Comparison of Statistical Methods for Assessing Spatial Correlations Between Maps of Different Arterial Properties

2015 ◽  
Vol 137 (10) ◽  
Author(s):  
Ethan M. Rowland ◽  
Yumnah Mohamied ◽  
K. Yean Chooi ◽  
Emma L. Bailey ◽  
Peter D. Weinberg
Keyword(s):  
Wavelet Transforms ◽  
Degrees Of Freedom ◽  
Arterial Wall ◽  
Atherosclerotic Lesion ◽  
Null Distribution ◽  
Correlation Coefficients ◽  
Spatial Correlations ◽  
Aggregated Data ◽  
Anatomical Correlation ◽  
Lesion Frequency

Assessing the anatomical correlation of atherosclerosis with biomechanical localizing factors is hindered by spatial autocorrelation (SA), wherein neighboring arterial regions tend to have similar properties rather than being independent, and by the use of aggregated data, which artificially inflates correlation coefficients. Resampling data at lower resolution or reducing degrees-of-freedom in significance tests negated effects of SA but only in artificial situations where it occurred at a single length scale. Using Fourier or wavelet transforms to generate autocorrelation-preserving surrogate datasets, and thus to compute the null distribution, avoided this problem. Bootstrap methods additionally circumvented the errors caused by aggregating data. The bootstrap technique showed that wall shear stress (WSS) was significantly correlated with atherosclerotic lesion frequency and endothelial nuclear elongation, but not with the permeability of the arterial wall to albumin, in immature rabbits.

Dynamic Behavior and Synchronization of an Automobile as a Complex System

2014 ◽  
Author(s):  
Claudia A. González-Cruz ◽  
Juan C. Jáuregui-Correa ◽  
Carlos S. López-Cajún ◽  
Mihir Sen
Keyword(s):  
Complex System ◽  
Wavelet Transforms ◽  
Cross Correlation ◽  
Correlation Coefficients ◽  
The Other ◽  
Accelerometer Data ◽  
Hilbert Transforms ◽  
The Road ◽  
The Individual ◽  
Analytical Tools

A complex system is composed of many interacting components, but the behavior of the system as a whole can be quite different from that of the individual components. An automobile is an example of a common mechanical system composed of a large number of individual components that are mechanically connected in some way and hence transmit vibrations to each other. This paper proposes a variety of inter-related analytical tools for the study of experimental data from such systems. In this work, experimental results of accelerometer data acquired at two locations in the automobile for two different kinds of tests are analyzed. One test is the response to impact on a stationary vehicle, and the other is the road-response to the vehicle being driven on a flat road at different speeds. Signals were processed via Fourier and wavelet transforms, cross-correlation coefficients were computed, and Hilbert transforms and Kuramoto order parameters were determined. A new parameter representing synchronization deficit is introduced. There is indeed some degree of synchronization that can be quantified between the accelerations measured at these two locations in the vehicle.

scholarly journals Statistical Beamforming for Massive MIMO Systems with Distinct Spatial Correlations

Sensors ◽  
2020 ◽  
Vol 20 (21) ◽  
pp. 6255
Author(s):  
Taehyoung Kim ◽  
Sangjoon Park
Keyword(s):  
Massive Mimo ◽  
Degrees Of Freedom ◽  
Mimo Systems ◽  
Mimo System ◽  
Multiple Input Multiple Output ◽  
High Signal ◽  
Spatial Correlations ◽  
Channel Correlation ◽  
Low Correlation ◽  
Noise Ratio

In this paper, we propose a novel statistical beamforming (SBF) method called the partial-nulling-based SBF (PN-SBF) to serve a number of users that are undergoing distinct degrees of spatial channel correlations in massive multiple-input multiple-output (MIMO) systems. We consider a massive MIMO system with two user groups. The first group experiences a low spatial channel correlation, whereas the second group has a high spatial channel correlation, which can happen in massive MIMO systems that are based on fifth-generation networks. By analyzing the statistical signal-to-interference-plus-noise ratio, it can be observed that the statistical beamforming vector for the low-correlation group should be designed as the orthogonal complement for the space spanned by the aggregated channel covariance matrices of the high-correlation group. Meanwhile, the spatial degrees of freedom for the high-correlation group should be preserved without cancelling the interference to the low-correlation group. Accordingly, a group-common pre-beamforming matrix is applied to the low-correlation group to cancel the interference to the high-correlation group. In addition, to deal with the intra-group interference in each group, the post-beamforming vector for each group is designed in the manner of maximizing the signal-to-leakage-and-noise ratio, which yields additional performance improvements for the PN-SBF. The simulation results verify that the proposed PN-SBF outperforms the conventional SBF schemes in terms of the ergodic sum rate for the massive MIMO systems with distinct spatial correlations, without the rate ceiling effect in the high signal-to-noise ratio region unlike conventional SBF schemes.

The Effect of Arterial Wall Deformability on Hemodynamics of CABG

2008 ◽  
Author(s):  
Esfandyar Kouhi ◽  
Yos Morsi ◽  
S. H. Masood
Keyword(s):  
Degrees Of Freedom ◽  
Arterial Wall ◽  
Artery Bypass ◽  
Three Dimensional ◽  
Rigid Wall ◽  
Hemodynamic Forces ◽  
Velocity Magnitude ◽  
Hyper Elastic ◽  
Rigid Model ◽  
Rigid Walls

In this study, hemodynamic forces in a three-dimensional (3D) computational model of Coronary Artery Bypass Grafting (CABG) with deformable and rigid walls were compared. A physiologic pulsatile non-Newtonian blood flow was considered in the arteries for both models. The artery walls in the distensible model were considered to be hyper-elastic with nonlinear strain dependent Young’s module and axial and radial degrees of freedom, while the deformability in all directions of the rigid model was restricted. The velocity distributions and magnitudes, vortex motions and the occurrence of recirculation zones were selected as the primary hemodynamic parameters in order to show the effect of deformability in the arterial wall and in calculating differences versus the rigid wall model. It was found that during systolic, the velocity magnitude at the host artery bed could vary by up to 80% depending on the longitudinal distance from the center of the anastomosis junction.

scholarly journals Towards an improved description of ocean uncertainties: effect of local anamorphic transformations on spatial correlations

2011 ◽  
Vol 8 (5) ◽  
pp. 2147-2195 ◽  
Author(s):  
J.-M. Brankart ◽  
C.-E. Testut ◽  
D. Béal ◽  
M. Doron ◽  
C. Fontana ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Piecewise Linear ◽  
Correlation Radius ◽  
Correlation Structure ◽  
General Tendency ◽  
Spatial Correlations ◽  
Parameter Uncertainties ◽  
Large Size ◽  
Observation Network ◽  
Spatial Correlation Structure

Abstract. The objective of this paper is to investigate if the description of ocean uncertainties can be significantly improved by applying a local anamorphic transformation to each model variable, and by making the assumption of joint Gaussianity for the transformed variables, rather than for the original variables. For that purpose, it is first argued that a significant improvement can already be obtained by deriving the local transformations from a simple histogram description of the marginal distributions. Two distinctive advantages of this solution for large size applications are the conciseness and the numerical efficiency of the description. Second, various oceanographic examples are used to evaluate the effect of the resulting piecewise linear local anamorphic transformations on the spatial correlation structure. These examples include (i) stochastic ensemble descriptions of the effect of atmospheric uncertainties on the ocean mixed layer, and of wind uncertainties or parameter uncertainties on the ecosystem, and (ii) non-stochastic ensemble descriptions of forecast uncertainties in current sea ice and ecosystem pre-operational developments. The results indicate that (i) the transformation is accurate enough to faithfully preserve the correlation structure if the joint distribution is already close to Gaussian, and (ii) the transformation has the general tendency of increasing the correlation radius as soon as the spatial dependence between random variables becomes nonlinear, with the important consequence of reducing the number of degrees of freedom in the uncertainties, and thus increasing the benefit that can be expected from a given observation network.

Investigating Coordination in Multidegree of Freedom Control I: Time-On-Target Analysis of 6 DOF Tracking

1997 ◽  
Vol 41 (2) ◽  
pp. 1249-1253 ◽  
Author(s):  
Shumin Zhai ◽  
John W. Senders
Keyword(s):  
Virtual Environments ◽  
Linear Correlation ◽  
Degrees Of Freedom ◽  
Correlation Coefficients ◽  
Modern Human ◽  
Tracking Errors ◽  
Human Machine Interfaces ◽  
Control Devices ◽  
Machine Systems ◽  
Component Time

In these two companion papers, methods developed in a series of studies in the 1940's and 1950's are applied to the analysis of 6 DOF control devices used in modern human machine systems such as teleoperation and virtual environments. Contrary to the early studies, the current work showed that the simultaneous time-on-target in multidegree of freedom tracking was higher than the product of component time on target scores. The distribution of linear correlation coefficients between the tracking errors of different degrees of freedom tended to be skewed towards the positive values. These results suggested that subjects' discoordination in early multidegree of freedom tracking studies was likely due to the limitation of human machine interfaces at that time. With well designed interfaces, subjects exhibited more coordinated trials than discoordinated trials in multidegree of freedom tracking.

Chronic unilateral arm lymphedema correlates with increased intima-media thickness in the brachial artery

VASA ◽  
2021 ◽  
Author(s):  
Victoria Klüsch ◽  
Erin C. Boyle ◽  
Saad Rustum ◽  
Maximilian Franz ◽  
Tjoung-Won Park-Simon ◽  
...  
Keyword(s):  
Arterial Wall ◽  
Lymphatic Vessels ◽  
Atherosclerotic Lesion ◽  
Intima Media Thickness ◽  
Cholesterol Transport ◽  
Contralateral Limb ◽  
Arm Lymphedema ◽  
Human Arteries ◽  
Clinical Experiment ◽  
Atherosclerotic Lesion Formation

Summary: Drainage of the arterial wall via adventitial lymphatic vessels has been shown to play a pivotal role for vessel wall homeostasis. Also, retrograde cholesterol transport is ensured via this route, but no studies exist to demonstrate that lymphatic stasis would represent a mechanism to initiate atherosclerotic lesion formation in human arteries. To test this hypothesis, we embarked on a simple clinical experiment, assessing wall thickness in limb arteries with lymphedema after surgical intervention, with the contralateral limb serving as control. Using ultrasound imaging, the differential thickness was assessed separately for the three arterial wall layers. The potential of disease progression by lymphostasis was addressed by depiction of longitudinal results according to the time after lymph dissection.

A statistical, spatial, and hydrologic comparison of gauge-based and MPE-based rainfall measurements

2017 ◽  
Vol 124 (1-4) ◽  
pp. 11-23
Author(s):  
Richard Bernatz
Keyword(s):  
Goodness Of Fit ◽  
Correlation Coefficients ◽  
Relative Bias ◽  
Rainfall Time Series ◽  
Spatial Correlations ◽  
Event Time ◽  
Moment Coefficient ◽  
Significant Difference ◽  
Precipitation Estimation ◽  
The Difference

Gauge-based and multi-sensor precipitation estimation (MPE) data are compared on hourly, daily, monthly and event time scales at site locations over a 12-year period. Gauge data is collected at 16 sites within a 950 km2 portion of the Upper Iowa River in northeast Iowa. Average relative MPE bias is positive for all but the event time scale, and has a magnitude of less than 0.10 for all scales. Gauge and MPE average correlation coefficients range from 0.73 on the hourly scale to 0.92 on the event and monthly scales. The MPE relative bias standard deviation decreases from 1.70 mm on the hourly scale to 0.27 mm on the monthly scale. Decomposition of hourly bias reveals that the false positive portion is the most significant component. Seventy percent of MPE accumulation have a relative bias of 0.5 or less when hourly accumulations are 7 mm or greater. Pearson product-moment coefficient analysis reveals strong similarities in spatial correlations as a function of site separation. Rainfall time series for the basin are constructed from the two data sources and used as input to a Blocked Topmodel rainfall runoff scheme to provide another means of comparison on a basin-wide spatial scale. Five goodness-of-fit measures are used for quantifying the viability of simulated flows. No statistically significant difference in annual means using the difference sources is found for any of the measures.

scholarly journals Monitoring the lowermost tropospheric ozone with thermal infrared observations from a geostationary platform: performance analyses for a future dedicated instrument

2014 ◽  
Vol 7 (2) ◽  
pp. 391-407 ◽  
Author(s):  
P. Sellitto ◽  
G. Dufour ◽  
M. Eremenko ◽  
J. Cuesta ◽  
G. Forêt ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Degrees Of Freedom ◽  
Transport Model ◽  
Correlation Coefficients ◽  
Thermal Infrared ◽  
Lower Surface ◽  
Maximum Sensitivity ◽  
Performance Analyses ◽  
Mean Square Errors ◽  
Ozone Column

Abstract. In this paper, we present performance analyses for a concept geostationary observing system called MAGEAQ (Monitoring the Atmosphere from Geostationary orbit for European Air Quality). The MAGEAQ mission is designed to include a TIR (thermal infrared) spectrometer and a broadband VIS (visible) radiometer; in this work we study only the TIR component (MAGEAQ-TIR). We have produced about 20 days of MAGEAQ-TIR tropospheric ozone pseudo-observations with a full forward and inverse radiative transfer pseudo-observations simulator. We have studied the expected sensitivity of MAGEAQ-TIR and we have found that it is able to provide a full single piece of information for the ozone column from surface to 6 km (about 1.0 DOF (degrees of freedom) and maximum sensitivity at about 3.0 km, on average), as well as a partially independent surface–3 km ozone column (about 0.6 DOF and maximum sensitivity at about 2.5 km, on average). Then, we have compared the tropospheric ozone profiles and the lower (surface–6 km) and lowermost (surface–3 km) tropospheric ozone column pseudo-observations to the target pseudo-reality, produced with the MOCAGE (MOdèle de Chimie Atmosphérique à Grande Echelle) chemistry and transport model. We have found very small to not significant average biases (< 1% in absolute value, for the surface–6 km TOC (tropospheric ozone column), and about −2 to −3 %, for the surface–3 km TOC) and small RMSEs (root mean square errors; about 1.3 DU (5%), for the surface–6 km TOC, and about 1.5 DU (10%), for the surface–3 km TOC). We have tested the performance of MAGEAQ-TIR at some selected small (0.2° × 0.2°) urban and rural locations. We have found that, while the vertical structures of the lower tropospheric ozone pseudo-reality are sometimes missed, MAGEAQ-TIR's lower and lowermost column pseudo-observations follow stunningly good the MOCAGE column pseudo-reality, with correlation coefficients reaching values of 0.9 or higher. Unprecedented retrieval performance for the lowermost tropospheric ozone column is shown. In any case, our MAGEAQ-TIR pseudo-observations are only partially able to replicate the MOCAGE pseudo-reality variability and temporal cycle at the very lowest layers (surface and 1 km altitude), especially at southern European urban locations, where the photochemistry signal is partially missed or shifted at higher altitudes. Temporal artifacts on the daily cycle are sometimes observed. Stratospheric-to-tropospheric exchanges during short time periods (of the order of 1 day) are detected by the MAGEAQ-TIR pseudo-observations.

scholarly journals Monitoring the lowermost tropospheric ozone with thermal infrared observations from a geostationary platform: performance analyses for a future dedicated instrument

2013 ◽  
Vol 6 (4) ◽  
pp. 6445-6490 ◽  
Author(s):  
P. Sellitto ◽  
G. Dufour ◽  
M. Eremenko ◽  
J. Cuesta ◽  
G. Forêt ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Degrees Of Freedom ◽  
Transport Model ◽  
Correlation Coefficients ◽  
Lower Surface ◽  
Maximum Sensitivity ◽  
Infrared Observations ◽  
Performance Analyses ◽  
Short Time ◽  
Ozone Column

Abstract. In this paper, we present performance analyses for a concept geostationary observing system called MAGEAQ (Monitoring the Atmosphere from Geostationary orbit for European Air Quality). The MAGEAQ mission is designed to include a TIR spectrometer and a broadband VIS radiometer; in this work we study only the TIR component (MAGEAQ-TIR). We have produced about 20 days of MAGEAQ-TIR tropospheric ozone pseudo-observations with a full forward and inverse radiative transfer pseudo-observations simulator. We have studied the expected sensitivity of MAGEAQ-TIR and we have found that a completely independent surface −6 km ozone column (about 1.0 DOF (degrees of freedom) and maximum sensitivity at about 3.0 km, on average), as well as a partially independent surface −3 km ozone column (about 0.6 DOF and maximum sensitivity at about 2.5 km, on average) can be achieved. Then, we have compared the tropospheric ozone profiles and the lower (surface −6 km) and lowermost (surface −3 km) tropospheric ozone column pseudo-observations to the target pseudo-reality, produced with the MOCAGE (MOdèle de Chimie Atmosphérique à Grande Echelle) chemistry and transport model. We have found very small to not significant average biases (< 1% in absolute value, for the surface −6 km TOC, and about −2 to −3%, for the surface −3 km TOC) and small RMSEs (about 1.3 DU (5%), for the surface −6 km TOC, and about 1.5 DU (10%), for the surface −3 km TOC). We have tested the performances of MAGEAQ-TIR at some selected small (0.2° × 0.2°) urban and rural locations. We have found that, while the vertical structures of the lower tropospheric ozone pseudo-reality are sometimes missed, MAGEAQ-TIR lower and lowermost column pseudo-observations follow stunningly good the MOCAGE column pseudo-reality, with correlation coefficients reaching values of 0.9 or higher. Unprecedented retrieval performances for the lowermost tropospheric ozone column are shown. In any case, our MAGEAQ-TIR pseudo-observations are only partially able to replicate the MOCAGE pseudo-reality variability and temporal cycle at the very lowest layers (surface and 1 km altitude), especially at Southern European urban locations, where the photochemistry signal is partially missed or shifted at higher altitudes. Temporal artifact on the daily cycle are sometimes observed. Stratospheric-to-tropospheric exchanges during short time periods (of the order of 1 day) are detected by the MAGEAQ-TIR pseudo-observations.

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