373 research outputs found
Spatio-temporal Analysis of Precipitation and Flood Data from South Carolina
No full textSpatio-temporal data are everywhere: we encounter them on TV, in newspapers, on computer screens, on tablets, and on plain paper maps. As a result, researchers in di- verse areas are increasingly faced with the task of modeling geographically-referenced and temporally-correlated data. In this dissertation, we propose two different spa- tiotemporal models to capture the behavior of rainfall and flood data in the state of South Carolina.
Both models are built using a Bayesian hierarchical framework, which involves specifying the true underlying process in the first level and the spatio-temporal ran- dom effect in the second level of the hierarchy. The prior distribution of the param- eters or hyper-parameters is specified in the third stage. The two models differ in the covariance structure of the spatial random effects. In the rainfall spatiotemporal model, we employ a Gaussian process model which has a distance-based covariance. To model the flood data, we use a conditional autoregressive (CAR) model with a proximity matrix.
Another aspect that sets the models apart is the covariates considered. In particu- lar, the precipitation model incorporates a variable related to sea surface temperature (SST) to reflect the effect of El Niño-Southern Oscillation (ENSO) activity, along with monthly maximum temperature among other predictors. In the flood model, a gridded field of precipitation values with a spatial resolution of roughly 4 × 4 km is used as one of the covariates since investigating the dynamics between the rainfall and flood levels is of interest
Modeling Minimal Spanning Trees with Beta Vectors
No full textWe examine methods of generating beta random vectors to model the normalized interpoint distances on the minimal spanning tree (MST). Using properties of the univariate beta distribution, we propose three methods for generating multivariate beta vectors. We use overlapping sums of the components of a Dirichlet distribution to construct beta vectors. We investigate the products of beta variables that follow an ordered Dirichlet distribution. The geometric mean of beta variables is explored to produce a multivariate beta distribution. We define a multivariate Gini index for the normalized distances on the MST to measure the amount of scatter in a multivariate sample and the inequity among the interpoint distances. An example shows the MST of 11 European languages with respect to the first 10 numerals. A simulation study compares the parametric bootstrap of the Gini index, the maximum and the range of the interpoint distances with results from modeling the distances on the MST. Keywords: Minimal Spanning Tree; Multivariate Beta; Dirichlet; Gini index; Lorenz Curve
Mathematical model of water quality rehabilitation with rainwater utilization : a case study at Haigang
No full textAuthor name used in this publication: K. W. Chau2006-2007 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishedGreen (AAM
Research on Information Services of Sustainable Utilization of Natural Resources Based on Web
No full textA Two Level TDMA Scheduling Protocol with Intra-cluster Coverage for Large Scale Wireless Sensor Network
No full textOne of the key problem for Wireless Sensor Network (WSN) is the design of Medium Access Control(MAC) protocol, which medium access is the major consumer of sensor energy. TDMAbased MAC protocol is inherently collision free, and can rule out idle listening since nodes know when to transmit. Cluster-based TDMA protocol is more scalable than traditional TDMA protocol, but it introduces inter-cluster interference for which FDMA and CDMA are not good solutions due to their hardware complexity and high cost. In this paper, we present TLTS, a Two Lever TDMA Scheduling protocol, in which the first scheduling ensures that neighboring clusters collecting their member’s data during different frames in order to avoid inter-cluster interference and the second scheduling schedules members of cluster sending their data to their respectively cluster heads during different slots to avoid intra-cluster interference. Simulation results show that TLTS performs better than HEED when node density turns higher. TLTS is more practical than HEED which uses CDMA code to avoid inter-cluster interference for deploying large scale WSN. Key words: wireless sensor networks; media access control; TDMA; energy efficiency; Intra-cluster coverag
Optimal gradient estimates for the insulated conductivity problem with general convex inclusions case
No full textWe study the insulated conductivity problem which involves two adjacent convex insulators embedded in a bounded domain. It is known that the gradient of solutions may blow up as the distance between the two inclusions tends to zero. However, the sharpness of the blow up rate for general convex insulator case in dimension has remained open. The novelty of this paper is that we answer this problem affirmatively by establishing a pointwise upper bound of the gradient for general convex insulators, along with a corresponding lower bound that achieves optimal blow up rates. These rates are associated with the first nonzero eigenvalue of an elliptic operator determined by the geometry of insulators. Our results improve and make complete the previous result for ball insulators case studied in \cite{DLY}.arXiv admin note: text overlap with arXiv:2203.10081 by other author
The interaction between two close-to-touching convex acoustic subwavelength resonators
No full textThe Minneart resonance is a low frequency resonance in which the wavelength
is much larger than the size of the resonators. It is interesting to study the
interaction between two adjacent bubbles when they are brought close together.
Because the bubbles are usually compressible, in this paper we mainly
investigate resonant modes of two general convex resonators with arbitrary
shapes to extend the results of Ammari, Davies, Yu in [4], where a pair of
spherical resonators are considered by using bispherical coordinates. We
combine the layer potential method for Helmholtz equation in [4,5] and the
elliptic theory for gradient estimates in [26,30] to calculate the capacitance
coefficients for the coupled resonators, then show the
leading-order asymptotic behaviors of two different resonant modes and reveal
the dependance of the resonant frequencies on their geometric properties, such
as convexity, volumes and curvatures. By the way, the blow-up rates of gradient
of the scattered pressure are also presented.Comment: 22 pages, to appear in SIAM Multiscale Model. Simul. arXiv admin
note: substantial text overlap with arXiv:2001.04888 by other author
Correlation Between Dynamic Contrast-Enhanced CT Imaging Signs and Differentiation Grade and Microvascular Invasion of Hepatocellular Carcinoma
No full textYang Liu,1,2 Yunhui Zhou,3 Cong Liao,1,2 Hang Li,2 Xiaolan Zhang,4 Haigang Gong,5 Hong Pu1,2 1School of Medicine, University of Electronic Science and Technology, Sichuan, China; 2Department of Radiology, Sichuan Academy of Medical Sciences & Sichuan Provincial People’s Hospital, Sichuan, People’s Republic of China; 3Department of Radiology, Chengdu Pidu District People’s Hospital, Sichuan, People’s Republic of China; 4Shukun Technology Co., Ltd, Beijing, People’s Republic of China; 5School of Computer Science and Engineering, University of Electronic Science and Technology, Sichuan, People’s Republic of ChinaCorrespondence: Hong Pu, Department of Radiology, Sichuan Academy of Medical Sciences, Sichuan Provincial People’s Hospital; School of Medicine, University of Electronic Science and Technology, Chengdu, Sichuan Province, 610000, People’s Republic of China, Email [email protected] Haigang Gong, School of Computer Science and Engineering, University of Electronic Science and Technology, Chengdu, Sichuan Province, 610000, People’s Republic of China, Email [email protected]: This study aimed to investigate how dynamic contrast-enhanced CT imaging signs correlate with the differentiation grade and microvascular invasion (MVI) of hepatocellular carcinoma (HCC), and to assess their predictive value for MVI when combined with clinical characteristics.Methods: We conducted a retrospective analysis of clinical data from 232 patients diagnosed with HCC at our hospital between 2021 and 2022. All patients underwent preoperative enhanced CT scans, laboratory tests, and postoperative pathological examinations. Among the 232 patients, 89 were identified as MVI-positive and 143 as MVI-negative. Regarding tumor differentiation, 56 patients were well-differentiated, 145 moderately, and 31 poorly. Multivariate logistic regression analysis was employed to establish a prediction model for variables showing significant differences. Additionally, the diagnostic performance of various indicators were evaluated using ROC analysis.Results: Among the qualitative data, significant differences (P< 0.05) were observed between the MVI-positive and MVI-negative groups in 5 items such as peritumoral enhancement. In terms of quantitative data, the MVI-positive group exhibited higher maximum tumor length, AST, ALT, AFP levels and the ALBI score (P< 0.05). Conversely, CT values in the arterial phase (AP), portal venous phase (PVP), and PT levels were lower in the MVI-positive group (P< 0.05). Multivariate Logistic regression analysis identified ALBI score, PT level, CT value in PVP, and tumor capsule as independent risk factors for MVI occurrence (AUC: 0.71, 0.58, 0.66, and 0.60). The combined diagnostic AUC value was 0.82 (95% CI: 0.76– 0.87). Significant differences were found among different differentiation grade groups in 10 items such as non-smooth tumor margin (P< 0.05).Conclusion: Preoperative dynamic contrast-enhanced CT examination in patients with HCC can be utilized to predict the presence of MVI. When combined with clinical characteristics, these imaging signs demonstrate good predictive performance for MVI status. Furthermore, this approach has significant implications for determining the differentiation grade of tumors.Keywords: hepatocellular carcinoma, microvascular invasion, computed tomography, differentiation grad
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