flex-OA shoe. Significant differences were observed between the responder and non-responder subgroups in the hip rotation range ratio (p=0.044) and the hip rotators strength ratio (p=0.028). Significant differences were seen in clinical assessments of hip rotation range and hip rotator strength between responders and non-responders using a cut-off of 0.02Nm/kg change in the KAM. [Abstract copyright: Copyright © 2017 Elsevier B.V. All rights reserved.

Evaluation of Electrospun Fibrous Mats Targeted for Use as Flow Battery Electrodes

Electrospinning was used to create custom-made fibrous electrode materials for redox flow batteries with targeted structural properties. The aim was to increase the available surface area for electrochemical reaction without diminishing the transport properties of the electrode. Electrospinning conditions were identified that could produce fibers several times larger than those typically yielded by the technique, yet much smaller than in commercially available electrodes. These materials were subsequently carbonized using widely reported protocols. The resultant materials were subjected to a range of characterization tests to confirm that the feasibility of the target material, including surface area, pore and fiber sizes, porosity, conductivity, and permeability. The most promising material to emerge from this selection processes was then tested for electrochemical performance in a flow cell. The produced material performed markedly better than a commercially available material. Further optimizations such as improved consistency in the production and some surface activation treatments could provide significant advancements.NSERC Discovery grant Post-Graduate Scholarship program Eugenie-Ulmer Lamothe Fund of Department of Chemical Engineering at McGill Flow cell testing funded by the Joint Center for Energy Storage Research (JCESR) managed by Argonne National Laborator

Effects of Metatarsal Foot Orthosis on Biomechanical 3D Ground Reaction Force in Individuals with Morton Foot Syndrome during Gait: A Cross-Sectional Study

Morton’s foot syndrome (MFS) is characterized by a distally longer head of the second metatarsal bone compared to the head of the first metatarsal bone. Few studies have investigated the effects of a foot orthosis on kinetic characteristics, such as ground reaction force (GRF), during walking in individuals with MFS. This study aimed to verify dynamic GRF using a 3D motion analysis system, including two platforms with and without a foot orthosis condition. Kinetic GRF data of 26 participants with MFS were collected using a motion analysis system and a force platform. Participants were asked to walk wearing standard shoes or shoes with a pad-type foot orthosis. Repeated-measures analysis of variance (ANOVA) was used to compare the kinetic GRF data in the stance phase during gait according to the side of the leg and orthotic conditions for MFS. The late sagittal and frontal peak forces showed that the presence of a foot orthosis condition significantly increased the GRF when compared with the absence of a foot orthosis condition for both sides of the feet (p p = 0.023). Significant effects were observed in the late sagittal and frontal peak GRFs when wearing the pad-type foot orthosis in individuals with MFS during gait. Thus, even if there are no signs and symptoms of MFS in patients diagnosed with the disease condition, clinical interventions, such as a foot orthosis, that can be simply applied to shoe insoles are needed to manage and prevent various musculoskeletal disorders that may develop in the future. It was hypothesized that when wearing a foot orthosis, the participants would walk with increased GRF during gait compared to those without an orthosis