In this study, we aimed to elicit cerebellar activity using a visually cued task involving alternating button presses and foot pedaling at varying speeds. Functional MRI data were acquired using a multiband sequence on a 3T scanner. Thirty-three healthy volunteers participated, and their blood oxygen-level dependent (BOLD) signals were recorded at a spatial resolution of [Formula: see text] [Formula: see text]2.5[Formula: see text]mm 3 . The fMRI data were analyzed using a general linear model (GLM) to delineate brain regions activated by the button press and foot pedaling conditions, respectively. The BOLD signal changes in each active region of interest (ROI) were then linearly regressed against the mean reaction times (RTs), with age as a covariate, for all participants. All ROIs exhibited a negative relationship with RTs, indicating that higher BOLD activations were associated with faster responses across all conditions. Interestingly, the button press task significantly activated the pyramis (inferior cerebellar vermis), whereas the foot pedaling task activated the superior cerebellar vermis. This finding reflects a functional segmentation along the superior–inferior axis of the cerebellar vermis, corresponding to a foot–hand distribution. Using multiband fMRI, we achieved the spatial resolution necessary to delineate this functional topography within the cerebellum.

This study conducts a guided writing practice inside the fMRI machine and investigates differences of neural correlations in the brains between the participants' native language (traditional Chinese) and English as a foreign language (EFL). This is a cross-sectional study adapts a 2X2 clusters time-series experimental design. 27 subjects were sampled and grouped by their English proficiency level (high vs. low). Each subject did four writing tasks and received fMRI scanning during 40 minutes writing periods, which generates large amounts of spatial temporal data. Results showed: (1) the lower level group had significantly higher activation in the right insula when doing English writing; (2) activations were observed in areas associated with motor, visual, and language circuits in the brain; (3) learners had stronger brain activations on relevant areas when doing familiar tasks. Teaching implications suggest that the learning effects may help reduce learners' risk-taking perceptions and anxiety, and handwriting activities deserve more attention from the teachers and educators. Moreover, novice writers are advised to establish stronger brain networks through drill practices to become more proficient in performing writing skills.

Local distribution search is used in query-driven visualization for identifying salient features. Due to the high computational and storage costs, local distribution search in multi-field datasets is challenging. In this paper, we introduce two high performance, memory efficient algorithms for searching for local distributions that are characterized by marginal and joint features in multi-field datasets. They leverage bitmap indexing and local voting to efficiently extract regions that match a target distribution, by first approximating search results and refining to generate the final result. The first algorithm, merged-bin-comparison (MBC), reduces the computation of histogram dissimilarity measures by clustering bins. The second algorithm, sampled-active voxels (SAV), adopts stratified sampling to reduce the workload for searching local distributions with large spatial neighborhoods. The efficiency and efficacy of our algorithms are demonstrated in multiple experiments.

Study of flow instability in turbine engine compressors is crucial to understand the inception and evolution of engine stall. Aerodynamics experts have been working on detecting the early signs of stall in order to devise novel stall suppression technologies. A state-of-the-art Navier-Stokes based, time-accurate computational fluid dynamics simulator, TURBO, has been developed in NASA to enhance the understanding of flow phenomena undergoing rotating stall. Despite the proven high modeling accuracy of TURBO, the excessive simulation data prohibits post-hoc analysis in both storage and I/O time. To address these issues and allow the expert to perform scalable stall analysis, we have designed an in situ distribution guided stall analysis technique. Our method summarizes statistics of important properties of the simulation data in situ using a probabilistic data modeling scheme. This data summarization enables statistical anomaly detection for flow instability in post analysis, which reveals the spatiotemporal trends of rotating stall for the expert to conceive new hypotheses. Furthermore, the verification of the hypotheses and exploratory visualization using the summarized data are realized using probabilistic visualization techniques such as uncertain isocontouring. Positive feedback from the domain scientist has indicated the efficacy of our system in exploratory stall analysis.

Streamline-based techniques play an important role in visualizing and analyzing uncertain steady vector fields. It is a challenging problem to generate accurate streamlines in uncertain vector fields due to the global uncertainty transportation. In this work, we present a novel probabilistic method for streamline computation on uncertain steady vector fields using a Bayesian framework. In our framework, a streamline is modeled as a state space model which captures the spatial coherence of integration steps and uncertainty in local distributions using the conditional prior density and the likelihood function. To approximate the posterior distribution for all the possible traces originating from a given seed position, a set of weighted samples are iteratively updated from which streamlines with higher likelihood can be derived. We qualitatively and quantitatively compare our method with alternative methods on different types of flow field data sets. Our method can generate possible streamlines with higher certainty and hence more accurate flow traces.

Identification of early signs of rotating stall is essential for the study of turbine engine stability. With recent advancements of high performance computing, high-resolution unsteady flow fields allow in depth exploration of rotating stall and its possible causes. Performing stall analysis, however, involves Significant effort to process large amounts of simulation data, especially when investigating abnormalities across many time steps. In order to assist scientists during the exploration process, we present a visual analytics framework to identify suspected spatiotemporal regions through a comparative visualization so that scientists are able to focus on relevant data in more detail. To achieve this, we propose efficient stall analysis algorithms derived from domain knowledge and convey the analysis results through juxtaposed interactive plots. Using our integrated visualization system, scientists can visually investigate the detected regions for potential stall initiation and further explore these regions to enhance the understanding of this phenomenon. Positive feedback from scientists demonstrate the efficacy of our system in analyzing rotating stall.

Occlusion presents a major challenge in visualizing 3D flow and tensor fields using streamlines. Displaying too many streamlines creates a dense visualization filled with occluded structures, but displaying too few streams risks losing important features. We propose a new streamline exploration approach by visually manipulating the cluttered streamlines by pulling visible layers apart and revealing the hidden structures underneath. This paper presents a customized view-dependent deformation algorithm and an interactive visualization tool to minimize visual clutter in 3D vector and tensor fields. The algorithm is able to maintain the overall integrity of the fields and expose previously hidden structures. Our system supports both mouse and direct-touch interactions to manipulate the viewing perspectives and visualize the streamlines in depth. By using a lens metaphor of different shapes to select the transition zone of the targeted area interactively, the users can move their focus and examine the vector or tensor field freely.

Although vortex analysis and detection have been extensively investigated in the past, none of the existing techniques are able to provide fully robust and reliable identification results. Local vortex detection methods are popular as they are efficient and easy to implement, and produce binary outputs based on a user-specified, hard threshold. However, vortices are global features, which present challenges for local detectors. On the other hand, global detectors are computationally intensive and require considerable user input. In this work, we propose a consensus-based uncertainty model and introduce spatial proximity to enhance vortex detection results obtained using point-based methods. We use four existing local vortex detectors and convert their outputs into fuzzy possibility values using a sigmoid-based soft-thresholding approach. We apply a majority voting scheme that enables us to identify candidate vortex regions with a higher degree of confidence. Then, we introduce spatial proximity- based analysis to discern the final vortical regions. Thus, by using spatial proximity coupled with fuzzy inputs, we propose a novel uncertainty analysis approach for vortex detection. We use expert's input to better estimate the system parameters and results from two real-world data sets demonstrate the efficacy of our method.

When the spatial and temporal resolutions of a time-varying simulation become very high, it is not possible to process or store data from every time step due to the high computation and storage cost. Although using uniformly down-sampled data for visualization is a common practice, important information in the un-stored data can be lost. Currently, linear interpolation is a popular method used to approximate data between the stored time steps. For pathline computation, however, errors from the interpolated velocity in the time dimension can accumulate quickly and make the trajectories rather unreliable. To inform the scientist the error involved in the visualization, it is important to quantify and display the uncertainty, and more importantly, to reduce the error whenever possible. In this paper, we present an algorithm to model temporal interpolation error, and an error reduction scheme to improve the data accuracy for temporally down-sampled data. We show that it is possible to compute polynomial regression and measure the interpolation errors incrementally with one sequential scan of the time-varying flow field. We also show empirically that when the data sequence is fitted with least-squares regression, the errors can be approximated with a Gaussian distribution. With the end positions of particle traces stored, we show that our error modeling scheme can better estimate the intermediate particle trajectories between the stored time steps based on a maximum likelihood method that utilizes forward and backward particle traces.

Occlusion presents a major challenge in visualizing 3D flow fields using streamlines. Displaying too many streamlines creates a dense visualization filled with occluded structures, but displaying too few streams risks losing important features. A more ideal streamline exploration approach is to visually manipulate the cluttered streamlines by pulling visible layers apart and revealing the hidden structures underneath. This paper presents a customized deformation algorithm and an interactive visualization tool to minimize visual cluttering. The algorithm is able to maintain the overall integrity of the flow field and expose the previously hidden structures. Our system supports both mouse and direct-touch interactions to manipulate the viewing perspectives and visualize the streamlines in depth. By using a lens metaphor of different shapes to select the transition zone of the targeted area interactively, the users can move their focus and examine the flow field freely.

Abstract Representing features by local histograms is a proven technique in several volume analysis and visualization applications including feature tracking and transfer function design. The efficiency of these applications, however, is hampered by the high computational complexity of local histogram computation and matching. In this paper, we propose a novel algorithm to accelerate local histogram search by leveraging bitmap indexing. Our method avoids exhaustive searching of all voxels in the spatial domain by examining only the voxels whose values fall within the value range of user‐defined local features and their neighborhood. Based on the idea that the value range of local features is in general much smaller than the dynamic range of the entire dataset, we propose a local voting scheme to construct the local histograms so that only a small number of voxels need to be examined. Experimental results show that our method can reduce much computational workload compared to the conventional approaches. To demonstrate the utility of our method, an interactive interface was developed to assist users in defining target features as local histograms and identify the locations of these features in the dataset.

We study the problem of business model mining and prediction in the e-commerce context. Unlike most existing approaches where this is typically formulated as a regression problem or a time-series prediction problem, we take a different formulation to this problem by noting that these existing approaches fail to consider the potential relationships both among the consumers (consumer influence) and among the shops (competitions or collaborations). Taking this observation into consideration, we propose a new method for e-commerce business model mining and prediction, called EBMM, which combines regression with community analysis. The challenge is that the links in the network are typically not directly observed, which is addressed by applying information diffusion theory through the consumer-shop network. Extensive evaluations using Alibaba Group e-commerce data demonstrate the promise and superiority of EBMM to the state-of-the-art methods in terms of business model mining and prediction.

Frequency estimation of a complex sinusoidal signal is a fundamental problem in signal processing. In this regard, Aboutanios and Mulgrew (A&M) proposed an iterative frequency estimator which can approach the theoretical bound in two iterations, thus, made it one of the best iterative estimators. In this paper, we theoretically analyze the two versions of the A&M estimator and show that the estimation biases of the two versions are not equivalent. The results of the theoretical analysis indicate that the bias of the first iteration can be accurately predicted by a polynomial equation. We then propose to use the roots of the polynomial equation to improve the estimation and reduce the bias. Experiments show that the proposed new estimator can significantly reduce the bias.

We present a file layout algorithm for flow fields to improve runtime I/O efficiency for out-of-core streamline computation. Because of the increasing discrepancy between the speed of processors and storage devices, the cost of I/O becomes a major bottleneck for out-of-core computation. To reduce the I/O cost, loading data with better spatial locality has proved to be effective. It is also known that sequential file access is more efficient. To facilitate efficient streamline computation, we propose to reorganize the data blocks in a file following the data access pattern so that more efficient I/O and effective prefetching can be accomplished. To achieve the goal, we divide the domain into small spatial blocks and order the blocks into a linear layout based on the underlying flow directions. The ordering is done using a weighted directed graph model which can be formulated as a linear graph arrangement problem. Our goal is to arrange the file in a way consistent with the data access pattern during streamline computation. This allows us to prefetch a contiguous segment of data at a time from disk and minimize the memory cache miss rate. We use a recursive partitioning method to approximate the optimal layout. Our experimental results show that the resulting file layout reduces I/O cost and hence enables more efficient out-of-core streamline computation.