1,721,013 research outputs found
Dynamic analysis of flexible rotors subjected to torque and force
No full textThe effect of the direction of application and magnitude of loads on the stability and natural frequency of flexible rotors is analyzed, when the rotors are subject to non-conservative torque and force. The stability criterion derived from the energy and variational principle is discussed and a general Galerkin method in which admissible functions are used is employed for numerical analysis. Illustrative examples are treated to demonstrate the analytical developments and the practical relevance of the work is discussed. (C) 1996 Academic Press Limite
Asymptotic performance comparison of known signal detection schemes in weakly dependent noise
No full text
Exploring Fat Fraction and Vertebral Bone Quality Score in Lumbar Spine Magnetic Resonance Imaging: A Cross-Sectional Study on Associations and Clinical Implication
No full textBackground/Objectives: While gradient-echo (GRE)-based chemical shift-encoded magnetic resonance imaging (CSE-MRI) offers precise method for measuring adiposity in bone marrow, its limitation lies in the need for additional imaging. On the other hand, spin-echo (SE)-based CSE-MRI can seamlessly integrate into conventional protocols. Recently, a novel technique called the vertebral bone quality (VBQ) score has been introduced. The objective of this study was to investigate the association between fat fraction (FF) measured by GRE-based CSE-MRI (FF(GRE)) and FF measured by SE-based CSE-MRI (FF(SE)) or the VBQ score. Methods: A retrospective study with 344 patients assessed the correlation between FF and the VBQ score and each measurement's correlation with age using Pearson's correlation (r). Concordance between FF(GRE) and FF(SE) was assessed using Lin's concordance correlation coefficient (rho(c)). Vertebral lesions (n = 41) were categorized as benign and malignant, and the Mann-Whitney U test was used for comparison. Results: FF(GRE) demonstrated strong positive correlations with FF(SE) and the VBQ score (r = 0.861 and 0.708, respectively). However, the concordance between FF(GRE) and FF(SE) was poor (rho(c) = 0.295). All measurements moderately correlated with age (FF(GRE), r = 0.583; FF(SE), r = 0.477; VBQ score, r = 0.468). FF was significantly higher in benign lesions (FF(GRE), p = 0.004; FF(SE), p = 0.007), while the VBQ score did not show statistically significant differences between the two groups (p = 0.089). Conclusions: FF(GRE) exhibited a high correlation with the VBQ score. FF(SE) showed a strong correlation with FF(GRE), but replacing FF(GRE) with FF(SE) may be challenging. Both FF and the VBQ score moderately correlated with age. FF demonstrated statistically significant differences between benign and malignant lesions, while the VBQ score did not provide a distinguishable separation
Physiological gradient in lumbar spine fat fraction and R2* and its impact on osteoporosis diagnosis
No full textBACKGROUND: Bone marrow adiposity and R2* have been explored as an imaging biomarker for osteoporosis. Chemical shift-encoded MRI (CSE-MRI) is a method that allows for relatively accurate measurement of adiposity and R2* in bone marrow in a simple manner. Additionally, there are reports of a physiological gradient of fat distribution in the lumbar spine. This physiological gradient of fat distribution can potentially impact the prediction of osteoporosis. Furthermore, the distribution of R2* is not well understood. PURPOSE: This study examined how lumbar spine fat fraction (FF) and R2* change with different levels of the lumbar spine, how they influence osteoporosis prediction, and how they change according to measurement methods. STUDY DESIGN/SETTING: Cross-sectional study using retrospectively collected data. PATIENT SAMPLE: The study included patients who underwent dual-energy X-ray absorptiometry and lumbar spine CSE-MRI within one-month intervals between 2017 and 2022. OUTCOME MEASURES: Reproducibility of FF and R2* based on measurement techniques, changes in FF and R2* according to vertebral level and osteoporosis status, and diagnostic power of osteoporosis based on vertebral level. METHODS: Patients were categorized into the normal bone density, osteopenia, and osteoporosis groups based on bone mineral density. The relationship between groups and spine level before and after BMD adjustment was investigated using generalized estimating equations. Comparisons between the three groups and various measures of reliability were conducted using intraclass correlation coefficient. The diagnostic performance for predicting osteoporosis was evaluated with a receiver operating characteristic curve. RESULTS: Comparing the three groups, FF increased with osteoporosis severity, while R2* decreased (p<.001). The intra/inter-rater agreement for FF and R2* was excellent. A physiological gradient within individuals was observed, where FF increased towards the lower lumbar spine (p=.002). R2* tended to decrease, but it was not statistically significant (p=.218). There was no statistically significant difference in the diagnosis of osteoporosis based on FF or R2* across different lumbar spine levels. CONCLUSIONS: There was an increase in FF and a decrease in R2* from T12 to L5. However, the predictive power of osteoporosis did not significantly differ between each level
Square-law detector in FHSS BFSK systems and its performance characteristics in impulsive environment
No full textCOMPARISON OF KNOWN SIGNAL-DETECTION SCHEMES UNDER A WEAKLY DEPENDENT NOISE MODEL
No full textThe authors consider the discrete-time signal detection problem under the presence of additive noise exhibiting weak dependence. They first propose a weakly dependent noise model, in which the additive noise is modelled as a moving average process. They derive the locally optimum, memoryless, and one-memory detector test statistics under the model. The asymptotic performance of the one-memory detector is compared with that of the locally optimum and memoryless detectors. Specific examples for the asymptotic performance comparison of these detectors are considered. The authors also investigate the finite sample-size performance of several detectors through Monte-Carlo simulation. It is observed that the one-memory detector can achieve almost optimum performance at the expense of only one memory unit under the weakly dependent noise model, and is rather insensitive to slight model change.Korea Science and Engineering Foundation (KOSEF) under grants 921-0800-0022 and 941-0900-040-
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