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1

Blind Separation of Spatio-Temporal Synfire Sources and Visualization of Neural Cliques  

E-print Network

and behavior to synchronous spatio-temporal activities of subsets of neurons within neural networks ­ the so analysis of neural networks. To demonstrate the concept of dynamic BSS, we first apply it in a relatively of neural networks, the problem is much more involved, and the assumptions of linearity and stationarity

Zeevi, Yehoshua Y. "Josh"

2

ORIGINAL ARTICLE Spatio-temporal trends of heavy metals and source  

E-print Network

ORIGINAL ARTICLE Spatio-temporal trends of heavy metals and source apportionment in Tolo Harbour, Zn, As, Cd and Pb in bottom sediments of Tolo Harbour. The concentrations of the eight heavy metals. As, however, is not well correlated with the other seven heavy metals. The average concentrations

Jiao, Jiu Jimmy

3

Resolving Trends in Antarctic Ice Sheet Mass Loss and Glacio-isostatic Adjustment Through Spatio-temporal Source-separation  

NASA Astrophysics Data System (ADS)

There remains considerable inconsistency between different methods and approaches for determining ice mass trends for Antarctica from satellite observations. There are three approaches that can provide near global coverage for mass trends: altimetry, gravimetry and mass budget calculations. All three approaches suffer from a source separation problem where other geophysical processes limit the capability of the method to resolve the origin and magnitude of a mass change. A fourth approach, GPS vertical motion, provides localised estimates of mass change due to elastic uplift and an indirect estimate of GIA. Each approach has different source separation issues and different spatio-temporal error characteristics. In principle, it should be possible to combine the data and process covariances to minimize the uncertainty in the solution and to produce robust, posterior errors for the trends. In practice, this is a challenging problem in statistics because of the large number of degrees of freedom, the variable spatial and temporal sampling between the different observations and the fact that some processes remain under-sampled, such as firn compaction. Here, we present a novel solution to this problem using the latest methods in statistical modelling of spatio-temporal processes. We use Bayesian hierarchical modelling and employ stochastic partial differential equations to capture our physical understanding of the key processes that influence our observations. Due to the huge number of observations involved (> 10^8) methods are required to reduce the dimensionality of the problem and care is required in treatment of the observations as they are not independent. Here, we focus mainly on the results rather than the full suite of methods and we present time evolving fields of surface mass balance, ice dynamic-driven mass loss, and firn compaction for the period 2003-2009, derived from a combination of ICESat, ENVISAT, GRACE, InSAR, GPS and regional climate model output data. We also present a time-invariant GIA field and an elastic vertical motion field for the bedrock. All fields are solved for simultaneously alongside posterior errors that are consistent with the full suite of observations and priors. The framework we have developed can incorporate other data, such as shallow/deep ice core records of accumulation, coffee-can point measurements of mass balance, and snow radar data. The framework can also be applied to other ice masses and components of the climate system that suffer similar source separation issues: for example, solving the sea level budget.

Bamber, J. L.; Schoen, N.; Zammit-Mangion, A.; Rougier, J.; Flament, T.; Luthcke, S. B.; Petrie, E. J.; Rémy, F.

2013-12-01

4

SPATIO-TEMPORAL ANALYSIS OF BEACH MORPHOLOGY USING LIDAR, RTK- GPS AND OPEN SOURCE GRASS GIS  

Microsoft Academic Search

Modern mapping technologies used for coastal studies such as LIDAR and RTK-GPS produce massive amounts of data characterized by oversampling and noise. The physical phenomena and landscape changes examined are often subtle and besides statistical accuracy, adequate representation of surface geometry is crucial for correct interpretation of measured data. We have explored the suitability of the Open source GRASS GIS

Helena Mitasova; David Bernstein; Thomas G. Drake; Russell Harmon; Carl Miller

5

Ozone in Rural Nevada: Investigating spatio-temporal patterns and source regions contributing to elevated concentrations  

NASA Astrophysics Data System (ADS)

In 1993, an ozone (O3) monitoring site was established at Great Basin National Park (GBNP), located in rural eastern Nevada. Analyses of data from this site indicate that compliance with a revised National Ambient Air Quality Standard (NAAQS) ?70 ppb will be challenging. With the exception of GBNP, ambient O3 monitoring has been limited to the areas in and around the 3 urban areas of Nevada. The objectives of the research presented here were to (1) characterize spatial and temporal trends in ambient O 3 across rural Nevada, and (2) identify source regions contributing to elevated O3 in rural Nevada. To pursue these objectives, a network of 13 monitoring sites was established throughout rural Nevada over a period ranging from July 2011 to June 2014. Data from 6 sites during the first 2 years of measurement indicate that maximum MDA8 O3 ranged from 68 to 80 ppb. Ambient O3 measured at GBNP was significantly higher than that measured at other rural Nevada sites. Back trajectory analyses, vertical profile measurements from aircrafts and sondes, statistical analyses, as well as results of regional and global models were employed to identify sources contributing to elevated O3. Our analyses indicate that regional and global sources contribute to O3 at surface sites throughout rural Nevada and that the high elevation and complex terrain make the State ideally situated to intercept air from the free troposphere and thus, pollution derived from complex sources included long-range transport, stratospheric intrusions, and regional emissions. Our data suggest that regional and global cooperation will be necessary to comply with a revised NAAQS in rural Nevada.

Fine, Rebekka

6

Spatio-temporal patterns and source apportionment of pollution in Qiantang River (China) using neural-based modeling and multivariate statistical techniques  

NASA Astrophysics Data System (ADS)

Characterizing the spatio-temporal patterns and apportioning the pollution sources of water bodies are important for the management and protection of water resources. The main objective of this study is to describe the dynamics of water quality and provide references for improving river pollution control practices. Comprehensive application of neural-based modeling and different multivariate methods was used to evaluate the spatio-temporal patterns and source apportionment of pollution in Qiantang River, China. Measurement data were obtained and pretreated for 13 variables from 41 monitoring sites for the period of 2001-2004. A self-organizing map classified the 41 monitoring sites into three groups (Group A, B and C), representing different pollution characteristics. Four significant parameters (dissolved oxygen, biochemical oxygen demand, total phosphorus and total lead) were identified by discriminant analysis for distinguishing variations of different years, with about 80% correct assignment for temporal variation. Rotated principal component analysis (PCA) identified four potential pollution sources for Group A (domestic sewage and agricultural pollution, industrial wastewater pollution, mineral weathering, vehicle exhaust and sand mining), five for Group B (heavy metal pollution, agricultural runoff, vehicle exhaust and sand mining, mineral weathering, chemical plants discharge) and another five for Group C (vehicle exhaust and sand mining, chemical plants discharge, soil weathering, biochemical pollution, mineral weathering). The identified potential pollution sources explained 75.6% of the total variances for Group A, 75.0% for Group B and 80.0% for Group C, respectively. Receptor-based source apportionment was applied to further estimate source contributions for each pollution variable in the three groups, which facilitated and supported the PCA results. These results could assist managers to develop optimal strategies and determine priorities for river pollution control and effective water resources management.

Su, Shiliang; Zhi, Junjun; Lou, Liping; Huang, Fang; Chen, Xia; Wu, Jiaping

7

Data assimilation using spatio-temporal descriptors  

NASA Astrophysics Data System (ADS)

Data assimilation is the process by which numerical model output is fused with observations in order to provide consensus estimates. In a Bayesian framework, this typically consists of constructing a 'process model prior' centred on the numerical model output and an 'observation model' which describes the relationship between the observed variable and the process of interest. This approach, while straightforward and ubiquitous in the geophysical sciences, can lead to erroneous inferences when the numerical output is biased (both spatially and temporally) in an undefined way. Here we show an alternative way in which to carry out data assimilation, whereby only the spatial and temporal properties of the numerical model are fused with the data. The method, couched in a spatio-temporal Bayesian framework, follows a two-stage approach: (i) Spatio-temporal modelling of the numerical model outputs in order to extract spectral spatio-temporal characteristics which are deemed faithful to the processes of interest (e.g. length scales and marginal variances), and (ii) Spatio-temporal modelling of the processes of interest with informative priors (based on (i)) in order to provide updated estimates. We apply this method to estimating the mass balance of Antarctic ice-sheet processes from multiple observations sources: GRACE, ICESat, ENVISat and GPS data. We show that although this problem is under-determined due to lack of observation diversity, spectral characterisation using the two-stage approach allows us to tease out the individual processes and reduce confounding between the processes whilst concurrently providing inferences which are largely data-driven.

Zammit-Mangion, Andrew; Schoen, Nana; Rougier, Jonathan; Bamber, Jonathan

2014-05-01

8

Database Organisation in a Web-Enabled Free and Open-Source Software (foss) Environment for Spatio-Temporal Landslide Modelling  

NASA Astrophysics Data System (ADS)

Landslides exhibit themselves in different mass movement processes and are considered among the most complex natural hazards occurring on the earth surface. Making landslide database available online via WWW (World Wide Web) promotes the spreading and reaching out of the landslide information to all the stakeholders. The aim of this research is to present a comprehensive database for generating landslide hazard scenario with the help of available historic records of landslides and geo-environmental factors and make them available over the Web using geospatial Free & Open Source Software (FOSS). FOSS reduces the cost of the project drastically as proprietary software's are very costly. Landslide data generated for the period 1982 to 2009 were compiled along the national highway road corridor in Indian Himalayas. All the geo-environmental datasets along with the landslide susceptibility map were served through WEBGIS client interface. Open source University of Minnesota (UMN) mapserver was used as GIS server software for developing web enabled landslide geospatial database. PHP/Mapscript server-side application serve as a front-end application and PostgreSQL with PostGIS extension serve as a backend application for the web enabled landslide spatio-temporal databases. This dynamic virtual visualization process through a web platform brings an insight into the understanding of the landslides and the resulting damage closer to the affected people and user community. The landslide susceptibility dataset is also made available as an Open Geospatial Consortium (OGC) Web Feature Service (WFS) which can be accessed through any OGC compliant open source or proprietary GIS Software.

Das, I.; Oberai, K.; Sarathi Roy, P.

2012-07-01

9

IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 53, NO. 3, MARCH 2006 503 Bayesian Spatio-Temporal Approach for EEG Source  

E-print Network

-Temporal Approach for EEG Source Reconstruction: Conciliating ECD and Distributed Models Jean Daunizeau*, Jérémie--Characterizing the cortical activity sources of elec- troencephalography (EEG)/magnetoencephalography data is a critical issue. In this paper, we show how those two representations of the brain electro- magnetic activity can be cast

Daunizeau, Jean

10

The spatio-temporal mapping of epileptic networks: Combination of EEG–fMRI and EEG source imaging  

PubMed Central

Simultaneous EEG–fMRI acquisitions in patients with epilepsy often reveal distributed patterns of Blood Oxygen Level Dependant (BOLD) change correlated with epileptiform discharges. We investigated if electrical source imaging (ESI) performed on the interictal epileptiform discharges (IED) acquired during fMRI acquisition could be used to study the dynamics of the networks identified by the BOLD effect, thereby avoiding the limitations of combining results from separate recordings. Nine selected patients (13 IED types identified) with focal epilepsy underwent EEG–fMRI. Statistical analysis was performed using SPM5 to create BOLD maps. ESI was performed on the IED recorded during fMRI acquisition using a realistic head model (SMAC) and a distributed linear inverse solution (LAURA). ESI could not be performed in one case. In 10/12 remaining studies, ESI at IED onset (ESIo) was anatomically close to one BOLD cluster. Interestingly, ESIo was closest to the positive BOLD cluster with maximal statistical significance in only 4/12 cases and closest to negative BOLD responses in 4/12 cases. Very small BOLD clusters could also have clinical relevance in some cases. ESI at later time frame (ESIp) showed propagation to remote sources co-localised with other BOLD clusters in half of cases. In concordant cases, the distance between maxima of ESI and the closest EEG–fMRI cluster was less than 33 mm, in agreement with previous studies. We conclude that simultaneous ESI and EEG–fMRI analysis may be able to distinguish areas of BOLD response related to initiation of IED from propagation areas. This combination provides new opportunities for investigating epileptic networks. PMID:19408351

Vulliemoz, S.; Thornton, R.; Rodionov, R.; Carmichael, D.W.; Guye, M.; Lhatoo, S.; McEvoy, A.W.; Spinelli, L.; Michel, C.M.; Duncan, J.S.; Lemieux, L.

2009-01-01

11

Spatio-temporal modulated polarimetry  

NASA Astrophysics Data System (ADS)

Recently, a polarimetric data reduction technique has been developed that in the presence of a time varying signals and noise free measurement process can achieve an error free reconstruction provided that the signal was band limited. Error free reconstruction for such a signal is not possible using conventional data reduction methods. The new approach provides insight for processing arbitrary modulation schemes in space, time, and wavelength. Theory predicts that a polarimeter that employs a spatio-temporal modulation scheme may be able to use the high temporal resolution of a spatially modulated device combined with the high spatial resolution of a temporally modulated system to attain greater combined resolution capabilities than either modulation on scheme can produce alone. A polarimeter that contains both spatial and temporal modulation can be constructed (for example) by placing a rotating retarder in front of a micropolarizer array (microgrid). This study develops theory and analysis for the rotating retarder microgrid polarimeter to show how the available bandwidth for each channel is affected by additional dimensions of modulation and demonstrates a working polarimeter with a simulation of Stokes parameters that are band limited in both space and time with a noisy measurement process.

LaCasse, Charles F.; Ririe, Tyson; Chipman, Russell A.; Tyo, J. Scott

2011-10-01

12

Spatio-temporal hybrid Anderson localization  

NASA Astrophysics Data System (ADS)

We address the localization of spatio-temporal wave packets in disordered waveguide arrays whereby temporal localization is mediated by nonlinearity while strong disorder provides Anderson statistical spatial localization. This combination of two different mechanisms allows localization to occur outside the range of parameters where diffraction, dispersion, and self-action have similar strengths, as required for the formation of standard spatio-temporal solitons. Under suitable conditions, nonlinearity is shown to weakly affect the statistically averaged spatial intensity distributions. In contrast, the temporal duration of the localized wave packets strongly depends on the level of disorder.

Lobanov, V. E.; Borovkova, O. V.; Kartashov, Y. V.; Szameit, A.

2014-12-01

13

Spatio-temporal Feature Recogntion using Randomised Ferns  

E-print Network

Spatio-temporal Feature Recogntion using Randomised Ferns Olusegun Oshin, Andrew Gilbert, John Bayesian classifier of Ferns to the spatio-temporal domain and learn clas- sifiers that duplicate video sequence. We extend a Naive Bayesian classifier called Ferns [1] to the spatio-temporal domain

Paris-Sud XI, Université de

14

Spatial and Spatio-temporal Data Mining  

Microsoft Academic Search

Summary form only given. The recent advances and price reduction of technologies for collecting spatial and spatio-temporal data like Satellite Images, Cellular Phones, Sensor Networks, and GPS devices has facilitated the collection of data referenced in space and time. These huge collections of data often hide interesting information which conventional systems and classical data mining techniques are unable to discover.

Vania Bogorny; Shashi Shekhar

2010-01-01

15

Mining Complex Spatio-Temporal Sequence Patterns  

Microsoft Academic Search

Mining sequential movement patterns describing group behaviour in potentially streaming spatio-temporal data sets is a challenging problem. Movements are typically noisy and often overlap each other. This makes a set of simple patterns difficult to interpret and sequences diffi- cult to mine. Furthermore, group behaviour is complex. Objects in a group may behave similarly for a period of time (an

Florian Verhein

2009-01-01

16

Bayesian spatio-temporal analysis and geospatial risk factors of human monocytic ehrlichiosis.  

PubMed

Variations in spatio-temporal patterns of Human Monocytic Ehrlichiosis (HME) infection in the state of Kansas, USA were examined and the relationship between HME relative risk and various environmental, climatic and socio-economic variables were evaluated. HME data used in the study was reported to the Kansas Department of Health and Environment between years 2005-2012, and geospatial variables representing the physical environment [National Land cover/Land use, NASA Moderate Resolution Imaging Spectroradiometer (MODIS)], climate [NASA MODIS, Prediction of Worldwide Renewable Energy (POWER)], and socio-economic conditions (US Census Bureau) were derived from publicly available sources. Following univariate screening of candidate variables using logistic regressions, two Bayesian hierarchical models were fit; a partial spatio-temporal model with random effects and a spatio-temporal interaction term, and a second model that included additional covariate terms. The best fitting model revealed that spatio-temporal autocorrelation in Kansas increased steadily from 2005-2012, and identified poverty status, relative humidity, and an interactive factor, 'diurnal temperature range x mixed forest area' as significant county-level risk factors for HME. The identification of significant spatio-temporal pattern and new risk factors are important in the context of HME prevention, for future research in the areas of ecology and evolution of HME, and as well as climate change impacts on tick-borne diseases. PMID:24992684

Raghavan, Ram K; Neises, Daniel; Goodin, Douglas G; Andresen, Daniel A; Ganta, Roman R

2014-01-01

17

Bayesian Spatio-Temporal Analysis and Geospatial Risk Factors of Human Monocytic Ehrlichiosis  

PubMed Central

Variations in spatio-temporal patterns of Human Monocytic Ehrlichiosis (HME) infection in the state of Kansas, USA were examined and the relationship between HME relative risk and various environmental, climatic and socio-economic variables were evaluated. HME data used in the study was reported to the Kansas Department of Health and Environment between years 2005–2012, and geospatial variables representing the physical environment [National Land cover/Land use, NASA Moderate Resolution Imaging Spectroradiometer (MODIS)], climate [NASA MODIS, Prediction of Worldwide Renewable Energy (POWER)], and socio-economic conditions (US Census Bureau) were derived from publicly available sources. Following univariate screening of candidate variables using logistic regressions, two Bayesian hierarchical models were fit; a partial spatio-temporal model with random effects and a spatio-temporal interaction term, and a second model that included additional covariate terms. The best fitting model revealed that spatio-temporal autocorrelation in Kansas increased steadily from 2005–2012, and identified poverty status, relative humidity, and an interactive factor, ‘diurnal temperature range x mixed forest area’ as significant county-level risk factors for HME. The identification of significant spatio-temporal pattern and new risk factors are important in the context of HME prevention, for future research in the areas of ecology and evolution of HME, and as well as climate change impacts on tick-borne diseases. PMID:24992684

Raghavan, Ram K.; Neises, Daniel; Goodin, Douglas G.; Andresen, Daniel A.; Ganta, Roman R.

2014-01-01

18

Spatio-temporal organisation of natural prehension  

Microsoft Academic Search

Bootsma, R.J. and P.C.W. van Wieringen, 1992. Spatio-temporal organisation of natural prehen- sion. Human Movement Science 11, 205-215. An information-based model of natural prehension is proposed that can account for a large number of experimental findings without taking recourse to prestructured movement plans. It is suggested that coordination of the transport and grasping components is guaranteed because both components are

Reinoud J. Bootsma; Piet C. W. van Wieringen

1992-01-01

19

Probabilistic Spatio-Temporal Video Object Segmentation Incorporating Shape Information  

Microsoft Academic Search

From a video object segmentation perspective, using a joint spatio-temporal strategy is superior to processing with priority in either the spatial or temporal domains, as it considers a video sequence as a spatio-temporal grouping of pixels. However, existing spatio-temporal object segmentation techniques consider only pixel features, which tend to limit their performance in being able to segment arbitrary shaped objects.

Rakib Ahmed; Gour C. Karmakar; Laurence S. Dooley

2006-01-01

20

Event Detection using Twitter: A Spatio-Temporal Approach  

PubMed Central

Background Every day, around 400 million tweets are sent worldwide, which has become a rich source for detecting, monitoring and analysing news stories and special (disaster) events. Existing research within this field follows key words attributed to an event, monitoring temporal changes in word usage. However, this method requires prior knowledge of the event in order to know which words to follow, and does not guarantee that the words chosen will be the most appropriate to monitor. Methods This paper suggests an alternative methodology for event detection using space-time scan statistics (STSS). This technique looks for clusters within the dataset across both space and time, regardless of tweet content. It is expected that clusters of tweets will emerge during spatio-temporally relevant events, as people will tweet more than expected in order to describe the event and spread information. The special event used as a case study is the 2013 London helicopter crash. Results and Conclusion A spatio-temporally significant cluster is found relating to the London helicopter crash. Although the cluster only remains significant for a relatively short time, it is rich in information, such as important key words and photographs. The method also detects other special events such as football matches, as well as train and flight delays from Twitter data. These findings demonstrate that STSS is an effective approach to analysing Twitter data for event detection. PMID:24893168

Cheng, Tao; Wicks, Thomas

2014-01-01

21

CUTOFF: A spatio-temporal imputation method  

NASA Astrophysics Data System (ADS)

Missing values occur frequently in many different statistical applications and need to be dealt with carefully, especially when the data are collected spatio-temporally. We propose a method called CUTOFF imputation that utilizes the spatio-temporal nature of the data to accurately and efficiently impute missing values. The main feature of this method is that the estimate of a missing value is produced by incorporating similar observed temporal information from the value's nearest spatial neighbors. Extensions to this method are also developed to expand the method's ability to accommodate other data generating processes. We develop a cross-validation procedure that optimally chooses parameters for CUTOFF, which can be used by other imputation methods as well. We analyze some rainfall data from 78 gauging stations in the Murray-Darling Basin in Australia using the CUTOFF imputation method and compare its performance to four well-studied competing imputation methods, namely, k-nearest neighbors, singular value decomposition, multiple imputation and random forest. Empirical results show that our method captures the temporal patterns well and is effective at imputing large gaps in the data. Compared to the competing methods, CUTOFF is more accurate and much faster. We analyze further examples to demonstrate CUTOFF's applications to two different data sets and provide extra evidence of its validity and usefulness. We implement a simulation study based on the Murray-Darling Basin data to evaluate the method; the results show that our method performs well in both accuracy and computational efficiency.

Feng, Lingbing; Nowak, Gen; O'Neill, T. J.; Welsh, A. H.

2014-11-01

22

a Framework for Online Spatio-Temporal Data Visualization Based on HTML5  

NASA Astrophysics Data System (ADS)

Web is entering a new phase - HTML5. New features of HTML5 should be studied for online spatio-temporal data visualization. In the proposed framework, spatio-temporal data is stored in the data server and is sent to user browsers with WebSocket. Public geo-data such as Internet digital map is integrated into the browsers. Then animation is implemented through the canvas object defined by the HTML5 specification. To simulate the spatio-temporal data source, we collected the daily location of 15 users with GPS tracker. The current positions of the users are collected every minute and are recorded in a file. Based on this file, we generate a real time spatio-temporal data source which sends out current user location every second.By enlarging the real time scales by 60 times, we can observe the movement clearly. The data transmitted with WebSocket is the coordinates of users' current positions, which will can be demonstrated in client browsers.

Mao, B.; Wu, Z.; Cao, J.

2012-07-01

23

Plasma Sources Sci. Technol. 9 (2000) 256269. Printed in the UK PII: S0963-0252(00)13664-3 Spatio-temporal evolution of a pulsed  

E-print Network

-temporal evolution of a pulsed chlorine discharge Vikas Midha and Demetre J Economou Plasma Processing LaboratoryPlasma Sources Sci. Technol. 9 (2000) 256­269. Printed in the UK PII: S0963-0252(00)13664-3 Spatio, in final form 22 December 1999 Abstract. A one-dimensional fluid model of a pulsed (square-wave power

Economou, Demetre J.

24

Spatio-temporal variation of stable isotopes of river waters, water source identification and water security in the Heishui Valley (China) during the dry-season  

Microsoft Academic Search

Spatial variations of ?D and ?18O among seven tributaries and their water sources were investigated in the Heishui Valley of the Yangtze River, China during\\u000a the dry-season in 2004. A one-way ANOVA (analysis of variation) test showed that both ?D (p?18O (p?=?0.045) spatially varied among the seven tributaries. The plot of ?18O versus ?D for the river water collected at

Yuhong Liu; Shuqing An; Zhen Xu; Ningjiang Fan; Jun Cui; Zhongsheng Wang; Shirong Liu; Jiayong Pan; Guanghui Lin

2008-01-01

25

Spatio-Temporal Clustering of Monitoring Network  

NASA Astrophysics Data System (ADS)

Pakistan has much diversity in seasonal variation of different locations. Some areas are in desserts and remain very hot and waterless, for example coastal areas are situated along the Arabian Sea and have very warm season and a little rainfall. Some areas are covered with mountains, have very low temperature and heavy rainfall; for instance Karakoram ranges. The most important variables that have an impact on the climate are temperature, precipitation, humidity, wind speed and elevation. Furthermore, it is hard to find homogeneous regions in Pakistan with respect to climate variation. Identification of homogeneous regions in Pakistan can be useful in many aspects. It can be helpful for prediction of the climate in the sub-regions and for optimizing the number of monitoring sites. In the earlier literature no one tried to identify homogeneous regions of Pakistan with respect to climate variation. There are only a few papers about spatio-temporal clustering of monitoring network. Steinhaus (1956) presented the well-known K-means clustering method. It can identify a predefined number of clusters by iteratively assigning centriods to clusters based. Castro et al. (1997) developed a genetic heuristic algorithm to solve medoids based clustering. Their method is based on genetic recombination upon random assorting recombination. The suggested method is appropriate for clustering the attributes which have genetic characteristics. Sap and Awan (2005) presented a robust weighted kernel K-means algorithm incorporating spatial constraints for clustering climate data. The proposed algorithm can effectively handle noise, outliers and auto-correlation in the spatial data, for effective and efficient data analysis by exploring patterns and structures in the data. Soltani and Modarres (2006) used hierarchical and divisive cluster analysis to categorize patterns of rainfall in Iran. They only considered rainfall at twenty-eight monitoring sites and concluded that eight clusters existed. Soltani and Modarres (2006) classified the sites by using only average rainfall of sites, they did not consider time replications and spatial coordinates. Kerby et.al (2007) purposed spatial clustering method based on likelihood. They took account of the geographic locations through the variance covariance matrix. Their purposed method works like hierarchical clustering methods. Moreovere, it is inappropiriate for time replication data and could not perform well for large number of sites. Tuia.et.al (2008) used scan statistics for identifying spatio-temporal clusters for fire sequences in the Tuscany region in Italy. The scan statistics clustering method was developed by Kulldorff et al. (1997) to detect spatio-temporal clusters in epidemiology and assessing their significance. The purposed scan statistics method is used only for univariate discrete stochastic random variables. In this paper we make use of a very simple approach for spatio-temporal clustering which can create separable and homogeneous clusters. Most of the clustering methods are based on Euclidean distances. It is well known that geographic coordinates are spherical coordinates and estimating Euclidean distances from spherical coordinates is inappropriate. As a transformation from geographic coordinates to rectangular (D-plane) coordinates we use the Lambert projection method. The partition around medoids clustering method is incorporated on the data including D-plane coordinates. Ordinary kriging is taken as validity measure for the precipitation data. The kriging results for clusters are more accurate and have less variation compared to complete monitoring network precipitation data. References Casto.V.E and Murray.A.T (1997). Spatial Clustering with Data Mining with Genetic Algorithms. http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.56.8573 Kaufman.L and Rousseeuw.P.J (1990). Finding Groups in Data: An Introduction to Cluster Analysis. Wiley series of Probability and Mathematical Statistics, New York. Kulldorf.M (1997). A spatial scan statistic. Commun. Stat.-Theor. Math. 26(6)

Hussain, I.; Pilz, J.

2009-04-01

26

Research on spatio-temporal ontology based on description logic  

NASA Astrophysics Data System (ADS)

DL, short for Description Logic, is aimed at getting a balance between describing ability and reasoning complexity. Users can adopt DL to write clear and formalized concept description for domain model, which makes ontology description possess well-defined syntax and semantics and helps to resolve the problem of spatio-temporal reasoning based on ontology. This paper studies on basic theory of DL and relationship between DL and OWL at first. By analyzing spatio-temporal concepts and relationship of spatio-temporal GIS, the purpose of this paper is adopting ontology language based on DL to express spatio-temporal ontology, and employing suitable ontology-building tool to build spatio-temporal ontology. With regard to existing spatio-temporal ontology based on first-order predicate logic, we need to transform it into spatio-temporal ontology based on DL so as to make the best of existing research fruits. This paper also makes a research on translating relationships between DL and first-order predicate logic.

Huang, Yongqi; Ding, Zhimin; Zhao, Zhui; Ouyang, Fucheng

2008-10-01

27

Spatio-temporal activity of lightnings over Greece  

NASA Astrophysics Data System (ADS)

Extreme precipitation events are always associated with convective weather conditions driving to intense lightning activity: Cloud to Ground (CG), Ground to Cloud (GC) and Cloud to Cloud (CC). Thus, the study of lightnings, which typically occur during thunderstorms, gives evidence of the spatio-temporal variability of intense precipitation. Lightning is a natural phenomenon in the atmosphere, being a major cause of storm related with deaths and main trigger of forest fires during dry season. Lightning affects the many electrochemical systems of the body causing nerve damage, memory loss, personality change, and emotional problems. Besides, among the various nitrogen oxides sources, the contribution from lightning likely represents the largest uncertainty. An operational lightning detection network (LDN) has been established since 2007 by HNMS, consisting of eight time-of-arrival sensors (TOA), spatially distributed across Greek territory. In this study, the spatial and temporal variability of recorded lightnings (CG, GC and CC) are analyzed over Greece, during the period from January 14, 2008 to December 31, 2009, for the first time. The data for retrieving the location and time-of-occurrence of lightning were acquired from Hellenic National Meteorological Service (HNMS). In addition to the analysis of spatio-temporal activity over Greece, the HNMS-LDN characteristics are also presented. The results of the performed analysis reveal the specific geographical sub-regions associated with lightnings incidence. Lightning activity occurs mainly during the autumn season, followed by summer and spring. Higher frequencies of flashes appear over Ionian and Aegean Sea than over land during winter period against continental mountainous regions during summer period.

Nastos, P. T.; Matsangouras, I. T.; Chronis, T. G.

2012-04-01

28

Spatio-temporal variation of stable isotopes of river waters, water source identification and water security in the Heishui Valley (China) during the dry-season  

NASA Astrophysics Data System (ADS)

Spatial variations of ?D and ?18O among seven tributaries and their water sources were investigated in the Heishui Valley of the Yangtze River, China during the dry-season in 2004. A one-way ANOVA (analysis of variation) test showed that both ?D ( p < 0.01) and ?18O ( p = 0.045) spatially varied among the seven tributaries. The plot of ?18O versus ?D for the river water collected at different locations showed that isotopic fractionation occurred during the snow and glacial melting process. The depleted ?18O and ?D in the tributary waters distributed above the local meteoric water line (LMWL) suggested that the glacial and early snowpack meltwater largely recharged these streams during the early spring. The meltwater was isotopically distinguishable from the precipitation and river water, which had been evaporated during warmer and drier times. If glaciers and snow accumulation diminish with future climate warming, the recharge of these tributaries’ baseflow will decline and the security of the water resource in this watershed will be threatened.

Liu, Yuhong; An, Shuqing; Xu, Zhen; Fan, Ningjiang; Cui, Jun; Wang, Zhongsheng; Liu, Shirong; Pan, Jiayong; Lin, Guanghui

2008-03-01

29

Spatio-temporal distribution of phytoplankton in the Danjiangkou Reservoir, a water source area for the Southto-North Water Diversion Project (Middle Route), China  

NASA Astrophysics Data System (ADS)

One of the water source areas of the South-to-North Water Diversion Project is the Danjiangkou Reservoir (DJKR). To understand seasonal variation in phytoplankton composition, abundance and distribution in the DJKR area before water diversion, as well as to estimate potential risks of water quality after water diversion, we conducted an investigation on phytoplankton in the DJKR from August 2008 to May 2009. The investigation included 10 sampling sites, each with four depths of 0.5, 5, 10, and 20 m. In this study, 117 taxa belonging to 76 genera were identified, consisting of diatoms (39 taxa), green algae (47 taxa), blue-green algae (19 taxa), and others (12 taxa). Annual average phytoplankton abundance was 2.01 × 106 ind./L, and the highest value was 14.72 × 106 ind/L (at site 3 in August 2008). Phytoplankton abundance in front of the Danjiangkou Dam (DJKD) was higher than that of the Danjiang Reservoir Basin. Phytoplankton distribution showed a vertical declining trend from 0.5 m to 20 m at most sites in August 2008 (especially at sites of 1, 2, 4 and 10), but no distinct pattern in other sampling months. In December 2008 and March 2009, Stephanodiscus sp. was the most abundant species, amounting to 55.23% and 72.34%, respectively. We propose that high abundance of Stephanodiscus sp. may have contributed greatly to the frequent occurrence of Stephanodiscus sp. blooms in middle-low reaches of the Hanjiang River during the early spring of 2009. In comparison with previous studies conducted from 1992 to 2006, annual average phytoplankton density, green algae and blue-green algae species, as well as major nutrient concentrations increased, while phytoplankton diversity indices declined. This indicates a gradual decline in water quality. More research should be conducted and countermeasures taken to prevent further deterioration of water quality in the DJKR.

Yin, Dacong; Zheng, Lingling; Song, Lirong

2011-05-01

30

A LANGUAGE FOR MODULAR SPATIO-TEMPORAL SIMULATION (R824766)  

EPA Science Inventory

Creating an effective environment for collaborative spatio-temporal model development will require computational systems that provide support for the user in three key areas: (1) Support for modular, hierarchical model construction and archiving/linking of simulation modules; (2)...

31

SVM spatio-temporal vegetation classification using HR satellite images  

Microsoft Academic Search

This paper proposes a new HR spatio-temporal vegetation classification approach based on SVM. A multi-band SVM approach is first applied on satellite images time series then a graph based SVM algorithm is used for temporal analysis.

S. Réjichi; F. Chaâbane

2011-01-01

32

SVM spatio-temporal vegetation classification using HR satellite images  

NASA Astrophysics Data System (ADS)

This paper proposes a new HR spatio-temporal vegetation classification approach based on SVM. A multi-band SVM approach is first applied on satellite images time series then a graph based SVM algorithm is used for temporal analysis.

Réjichi, S.; Chaâbane, F.

2011-11-01

33

The Change-of-Feature Spatio-temporal Object Relational Model and Its implement  

Microsoft Academic Search

Now more and more application demand to spatio-temporal database is proposed and the spatio-temporal data model is the fundamental basic to spatial-temporal database. But till today the study on spatio-temporal data model still more concerned with the theory research. The article proposes a new model-the change-of-feature based spatio-temporal object relational data model by researching and analyzing the current spatio-temporal data

Xiaochun Wu; Yongqi Huang; Liyan Wang; Fengyun Mou

2009-01-01

34

Spatio-temporal patterns of schistosomiasis japonica in lake and marshland areas in China: the effect of snail habitats.  

PubMed

The progress of the integrated control policy for schistosomiasis implemented since 2005 in China, which is aiming at reducing the roles of bovines and humans as infection sources, may be challenged by persistent presence of infected snails in lake and marshland areas. Based on annual parasitologic data for schistosomiasis during 2004-2011 in Xingzi County, a spatio-temporal kriging model was used to investigate the spatio-temporal pattern of schistosomiasis risk. Results showed that environmental factors related to snail habitats can explain the spatio-temporal variation of schistosomiasis. Predictive maps of schistosomiasis risk illustrated that clusters of the disease fluctuated during 2004-2008; there was an extensive outbreak in 2008 and attenuated disease occurrences afterwards. An area with an annually constant cluster of schistosomiasis was identified. Our study suggests that targeting snail habitats located within high-risk areas for schistosomiasis would be an economic and sustainable way of schistosomiasis control in the future. PMID:24980498

Hu, Yi; Gao, Jie; Chi, Meina; Luo, Can; Lynn, Henry; Sun, Liqian; Tao, Bo; Wang, Decheng; Zhang, Zhijie; Jiang, Qingwu

2014-09-01

35

Looking at catchments in colors: combining thermal IR imagery with geochemical and isotopic tracers to document spatio-temporal dynamics of water source and flowpaths in the hillslope-riparian zone-stream system  

NASA Astrophysics Data System (ADS)

At present, our conceptual understanding of catchment-scale water mixing, source apportionment and hydrological connectivity is thwarted by measurement limitations. For instance, the measurement and documentation of HRS connectivity is a major impediment to better process understanding. In recent literature, there have been repeatedly calls for interdisciplinary approaches to expand the frontier of hydrological theory and eventually overcome the well-known limitations that are inherent to conventional techniques used for tracing water source, flowpaths and residence times. The 2010 edition of the EGU Leonardo Topical Conference Series on the hydrological cycle had concluded that a major challenge for hydrology in the near future will be to apply more often multidisciplinary approaches, so to find creative solutions that will eventually allow us to move away from 'monochrome pictures of reality', and 'see the catchments in colors'. Here, we demonstrate the potential for thermal infrared imagery to both determine adequate water sampling sites and validate the identification of water source and connectivity through conventional tracers. Until recently, the use of heat as a ground water tracer had been largely restricted to the hydrogeological literature. Thermal remote sensing of riparian and water surface temperatures has been of interest in aquatic management issues, as well as for the assessment of spatial heterogeneities. Our proof-of-concept study in the Weierbach experimental watershed further extended the potential for infrared thermography via hand-held cameras to hydrological processes studies across various hydrological response units (HRU). Infrared thermography of surface water dynamics stemming either from infiltration excess overland flow or saturation excess overland flow was mapped throughout a complete rainfall-runoff event. In order to grasp the spatial and temporal variability of geochemical and isotopic signatures, during and after a storm event, we have combined thermal IR imagery with grab sampling of water inside the hillslope-riparian zone-stream system. While relying on IR thermography, we also used simultaneous optical image capture to aid in classifying the incoming IR signal and differentiating between substances of different temperature. The distinction between flowing water, saturated zones, soil, wooden branches, pebbles or leaves is extremely difficult when observing the optical image alone. The IR thermography interprets the heat signal from the same source and provides a much better view for identifying both areas where water is flowing and areas where water is either seeping from the soil, flowing as surface runoff or accumulating temporarily in micro-depressions during a rainfall event. This approach has revealed how crucial the location of the grab sampling can be within extremely small geographical zones (a few square meters) due to incomplete mixing, as well as it has helped to map the dynamics of geochemical and isotopic signatures in the area of interest. To date, our investigations have revealed: (a) the potential for infrared thermography to identify, discriminate and observe the spatio-temporal dynamics of hydrological processes, namely infiltration excess overland flow, saturation excess overland flow and subsurface return flow; and (b) the complementarity of information gained from conventional tracers (geochemicals and stable isotopes) and remote sensing (infrared thermography). Our next step will consist in assessing the individual and combined potential of these techniques for reducing uncertainties in hydrological process identification and quantification (especially with respect to hydrograph separation).

Pfister, L.; Martínez-Carreras, N.; Wetzel, C.; Ector, L.; Hissler, C.; Hoffmann, L.; Frentress, J. J.; McDonnell, J. J.

2012-04-01

36

A Distributed Spatio-Temporal EEG/MEG Inverse Solver  

PubMed Central

We propose a novel ?1?2-norm inverse solver for estimating the sources of EEG/MEG signals. Developed based on the standard ?1-norm inverse solvers, this sparse distributed inverse solver integrates the ?1-norm spatial model with a temporal model of the source signals in order to avoid unstable activation patterns and “spiky” reconstructed signals often produced by the currently used sparse solvers. The joint spatio-temporal model leads to a cost function with an ?1?2-norm regularizer whose minimization can be reduced to a convex second-order cone programming (SOCP) problem and efficiently solved using the interior-point method. The efficient computation of the SOCP problem allows us to implement permutation tests for estimating statistical significance of the inverse solution. Validation with simulated and real MEG data shows that the proposed solver yields source time course estimates qualitatively similar to those obtained through dipole fitting, but without the need to specify the number of dipole sources in advance. Furthermore, the ?1?2-norm solver achieves fewer false positives and a better representation of the source locations than the conventional ?2 minimum-norm estimates. PMID:18603008

Hämäläinen, Matti S.; Golland, Polina

2009-01-01

37

A distributed spatio-temporal EEG/MEG inverse solver  

PubMed Central

We propose a novel ?1?2-norm inverse solver for estimating the sources of EEG/MEG signals. Based on the standard ?1-norm inverse solvers, this sparse distributed inverse solver integrates the ?1-norm spatial model with a temporal model of the source signals in order to avoid unstable activation patterns and “spiky” reconstructed signals often produced by the currently used sparse solvers. The joint spatio-temporal model leads to a cost function with an ?1?2-norm regularizer whose minimization can be reduced to a convex second-order cone programming (SOCP) problem and efficiently solved using the interior-point method. The efficient computation of the SOCP problem allows us to implement permutation tests for estimating statistical significance of the inverse solution. Validation with simulated and human MEG data shows that the proposed solver yields source time course estimates qualitatively similar to those obtained through dipole fitting, but without the need to specify the number of dipole sources in advance. Furthermore, the ?1?2-norm solver achieves fewer false positives and a better representation of the source locations than the conventional ?2 minimum-norm estimates. PMID:18979728

Ou, Wanmei; Hämäläinen, Matti S.; Golland, Polina

2009-01-01

38

Spatio-Temporal Analysis of Epidemic Phenomena Using the R Package surveillance  

E-print Network

The availability of geocoded health data and the inherent temporal structure of communicable diseases have led to an increased interest in statistical models and software for spatio-temporal data with epidemic features. The open source R package surveillance can handle various levels of aggregation at which infective events have been recorded: individual-level time-stamped geo-referenced data (case reports) in either continuous space or discrete space, as well as counts aggregated by period and region. For each of these data types, the surveillance package implements tools for visualization, likelihoood inference and simulation from recently developed statistical regression frameworks capturing endemic and epidemic dynamics. Altogether, this paper is a guide to the spatio-temporal modeling of epidemic phenomena, exemplified by analyses of public health surveillance data on measles and invasive meningococcal disease.

Meyer, Sebastian; Höhle, Michael

2014-01-01

39

Spatio-temporal controls on diurnal streamflow fluctuations  

NASA Astrophysics Data System (ADS)

Diurnal fluctuations in stream flow are widely observed across the world, yet the spatio-temporal sources of these fluctuations are poorly understood and conceptualized. Evapotranspiration (ET) is often assumed to be the main driver of diurnal fluctuations during the growing season. We compared eddy covariance derived evapotranspiration dynamics to groundwater and stream flow diurnal fluctuations across 5 growing seasons in the Tenderfoot Creek Experimental Forest, MT. We analyzed the timing of peak daily ET to the minima of hillslope, riparian and stream diurnal water levels (diurnal time differences; DTDs). DTDs were consistently between 5 and 8 hours during the growing season and there was a subsequent decoupling with more variability (up to 24 hours) during non-growing season periods. In order to better understand the mechanisms and transfer of ET signals that lead to diurnal fluctuations in stream flow, we analyzed the DTDs of shallow groundwater wells across different landscape positions (with varying degrees of saturation and hydrologic connectivity). The riparian zone DTDs were similar to those observed for streamflow. However, across hillslope well landscape positions, the DTDs were progressively different from the streamflow and riparian DTDs as a function of hydrologic connectivity to the stream network. Our analyses suggest that stream diurnal signatures result from landscape propagation of ET signals from hydrologically connected landscape positions that vary through time.

Broer, M.; Jencso, K. G.; McGlynn, B. L.; Mallard, J. M.; Carlson, S.; Bloeschl, G.

2012-12-01

40

Time reversal and the spatio-temporal matched filter  

SciTech Connect

It is known that focusing of an acoustic field by a time-reversal mirror (TRM) is equivalent to a spatio-temporal matched filter under conditions where the Green's function of the field satisfies reciprocity and is time invariant, i.e. the Green's function is independent of the choice of time origin. In this letter, it is shown that both reciprocity and time invariance can be replaced by a more general constraint on the Green's function that allows a TRM to implement the spatio-temporal matched filter even when conditions are time varying.

Lehman, S K; Poggio, A J; Kallman, J S; Meyer, A W; Candy, J V

2004-03-08

41

Transient dynamics and rhythm coordination of inferior olive spatio-temporal patterns  

PubMed Central

The inferior olive (IO) is a neural network belonging to the olivo-cerebellar system whose neurons are coupled with electrical synapses and display subthreshold oscillations and spiking activity. The IO is frequently proposed as the generator of timing signals to the cerebellum. Electrophysiological and imaging recordings show that the IO network generates complex spatio-temporal patterns. The generation and modulation of coherent spiking activity in the IO is one key issue in cerebellar research. In this work, we build a large scale IO network model of electrically coupled conductance-based neurons to study the emerging spatio-temporal patterns of its transient neuronal activity. Our modeling reproduces and helps to understand important phenomena observed in IO in vitro and in vivo experiments, and draws new predictions regarding the computational properties of this network and the associated cerebellar circuits. The main factors studied governing the collective dynamics of the IO network were: the degree of electrical coupling, the extent of the electrotonic connections, the presence of stimuli or regions with different excitability levels and the modulatory effect of an inhibitory loop (IL). The spatio-temporal patterns were analyzed using a discrete wavelet transform to provide a quantitative characterization. Our results show that the electrotonic coupling produces quasi-synchronized subthreshold oscillations over a wide dynamical range. The synchronized oscillatory activity plays the role of a timer for a coordinated representation of spiking rhythms with different frequencies. The encoding and coexistence of several coordinated rhythms is related to the different clusterization and coherence of transient spatio-temporal patterns in the network, where the spiking activity is commensurate with the quasi-synchronized subthreshold oscillations. In the presence of stimuli, different rhythms are encoded in the spiking activity of the IO neurons that nevertheless remains constrained to a commensurate value of the subthreshold frequency. The stimuli induced spatio-temporal patterns can reverberate for long periods, which contributes to the computational properties of the IO. We also show that the presence of regions with different excitability levels creates sinks and sources of coordinated activity which shape the propagation of spike wave fronts. These results can be generalized beyond IO studies, as the control of wave pattern propagation is a highly relevant problem in the context of normal and pathological states in neural systems (e.g., related to tremor, migraine, epilepsy) where the study of the modulation of activity sinks and sources can have a potential large impact. PMID:24046731

Latorre, Roberto; Aguirre, Carlos; Rabinovich, Mikhail I.; Varona, Pablo

2013-01-01

42

Fast Spatio-Temporal Data Mining from Large Geophysical Datasets  

NASA Technical Reports Server (NTRS)

Use of the UCLA CONQUEST (CONtent-based Querying in Space and Time) is reviewed for performance of automatic cyclone extraction and detection of spatio-temporal blocking conditions on MPP. CONQUEST is a data analysis environment for knowledge and data mining to aid in high-resolution modeling of climate modeling.

Stolorz, P.; Mesrobian, E.; Muntz, R.; Santos, J. R.; Shek, E.; Yi, J.; Mechoso, C.; Farrara, J.

1995-01-01

43

Visual Experience Modulates Spatio-Temporal Dynamics of Circuit Activation  

PubMed Central

Persistent reduction in sensory drive in early development results in multiple plastic changes of different cortical synapses. How these experience-dependent modifications affect the spatio-temporal dynamics of signal propagation in neocortical circuits is poorly understood. Here we demonstrate that brief visual deprivation significantly affects the propagation of electrical signals in the primary visual cortex. The spatio-temporal spread of circuit activation upon direct stimulation of its input layer (Layer 4) is reduced, as is the activation of L2/3 – the main recipient of the output from L4. Our data suggest that the decrease in spatio-temporal activation of L2/3 depends on reduced L4 output, and is not intrinsically generated within L2/3. The data shown here suggest that changes in the synaptic components of the visual cortical circuit result not only in alteration of local integration of excitatory and inhibitory inputs, but also in a significant decrease in overall circuit activation. Furthermore, our data indicate a differential effect of visual deprivation on L4 and L2/3, suggesting that while feedforward activation of L2/3 is reduced, its activation by long range, within layer inputs is unaltered. Thus, brief visual deprivation induces experience-dependent circuit re-organization by modulating not only circuit excitability, but also the spatio-temporal patterns of cortical activation within and between layers. PMID:21743804

Wang, Lang; Fontanini, Alfredo; Maffei, Arianna

2011-01-01

44

Spatio-temporal Spike Pattern Classification in Neuromorphic Systems  

E-print Network

architectures offer an attractive solution for implementing compact efficient sensory-motor neural processing, classify the spatio-temporal information contained in the data, and pro- duce appropriate motor outputs and asynchronous streams of spikes, and spiking multi-neuron chips [5, 6, 7] for implementing state dependent

45

Kernel Averaged Predictors for Spatio-Temporal Regression Models  

PubMed Central

In applications where covariates and responses are observed across space and time, a common goal is to quantify the effect of a change in the covariates on the response while adequately accounting for the spatio-temporal structure of the observations. The most common approach for building such a model is to confine the relationship between a covariate and response variable to a single spatio-temporal location. However, oftentimes the relationship between the response and predictors may extend across space and time. In other words, the response may be affected by levels of predictors in spatio-temporal proximity to the response location. Here, a flexible modeling framework is proposed to capture such spatial and temporal lagged effects between a predictor and a response. Specifically, kernel functions are used to weight a spatio-temporal covariate surface in a regression model for the response. The kernels are assumed to be parametric and non-stationary with the data informing the parameter values of the kernel. The methodology is illustrated on simulated data as well as a physical data set of ozone concentrations to be explained by temperature. PMID:24010051

Gelfand, Alan E.

2013-01-01

46

Finding Spatio-Temporal Patterns in Large Sensor Datasets  

ERIC Educational Resources Information Center

Spatial or temporal data mining tasks are performed in the context of the relevant space, defined by a spatial neighborhood, and the relevant time period, defined by a specific time interval. Furthermore, when mining large spatio-temporal datasets, interesting patterns typically emerge where the dataset is most dynamic. This dissertation is…

McGuire, Michael Patrick

2010-01-01

47

Cubic map algebra functions for spatio-temporal analysis  

USGS Publications Warehouse

We propose an extension of map algebra to three dimensions for spatio-temporal data handling. This approach yields a new class of map algebra functions that we call "cube functions." Whereas conventional map algebra functions operate on data layers representing two-dimensional space, cube functions operate on data cubes representing two-dimensional space over a third-dimensional period of time. We describe the prototype implementation of a spatio-temporal data structure and selected cube function versions of conventional local, focal, and zonal map algebra functions. The utility of cube functions is demonstrated through a case study analyzing the spatio-temporal variability of remotely sensed, southeastern U.S. vegetation character over various land covers and during different El Nin??o/Southern Oscillation (ENSO) phases. Like conventional map algebra, the application of cube functions may demand significant data preprocessing when integrating diverse data sets, and are subject to limitations related to data storage and algorithm performance. Solutions to these issues include extending data compression and computing strategies for calculations on very large data volumes to spatio-temporal data handling.

Mennis, J.; Viger, R.; Tomlin, C.D.

2005-01-01

48

Spatio-temporal Information Ranking in VANET Applications  

E-print Network

Spatio-temporal Information Ranking in VANET Applications PIOTR SZCZUREK, BO XU, JIE LIN, AND OURI WOLFSON University of Illinois at Chicago Vehicular ad-hoc networks (VANETs) is a promising approach ranking in VANETs. In this method, mobile nodes such as vehicles judge the relevance of incoming

Wolfson, Ouri E.

49

A Probabilistic Framework for Spatio-Temporal Video Representation & Indexing  

E-print Network

. A key feature of the system is the analysis of video input as a single entity as opposed to a sequenceA Probabilistic Framework for Spatio-Temporal Video Representation & Indexing Hayit Greenspan1, Israel 2 CUTe Ltd., Tel-Aviv, Israel Abstract. In this work we describe a novel statistical video

Goldberger, Jacob

50

Spatio-Temporal Saliency Perception via Hypercomplex Frequency Spectral Contrast  

PubMed Central

Salient object perception is the process of sensing the salient information from the spatio-temporal visual scenes, which is a rapid pre-attention mechanism for the target location in a visual smart sensor. In recent decades, many successful models of visual saliency perception have been proposed to simulate the pre-attention behavior. Since most of the methods usually need some ad hoc parameters or high-cost preprocessing, they are difficult to rapidly detect salient object or be implemented by computing parallelism in a smart sensor. In this paper, we propose a novel spatio-temporal saliency perception method based on spatio-temporal hypercomplex spectral contrast (HSC). Firstly, the proposed HSC algorithm represent the features in the HSV (hue, saturation and value) color space and features of motion by a hypercomplex number. Secondly, the spatio-temporal salient objects are efficiently detected by hypercomplex Fourier spectral contrast in parallel. Finally, our saliency perception model also incorporates with the non-uniform sampling, which is a common phenomenon of human vision that directs visual attention to the logarithmic center of the image/video in natural scenes. The experimental results on the public saliency perception datasets demonstrate the effectiveness of the proposed approach compared to eleven state-of-the-art approaches. In addition, we extend the proposed model to moving object extraction in dynamic scenes, and the proposed algorithm is superior to the traditional algorithms. PMID:23482090

Li, Ce; Xue, Jianru; Zheng, Nanning; Lan, Xuguang; Tian, Zhiqiang

2013-01-01

51

Efficient Probabilistic Spatio-Temporal Video Object Segmentation  

Microsoft Academic Search

One of the major objectives in multimedia technology is to be able to segment objects automatically from a video sequence, for a diverse range of applications from video surveillance and object tracking through to content-based video retrieval, coding and medical imaging. Probabilistic spatio-temporal (PST) video object segmentation has been shown to be of pivotal importance in achieving better segmentation, because

Rakib Ahmed; Gour C. Karmakar; Laurence S. Dooley

2007-01-01

52

Spatial clustering in the spatio-temporal dynamics of endemic cholera  

PubMed Central

Background The spatio-temporal patterns of infectious diseases that are environmentally driven reflect the combined effects of transmission dynamics and environmental heterogeneity. They contain important information on different routes of transmission, including the role of environmental reservoirs. Consideration of the spatial component in infectious disease dynamics has led to insights on the propagation of fronts at the level of counties in rabies in the US, and the metapopulation behavior at the level of cities in childhood diseases such as measles in the UK, both at relatively coarse scales. As epidemiological data on individual infections become available, spatio-temporal patterns can be examined at higher resolutions. Methods The extensive spatio-temporal data set for cholera in Matlab, Bangladesh, maps the individual location of cases from 1983 to 2003. This unique record allows us to examine the spatial structure of cholera outbreaks, to address the role of primary transmission, occurring from an aquatic reservoir to the human host, and that of secondary transmission, involving a feedback between current and past levels of infection. We use Ripley's K and L indices and bootstrapping methods to evaluate the occurrence of spatial clustering in the cases during outbreaks using different temporal windows. The spatial location of cases was also confronted against the spatial location of water sources. Results Spatial clustering of cholera cases was detected at different temporal and spatial scales. Cases relative to water sources also exhibit spatial clustering. Conclusions The clustering of cases supports an important role of secondary transmission in the dynamics of cholera epidemics in Matlab, Bangladesh. The spatial clustering of cases relative to water sources, and its timing, suggests an effective role of water reservoirs during the onset of cholera outbreaks. Once primary transmission has initiated an outbreak, secondary transmission takes over and plays a fundamental role in shaping the epidemics in this endemic area. PMID:20205935

2010-01-01

53

A Hierarchical Bayesian Approach for Learning Sparse Spatio-Temporal Decomposition of Multichannel EEG  

PubMed Central

Multichannel electroencephalography (EEG) offers a non-invasive tool to explore spatio-temporal dynamics of brain activity. With EEG recordings consisting of multiple trials, traditional signal processing approaches that ignore inter-trial variability in the data may fail to accurately estimate the underlying spatio-temporal brain patterns. Moreover, precise characterization of such inter-trial variability per se can be of high scientific value in establishing the relationship between brain activity and behavior. In this paper, a statistical modeling framework is introduced for learning spatiotemporal decomposition of multiple-trial EEG data recorded under two contrasting experimental conditions. By modeling the variance of source signals as random variables varying across trials, the proposed two-stage hierarchical Bayesian model is able to capture inter-trial amplitude variability in the data in a sparse way where a parsimonious representation of the data can be obtained. A variational Bayesian (VB) algorithm is developed for statistical inference of the hierarchical model. The efficacy of the proposed modeling framework is validated with the analysis of both synthetic and real EEG data. In the simulation study we show that even at low signal-to-noise ratios our approach is able to recover with high precision the underlying spatiotemporal patterns and the evolution of source amplitude across trials; on two brain-computer interface (BCI) data sets we show that our VB algorithm can extract physiologically meaningful spatio-temporal patterns and make more accurate predictions than other two widely used algorithms: the common spatial patterns (CSP) algorithm and the Infomax algorithm for independent component analysis (ICA). The results demonstrate that our statistical modeling framework can serve as a powerful tool for extracting brain patterns, characterizing trial-to-trial brain dynamics, and decoding brain states by exploiting useful structures in the data. PMID:21420499

Wu, Wei; Chen, Zhe; Gao, Shangkai; Brown, Emery N.

2011-01-01

54

An autoregressive approach to spatio-temporal disease mapping.  

PubMed

Disease mapping has been a very active research field during recent years. Nevertheless, time trends in risks have been ignored in most of these studies, yet they can provide information with a very high epidemiological value. Lately, several spatio-temporal models have been proposed, either based on a parametric description of time trends, on independent risk estimates for every period, or on the definition of the joint covariance matrix for all the periods as a Kronecker product of matrices. The following paper offers an autoregressive approach to spatio-temporal disease mapping by fusing ideas from autoregressive time series in order to link information in time and by spatial modelling to link information in space. Our proposal can be easily implemented in Bayesian simulation software packages, for example WinBUGS. As a result, risk estimates are obtained for every region related to those in their neighbours and to those in the same region in adjacent periods. PMID:17979141

Martínez-Beneito, M A; López-Quilez, A; Botella-Rocamora, P

2008-07-10

55

Finding Spatio-Temporal Patterns in Earth Science Data  

Microsoft Academic Search

This paper presents preliminary work in using data mining techniques to find interesting spatio-temporal patterns from Earth Science data. The data consists of time series measurements for various Earth science and climate variables (e.g. soil moisture, temperature, and precipitation), along with additional data from existing ecosystem models (e.g. Net Primary Production). The ecological patterns of interest include associations, clusters, predictive

Pang-Ning Tan; Michael Steinbach; Vipin Kumar; Christopher Potter; Steven Klooster; Alicia Torregrosa

2001-01-01

56

Spatio-temporal patterns in simple models of marine systems  

NASA Astrophysics Data System (ADS)

Spatio-temporal patterns in marine systems are a result of the interaction of population dynamics with physical transport processes. These physical transport processes can be either diffusion processes in marine sediments or in the water column. We study the dynamics of one population of bacteria and its nutrient in in a simplified model of a marine sediments, taking into account that the considered bacteria possess an active as well as an inactive state, where activation is processed by signal molecules. Furthermore the nutrients are transported actively by bioirrigation and passively by diffusion. It is shown that under certain conditions Turing patterns can occur which yield heterogeneous spatial patterns of the species. The influence of bioirrigation on Turing patterns leads to the emergence of ''hot spots``, i.e. localized regions of enhanced bacterial activity. All obtained patterns fit quite well to observed patterns in laboratory experiments. Spatio-temporal patterns appear in a predator-prey model, used to describe plankton dynamics. These patterns appear due to the simultaneous emergence of Turing patterns and oscillations in the species abundance in the neighborhood of a Turing-Hopf bifurcation. We observe a large variety of different patterns where i) stationary heterogeneous patterns (e.g. hot and cold spots) compete with spatio-temporal patterns ii) slowly moving patterns are embedded in an oscillatory background iii) moving fronts and spiral waves appear.

Feudel, U.; Baurmann, M.; Gross, T.

2009-04-01

57

A Spatio-Temporal Downscaler for Output From Numerical Models  

PubMed Central

Often, in environmental data collection, data arise from two sources: numerical models and monitoring networks. The first source provides predictions at the level of grid cells, while the second source gives measurements at points. The first is characterized by full spatial coverage of the region of interest, high temporal resolution, no missing data but consequential calibration concerns. The second tends to be sparsely collected in space with coarser temporal resolution, often with missing data but, where recorded, provides, essentially, the true value. Accommodating the spatial misalignment between the two types of data is of fundamental importance for both improved predictions of exposure as well as for evaluation and calibration of the numerical model. In this article we propose a simple, fully model-based strategy to downscale the output from numerical models to point level. The static spatial model, specified within a Bayesian framework, regresses the observed data on the numerical model output using spatially-varying coefficients which are specified through a correlated spatial Gaussian process. As an example, we apply our method to ozone concentration data for the eastern U.S. and compare it to Bayesian melding (Fuentes and Raftery 2005) and ordinary kriging (Cressie 1993; Chilès and Delfiner 1999). Our results show that our method outperforms Bayesian melding in terms of computing speed and it is superior to both Bayesian melding and ordinary kriging in terms of predictive performance; predictions obtained with our method are better calibrated and predictive intervals have empirical coverage closer to the nominal values. Moreover, our model can be easily extended to accommodate for the temporal dimension. In this regard, we consider several spatio-temporal versions of the static model. We compare them using out-of-sample predictions of ozone concentration for the eastern U.S. for the period May 1–October 15, 2001. For the best choice, we present a summary of the analysis. Supplemental material, including color versions of Figures 4, 5, 6, 7, and 8, and MCMC diagnostic plots, are available online. PMID:21113385

Berrocal, Veronica J.; Gelfand, Alan E.; Holland, David M.

2010-01-01

58

Spatio-temporal filtration of dynamic CT data using diffusion filters  

NASA Astrophysics Data System (ADS)

We present a method for spatio-temporal filtration of dynamic CT data, to increase the signal-to-noise ratio (SNR) of image data at the same time maintaining image quality, in particular spatial and temporal sharpness of the images. Alternatively, the radiation dose applied to the patient can be reduced at the same time maintaining the noise level and the image sharpness. In contrast to classical methods, which generally operate on the three spatial dimensions of image data, noise statistics is improved by extending the filtration to the temporal dimension. Our approach is based on nonlinear and anisotropic diffusion filters, which are based on a model of heat diffusion adapted to medical CT data. Bilateral filters are a special class of diffusion filters, which do not need iteration to reach a convergence image, but represent the fixed point of a dedicated diffusion filter. Spatio-temporal, anisotropic bilateral filters are developed and applied to dynamic CT image data. The potential was evaluated using data from perfusion CT and cardiac dual source CT (DSCT) data, respectively. It was shown, that in perfusion CT, SNR can be improved by a factor of 4 at the same radiation dose. On basis of clinical data it was shown, that alternatively the radiation dose to the patient can be reduced by a factor of at least 2. A more accurate evaluation of the perfusion parameters blood flow, blood volume and time-to-peak is supported. In DSCT noise statistics can be improved using more projection data than needed for image reconstruction, however, as a consequence the temporal resolution is significantly impaired. Due to the anisotropy of the spatio-temporal bilateral filter temporal contrast edges between adjacent time samples are preserved, at the same time substantially smoothing image data in homogeneous regions. Also temporal contrast edges are preserved, maintaining the very high temporal resolution of DSCT acquisitions (~ 80 ms). CT examinations of the heart require careful dose management to reduce the radiation dose burden to the patient. The use of spatio-temporal diffusion filters allows for dose reduction at the same noise level, at the same time preserving spatial and temporal image resolution. Our approach can be extended to any imaging method, that is based on dynamic data, as an efficient tool for edge-preserving noise reduction.

Bruder, H.; Raupach, R.; Klotz, E.; Stierstorfer, K.; Flohr, T.

2009-02-01

59

Visual tracking with spatio-temporal Dempster-Shafer information fusion.  

PubMed

A key problem in visual tracking is how to effectively combine spatio-temporal visual information from throughout a video to accurately estimate the state of an object. We address this problem by incorporating Dempster-Shafer (DS) information fusion into the tracking approach. To implement this fusion task, the entire image sequence is partitioned into spatially and temporally adjacent subsequences. A support vector machine (SVM) classifier is trained for object/nonobject classification on each of these subsequences, the outputs of which act as separate data sources. To combine the discriminative information from these classifiers, we further present a spatio-temporal weighted DS (STWDS) scheme. In addition, temporally adjacent sources are likely to share discriminative information on object/nonobject classification. To use such information, an adaptive SVM learning scheme is designed to transfer discriminative information across sources. Finally, the corresponding DS belief function of the STWDS scheme is embedded into a Bayesian tracking model. Experimental results on challenging videos demonstrate the effectiveness and robustness of the proposed tracking approach. PMID:23529089

Li, Xi; Dick, Anthony; Shen, Chunhua; Zhang, Zhongfei; van den Hengel, Anton; Wang, Hanzi

2013-08-01

60

A Comparison Between Complexity and Temporal GIS Models for Spatio-temporal Urban Applications  

Microsoft Academic Search

Spatio-temporal modeling for urban applications has received special attention lately. Due to the recent advances in computer\\u000a and geospatial technologies, the temporal aspect of urban applications which was ignored in conventional systems, is under\\u000a consideration nowadays. This new interest in spatio-temporal modeling, in spite of all its deficiencies, has brought about\\u000a great advances in spatio-temporal modeling and will enhance the

Majeed Pooyandeh; Saadi Mesgari; Abbas Alimohammadi; Rouzbeh Shad

2007-01-01

61

SINA: scalable incremental processing of continuous queries in spatio-temporal databases  

Microsoft Academic Search

This paper intoduces the Scalable INcremental hash-based Algorithm (SINA, for short); a new algorithm for evaluting a set of concurrent continuous spatio-temporal queries. SINA is designed with two goals in mind: (1) Scalability in terms of the number of concurrent continuous spatio-temporal queries, and (2) Incremental evaluation of continyous spatio-temporal queries. SINA achieves scalability by empolying a shared execution paradigm

Mohamed F. Mokbel; Xiaopeing Xiong; Walid G. Aref

2004-01-01

62

Dim moving target detection algorithm based on spatio-temporal classification sparse representation  

NASA Astrophysics Data System (ADS)

A dim moving target detection algorithm based on spatio-temporal classification sparse representation, which can characterize the motion information and morphological feature of target and background clutter, is proposed to enhance the performance of target detection. A spatio-temporal redundant dictionary is trained according to the content of infrared image sequence, and then is subdivided into target spatio-temporal redundant dictionary describing moving target, and background spatio-temporal redundant dictionary embedding background by the criterion that the target spatio-temporal atom could be decomposed more sparsely over Gaussian spatio-temporal redundant dictionary. The target and background clutter can be sparsely decomposed over their corresponding spatio-temporal redundant dictionary, yet could not be sparsely decomposed on their opposite spatio-temporal redundant dictionary, and so their residuals after reconstruction by the prescribed number of target and background spatio-temporal atoms would differ very visibly. Some experimental results show this proposed approach could not only improve the sparsity more efficiently, but also enhance the target detection performance more effectively.

Li, Zhengzhou; Dai, Zhen; Fu, Hongxia; Hou, Qian; Wang, Zhen; Yang, Lijiao; Jin, Gang; Liu, Changju; Li, Ruzhang

2014-11-01

63

Spatio-temporal topological relationships between land parcels in cadastral database  

NASA Astrophysics Data System (ADS)

There are complex spatio-temporal relationships among cadastral entities. Cadastral spatio-temporal data model should not only describe the data structure of cadastral objects, but also express cadastral spatio-temporal relationships between cadastral objects. In the past, many experts and scholars have proposed a variety of cadastral spatio-temporal data models, but few of them concentrated on the representation of spatiotemporal relationships and few of them make systematic studies on spatiotemporal relationships between cadastral objects. The studies on spatio-temporal topological relationships are not abundant. In the paper, we initially review current approaches to the studies of spatio-temporal topological relationships, and argue that spatio-temporal topological relation is the combination of temporal topology on the time dimension and spatial topology on the spatial dimension. Subsequently, we discuss and develop an integrated representation of spatio-temporal topological relationships within a 3-dimensional temporal space. In the end, based on the semantics of spatiotemporal changes between land parcels, we conclude the possible spatio-temporal topological relations between land parcels, which provide the theoretical basis for creating, updating and maintaining of land parcels in the cadastral database.

Song, W.; Zhang, F.

2014-04-01

64

A spatio-temporal database for diagnosing drought vulnerability in the Upper Colorado River Basin, Colorado  

NASA Astrophysics Data System (ADS)

Effective drought planning and mitigation requires an understanding of water supply and demand, including historical biophysical and legal conditions that lead to water shortages among various end-users. With the goal of providing information that is useful for managing current drought risks and for adapting to changing climate, this project aims to fill the gaps in the knowledge about spatio-temporal variations in water demand patterns in the Upper Colorado River Basin (UCRB). This information will help to identify vulnerabilities in the water management structure for more targeted drought preparedness and early warning. Though monitoring of hydro-meteorological properties is important to the forecast of drought conditions, the availability of water is complicated by the administration of existing water rights. The picture is increasingly complicated by the common practice of transmountain diversion, in which water in one basin is transported to another basin for use. This presentation will discuss development of a water demand data model and a spatio-temporal database that will support topological relationships among water users and their respective sources of water supply, including transfers and exchanges. GIS processes for linking water supply to the end users and their water demands will be discussed.

Sampson, K. M.; Wilhelmi, O.

2009-12-01

65

Spatio-temporal Variability of Nitrate Across Scales in Texas Aquifers  

NASA Astrophysics Data System (ADS)

Nitrate (NO3-) is considered the most prevalent contaminant in groundwater (GW). NO3- in GW shows significant spatio-temporal variability which comes from interaction among multiple geophysical factors such as source availability (land use), thickness and composition of the vadose zone, types of aquifers (confined or unconfined), aquifer heterogeneity (geological and alluvial), and precipitation characteristics etc. The present work seeks to describe the spatio-temporal variability of NO3- at multiple scales in two different hydrogeologic settings— the Trinity and Ogallala Aquifers in Texas at three spatial scales, fine (25 km.×25 km.), intermediate (50 km.×50 km.), and coarse (100 km.×100 km.) grids. An entropy-based approach was used to analyze spatial-temporal variability of NO3- within the aquifers. The Hurst exponent was used to evaluate the long-term persistence and trend in the variability of NO3-. The results demonstrate that the spatial variability of NO3- is controlled by the effect of soil type, irrigation-pumping, and local flow at the small scale and by the complex interactions between rivers and aquifers along with land use at the intermediate scale, and by lithology and geology at the coarse scale. The trends of variability of NO3- show long term persistence at the intermediate and coarse scales.

Dwivedi, D.; Mohanty, B. P.

2010-12-01

66

OFDM Radar Space-Time Adaptive Processing by Exploiting Spatio-Temporal Sparsity  

SciTech Connect

We propose a sparsity-based space-time adaptive processing (STAP) algorithm to detect a slowly-moving target using an orthogonal frequency division multiplexing (OFDM) radar. We observe that the target and interference spectra are inherently sparse in the spatio-temporal domain. Hence, we exploit that sparsity to develop an efficient STAP technique that utilizes considerably lesser number of secondary data and produces an equivalent performance as the other existing STAP techniques. In addition, the use of an OFDM signal increases the frequency diversity of our system, as different scattering centers of a target resonate at different frequencies, and thus improves the target detectability. First, we formulate a realistic sparse-measurement model for an OFDM radar considering both the clutter and jammer as the interfering sources. Then, we apply a residual sparse-recovery technique based on the LASSO estimator to estimate the target and interference covariance matrices, and subsequently compute the optimal STAP-filter weights. Our numerical results demonstrate a comparative performance analysis of the proposed sparse-STAP algorithm with four other existing STAP methods. Furthermore, we discover that the OFDM-STAP filter-weights are adaptable to the frequency-variabilities of the target and interference responses, in addition to the spatio-temporal variabilities. Hence, by better utilizing the frequency variabilities, we propose an adaptive OFDM-waveform design technique, and consequently gain a significant amount of STAP-performance improvement.

Sen, Satyabrata [ORNL

2013-01-01

67

Spatio-Temporal Equalizer for a Receiving-Antenna Feed Array  

NASA Technical Reports Server (NTRS)

A spatio-temporal equalizer has been conceived as an improved means of suppressing multipath effects in the reception of aeronautical telemetry signals, and may be adaptable to radar and aeronautical communication applications as well. This equalizer would be an integral part of a system that would also include a seven-element planar array of receiving feed horns centered at the focal point of a paraboloidal antenna that would be nominally aimed at or near the aircraft that would be the source of the signal that one seeks to receive (see Figure 1). This spatio-temporal equalizer would consist mostly of a bank of seven adaptive finite-impulse-response (FIR) filters one for each element in the array - and the outputs of the filters would be summed (see Figure 2). The combination of the spatial diversity of the feedhorn array and the temporal diversity of the filter bank would afford better multipath-suppression performance than is achievable by means of temporal equalization alone. The seven-element feed array would supplant the single feed horn used in a conventional paraboloidal ground telemetry-receiving antenna. The radio-frequency telemetry signals re ceiv ed by the seven elements of the array would be digitized, converted to complex baseband form, and sent to the FIR filter bank, which would adapt itself in real time to enable reception of telemetry at a low bit error rate, even in the presence of multipath of the type found at many flight test ranges.

Mukai, Ryan; Lee, Dennis; Vilnrotter, Victor

2010-01-01

68

Spatio-temporal Dynamics of Audiovisual Speech Processing  

PubMed Central

The cortical processing of auditory-alone, visual-alone, and audiovisual speech information is temporally and spatially distributed, and functional magnetic resonance imaging (fMRI) cannot adequately resolve its temporal dynamics. In order to investigate a hypothesized spatio-temporal organization for audiovisual speech processing circuits, event-related potentials (ERPs) were recorded using electroencephalography (EEG). Stimuli were congruent audiovisual /b?/, incongruent auditory /b?/ synchronized with visual /g?/, auditory-only /b?/, and visual-only /b?/ and /g?/. Current density reconstructions (CDRs) of the ERP data were computed across the latency interval of 50-250 milliseconds. The CDRs demonstrated complex spatio-temporal activation patterns that differed across stimulus conditions. The hypothesized circuit that was investigated here comprised initial integration of audiovisual speech by the middle superior temporal sulcus (STS), followed by recruitment of the intraparietal sulcus (IPS), followed by activation of Broca's area (Miller and d'Esposito, 2005). The importance of spatio-temporally sensitive measures in evaluating processing pathways was demonstrated. Results showed, strikingly, early (< 100 msec) and simultaneous activations in areas of the supramarginal and angular gyrus (SMG/AG), the IPS, the inferior frontal gyrus, and the dorsolateral prefrontal cortex. Also, emergent left hemisphere SMG/AG activation, not predicted based on the unisensory stimulus conditions was observed at approximately 160 to 220 msec. The STS was neither the earliest nor most prominent activation site, although it is frequently considered the sine qua non of audiovisual speech integration. As discussed here, the relatively late activity of the SMG/AG solely under audiovisual conditions is a possible candidate audiovisual speech integration response. PMID:17920933

Bernstein, Lynne E.; Auer, Edward T.; Wagner, Michael; Ponton, Curtis W.

2007-01-01

69

Spatio-temporal dynamics in the origin of genetic information  

NASA Astrophysics Data System (ADS)

We study evolutionary processes induced by spatio-temporal dynamics in prebiotic evolution. Using numerical simulations, we demonstrate that hypercycles emerge from complex interaction structures in multispecies systems. In this work, we also find that ‘hypercycle hybrid’ protects the hypercycle from its environment during the growth process. There is little selective advantage for one hypercycle to maintain coexistence with others. This brings the possibility of the outcompetition between hypercycles resulting in the negative effect on information diversity. To enrich the information in hypercycles, symbiosis with parasites is suggested. It is shown that symbiosis with parasites can play an important role in the prebiotic immunology.

Kim, Pan-Jun; Jeong, Hawoong

2005-04-01

70

Large scale stochastic spatio-temporal modelling with PCRaster  

NASA Astrophysics Data System (ADS)

PCRaster is a software framework for building spatio-temporal models of land surface processes (http://www.pcraster.eu). Building blocks of models are spatial operations on raster maps, including a large suite of operations for water and sediment routing. These operations are available to model builders as Python functions. The software comes with Python framework classes providing control flow for spatio-temporal modelling, Monte Carlo simulation, and data assimilation (Ensemble Kalman Filter and Particle Filter). Models are built by combining the spatial operations in these framework classes. This approach enables modellers without specialist programming experience to construct large, rather complicated models, as many technical details of modelling (e.g., data storage, solving spatial operations, data assimilation algorithms) are taken care of by the PCRaster toolbox. Exploratory modelling is supported by routines for prompt, interactive visualisation of stochastic spatio-temporal data generated by the models. The high computational requirements for stochastic spatio-temporal modelling, and an increasing demand to run models over large areas at high resolution, e.g. in global hydrological modelling, require an optimal use of available, heterogeneous computing resources by the modelling framework. Current work in the context of the eWaterCycle project is on a parallel implementation of the modelling engine, capable of running on a high-performance computing infrastructure such as clusters and supercomputers. Model runs will be distributed over multiple compute nodes and multiple processors (GPUs and CPUs). Parallelization will be done by parallel execution of Monte Carlo realizations and sub regions of the modelling domain. In our approach we use multiple levels of parallelism, improving scalability considerably. On the node level we will use OpenCL, the industry standard for low-level high performance computing kernels. To combine multiple nodes we will use software from the eScience Technology Platform (eSTeP), developed at the Netherlands eScience Center. This will allow us to scale up to hundreds of machines, with thousands of compute cores. A key requirement is not to change the user experience of the software. PCRaster operations and the use of the Python framework classes should work in a similar manner on machines ranging from a laptop to a supercomputer. This enables a seamless transfer of models from small machines, where model development is done, to large machines used for large-scale model runs. Domain specialists from a large range of disciplines, including hydrology, ecology, sedimentology, and land use change studies, currently use the PCRaster Python software within research projects. Applications include global scale hydrological modelling and error propagation in large-scale land use change models. The software runs on MS Windows, Linux operating systems, and OS X.

Karssenberg, Derek; Drost, Niels; Schmitz, Oliver; de Jong, Kor; Bierkens, Marc F. P.

2013-04-01

71

Stochastic spatio-temporal modelling with PCRaster Python  

NASA Astrophysics Data System (ADS)

PCRaster Python is a software framework for building spatio-temporal models of land surface processes (Karssenberg, Schmitz, Salamon, De Jong, & Bierkens, 2010; PCRaster, 2012). Building blocks of models are spatial operations on raster maps, including a large suite of operations for water and sediment routing. These operations, developed in C++, are available to model builders as Python functions. Users create models by combining these functions in a Python script. As construction of large iterative models is often difficult and time consuming for non-specialists in programming, the software comes with a set of Python framework classes that provide control flow for static modelling, temporal modelling, stochastic modelling using Monte Carlo simulation, and data assimilation techniques including the Ensemble Kalman filter and the Particle Filter. A framework for integrating model components with different time steps and spatial discretization is currently available as a prototype (Schmitz, de Jong, & Karssenberg, in review). The software includes routines for visualisation of stochastic spatio-temporal data for prompt, interactive, visualisation of model inputs and outputs. Visualisation techniques include animated maps, time series, probability distributions, and animated maps with exceedance probabilities. The PCRaster Python software is used by researchers from a large range of disciplines, including hydrology, ecology, sedimentology, and land use change studies. Applications include global scale hydrological modelling and error propagation in large-scale land use change models. The software runs on MS Windows and Linux operating systems, and OS X (under development).

Karssenberg, D.; Schmitz, O.; de Jong, K.

2012-04-01

72

Spatio-temporal statistical models with applications to atmospheric processes  

SciTech Connect

This doctoral dissertation is presented as three self-contained papers. An introductory chapter considers traditional spatio-temporal statistical methods used in the atmospheric sciences from a statistical perspective. Although this section is primarily a review, many of the statistical issues considered have not been considered in the context of these methods and several open questions are posed. The first paper attempts to determine a means of characterizing the semiannual oscillation (SAO) spatial variation in the northern hemisphere extratropical height field. It was discovered that the midlatitude SAO in 500hPa geopotential height could be explained almost entirely as a result of spatial and temporal asymmetries in the annual variation of stationary eddies. It was concluded that the mechanism for the SAO in the northern hemisphere is a result of land-sea contrasts. The second paper examines the seasonal variability of mixed Rossby-gravity waves (MRGW) in lower stratospheric over the equatorial Pacific. Advanced cyclostationary time series techniques were used for analysis. It was found that there are significant twice-yearly peaks in MRGW activity. Analyses also suggested a convergence of horizontal momentum flux associated with these waves. In the third paper, a new spatio-temporal statistical model is proposed that attempts to consider the influence of both temporal and spatial variability. This method is mainly concerned with prediction in space and time, and provides a spatially descriptive and temporally dynamic model.

Wikle, C.K.

1996-12-31

73

Spatio-temporal Granger causality: a new framework  

PubMed Central

That physiological oscillations of various frequencies are present in fMRI signals is the rule, not the exception. Herein, we propose a novel theoretical framework, spatio-temporal Granger causality, which allows us to more reliably and precisely estimate the Granger causality from experimental datasets possessing time-varying properties caused by physiological oscillations. Within this framework, Granger causality is redefined as a global index measuring the directed information flow between two time series with time-varying properties. Both theoretical analyses and numerical examples demonstrate that Granger causality is a monotonically increasing function of the temporal resolution used in the estimation. This is consistent with the general principle of coarse graining, which causes information loss by smoothing out very fine-scale details in time and space. Our results confirm that the Granger causality at the finer spatio-temporal scales considerably outperforms the traditional approach in terms of an improved consistency between two resting-state scans of the same subject. To optimally estimate the Granger causality, the proposed theoretical framework is implemented through a combination of several approaches, such as dividing the optimal time window and estimating the parameters at the fine temporal and spatial scales. Taken together, our approach provides a novel and robust framework for estimating the Granger causality from fMRI, EEG, and other related data. PMID:23643924

Luo, Qiang; Lu, Wenlian; Cheng, Wei; Valdes-Sosa, Pedro A.; Wen, Xiaotong; Ding, Mingzhou; Feng, Jianfeng

2015-01-01

74

Scale-free model for spatio-temporal distribution of outbreaks of avian influenza  

E-print Network

Scale-free model for spatio-temporal distribution of outbreaks of avian influenza Michael Small influenza outbreaks among wild and domestic birds, we show that this model is not appropriate. We find the global spatio-temporal distribution of avian influenza cases in both wild and domestic birds and find

Tse, Chi K. "Michael"

75

A new spatio-temporal equalization method based on estimated channel response  

Microsoft Academic Search

This paper proposes a new spatio-temporal equalization method, which simultaneously utilizes an adaptive antenna array and a decision feedback equalizer (DFE). For effective spatio-temporal equalization with less computational cost, how to split equalization functionality into spatial processing, and temporal processing is quite important. One of the answers which we have given is “incoming signals with larger time delays should be

Kazunori Hayashi; Shinsuke Hara

2001-01-01

76

Hierarchical Representation of Videos with Spatio-Temporal Fibers Ratnesh Kumar Guillaume Charpiat Monique Thonnat  

E-print Network

Hierarchical Representation of Videos with Spatio-Temporal Fibers Ratnesh Kumar Guillaume Charpiat representation of videos, as spatio- temporal fibers. These fibers are clusters of trajectories that are meshed spatially in the image domain. They form a hier- archical partition of the video into regions

Paris-Sud XI, Université de

77

Mercury: A Memory-Constrained Spatio-temporal Real-time Search on Microblogs  

E-print Network

Mercury: A Memory-Constrained Spatio-temporal Real-time Search on Microblogs Amr Magdy1§ , Mohamed Mercury; a system for real-time support of top-k spatio-temporal queries on microblogs, where users are able to browse recent microblogs near their locations. With high arrival rates of microblogs, Mercury

Bernstein, Phil

78

The Complex Spatio-Temporal Regulation of the Drosophila Myoblast Attractant Gene duf/kirre  

E-print Network

The Complex Spatio-Temporal Regulation of the Drosophila Myoblast Attractant Gene duf/kirre K. GRaghavan K (2009) The Complex Spatio-Temporal Regulation of the Drosophila Myoblast Attractant Gene duf number of FCs are chosen from a pool of equivalent myoblasts and serve to attract fusion

79

AN ITERATIVE SPATIO-TEMPORAL SPEECH ENHANCEMENT ALGORITHM FOR MICROPHONE ARRAYS  

E-print Network

AN ITERATIVE SPATIO-TEMPORAL SPEECH ENHANCEMENT ALGORITHM FOR MICROPHONE ARRAYS !"#"$ %&'t" "nd +c ABSTRACT We present a new spatio-temporal algorithm for speech enhancement using microphone arrays. Our-dependent parameter settings. Index Terms4 Speech enhancement, acoustic arrays, adaptive arrays, eigenvalues

Douglas, Scott C.

80

Finding Spatio-Temporal Patterns in Earth Science Data * Pang-Ning Tan+  

E-print Network

1 Finding Spatio-Temporal Patterns in Earth Science Data * Pang-Ning Tan+ Michael Steinbach+ Vipin-temporal patterns from Earth Science data. The data consists of time series measurements for various Earth science of the spatio-temporal issues. Earth Science data has strong seasonal components that need to be removed prior

Kumar, Vipin

81

A latent Gaussian Markov random field model for spatio-temporal rainfall disaggregation  

E-print Network

A latent Gaussian Markov random field model for spatio- temporal rainfall disaggregation David J. We therefore describe a spatio-temporal model which allows multiple imputation of rainfall at fine of the fine-scale rainfall to a thresh- olded Gaussian process which we model as a Gaussian Markov random

Stone, J. V.

82

INCORPORATING THE SPATIO-TEMPORAL DISTRIBUTION OF RAINFALL AND BASIN GEOMORPHOLOGY INTO NONLINEAR  

E-print Network

1 INCORPORATING THE SPATIO-TEMPORAL DISTRIBUTION OF RAINFALL AND BASIN GEOMORPHOLOGY INTO NONLINEAR streamflow series, spatio-temporal structure of precipitation and catchment geomorphology into a nonlinear of incorporating process-specific information (in terms of catchment geomorphology and an a-priori chosen

Foufoula-Georgiou, Efi

83

Spatio-temporal analysis of nucleate pool boiling: identi cation of nucleation sites using  

E-print Network

Spatio-temporal analysis of nucleate pool boiling: identi#12;cation of nucleation sites using non are often limited by the available techniques. These limitations are especially evident in nucleate boiling boiling experiment. Spatio-temporal data for the wall temperature in pool nu- cleate boiling of water

McSharry, Patrick E.

84

Spatio-temporal response of maize yield to edaphic and meteorological conditions in a saline farmland  

Technology Transfer Automated Retrieval System (TEKTRAN)

Spatio-temporal variability of crop production strongly depends on soil heterogeneity, meteorological conditions, and their interaction. Canopy reflectance can be used to describe crop status and yield spatial variability. The objectives of this work were to understand the spatio-temporal variabilit...

85

Spatio-temporal characteristics of Trichel pulse at low pressure  

NASA Astrophysics Data System (ADS)

Trichel pulses are investigated using a needle-to-plane electrode geometry at low pressure. The evolution of current and voltage, the spatio-temporal discharge images of Trichel pulse are measured. The rising time and duration time in a pulse are about 10 ?s and several tens of microseconds, respectively. One period of pulse can be divided into three stages: the stage preceding cathode breakdown, cathode glow formation, and discharge decaying process. Besides a cathode glow and a dark space, an anode glow is also observed. The emission spectra mainly originate from the C3?u ? B3?g transition for nitrogen. In addition, the capacitances in parallel connected with the discharge cell have important influence on the pulsing frequency.

He, Shoujie; Jing, Ha

2014-01-01

86

Spatio-temporal characteristics of Trichel pulse at low pressure  

SciTech Connect

Trichel pulses are investigated using a needle-to-plane electrode geometry at low pressure. The evolution of current and voltage, the spatio-temporal discharge images of Trichel pulse are measured. The rising time and duration time in a pulse are about 10??s and several tens of microseconds, respectively. One period of pulse can be divided into three stages: the stage preceding cathode breakdown, cathode glow formation, and discharge decaying process. Besides a cathode glow and a dark space, an anode glow is also observed. The emission spectra mainly originate from the C{sup 3}?{sub u} ? B{sup 3}?{sub g} transition for nitrogen. In addition, the capacitances in parallel connected with the discharge cell have important influence on the pulsing frequency.

He, Shoujie, E-mail: hedajingdian@126.com [College of Physics Science and Technology, Hebei University, Baoding (China)] [College of Physics Science and Technology, Hebei University, Baoding (China); Jing, Ha [Institute of Science, Hebei Agriculture University, Baoding (China)] [Institute of Science, Hebei Agriculture University, Baoding (China)

2014-01-15

87

Spatial and spatio-temporal models with R-INLA.  

PubMed

During the last three decades, Bayesian methods have developed greatly in the field of epidemiology. Their main challenge focusses around computation, but the advent of Markov Chain Monte Carlo methods (MCMC) and in particular of the WinBUGS software has opened the doors of Bayesian modelling to the wide research community. However model complexity and database dimension still remain a constraint. Recently the use of Gaussian random fields has become increasingly popular in epidemiology as very often epidemiological data are characterised by a spatial and/or temporal structure which needs to be taken into account in the inferential process. The Integrated Nested Laplace Approximation (INLA) approach has been developed as a computationally efficient alternative to MCMC and the availability of an R package (R-INLA) allows researchers to easily apply this method. In this paper we review the INLA approach and present some applications on spatial and spatio-temporal data. PMID:24377114

Blangiardo, Marta; Cameletti, Michela; Baio, Gianluca; Rue, Håvard

2013-12-01

88

Spatial and spatio-temporal models with R-INLA.  

PubMed

During the last three decades, Bayesian methods have developed greatly in the field of epidemiology. Their main challenge focusses around computation, but the advent of Markov Chain Monte Carlo methods (MCMC) and in particular of the WinBUGS software has opened the doors of Bayesian modelling to the wide research community. However model complexity and database dimension still remain a constraint. Recently the use of Gaussian random fields has become increasingly popular in epidemiology as very often epidemiological data are characterised by a spatial and/or temporal structure which needs to be taken into account in the inferential process. The Integrated Nested Laplace Approximation (INLA) approach has been developed as a computationally efficient alternative to MCMC and the availability of an R package (R-INLA) allows researchers to easily apply this method. In this paper we review the INLA approach and present some applications on spatial and spatio-temporal data. PMID:23481252

Blangiardo, Marta; Cameletti, Michela; Baio, Gianluca; Rue, Håvard

2013-03-01

89

Spatio-temporal patterns of Campylobacter colonization in Danish broilers.  

PubMed

Despite a number of risk-factor studies in different countries, the epidemiology of Campylobacter colonization in broilers, particularly spatial dependencies, is still not well understood. A series of analyses (visualization and exploratory) were therefore conducted in order to obtain a better understanding of the spatial and temporal distribution of Campylobacter in the Danish broiler population. In this study, we observed a non-random temporal occurrence of Campylobacter, with high prevalence during summer and low during winter. Significant spatio-temporal clusters were identified in the same areas in the summer months from 2007 to 2009. Range of influence between broiler farms were estimated at distances of 9.6 km and 13.5 km in different years. Identification of areas and time with greater risk indicates variable presence of risk factors with space and time. Implementation of safety measures on farms within high-risk clusters during summer could have an impact in reducing prevalence. PMID:22814565

Chowdhury, S; Themudo, G E; Sandberg, M; Ersbøll, A K

2013-05-01

90

Mathematical modelling of spatio-temporal glioma evolution  

PubMed Central

Background Gliomas are the most common types of brain cancer, well known for their aggressive proliferation and the invasive behavior leading to a high mortality rate. Several mathematical models have been developed for identifying the interactions between glioma cells and tissue microenvironment, which play an important role in the mechanism of the tumor formation and progression. Methods Building and expanding on existing approaches, this paper develops a continuous three-dimensional model of avascular glioma spatio-temporal evolution. The proposed spherical model incorporates the interactions between the populations of four different glioma cell phenotypes (proliferative, hypoxic, hypoglychemic and necrotic) and their tissue microenvironment, in order to investigate how they affect tumor growth and invasion in an isotropic and homogeneous medium. The model includes two key variables involved in the proliferation and invasion processes of cancer cells; i.e. the extracellular matrix and the matrix-degradative enzymes concentrations inside the tumor and its surroundings. Additionally, the proposed model focuses on innovative features, such as the separate and independent impact of two vital nutrients, namely oxygen and glucose, in tumor growth, leading to the formation of cell populations with different metabolic profiles. The model implementation takes under consideration the variations of particular factors, such as the local cell proliferation rate, the variable conversion rates of cells from one category to another and the nutrient-dependent thresholds of conversion. All model variables (cell densities, ingredients concentrations) are continuous and described by reaction-diffusion equations. Results Several simulations were performed using combinations of growth and invasion rates, for different evolution times. The model results were evaluated by medical experts and validated on experimental glioma models available in the literature, revealing high agreement between simulated and experimental results. Conclusions Based on the experimental validation, as well as the evaluation by clinical experts, the proposed model may provide an essential tool for the patient-specific simulation of different tumor evolution scenarios and reliable prognosis of glioma spatio-temporal progression. PMID:23880133

2013-01-01

91

Spatio-temporal clustering of wildfires in Portugal  

NASA Astrophysics Data System (ADS)

Several studies have shown that wildfires in Portugal presenthigh temporal as well as high spatial variability (Pereira et al., 2005, 2011). The identification and characterization of spatio-temporal clusters contributes to a comprehensivecharacterization of the fire regime and to improve the efficiency of fire prevention and combat activities. The main goalsin this studyare: (i) to detect the spatio-temporal clusters of burned area; and, (ii) to characterize these clusters along with the role of human and environmental factors. The data were supplied by the National Forest Authority(AFN, 2011) and comprises: (a)the Portuguese Rural Fire Database, PRFD, (Pereira et al., 2011) for the 1980-2007period; and, (b) the national mapping burned areas between 1990 and 2009. In this work, in order to complement the more common cluster analysis algorithms, an alternative approach based onscan statistics and on the permutation modelwas used. This statistical methodallows the detection of local excess events and to test if such an excess can reasonably have occurred by chance.Results obtained for different simulations performed for different spatial and temporal windows are presented, compared and interpreted.The influence of several fire factors such as (climate, vegetation type, etc.) is also assessed. Pereira, M.G., Trigo, R.M., DaCamara, C.C., Pereira, J.M.C., Leite, S.M., 2005:"Synoptic patterns associated with large summer forest fires in Portugal".Agricultural and Forest Meteorology. 129, 11-25. Pereira, M. G., Malamud, B. D., Trigo, R. M., and Alves, P. I.: The history and characteristics of the 1980-2005 Portuguese rural fire database, Nat. Hazards Earth Syst. Sci., 11, 3343-3358, doi:10.5194/nhess-11-3343-2011, 2011 AFN, 2011: AutoridadeFlorestalNacional (National Forest Authority). Available at http://www.afn.min-agricultura.pt/portal.

Costa, R.; Pereira, M. G.; Caramelo, L.; Vega Orozco, C.; Kanevski, M.

2012-04-01

92

A Hybrid Spatio-Temporal Data Indexing Method for Trajectory Databases  

PubMed Central

In recent years, there has been tremendous growth in the field of indoor and outdoor positioning sensors continuously producing huge volumes of trajectory data that has been used in many fields such as location-based services or location intelligence. Trajectory data is massively increased and semantically complicated, which poses a great challenge on spatio-temporal data indexing. This paper proposes a spatio-temporal data indexing method, named HBSTR-tree, which is a hybrid index structure comprising spatio-temporal R-tree, B*-tree and Hash table. To improve the index generation efficiency, rather than directly inserting trajectory points, we group consecutive trajectory points as nodes according to their spatio-temporal semantics and then insert them into spatio-temporal R-tree as leaf nodes. Hash table is used to manage the latest leaf nodes to reduce the frequency of insertion. A new spatio-temporal interval criterion and a new node-choosing sub-algorithm are also proposed to optimize spatio-temporal R-tree structures. In addition, a B*-tree sub-index of leaf nodes is built to query the trajectories of targeted objects efficiently. Furthermore, a database storage scheme based on a NoSQL-type DBMS is also proposed for the purpose of cloud storage. Experimental results prove that HBSTR-tree outperforms TB*-tree in some aspects such as generation efficiency, query performance and query type. PMID:25051028

Ke, Shengnan; Gong, Jun; Li, Songnian; Zhu, Qing; Liu, Xintao; Zhang, Yeting

2014-01-01

93

Spatio-temporal prediction of daily temperatures using time-series of MODIS LST images  

NASA Astrophysics Data System (ADS)

A computational framework to generate daily temperature maps using time-series of publicly available MODIS MOD11A2 product Land Surface Temperature (LST) images (1 km resolution; 8-day composites) is illustrated using temperature measurements from the national network of meteorological stations (159) in Croatia. The input data set contains 57,282 ground measurements of daily temperature for the year 2008. Temperature was modeled as a function of latitude, longitude, distance from the sea, elevation, time, insolation, and the MODIS LST images. The original rasters were first converted to principal components to reduce noise and filter missing pixels in the LST images. The residual were next analyzed for spatio-temporal auto-correlation; sum-metric separable variograms were fitted to account for zonal and geometric space-time anisotropy. The final predictions were generated for time-slices of a 3D space-time cube, constructed in the R environment for statistical computing. The results show that the space-time regression model can explain a significant part of the variation in station-data (84%). MODIS LST 8-day (cloud-free) images are unbiased estimator of the daily temperature, but with relatively low precision (±4.1°C); however their added value is that they systematically improve detection of local changes in land surface temperature due to local meteorological conditions and/or active heat sources (urban areas, land cover classes). The results of 10-fold cross-validation show that use of spatio-temporal regression-kriging and incorporation of time-series of remote sensing images leads to significantly more accurate maps of temperature than if plain spatial techniques were used. The average (global) accuracy of mapping temperature was ±2.4°C. The regression-kriging explained 91% of variability in daily temperatures, compared to 44% for ordinary kriging. Further software advancement—interactive space-time variogram exploration and automated retrieval, resampling and filtering of MODIS images—are anticipated.

Hengl, Tomislav; Heuvelink, Gerard B. M.; Per?ec Tadi?, Melita; Pebesma, Edzer J.

2012-01-01

94

Spatio-temporal variability and predictability of summer monsoon onset over the Philippines  

E-print Network

1 Spatio-temporal variability and predictability of summer monsoon onset over the Philippines V + International Research Institute for Climate and Society, Columbia University, USA * Philippine Atmospheric Geophysical and Astronomical Services Administration, Manila, Philippines Submitted to Climate Dynamics

Robertson, Andrew W.

95

Spatio-temporal ranging behaviour and its relevance to foraging strategies in wide-ranging wolverines  

Microsoft Academic Search

Conservation of carnivores in an increasingly changing environment is greatly helped by understanding the decision-making processes underlying habitat patch choice. Foraging theory may give us insight into spatio-temporal search patterns and consequent foraging decisions that carnivores make in heterogeneous and fluctuating environments. Constraints placed on central-place foragers in particular are likely to influence both foraging decisions and related spatio-temporal movement

Roel May; Jiska van Dijk; Arild Landa; Roy Andersen; Reidar Andersen

2010-01-01

96

Spatio-temporal analysis of Texas shoreline changes using GIS technique  

E-print Network

SPATIO-TEMPORAL ANALYSIS OF TEXAS SHORELINE CHANGES USING GIS TECHNIQUE A Thesis by CESAR AUGUSTO ARIAS MORAN Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE December 2003 Major Subject: Geography SPATIO-TEMPORAL ANALYSIS OF TEXAS SHORELINE CHANGES USING GIS TECHNIQUE A Thesis by CESAR AUGUSTO ARIAS MORAN...

Arias Moran, Cesar Augusto

2004-09-30

97

Spatio-temporal foraging patterns of a giant zooplanktivore, the leatherback turtle  

Microsoft Academic Search

Understanding food web functioning through the study of natural bio-indicators may constitute a valuable and original approach. In the context of jellyfish proliferation in many overexploited marine ecosystems studying the spatio-temporal foraging patterns of the giant “jellyvore” leatherback turtle turns out to be particularly relevant. Here we analyzed long-term tracking data to assess spatio-temporal foraging patterns in 21 leatherback turtles

Sabrina Fossette; Victoria J. Hobson; Charlotte Girard; Beatriz Calmettes; Philippe Gaspar; Jean-Yves Georges; Graeme C. Hays

2010-01-01

98

Network-oriented massive spatio-temporal data model and its applications  

NASA Astrophysics Data System (ADS)

It is foundation and key of developing GIS platforms of new generation to study the network-oriented massive spatial and spatio-temporal data model. But the research has met many difficulties. The paper combines two models of massive spatial data and spatio-temporal data seemed to be independent to study together in theory and technique. On the base of analyzing the limitations of present geographical spatial data model and spatio-temporal data model, a new model with characteristics of new generation's GIS platform, that is, Feature-Oriented Massive Spatio-temporal Object Tree (FOMSOT) with four-tier architectures is presented. The FOMSOT breaks down the constraint of map layer. It can deal with the massive spatio-temporal data better. The dynamic multi-base state with amendment (DMSA), fast index of base state with amendment in section, storage factors of variable granularity (SFVG) are used in FOMSOT which can manage the massive spatio-temporal data in high efficiency. A prototype "LyranMap" of new generation's GIS platform with the theory and technical method of FOMSOT has been realized, and it has been used in some application systems, for example, the land planning system "LandPlanner", land investigation system "LandExplorer" and land cadastral system "LandReGIS". These verify the correctness and effectiveness of the FOMSOT.

Liu, Renyi; Liu, Nan; Bao, Weizheng; Zhu, Yan

2006-10-01

99

Research on testing field flaws of image intensifier based on spatio-temporal SNR  

NASA Astrophysics Data System (ADS)

Image intensifier is the kernel of low-light-level device. The field flaw is one of the important index parameters of the image intensifier. Traditionally the statistic number of the image intensifier's field flaws is calculated through the people's eyes by the aid of an optical microscope, which main limitation is subjective and inefficient. With the broad application of the high-powered CCD and digital imaging processing method in testing performance of image intensifier, the method of appraising SNR based on spatio-temporal noise theory can accurately reflect the spatio-temporal heterogeneous of fluorescence's output image and fulfill the requirements of digital and automatic test. The limitation of the flaws' shape and position can be disregard and the accurate flaws' inspection can be realized rapidly by this method. In this paper, the main factors of forming the field flaws are analyzed and the mathematic model of spatio-temporal SNR is deduced. The hardware devices of the test system for image intensifier's spatio-temporal SNR are discussed. The spatio-temporal SNR of Gen image intensifier is tested by this test system and the test software based on Visual C++ and Matlab. The digital and automatic test of a factitious field flaw is realized by the theory of spatio-temporal SNR. The test precision can achieve pixel level. The experimental results show that this new method is rational, reliable and visualized.

Zhou, Bin; Liu, Bingqi; Wu, Dongsheng

2010-10-01

100

Stability and dynamics of spatio-temporal structures  

SciTech Connect

The main goal of the project supported in this grant is to contribute to the understanding of localized spatial and spatio-temporal structures far from thermodynamic equilibrium. Here we report on our progress in the study of two classes of systems. (1) We have started to investigate localized wave-pulses in binary-mixture convection. This work is based on our recently derived extension of the conventionally used complex Ginzburg-Landau equations. We are considering three regimes: Dispersion-less supercritical waves; strongly dispersive subcritical waves; and localized waves as bound states of fronts between dispersionless subcritical waves and the motionless conductive state. (2) We have completed our investigation of steady domain structures in which domains of structures with different wave numbers alternate, separated by domain walls. In particular, we have studied their regimes of existence and stability within the framework of a Ginzburg-Landau equation and have compared it to previous results. Those were based on a long-wavelength approximation, which misses certain aspects which turn out to be important for the stability of the domain structures in realistic situations. In addition, we give a description of our work on resonantly forced waves in two-dimensional anisotropic systems.

Riecke, H.

1993-03-01

101

Spatio-temporal self-organization in mudstones.  

SciTech Connect

Shales and other mudstones are the most abundant rock types in sedimentary basins, yet have received comparatively little attention. Common as hydrocarbon seals, these are increasingly being targeted as unconventional gas reservoirs, caprocks for CO2 sequestration, and storage repositories for waste. The small pore and grain size, large specific surface areas, and clay mineral structures lend themselves to rapid reaction rates, high capillary pressures, and semi-permeable membrane behavior accompanying changes in stress, pressure, temperature and chemical conditions. Under far from equilibrium conditions, mudrocks display a variety of spatio-temporal self-organized phenomena arising from nonlinear thermo-mechano-chemo-hydro coupling. Beginning with a detailed examination of nano-scale pore network structures in mudstones, we discuss the dynamics behind such self-organized phenomena as pressure solitons in unconsolidated muds, chemically-induced flow self focusing and permeability transients, localized compaction, time dependent well-bore failure, and oscillatory osmotic fluxes as they occur in clay-bearing sediments. Examples are draw from experiments, numerical simulation, and the field. These phenomena bear on the ability of these rocks to serve as containment barriers.

Dewers, Thomas A.

2010-12-01

102

Workload induced spatio-temporal distortions and safety of flight  

SciTech Connect

A theoretical analysis of the relationship between cognitive complexity and the perception of time and distance is presented and experimentally verified. Complex tasks produce high rates of mental representation which affect the subjective sense of duration and, through the subjective time scale, the percept of distance derived from dynamic visual cues (i.e., visual cues requiring rate integration). The analysis of the interrelationship of subjective time and subjective distance yields the prediction that, as a function of cognitive complexity, distance estimates derived from dynamic visual cues will be longer than the actual distance whereas estimates based on perceived temporal duration will be shorter than the actual distance. This prediction was confirmed in an experiment in which subjects (both pilots and non-pilots) estimated distances using either temporal cues or dynamic visual cues. The distance estimation task was also combined with secondary loading tasks in order to vary the overall task complexity. The results indicated that distance estimates based on temporal cues were underestimated while estimates based on visual cues were overestimated. This spatio-temporal distortion effect increased with increases in overall task complexity. 30 refs., 6 figs., 1 tab.

Barrett, C.L.; Weisgerber, S.A. (Los Alamos National Lab., NM (USA); Naval Weapons Center, China Lake, CA (USA))

1989-01-01

103

An object-relational spatio-temporal geoscience data model  

NASA Astrophysics Data System (ADS)

A model for spatially and temporally indexed multi-dimensional geoscience data has been developed by first embedding a combinatorial topological model in terms of G-Maps in the domain Rm×Time(m?N), and then converting it into an object-relational model which can easily be implemented in an object-relational database system. Geoscience objects referring to space and time often have complex geometries which are usually partitioned into simpler cells and have geometrical, topological, geological, geophysical, geochemical and other relevant properties assigned to their cells. These objects may exist in a Euclidean space Rm of arbitrary dimension m depending on which properties are chosen as "coordinates", where usually m=3 and refers to three spatial dimensions, and evolve in one dimensional valid time (Time). The valid time is independent of geometry, topology and properties but not vice versa, i.e., the geometry of an object, for example, and all its properties are modeled as functions of the valid time. Then the objects are assumed to be sampled at arbitrary but fixed instances of time, and their evolution between these instances is modeled by appropriate interpolation. The structure of the data model is well adapted to the interpolation required to represent the objects in between the instances of their observation. The data model provides the basis prerequisite of our envisioned spatio-temporal geoscience information system.

Le, Hai Ha; Gabriel, Paul; Gietzel, Jan; Schaeben, Helmut

2013-08-01

104

Complex background subtraction by pursuing dynamic spatio-temporal models.  

PubMed

Although it has been widely discussed in video surveillance, background subtraction is still an open problem in the context of complex scenarios, e.g., dynamic backgrounds, illumination variations, and indistinct foreground objects. To address these challenges, we propose an effective background subtraction method by learning and maintaining an array of dynamic texture models within the spatio-temporal representations. At any location of the scene, we extract a sequence of regular video bricks, i.e., video volumes spanning over both spatial and temporal domain. The background modeling is thus posed as pursuing subspaces within the video bricks while adapting the scene variations. For each sequence of video bricks, we pursue the subspace by employing the auto regressive moving average model that jointly characterizes the appearance consistency and temporal coherence of the observations. During online processing, we incrementally update the subspaces to cope with disturbances from foreground objects and scene changes. In the experiments, we validate the proposed method in several complex scenarios, and show superior performances over other state-of-the-art approaches of background subtraction. The empirical studies of parameter setting and component analysis are presented as well. PMID:24876126

Lin, Liang; Xu, Yuanlu; Liang, Xiaodan; Lai, Jianhuang

2014-07-01

105

Contextualized Trajectory Parsing with Spatio-Temporal Graph.  

PubMed

This work investigates how to automatically parse object trajectories in surveillance videos, that aims to jointly solve three subproblems: i) spatial segmentation, ii) temporal tracking, and iii) object categorization. We present a novel representation spatio-temporal graph (ST-Graph), in which: i) graph nodes express the motion primitives, each representing a short sequence of small-size patches over consecutive images; and ii) every two neighbor nodes are linked with either a positive edge or a negative edge to describe their collaborative or exclusive relationship of belonging to the same object trajectory. Phrasing the trajectory parsing as a graph multi-coloring problem, we propose a unified probabilistic formulation to integrate various types of context knowledge as informative priors. An efficient composite cluster sampling algorithm is employed in search of the optimal solution by exploiting both the collaborative and the exclusive relationships between nodes. The proposed framework is evaluated over challenging videos from public datasets, and results show that it can achieve state-of-the-art tracking accuracy. PMID:23648583

Liu, Xiaobai; Lin, Liang; Jin, Hai

2013-04-30

106

A sensitivity analysis of the point reference global correlation (PRGC) technique for spatio-temporal correlations in turbulent flows  

NASA Astrophysics Data System (ADS)

The point reference global correlation (PRGC) technique which combines single and global measurements as proposed by Chatellier and Fitzpatrick (Exp Fluids 38(5):563-757, 2005) is of significant interest for the analysis of the turbulent statistics for noise source modeling in jet flows as it allows the 2D spatio-temporal correlation functions to be obtained over a region of the flow. This enables the statistical characteristics including inhomogeneous and anisotropic features to be determined. The sensitivity of the technique is examined in some detail for the specific case of laser doppler velocimetry (LDV) and particle image velocimetry (PIV). Simulated data are used to enable a parametric study of the accuracy of the PRGC technique to be determined as a function of the various measurement parameters. The sample frequencies and the number of samples of both the LDV and PIV signals are shown to be critical to errors associated with the estimated spatio-temporal correlations and that low data rates can lead to significant errors in the estimates. Measurements performed in single stream and co-axial jet flows at Mach 0.24 using PIV and LDV systems are reported and the 2D space-time correlation functions for these flows are determined using the PRGC technique. The results are discussed in the context of noise source modeling for jet flows.

Kerhervé, F.; Fitzpatrick, J.; Chatellier, Ludovic

2008-04-01

107

Spatio-temporal reconstruction of bilateral auditory steady-state responses using MEG beamformers.  

PubMed

A rapidly growing number of neuromagnetic studies focus on the analysis of auditory steady-state responses (ASSR) in relation to a diverse array of factors including age, selective attention, and presence of psychopathology. The objectives of these studies require accurate spatio-temporal estimation of the underlying neural generators, a challenging task due to the relatively low signal strength and high correlation between bilateral auditory cortical sources. This paper evaluates the performance of two beamforming schemes that can potentially overcome such difficulties: 1) the linearly constrained minimum variance beamformer with partial sensor coverage (LCMV-PSC), and 2) the multiple constrained minimum-variance beamformer with coherent source region suppression (MCMV-CSRS). Simulation experiments are conducted to assess the impact of source parameters on the reconstruction accuracy. The results indicate that the LCMV-PSC method is prone to localization errors that essentially occur along medio-lateral directions, increase with source depth, and are associated to amplitude and phase distortions of the estimated time courses of activity. Comparatively, the MCMV-CSRS method exhibits precise localization and minimal amplitude and phase distortion for a broad range of relative interferer's positions within the suppression region. The results from the numerical experiments are validated on real magnetoencephalographic (MEG) data collected from a 40-Hz ASSR paradigm. PMID:18334401

Popescu, Mihai; Popescu, Elena-Anda; Chan, Tszping; Blunt, Shannon D; Lewine, Jeffrey D

2008-03-01

108

Predicting BCI subject performance using probabilistic spatio-temporal filters.  

PubMed

Recently, spatio-temporal filtering to enhance decoding for Brain-Computer-Interfacing (BCI) has become increasingly popular. In this work, we discuss a novel, fully Bayesian-and thereby probabilistic-framework, called Bayesian Spatio-Spectral Filter Optimization (BSSFO) and apply it to a large data set of 80 non-invasive EEG-based BCI experiments. Across the full frequency range, the BSSFO framework allows to analyze which spatio-spectral parameters are common and which ones differ across the subject population. As expected, large variability of brain rhythms is observed between subjects. We have clustered subjects according to similarities in their corresponding spectral characteristics from the BSSFO model, which is found to reflect their BCI performances well. In BCI, a considerable percentage of subjects is unable to use a BCI for communication, due to their missing ability to modulate their brain rhythms-a phenomenon sometimes denoted as BCI-illiteracy or inability. Predicting individual subjects' performance preceding the actual, time-consuming BCI-experiment enhances the usage of BCIs, e.g., by detecting users with BCI inability. This work additionally contributes by using the novel BSSFO method to predict the BCI-performance using only 2 minutes and 3 channels of resting-state EEG data recorded before the actual BCI-experiment. Specifically, by grouping the individual frequency characteristics we have nicely classified them into the subject 'prototypes' (like ? - or ? -rhythm type subjects) or users without ability to communicate with a BCI, and then by further building a linear regression model based on the grouping we could predict subjects' performance with the maximum correlation coefficient of 0.581 with the performance later seen in the actual BCI session. PMID:24551050

Suk, Heung-Il; Fazli, Siamac; Mehnert, Jan; Müller, Klaus-Robert; Lee, Seong-Whan

2014-01-01

109

Predicting BCI Subject Performance Using Probabilistic Spatio-Temporal Filters  

PubMed Central

Recently, spatio-temporal filtering to enhance decoding for Brain-Computer-Interfacing (BCI) has become increasingly popular. In this work, we discuss a novel, fully Bayesian–and thereby probabilistic–framework, called Bayesian Spatio-Spectral Filter Optimization (BSSFO) and apply it to a large data set of 80 non-invasive EEG-based BCI experiments. Across the full frequency range, the BSSFO framework allows to analyze which spatio-spectral parameters are common and which ones differ across the subject population. As expected, large variability of brain rhythms is observed between subjects. We have clustered subjects according to similarities in their corresponding spectral characteristics from the BSSFO model, which is found to reflect their BCI performances well. In BCI, a considerable percentage of subjects is unable to use a BCI for communication, due to their missing ability to modulate their brain rhythms–a phenomenon sometimes denoted as BCI-illiteracy or inability. Predicting individual subjects’ performance preceding the actual, time-consuming BCI-experiment enhances the usage of BCIs, e.g., by detecting users with BCI inability. This work additionally contributes by using the novel BSSFO method to predict the BCI-performance using only 2 minutes and 3 channels of resting-state EEG data recorded before the actual BCI-experiment. Specifically, by grouping the individual frequency characteristics we have nicely classified them into the subject ‘prototypes’ (like ? - or ? -rhythm type subjects) or users without ability to communicate with a BCI, and then by further building a linear regression model based on the grouping we could predict subjects' performance with the maximum correlation coefficient of 0.581 with the performance later seen in the actual BCI session. PMID:24551050

Suk, Heung-Il; Fazli, Siamac; Mehnert, Jan; Müller, Klaus-Robert; Lee, Seong-Whan

2014-01-01

110

Modeling sediment transport as a spatio-temporal Markov process.  

NASA Astrophysics Data System (ADS)

Despite a century of research about sediment transport by bedload occuring in rivers, its constitutive laws remain largely unknown. The proof being that our ability to predict mid-to-long term transported volumes within reasonable confidence interval is almost null. The intrinsic fluctuating nature of bedload transport may be one of the most important reasons why classical approaches fail. Microscopic probabilistic framework has the advantage of taking into account these fluctuations at the particle scale, to understand their effect on the macroscopic variables such as sediment flux. In this framework, bedload transport is seen as the random motion of particles (sand, gravel, pebbles...) over a two-dimensional surface (the river bed). The number of particles in motion, as well as their velocities, are random variables. In this talk, we show how a simple birth-death Markov model governing particle motion on a regular lattice accurately reproduces the spatio-temporal correlations observed at the macroscopic level. Entrainment, deposition and transport of particles by the turbulent fluid (air or water) are supposed to be independent and memoryless processes that modify the number of particles in motion. By means of the Poisson representation, we obtained a Fokker-Planck equation that is exactly equivalent to the master equation and thus valid for all cell sizes. The analysis shows that the number of moving particles evolves locally far from thermodynamic equilibrium. Several analytical results are presented and compared to experimental data. The index of dispersion (or variance over mean ratio) is proved to grow from unity at small scales to larger values at larger scales confirming the non Poisonnian behavior of bedload transport. Also, we study the one and two dimensional K-function, which gives the average number of moving particles located in a ball centered at a particle centroid function of the ball's radius.

Heyman, Joris; Ancey, Christophe

2014-05-01

111

In-situ image data capturing and spatio-temporal data management in the context of a multi-hazard risk assessment  

NASA Astrophysics Data System (ADS)

Monitoring of the spatio-temporal variability of exposure and vulnerability indicators for risk assessments is dependent not only on the amount and quality of the data upon which the assessment is made, but also on the tools and methodologies employed to capture, store, manage and analyse the information. Spatio-temporal changes need to be properly integrated into a sound, comprehensive conceptual and methodological framework, which is able to deal with multi-dimensional data coming from different sources, at varying scales and changing over time. Commonly used approaches to capture data about an exposed building stock with respect to its physical characteristics and vulnerability usually entail a detailed (inside and outside) screening of buildings by structural engineers. These approaches are often not suitable for the rapidly changing spatio-temporal conditions in many present-day cities, and moreover do not often scale well with end-user's limited resource allocation. Also purely satellite-based approaches, which are used as time- and cost-effective alternative, show limitations in that they are only capable of providing information about vulnerability-related characteristics that can be assessed from the top view. This work, therefore, introduces a methodological and technical framework to combine remote sensing with in-situ image data capturing to overcome the limitations of previous approaches. A novel mobile mapping system and Remote Rapid Visual Screening (RRVS) technique based on omnidirectional imaging is presented. A key objective of this work is, moreover, to present a prototype spatio-temporal database system that functions as basis for the storage and management of data from different sources, at varying scales and changing over time. Examples from our study sites in Central Asia and Germany will be presented to highlight the application of the proposed approach.

Wieland, Marc; Pittore, Massimiliano

2014-05-01

112

A spatio-temporal detective quantum efficiency and its application to fluoroscopic systems  

SciTech Connect

Purpose: Fluoroscopic x-ray imaging systems are used extensively in spatio-temporal detection tasks and require a spatio-temporal description of system performance. No accepted metric exists that describes spatio-temporal fluoroscopic performance. The detective quantum efficiency (DQE) is a metric widely used in radiography to quantify system performance and as a surrogate measure of patient ''dose efficiency.'' It has been applied previously to fluoroscopic systems with the introduction of a temporal correction factor. However, the use of a temporally-corrected DQE does not provide system temporal information and it is only valid under specific conditions, many of which are not likely to be satisfied by suboptimal systems. The authors propose a spatio-temporal DQE that describes performance in both space and time and is applicable to all spatio-temporal quantum-based imaging systems. Methods: The authors define a spatio-temporal DQE (two spatial-frequency axes and one temporal-frequency axis) in terms of a small-signal spatio-temporal modulation transfer function (MTF) and spatio-temporal noise power spectrum (NPS). Measurements were made on an x-ray image intensifier-based bench-top system using continuous fluoroscopy with an RQA-5 beam at 3.9 {mu}R/frame and hardened 50 kVp beam (0.8 mm Cu filtration added) at 1.9 {mu}R/frame. Results: A zero-frequency DQE value of 0.64 was measured under both conditions. Nonideal performance was noted at both larger spatial and temporal frequencies; DQE values decreased by {approx}50% at the cutoff temporal frequency of 15 Hz. Conclusions: The spatio-temporal DQE enables measurements of decreased temporal system performance at larger temporal frequencies analogous to previous measurements of decreased (spatial) performance. This marks the first time that system performance and dose efficiency in both space and time have been measured on a fluoroscopic system using DQE and is the first step toward the generalized use of DQE on clinical fluoroscopic systems.

Friedman, S. N.; Cunningham, I. A. [Sackler School of Medicine, Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978 (Israel); Imaging Research Laboratories, Robarts Research Institute and Lawson Health Research Institute, 100 Perth Drive, London, Ontario N6A 5K8 (Canada) and Department of Medical Biophysics, University of Western Ontario, 1151 Richmond Street, London, Ontario N6A 5B8 (Canada)

2010-11-15

113

Hydrograph transposition to ungauged basin accounting for spatio-temporal rainfall variability  

NASA Astrophysics Data System (ADS)

Lack of measurements is one of the main issues in hydrological modelling. However, neighbours and nested gauged catchment are precious sources of information to understand the catchment behaviours within one region. Extracting the maximum of information from those points of measurements, that could be then transposed to ungauged catchment, is still a great challenge. We propose a methodology to transpose hydrological information from gauged catchments to ungauged ones, in order to simulate streamflow hydrographs. It uses geomorphology-based hydrological modelling, which is particularly well adapted to ungauged basins thanks to its robustness, generality and flexibility. We develop a geomorphology-based model on the gauged catchment which has been built in order to capture the main behaviour of the basin. Its transfer function considers the different dynamics of the catchment through the combination of velocities and width functions. Moreover, the explicit structure of the model enables to easily create a map of isochrone areas describing the time to the outlet. Therefore, spatially distributed rainfall can then be split into those isochrone areas, permitting the transfer function to deal with spatio-temporal variability of rainfall. Once the model calibrated, using a particle swarm optimisation algorithm, its transfer function is inversed to assess the net rainfall time series. In this way, we obtained a standardized variable which is used to estimate discharge in ungauged basin. Therefore, net rainfall time series is transposed and convoluted on the ungauged catchment using its own transfer function. Spatio-temporal rainfall variability between basins is considered through a correction of this net rainfall time series. This correction is based on differences between mean gross rainfall observation among those two catchments. This methodology is applied on pairs of basins among 6 gauged basins (from 5km² to 316km²) located in Brittany, France. For the benefit of the exercise, within each pair of basins, one is considered as "gauged" and the other one as "ungauged". Different spatial configurations of pairs of basins are compared. Results demonstrates the benefit of a well defined transfer function, as well as the importance of considering rainfall variability. Finally, through the assessment of transposition efficiency, this framework is presented as an original way to describe and understand hydrological similarities in catchment behavior.

de Lavenne, Alban; Cudennec, Christophe

2013-04-01

114

Transfer of spatio-temporal multifractal properties of rainfall to simulated surface runoff  

NASA Astrophysics Data System (ADS)

In this paper we suggest to use scaling laws and more specifically Universal Multifractals (UM) to analyse in a spatio-temporal framework both the radar rainfall and the simulated surface runoff. Such tools have been extensively used to analyse and simulate geophysical fields extremely variable over wide range of spatio-temporal scales such as rainfall, but have not often if ever been applied to surface runoff. Such novel combined analysis helps to improve the understanding of the rainfall-runoff relationship. Two catchments of the chair "Hydrology for resilient cities" sponsored by Véolia, and of the European Interreg IV RainGain project are used. They are both located in the Paris area: a 144 ha flat urban area in the Seine-Saint-Denis County, and a 250 ha urban area with a significant portion of forest located on a steep hillside of the Bièvre River. A fully distributed urban hydrological model currently under development called Multi-Hydro is implemented to represent the catchments response. It consists in an interacting core between open source software packages, each of them representing a portion of the water cycle in urban environment. The fully distributed model is tested with pixels of size 5, 10 and 20 m. In a first step the model is validated for three rainfall events that occurred in 2010 and 2011, for which the Météo-France radar mosaic with a resolution of 1 km in space and 5 min in time is available. These events generated significant surface runoff and some local flooding. The sensitivity of the model to the rainfall resolution is briefly checked by stochastically generating an ensemble of realistic downscaled rainfall fields (obtained by continuing the underlying cascade process which is observed on the available range of scales) and inputting them into the model. The impact is significant on both the simulated sewer flow and surface runoff. Then rainfall fields are generated with the help of discrete multifractal cascades and inputted in the numerical hydrological model. It appears that the outputs (maps of water depth and velocity) of the hydrological model exhibit a scaling behaviour both in space and time. Various sets of UM parameters are tested. The three UM parameters of the various processes at stake are then compared which enables to analyse how the extremes are either dampened or enhanced. This hints at innovative techniques to quantify the extremes at very high resolution (typically 1 m) without having to run the model at these resolutions which would require too much time especially for real time applications.

Gires, Auguste; Giangola-Murzyn, Agathe; Richard, Julien; Abbes, Jean-Baptiste; Tchiguirinskaia, Ioulia; Schertzer, Daniel; Willinger, Bernard; Cardinal, Hervé; Thouvenot, Thomas

2014-05-01

115

Spatio-temporal Hotelling observer for signal detection from image sequences.  

PubMed

Detection of signals in noisy images is necessary in many applications, including astronomy and medical imaging. The optimal linear observer for performing a detection task, called the Hotelling observer in the medical literature, can be regarded as a generalization of the familiar prewhitening matched filter. Performance on the detection task is limited by randomness in the image data, which stems from randomness in the object, randomness in the imaging system, and randomness in the detector outputs due to photon and readout noise, and the Hotelling observer accounts for all of these effects in an optimal way. If multiple temporal frames of images are acquired, the resulting data set is a spatio-temporal random process, and the Hotelling observer becomes a spatio-temporal linear operator. This paper discusses the theory of the spatio-temporal Hotelling observer and estimation of the required spatio-temporal covariance matrices. It also presents a parallel implementation of the observer on a cluster of Sony PLAYSTATION 3 gaming consoles. As an example, we consider the use of the spatio-temporal Hotelling observer for exoplanet detection. PMID:19550494

Caucci, Luca; Barrett, Harrison H; Rodriguez, Jeffrey J

2009-06-22

116

Spatio-temporal Hotelling observer for signal detection from image sequences  

PubMed Central

Detection of signals in noisy images is necessary in many applications, including astronomy and medical imaging. The optimal linear observer for performing a detection task, called the Hotelling observer in the medical literature, can be regarded as a generalization of the familiar prewhitening matched filter. Performance on the detection task is limited by randomness in the image data, which stems from randomness in the object, randomness in the imaging system, and randomness in the detector outputs due to photon and readout noise, and the Hotelling observer accounts for all of these effects in an optimal way. If multiple temporal frames of images are acquired, the resulting data set is a spatio-temporal random process, and the Hotelling observer becomes a spatio-temporal linear operator. This paper discusses the theory of the spatio-temporal Hotelling observer and estimation of the required spatio-temporal covariance matrices. It also presents a parallel implementation of the observer on a cluster of Sony PLAYSTATION 3 gaming consoles. As an example, we consider the use of the spatio-temporal Hotelling observer for exoplanet detection. PMID:19550494

Caucci, Luca; Barrett, Harrison H.; Rodríguez, Jeffrey J.

2010-01-01

117

An Accessible Method for Implementing Hierarchical Models with Spatio-Temporal Abundance Data  

PubMed Central

A common goal in ecology and wildlife management is to determine the causes of variation in population dynamics over long periods of time and across large spatial scales. Many assumptions must nevertheless be overcome to make appropriate inference about spatio-temporal variation in population dynamics, such as autocorrelation among data points, excess zeros, and observation error in count data. To address these issues, many scientists and statisticians have recommended the use of Bayesian hierarchical models. Unfortunately, hierarchical statistical models remain somewhat difficult to use because of the necessary quantitative background needed to implement them, or because of the computational demands of using Markov Chain Monte Carlo algorithms to estimate parameters. Fortunately, new tools have recently been developed that make it more feasible for wildlife biologists to fit sophisticated hierarchical Bayesian models (i.e., Integrated Nested Laplace Approximation, ‘INLA’). We present a case study using two important game species in North America, the lesser and greater scaup, to demonstrate how INLA can be used to estimate the parameters in a hierarchical model that decouples observation error from process variation, and accounts for unknown sources of excess zeros as well as spatial and temporal dependence in the data. Ultimately, our goal was to make unbiased inference about spatial variation in population trends over time. PMID:23166658

Ross, Beth E.; Hooten, Mevin B.; Koons, David N.

2012-01-01

118

An Accessible Method for Implementing Hierarchical Models with Spatio-Temporal Abundance Data  

USGS Publications Warehouse

A common goal in ecology and wildlife management is to determine the causes of variation in population dynamics over long periods of time and across large spatial scales. Many assumptions must nevertheless be overcome to make appropriate inference about spatio-temporal variation in population dynamics, such as autocorrelation among data points, excess zeros, and observation error in count data. To address these issues, many scientists and statisticians have recommended the use of Bayesian hierarchical models. Unfortunately, hierarchical statistical models remain somewhat difficult to use because of the necessary quantitative background needed to implement them, or because of the computational demands of using Markov Chain Monte Carlo algorithms to estimate parameters. Fortunately, new tools have recently been developed that make it more feasible for wildlife biologists to fit sophisticated hierarchical Bayesian models (i.e., Integrated Nested Laplace Approximation, ‘INLA’). We present a case study using two important game species in North America, the lesser and greater scaup, to demonstrate how INLA can be used to estimate the parameters in a hierarchical model that decouples observation error from process variation, and accounts for unknown sources of excess zeros as well as spatial and temporal dependence in the data. Ultimately, our goal was to make unbiased inference about spatial variation in population trends over time.

Ross, Beth E.; Hooten, Melvin B.; Koons, David N.

2012-01-01

119

Geovisualization Approaches for Spatio-temporal Crime Scene Analysis - Towards 4D Crime Mapping  

NASA Astrophysics Data System (ADS)

This paper presents a set of methods and techniques for analysis and multidimensional visualisation of crime scenes in a German city. As a first step the approach implies spatio-temporal analysis of crime scenes. Against this background a GIS-based application is developed that facilitates discovering initial trends in spatio-temporal crime scene distributions even for a GIS untrained user. Based on these results further spatio-temporal analysis is conducted to detect variations of certain hotspots in space and time. In a next step these findings of crime scene analysis are integrated into a geovirtual environment. Behind this background the concept of the space-time cube is adopted to allow for visual analysis of repeat burglary victimisation. Since these procedures require incorporating temporal elements into virtual 3D environments, basic methods for 4D crime scene visualisation are outlined in this paper.

Wolff, Markus; Asche, Hartmut

120

Low-complexity algorithms for spatio-temporal directional spectrum sensing with applications in cognitive radio  

NASA Astrophysics Data System (ADS)

A suit of low complexity signal processing algorithms are identified for the directional spectrum sensing and two-dimensional (2-D) spatio-temporal white space detection in cognitive radio systems. The concept of spectral white spaces in 2-D spatio-temporal frequency space is reviewed based on the specific spectral properties of 2-D spatio-temporal array signals. The proposed system contains an array processing stage, magnitude-fast-Fourier-transform (FFT) stage followed by an energy detection stage. The use of 2-D infinite impulse response (IIR) filters having beam-shaped passbands in the 2-D frequency space is identi_ed as a low complexity solution for the array processing stage for the directional enhancement of radio signals. A low complexity algorithm that delivers the magnitude FFT is described for the 16-point case and computational complexity is expressed in closed-form.

Madanayake, Arjuna; Wijenayake, Chamith; Potluri, Uma; Abeysekara, Judith; Mugler, Dale

2013-05-01

121

Spatio-Temporal Frequency Analysis for Removing Rain and Snow from Videos Peter Barnum Takeo Kanade Srinivasa G Narasimhan  

E-print Network

Spatio-Temporal Frequency Analysis for Removing Rain and Snow from Videos Peter Barnum Takeo Kanade changes, and most relevant to this work, dynamic weather. Particulate weather, such as rain and snow with the statistical properties of rain and snow, to determine how they effect the spatio-temporal frequencies

Boyer, Edmond

122

Blind source separation-semiparametric statistical approach  

Microsoft Academic Search

The semiparametric statistical model is used to formulate the problem of blind source separation. The method of estimating functions is applied to this problem. It is shown that an estimator of the mixing matrix or its learning version can be described in terms of an estimating function. The statistical efficiencies of these algorithms are studied. The main results are as

Shun-Ichi Amari; Jean-francois Cardoso

1997-01-01

123

Spatio-temporal radiation biology with conventionally or laser-accelerated particles for ELIMED  

NASA Astrophysics Data System (ADS)

The aim of this study is to investigate the behavior of radio-resistant human malignant cells, thus enabling better understanding of radiobiological effects of ions in such a case. Radiation sources such as accelerated continuous ion beams and laser technology-based ultra short radiation sources with energy of around 10 MeV will be used. The HTB140 melanoma cells are chosen since it has been shown that they represent the limit case of cellular radio-resistance among the studied tumor cell lines. These cells are particularly interesting as they provide data on the very edge of inactivation capacity of each beam line that is tested. After exposing the cell monolayers to continuous radiations of low (?-rays) and high (protons) linear energy transfer, the kinetics of disappearance of the phosphorylated histone H2AX (?-H2AX) foci per cell will be determined. The same procedure will be performed with the pulsed high dose rate protons. Detection and quantification of ?-H2AX foci will be performed by immunohistochemical 3D time-dependent imaging analyses using laser scanning confocal microscopy. Immunoblotting will enable the follow-up of the relation between ?-H2AX and cell cycle arrest via the p53/p21 pathway. In such a way the spatio-temporal changes on sub-cellular level will be visualized, quantified and compared. These results will show whether there is a difference in the effects on cells between continuous and pulsed irradiation mode. Therefore, they will contribute to the data base that might promote pulsed sources for medical treatments of malignant growths.

Risti?-Fira, A.; Bulat, T.; Keta, O.; Romano, F.; Cirrone, P.; Cuttone, G.; Petrovi?, I.

2013-07-01

124

Spatio-temporal radiation biology with conventionally or laser-accelerated particles for ELIMED  

SciTech Connect

The aim of this study is to investigate the behavior of radio-resistant human malignant cells, thus enabling better understanding of radiobiological effects of ions in such a case. Radiation sources such as accelerated continuous ion beams and laser technology-based ultra short radiation sources with energy of around 10 MeV will be used. The HTB140 melanoma cells are chosen since it has been shown that they represent the limit case of cellular radio-resistance among the studied tumor cell lines. These cells are particularly interesting as they provide data on the very edge of inactivation capacity of each beam line that is tested. After exposing the cell monolayers to continuous radiations of low (?-rays) and high (protons) linear energy transfer, the kinetics of disappearance of the phosphorylated histone H2AX (?-H2AX) foci per cell will be determined. The same procedure will be performed with the pulsed high dose rate protons. Detection and quantification of ?-H2AX foci will be performed by immunohistochemical 3D time-dependent imaging analyses using laser scanning confocal microscopy. Immunoblotting will enable the follow-up of the relation between ?-H2AX and cell cycle arrest via the p53/p21 pathway. In such a way the spatio-temporal changes on sub-cellular level will be visualized, quantified and compared. These results will show whether there is a difference in the effects on cells between continuous and pulsed irradiation mode. Therefore, they will contribute to the data base that might promote pulsed sources for medical treatments of malignant growths.

Risti?-Fira, A.; Bulat, T.; Keta, O.; Petrovi?, I. [Vin?a Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11001 Belgrade (Serbia)] [Vin?a Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522, 11001 Belgrade (Serbia); Romano, F.; Cirrone, P.; Cuttone, G. [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, via S. Sofia 62, Catania (Italy)] [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, via S. Sofia 62, Catania (Italy)

2013-07-26

125

Blind Source Separation of Multispectral Astronomical Images  

NASA Astrophysics Data System (ADS)

Multispectral images lead to classify pixels, but often with the drawback that each pixel value is the result of a combination of different sources. We examined the ability of Blind Source Separation (BSS) methods to restore the independent sources. We tested different tools on HST images of the Seyfert galaxy 3C120: the Karhunen-Loéve expansion based on the diagonalization of the cross correlation matrix, algorithms which maximize contrast functions and programs which take into account the cross correlation between shift sources. With the last tools we obtained similar decompositions corresponding mainly to real phenomena. BSS can be considered as an interesting exploratory tool for astronomical data mining.

Bijaoui, Albert; Nuzillard, Danielle

126

Quantitative image quality analysis of a nonlinear spatio-temporal filter  

Microsoft Academic Search

Digital temporal and spatial filtering of fluoroscopic image sequences can be used to improve the quality of images acquired at low X-ray exposure. In this study, we characterized a nonlinear edge preserving, spatio-temporal noise reduction filter, the bidirectional multistage (BMS) median filter of Arce (1991). To assess image quality, signal detection and discrimination experiments were performed on stationary targets using

Francisco J. Sánchez-marin; Yogesh Srinivas; Kadri N. Jabri; David L. Wilson

2001-01-01

127

A spatio-temporal database for diagnosing drought vulnerability in the Upper Colorado River Basin, Colorado  

Microsoft Academic Search

Effective drought planning and mitigation requires an understanding of water supply and demand, including historical biophysical and legal conditions that lead to water shortages among various end-users. With the goal of providing information that is useful for managing current drought risks and for adapting to changing climate, this project aims to fill the gaps in the knowledge about spatio-temporal variations

K. M. Sampson; O. Wilhelmi

2009-01-01

128

The Impact of Spatio-Temporal Constraints on Cursive Letter Handwriting in Children  

ERIC Educational Resources Information Center

The study assessed the impact of spatial and temporal constraints on handwriting movements in young children. One hundred children of 5-7 years of age of both genders were given the task of copying isolated cursive letters under four conditions: normal, with temporal, spatial, or spatio-temporal constraints. The results showed that imposing…

Chartrel, Estelle; Vinter, Annie

2008-01-01

129

On modeling of large-scale environments for solving spatio-temporal planning problems  

E-print Network

: the paper introduces a cognitively motivated approach for structuring and representing of unfamiliar large-scaleOn modeling of large-scale environments for solving spatio- temporal planning problems Inessa Seifert SFB TR 8/ Spatial Cognition, University of Bremen, Germany seifert@sfbtr8.uni-bremen.de Abstract

Bremen, Universität

130

Spatio-Temporal Analysis of Forest Fire Risk and Danger Using LANDSAT Imagery  

PubMed Central

Computing fire danger and fire risk on a spatio-temporal scale is of crucial importance in fire management planning, and in the simulation of fire growth and development across a landscape. However, due to the complex nature of forests, fire risk and danger potential maps are considered one of the most difficult thematic layers to build up. Remote sensing and digital terrain data have been introduced for efficient discrete classification of fire risk and fire danger potential. In this study, two time-series data of Landsat imagery were used for determining spatio-temporal change of fire risk and danger potential in Korudag forest planning unit in northwestern Turkey. The method comprised the following two steps: (1) creation of indices of the factors influencing fire risk and danger; (2) evaluation of spatio-temporal changes in fire risk and danger of given areas using remote sensing as a quick and inexpensive means and determining the pace of forest cover change. Fire risk and danger potential indices were based on species composition, stand crown closure, stand development stage, insolation, slope and, proximity of agricultural lands to forest and distance from settlement areas. Using the indices generated, fire risk and danger maps were produced for the years 1987 and 2000. Spatio-temporal analyses were then realized based on the maps produced. Results obtained from the study showed that the use of Landsat imagery provided a valuable characterization and mapping of vegetation structure and type with overall classification accuracy higher than 83%.

Sa?lam, Bülent; Bilgili, Ertu?rul; Durmaz, Bahar Dinç; Kad?o?ullar?, Ali ?hsan; Küçük, Ömer

2008-01-01

131

An integrated environment for spatio-temporal analysis, simulation, and representation for public health research  

NASA Astrophysics Data System (ADS)

Geographic space, as the arena within which all of the natural and social processes occur, and time, have become key research components of social science for the past two decades. However, most GIS software packages lack the predictive and analytic capabilities for complex problems, such as spatial statistical methods and spatial modeling. Meanwhile, the spatio-temporally explicit representation of complex, heterogeneous and dynamic geographic data sets is a particularly challenging issue. Many efforts have been made in developing tools for effective representation of health data, spatio-temporal analysis of the data, and the dynamic process simulation of disease transmission. To meet this demand, we attempted to develop a tool for integrating spatio-temporal analysis, simulation and representation of health data and processes. In this paper, we will introduce some methods for spatial temporal data analysis and their applications in public health. We'll describe the conceptual model of spatial temporal process simulation and the process-oriented spatio-temporal data model adopted in the tool we developed. After that, we'll present the framework of our integrated research toolkit, and demonstrate how to conduct analysis, modeling, and simulation with this software. Finally, we will discuss some issues for future studies.

Hu, Haitang; Bao, Shuming; Xu, Bing; Liang, Song

2006-10-01

132

Developmental regulation of spatio-temporal patterns of cortical circuit activation  

PubMed Central

Neural circuits are refined in an experience-dependent manner during early postnatal development. How development modulates the spatio-temporal propagation of activity through cortical circuits is poorly understood. Here we use voltage-sensitive dye imaging (VSD) to show that there are significant changes in the spatio-temporal patterns of intracortical signals in primary visual cortex (V1) from postnatal day 13 (P13), eye opening, to P28, the peak of the critical period for rodent visual cortical plasticity. Upon direct stimulation of layer 4 (L4), activity spreads to L2/3 and to L5 at all ages. However, while from eye opening to the peak of the critical period, the amplitude and persistence of the voltage signal decrease, peak activation is reached more quickly and the interlaminar gain increases with age. The lateral spread of activation within layers remains unchanged throughout the time window under analysis. These developmental changes in spatio-temporal patterns of intracortical circuit activation are mediated by differences in the contributions of excitatory and inhibitory synaptic components. Our results demonstrate that after eye opening the circuit in V1 is refined through a progression of changes that shape the spatio-temporal patterns of circuit activation. Signals become more efficiently propagated across layers through developmentally regulated changes in interlaminar gain. PMID:23316135

Griffen, Trevor C.; Wang, Lang; Fontanini, Alfredo; Maffei, Arianna

2013-01-01

133

Spatio-temporal Information in Intelligent Transportation Ouri Wolfson and Bo Xu  

E-print Network

Spatio-temporal Information in Intelligent Transportation Systems1 Ouri Wolfson and Bo Xu University of Illinois {wolfson, boxu}@cs.uic.edu The impact of Computer Science (CS) and Information) are some examples of the improvements in urban transportation brought by IT. The rapid advances in mobile

Wolfson, Ouri E.

134

On fitting spatio-temporal disease mapping models using approximate Bayesian inference.  

PubMed

Spatio-temporal disease mapping comprises a wide range of models used to describe the distribution of a disease in space and its evolution in time. These models have been commonly formulated within a hierarchical Bayesian framework with two main approaches: an empirical Bayes (EB) and a fully Bayes (FB) approach. The EB approach provides point estimates of the parameters relying on the well-known penalized quasi-likelihood (PQL) technique. The FB approach provides the posterior distribution of the target parameters. These marginal distributions are not usually available in closed form and common estimation procedures are based on Markov chain Monte Carlo (MCMC) methods. However, the spatio-temporal models used in disease mapping are often very complex and MCMC methods may lead to large Monte Carlo errors and a huge computation time if the dimension of the data at hand is large. To circumvent these potential inconveniences, a new technique called integrated nested Laplace approximations (INLA), based on nested Laplace approximations, has been proposed for Bayesian inference in latent Gaussian models. In this paper, we show how to fit different spatio-temporal models for disease mapping with INLA using the Leroux CAR prior for the spatial component, and we compare it with PQL via a simulation study. The spatio-temporal distribution of male brain cancer mortality in Spain during the period 1986-2010 is also analysed. PMID:24713158

Ugarte, María Dolores; Adin, Aritz; Goicoa, Tomas; Militino, Ana Fernandez

2014-12-01

135

Seasonal forcing drives spatio-temporal pattern formation in rabies epidemics  

E-print Network

Seasonal forcing drives spatio-temporal pattern formation in rabies epidemics Niels v. Festenberg1 of rabies dispersal. We reduce an established individual-based high- detail model down to a deterministic of epidemic wave fronts. Keywords: pattern formation, epidemics, rabies, seasonal forcing AMS classification

136

Estimating second-order characteristics of inhomogeneous spatio-temporal point processes  

E-print Network

distribution of the population at risk and systematic temporal variation in risk (Gabriel and Diggle, 2009, because the scientific objectives of the analysis are to understand and to model the underlying spatio-temporally interacting stochastic mechanisms. Generic methods for analysing such processes are growing; see for example

Boyer, Edmond

137

AN FPGA-BASED IMPLEMENTATION OF SPATIO-TEMPORAL OBJECT SEGMENTATION Kumara Ratnayake and Aishy Amer  

E-print Network

AN FPGA-BASED IMPLEMENTATION OF SPATIO-TEMPORAL OBJECT SEGMENTATION Kumara Ratnayake and Aishy Amer]@ece.concordia.ca ABSTRACT This paper proposes a robust real-time, scalable and modular Field Programmable Gate Array (FPGA on an actual hardware platform which consists of a frame grabber with a user programmable FPGA - Xilinx Virtex

Amer, Aishy

138

A Spatio-Temporal GIS Database for Monitoring Alpine Glacier Change  

E-print Network

A Spatio-Temporal GIS Database for Monitoring Alpine Glacier Change Jeremy L. Mennis Department Monitoring alpine glacier change has many practical and scientific benefits, including yielding information on glacier-fed water supplies, glacier-associated natural hazards, and climate variability. This paper

Mennis, Jeremy

139

A Fully Automated Content Based Video Search Engine Supporting Spatio-Temporal Queries  

Microsoft Academic Search

The rapidity with which digital information, particularlyvideo, is being gener- ated, has necessitated the development of tools for efficien t search of these media. Content based visual queries have been primarily focused on still image retrieval. In this paper, we propose a novel, interactive system on the W eb, based on the visual paradigm, with spatio-temporal attributes playinga key role

Shih-Fu Chang; William Chen; Horace J. Meng; Hari Sundaram

1997-01-01

140

Aspects of Spatio-Temporal Variability during Consonant Production by Greek Speakers with Hearing Impairment  

ERIC Educational Resources Information Center

This paper investigates spatio-temporal variability during the production of the lingual consonants /t, k, s, x, n, l, "r"/ by four Greek speakers with profound hearing impairment and with differences in the intelligibility of their speech. It examines important factors that have been documented to influence intelligibility, i.e. durational…

Nicolaidis, Katerina

2007-01-01

141

A Comparison of Neighbourhood Selection Techniques in Spatio-Temporal Forecasting Models  

NASA Astrophysics Data System (ADS)

Spatio-temporal neighbourhood (STN) selection is an important part of the model building procedure in spatio-temporal forecasting. The STN can be defined as the set of observations at neighbouring locations and times that are relevant for forecasting the future values of a series at a particular location at a particular time. Correct specification of the STN can enable forecasting models to capture spatio-temporal dependence, greatly improving predictive performance. In recent years, deficiencies have been revealed in models with globally fixed STN structures, which arise from the problems of heterogeneity, nonstationarity and nonlinearity in spatio-temporal processes. Using the example of a large dataset of travel times collected on London's road network, this study examines the effect of various STN selection methods drawn from the variable selection literature, varying from simple forward/backward subset selection to simultaneous shrinkage and selection operators. The results indicate that STN selection methods based on L1 penalisation are effective. In particular, the maximum concave penalty (MCP) method selects parsimonious models that produce good forecasting performance.

Haworth, J.; Cheng, T.

2014-11-01

142

Predicting spatio-temporal variability in fire return intervals using a topographic roughness index  

E-print Network

roughness index; Surface measures; Fire history; Mean fire return interval; Disturbance; Landscape; ModelPredicting spatio-temporal variability in fire return intervals using a topographic roughness index Michael C. Stambaugh *, Richard P. Guyette Missouri Tree-Ring Laboratory, Department of Forestry, 203

Stambaugh, Michael C

143

FROM SINGLE POINT GAUGE TO SPATIO-TEMPORAL MEASUREMENT OF OCEAN WAVES PROSPECTS AND PERSPECTIVES  

E-print Network

FROM SINGLE POINT GAUGE TO SPATIO-TEMPORAL MEASUREMENT OF OCEAN WAVES ­ PROSPECTS AND PERSPECTIVES With the recent advancement of spatial measurements of ocean waves, we are clearly facing new challenges regarding world of truly spatial ocean waves. INTRODUCTION Since the first successful development of a wave gauge

144

Design and implementation of spatio-temporal database of water and soil loss  

NASA Astrophysics Data System (ADS)

This paper analyzed the features and limitations of several typical spatio-temporal data models. "spatio-temporal cube": the main disadvantage is that the target change will produce great data redundancy when under non-consecutive circumstances. "Snapshots": it repeatedly saves graphics and attribute of no changes which resulted in waste of storage spaces, and it is impossible to reflect space objects under the same domain and the relationship between the attributes. "Base State with Amendments": merely modify changing object, but it's not suitable for continuous variation space object. "space-frame composite": currently, the model is lacking of sound framework structure and application model. "Object-oriented spatio-temporal model": The modeling concept, theoretical foundation and technical realization has not yet reached a consensus, it's not mature enough. In allusion to the features of the spatial database of water and soil loss, this essay expounded the characteristics of spatiotemporal databases. Spatial features in many practical circumstances ( such as thematic maps in soil and water conservation projects and space elements of soil erosion distribution map) have spatial data features, and also change with time, consequently, required us to establish spatio-temporal database, STDB, which can capture time data and space data at the same time. This analysis based on "ArcSDE versioning mechanisms" temporal and spatial database implement technologies, discussed the construction methods, process and data features of the database, and introduced the implementation of historical data rebuilding and version merging.

Lu, XinHai; Bian, Fulin; Tan, Xiaojun

2008-12-01

145

The electromagnetic fields and the radiation of a spatio-temporally varying electric current loop  

E-print Network

The electric and magnetic fields of a spatio-temporally varying electric current loop are calculated using the Jefimenko equations. The radiation and the nonradiation parts of the electromagnetic fields are derived in the framework of Maxwell's theory of electromagnetic fields. In this way, a new, exact, analytical solution of the Maxwell equation is found.

Markus Lazar

2013-04-12

146

Detection of Aircrafts on a Collision Course using Spatio-Temporal HOG*  

E-print Network

Detection of Aircrafts on a Collision Course using Spatio-Temporal HOG* Artem Rozantsev (artem. #12;Abstract. We have developed a method for the detection of both generic flight neighbouring for the detection of aircrafts on a collision path. We evaluated our approach for the detection of both small

Candea, George

147

Spatio-Temporal Analysis for Parameterizing Animated Lines Bert Buchholz1  

E-print Network

formulation of the problem as a parameterization of the space-time surface swept by a 2D line duringSpatio-Temporal Analysis for Parameterizing Animated Lines Bert Buchholz1 Noura Faraj1 Sylvain a temporally consistent parameterization for lines extracted from an animated 3D scene. Abstract We describe

Boubekeur, Tamy

148

Video coding with spatio-temporal texture synthesis and edge-based inpainting  

Microsoft Academic Search

This paper proposes a video coding scheme, in which textural and structural regions are selectively removed in the encoder, and restored in the decoder by spatio-temporal texture synthesis and edge-based inpainting. In the proposed scheme, two types of regions are classified based on two motion models: local motion and global motion. In local motion regions, conventional block- based motion estimation

Chunbo Zhu; Xiaoyan Sun; Feng Wu; Houqiang Li

2008-01-01

149

Statistical Analysis of Spatio-temporal Variations of Sea Surface Height Observed by Topex Altimeter  

NASA Technical Reports Server (NTRS)

Using non-gridded Topex altimeter data, high resolution 2-d power spectra and spatio-temporal autocorrelation functions of sea surface height (SSH) variations are estimated and employed for studying anisotropic SSH fields varying in a broad range of scales.

Fabrikant, A.; Glazman, R. E.; Greysukh, A.

1994-01-01

150

Spatio-temporal segmentation of mesoscale ocean surface dynamics using satellite data  

E-print Network

Spatio-temporal segmentation of mesoscale ocean surface dynamics using satellite data Pierre Tandeo, Ronan Fablet and Ren´e Garello Institut Mines-Telecom - Telecom Bretagne CNRS UMR 6285 LabSTICC - P-temporal segmentation of the upper ocean dynamics. I. INTRODUCTION In the last two decades, multi-satellite measurements

Paris-Sud XI, Université de

151

Panda: A Predictive Spatio-Temporal Query Processor Abdeltawab M. Hendawi Mohamed F. Mokbel  

E-print Network

Panda: A Predictive Spatio-Temporal Query Processor Abdeltawab M. Hendawi Mohamed F. Mokbel, mokbel}@cs.umn.edu ABSTRACT This paper presents the Panda system for efficient support of a wide variety, Panda targets long-term query prediction as it relies on adapting a well-designed long-term prediction

Mokbel, Mohamed F.

152

Impacts of demographic and socioeconomic factors on spatio-temporal dynamics of panda habitat  

E-print Network

-1 Impacts of demographic and socioeconomic factors on spatio-temporal dynamics of panda habitat LI 2004 Key words: Agent-based modeling, Giant panda conservation, Households, Human demography-temporal dynamics of wildlife habitat and local biodiversity. In the Wolong Nature Reserve (China) for giant panda

153

The Auckland volcanic field, New Zealand: Geophysical evidence for structural and spatio-temporal relationships  

Microsoft Academic Search

Geophysical data from the monogenetic Auckland volcanic field reveal complex structural and spatio-temporal relationships at different scales. The volcanic field is coincident with regional magnetic and gravity anomalies that mark a major crustal suture and with a discontinuity marking a significant structural asperity. Here, the linear regional magnetic anomaly splays into a wide band of NNW-trending lineaments, arising from serpentinised

John Cassidy; Corinne A. Locke

2010-01-01

154

Latent Spatio-temporal Models for Action Localization and Recognition in Nursing Home Surveillance Video  

E-print Network

Latent Spatio-temporal Models for Action Localization and Recognition in Nursing Home Surveillance- velop an algorithm to detect events of interest, partic- ularly falls by elderly residents in monitoring residents in long-term care facilities ­ detecting actions, particularly falls by resi- dents

Mori, Greg

155

Spatio-temporal genetic variability in sea trout (Salmo trutta) populations from north-western Spain  

E-print Network

Spatio-temporal genetic variability in sea trout (Salmo trutta) populations from north variation at five microsatellite loci was investigated in six sea trout (Salmo trutta) populations, sea trout Introduction The brown trout (Salmo trutta L.) presents two alternative life strategies

Posada, David

156

A Generalized Low-Rank Appearance Model for Spatio-Temporally Correlated Rain Streaks  

E-print Network

A Generalized Low-Rank Appearance Model for Spatio-Temporally Correlated Rain Streaks Yi-Lei Chen rain streaks, just exploit the repeatability/similarity of rain steaks taken in the same scene! Our advantages:(1) no pre-processing (e.g., rain detection); (2) training-free (e.g., dictionary learning

Hsu, Chiou-Ting Candy

157

LEFT ENDOCARDIUM SEGMENTATION USING SPATIO-TEMPORAL METAMORPHS , Shaoting Zhang1  

E-print Network

LEFT ENDOCARDIUM SEGMENTATION USING SPATIO-TEMPORAL METAMORPHS Xinyi Cui1 , Shaoting Zhang1, Bethlehem, PA, USA 4 Radiology Department, New York University, New York, NY, USA ABSTRACT The Metamorphs. The standard Metamorphs model does not encode temporal information. Thus it is not effective in segmenting time

Huang, Junzhou

158

Scaling, universality and spatio-temporal clustering in seismicity and rock fracture phenomena  

Microsoft Academic Search

In this talk, I will discuss new methods from nonlinear sciences and complex network theory to characterize temporal and spatio-temporal clustering of point processes with a particular focus on their application to seismicity and rock fracture. Many striking features of natural processes can be portrayed as patterns or clusters of localized events. A generic attribute in all these cases is

J. Davidsen

2007-01-01

159

NextPlace: A Spatio-Temporal Prediction Framework for Pervasive Systems  

E-print Network

based on nonlinear time series analysis of the arrival and residence times of users in relevant places series analysis [12] for forecasting user behavior in different locations from a spatio-temporal point to a back-end server, where analysis of the data can be per- formed at run-time in order to predict future

Hand, Steven

160

SPATIO-TEMPORAL VIDEO INTERPOLATION AND DENOISING USING MOTION-ASSISTED STEERING KERNEL (MASK) REGRESSION  

E-print Network

SPATIO-TEMPORAL VIDEO INTERPOLATION AND DENOISING USING MOTION-ASSISTED STEERING KERNEL (MASK propose a motion- assisted steering kernel (MASK) suitable for interpolating video data spatially interpolation are: edge jaggedness, ringing, blurring of edges and texture detail, motion blur and/or judder

Milanfar, Peyman

161

Cortical Spatio-Temporal Dynamics Underlying Phonological Target Detection in Humans  

ERIC Educational Resources Information Center

Selective processing of task-relevant stimuli is critical for goal-directed behavior. We used electrocorticography to assess the spatio-temporal dynamics of cortical activation during a simple phonological target detection task, in which subjects press a button when a prespecified target syllable sound is heard. Simultaneous surface potential…

Chang, Edward F.; Edwards, Erik; Nagarajan, Srikantan S.; Fogelson, Noa; Dalal, Sarang S.; Canolty, Ryan T.; Kirsch, Heidi E.; Barbaro, Nicholas M.; Knight, Robert T.

2011-01-01

162

SPATIO-TEMPORAL DISTRIBUTION OF PLASMODIUM FALCIPARUM AND P. VIVAX MALARIA IN THAILAND  

E-print Network

SPATIO-TEMPORAL DISTRIBUTION OF PLASMODIUM FALCIPARUM AND P. VIVAX MALARIA IN THAILAND GUOFA ZHOU of Medical Sciences, United States Army Military Component, Bangkok, Thailand Abstract. Malaria incidence data at the district level from 1997 to 2002 and total malaria case data from 1965 to 2002 in Thailand

163

Forecast Oriented Classification of Spatio-Temporal Extreme Events Zhengzhang Chen1,  

E-print Network

Forecast Oriented Classification of Spatio-Temporal Extreme Events Zhengzhang Chen1, , Yusheng Xie1 , Yu Cheng1 ,Kunpeng Zhang1 , Ankit Agrawal1 , Wei-keng Liao1 , Nagiza F. Samatova2 , Alok Choudhary1 1 zhengzhang.chen@northwestern.edu Abstract In complex dynamic systems, accurate forecast- ing of extreme

164

Ocean Wave Reconstruction Algorithms Based on Spatio-temporal Data Acquired by a Flash LIDAR Camera  

E-print Network

Ocean Wave Reconstruction Algorithms Based on Spatio-temporal Data Acquired by a Flash LIDAR Camera made with a high frequency ASC Flash LIDAR camera. We assume that the camera is mounted on a vessel, and simulated LIDAR data sets are constructed by performing geometric in- tersections of laser rays with each

Grilli, Stéphan T.

165

Title of dissertation: Spatio-Temporal Dynamics of the Magnetosphere during Geospace Storms  

E-print Network

ABSTRACT Title of dissertation: Spatio-Temporal Dynamics of the Magnetosphere during Geospace magnetospheric dynamics driven by solar wind inputs. In this thesis, the techniques of phase space reconstruction compiled to enable accurate modeling of the magnetosphere during intense geospace storms. The main

Gruner, Daniel S.

166

Spatio-temporal distribution of interplate coupling in southwest Japan deduced from inversion analysis  

Microsoft Academic Search

We obtain the spatio-temporal distribution of the slip on the subduction interface of the Nankai trough over an entire earthquake cycle, using geodetic data (including leveling, triangulation and trilateration, sea level, and GPS surveys) observed during the last 100 years in southwest Japan. We develop a new inversion method that can treat the long-term crustal deformations, the coseismic earthquake displacements

T. Ito; M. Hashimoto

2003-01-01

167

Effects of Spatio-Temporal Aliasing on Pilot Performance in Active Control Tasks  

NASA Technical Reports Server (NTRS)

Spatio-temporal aliasing affects pilot performance and control behavior. For increasing refresh rates: 1) Significant change in control behavior: a) Increase in visual gain and neuromuscular frequency. b) Decrease in visual time delay. 2) Increase in tracking performance: a) Decrease in RMSe. b) Increase in crossover frequency.

Zaal, Peter; Sweet, Barbara

2010-01-01

168

Analyzing the Potential of Microblogs for Spatio-Temporal Popularity Estimation of Music Artists  

E-print Network

Analyzing the Potential of Microblogs for Spatio-Temporal Popularity Estimation of Music Artists- search, namely popularity estimation of music artists. The research questions addressed are the following: To which extent are microblogs used to communicate music listening behavior? Are there differences between

Widmer, Gerhard

169

Spatio-Temporal and Events Based Analysis of Topic Popularity in Twitter  

E-print Network

and spatial behavior of popular topics and support our hypotheses by showing that non-popular topics displaySpatio-Temporal and Events Based Analysis of Topic Popularity in Twitter Sebastien Ardon Amitabha- lion topics that include both popular and less popular to- pics. On a data set containing approximately

Bagchi, Amitabha

170

Multi-robot routing for servicing spatio-temporal requests: A musically inspired problem  

E-print Network

, an autonomous structure assembly system, or a car manufacturing system, may require multiple robots to serviceMulti-robot routing for servicing spatio-temporal requests: A musically inspired problem Smriti.chopra, magnus}@ece.gatech.edu) Abstract: In this paper, we consider the problem of routing multiple robots

Egerstedt, Magnus

171

Spatio-temporal community structure of peat bog benthic desmids on a microscale  

E-print Network

Spatio-temporal community structure of peat bog benthic desmids on a microscale Jiri´ Neustupa- scale transects were delimited at 4 temperate lowland peat bog localities to investigate spatial represented by dynamics of the common species. Keywords Desmidiales Á Microscale Á Microphytobenthos Á Peat

172

Composite Spatio-Temporal Event Detection in Multi-Camera Surveillance Networks  

E-print Network

Composite Spatio-Temporal Event Detection in Multi-Camera Surveillance Networks Yun Zhai, Ying, we present a composite event detection system for multi- camera surveillance networks. The proposed and affordable. Multi-camera surveil- lance systems require an intelligent framework for effectively extracting

Paris-Sud XI, Université de

173

Spatio-temporal analysis of nucleate pool boiling: identication of nucleation sites using non-orthogonal  

E-print Network

Spatio-temporal analysis of nucleate pool boiling: identi®cation of nucleation sites using non techniques. These limitations are especially evident in nucleate boiling. This paper investigates the analysis of a sequence of temperature ®elds obtained from a pool nucleate boiling experiment. Spatio

Stevenson, Paul

174

Spatio-temporal parameters of gait measured by an ambulatory system using miniature gyroscopes  

Microsoft Academic Search

In this study we describe an ambulatory system for estimation of spatio-temporal parameters during long periods of walking. This original method based on wavelet analysis is proposed to compute the values of temporal gait parameters from the angular velocity of lower limbs. Based on a mechanical model, the medio-lateral rotation of the lower limbs during stance and swing, the stride

K. Aminian; B. Najafi; C. Büla; P.-F. Leyvraz; Ph. Robert

2002-01-01

175

The design and realization of a socio-economic statistical spatio-temporal database  

NASA Astrophysics Data System (ADS)

This paper aims to introduce a case of Socio-economic statistical Spatio-temporal Database. This database system services in the rural socio-economic statistical work, which is a combination of statistical tables, spatial data, search algorithm and maintenance interface. Administrative codes are the conjunction media of spatial data and attribute data, and also are the key words of database query processing. Through storing the changing information in the database, it could reflect the change of administrative divisions. As the main issues of database design, the studying of the approach to recording and querying these changes as well as the processing of statistical data by the rules of administrative divisions changes, requires a large amount of research work. To address these problems, a series of management analysis tools have been developed to deal with the processing of socio-economic statistical data with changes in the administrative division. A searching algorithm of spatio-temporal database is used to ensure the comparability of the results, which are acquired by the positive sequence and the anti-sequence temporal query under complex spatial changes in the administrative division. According to the spatial changes, searching algorithm of spatio-temporal database mainly translates temporal series statistical data into standard format data which is matched to the benchmark year. The searching algorithm controls the process of inquiry through recursion of the table of the administrative code changes, which are composed of multi-way tree structure and double linked list and record the relationship between upper and lower level administrative units. These search algorithms and meta-data storage structures constitute the spatio-temporal database, so as to serve the spatial analysis of statistical data. The comparability problem mentioned above was well solved by this approach. And a set of functions was provided by this system with spatio-temporal database, such as specialization of statistical data, temporal query, spatial data which can be automatically updated, and maintenance interface.

Yang, Cankun; Li, Xiaojuan; Liu, Qiang; Zhao, Huimin; Zhang, Jia; Zhang, Haibo

2010-11-01

176

Annotating spatio-temporal datasets for meaningful analysis in the Web  

NASA Astrophysics Data System (ADS)

More and more environmental datasets that vary in space and time are available in the Web. This comes along with an advantage of using the data for other purposes than originally foreseen, but also with the danger that users may apply inappropriate analysis procedures due to lack of important assumptions made during the data collection process. In order to guide towards a meaningful (statistical) analysis of spatio-temporal datasets available in the Web, we have developed a Higher-Order-Logic formalism that captures some relevant assumptions in our previous work [1]. It allows to proof on meaningful spatial prediction and aggregation in a semi-automated fashion. In this poster presentation, we will present a concept for annotating spatio-temporal datasets available in the Web with concepts defined in our formalism. Therefore, we have defined a subset of the formalism as a Web Ontology Language (OWL) pattern. It allows capturing the distinction between the different spatio-temporal variable types, i.e. point patterns, fields, lattices and trajectories, that in turn determine whether a particular dataset can be interpolated or aggregated in a meaningful way using a certain procedure. The actual annotations that link spatio-temporal datasets with the concepts in the ontology pattern are provided as Linked Data. In order to allow data producers to add the annotations to their datasets, we have implemented a Web portal that uses a triple store at the backend to store the annotations and to make them available in the Linked Data cloud. Furthermore, we have implemented functions in the statistical environment R to retrieve the RDF annotations and, based on these annotations, to support a stronger typing of spatio-temporal datatypes guiding towards a meaningful analysis in R. [1] Stasch, C., Scheider, S., Pebesma, E., Kuhn, W. (2014): "Meaningful spatial prediction and aggregation", Environmental Modelling & Software, 51, 149-165.

Stasch, Christoph; Pebesma, Edzer; Scheider, Simon

2014-05-01

177

Waveform-preserving blind estimation of multiple independent sources  

Microsoft Academic Search

The problem of blind estimation of source signals is to estimate the source signals without knowing the characteristics of the transmission channel. It is shown that the minimum-variance unbiased estimates can be obtained if and only if the transmission channel can be identified blindly. It is shown that the channel can be blindly identified if and only if there is

Lang Tong; Yujiro Inouye; Ruey-wen Liu

1993-01-01

178

Spatio-temporal variation in Helicoverpa egg parasitism by Trichogramma in a tropical Bt-transgenic cotton landscape  

Technology Transfer Automated Retrieval System (TEKTRAN)

Understanding the spatio-temporal dynamics of insects in agroecosystems is crucial when developing effective management strategies that emphasise biological control of pests. Wild populations of Trichogramma Westwood egg parasitoids are utilised for biological suppression of the potentially resistan...

179

A Framework of Incorporating Spatio-temporal Forecast in Look-ahead Grid Dispatch with Photovoltaic Generation  

E-print Network

case is used to quantify the value of improved forecast quality through the reduction of system dispatch cost. The Modified spatio-temporal forecast model which has the least forecast PV overestimate percentage shows the best performance in the dispatch...

Yang, Chen

2013-05-02

180

Spatio-temporal urban landscape change analysis using the Markov chain model and a modified genetic algorithm  

E-print Network

Spatio-temporal urban landscape change analysis using the Markov chain model and a modified genetic from a modified genetic algorithm (GA). Model performance was evaluated between the empirical landscape

Wang, Le

181

Spatio-temporal analysis in functional brain imaging  

E-print Network

Localizing sources of activity from electroencephalography (EEG) and magnetoencephalography (MEG) measurements involves solving an ill-posed inverse problem, where infinitely many source distribution patterns can give rise ...

Ou, Wanmei

2010-01-01

182

Visual pattern recognition based on spatio-temporal patterns of retinal ganglion cells' activities.  

PubMed

Neural information is processed based on integrated activities of relevant neurons. Concerted population activity is one of the important ways for retinal ganglion cells to efficiently organize and process visual information. In the present study, the spike activities of bullfrog retinal ganglion cells in response to three different visual patterns (checker-board, vertical gratings and horizontal gratings) were recorded using multi-electrode arrays. A measurement of subsequence distribution discrepancy (MSDD) was applied to identify the spatio-temporal patterns of retinal ganglion cells' activities in response to different stimulation patterns. The results show that the population activity patterns were different in response to different stimulation patterns, such difference in activity pattern was consistently detectable even when visual adaptation occurred during repeated experimental trials. Therefore, the stimulus pattern can be reliably discriminated according to the spatio-temporal pattern of the neuronal activities calculated using the MSDD algorithm. PMID:21886670

Jing, Wei; Liu, Wen-Zhong; Gong, Xin-Wei; Gong, Hai-Qing; Liang, Pei-Ji

2010-09-01

183

Visual pattern recognition based on spatio-temporal patterns of retinal ganglion cells’ activities  

PubMed Central

Neural information is processed based on integrated activities of relevant neurons. Concerted population activity is one of the important ways for retinal ganglion cells to efficiently organize and process visual information. In the present study, the spike activities of bullfrog retinal ganglion cells in response to three different visual patterns (checker-board, vertical gratings and horizontal gratings) were recorded using multi-electrode arrays. A measurement of subsequence distribution discrepancy (MSDD) was applied to identify the spatio-temporal patterns of retinal ganglion cells’ activities in response to different stimulation patterns. The results show that the population activity patterns were different in response to different stimulation patterns, such difference in activity pattern was consistently detectable even when visual adaptation occurred during repeated experimental trials. Therefore, the stimulus pattern can be reliably discriminated according to the spatio-temporal pattern of the neuronal activities calculated using the MSDD algorithm. PMID:21886670

Jing, Wei; Liu, Wen-Zhong; Gong, Xin-Wei; Gong, Hai-Qing

2010-01-01

184

DSTiPE Algorithm for Fuzzy Spatio-Temporal Risk Calculation in Wireless Environments  

SciTech Connect

Time and location data play a very significant role in a variety of factory automation scenarios, such as automated vehicles and robots, their navigation, tracking, and monitoring, to services of optimization and security. In addition, pervasive wireless capabilities combined with time and location information are enabling new applications in areas such as transportation systems, health care, elder care, military, emergency response, critical infrastructure, and law enforcement. A person/object in proximity to certain areas for specific durations of time may pose a risk hazard either to themselves, others, or the environment. This paper presents a novel fuzzy based spatio-temporal risk calculation DSTiPE method that an object with wireless communications presents to the environment. The presented Matlab based application for fuzzy spatio-temporal risk cluster extraction is verified on a diagonal vehicle movement example.

Kurt Derr; Milos Manic

2008-09-01

185

Sensing Solutions for Collecting Spatio-Temporal Data for Wildlife Monitoring Applications: A Review  

PubMed Central

Movement ecology is a field which places movement as a basis for understanding animal behavior. To realize this concept, ecologists rely on data collection technologies providing spatio-temporal data in order to analyze movement. Recently, wireless sensor networks have offered new opportunities for data collection from remote places through multi-hop communication and collaborative capability of the nodes. Several technologies can be used in such networks for sensing purposes and for collecting spatio-temporal data from animals. In this paper, we investigate and review technological solutions which can be used for collecting data for wildlife monitoring. Our aim is to provide an overview of different sensing technologies used for wildlife monitoring and to review their capabilities in terms of data they provide for modeling movement behavior of animals. PMID:23666132

Baratchi, Mitra; Meratnia, Nirvana; Havinga, Paul J. M.; Skidmore, Andrew K.; Toxopeus, Bert A. G.

2013-01-01

186

Meteorological factors-based spatio-temporal mapping and predicting malaria in central China.  

PubMed

Despite significant reductions in the overall burden of malaria in the 20th century, this disease still represents a significant public health problem in China, especially in central areas. Understanding the spatio-temporal distribution of malaria is essential in the planning and implementing of effective control measures. In this study, normalized meteorological factors were incorporated in spatio-temporal models. Seven models were established in WinBUGS software by using Bayesian hierarchical models and Markov Chain Monte Carlo methods. M?, M?, and M? modeled separate meteorological factors, and M?, which modeled rainfall performed better than M? and M?, which modeled average temperature and relative humidity, respectively. M? was the best fitting models on the basis of based on deviance information criterion and predicting errors. The results showed that the way rainfall influencing malaria incidence was different from other factors, which could be interpreted as rainfall having a greater influence than other factors. PMID:21896823

Huang, Fang; Zhou, Shuisen; Zhang, Shaosen; Zhang, Hongwei; Li, Weidong

2011-09-01

187

A spatio-temporal model of housing prices based on individual sales transactions over time  

NASA Astrophysics Data System (ADS)

A spatio-temporal model of housing price trends is developed that focuses on individual housing sales over time. The model allows for both the spatio-temporal lag effects of previous sales in the vicinity of each housing sale, and for general autocorrelation effects over time. A key feature of this model is the recognition of the unequal spacing between individual housing sales over time. Hence the residuals are modeled as a first-order autoregressive process with unequally spaced events. The maximum-likelihood estimation of this model is developed in detail, and tested in terms of simulations based on selected data. In addition, the model is applied to a small data set in the Philadelphia area.

Smith, Tony E.; Wu, Peggy

2009-12-01

188

Multi-antenna spectrum sensing by exploiting spatio-temporal correlation  

NASA Astrophysics Data System (ADS)

In this paper, we propose a novel mechanism for spectrum sensing that leads us to exploit the spatio-temporal correlation present in the received signal at a multi-antenna receiver. For the proposed mechanism, we formulate the spectrum sensing scheme by adopting the generalized likelihood ratio test (GLRT). However, the GLRT degenerates in the case of limited sample support. To circumvent this problem, several extensions are proposed that bring robustness to the GLRT in the case of high dimensionality and small sample size. In order to achieve these sample-efficient detection schemes, we modify the GLRT-based detector by exploiting the covariance structure and factoring the large spatio-temporal covariance matrix into spatial and temporal covariance matrices. The performance of the proposed detectors is evaluated by means of numerical simulations, showing important advantages over existing detectors.

Ali, Sadiq; Ramírez, David; Jansson, Magnus; Seco-Granados, Gonzalo; López-Salcedo, José A.

2014-12-01

189

Spatio-temporal pattern of viral meningitis in Michigan, 1993-2001  

NASA Astrophysics Data System (ADS)

To characterize Michigan's high viral meningitis incidence rates, 8,803 cases from 1993-2001 were analyzed for standard epidemiological indices, geographic distribution, and spatio-temporal clusters. Blacks and infants were found to be high-risk groups. Annual seasonality and interannual variability in epidemic magnitude were apparent. Cases were concentrated in southern Michigan, and cumulative incidence was correlated with population density at the county level (r=0.45, p<0.001). Kulldorff's Scan test identified the occurrence of spatio-temporal clusters in Lower Michigan during July-October 1998 and 2001 (p=0.01). More extensive data on cases, laboratory isolates, sociodemographics, and environmental exposures should improve detection and enhance the effectiveness of a Space-Time Information System aimed at prevention.

Greene, Sharon K.; Schmidt, Mark A.; Stobierski, Mary Grace; Wilson, Mark L.

2005-05-01

190

Kronecker PCA based spatio-temporal modeling of video for dismount classification  

NASA Astrophysics Data System (ADS)

We consider the application of KronPCA spatio-temporal modeling techniques1, 2 to the extraction of spatiotemporal features for video dismount classification. KronPCA performs a low-rank type of dimensionality reduction that is adapted to spatio-temporal data and is characterized by the T frame multiframe mean ? and covariance ? of p spatial features. For further regularization and improved inverse estimation, we also use the diagonally corrected KronPCA shrinkage methods we presented in.1 We apply this very general method to the modeling of the multivariate temporal behavior of HOG features extracted from pedestrian bounding boxes in video, with gender classification in a challenging dataset chosen as a specific application. The learned covariances for each class are used to extract spatiotemporal features which are then classified, achieving competitive classification performance.

Greenewald, Kristjan H.; Hero, Alfred O.

2014-06-01

191

Activity Changes Induced by Spatio-Temporally Correlated Stimuli in Cultured Cortical Networks  

NASA Astrophysics Data System (ADS)

Activity-dependent plasticity probably plays a key role in learning and memory in biological information processing systems. Though long-term potentiation and depression have been extensively studied in the filed of neuroscience, little is known on the mechanisms for integrating these modifications on network-wide activity changes. In this report, we studied effects of spatio-temporally correlated stimuli on the neuronal network activity. Rat cortical neurons were cultured on substrates with 64 embedded micro-electrodes and the evoked responses were extracellularly recorded and analyzed. We compared spatio-temporal patterns of the responses between before and after repetitive application of correlated stimuli. After the correlated stimuli, the networks showed significantly different responses from those in the initial states. The modified activity reflected structures of the repeatedly applied correlated stimuli. The results suggested that spatiotemporally correlated inputs systematically induced modification of synaptic strengths in neuronal networks, which could serve as an underlying mechanism of associative memory.

Takayama, Yuzo; Moriguchi, Hiroyuki; Jimbo, Yasuhiko

192

Soil respiration and microbial biomass in a savanna parkland landscape: spatio-temporal variation and environmental controls  

E-print Network

microbial biomass nitrogen . . . . . . . 10 Spatio-temporal variation in potential carbon mineralization rates . 30 33 34 11 Spatio-temporal variation in potential N-mineralization and nitrification rates... concentration) are known to influence rates of microbial activity (Schimel et al. 1994, Zak et al. 1994, Scott er al. 1996) as well as the diffusivity of trace gases through the soil column (Buyanovsky and Wagner 1995, Zepp et al. 1996). In addition...

McCulley, Rebecca Lynne

1998-01-01

193

Spatio-temporal Transmission and Environmental Determinants of Schistosomiasis Japonica in Anhui Province, China  

PubMed Central

Background Schistosomiasis japonica still remains of public health and economic significance in China, especially in the lake and marshland areas along the Yangtze River Basin, where the control of transmission has proven difficult. In the study, we investigated spatio-temporal variations of S. japonicum infection risk in Anhui Province and assessed the associations of the disease with key environmental factors with the aim of understanding the mechanism of the disease and seeking clues to effective and sustainable schistosomiasis control. Methodology/Principal Findings Infection data of schistosomiasis from annual conventional surveys were obtained at the village level in Anhui Province, China, from 2000 to 2010 and used in combination with environmental data. The spatio-temporal kriging model was used to assess how these environmental factors affected the spatio-temporal pattern of schistosomiasis risk. Our results suggested that seasonal variation of the normalized difference vegetation index (NDVI), seasonal variation of land surface temperature at daytime (LSTD), and distance to the Yangtze River were negatively significantly associated with risk of schistosomiasis. Predictive maps showed that schistosomiasis prevalence remained at a low level and schistosomiasis risk mainly evolved along the Yangtze River. Schistosomiasis risk also followed a focal spatial pattern, fluctuating temporally with a peak (the largest spatial extent) in 2005 and then contracting gradually but with a scattered distribution until 2010. Conclusion The fitted spatio-temporal kriging model can capture variations of schistosomiasis risk over space and time. Combined with techniques of geographic information system (GIS) and remote sensing (RS), this approach facilitates and enriches risk modeling of schistosomiasis, which in turn helps to identify prior areas for effective and sustainable control of schistosomiasis in Anhui Province and perhaps elsewhere in China. PMID:25659112

Hu, Yi; Li, Rui; Bergquist, Robert; Lynn, Henry; Gao, Fenghua; Wang, Qizhi; Zhang, Shiqing; Sun, Liqian; Zhang, Zhijie; Jiang, Qingwu

2015-01-01

194

Spatio-temporal structure of the wave packets generated by the solar terminator  

Microsoft Academic Search

Using long-term (1998--2009) total electron content (TEC) measurements from the GPS global network including dense network of GPS sites in USA and Japan, we have obtained the first data regarding the spatio-temporal structure and the statistics of medium-scale traveling wave packets (MS TWPs) excited by the solar terminator (ST). Total amount of the detected TWPs exceeds 565,000. There is no

E. L. Afraimovich; I. K. Edemskiy; S. V. Voeykov; Yu. V. Yasyukevich; I. V. Zhivetiev

2009-01-01

195

NextPlace: A Spatio-temporal Prediction Framework for Pervasive Systems  

Microsoft Academic Search

\\u000a Accurate and fine-grained prediction of future user location and geographical profile has interesting and promising applications\\u000a including targeted content service, advertisement dissemination for mobile users, and recreational social networking tools\\u000a for smart-phones. Existing techniques based on linear and probabilistic models are not able to provide accurate prediction\\u000a of the location patterns from a spatio-temporal perspective, especially for long-term estimation. More

Salvatore Scellato; Mirco Musolesi; Cecilia Mascolo; Vito Latora; Andrew T. Campbell

196

Spatio-temporal dynamics of Quercus faginea forests in the Spanish Central Pre-Pyrenees  

Microsoft Academic Search

Anthropomorphic changes in land use have extensively modified natural forests in the European countries over the twentieth\\u000a century. This yielded a decline in the number of plant species and fragmentation of their populations. Understanding of the\\u000a impact of land use changes on the spatio-temporal dynamics of forest species is essential to the ecological sustainability\\u000a of the natural forests in the

Yacine KoubaConcepcion; Concepción L. Alados

197

The Cluster Spatio-Temporal Analysis of Field Fluctuations (STAFF) Experiment  

Microsoft Academic Search

The Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment is one of five experiments which together comprise the Wave Experiment Consortium (WEC). STAFF consists of a three-axis search coil magnetometer to measure magnetic fluctuations at frequencies up to 4 kHz, and a spectrum analyser to calculate in near-real time aboard the spacecraft, the complete auto- and cross-spectral matrices using the three

N. Cornilleau-Wehrlin; P. Chauveau; S. Louis; A. Meyer; J. M. Nappa; S. Perraut; L. Rezeau; P. Robert; A. Roux; C. De Villedary; Y. De Conchy; L. Friel; C. C. Harvey; D. Hubert; C. Lacombe; R. Manning; F. Wouters; F. Lefeuvre; M. Parrot; J. L. Pinçon; B. Poirier; W. Kofman; Ph. Louarn

1997-01-01

198

On the spatio-temporal patterns formation in low-temperature plasmas  

Microsoft Academic Search

Experimental results concerning the formation of spatial and spatio-temporal patterns in low-temperature discharge plasmas are presented. These structures appear as single or multiple luminous structures attached to the anode surface, or electrode-free in the case of radio-frequency or microwave plasmas. Probe measurements revealed that a double layer exists at the edge of each structure, controlling the particle and energy exchange

D. G. Dimitriu

2008-01-01

199

An evaluation of bags-of-words and spatio-temporal shapes for action recognition  

Microsoft Academic Search

Bags-of-visual-Words (BoW) and Spatio-Temporal Shapes (STS) are two very popular approaches for action recognition from video. The former (BoW) is an un-structured global representation of videos which is built using a large set of local features. The latter (STS) uses a single feature located on a region of interest (where the actor is) in the video. Despite the popularity of

Teofilo de Campos; Mark Barnard; Krystian Mikolajczyk; Josef Kittler; Fei Yan; William Christmas; David Windridge

2011-01-01

200

Spatio-temporal dynamics of reach-related neural activity for visual and somatosensory targets  

Microsoft Academic Search

The parieto-frontal network plays a crucial role in the transformations that convert visual information into motor commands for hand reaching movements. Here we use electroencephalography to determine whether the planning of reaching movements to visual and somatosensory targets involves a similar spatio-temporal pattern of neural activity. Subjects performed reaching movements toward spatial locations defined either by visual (light-emitting diode) or

Pierre-Michel Bernier; Borís Burle; Thierry Hasbroucq; Jean Blouin

2009-01-01

201

A general science-based framework for dynamical spatio-temporal models  

Microsoft Academic Search

Spatio-temporal statistical models are increasingly being used across a wide variety of scientific disciplines to describe\\u000a and predict spatially-explicit processes that evolve over time. Correspondingly, in recent years there has been a significant\\u000a amount of research on new statistical methodology for such models. Although descriptive models that approach the problem from\\u000a the second-order (covariance) perspective are important, and innovative work

Christopher K. Wikle; Mevin B. Hooten

2010-01-01

202

Simultaneous Team Assignment and Behavior Recognition from Spatio-Temporal Agent Traces  

Microsoft Academic Search

This paper addresses the problem of activity recogni- tion for physically-embodied agent teams. We define team activity recognition as the process of identifying team behaviors from traces of agent positions over time; for many physical domains, military or athletic, coordi- nated team behaviors create distinctive spatio-temporal patterns that can be used to identify low-level action sequences. This paper focuses on

Gita Sukthankar; Katia P. Sycara

2006-01-01

203

On augmenting database design-support environments to capture the geo-spatio-temporal data semantics  

Microsoft Academic Search

A database design-support environment supports a data analyst in eliciting, articulating, specifying and validating data-related requirements. Extant design-support environments—based on conventional conceptual models—do not adequately support applications that need to organize data based on time (e.g., accounting, portfolio management, personnel management) and\\/or space (e.g., facility management, transportation, logistics). For geo-spatio-temporal applications, it is left to database designers to discover, design

Vijay Khatri; Sudha Ram; Richard T. Snodgrass

2006-01-01

204

Spatio-temporal processing of femtosecond laser pulses with thin film micro-optics  

Microsoft Academic Search

For spatio-temporal processing of ultrashort-pulse laser beams, design constraints arise from dispersion and diffraction. In sub-10-fs region, temporal and spatial coordinates of propagating wavepackets get non-separable. To enable controlled shaping and detection with spatial resolution, specific advantages of thin-film microoptical arrays are exploited. Transmitting and reflecting components of extremely small conical angles were used to generate multiple nondiffracting beams and

Rüdiger Grunwald; Volker Kebbel; Uwe Neumann; Uwe Griebner; Michel Piché

2003-01-01

205

Modeling the spatio-temporal heterogeneity in the PM10-PM2.5 relationship  

NASA Astrophysics Data System (ADS)

This paper explores the spatio-temporal patterns of particulate matter (PM) in Taiwan based on a series of methods. Using fuzzy c-means clustering first, the spatial heterogeneity (six clusters) in the PM data collected between 2005 and 2009 in Taiwan are identified and the industrial and urban areas of Taiwan (southwestern, west central, northwestern, and northern Taiwan) are found to have high PM concentrations. The PM10-PM2.5 relationship is then modeled with global ordinary least squares regression, geographically weighted regression (GWR), and geographically and temporally weighted regression (GTWR). The GTWR and GWR produce consistent results; however, GTWR provides more detailed information of spatio-temporal variations of the PM10-PM2.5 relationship. The results also show that GTWR provides a relatively high goodness of fit and sufficient space-time explanatory power. In particular, the PM2.5 or PM10 varies with time and space, depending on weather conditions and the spatial distribution of land use and emission patterns in local areas. Such information can be used to determine patterns of spatio-temporal heterogeneity in PM that will allow the control of pollutants and the reduction of public exposure.

Chu, Hone-Jay; Huang, Bo; Lin, Chuan-Yao

2015-02-01

206

Controlling for localised spatio-temporal autocorrelation in long-term air pollution and health studies  

PubMed Central

Estimating the long-term health impact of air pollution using an ecological spatio-temporal study design is a challenging task, due to the presence of residual spatio-temporal autocorrelation in the health counts after adjusting for the covariate effects. This autocorrelation is commonly modelled by a set of random effects represented by a Gaussian Markov random field (GMRF) prior distribution, as part of a hierarchical Bayesian model. However, GMRF models typically assume the random effects are globally smooth in space and time, and thus are likely to be collinear to any spatially and temporally smooth covariates such as air pollution. Such collinearity leads to poor estimation performance of the estimated fixed effects, and motivated by this epidemiological problem, this paper proposes new GMRF methodology to allow for localised spatio-temporal smoothing. This means random effects that are either geographically or temporally adjacent are allowed to be autocorrelated or conditionally independent, which allows more flexible autocorrelation structures to be represented. This increased flexibility results in improved fixed effects estimation compared with global smoothing models, which is evidenced by our simulation study. The methodology is then applied to the motivating study investigating the long-term effects of air pollution on respiratory ill health in Greater Glasgow, Scotland between 2007 and 2011. PMID:24648100

Mitchell, Richard

2014-01-01

207

Real-Time Spatio-Temporal Twice Whitening for MIMO Energy Detector  

SciTech Connect

While many techniques exist for local spectrum sensing of a primary user, each represents a computationally demanding task to secondary user receivers. In software-defined radio, computational complexity lengthens the time for a cognitive radio to recognize changes in the transmission environment. This complexity is even more significant for spatially multiplexed receivers, e.g., in SIMO and MIMO, where the spatio-temporal data sets grow in size with the number of antennae. Limits on power and space for the processor hardware further constrain SDR performance. In this report, we discuss improvements in spatio-temporal twice whitening (STTW) for real-time local spectrum sensing by demonstrating a form of STTW well suited for MIMO environments. We implement STTW on the Coherent Logix hx3100 processor, a multicore processor intended for low-power, high-throughput software-defined signal processing. These results demonstrate how coupling the novel capabilities of emerging multicore processors with algorithmic advances can enable real-time, software-defined processing of large spatio-temporal data sets.

Humble, Travis S [ORNL; Mitra, Pramita [ORNL; Barhen, Jacob [ORNL; Schleck, Bryan [Coherent Logix, Inc.

2010-01-01

208

Evaluating the Spatio-Temporal Factors that Structure Network Parameters of Plant-Herbivore Interactions  

PubMed Central

Despite the dynamic nature of ecological interactions, most studies on species networks offer static representations of their structure, constraining our understanding of the ecological mechanisms involved in their spatio-temporal stability. This is the first study to evaluate plant-herbivore interaction networks on a small spatio-temporal scale. Specifically, we simultaneously assessed the effect of host plant availability, habitat complexity and seasonality on the structure of plant-herbivore networks in a coastal tropical ecosystem. Our results revealed that changes in the host plant community resulting from seasonality and habitat structure are reflected not only in the herbivore community, but also in the emergent properties (network parameters) of the plant-herbivore interaction network such as connectance, selectiveness and modularity. Habitat conditions and periods that are most stressful favored the presence of less selective and susceptible herbivore species, resulting in increased connectance within networks. In contrast, the high degree of selectivennes (i.e. interaction specialization) and modularity of the networks under less stressful conditions was promoted by the diversification in resource use by herbivores. By analyzing networks at a small spatio-temporal scale we identified the ecological factors structuring this network such as habitat complexity and seasonality. Our research offers new evidence on the role of abiotic and biotic factors in the variation of the properties of species interaction networks. PMID:25340790

López-Carretero, Antonio; Díaz-Castelazo, Cecilia; Boege, Karina; Rico-Gray, Víctor

2014-01-01

209

Characteristics, processes, and causes of the spatio-temporal variabilities of the East Asian monsoon system  

NASA Astrophysics Data System (ADS)

Recent advances in the study of the characteristics, processes, and causes of spatio-temporal variabilities of the East Asian monsoon (EAM) system are reviewed in this paper. The understanding of the EAM system has improved in many aspects: the basic characteristics of horizontal and vertical structures, the annual cycle of the East Asian summer monsoon (EASM) system and the East Asian winter monsoon (EAWM) system, the characteristics of the spatio-temporal variabilities of the EASM system and the EAWM system, and especially the multiple modes of the EAM system and their spatio-temporal variabilities. Some new results have also been achieved in understanding the atmosphere-ocean interaction and atmosphere-land interaction processes that affect the variability of the EAM system. Based on recent studies, the EAM system can be seen as more than a circulation system, it can be viewed as an atmosphere-ocean-land coupled system, namely, the EAM climate system. In addition, further progress has been made in diagnosing the internal physical mechanisms of EAM climate system variability, especially regarding the characteristics and properties of the East Asia-Pacific (EAP) teleconnection over East Asia and the North Pacific, the "Silk Road" teleconnection along the westerly jet stream in the upper troposphere over the Asian continent, and the dynamical effects of quasi-stationary planetary wave activity on EAM system variability. At the end of the paper, some scientific problems regarding understanding the EAM system variability are proposed for further study.

Huang, Ronghui; Chen, Jilong; Wang, Lin; Lin, Zhongda

2012-09-01

210

Ontology Driven Analysis of Spatio-temporal Phenomena, Aimed At Spatial Planning And Environmental Forecasting  

NASA Astrophysics Data System (ADS)

Spatial planning is a crucial area for balancing civilization development with environmental protection. Spatial planning has a multidisciplinary nature. It must take into account the dynamics of the processes, which could affect the integrity of the environmental system. That is why we need a new approach to modelling phenomena occurring in space. Such approach is offered by ontologies, based on Description Logic (DL) and related to inference systems. Ontology is a system for the knowledge representation, including conceptual scheme and based on this scheme representation of reality. Ontologies can be enriched with additional logical systems. The authors present a way of building domain ontologies for spatial planning, including the representation of spatio-temporal phenomena. Description Logic is supplemented by structures of temporal logic. As a result, the analysis for exploring the topological relations between spatial objects will be extended to include temporal relationships: coincidence, precedence and succession, cause and effect relationship. Spatio-temporal models with temporal logic structures, encoded in ontologies, could be a subject of inference process, performed by semantic reasoners (reasoner engines). Spatio-temporal representations are offered, by so-called upper ontologies, such as GFO, BFO, OCHRE and others. Temporal structures provided in such ontologies, are useful for the analysis of data obtained from environmental and development monitoring systems and for description and representation of historical phenomena. They allow creating the models and scenarios of expected spatial transformation. They will support analysis for spatial development design, decision-making in spatial planning and forecasting of environmental impact.

Iwaniak, A.; ?ukowicz, J.; Strzelecki, M.; Kaczmarek, I.

2013-10-01

211

A SPATIO-TEMPORAL DOWNSCALER FOR OUTPUT FROM NUMERICAL MODELS  

EPA Science Inventory

Often, in environmental data collection, data arise from two sources: numerical models and monitoring networks. The first source provides predictions at the level of grid cells, while the second source gives measurements at points. The first is characterized by full spatial cove...

212

Spatio-Temporal Modelling of Dust Transport over Surface Mining Areas and Neighbouring Residential Zones  

PubMed Central

Projects focusing on spatio-temporal modelling of the living environment need to manage a wide range of terrain measurements, existing spatial data, time series, results of spatial analysis and inputs/outputs from numerical simulations. Thus, GISs are often used to manage data from remote sensors, to provide advanced spatial analysis and to integrate numerical models. In order to demonstrate the integration of spatial data, time series and methods in the framework of the GIS, we present a case study focused on the modelling of dust transport over a surface coal mining area, exploring spatial data from 3D laser scanners, GPS measurements, aerial images, time series of meteorological observations, inputs/outputs form numerical models and existing geographic resources. To achieve this, digital terrain models, layers including GPS thematic mapping, and scenes with simulation of wind flows are created to visualize and interpret coal dust transport over the mine area and a neighbouring residential zone. A temporary coal storage and sorting site, located near the residential zone, is one of the dominant sources of emissions. Using numerical simulations, the possible effects of wind flows are observed over the surface, modified by natural objects and man-made obstacles. The coal dust drifts with the wind in the direction of the residential zone and is partially deposited in this area. The simultaneous display of the digital map layers together with the location of the dominant emission source, wind flows and protected areas enables a risk assessment of the dust deposition in the area of interest to be performed. In order to obtain a more accurate simulation of wind flows over the temporary storage and sorting site, 3D laser scanning and GPS thematic mapping are used to create a more detailed digital terrain model. Thus, visualization of wind flows over the area of interest combined with 3D map layers enables the exploration of the processes of coal dust deposition at a local scale. In general, this project could be used as a template for dust-transport modelling which couples spatial data focused on the construction of digital terrain models and thematic mapping with data generated by numerical simulations based on Reynolds averaged Navier-Stokes equations.

Matejicek, Lubos; Janour, Zbynek; Benes, Ludek; Bodnar, Tomas; Gulikova, Eva

2008-01-01

213

A physiologically plausible spatio-temporal model for EEG signals recorded with intracerebral electrodes in human partial epilepsy.  

PubMed

Stereoelectroencephalography (depth-EEG signals) is a presurgical investigation technique of drug-resistant partial epilepsy, in which multiple sensor intracerebral electrodes are used to directly record brain electrical activity. In order to interpret depth-EEG signals, we developed an extended source model which connects two levels of representation: (1) a distributed current dipole model which describes the spatial distribution of neuronal sources; (2) a model of coupled neuronal populations which describes their temporal dynamics. From this extended source model, depth-EEG signals were simulated from the forward solution at each electrode sensor located inside the brain. Results showed that realistic transient epileptiform activities (spikes) are obtained under specific conditions in the model in terms of degree of coupling between neuronal populations and spatial extent of the source. In particular, the cortical area involved in the generation of epileptic spikes was estimated to vary from 18 to 25 cm2, for brain conductivity values ranging from 30 to 35 x 10(-5) S/mm, for high coupling degree between neuronal populations and for a volume conductor model that accounts for the three main tissues of the head (brain, skull, and scalp). This study provides insight into the relationship between spatio-temporal properties of cortical neuronal sources and depth-EEG signals. PMID:17355049

Cosandier-Rimélé, Delphine; Badier, Jean-Michel; Chauvel, Patrick; Wendling, Fabrice

2007-03-01

214

Modelling natural grass production and its spatio-temporal variations in a semiarid Mediterranean watershed  

NASA Astrophysics Data System (ADS)

Natural grasses are found in semiarid rangelands with disperse tree cover of part of the Iberian Peninsula and constitute a resource with high ecologic and economic value worth, being an important source of food for livestock, playing a significant role in the hydrologic cycle, controlling the soil thermal regime, and are a key factor in reducing soil erosion and degradation. However, increasing pressure on the resources, changes in land use as well as possible climate variations threaten the sustainability of natural grasses. Despite of their importance, the spatio-temporal variations of pasture production over whole watersheds are poorly known. In this sense, previous studies by other authors have indicated its dependence on a balance of positive and negative effects brought about by the main limiting factors: water, light, nutrients and space. Nevertheless, the specific weight of each factor is not clear because they are highly variable due to climate characteristics and the structure of these agroforestry systems. We have used a physical spatially-distributed ecohydrologic model to investigate the specific weight of factors that contribute to pasture production in a semiarid watershed of 99.5 ha in western Spain. This model couples a two layer (canopy and understory) vertical local closure energy balance scheme, a hydrologic model and a carbon uptake and vegetation growth component, and it was run using a synthetic daily climate dataset generated by a stochastic weather generator, which reproduced the range of climatic variations observed under mediterranean current climate. The modelling results reproduced satisfactorily the seasonality effects of climate as precipitation and temperatures, as well as annual and inter-annual variations of pasture production. Spatial variations of pasture production were largely controlled by topographic and tree effects, showing medium-low values depending of considered areas. These low values require introduction of feed to livestock. Valley bottoms, areas with low slopes, and spaces with low tree density are characterized by higher pasture production. Temporal variations of pasture production largely depended on the availability of soil moisture, which in turn depended on the temporal distribution of rainfall. This ecohydrologic model constitutes a valuable tool to investigate water and energy fluxes, as well as vegetation dynamics in semiarid rangelands, as was proved by a quantitative assessment of the quality of the simulations. The range of applications and possibilities contained in the model opens a wide field for future research.

Schnabel, Susanne; Lozano-Parra, Javier; Maneta-López, Marco

2014-05-01

215

Spatio-temporal modelling of Antarctic mass balance from multi-satellite observations  

NASA Astrophysics Data System (ADS)

Quantifying ice mass changes, identifying its causes and determining rigorous error estimates, is important for estimating present-day sea-level rise. Yet this remains a challenging task: (i) estimates obtained from altimetry, gravimetry, and mass-budget methods can yield conflicting results with error estimates that do not always overlap, and (ii) the use of different forward models to separate the effects of GIA and surface mass balance (SMB) processes, as is generally done, introduces another source of uncertainty which is hard to quantify. We present a statistical modelling approach that tackles these issues. We combine the observational data together, including radar and laser altimetry, GRACE, GPS and InSAR, and use the different degrees of spatial and temporal smoothness to constrain the underlying geophysical processes. This is achieved via a spatio-temporal Bayesian hierarchical model, employing dimensionality reduction methods to allow the solution to remain tractable in the presence of the large number (> 10^6) of observations involved. The resulting trend estimates are only dependent on length and smoothness properties obtained from numerical models, but are otherwise data-driven. We present annual, time-varying trend fields of dynamic ice loss, SMB, firn compaction and GIA; using a combination of GRACE, ICESat, ENVISat, and GPS vertical uplift rates, for 2003-2009. The elastic flexure of the crust is also determined simultaneously. We estimate that, between 2003 and 2009, there has been an acceleration in ice loss, from balance in 2003/2004 to a rate of -200±50Gt/yr by 2009. This was predominantly driven by ice dynamic losses in West Antarctica and the Antarctic Peninsula. However, this has been partially compensated by an overall positive trend in SMB over the whole continent. We conclude that there was no statistically significant net loss or gain in the seven year period. Other data will be included to allow extension back to 1995 and forward to the present day using, for example, CryoSat 2, ice core records and accumulation radar data.

Schoen, Nana; Zammit-Mangion, Andrew; Bamber, Jonathan; Rougier, Jonathan; Luthcke, Scott; Rémy, Frédérique; Flament, Thomas; Petrie, Elizabeth

2014-05-01

216

Probing on suitability of TRMM data to explain spatio-temporal pattern of severe storms in tropic region  

NASA Astrophysics Data System (ADS)

Spatial and temporal pattern of rainfall play an important role in runoff generation. Raingauge density influences the accuracy of spatial pattern and time interval influence the accuracy of temporal pattern of storms. Usually due to practical and financial limitation the perfect distribution is not achievable. Several sources of data are used to define the behavior of rainfall over a watershed. Raingauges station, radar operation and satellite sensor are the main source of rainfall estimation over the space and time. Recording raingauges are the most common source of rainfall data in many countries. However raingauge network has not adequate coverage in many watersheds spatially in developing countries. Therefore other global source of rainfall data may be useful for hydrological analysis such as flood modeling. This research assessed the ability of TRMM rainfall estimates for explain the Spatio-temporal pattern of severe storm over Klang watershed which is a hydrologically well instrumented watershed. It was experienced that TRMM rainfall estimates are 35% less than actual data for the investigated events. Due to coarse temporal resolution of TRMM (3 h) compare to gauge rainfall (15 min), significant uncertainty influences identifying the start and end of storm event and consequently their resultant time to peak of flood hydrograph which is extremely important in flood forecasting systems. Due to coarse pixel size of TRMM data, watershed scale is important issue.

Akbari, A.; Othman, F.; Abu Samah, A.

2011-10-01

217

Blind source separation of convolutive mixtures  

NASA Astrophysics Data System (ADS)

This paper introduces the blind source separation (BSS) of convolutive mixtures of acoustic signals, especially speech. A statistical and computational technique, called independent component analysis (ICA), is examined. By achieving nonlinear decorrelation, nonstationary decorrelation, or time-delayed decorrelation, we can find source signals only from observed mixed signals. Particular attention is paid to the physical interpretation of BSS from the acoustical signal processing point of view. Frequency-domain BSS is shown to be equivalent to two sets of frequency domain adaptive microphone arrays, i.e., adaptive beamformers (ABFs). Although BSS can reduce reverberant sounds to some extent in the same way as ABF, it mainly removes the sounds from the jammer direction. This is why BSS has difficulties with long reverberation in the real world. If sources are not "independent," the dependence results in bias noise when obtaining the correct separation filter coefficients. Therefore, the performance of BSS is limited by that of ABF. Although BSS is upper bounded by ABF, BSS has a strong advantage over ABF. BSS can be regarded as an intelligent version of ABF in the sense that it can adapt without any information on the array manifold or the target direction, and sources can be simultaneously active in BSS.

Makino, Shoji

2006-04-01

218

Mutual information minimization: application to Blind Source Separation  

E-print Network

1 Mutual information minimization: application to Blind Source Separation Massoud Babaie-Zadeh½ and Christian Jutten¾ Abstract In this paper, the problem of Blind Source Separation (BSS) through mutual information minimization is addressed. For mutual information minimization, multi-variate score functions

Paris-Sud XI, Université de

219

Spatio-Temporal Trends and Risk Factors for Shigella from 2001 to 2011 in Jiangsu Province, People's Republic of China  

PubMed Central

Objective This study aimed to describe the spatial and temporal trends of Shigella incidence rates in Jiangsu Province, People's Republic of China. It also intended to explore complex risk modes facilitating Shigella transmission. Methods County-level incidence rates were obtained for analysis using geographic information system (GIS) tools. Trend surface and incidence maps were established to describe geographic distributions. Spatio-temporal cluster analysis and autocorrelation analysis were used for detecting clusters. Based on the number of monthly Shigella cases, an autoregressive integrated moving average (ARIMA) model successfully established a time series model. A spatial correlation analysis and a case-control study were conducted to identify risk factors contributing to Shigella transmissions. Results The far southwestern and northwestern areas of Jiangsu were the most infected. A cluster was detected in southwestern Jiangsu (LLR?=?11674.74, P<0.001). The time series model was established as ARIMA (1, 12, 0), which predicted well for cases from August to December, 2011. Highways and water sources potentially caused spatial variation in Shigella development in Jiangsu. The case-control study confirmed not washing hands before dinner (OR?=?3.64) and not having access to a safe water source (OR?=?2.04) as the main causes of Shigella in Jiangsu Province. Conclusion Improvement of sanitation and hygiene should be strengthened in economically developed counties, while access to a safe water supply in impoverished areas should be increased at the same time. PMID:24416167

Bao, Changjun; Hu, Jianli; Liu, Wendong; Liang, Qi; Wu, Ying; Norris, Jessie; Peng, Zhihang; Yu, Rongbin; Shen, Hongbing; Chen, Feng

2014-01-01

220

Assessing spatio-temporal eruption forecasts in a monogenetic volcanic field  

NASA Astrophysics Data System (ADS)

Many spatio-temporal models have been proposed for forecasting the location and timing of the next eruption in a monogenetic volcanic field. These have almost invariably been fitted retrospectively. That is, the model has been tuned to all of the data, and hence an assessment of the goodness of fit has not been carried out on independent data. The low rate of eruptions in monogenetic fields means that there is not the opportunity to carry out a purely prospective test, as thousands of years would be required to accumulate the necessary data. This leaves open the possibility of a retrospective sequential test, where the parameters are calculated only on the basis of prior events and the resulting forecast compared statistically with the location and time of the next eruption. In general, events in volcanic fields are not dated with sufficient accuracy and precision to pursue this line of investigation; An exception is the Auckland Volcanic Field (New Zealand), consisting of c. 50 centers formed during the last c. 250 kyr, for which an age-order model exists in the form of a Monte Carlo sampling algorithm, facilitating repeated sequential testing. I examine a suite of spatial, temporal and spatio-temporal hazard models, comparing the degree of fit, and attempt to draw lessons from how and where each model is particularly successful or unsuccessful. A relatively simple (independent) combination of a renewal model (temporal term) and a spatially uniform ellipse (spatial term) performs as well as any other model. Both avoid over fitting the data, and hence large errors, when the spatio-temporal occurrence pattern changes.

Bebbington, Mark S.

2013-02-01

221

Sensitivity of cochlear nucleus neurons to spatio-temporal changes in auditory nerve activity  

PubMed Central

The spatio-temporal pattern of auditory nerve (AN) activity, representing the relative timing of spikes across the tonotopic axis, contains cues to perceptual features of sounds such as pitch, loudness, timbre, and spatial location. These spatio-temporal cues may be extracted by neurons in the cochlear nucleus (CN) that are sensitive to relative timing of inputs from AN fibers innervating different cochlear regions. One possible mechanism for this extraction is “cross-frequency” coincidence detection (CD), in which a central neuron converts the degree of coincidence across the tonotopic axis into a rate code by preferentially firing when its AN inputs discharge in synchrony. We used Huffman stimuli (Carney LH. J Neurophysiol 64: 437–456, 1990), which have a flat power spectrum but differ in their phase spectra, to systematically manipulate relative timing of spikes across tonotopically neighboring AN fibers without changing overall firing rates. We compared responses of CN units to Huffman stimuli with responses of model CD cells operating on spatio-temporal patterns of AN activity derived from measured responses of AN fibers with the principle of cochlear scaling invariance. We used the maximum likelihood method to determine the CD model cell parameters most likely to produce the measured CN unit responses, and thereby could distinguish units behaving like cross-frequency CD cells from those consistent with same-frequency CD (in which all inputs would originate from the same tonotopic location). We find that certain CN unit types, especially those associated with globular bushy cells, have responses consistent with cross-frequency CD cells. A possible functional role of a cross-frequency CD mechanism in these CN units is to increase the dynamic range of binaural neurons that process cues for sound localization. PMID:22972956

Wang, Grace I.

2012-01-01

222

Spatio-Temporal Process Variability in Watershed Scale Wetland Restoration Planning  

NASA Astrophysics Data System (ADS)

Watershed scale restoration decision making processes are increasingly informed by quantitative methodologies providing site-specific restoration recommendations - sometimes referred to as "systematic planning." The more advanced of these methodologies are characterized by a coupling of search algorithms and ecological models to discover restoration plans that optimize environmental outcomes. Yet while these methods have exhibited clear utility as decision support toolsets, they may be critiqued for flawed evaluations of spatio-temporally variable processes fundamental to watershed scale restoration. Hydrologic and non-hydrologic mediated process connectivity along with post-restoration habitat dynamics, for example, are commonly ignored yet known to appreciably affect restoration outcomes. This talk will present a methodology to evaluate such spatio-temporally complex processes in the production of watershed scale wetland restoration plans. Using the Tuscarawas Watershed in Eastern Ohio as a case study, a genetic algorithm will be coupled with the Soil and Water Assessment Tool (SWAT) to reveal optimal wetland restoration plans as measured by their capacity to maximize nutrient reductions. Then, a so-called "graphical" representation of the optimization problem will be implemented in-parallel to promote hydrologic and non-hydrologic mediated connectivity amongst existing wetlands and sites selected for restoration. Further, various search algorithm mechanisms will be discussed as a means of accounting for temporal complexities such as post-restoration habitat dynamics. Finally, generalized patterns of restoration plan optimality will be discussed as an alternative and possibly superior decision support toolset given the complexity and stochastic nature of spatio-temporal process variability.

Evenson, G. R.

2012-12-01

223

Spatio-temporal foraging patterns of a giant zooplanktivore, the leatherback turtle  

NASA Astrophysics Data System (ADS)

Understanding food web functioning through the study of natural bio-indicators may constitute a valuable and original approach. In the context of jellyfish proliferation in many overexploited marine ecosystems studying the spatio-temporal foraging patterns of the giant "jellyvore" leatherback turtle turns out to be particularly relevant. Here we analyzed long-term tracking data to assess spatio-temporal foraging patterns in 21 leatherback turtles during their pluri-annual migration in the Northern Atlantic. Through an analytical approach based on the animal's own motion (independent of currents) and diving behavior distinct zones of high and low foraging success were identified. High foraging success occurred in a sub-equatorial zone spanning the width of the Atlantic and at high (>30°N) latitudes. Between these zones in the centre of North Atlantic gyre there was low foraging success. This "ocean desert" area was traversed at high speed by leatherbacks on their way to more productive areas at higher latitudes. Animals traveled slowly in high foraging success areas and dived shallower (17.2 ± 8.0 km day - 1 and 53.6 ± 33.1 m mean ± SD respectively) than in low foraging success areas (51.0 ± 13.1 km day - 1 and 81.8 ± 56.2 m mean ± SD respectively). These spatio-temporal foraging patterns seem to relatively closely match the main features of the integrated meso-zooplankton distribution in the North Atlantic. Our method of defining high foraging success areas is intuitive and relatively easy to implement but also takes into account the impact of oceanic currents on animal's behavior.

Fossette, Sabrina; Hobson, Victoria J.; Girard, Charlotte; Calmettes, Beatriz; Gaspar, Philippe; Georges, Jean-Yves; Hays, Graeme C.

2010-05-01

224

Spatio-temporal resolution of primary processes of photosynthesis.  

PubMed

Technical progress in laser-sources and detectors has allowed the temporal and spatial resolution of chemical reactions down to femtoseconds and Å-units. In photon-excitable systems the key to chemical kinetics, trajectories across the vibrational saddle landscape, are experimentally accessible. Simple and thus well-defined chemical compounds are preferred objects for calibrating new methodologies and carving out paradigms of chemical dynamics, as shown in several contributions to this Faraday Discussion. Aerobic life on earth is powered by solar energy, which is captured by microorganisms and plants. Oxygenic photosynthesis relies on a three billion year old molecular machinery which is as well defined as simpler chemical constructs. It has been analysed to a very high precision. The transfer of excitation between pigments in antennae proteins, of electrons between redox-cofactors in reaction centres, and the oxidation of water by a Mn4Ca-cluster are solid state reactions. ATP, the general energy currency of the cell, is synthesized by a most agile, rotary molecular machine. While the efficiency of photosynthesis competes well with photovoltaics at the time scale of nanoseconds, it is lower by an order of magnitude for crops and again lower for bio-fuels. The enormous energy demand of mankind calls for engineered (bio-mimetic or bio-inspired) solar-electric and solar-fuel devices. PMID:25824647

Junge, Wolfgang

2015-01-01

225

Underdetermined Blind Source Separation Based on Subspace Representation  

E-print Network

This paper considers the problem of blindly separating sub- and super-Gaussian sources from underdetermined mixtures. The underlying sources are assumed to be composed of two orthogonal components: one lying in the rowspace ...

Kim, Sanggyun

226

Harmonizing Disparate Data across Time and Place: The Integrated Spatio-Temporal Aggregate Data Series  

PubMed Central

In this article, the authors describe a new data infrastructure project being developed at the Minnesota Population Center. The Integrated Spatio-Temporal Aggregate Data Series (ISTADS) will make it easier for researchers to use publicly available aggregate data for the United States over a time span that covers virtually the entire life of the nation: 1790–2012. In addition to facilitating access and ease of use, ISTADS will facilitate the use of these various data sets in mapping and spatial analysis. PMID:23847389

NOBLE, PETRA; VAN RIPER, DAVID; RUGGLES, STEVEN; SCHROEDER, JONATHAN; HINDMAN, MONTY

2012-01-01

227

Study of Spatio-Temporal Immunofluorescence on Bead Patterns in a Microfluidic Channel  

NASA Astrophysics Data System (ADS)

We performed a direct immunoassay inside a microfluidic channel on patterned streptavidin-coated beads, which captured fluorescently-labeled biotin target molecules from a continuous flow. We arranged the beads in a dot array at the bottom of the channel and demonstrated their position- and flow rate-dependent fluorescence. As the target analyte gets gradually depleted from the flow when passing downstream the channel, the highest fluorescence intensity was observed on the most upstream positioned dot patterns. We propose a simple analytical convection model to explain this spatio-temporal fluorescence.

Sivagnanam, Venkataragavalu; Yang, Hui; Gijs, Martin A. M.

2010-12-01

228

A general science-based framework for dynamical spatio-temporal models  

USGS Publications Warehouse

Spatio-temporal statistical models are increasingly being used across a wide variety of scientific disciplines to describe and predict spatially-explicit processes that evolve over time. Correspondingly, in recent years there has been a significant amount of research on new statistical methodology for such models. Although descriptive models that approach the problem from the second-order (covariance) perspective are important, and innovative work is being done in this regard, many real-world processes are dynamic, and it can be more efficient in some cases to characterize the associated spatio-temporal dependence by the use of dynamical models. The chief challenge with the specification of such dynamical models has been related to the curse of dimensionality. Even in fairly simple linear, first-order Markovian, Gaussian error settings, statistical models are often over parameterized. Hierarchical models have proven invaluable in their ability to deal to some extent with this issue by allowing dependency among groups of parameters. In addition, this framework has allowed for the specification of science based parameterizations (and associated prior distributions) in which classes of deterministic dynamical models (e. g., partial differential equations (PDEs), integro-difference equations (IDEs), matrix models, and agent-based models) are used to guide specific parameterizations. Most of the focus for the application of such models in statistics has been in the linear case. The problems mentioned above with linear dynamic models are compounded in the case of nonlinear models. In this sense, the need for coherent and sensible model parameterizations is not only helpful, it is essential. Here, we present an overview of a framework for incorporating scientific information to motivate dynamical spatio-temporal models. First, we illustrate the methodology with the linear case. We then develop a general nonlinear spatio-temporal framework that we call general quadratic nonlinearity and demonstrate that it accommodates many different classes of scientific-based parameterizations as special cases. The model is presented in a hierarchical Bayesian framework and is illustrated with examples from ecology and oceanography. ?? 2010 Sociedad de Estad??stica e Investigaci??n Operativa.

Wikle, C.K.; Hooten, M.B.

2010-01-01

229

Coupled map lattices as spatio-temporal fitness functions: Landscape measures and evolutionary optimization  

NASA Astrophysics Data System (ADS)

Coupled Map Lattices (CML) can be interpreted as spatio-temporal fitness landscapes which may pose a dynamic optimization problem. In this paper, we analyze such dynamic fitness landscapes in terms of the landscape measures modality, ruggedness, information content and epistasis. These measures account for different aspects of problem hardness. We use an evolutionary algorithm to solve the dynamic optimization problem and study the relationship between performance criteria of the algorithm and the landscape measures. In this way we relate problem hardness to expectable performance.

Richter, Hendrik

2008-02-01

230

Spatio-Temporal Variation and Prediction of Ischemic Heart Disease Hospitalizations in Shenzhen, China  

PubMed Central

Ischemic heart disease (IHD) is a leading cause of death worldwide. Urban public health and medical management in Shenzhen, an international city in the developing country of China, is challenged by an increasing burden of IHD. This study analyzed the spatio-temporal variation of IHD hospital admissions from 2003 to 2012 utilizing spatial statistics, spatial analysis, and space-time scan statistics. The spatial statistics and spatial analysis measured the incidence rate (hospital admissions per 1,000 residents) and the standardized rate (the observed cases standardized by the expected cases) of IHD at the district level to determine the spatio-temporal distribution and identify patterns of change. The space-time scan statistics was used to identify spatio-temporal clusters of IHD hospital admissions at the district level. The other objective of this study was to forecast the IHD hospital admissions over the next three years (2013–2015) to predict the IHD incidence rates and the varying burdens of IHD-related medical services among the districts in Shenzhen. The results show that the highest hospital admissions, incidence rates, and standardized rates of IHD are in Futian. From 2003 to 2012, the IHD hospital admissions exhibited similar mean centers and directional distributions, with a slight increase in admissions toward the north in accordance with the movement of the total population. The incidence rates of IHD exhibited a gradual increase from 2003 to 2012 for all districts in Shenzhen, which may be the result of the rapid development of the economy and the increasing traffic pollution. In addition, some neighboring areas exhibited similar temporal change patterns, which were also detected by the spatio-temporal cluster analysis. Futian and Dapeng would have the highest and the lowest hospital admissions, respectively, although these districts have the highest incidence rates among all of the districts from 2013 to 2015 based on the prediction using the GM (1,1). In addition, the combined analysis of the prediction of IHD hospital admissions and the general hospital distributions shows that Pingshan and Longgang might experience the most serious burden of IHD hospital services in the near future, although Futian would still have the greatest number and the highest incidence rate of hospital admissions for IHD. PMID:24806191

Wang, Yanxia; Du, Qingyun; Ren, Fu; Liang, Shi; Lin, De-nan; Tian, Qin; Chen, Yan; Li, Jia-jia

2014-01-01

231

Spatio-temporal variation and prediction of ischemic heart disease hospitalizations in Shenzhen, China.  

PubMed

Ischemic heart disease (IHD) is a leading cause of death worldwide. Urban public health and medical management in Shenzhen, an international city in the developing country of China, is challenged by an increasing burden of IHD. This study analyzed the spatio-temporal variation of IHD hospital admissions from 2003 to 2012 utilizing spatial statistics, spatial analysis, and space-time scan statistics. The spatial statistics and spatial analysis measured the incidence rate (hospital admissions per 1,000 residents) and the standardized rate (the observed cases standardized by the expected cases) of IHD at the district level to determine the spatio-temporal distribution and identify patterns of change. The space-time scan statistics was used to identify spatio-temporal clusters of IHD hospital admissions at the district level. The other objective of this study was to forecast the IHD hospital admissions over the next three years (2013-2015) to predict the IHD incidence rates and the varying burdens of IHD-related medical services among the districts in Shenzhen. The results show that the highest hospital admissions, incidence rates, and standardized rates of IHD are in Futian. From 2003 to 2012, the IHD hospital admissions exhibited similar mean centers and directional distributions, with a slight increase in admissions toward the north in accordance with the movement of the total population. The incidence rates of IHD exhibited a gradual increase from 2003 to 2012 for all districts in Shenzhen, which may be the result of the rapid development of the economy and the increasing traffic pollution. In addition, some neighboring areas exhibited similar temporal change patterns, which were also detected by the spatio-temporal cluster analysis. Futian and Dapeng would have the highest and the lowest hospital admissions, respectively, although these districts have the highest incidence rates among all of the districts from 2013 to 2015 based on the prediction using the GM (1,1). In addition, the combined analysis of the prediction of IHD hospital admissions and the general hospital distributions shows that Pingshan and Longgang might experience the most serious burden of IHD hospital services in the near future, although Futian would still have the greatest number and the highest incidence rate of hospital admissions for IHD. PMID:24806191

Wang, Yanxia; Du, Qingyun; Ren, Fu; Liang, Shi; Lin, De-nan; Tian, Qin; Chen, Yan; Li, Jia-jia

2014-05-01

232

Spatio-temporal Dynamics of Pond Use and Recruitment in Florida Gopher Frogs (Rana Capito aesopus)  

SciTech Connect

We examined spatio-temporal dynamics of the Florida Gopher frog breeding and juvenile recruitment. Ponds were situated in a hardwood or pine-savanna matrix of upland forest. Movement was monitored from 1994-1999. Adult pond use was low but relatively constant. Juvenile recruitment was higher in the upland savanna matrix. Body size was negatively correlated with the number of juveniles exiting the pond in only one year suggesting intraspecific competition is one of many factors. Most immigration occurred in May through August and was unrelated to rainfall.

Greenberg, C.H.

2000-05-16

233

Spatio-temporal changes of seismic anisotropy in seismogenic zones  

NASA Astrophysics Data System (ADS)

Seismic anisotropy plays a key role in the study of stress and strain fields in the earth. Potential temporal change of seismic anisotropy can be interpreted as change of the orientation of cracks in seismogenic zones and thus change of the stress field. Such temporal changes have been observed in seismogenic zones before and after earthquakes (Durand et al. , 2011) but are still not well understood. In this study, from a numerical point of view, we investigate the variations of the polarization of surface waves in anisotropic media. These variations are related to the elastic properties of the medium, in particular to anisotropy. The technique used is based on the calculation of the whole cross-correlation tensor (CCT) of ambient seismic noise. If the sources are randomly distributed in homogeneous medium, it allows us to reconstruct the Green's tensor between two stations continuously and to monitor the region through the use of its fluctuations. Therefore, the temporal change of the Green's cross-correlation tensor enables the monitoring of stress and strain fields. This technique is applied to synthetic seismograms computed in a transversally isotropic medium with horizontal symmetry axis (hereafter referred to an HTI medium) using a code RegSEM (Cupillard et al. , 2012) based on the spectral element method. We designed an experiment in order to investigate the influence of anisotropy on the CCT. In homogeneous, isotropic medium the off-diagonal terms of the Green's tensor are null. The CCT is computed between each pair of stations and then rotated in order to approximate the Green's tensor by minimizing the off-diagonal components. This procedure permits the calculation of the polarization angle of quasi-Rayleigh and quasi-Love waves, and to observe the azimuthal variation of their polarization. The results show that even a small variation of the azimuth of seismic anisotropy with respect to a certain pair of stations can induce, in some cases, a large variation in the horizontal polarization of surface waves along the direction of this pair of stations. It depends on the relative azimuth angle between the pair of stations and the direction of anisotropy, on the amplitude of anisotropy and the frequency band of the signal. Therefore, it is now possible to explain the large, rapid and very localized variations of surface waves horizontal polarization observed by Durand et al. (2011) during the Parkfield earthquake of 2004. Furthermore, some preliminary results about the investigation of seismic anisotropy change caused by the June 13, 2008 Iwate-Miyagi Nairiku earthquake (Mw = 6.9) will be presented.

Saade, M.; Montagner, J.; Roux, P.; Paul, C.; Brenguier, F.; Enescu, B.; Shiomi, K.

2013-12-01

234

Enhancing the emergence rate of coherent wavefronts from ocean ambient noise correlations using spatio-temporal filters.  

PubMed

Extracting coherent wavefronts between passive receivers using cross-correlations of ambient noise (CAN) provides a means for monitoring the seismoacoustic environment without using active sources. However, using cross-correlations between single receivers can require a long recording time in order to extract stable coherent arrivals from CAN. This becomes an issue if the propagation medium fluctuates significantly during the recording period. To address this issue, this article presents a general spatio-temporal filtering procedure to enhance the emergence rate for coherent wavefronts extracted from time-averaged ambient noise correlations between two spatially separated arrays. The robustness of this array-based CAN technique is investigated using ambient shipping noise recorded over 24 h in the frequency band [250-850 Hz] on two vertical line arrays deployed 143 m apart in shallow water (depth 20 m). Experimental results confirm that the array-based CAN technique can significantly reduce the recording duration (e.g., from 22 h to 30 min) required for extracting coherent wavefronts of sufficient amplitude (e.g., 20 dB over residual temporal fluctations) when compared to conventional CAN implementations between single pairs of hydrophones. These improvements of the CAN technique could benefit the development of noise-based ocean monitoring applications such as passive acoustic tomography. PMID:22894211

Leroy, Charlotte; Lani, Shane; Sabra, Karim G; Hodgkiss, William S; Kuperman, W A; Roux, Philippe

2012-08-01

235

Detecting Deforestation In Paraguay From Multi-temporal Landsat Imagery Using A Spatio-temporally Explicit Algorithm  

NASA Astrophysics Data System (ADS)

Forests in Paraguay have undergone extensive loss in the last decades. Detecting deforestation in this area with the use of satellite remote sensing data has particular scientific interests in a broad range of research fields. Conventional methods addressing this issue in terms of change analysis of difference image or post-classification comparison are incapable of modeling both spatial and temporal contextual information. In this paper, we propose a spatio-temporally explicit algorithm using multi-temporal Landsat imagery to detect the deforestation in Paraguay during the period between 1990 and 2000. In this algorithm, change analysis of difference image and classification of multi-temporal images are combined in a spatio-temporal model. Specifically, this algorithm includes the following three steps. First, a machine learning algorithm, Support Vector Machines (SVM), is trained with spectral observations to initialize the classification and to estimate pixel-wise class conditional probabilities for each individual image. Second, a modified Markov Random Fields (MRF) model accounting for pixel-wise transition probability is used to model the spatio-temporal contextual prior probabilities of images. Finally, an iterative algorithm, Iterative Conditional Mode (ICM), is used to update the classification based on the combination of spectral class conditional probability and spatio-temporal contextual prior probability. The results showed that the proposed algorithm achieved significant improvements over traditional pixel-based single-date approaches. The improvement from the contributions of spatio-temporal contextual evidence indicated the importance of spatio-temporal modeling in multi-temporal remote sensing in general and deforestation in particular.

Liu, D.; Kelly, M.; Gong, P.; Townshend, J. R.

2005-12-01

236

Dissecting spatio-temporal protein networks driving human heart development and related disorders  

PubMed Central

Aberrant organ development is associated with a wide spectrum of disorders, from schizophrenia to congenital heart disease, but systems-level insight into the underlying processes is very limited. Using heart morphogenesis as general model for dissecting the functional architecture of organ development, we combined detailed phenotype information from deleterious mutations in 255 genes with high-confidence experimental interactome data, and coupled the results to thorough experimental validation. Hereby, we made the first systematic analysis of spatio-temporal protein networks driving many stages of a developing organ identifying several novel signaling modules. Our results show that organ development relies on surprisingly few, extensively recycled, protein modules that integrate into complex higher-order networks. This design allows the formation of a complicated organ using simple building blocks, and suggests how mutations in the same genes can lead to diverse phenotypes. We observe a striking temporal correlation between organ complexity and the number of discrete functional modules coordinating morphogenesis. Our analysis elucidates the organization and composition of spatio-temporal protein networks that drive the formation of organs, which in the future may lay the foundation of novel approaches in treatments, diagnostics, and regenerative medicine. PMID:20571530

Lage, Kasper; Møllgård, Kjeld; Greenway, Steven; Wakimoto, Hiroko; Gorham, Joshua M; Workman, Christopher T; Bendsen, Eske; Hansen, Niclas T; Rigina, Olga; Roque, Francisco S; Wiese, Cornelia; Christoffels, Vincent M; Roberts, Amy E; Smoot, Leslie B; Pu, William T; Donahoe, Patricia K; Tommerup, Niels; Brunak, Søren; Seidman, Christine E; Seidman, Jonathan G; Larsen, Lars A

2010-01-01

237

Spatio-temporal heterogeneity of riparian soil morphology in a restored floodplain  

NASA Astrophysics Data System (ADS)

Floodplains have been intensively altered in industrialized countries, but are now increasingly being restored and it is therefore important to assess the effect of these restoration projects on the aquatic and terrestrial components of ecosystems. Soils are a functionally crucial component of terrestrial ecosystems but are generally overlooked in floodplain restoration assessment. We studied the spatio-temporal heterogeneity of soil morphology in a restored (riverbed widening) river reach along River Thur (Switzerland) using three criteria (soil diversity, dynamism and typicality) and their associated indicators. We hypothesized that these criteria would correctly discriminate the post-restoration changes in soil morphology within the study site, and that these changes correspond to patterns of vascular plant diversity. Soil diversity and dynamism increased five years after the restoration, but typical soils of braided rivers were still missing. Soil typicality and dynamism correlated to vegetation changes. These results suggest a limited success of the project in agreement with evaluations carried out at the same site using other, more resource demanding methods (e.g. soil fauna, fish, ecosystem functioning). Soil morphology provides structural and functional information on floodplain ecosystems and allows predicting broad changes in plant diversity. The spatio-temporal heterogeneity of soil morphology represents a cost-efficient ecological indicator that could easily be integrated into rapid assessment protocols of floodplain and river restoration projects.

Fournier, B.; Guenat, C.; Bullinger-Weber, G.; Mitchell, E. A. D.

2013-04-01

238

A dense array stimulator to generate arbitrary spatio-temporal tactile stimuli  

PubMed Central

The generation and presentation of tactile stimuli presents a unique challenge. Unlike vision and audition, in which standard equipment such as monitors and audio systems can be used for most experiments, tactile stimuli and/or stimulators often have to be tailor-made for a given study. Here, we present a novel tactile stimulator designed to present arbitrary spatio-temporal stimuli to the skin. The stimulator consists of 400 pins, arrayed over a 1 cm2 area, each under independent computer control. The dense array allows for an unprecedented number of stimuli to be presented within an experimental session (e.g., up to 1200 stimuli per minute) and for stimuli to be generated adaptively. The stimulator can be used in a variety of modes and can deliver indented and scanned patterns as well as stimuli defined by mathematical spatio-temporal functions (e.g., drifting sinusoids). We describe the hardware and software of the system, and discuss previous and prospective applications. PMID:17134760

Killebrew, Justin H.; Bensmaïa, Sliman J.; Dammann, John F.; Denchev, Peter; Hsiao, Steven S.; Craig, James C.

2007-01-01

239

Rational spatio-temporal strategies for controlling a Chagas disease vector in urban environments  

PubMed Central

The rational design of interventions is critical to controlling communicable diseases, especially in urban environments. In the case of the Chagas disease vector Triatoma infestans, successful control is stymied by the return of the insect after the effectiveness of the insecticide wanes. Here, we adapt a genetic algorithm, originally developed for the travelling salesman problem, to improve the spatio-temporal design of insecticide campaigns against T. infestans, in a complex urban environment. We find a strategy that reduces the expected instances of vector return 34-fold compared with the current strategy of sequential insecticide application to spatially contiguous communities. The relative success of alternative control strategies depends upon the duration of the effectiveness of the insecticide, and it shows chaotic fluctuations in response to unforeseen delays in a control campaign. We use simplified models to analyse the outcomes of qualitatively different spatio-temporal strategies. Our results provide a detailed procedure to improve control efforts for an urban Chagas disease vector, as well as general guidelines for improving the design of interventions against other disease agents in complex environments. PMID:20061346

Levy, Michael Z.; Malaga Chavez, Fernando S.; Cornejo del Carpio, Juan G.; Vilhena, Daril A.; McKenzie, F. Ellis; Plotkin, Joshua B.

2010-01-01

240

Scaling, universality and spatio-temporal clustering in seismicity and rock fracture phenomena  

NASA Astrophysics Data System (ADS)

In this talk, I will discuss new methods from nonlinear sciences and complex network theory to characterize temporal and spatio-temporal clustering of point processes with a particular focus on their application to seismicity and rock fracture. Many striking features of natural processes can be portrayed as patterns or clusters of localized events. A generic attribute in all these cases is that one event can trigger or somehow induce another one to occur - or possibly numerous further events. Sometimes, an accounting of causal connections between clustered events is explicitly rationalized by the microscopic state and rules of the dynamical system. More often than not, though, the causal connections cannot be resolved from the data at hand and remain ambiguous. Thus, one is confronted with inferring a plausible causal structure from clusters of localized events without a detailed or "fundamental" knowledge of the true microscopic dynamics. I will present a method to search for such signs of causal structure in spatio-temporal data making minimal a priori assumptions about the underlying microscopic dynamics. For earthquakes, the method allows to recover the scaling of the rupture length with magnitude. Moreover, I will present a detailed statistical analysis of acoustic emission time series from a range of rock fracture experiments. In all considered cases, the waiting time distribution can be described by a unique scaling function indicating its universality. This scaling function is even indistinguishable from that for earthquakes suggesting its general validity for fracture processes independent of time, space and magnitude scales.

Davidsen, J.

2007-12-01

241

Spatio-temporal parameters and lower-limb kinematics of turning gait in typically developing children.  

PubMed

Turning is a requirement for most locomotor tasks; however, knowledge of the biomechanical requirements of successful turning is limited. Therefore, the aims of this study were to investigate the spatio-temporal and lower-limb kinematics of 90° turning. Seventeen typically developing children, fitted with full body and multi-segment foot marker sets, having performed both step (outside leg) and spin (inside leg) turning strategies at self-selected velocity, were included in the study. Three turning phases were identified: approach, turn, and depart. Stride velocity and stride length were reduced for both turning strategies for all turning phases (p<0.03 and p<0.01, respectively), while stance time and stride width were increased during only select phases (p<0.05 and p<0.01, respectively) for both turn conditions compared to straight gait. Many spatio-temporal differences between turn conditions and phases were also found (p<0.03). Lower-limb kinematics revealed numerous significant differences mainly in the coronal and transverse planes for the hip, knee, ankle, midfoot, and hallux between conditions (p<0.05). The findings summarized in this study help explain how typically developing children successfully execute turns and provide greater insight into the biomechanics of turning. This knowledge may be applied to a clinical setting to help improve the management of gait disorders in pathological populations, such as children with cerebral palsy. PMID:23684101

Dixon, Philippe C; Stebbins, Julie; Theologis, Tim; Zavatsky, Amy B

2013-09-01

242

An exact stochastic hybrid model of excitable membranes including spatio-temporal evolution.  

PubMed

In this paper, we present a mathematical description for excitable biological membranes, in particular neuronal membranes. We aim to model the (spatio-) temporal dynamics, e.g., the travelling of an action potential along the axon, subject to noise, such as ion channel noise. Using the framework of Piecewise Deterministic Processes (PDPs) we provide an exact mathematical description-in contrast to pseudo-exact algorithms considered in the literature-of the stochastic process one obtains coupling a continuous time Markov chain model with a deterministic dynamic model of a macroscopic variable, that is coupling Markovian channel dynamics to the time-evolution of the transmembrane potential. We extend the existing framework of PDPs in finite dimensional state space to include infinite-dimensional evolution equations and thus obtain a stochastic hybrid model suitable for modelling spatio-temporal dynamics. We derive analytic results for the infinite-dimensional process, such as existence, the strong Markov property and its extended generator. Further, we exemplify modelling of spatially extended excitable membranes with PDPs by a stochastic hybrid version of the Hodgkin-Huxley model of the squid giant axon. Finally, we discuss the advantages of the PDP formulation in view of analytical and numerical investigations as well as the application of PDPs to structurally more complex models of excitable membranes. PMID:21243359

Buckwar, Evelyn; Riedler, Martin G

2011-12-01

243

A geomatic methodology for spatio-temporal analysis of climatologic variables and water related diseases  

NASA Astrophysics Data System (ADS)

The main objective of this research is to propose, by the way of geomatic developments, an integrated tool to analyze and model the spatio-temporal pattern of human diseases related to environmental conditions, in particular the ones that are linked to water resources. The geomatic developments follows four generic steps : requirement analysis, conceptual modeling, geomatic modeling and implementation (in Idrisi GIS software). A first development consists of the preprocessing of water, population and health data in order to facilitate the conversion and validation of tabular data into the required structure for spatio-temporal analysis. Three parallel developments follow : water balance, demographic state and evolution, epidemiological measures (morbidity and mortality rates, diseases burden). The new geomatic modules in their actual state have been tested on various regions of Mexico Republic (Lerma watershed, Chiapas state) focusing on diarrhea and vector borne diseases (dengue and malaria) and considering records over the last decade : a yearly as well as seasonal spreading trend can be observed in correlation with precipitation and temperature data. In an ecohealth perspective, the geomatic approach results particularly appropriate since one of its purposes is the integration of the various spatial themes implied in the study problem, environmental as anthropogenic. By the use of powerful spatial analysis functions, it permits the detection of spatial trends which, combined to the temporal evolution, can be of particularly use for example in climate change context, if sufficiently valid historical data can be obtain.

Quentin, E.; Gómez Albores, M. A.; Díaz Delgado, C.

2009-04-01

244

Toward a robust 2D spatio-temporal self-organization  

E-print Network

Abstract. Several models have been proposed for spatio-temporal selforganization, among which the TOM model by Wiemer [1] is particularly promising. In this paper, we propose to adapt and extend this model to 2D maps to make it more generic and biologically plausible and more adapted to realistic applications, illustrated here by an application to speech analysis. 1 Spatio-temporal self-organization Fundamental property, in biological as well as artificial systems, is that of adaptive information representation. Self-Organizing Maps (SOM), proposed by Kohonen [2] in the framework of cortical modeling and extensively used for various tasks of information processing, underline how, from simple learning and connectivity rules within a map of neurons, a topological representation can emerge, where similar data activate close regions of the map. The resulting representation is interesting for several reasons: using short connections in the brain saves energy; the neighborhood property is robust to noise and makes easier communication between neurons representing close stimuli. Even if there is no strong

245

Spatio-temporal dynamics induced by competing instabilities in two asymmetrically coupled nonlinear evolution equations  

NASA Astrophysics Data System (ADS)

Pattern formation often occurs in spatially extended physical, biological, and chemical systems due to an instability of the homogeneous steady state. The type of the instability usually prescribes the resulting spatio-temporal patterns and their characteristic length scales. However, patterns resulting from the simultaneous occurrence of instabilities cannot be expected to be simple superposition of the patterns associated with the considered instabilities. To address this issue, we design two simple models composed by two asymmetrically coupled equations of non-conserved (Swift-Hohenberg equations) or conserved (Cahn-Hilliard equations) order parameters with different characteristic wave lengths. The patterns arising in these systems range from coexisting static patterns of different wavelengths to traveling waves. A linear stability analysis allows to derive a two parameter phase diagram for the studied models, in particular, revealing for the Swift-Hohenberg equations, a co-dimension two bifurcation point of Turing and wave instability and a region of coexistence of stationary and traveling patterns. The nonlinear dynamics of the coupled evolution equations is investigated by performing accurate numerical simulations. These reveal more complex patterns, ranging from traveling waves with embedded Turing patterns domains to spatio-temporal chaos, and a wide hysteretic region, where waves or Turing patterns coexist. For the coupled Cahn-Hilliard equations the presence of a weak coupling is sufficient to arrest the coarsening process and to lead to the emergence of purely periodic patterns. The final states are characterized by domains with a characteristic length, which diverges logarithmically with the coupling amplitude.

Schüler, D.; Alonso, S.; Torcini, A.; Bär, M.

2014-12-01

246

Spatio-temporal dynamics in the phenology of croplands across the Indo-Gangetic Plains  

NASA Astrophysics Data System (ADS)

Spatio-temporal dynamics in land surface phenology parameters observed over croplands can inform on crop-climate interactions and, elucidate local to regional scale vulnerabilities either due to climate change or prevailing sub-optimal agricultural practices. Here, we observe spatio-temporal trends in land surface phenology parameters (cropping intensity, length of growing season and productivity) for kharif and rabi cropping seasons from satellite data across the Indo-Gangetic Plains from 1982 to 2006. The productivity of the Indo-Gangetic Plains croplands is of regional importance and is a vital component of Indian national food security efforts. Aside from local and intra-state heterogeneity in observed trends there was a clear west-to-east gradient in cropping intensity. Key observed trends include increasing cropping intensity in the eastern IGP, increasing number of growing days per year in Bihar, Uttar Pradesh and Haryana and increasing productivity in both cropping seasons across the IGP. This information is a crucial input to integrated assessments of the croplands to ensure management of the agricultural system shifts towards a trajectory of climate-resilience and environmental sustainability. To create spatially explicit time-series, at a spatial resolution of 8 km across the IGP of the following LSP parameters: (i) cropping intensity, (ii) LGS and (iii) agro-ecosystem productivity. To quantify normal conditions, inter-annual variation and long-term trends in these LSP parameters at an 8 km spatial resolution across the IGP croplands.

Duncan, John M. A.; Dash, Jadunandan; Atkinson, Peter M.

2014-08-01

247

Quantifying human sensitivity to spatio-temporal information in dynamic faces.  

PubMed

A great deal of perceptual and social information is conveyed by facial motion. Here, we investigated observers' sensitivity to the complex spatio-temporal information in facial expressions and what cues they use to judge the similarity of these movements. We motion-captured four facial expressions and decomposed them into time courses of semantically meaningful local facial actions (e.g., eyebrow raise). We then generated approximations of the time courses which differed in the amount of information about the natural facial motion they contained, and used these and the original time courses to animate an avatar head. Observers chose which of two animations based on approximations was more similar to the animation based on the original time course. We found that observers preferred animations containing more information about the natural facial motion dynamics. To explain observers' similarity judgments, we developed and used several measures of objective stimulus similarity. The time course of facial actions (e.g., onset and peak of eyebrow raise) explained observers' behavioral choices better than image-based measures (e.g., optic flow). Our results thus revealed observers' sensitivity to changes of natural facial dynamics. Importantly, our method allows a quantitative explanation of the perceived similarity of dynamic facial expressions, which suggests that sparse but meaningful spatio-temporal cues are used to process facial motion. PMID:24784699

Dobs, Katharina; Bülthoff, Isabelle; Breidt, Martin; Vuong, Quoc C; Curio, Crist?bal; Schultz, Johannes

2014-07-01

248

Disclosing the spatio-temporal structure of PDC entanglement through frequency up-conversion  

E-print Network

In this work we propose and analyse a scheme where the full spatio-temporal correlation of twin photons/beams generated by parametric down-conversion is detected by using its inverse process, i.e. sum frequency generation. Our main result is that, by imposing independently a temporal delay \\Delta t and a transverse spatial shift \\Delta x between two twin components of PDC light, the up-converted light intensity provides information on the correlation of the PDC light in the full spatio-temporal domain, and should enable the reconstruction of the peculiar X-shaped structure of the correlation predicted in [gatti2009,caspani2010,brambilla2010]. Through both a semi-analytical and a numerical modeling of the proposed optical system, we analyse the feasibility of the experiment and identify the best conditions to implement it. In particular, the tolerance of the phase-sensitive measurement against the presence of dispersive elements, imperfect imaging conditions and possible misalignments of the two crystals is evaluated.

Enrico Brambilla; Ottavia Jedrkiewicz; Luigi Lugiato; Alessandra Gatti

2012-05-09

249

Disclosing the spatio-temporal structure of PDC entanglement through frequency  

E-print Network

In this work we propose and analyse a scheme where the full spatio-temporal correlation of twin photons/beams generated by parametric down-conversion is detected by using its inverse process, i.e. sum frequency generation. Our main result is that, by imposing independently a temporal delay \\Delta t and a transverse spatial shift \\Delta x between two twin components of PDC light, the up-converted light intensity provides information on the correlation of the PDC light in the full spatio-temporal domain, and should enable the reconstruction of the peculiar X-shaped structure of the correlation predicted in [gatti2009,caspani2010,brambilla2010]. Through both a semi-analytical and a numerical modeling of the proposed optical system, we analyse the feasibility of the experiment and identify the best conditions to implement it. In particular, the tolerance of the phase-sensitive measurement against the presence of dispersive elements, imperfect imaging conditions and possible misalignments of the two crystals is ev...

Brambilla, Enrico; Lugiato, Luigi; Gatti, Alessandra

2012-01-01

250

Spatio-temporal dynamics of security investments in an interdependent risk environment  

NASA Astrophysics Data System (ADS)

In a globalised world where risks spread through contagion, the decision of an entity to invest in securing its premises from stochastic risks no longer depends solely on its own actions but also on the actions of other interacting entities in the system. This phenomenon is commonly seen in many domains including airline, logistics and computer security and is referred to as Interdependent Security (IDS). An IDS game models this decision problem from a game-theoretic perspective and deals with the behavioural dynamics of risk-reduction investments in such settings. This paper enhances this model and investigates the spatio-temporal aspects of the IDS games. The spatio-temporal dynamics are studied using simple replicator dynamics on a variety of network structures and for various security cost tradeoffs that lead to different Nash equilibria in an IDS game. The simulation results show that the neighbourhood configuration has a greater effect on the IDS game dynamics than network structure. An in-depth empirical analysis of game dynamics is carried out on regular graphs, which leads to the articulation of necessary and sufficient conditions for dominance in IDS games under spatial constraints.

Shafi, Kamran; Bender, Axel; Zhong, Weicai; Abbass, Hussein A.

2012-10-01

251

Spatio-temporal changes in the structure of archaeal communities in two deep freshwater lakes.  

PubMed

In this study, we evaluated the driving forces exerted by a large set of environmental and biological parameters on the spatial and temporal dynamics of archaeal community structure in two neighbouring peri-alpine lakes that differ in terms of trophic status. We analysed monthly data from a 2-year sampling period at two depths corresponding to the epi- and hypolimnetic layers. The archaeal communities seemed to be mainly composed of ammonia-oxidizing archaea belonging to the thaumarchaeotal phylum. The spatio-temporal dynamics of these communities were very similar in the two lakes and were characterized by (1) disparities in archaeal community structure in both time and space and (2) no seasonal reproducibility between years. The archaeal communities were regulated by a complex combination of abiotic factors, including temperature, nutrients, chlorophyll a and dissolved oxygen, and biotic factors such as heterotrophic nanoflagellates and ciliates. However, in most cases, these factors explained < 52% of the variance in archaeal community structure, while we showed in a previous study that these factors explained 70-90% of the temporal variance for bacteria. This suggests that Bacteria and Archaea may be influenced by different factors and could occupy different ecological niches despite similar spatio-temporal dynamics. PMID:23730709

Berdjeb, Lyria; Pollet, Thomas; Chardon, Cécile; Jacquet, Stéphan

2013-11-01

252

Model for the spatio-temporal intermittency of the energy dissipation in turbulent flows  

E-print Network

Modeling the intermittent behavior of turbulent energy dissipation processes both in space and time is often a relevant problem when dealing with phenomena occurring in high Reynolds number flows, especially in astrophysical and space fluids. In this paper, a dynamical model is proposed to describe the spatio-temporal intermittency of energy dissipation rate in a turbulent system. This is done by using a shell model to simulate the turbulent cascade and introducing some heuristic rules, partly inspired by the well known $p$-model, to construct a spatial structure of the energy dissipation rate. In order to validate the model and to study its spatially intermittency properties, a series of numerical simulations have been performed. These show that the level of spatial intermittency of the system can be simply tuned by varying a single parameter of the model and that scaling laws in agreement with those obtained from experiments on fully turbulent hydrodynamic flows can be recovered. It is finally suggested that the model could represent a useful tool to simulate the spatio-temporal intermittency of turbulent energy dissipation in those high Reynolds number astrophysical fluids where impulsive energy release processes can be associated to the dynamics of the turbulent cascade.

Fabio Lepreti; Vincenzo Carbone; Pierluigi Veltri

2007-02-08

253

Characterization of UWB Antennas by Their Spatio-Temporal Transfer Function Based on FDTD Simulations  

NASA Astrophysics Data System (ADS)

In this paper we present a method for the efficient characterization of UWB antennas based on a combination of FDTD simulation and the Lorentz reciprocity principle. A complete spatio-temporal characterization can be optained by employing a methods consisting of a numerical simulation of the near field and a near field to far field transformation. In a first step a single numerical simulation in a small near field region is used to compute the electrical field of the antenna in transmit mode. A near field to far field transformation provides the transmit transfer function of the antenna. The application of the Lorentz reciprocity theorem then yields the receive transfer function from the transmit transfer function. The transfer functions of the antenna allow the calculation of all quality measures of interest (e. g. ringing or effective gain) either in the frequency domain or the time domain. Furthermore, as the transfer functions characterize completely the spatio-temporal behavior of the antenna they can be used as input data for propagation investigations in order to investigate the link between a transmitting and a receiving UWB system. The proposed method is validated by a comparison of its results with an EMPIRE™ FDTD simulation of a two antenna system. To investigate a first realistic example a monocone antenna integrated in a canonical model of a DVD player is characterized, and the link between the DVD player and a Vivaldi antenna is calculated for a simplified indoor scenario.

Manteuffel, D.; Kunisch, J.; Simon, W.

254

Dissecting spatio-temporal protein networks driving human heart development and related disorders.  

PubMed

Aberrant organ development is associated with a wide spectrum of disorders, from schizophrenia to congenital heart disease, but systems-level insight into the underlying processes is very limited. Using heart morphogenesis as general model for dissecting the functional architecture of organ development, we combined detailed phenotype information from deleterious mutations in 255 genes with high-confidence experimental interactome data, and coupled the results to thorough experimental validation. Hereby, we made the first systematic analysis of spatio-temporal protein networks driving many stages of a developing organ identifying several novel signaling modules. Our results show that organ development relies on surprisingly few, extensively recycled, protein modules that integrate into complex higher-order networks. This design allows the formation of a complicated organ using simple building blocks, and suggests how mutations in the same genes can lead to diverse phenotypes. We observe a striking temporal correlation between organ complexity and the number of discrete functional modules coordinating morphogenesis. Our analysis elucidates the organization and composition of spatio-temporal protein networks that drive the formation of organs, which in the future may lay the foundation of novel approaches in treatments, diagnostics, and regenerative medicine. PMID:20571530

Lage, Kasper; Møllgård, Kjeld; Greenway, Steven; Wakimoto, Hiroko; Gorham, Joshua M; Workman, Christopher T; Bendsen, Eske; Hansen, Niclas T; Rigina, Olga; Roque, Francisco S; Wiese, Cornelia; Christoffels, Vincent M; Roberts, Amy E; Smoot, Leslie B; Pu, William T; Donahoe, Patricia K; Tommerup, Niels; Brunak, Søren; Seidman, Christine E; Seidman, Jonathan G; Larsen, Lars A

2010-06-22

255

Spatio-temporal modelling of individual exposure to air pollution and its uncertainty  

NASA Astrophysics Data System (ADS)

We developed a generic spatio-temporal model to quantify individual exposure to air pollution, using personal activity profiles derived from GPS and diaries, ambient air quality, and an indoor model. To enhance accessibility and reusability, the model approach is deployed as a web service. The model is applied to estimate personal exposure towards PM10 and PM2.5 for ten individuals in Münster, Germany. Modelled daily averages range for PM10 between 17 and 126 and between 6 and 84 ?g m-3 for PM2.5. Comparison with personal monitoring data shows good agreement at temporal resolutions from 5 min to one day. Uncertainties in the model results are considerable and increase with higher exposure levels. Large deviations between modelled and measured exposure can often be explained by missing data on indoor emissions or insufficiently detailed activity diaries. The developed model allows the assessment of individual exposure with uncertainties on a high spatio-temporal resolution. By providing the methodology through a web service interface and using generic indoor parameter distributions, the model can be easily transferred to new application areas or could be provided for public use to identify hazardous exposure events.

Gerharz, Lydia E.; Klemm, Otto; Broich, Anna V.; Pebesma, Edzer

2013-01-01

256

Spatio-temporal evolution of biogeochemical processes at a landfill site  

NASA Astrophysics Data System (ADS)

Predictions of fate and transport of contaminants are strongly dependent on spatio-temporal variability of soil hydraulic and geochemical properties. This study focuses on time-series signatures of hydrological and geochemical properties at different locations within the Norman landfill site. Norman Landfill is a closed municipal landfill site with prevalent organic contamination. Monthly data at the site include specific conductance, ?18O, ?2H, dissolved organic carbon (DOC) and anions (chloride, sulfate, nitrate) from 1998-2006. Column scale data on chemical concentrations, redox gradients, and flow parameters are also available on daily and hydrological event (infiltration, drainage, etc.) scales. Since high-resolution datasets of contaminant concentrations are usually unavailable, Wavelet and Fourier analyses were used to infer the dominance of different biogeochemical processes at different spatio-temporal scales and to extract linkages between transport and reaction processes. Results indicate that time variability controls the progression of reactions affecting biodegradation of contaminants. Wavelet analysis suggests that iron-sulfide reduction reactions had high seasonal variability at the site, while fermentation processes dominated at the annual time scale. Findings also suggest the dominance of small spatial features such as layered interfaces and clay lenses in driving biogeochemical reactions at both column and landfill scales. A conceptual model that caters to increased understanding and remediating structurally heterogeneous variably-saturated media is developed from the study.

Arora, B.; Mohanty, B. P.; McGuire, J. T.

2011-12-01

257

Spatio-temporal coherence of free-electron laser radiation in the extreme ultraviolet determined by a Michelson interferometer  

SciTech Connect

A key feature of extreme ultraviolet (XUV) radiation from free-electron lasers (FELs) is its spatial and temporal coherence. We measured the spatio-temporal coherence properties of monochromatized FEL pulses at 13.5?nm using a Michelson interferometer. A temporal coherence time of (59±8) fs has been determined, which is in good agreement with the spectral bandwidth given by the monochromator. Moreover, the spatial coherence in vertical direction amounts to about 15% of the beam diameter and about 12% in horizontal direction. The feasibility of measuring spatio-temporal coherence properties of XUV FEL radiation using interferometric techniques advances machine operation and experimental studies significantly.

Hilbert, V.; Rödel, C.; Zastrau, U., E-mail: ulf.zastrau@uni-jena.de [Institut für Optik und Quantenelektronik, Friedrich-Schiller-Universität, Max-Wien-Platz 1, 07743 Jena (Germany); Brenner, G.; Düsterer, S.; Dziarzhytski, S.; Harmand, M.; Przystawik, A.; Redlin, H.; Toleikis, S. [Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, 22607 Hamburg (Germany); Döppner, T.; Ma, T. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550 (United States); Fletcher, L. [Department of Physics, University of California, Berkeley, California 94720 (United States); Förster, E. [Institut für Optik und Quantenelektronik, Friedrich-Schiller-Universität, Max-Wien-Platz 1, 07743 Jena (Germany); Helmholtz-Institut Jena, Fröbelstieg 3, 07743 Jena (Germany); Glenzer, S. H.; Lee, H. J. [SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Hartley, N. J. [Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Kazak, L.; Komar, D.; Skruszewicz, S. [Institut für Physik, Universität Rostock, 18051 Rostock (Germany); and others

2014-09-08

258

Spatio-temporal clustering of cholera: The impact of flood control in Matlab, Bangladesh, 1983–2003  

PubMed Central

Introducing flood control to an area of endemic waterborne diseases could have significant impacts on spatio-temporal occurrence of cholera. Using 21-years of data from Bangladesh, we conducted cluster analysis to explore changes in spatial and temporal distribution of cholera incidence since construction of flood control structures. Striking changes in temporal cluster patterns emerged, including a shift from dry season to rainy season clusters following flood protection and delayed clustering inside the protected areas. Spatial differences in pre-flood protection and post-protection cholera clusters are weaker. Changes in spatio-temporal cholera clustering, associated with implementation of flood protection strategies, could affect local cholera prevention efforts. PMID:19217821

Carrel, Margaret A.; Emch, Michael; Streatfield, Peter K.; Yunus, Mohammad

2009-01-01

259

Spatio-temporal coherence of free-electron laser radiation in the extreme ultraviolet determined by a Michelson interferometer  

NASA Astrophysics Data System (ADS)

A key feature of extreme ultraviolet (XUV) radiation from free-electron lasers (FELs) is its spatial and temporal coherence. We measured the spatio-temporal coherence properties of monochromatized FEL pulses at 13.5 nm using a Michelson interferometer. A temporal coherence time of (59±8) fs has been determined, which is in good agreement with the spectral bandwidth given by the monochromator. Moreover, the spatial coherence in vertical direction amounts to about 15% of the beam diameter and about 12% in horizontal direction. The feasibility of measuring spatio-temporal coherence properties of XUV FEL radiation using interferometric techniques advances machine operation and experimental studies significantly.

Hilbert, V.; Rödel, C.; Brenner, G.; Döppner, T.; Düsterer, S.; Dziarzhytski, S.; Fletcher, L.; Förster, E.; Glenzer, S. H.; Harmand, M.; Hartley, N. J.; Kazak, L.; Komar, D.; Laarmann, T.; Lee, H. J.; Ma, T.; Nakatsutsumi, M.; Przystawik, A.; Redlin, H.; Skruszewicz, S.; Sperling, P.; Tiggesbäumker, J.; Toleikis, S.; Zastrau, U.

2014-09-01

260

Spatio-temporal changes of photosynthesis in carnivorous plants in response to prey capture, retention and digestion  

PubMed Central

Carnivorous plants have evolved modified leaves into the traps that assist in nutrient uptake from captured prey. It is known that the traps of carnivorous plants usually have lower photosynthetic rates than assimilation leaves as a result of adaptation to carnivory. However, a few recent studies have indicated that photosynthesis and respiration undergo spatio-temporal changes during prey capture and retention, especially in the genera with active trapping mechanisms. This study describes the spatio-temporal changes of effective quantum yield of photochemical energy conversion in photosystem II (?PSII) in response to ant-derived formic acid during its capture and digestion. PMID:20523127

2010-01-01

261

Spatio-temporal development of streamflow droughts in north-west Europe Hydrology and Earth System Sciences, 5(4), 733751 (2001) EGS  

E-print Network

Spatio-temporal development of streamflow droughts in north-west Europe 733 Hydrology and Earth System Sciences, 5(4), 733­751 (2001) © EGS Spatio-temporal development of streamflow droughts in north.zaidman@jbaconsulting.co.uk Abstract This paper examines the spatial and temporal development of streamflow droughts in Europe over

Paris-Sud XI, Université de

262

centre for digital music Blind Audio Source Separation  

E-print Network

for digital music Blind Audio Source Separation EMMANUEL VINCENT, MARIA G. JAFARI, SAMER A. ABDALLAH, MARK D Separation Emmanuel Vincent, Maria G. Jafari, Samer A. Abdallah, Mark D. Plumbley and Mike E. Davies Centre

Plumbley, Mark

263

A new perspective on the spatio-temporal variability of soil moisture  

NASA Astrophysics Data System (ADS)

One of the key components controlling both the water and energy balance, is soil moisture. The characterization of its spatio-temporal variability is crucial to understand and predict processes in climate science and hydrology. A number of studies characterized the spatial variability and the rank stability (also called temporal stability) of the absolute soil moisture within a given network. These studies were generally based on short-term measurement campaigns and did not distinguish between the time invariant and time varying contributors of the absolute soil moisture. In the current study (Mittelbach and Seneviratne, 2012), we investigate this issue using measurements from 14 grassland sites of the SwissSMEX soil moisture network over a spatial extent of about 150x210 km and for the time period May 2010 to July 2011. The spatial variance of the absolute column soil moisture (integrated over 50 cm) is thereby decomposed over time in contributions from the spatial variance of the mean soil moisture at all sites (which is time invariant), and components that are related to soil moisture dynamics (which are time varying). These include the spatial variance of the temporal soil moisture anomalies at all sites and the covariance between the sites' anomalies to the spatial mean at a given time step and those for the temporal mean values. The analysis illustrates that the spatial variance of the time invariant term contributes 50-160% of the overall spatial soil moisture variance at any point in time. On the other hand the spatial variance of the temporal anomalies, which is most relevant for climate and hydrological applications as it is directly related to the soil moisture dynamics, contributes at most 2-30% to the overall variance. This result suggests that a large fraction of the spatial variability of soil moisture assessed from short-term campaigns is time invariant and that the rank (or "temporal") stability concept when applied to absolute soil moisture, mostly characterizes the time-invariant patterns. Indeed, sites that best represent the mean soil moisture dynamics of the network are not the same as those that best reflect mean soil moisture at any point in time. Overall this study indicates that conclusions derived from the analysis of the spatio-temporal variability of absolute soil moisture do not necessary apply to temporal soil moisture anomalies, and hence to soil moisture dynamics. Reference: Mittelbach, H. and S.I. Seneviratne, 2012: A new perspective on the spatio-temporal variability of soil moisture: Temporal dynamics versus time invariant contributions. Submitted to HESS.

Mittelbach, H.; Seneviratne, S. I.

2012-04-01

264

Challenges for modelling spatio-temporal variations of malaria risk in Malawi  

NASA Astrophysics Data System (ADS)

Malaria is the leading cause of morbidity and mortality in Malawi with more than 6 million episodes reported each year. Malaria poses a huge economic burden to Malawi in terms of the direct cost of treating malaria patients and also indirect costs resulting from workdays lost in agriculture and industry and absenteeism from school. Malawi implements malaria control activities within the Roll Back Malaria framework, with the objective to provide those most at risk (i.e. children under five years, pregnant woman and individuals with suppressed immune systems) access to personal and community protective measures. However, at present there is no mechanism by which to target the most 'at risk' populations ahead of an impending epidemic. Malaria transmission is influenced by variations in meteorological conditions, which impact the biology of the mosquito and the availability of breeding sites, but also socio-economic conditions such as levels of urbanisation, poverty and education, which influence human vulnerability and vector habitat. The many potential drivers of malaria, both extrinsic, such as climate, and intrinsic, such as population immunity are often difficult to disentangle. This presents a challenge for modelling of malaria risk in space and time. Using an age-stratified spatio-temporal dataset of malaria cases at the district level from July 2004 - June 2011, we use a spatio-temporal modelling framework to model variations in malaria risk in Malawi. Climatic and topographic variations are accounted for using an interpolation method to relate gridded products to administrative districts. District level data is tested in the model to account for confounding factors, including the proportion of the population living in urban areas; residing in traditional housing; with no toilet facilities; who do not attend school, etc, the number of health facilities per population and yearly estimates of insecticide-treated mosquito net distribution. In order to account for the unobserved confounding factors that influence malaria, which are not accounted for using measured covariates, a negative binomial generalised linear mixed model (GLMM) is adopted, which includes structured and unstructured spatial and temporal random effects. The parameters in this spatio-temporal Bayesian hierarchical model are estimated using Markov Chain Monte Carlo (MCMC). This allows posterior predictive distributions for disease risk to be derived for each spatial location and time period. A novel visualisation technique is then used to display seasonal probabilistic forecasts of malaria risk, derived from the developed model using pre-defined risk category thresholds, on a map. This technique allows decision makers to identify areas where the model predicts with certainty a particular malaria risk category (high, medium or low); in order to effectively target limited resources to those districts most at risk for a given season.

Lowe, R.; Chirombo, J.; Tompkins, A. M.

2012-04-01

265

Automatic validation of computational models using pseudo-3D spatio-temporal model checking.  

PubMed

BackgroundComputational models play an increasingly important role in systems biology for generating predictions and in synthetic biology as executable prototypes/designs. For real life (clinical) applications there is a need to scale up and build more complex spatio-temporal multiscale models; these could enable investigating how changes at small scales reflect at large scales and viceversa. Results generated by computational models can be applied to real life applications only if the models have been validated first. Traditional in silico model checking techniques only capture how non-dimensional properties (e.g. concentrations) evolve over time and are suitable for small scale systems (e.g. metabolic pathways). The validation of larger scale systems (e.g. multicellular populations) additionally requires capturing how spatial patterns and their properties change over time, which are not considered by traditional non-spatial approaches.ResultsWe developed and implemented a methodology for the automatic validation of computational models with respect to both their spatial and temporal properties. Stochastic biological systems are represented by abstract models which assume a linear structure of time and a pseudo-3D representation of space (2D space plus a density measure). Time series data generated by such models is provided as input to parameterised image processing modules which automatically detect and analyse spatial patterns (e.g. cell) and clusters of such patterns (e.g. cellular population). For capturing how spatial and numeric properties change over time the Probabilistic Bounded Linear Spatial Temporal Logic is introduced. Given a collection of time series data and a formal spatio-temporal specification the model checker Mudi (http://mudi.modelchecking.org) determines probabilistically if the formal specification holds for the computational model or not. Mudi is an approximate probabilistic model checking platform which enables users to choose between frequentist and Bayesian, estimate and statistical hypothesis testing based validation approaches. We illustrate the expressivity and efficiency of our approach based on two biological case studies namely phase variation patterning in bacterial colony growth and the chemotactic aggregation of cells.ConclusionsThe formal methodology implemented in Mudi enables the validation of computational models against spatio-temporal logic properties and is a precursor to the development and validation of more complex multidimensional and multiscale models. PMID:25440773

Pârvu, Ovidiu; Gilbert, David

2014-12-01

266

A working spatio-temporal model of the human visual system for image restoration and quality assessment applications  

Microsoft Academic Search

This paper describes a spatio-temporal model of the human visual system (HVS) for video imaging applications, predicting the response of the neurons of the primary visual cortex. The model simulates the behavior of the HVS with a three-dimensional filter bank which decomposes the data into perceptual channels, each one being tuned to a specific spatial frequency, orientation and temporal frequency.

1996-01-01

267

Fire, native species, and soil resource interactions influence the spatio-temporal invasion pattern of Bromus tectorum  

Microsoft Academic Search

Bromus tectorum (cheatgrass) is an invasive annual that occupies perennial grass and shrub communities throughout the western United States. Bromus tectorum exhibits an intriguing spatio-temporal pattern of invasion in low elevation ponderosa pine Pinus ponderosa\\/bunchgrass communities in western Montana where it forms dense rings beneath solitary pines following fire. This pattern provides a unique opportunity to investigate several indirect effects

Michael J. Gundale; Steve Sutherland; Thomas H. DeLuca

2008-01-01

268

Combined Spatio-Temporal Impacts of Climate and Longline Fisheries on the Survival of a Trans-Equatorial  

E-print Network

'Histoire Naturelle, Paris, France Abstract Predicting the impact of human activities and their derivable consequences relevant human impacts for the sustainability of our oceans [1,2]. Due to the complexity of theCombined Spatio-Temporal Impacts of Climate and Longline Fisheries on the Survival of a Trans

269

Predicting the rate of range expansion of an invasive alien bumblebee ( Bombus terrestris) using a stochastic spatio-temporal model  

Microsoft Academic Search

To develop effective strategies for managing biological invasions, it is important to understand and be able to predict patterns of invasion and range expansion, and particularly the rate of spread and factors controlling this rate. To predict the spatial dynamics of invasion by an alien bumblebee (Bombus terrestris) in Hokkaido, Japan, we explicitly constructed a stochastic spatio-temporal model that incorporates

Taku Kadoya; Izumi Washitani

2010-01-01

270

SocioScape a Tool for Interactive Exploration of Spatio-Temporal Group Dynamics in Social Networks  

E-print Network

SocioScape ­ a Tool for Interactive Exploration of Spatio-Temporal Group Dynamics in Social Networks Khairi Reda* Chayant Tantipathananandh Tanya Berger-Wolf Jason Leigh* Andrew Johnson* *Electronic exploration of spatially referenced, dynamic social networks. The tool combines a novel depiction methodology

Johnson, Andrew

271

Hierarchical Bayesian modeling of spatio-temporal patterns of lung cancer incidence risk in Georgia, USA: 2000-2007  

NASA Astrophysics Data System (ADS)

Lung cancer is the second most commonly diagnosed cancer in both men and women in Georgia, USA. However, the spatio-temporal patterns of lung cancer risk in Georgia have not been fully studied. Hierarchical Bayesian models are used here to explore the spatio-temporal patterns of lung cancer incidence risk by race and gender in Georgia for the period of 2000-2007. With the census tract level as the spatial scale and the 2-year period aggregation as the temporal scale, we compare a total of seven Bayesian spatio-temporal models including two under a separate modeling framework and five under a joint modeling framework. One joint model outperforms others based on the deviance information criterion. Results show that the northwest region of Georgia has consistently high lung cancer incidence risk for all population groups during the study period. In addition, there are inverse relationships between the socioeconomic status and the lung cancer incidence risk among all Georgian population groups, and the relationships in males are stronger than those in females. By mapping more reliable variations in lung cancer incidence risk at a relatively fine spatio-temporal scale for different Georgian population groups, our study aims to better support healthcare performance assessment, etiological hypothesis generation, and health policy making.

Yin, Ping; Mu, Lan; Madden, Marguerite; Vena, John E.

2014-10-01

272

Macroprogramming Spatio-temporal Event Detection and Data Collection in Wireless Sensor Networks: An Implementation and Evaluation Study  

Microsoft Academic Search

This paper proposes and evaluates a spatio-temporal macroprogramming paradigm for wireless sensor networks (WSNs). The proposed paradigm, called SpaceTime Oriented Programming (STOP), is designed to reduce the complexity to program event detection and data collection by specify- ing them from a global viewpoint as a whole rather than a viewpoint of sensor nodes as individuals. STOP treats space and time

Hiroshi Wada; Pruet Boonma; Junichi Suzuki

2008-01-01

273

In-situ, high spatio-temporal resolution measurements of CO2 flux and isotopic composition on Mammoth Mountain, CA  

NASA Astrophysics Data System (ADS)

Measurement of CO2 emissions from volcano flanks and in ground waters has become an integral part of many monitoring programs, as spatial and temporal variations in these emissions may be indicative of volcanic unrest. The source and magnitude of CO2 emissions have been intensely studied at Mammoth Mountain, a dacitic volcano located on the rim of Long Valley caldera, California. These observations, combined with multiple geophysical data sets, suggest that unrest at Mammoth Mountain is driven by periodic release of CO2-rich magmatic fluid derived from basaltic dikes and sills at mid-crustal depths. While measurements of CO2 flux and determination of CO2 sources at volcanoes can place important constraints on gas transport and its relationship to volcanic activity, the spatio-temporal resolution of these measurements has been limited by the time and cost associated with making “point” CO2 flux measurements using the accumulation chamber (AC) method and sample collection and analysis of isotopic (14C-CO2 and 13C-CO2) compositions. We present a novel instrument platform for real-time monitoring of spatio-temporal distribution, emission rate and source of CO2 in volcanic systems. Time and space averaged CO2 fluxes are measured every half hour by the eddy covariance (EC) method. Least-squares inversions of EC data and modeled footprint functions provide estimates of CO2 emission rate and surface flux spatial distribution. AC measurements of soil CO2 flux yield detailed maps of flux spatial distribution and comparative emission rate estimates. A new field-portable isotopic analyzer provides, for the first time, in-situ, high frequency measurements of 14C and 13C compositions of CO2 in the atmosphere, soil gas, and dissolved in ground water. We tested the CO2 flux-monitoring component of this platform at the Horseshoe Lake tree kill area on Mammoth Mountain from 8 September to 24 October 2006. EC CO2 fluxes ranged from 218 to 3500 g m-2d-1. Maps of surface CO2 flux were simulated based on AC measurements made repeatedly on a grid over a ten-day period; large meteorologically driven variations in surface flux distributions and emission rates (16 to 52 t d-1) were observed. Using footprint modeling, we compared EC to AC measurements of CO2 flux. Half-hour EC CO2 fluxes were moderately correlated (R2 = 0.42) with AC fluxes, whereas average-daily EC and AC fluxes were well correlated (R2 = 0.70). The integrated CO2 flux and isotopic monitoring platform will be deployed and tested in Fall 2010 at Mammoth Mountain. EC and AC measurements of CO2 fluxes will be made at the Horseshoe Lake tree kill area and modeled CO2 surface flux distributions and emission rates will be compared. Measurements of 14C and 13C compositions of atmospheric, soil, and ground water CO2 will provide real-time determination of CO2 source.

Lewicki, J. L.; Hilley, G. E.; Marino, B.; Bergfeld, D.; Fischer, M. L.; Hancyk, J.; Xu, L.

2010-12-01

274

Risk management in spatio-temporally varying field by true slime mold  

NASA Astrophysics Data System (ADS)

Revealing how lower organisms solve complicated problems is a challenging research area, which could reveal the evolutionary origin of biological information processing. Here we report on the ability of a single-celled organism, true slime mold, to find a smart solution of risk management under spatio-temporally varying conditions. We designed test conditions under which there were three food-locations at vertices of equilateral triangle and a toxic light illuminated the organism on alternating halves of the triangle. We found that the organism behavior depended on the period of the repeated illumination, even though the total exposure time was kept the same . A simple mathematical model for the experimental results is proposed from a dynamical system point of view. We discuss our results in the context of a strategy of risk management by Physarum.

Ito, Kentaro; Sumpter, David; Nakagaki, Toshiyuki

275

Taming of Modulation Instability by Spatio-Temporal Modulation of the Potential  

E-print Network

Spontaneous pattern formation in a variety of spatially extended nonlinear system always occurs through a modulation instability: homogeneous state of the system becomes unstable with respect to growing modulation modes. Therefore, the manipulation of the modulation instability is of primary importance in controlling and manipulating the character of spatial patterns initiated by that instability. We show that the spatio-temporal periodic modulation of the potential of the spatially extended system results in a modification of its pattern forming instability. Depending on the modulation character the instability can be partially suppressed, can change its spectrum (for instance the long wave instability can transform into short wave instability), can split into two, or can be completely eliminated. The latter result is of especial practical interest, as can be used to stabilize the intrinsically unstable system. The result bears general character, as it is shown here on a universal model of Complex Ginzburg-L...

Kumar, S; Botey, M; Staliunas, K

2015-01-01

276

Writer Identification Using Super Paramagnetic Clustering and Spatio Temporal Neural Network  

NASA Astrophysics Data System (ADS)

This paper discusses use of Super Paramagnetic Clustering (SPC) and Spatio Temporal Artificial Neuron in on-line writer identification, on Farsi handwriting. In online cases, speed and automation are advantages of one method on others, therefore we used unsupervised and relatively quick clustering method, which in comparison with conventional approaches, give us better result. Moreover, regardless of various parameters that available from acquisition systems, we only consider to displacement of pen tip at determined direction that lead to quick system due to its quick preprocessing and clustering. Also we use a threshold that remove displacement between disconnected point of a word that lead to a better classification result on on-line Farsi writers.

Taghavi Sangdehi, Seyyed Ataollah; Faez, Karim

277

Assessment of soil organic carbon distribution in Europe scale by spatio-temporal data and geostatistics  

NASA Astrophysics Data System (ADS)

Accuracy in assessing the distribution of soil organic carbon (SOC) is an important issue because SOC is an important soil component that plays key roles in the functions of both natural ecosystems and agricultural systems. The SOC content varies from place to place and it is strongly related with climate variables (temperature and rainfall), terrain features, soil texture, parent material, vegetation, land-use types, and human management (management and degradation) at different spatial scales. Geostatistical techniques allow for the prediction of soil properties using soil information and environmental covariates. In this study, assessment of SOC distribution has been predicted using combination of LUCAS soil samples with local soil data and ten spatio-temporal predictors (slope, aspect, elevation, CTI, CORINE land-cover classification, parent material, texture, WRB soil classification, average temperature and precipitation) with Regression-Kriging method in Europe scale. Significant correlation between the covariates and the organic carbon dependent variable was found.

Aksoy, Ece; Panagos, Panos; Montanarella, Luca

2013-04-01

278

Assessing the spatio-temporal variations of the completeness magnitude for seismic events in Venezuela  

NASA Astrophysics Data System (ADS)

We investigate the spatio temporal variation of the completeness magnitude Mc, for a set of 18774 well localized earthquakes registered by the Venezuelan Seismological Network over the period 2000-2010. In the entire seismicity region we defined two-dimensional grids of different sizes in order to map the Mc: 11 km, 22 km, 55 km and 111 km. We calculated the completeness magnitude using the Maximum Curvature method (MAXC) for every particular cell taking at least 15 earthquakes to perform computations. The results show an overall variation from 2.0 to 3.6. We found different thresholds and ranges of Mc depending on the dimension of the seismicity zone: western region from 2.2 to 2.8, north central from 2.0 to 3.2 and eastern region from 2.2 to 3.2. We also include remarks in border seismicity, close to Colombia and Trinidad, where the largest Mc values are estimated.

Vasquez, R.; Bravo, L.

2013-05-01

279

Analysis of Spatio-Temporal Preferences and Encounter Statistics for DTN Performance  

E-print Network

Spatio-temporal preferences and encounter statistics provide realistic measures to understand mobile user's behavioral preferences and transfer opportunities in Delay Tolerant Networks (DTNs). The time dependent behavior and periodic reappearances at specific locations can approximate future online presence while encounter statistics can aid to forward the routing decisions. It is theoretically shown that such characteristics heavily affect the performance of routing protocols. Therefore, mobility models demonstrating such characteristics are also expected to show identical routing performance. However, we argue models despite capturing these properties deviate from their expected routing performance. We use realistic traces to validate this observation on two mobility models. Our empirical results for epidemic routing show those models' largely differ (delay 67% & reachability 79%) from the observed values. This in-turn call for two important activities: (i) Analogous to routing, explore structural prope...

Thakur, Gautam S; Helmy, Ahmed; Hsu, Wei-Jen

2010-01-01

280

Spatio-Temporal Structuring of Brain Activity - Description of Interictal EEG in Paediatric Frontal Lobe Epilepsy  

E-print Network

A method for the quantitative assessment of spatio-temporal structuring of brain activity is presented. This approach is employed in a longitudinal case study of a child with frontal lobe epilepsy (FLE) and tested against an age-matched control group. Several correlation measures that are sensitive to linear and/or non-linear relations in multichannel scalp EEG are combined with an hierarchical cluster algorithm. Beside a quantitative description of the overall degree of synchronization the spatial relations are investigated by means of the cluster characteristics. The chosen information measures not only demonstrate their suitability in the characterization of the ictal and interictal phases but they also follow the course of delayed recovery of the psychiatric symptomatology during successful medication. The results based on this single case study suggest testing this approach for quantitative control of therapy in an extended clinical trial.

Bunk, W; Kluger, G; Springer, S

2009-01-01

281

Spatio-TemporalMetasurface for Real-time 2-D Spectrum Analysis  

E-print Network

A spatio-temporal metasurface is proposed to decompose in real time the temporal frequencies of electromagnetic waves into spatial frequencies onto a two-dimensional plane. The metasurface is analyzed and demonstrated using Fourier analysis. The required transmittance function is derived from an equivalent free-space optical system consisting of the cascade combination of a wedge, a diffraction grating and a focusing lens. The metasurface must exhibit both multi-resonance over a broad bandwidth and 1-D grating-type scanning to achieve the specified 2-D frequency scanning in space. Compared to state-of-the art related systems, the proposed metasurface system is more compact as it requires only one dispersive structure, while maintaining the high frequency resolution that characterizes 2-D spatial-temporal mapping systems.

Gupta, Shulabh

2014-01-01

282

Geographic boundary analysis in spatial and spatio-temporal epidemiology: Perspective and prospects  

PubMed Central

Geographic boundary analysis is a relatively new approach that is just beginning to be applied in spatial and spatio-temporal epidemiology to quantify spatial variation in health outcomes, predictors and correlates; generate and test epidemiologic hypotheses; to evaluate health-environment relationships; and to guide sampling design. Geographic boundaries are zones of rapid change in the value of a spatially distributed variable, and mathematically may be defined as those locations with a large second derivative of the spatial response surface. Here we introduce a pattern analysis framework based on Value, Change and Association questions, and boundary analysis is shown to fit logically into Change and Association paradigms. This article addresses fundamental questions regarding what boundary analysis can tell us in public health and epidemiology. It explains why boundaries are of interest, illustrates analysis approaches and limitations, and concludes with prospects and future research directions. PMID:21218153

Jacquez, Geoffrey M.

2010-01-01

283

A satellite-remote-sensing-based marine and atmospheric spatio-temporal data model  

NASA Astrophysics Data System (ADS)

In this study, a marine and atmospheric spatio-temporal data model (MASTDM) based on satellite remote sensing has been developed to support the global oceanic and atmospheric research and application in the Marine and Atmospheric Geographical Information System (MAGIS). MASTDM conceptualizes the spatial distribution and temporal sampling of the satellite remote sensing data. The model has provided a mechanism service to store data and some subroutines to retrieve and manipulate data. These subroutines can be classified into the fundamental functions (definition, access, inquiry, export) and the advanced functions (transform, operation, validation and mend and etc). MASTDM is not only a solid foundation of the three modules (database management, spatial-temporal analysis and visualization) of MAGIS, but also a key to integrate these three modules seamlessly. In this paper, the conceptual and logical designs of MASTDM have been presented. A prototype system based on MASTDM has been implemented in MAGIS, it is also illustrated by some case study.

Fang, Chaoyang; Lin, Hui; Guilbert, Eric; Chen, Ge

2006-10-01

284

Spatio-temporal variability of faunal and floral assemblages in Mediterranean temporary wetlands.  

PubMed

Six temporary wetlands in the region of Sejenane (Mogods, NW Tunisia) were studied in order to characterize the aquatic flora and fauna and to quantify their spatio-temporal variability. Samplings of aquatic fauna, phytosociological relevés, and measurements of the physicochemical parameters of water were taken during four different field visits carried out during the four seasons of the year (November 2009-July 2010). Despite the strong anthropic pressures on them, these temporary wetlands are home to rich and diversified biodiversity, including rare and endangered species. Spatial and temporal variations affect fauna and flora differently, as temporal variability influences the fauna rather more than the plants, which are relatively more dependent on spatial factors. These results demonstrate the interest of small water bodies for maintaining biodiversity at the regional level, and thus underscore the conservation issues of Mediterranean temporary wetlands that are declining on an ongoing basis currently. PMID:25433562

Rouissi, Maya; Boix, Dani; Muller, Serge D; Gascón, Stéphanie; Ruhí, Albert; Sala, Jordi; Bouattour, Ali; Ben Haj Jilani, Imtinen; Ghrabi-Gammar, Zeineb; Ben Saad-Limam, Samia; Daoud-Bouattour, Amina

2014-12-01

285

Dimensionality of the spatio-temporal entanglement of PDC photon pairs  

E-print Network

In this work the Schmidt number of the two-photon state generated by parametric-down conversion (PDC) is evaluated in the framework of a fully spatio-temporal model for PDC. A comparison with the results obtained in either purely spatial or purely temporal models shows that the degree of entanglement of the PDC state cannot be trivially reduced to the product of the Schmidt numbers obtained in models with lower dimensionality, unless the detected bandwidth is very narrow. This result is a consequence of the non-factorability of the state in the spatial and temporal degrees of freedoms of twin photons. In the limit of a broad pump beam, we provide a geometrical interpretation of the Schmidt number, as the ratio between the volume of the phase matching region and of a correlation volume.

A. Gatti; T. Corti; E. Brambilla; D. B. Horoshko

2012-07-30

286

The spatio-temporal distribution dynamics of Ebola virus proteins and RNA in infected cells  

PubMed Central

Here, we used a biologically contained Ebola virus system to characterize the spatio-temporal distribution of Ebola virus proteins and RNA during virus replication. We found that viral nucleoprotein (NP), the polymerase cofactor VP35, the major matrix protein VP40, the transcription activator VP30, and the minor matrix protein VP24 were distributed in cytoplasmic inclusions. These inclusions enlarged near the nucleus, became smaller pieces, and subsequently localized near the plasma membrane. GP was distributed in the cytoplasm and transported to the plasma membrane independent of the other viral proteins. We also found that viral RNA synthesis occurred within the inclusions. Newly synthesized negative-sense RNA was distributed inside the inclusions, whereas positive-sense RNA was distributed both inside and outside. These findings provide useful insights into Ebola virus replication. PMID:23383374

Nanbo, Asuka; Watanabe, Shinji; Halfmann, Peter; Kawaoka, Yoshihiro

2013-01-01

287

Effects of Spatio-Temporal Aliasing on Out-the-Window Visual Systems  

NASA Technical Reports Server (NTRS)

Designers of out-the-window visual systems face a challenge when attempting to simulate the outside world as viewed from a cockpit. Many methodologies have been developed and adopted to aid in the depiction of particular scene features, or levels of static image detail. However, because aircraft move, it is necessary to also consider the quality of the motion in the simulated visual scene. When motion is introduced in the simulated visual scene, perceptual artifacts can become apparent. A particular artifact related to image motion, spatiotemporal aliasing, will be addressed. The causes of spatio-temporal aliasing will be discussed, and current knowledge regarding the impact of these artifacts on both motion perception and simulator task performance will be reviewed. Methods of reducing the impact of this artifact are also addressed

Sweet, Barbara T.; Stone, Leland S.; Liston, Dorion B.; Hebert, Tim M.

2014-01-01

288

Heterogeneity in hotspots: spatio-temporal patterns in neglected parasitic diseases.  

PubMed

Cryptosporidiosis and giardiasis have been recognized by the WHO as 'Neglected Diseases'. Minimal attention has been paid to the spatial and temporal distribution of disease incidence patterns. Using disease notification data, we detected spatio-temporal clusters of cryptosporidiosis and giardiasis across three time periods: (i) 1997-2000, (ii) 2001-2004, (iii) 2005-2008. There was substantial variation in the geographical location and timing of recurrent cryptosporidiosis and giardiasis clusters. Statistically significant (P < 0·05) giardiasis clusters tended to occur in predominantly urban areas with little apparent seasonal influence, while statistically significant cryptosporidiosis clusters were detected in spring, in areas with high livestock land use. The location and timing of cryptosporidiosis clusters suggest an influence of livestock production practices, while urban exposures and host behaviour are likely to influence giardiasis clusters. This approach provides a resource-efficient method for public health authorities to prioritize future research needs and areas for intervention. PMID:24819745

Lal, A; Hales, S

2015-02-01

289

Holographic frequency resolved optical gating for spatio-temporal characterization of ultrashort optical pulse  

NASA Astrophysics Data System (ADS)

We introduce a novel method for characterizing the spatio-temporal evolution of ultrashort optical field by recording the spectral hologram of frequency resolved optical gating (FROG) trace. We show that FROG holography enables the measurement of phase (up to an overall constant) and group delay of the pulse which cannot be measured by conventional FROG method. To illustrate our method, we perform numerical simulation to generate holographic collinear FROG (cFROG) trace of a chirped optical pulse and retrieve its complex profile at multiple locations as it propagates through a hypothetical dispersive medium. Further, we experimentally demonstrate our method by retrieving a 67 fs pulse at three axial locations in the vicinity of focus of an objective lens and compute its group delay.

Mehta, Nikhil; Yang, Chuan; Xu, Yong; Liu, Zhiwen

2014-09-01

290

Predicted spatio-temporal dynamics of radiocesium deposited onto forests following the Fukushima nuclear accident  

PubMed Central

The majority of the area contaminated by the Fukushima Dai-ichi nuclear power plant accident is covered by forest. To facilitate effective countermeasure strategies to mitigate forest contamination, we simulated the spatio-temporal dynamics of radiocesium deposited into Japanese forest ecosystems in 2011 using a model that was developed after the Chernobyl accident in 1986. The simulation revealed that the radiocesium inventories in tree and soil surface organic layer components drop rapidly during the first two years after the fallout. Over a period of one to two years, the radiocesium is predicted to move from the tree and surface organic soil to the mineral soil, which eventually becomes the largest radiocesium reservoir within forest ecosystems. Although the uncertainty of our simulations should be considered, the results provide a basis for understanding and anticipating the future dynamics of radiocesium in Japanese forests following the Fukushima accident. PMID:23995073

Hashimoto, Shoji; Matsuura, Toshiya; Nanko, Kazuki; Linkov, Igor; Shaw, George; Kaneko, Shinji

2013-01-01

291

Spatio-temporal heterogeneity of riparian soil morphology in a restored floodplain  

NASA Astrophysics Data System (ADS)

Floodplains have been intensively altered in industrialized countries, but are now increasingly being restored. It is therefore important to assess the effect of these restoration projects on the aquatic and terrestrial components of ecosystems. However, despite being functionally crucial components of terrestrial ecosystems, soils are generally overlooked in floodplain restoration assessments. We studied the spatio-temporal heterogeneity of soil morphology in a restored (riverbed widening) river reach along the River Thur (Switzerland) using three criteria (soil diversity, dynamism and typicality) and their associated indicators. We hypothesized that these criteria would correctly discriminate the post-restoration changes in soil morphology, and that these changes correspond to patterns of vascular plant diversity. Soil diversity and dynamism increased 5 yr after the restoration, but some typical soils of braided rivers were still missing. Soil typicality and dynamism were correlated to vegetation changes. These results suggest a limited success of the project, in agreement with evaluations carried out at the same site using other, more resource-demanding, methods (e.g., soil fauna, fish diversity, ecosystem functioning). Soil morphology provides structural and functional information on floodplain ecosystems. The spatio-temporal heterogeneity of soil morphology represents a cost-efficient ecological indicator that could easily be integrated into rapid assessment protocols of floodplain and river restoration projects. The follow-up assessment after several major floods (? HQ20) should take place to allow for testing the longer-term validity of our conclusion for the River Thur site. More generally, it would be useful to apply the soil morphology indicator approach in different settings to test its broader applicability.

Fournier, B.; Guenat, C.; Bullinger-Weber, G.; Mitchell, E. A. D.

2013-10-01

292

Spatio-temporal dynamics induced by competing instabilities in two asymmetrically coupled nonlinear evolution equations.  

PubMed

Pattern formation often occurs in spatially extended physical, biological, and chemical systems due to an instability of the homogeneous steady state. The type of the instability usually prescribes the resulting spatio-temporal patterns and their characteristic length scales. However, patterns resulting from the simultaneous occurrence of instabilities cannot be expected to be simple superposition of the patterns associated with the considered instabilities. To address this issue, we design two simple models composed by two asymmetrically coupled equations of non-conserved (Swift-Hohenberg equations) or conserved (Cahn-Hilliard equations) order parameters with different characteristic wave lengths. The patterns arising in these systems range from coexisting static patterns of different wavelengths to traveling waves. A linear stability analysis allows to derive a two parameter phase diagram for the studied models, in particular, revealing for the Swift-Hohenberg equations, a co-dimension two bifurcation point of Turing and wave instability and a region of coexistence of stationary and traveling patterns. The nonlinear dynamics of the coupled evolution equations is investigated by performing accurate numerical simulations. These reveal more complex patterns, ranging from traveling waves with embedded Turing patterns domains to spatio-temporal chaos, and a wide hysteretic region, where waves or Turing patterns coexist. For the coupled Cahn-Hilliard equations the presence of a weak coupling is sufficient to arrest the coarsening process and to lead to the emergence of purely periodic patterns. The final states are characterized by domains with a characteristic length, which diverges logarithmically with the coupling amplitude. PMID:25554062

Schüler, D; Alonso, S; Torcini, A; Bär, M

2014-12-01

293

Spatio-Temporal Variability of Aquatic Vegetation in Taihu Lake over the Past 30 Years.  

PubMed

It is often difficult to track the spatio-temporal variability of vegetation distribution in lakes because of the technological limitations associated with mapping using traditional field surveys as well as the lack of a unified field survey protocol. Using a series of Landsat remote sensing images (i.e. MSS, TM and ETM+), we mapped the composition and distribution area of emergent, floating-leaf and submerged macrophytes in Taihu Lake, China, at approximate five-year intervals over the past 30 years in order to quantify the spatio-temporal dynamics of the aquatic vegetation. Our results indicated that the total area of aquatic vegetation increased from 187.5 km(2) in 1981 to 485.0 km(2) in 2005 and then suddenly decreased to 341.3 km(2) in 2010. Similarly, submerged vegetation increased from 127.0 km(2) in 1981 to 366.5 km(2) in 2005, and then decreased to 163.3 km(2). Floating-leaf vegetation increased continuously through the study period in both area occupied (12.9 km(2) in 1981 to 146.2 km(2) in 2010) and percentage of the total vegetation (6.88% in 1981 to 42.8% in 2010). In terms of spatial distribution, the aquatic vegetation in Taihu Lake has spread gradually from the East Bay to the surrounding areas. The proportion of vegetation in the East Bay relative to that in the entire lake has decreased continuously from 62.3% in 1981, to 31.1% in 2005 and then to 21.8% in 2010. Our findings have suggested that drastic changes have taken place over the past 30 years in the spatial pattern of aquatic vegetation as well as both its relative composition and the amount of area it occupies. PMID:23823189

Zhao, Dehua; Lv, Meiting; Jiang, Hao; Cai, Ying; Xu, Delin; An, Shuqing

2013-01-01

294

A spatio-temporal mining approach towards summarizing and analyzing protein folding trajectories  

PubMed Central

Understanding the protein folding mechanism remains a grand challenge in structural biology. In the past several years, computational theories in molecular dynamics have been employed to shed light on the folding process. Coupled with high computing power and large scale storage, researchers now can computationally simulate the protein folding process in atomistic details at femtosecond temporal resolution. Such simulation often produces a large number of folding trajectories, each consisting of a series of 3D conformations of the protein under study. As a result, effectively managing and analyzing such trajectories is becoming increasingly important. In this article, we present a spatio-temporal mining approach to analyze protein folding trajectories. It exploits the simplicity of contact maps, while also integrating 3D structural information in the analysis. It characterizes the dynamic folding process by first identifying spatio-temporal association patterns in contact maps, then studying how such patterns evolve along a folding trajectory. We demonstrate that such patterns can be leveraged to summarize folding trajectories, and to facilitate the detection and ordering of important folding events along a folding path. We also show that such patterns can be used to identify a consensus partial folding pathway across multiple folding trajectories. Furthermore, we argue that such patterns can capture both local and global structural topology in a 3D protein conformation, thereby facilitating effective structural comparison amongst conformations. We apply this approach to analyze the folding trajectories of two small synthetic proteins-BBA5 and GSGS (or Beta3S). We show that this approach is promising towards addressing the above issues, namely, folding trajectory summarization, folding events detection and ordering, and consensus partial folding pathway identification across trajectories. PMID:17407611

Yang, Hui; Parthasarathy, Srinivasan; Ucar, Duygu

2007-01-01

295

Sensor Web for Spatio-Temporal Monitoring of a Hydrological Environment  

NASA Technical Reports Server (NTRS)

The Sensor Web is a macroinstrument concept that allows for the spatio-temporal understanding of an environment through coordinated efforts between multiple numbers and types of sensing platforms, including, in its most general form, both orbital and terrestrial and both fixed and mobile. Each of these platforms, or pods, communicates within its local neighborhood and thus distributes information to the instrument as a whole. The result of sharing and continual processing of this information among all the Sensor Web elements will result in an information flow and a global perception of and reactive capability to the environment. As illustrated, the Sensor Web concept also allows for the recursive notion of a web of webs with individual distributed instruments possibly playing the role of a single node point on a larger Sensor Web instrument. In particular, the fusion of inexpensive, yet sophisticated, commercial technology from both the computation and telecommunication revolutions has enabled the development of practical, fielded, and embedded in situ systems that have been the focus of the NASA/JPL Sensor Webs Project (http://sensorwebs.jpl.nasa.gov/). These Sensor Webs are complete systems consisting of not only the pod elements that wirelessly communicate among themselves, but also interfacing and archiving software that allows for easy use by the end-user. Previous successful deployments have included environments as diverse as coastal regions, Antarctica, and desert areas. The Sensor Web has broad implications for Earth and planetary science and will revolutionize the way experiments and missions are conceived and performed. As part of our current efforts to develop a macrointelligence within the system, we have deployed a Sensor Web at the Central Avra Valley Storage and Recovery Project (CAVSARP) facility located west of Tucson, AZ. This particular site was selected because it is ideal for studying spatio-temporal phenomena and for providing a test site for more sophisticated hydrological studies in the future.

Delin, K. A.; Jackson, S. P.; Johnson, D. W.; Burleigh, S. C.; Woodrow, R. R.; McAuley, M.; Britton, J. T.; Dohm, J. M.; Ferre, T. P. A.; Ip, Felipe

2004-01-01

296

Spatio-temporal pattern recognizers using spiking neurons and spike-timing-dependent plasticity.  

PubMed

It has previously been shown that by using spike-timing-dependent plasticity (STDP), neurons can adapt to the beginning of a repeating spatio-temporal firing pattern in their input. In the present work, we demonstrate that this mechanism can be extended to train recognizers for longer spatio-temporal input signals. Using a number of neurons that are mutually connected by plastic synapses and subject to a global winner-takes-all mechanism, chains of neurons can form where each neuron is selective to a different segment of a repeating input pattern, and the neurons are feed-forwardly connected in such a way that both the correct input segment and the firing of the previous neurons are required in order to activate the next neuron in the chain. This is akin to a simple class of finite state automata. We show that nearest-neighbor STDP (where only the pre-synaptic spike most recent to a post-synaptic one is considered) leads to "nearest-neighbor" chains where connections only form between subsequent states in a chain (similar to classic "synfire chains"). In contrast, "all-to-all spike-timing-dependent plasticity" (where all pre- and post-synaptic spike pairs matter) leads to multiple connections that can span several temporal stages in the chain; these connections respect the temporal order of the neurons. It is also demonstrated that previously learnt individual chains can be "stitched together" by repeatedly presenting them in a fixed order. This way longer sequence recognizers can be formed, and potentially also nested structures. Robustness of recognition with respect to speed variations in the input patterns is shown to depend on rise-times of post-synaptic potentials and the membrane noise. It is argued that the memory capacity of the model is high, but could theoretically be increased using sparse codes. PMID:23087641

Humble, James; Denham, Susan; Wennekers, Thomas

2012-01-01

297

Spatio-temporal variability of the North Sea cod recruitment in relation to temperature and zooplankton.  

PubMed

The North Sea cod (Gadus morhua, L.) stock has continuously declined over the past four decades linked with overfishing and climate change. Changes in stock structure due to overfishing have made the stock largely dependent on its recruitment success, which greatly relies on environmental conditions. Here we focus on the spatio-temporal variability of cod recruitment in an effort to detect changes during the critical early life stages. Using International Bottom Trawl Survey (IBTS) data from 1974 to 2011, a major spatio-temporal change in the distribution of cod recruits was identified in the late 1990s, characterized by a pronounced decrease in the central and southeastern North Sea stock. Other minor spatial changes were also recorded in the mid-1980s and early 1990s. We tested whether the observed changes in recruits distribution could be related with direct (i.e. temperature) and/or indirect (i.e. changes in the quantity and quality of zooplankton prey) effects of climate variability. The analyses were based on spatially-resolved time series, i.e. sea surface temperature (SST) from the Hadley Center and zooplankton records from the Continuous Plankton Recorder Survey. We showed that spring SST increase was the main driver for the most recent decrease in cod recruitment. The late 1990s were also characterized by relatively low total zooplankton biomass, particularly of energy-rich zooplankton such as the copepod Calanus finmarchicus, which have further contributed to the decline of North Sea cod recruitment. Long-term spatially-resolved observations were used to produce regional distribution models that could further be used to predict the abundance of North Sea cod recruits based on temperature and zooplankton food availability. PMID:24551103

Nicolas, Delphine; Rochette, Sébastien; Llope, Marcos; Licandro, Priscilla

2014-01-01

298

Spatio-Temporal Variability of the North Sea Cod Recruitment in Relation to Temperature and Zooplankton  

PubMed Central

The North Sea cod (Gadus morhua, L.) stock has continuously declined over the past four decades linked with overfishing and climate change. Changes in stock structure due to overfishing have made the stock largely dependent on its recruitment success, which greatly relies on environmental conditions. Here we focus on the spatio-temporal variability of cod recruitment in an effort to detect changes during the critical early life stages. Using International Bottom Trawl Survey (IBTS) data from 1974 to 2011, a major spatio-temporal change in the distribution of cod recruits was identified in the late 1990s, characterized by a pronounced decrease in the central and southeastern North Sea stock. Other minor spatial changes were also recorded in the mid-1980s and early 1990s. We tested whether the observed changes in recruits distribution could be related with direct (i.e. temperature) and/or indirect (i.e. changes in the quantity and quality of zooplankton prey) effects of climate variability. The analyses were based on spatially-resolved time series, i.e. sea surface temperature (SST) from the Hadley Center and zooplankton records from the Continuous Plankton Recorder Survey. We showed that spring SST increase was the main driver for the most recent decrease in cod recruitment. The late 1990s were also characterized by relatively low total zooplankton biomass, particularly of energy-rich zooplankton such as the copepod Calanus finmarchicus, which have further contributed to the decline of North Sea cod recruitment. Long-term spatially-resolved observations were used to produce regional distribution models that could further be used to predict the abundance of North Sea cod recruits based on temperature and zooplankton food availability. PMID:24551103

Nicolas, Delphine; Rochette, Sébastien; Llope, Marcos; Licandro, Priscilla

2014-01-01

299

Spatio-temporal malaria transmission patterns in Navrongo demographic surveillance site, northern Ghana  

PubMed Central

Background The relationship between entomological measures of malaria transmission intensity and mortality remains uncertain. This is partly because transmission is heterogeneous even within small geographical areas. Studying this relationship requires high resolution, spatially structured, longitudinal entomological data. Geostatistical models that have been used to analyse the spatio-temporal heterogeneity have not considered the uncertainty in both sporozoite rate (SR) and mosquito density data. This study analysed data from Kassena-Nankana districts in northern Ghana to obtain small area estimates of malaria transmission rates allowing for this uncertainty. Methods Independent Bayesian geostatistical models for sporozoite rate and mosquito density were fitted to produce explicit entomological inoculation rate (EIR) estimates for small areas and short time periods, controlling for environmental factors. Results Mosquitoes were trapped from 2,803 unique locations for three years using mainly CDC light traps. Anopheles gambiae constituted 52%, the rest were Anopheles funestus. Mean biting rates for An. funestus and An. gambiae were 32 and 33 respectively. Most bites occurred in September, the wettest month. The sporozoite rates were higher in the dry periods of the last two years compared with the wet period. The annual EIR varied from 1,132 to 157 infective bites. Monthly EIR varied between zero and 388 infective bites. Spatial correlation for SR was lower than that of mosquito densities. Conclusion This study confirms the presence of spatio-temporal heterogeneity in malaria transmission within a small geographical area. Spatial variance was stronger than temporal especially in the SR. The estimated EIR will be used in mortality analysis for the area. PMID:23405912

2013-01-01

300

Spatio-Temporal Simulation of First Pass Drug Perfusion in the Liver  

PubMed Central

The liver is the central organ for detoxification of xenobiotics in the body. In pharmacokinetic modeling, hepatic metabolization capacity is typically quantified as hepatic clearance computed as degradation in well-stirred compartments. This is an accurate mechanistic description once a quasi-equilibrium between blood and surrounding tissue is established. However, this model structure cannot be used to simulate spatio-temporal distribution during the first instants after drug injection. In this paper, we introduce a new spatially resolved model to simulate first pass perfusion of compounds within the naive liver. The model is based on vascular structures obtained from computed tomography as well as physiologically based mass transfer descriptions obtained from pharmacokinetic modeling. The physiological architecture of hepatic tissue in our model is governed by both vascular geometry and the composition of the connecting hepatic tissue. In particular, we here consider locally distributed mass flow in liver tissue instead of considering well-stirred compartments. Experimentally, the model structure corresponds to an isolated perfused liver and provides an ideal platform to address first pass effects and questions of hepatic heterogeneity. The model was evaluated for three exemplary compounds covering key aspects of perfusion, distribution and metabolization within the liver. As pathophysiological states we considered the influence of steatosis and carbon tetrachloride-induced liver necrosis on total hepatic distribution and metabolic capacity. Notably, we found that our computational predictions are in qualitative agreement with previously published experimental data. The simulation results provide an unprecedented level of detail in compound concentration profiles during first pass perfusion, both spatio-temporally in liver tissue itself and temporally in the outflowing blood. We expect our model to be the foundation of further spatially resolved models of the liver in the future. PMID:24625393

Schwen, Lars Ole; Krauss, Markus; Niederalt, Christoph; Gremse, Felix; Kiessling, Fabian; Schenk, Andrea; Preusser, Tobias; Kuepfer, Lars

2014-01-01

301

Spatio-Temporal Expression of Peroxisome Proliferator-Activated Receptor ? During Human Prenatal Development.  

PubMed

Peroxisome proliferator-activated receptor ? (PPAR?) is a ligand-dependent transcription factor which is activated by various endogenous as well as exogenous compounds. It is involved in the regulation of a variety of biological processes, such as nutrient metabolism, energy homoeostasis, immunological response and xenobiotic metabolism. Little is known about its expression during human prenatal development. We examined the spatio-temporal expression pattern of PPAR? in human embryonic/foetal intestines, liver and kidney from the 5th to 20th week of prenatal life by indirect two-step immunohistochemistry. PPAR? expression can already be detected in the early stages of prenatal development; as early as the 7th week of intrauterine development (IUD) in the intestines, 5th week of IUD in the liver and 6th week of IUD in the kidney. We found age-dependent changes in the PPAR? expression pattern in the intestines and kidney. These events occur approximately at the commencement of function of these organs. In the intestines, we detected an obvious change of the PPAR? expression pattern along the crypt-villous axis in the 11th week of IUD. In the kidney, the most apparent change was increased expression of PPAR? in glomeruli in the 12th week of IUD. Moreover, in the liver, we detected a strong positivity in part of the developing blood elements. Information about the spatio-temporal expression pattern of PPAR? could be the first step in evaluating the potential harmful impact of a wide range of environmental or pharmaceutical compounds which serve as PPAR? ligands on the developing human organism. PMID:25225039

Cizkova, Katerina; Rajdova, Aneta; Ehrmann, Jiri

2015-04-01

302

Spatio-Temporal Variability of Aquatic Vegetation in Taihu Lake over the Past 30 Years  

PubMed Central

It is often difficult to track the spatio-temporal variability of vegetation distribution in lakes because of the technological limitations associated with mapping using traditional field surveys as well as the lack of a unified field survey protocol. Using a series of Landsat remote sensing images (i.e. MSS, TM and ETM+), we mapped the composition and distribution area of emergent, floating-leaf and submerged macrophytes in Taihu Lake, China, at approximate five-year intervals over the past 30 years in order to quantify the spatio-temporal dynamics of the aquatic vegetation. Our results indicated that the total area of aquatic vegetation increased from 187.5 km2 in 1981 to 485.0 km2 in 2005 and then suddenly decreased to 341.3 km2 in 2010. Similarly, submerged vegetation increased from 127.0 km2 in 1981 to 366.5 km2 in 2005, and then decreased to 163.3 km2. Floating-leaf vegetation increased continuously through the study period in both area occupied (12.9 km2 in 1981 to 146.2 km2 in 2010) and percentage of the total vegetation (6.88% in 1981 to 42.8% in 2010). In terms of spatial distribution, the aquatic vegetation in Taihu Lake has spread gradually from the East Bay to the surrounding areas. The proportion of vegetation in the East Bay relative to that in the entire lake has decreased continuously from 62.3% in 1981, to 31.1% in 2005 and then to 21.8% in 2010. Our findings have suggested that drastic changes have taken place over the past 30 years in the spatial pattern of aquatic vegetation as well as both its relative composition and the amount of area it occupies. PMID:23823189

Zhao, Dehua; Lv, Meiting; Jiang, Hao; Cai, Ying; Xu, Delin; An, Shuqing

2013-01-01

303

Spatio-temporal soil moisture patterns across gradients of vegetation and topography  

NASA Astrophysics Data System (ADS)

Soil moisture dynamics control hydrological processes on various scales: changes in local water storage and potential activation of preferential flow paths influence connectivity and runoff from hillslopes and ultimately the discharge response of the stream. The spatio-temporal patterns of soil moisture, however, are dependent on a combination of local parameters such as soil type, vegetation and topography as well as meteorological conditions, antecedent moisture and seasonality. In an integrative monitoring study carried out within the CAOS observatory in Luxemburg (http://www.caos-project.de/), soil moisture was measured at 21 sites with 3 soil moisture profiles each. These sites include grassland as well as forest on the one hand and cover different hillslope positions on the other hand. This setup allows us to study both vegetation and topographic effects. The spatio-temporal patterns of soil moisture were analysed using two approaches: 1) we examined temporal persistence of soil moisture patterns with rank stability plots and addressed the variability within and between sites for contrasting meteorological conditions. 2) In a next step we focused on specific hydrologic events: two periods during summer recession were distinguished, first the drying out of the soils during a period of no precipitation, but also the continuing decline even after summer rains have started. Furthermore, the soil moisture response to three different rainfall events was examined, varying in intensity and antecedent moisture conditions. The emerging contrasts in patterns were put into context of site-specific characteristics such as vegetation and topographical position to identify controls on soil moisture dynamics for our range of sites. Ultimately, linking similarity in soil moisture response in landscapes to these controls can elucidate the hydrological functioning of landscape units and thus facilitate modelling efforts.

Hassler, Sibylle; Weiler, Markus; Blume, Theresa

2014-05-01

304

Spatio-temporal processing of words and nonwords: hemispheric laterality and acute alcohol intoxication.  

PubMed

This study examined neurofunctional correlates of reading by modulating semantic, lexical, and orthographic attributes of letter strings. It compared the spatio-temporal activity patterns elicited by real words (RW), pseudowords, orthographically regular, pronounceable nonwords (PN) that carry no meaning, and orthographically illegal, nonpronounceable nonwords (NN). A double-duty lexical decision paradigm instructed participants to detect RW while ignoring nonwords and to additionally respond to words that refer to animals (AW). Healthy social drinkers (N=22) participated in both alcohol (0.6 g/kg ethanol for men, 0.55 g/kg for women) and placebo conditions in a counterbalanced design. Whole-head MEG signals were analyzed with an anatomically-constrained MEG method. Simultaneously acquired ERPs confirm previous evidence. Spatio-temporal MEG estimates to RW and PN are consistent with the highly replicable left-lateralized ventral visual processing stream. However, the PN elicit weaker activity than other stimuli starting at ~230 ms and extending to the M400 (magnetic equivalent of N400) in the left lateral temporal area, indicating their reduced access to lexicosemantic stores. In contrast, the NN uniquely engage the right hemisphere during the M400. Increased demands on lexicosemantic access imposed by AW result in greater activity in the left temporal cortex starting at ~230 ms and persisting through the M400 and response preparation stages. Alcohol intoxication strongly attenuates early visual responses occipito-temporally overall. Subsequently, alcohol selectively affects the left prefrontal cortex as a function of orthographic and semantic dimensions, suggesting that it modulates the dynamics of the lexicosemantic processing in a top-down manner, by increasing difficulty of semantic retrieval. PMID:24565928

Marinkovic, Ksenija; Rosen, Burke Q; Cox, Brendan; Hagler, Donald J

2014-04-16

305

Approach to analysis of multiscale space-distributed time series: separation of spatio-temporal modes with essentially different time scales  

NASA Astrophysics Data System (ADS)

Natural systems are in general space-distributed, and their evolution represents a broad spectrum of temporal scales. The multiscale nature may be resulted from multiplicity of mechanisms governing the system behaviour, and a large number of feedbacks and nonlinearities. A way to reveal and understand the underlying mechanisms as well as to model corresponding sub-systems is decomposition of the full (complex) system into well separated spatio-temporal patterns ("modes") that evolve with essentially different time scales. In the report a new method of a similar decomposition is discussed. The method is based on generalization of the MSSA (Multichannel Singular Spectral Analysis) [1] for expanding space-distributed time series in basis of spatio-temporal empirical orthogonal functions (STEOF), which makes allowance delayed correlations of the processes recorded in spatially separated points. The method is applied to decomposition of the Earth's climate system: on the base of 156 years time series of SST anomalies distributed over the globe [2] two climatic modes possessing by noticeably different time scales (3-5 and 9-11 years) are separated. For more accurate exclusion of "too slow" (and thus not represented correctly) processes from real data the numerically produced STEOF basis is used. For doing this the time series generated by the INM RAS Coupled Climate Model [3] is utilized. Relations of separated modes to ENSO and PDO are investigated. Possible development of the suggested approach in order to the separation of the modes that are nonlinearly uncorrelated is discussed. 1. Ghil, M., R. M. Allen, M. D. Dettinger, K. Ide, D. Kondrashov, et al. (2002) "Advanced spectral methods for climatic time series", Rev. Geophys. 40(1), 3.1-3.41. 2. http://iridl.ldeo.columbia.edu/SOURCES/.KAPLAN/.EXTENDED/.v2/.ssta/ 3. http://83.149.207.89/GCM_DATA_PLOTTING/GCM_INM_DATA_XY_en.htm

Feigin, Alexander; Mukhin, Dmitry; Gavrilov, Andrey; Volodin, Evgeny; Loskutov, Evgeny

2014-05-01

306

Spatio-temporal hazard estimation in the Auckland Volcanic Field, New Zealand, with a new event-order model  

NASA Astrophysics Data System (ADS)

The Auckland Volcanic Field (AVF) with 49 eruptive centres in the last c. 250 ka presents many challenges to our understanding of distributed volcanic field construction and evolution. We re-examine the age constraints within the AVF and perform a correlation exercise matching the well-dated record of tephras from cores distributed throughout the field to the most likely source volcanoes, using thickness and location information and a simple attenuation model. Combining this augmented age information with known stratigraphic constraints, we produce a new age-order algorithm for the field, with errors incorporated using a Monte Carlo procedure. Analysis of the new age model discounts earlier appreciations of spatio-temporal clustering in the AVF. Instead the spatial and temporal aspects appear independent; hence the location of the last eruption provides no information about the next location. The temporal hazard intensity in the field has been highly variable, with over 63% of its centres formed in a high-intensity period between 40 and 20 ka. Another, smaller, high-intensity period may have occurred at the field onset, while the latest event, at 504 ± 5 years B.P., erupted 50% of the entire field's volume. This emphasises the lack of steady-state behaviour that characterises the AVF, which may also be the case in longer-lived fields with a lower dating resolution. Spatial hazard intensity in the AVF under the new age model shows a strong NE-SW structural control of volcanism that may reflect deep-seated crustal or subduction zone processes and matches the orientation of the Taupo Volcanic Zone to the south.

Bebbington, Mark S.; Cronin, Shane J.

2011-01-01

307

Fast prototyping of wavelet spatio-temporal RS fusion with Raingauge time series with GDAL and Python-DWT  

NASA Astrophysics Data System (ADS)

Availability of rainfall time-series is limited in many parts of the World, and the continuity of such records is variable. This research endeavors to extend actual daily rainfall observations to ungauged areas using vegetation response as witnessed by remote sensing data and taking into account rainfall event histograms as well as cumulative total daily rainfall, over a period of 11 years. Open Source code development permitted to gain on several aspects. The first one pertains to space, Python and its numerical part (NumPy) are scientifically concise, as a bonus to be expressive. The second is the availability of the Discrete Wavelet Transform (DWT) in Python already, which permitted to reduce the Wavelet Transform to a small set of instructions, clarifying and simplifying the understanding of the code once it reaches the Public Domain. GDAL interface permitted to load satellite imagery and write fused rainfall time-series in spatio-temporal dimensions. Other scientific tool from Numerical Python were also used in the process of developing the algorithm (scipy.stats.stats and scipy.interpolate.griddata). Due to the large amount of days (4019) and the kilometer based resolution of the vegetation RS data, it takes about a week for the code to resolve the fusion problem. An attempt at using an multicore interpolation implementation in Python (hpgl) which unfortunately was not an active project anymore, though certainly deserving interest. Results show that rainfall events histograms can be reconstructed, and that total cumulative rainfall is estimated with 85% accuracy, using a surrounding network of rain gauges at 30-50 km of distance from the point of study. This research can strengthen various types of research and applications such as ungauged basins research, regional climate modeling, agricultural insurance systems, etc. Further development aims at porting the code to distributed computing.

Chemin, Yann

2013-04-01

308

Nathan Becker, UCSB (KITP Pattern Conf 8-20-03) Spatio-temporal chaos in rotating Rayleigh-Benard convection Page 1 Nathan Becker, UCSB (KITP Pattern Conf 8-20-03) Spatio-temporal chaos in rotating Rayleigh-Benard convection Page 2  

E-print Network

-Benard convection Page 1 #12;Nathan Becker, UCSB (KITP Pattern Conf 8-20-03) Spatio-temporal chaos in rotating Rayleigh-Benard convection Page 2 #12;Nathan Becker, UCSB (KITP Pattern Conf 8-20-03) Spatio-temporal chaos in rotating Rayleigh-Benard convection Page 3 #12;Nathan Becker, UCSB (KITP Pattern Conf 8-20-03) Spatio

Ahlers, Guenter

309

Infomax and maximum likelihood for blind source separation  

Microsoft Academic Search

Algorithms for the blind separation of sources can be derived from several different principles. This article shows that the infomax (information-maximization) principle is equivalent to the maximum likelihood. The application of the infomax principle to source separation consists of maximizing an output entropy

Jean-Francois Cardoso

1997-01-01

310

A blind source separation technique using second-order statistics  

Microsoft Academic Search

Separation of sources consists of recovering a set of signals of which only instantaneous linear mixtures are observed. In many situations, no a priori information on the mixing matrix is available: The linear mixture should be “blindly” processed. This typically occurs in narrowband array processing applications when the array manifold is unknown or distorted. This paper introduces a new source

Adel Belouchrani; Karim Abed-Meraim; J.-F. Cardoso; E. Moulines

1997-01-01

311

Adaptive blind separation of independent sources: A deflation approach  

Microsoft Academic Search

In this paper, we address the adaptive blind source separation of independent sources using higher order statistics. Although this problem was considered in numerous works, none of the existing algorithms is guaranteed to converge to a relevant solution. Here, we propose a new separation scheme whose convergence is proved analytically. It is based on the observation that it is possible

Nathalie Delfosse; Philippe Loubaton

1995-01-01

312

Nonlinear Static and Dynamic Blind Source Separation Using Ensemble Learning  

E-print Network

Nonlinear Static and Dynamic Blind Source Separation Using Ensemble Learning Harri Valpola, Antti Honkela, and Juha Karhunen Helsinki University of Technology, Neural Networks Research Centre P.O. Box the sources. In this paper, we #12;rst consider a static nonlinear mixture model, with a successful appli

Honkela, Antti

313

Blind Source Separation by Sparse Decomposition in a Signal Dictionary  

Microsoft Academic Search

The blind source separation problem is to extract the underlying source signals from aset of linear mixtures, where the mixing matrix is unknown. This situation is common,in acoustics, radio, medical signal and image processing, hyperspectral imaging, etc.. Wesuggest a two-stage separation process. First, a priori selection of a possibly overcompletesignal dictionary (for instance a wavelet frame, or a learned dictionary)

Michael Zibulevsky; Barak A. Pearlmutter

2001-01-01

314

Blind and non-blind source detection in WMAP 5-year maps  

E-print Network

We have analyzed the efficiency in source detection and flux density estimation of blind and non-blind detection techniques exploiting the MHW2 filter applied to the Wilkinson Microwave Anisotropy Probe (WMAP) 5-year maps. A comparison with the AT20G Bright Source Sample (Massardi et al. 2008), with a completeness limit of 0.5 Jy and accurate flux measurements at 20 GHz, close to the lowest frequency of WMAP maps, has allowed us to assess the completeness and the reliability of the samples detected with the two approaches, as well as the accuracy of flux and error estimates, and their variations across the sky. The uncertainties on flux estimates given by our procedure turned out to be about a factor of 2 lower than the rms differences with AT20G measurements, consistent with the smoothing of the fluctuation field yielded by map filtering. Flux estimates were found to be essentially unbiased except that, close to the detection limit, a substantial fraction of fluxes are found to be inflated by the contribution of underlying positive fluctuations. This is consistent with expectations for the Eddington bias associated to the true errors on flux density estimates. The blind and non-blind approaches are found to be complementary: each of them allows the detection of sources missed by the other. Combining results of the two methods on the WMAP 5-year maps we have expanded the non-blindly generated New Extragalactic WMAP Point Source (NEWPS) catalogue (Lopez-Caniego et al. 2007) that was based on WMAP 3-year maps. After having removed the probably spurious objects not identified with known radio sources, the new version of the NEWPS catalogue, NEWPS_5yr comprises 484 sources detected with a signal-to-noise ratio SNR>5.

M. Massardi; M. López-Caniego; J. González-Nuevo; D. Herranz; G. De Zotti; J. L. Sanz

2008-10-14

315

Spatio-temporal patterns of forest fires: a comprehensive application of the K-function  

NASA Astrophysics Data System (ADS)

The spatial distribution of uncontrolled hazardous events, such as forest fires, is largely investigated from the scientific community with the purpose of finding out the more vulnerable areas. Mapping the location of spatio-temporal sequences for a given environmental dataset is of great impact; however, the majority of the studies miss the analysis of the aggregation over time. Nonetheless discovering unusual temporal pattern for a given time sequence is fundamental to understand the phenomena and underlying processes. The present study aims investigating both the spatial and the temporal cluster behaviour of forest fires occurrences registered in Canton Ticino (Switzerland) over a period of about 40 years and testing if space and time interact in generate clusters. To do this, the purely spatial, the time and the space-time extensions of the Ripley's K-function were applied. The Ripley's K-function is a statistic exploratory method which enables detecting whether or not a point process (e.g. the location of the ignition points) is randomly distributed. The purely spatial K-function K(r) is defined as the expected number of further events within an area of radius r around an arbitrary point of the pattern, divided by the intensity of the phenomenon. Under completely spatial randomness, the value of the K(r) is equal to the area around the point (=?r2), while observations above this theoretical value imply a clustering behaviour at the corresponding distance r. For the purely time analysis, the Ripley's K-function K(t) can be taught as a reformulation of the spatial version to detect unexpected aggregation of events over the temporal scale. For its computation, the value of the intensity used in K(r) is replaced by the total duration of the time sequence divided by the total number of observed events, and the distance r is replaced by the time interval t. Under time-regularity, K(t) equals 2t, whereas, observed measures above this theoretical value indicate a temporal cluster behaviour at the corresponding temporal scale t. For the analysis of the space-time clustering, we applied the spatio-temporal (bivariate) K-function K(r,t), which evaluates if events are closer in both space and time. Intuitively, if there is no space-time interaction K(r,t) = K(r) * K(t). Accordingly, if K(r,t) minus K(r) * K(t) is positive, this indicates an interaction between space and time in producing clusters, which arise from a well detectable spatial and temporal scales. This study allowed detecting: 1) the purely spatial and the purely temporal scales at which the registered forest fires events are clustered, given by the results of the K(r) and the K(t) computations; and 2) the time period where spatial clusters take place at a given distance scale, exhibited by the results of the K(r,t) computation. Key words: spatio-temporal sequences, cluster, Ripley's K-function, forest fires. Acknowledgements This work was partly supported by the SNFS Project No. 200021-140658, "Analysis and Modelling of Space-Time Patterns in Complex Regions". References - Bivand R., Rowlingson B., and Diggle P. (2012) - splancs package in R project - Diggle P., Chetwynd A., Haggkvist R. and Morris S. (1995) Second-order analysis of space-time clustering. Statistical Methods in Medical Research, vol. 4(2): 124-136. - R Development Core Team (2012). R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria. URL: http://www.R-project.org/. - Vega Orozco C., Tonini M., Conedera M., Kanveski M. (2012) Cluster recognition in spatial-temporal sequences: the case of forest fires, GeoInformatica, vol. 16(4): 653-673.

Tonini, Marj; Vega Orozco, Carmen; Kanevski, Mikhaïl; Conedera, Marco

2013-04-01

316

Optimizing Spatio-Temporal Sampling Designs of Synchronous, Static, or Clustered Measurements  

NASA Astrophysics Data System (ADS)

When sampling spatio-temporal random variables, the cost of a measurement may differ according to the setup of the whole sampling design: static measurements, i.e. repeated measurements at the same location, synchronous measurements or clustered measurements may be cheaper per measurement than completely individual sampling. Such "grouped" measurements may however not be as good as individually chosen ones because of redundancy. Often, the overall cost rather than the total number of measurements is fixed. A sampling design with grouped measurements may allow for a larger number of measurements thus outweighing the drawback of redundancy. The focus of this paper is to include the tradeoff between the number of measurements and the freedom of their location in sampling design optimisation. For simple cases, optimal sampling designs may be fully determined. To predict e.g. the mean over a spatio-temporal field having known covariance, the optimal sampling design often is a grid with density determined by the sampling costs [1, Ch. 15]. For arbitrary objective functions sampling designs can be optimised relocating single measurements, e.g. by Spatial Simulated Annealing [2]. However, this does not allow to take advantage of lower costs when using grouped measurements. We introduce a heuristic that optimises an arbitrary objective function of sampling designs, including static, synchronous, or clustered measurements, to obtain better results at a given sampling budget. Given the cost for a measurement, either within a group or individually, the algorithm first computes affordable sampling design configurations. The number of individual measurements as well as kind and number of grouped measurements are determined. Random locations and dates are assigned to the measurements. Spatial Simulated Annealing is used on each of these initial sampling designs (in parallel) to improve them. In grouped measurements either the whole group is moved or single measurements within the group, e.g. static measurements may be moved to another location or the sampling times may be rearranged. After several optimisation steps, the objective functions of the sampling designs are compared. Only for the best ones optimisation is pursued. After several iterations the sampling designs are selected again. Thus more and more of the low performing sampling designs are deleted and computational effort is concentrated on the most promising candidates. The use case is optimisation of a monitoring sampling design for a river. We use a flow model to simulate the spread of a pollutant that enters the system at different locations with known, location-dependent probabilities and at random times. The objective function to be minimised is the amount of pollution that is not detected. Keywords: spatio-temporal sampling design, static sample, synchronous sample, spatial simulated annealing, cost function References [1] Jaap de Gruijter, Dick Brus, Marc Bierkens, and Martin Knotters. Sampling for Natural Ressource Monitoring. Springer, 2006. [2] J. W. van Groenigen. Spatial simulated annealing for optimizing sampling, In: GeoENV I Geostatistics for environmental applications, pages 351 - 361, 1997.

Helle, Kristina; Pebesma, Edzer

2010-05-01

317

Benefiting from a migratory prey: spatio-temporal patterns in allochthonous subsidization of an Arctic predator.  

PubMed

1.?Flows of nutrients and energy across ecosystem boundaries have the potential to subsidize consumer populations and modify the dynamics of food webs, but how spatio-temporal variations in autochthonous and allochthonous resources affect consumers' subsidization remains largely unexplored. 2.?We studied spatio-temporal patterns in the allochthonous subsidization of a predator living in a relatively simple ecosystem. We worked on Bylot Island (Nunavut, Canada), where arctic foxes (Vulpes lagopus L.) feed preferentially on lemmings (Lemmus trimucronatus and Dicrostonyx groenlandicus Traill), and alternatively on colonial greater snow geese (Anser caerulescens atlanticus L.). Geese migrate annually from their wintering grounds (where they feed on farmlands and marshes) to the Canadian Arctic, thus generating a strong flow of nutrients and energy across ecosystem boundaries. 3.?We examined the influence of spatial variations in availability of geese on the diet of fox cubs (2003-2005) and on fox reproductive output (1996-2005) during different phases of the lemming cycle. 4.?Using stable isotope analysis and a simple statistical routine developed to analyse the outputs of a multisource mixing model (SIAR), we showed that the contribution of geese to the diet of arctic fox cubs decreased with distance from the goose colony. 5.?The probability that a den was used for reproduction by foxes decreased with distance from the subsidized goose colony and increased with lemming abundance. When lemmings were highly abundant, the effect of distance from the colony disappeared. The goose colony thus generated a spatial patterning of reproduction probability of foxes, while the lemming cycle generated a strong temporal variation of reproduction probability of foxes. 6.?This study shows how the input of energy owing to the large-scale migration of prey affects the functional and reproductive responses of an opportunistic consumer, and how this input is spatially and temporally modulated through the foraging behaviour of the consumer. Thus, perspectives of both landscape and foraging ecology are needed to fully resolve the effects of subsidies on animal demographic processes and population dynamics. PMID:22268371

Giroux, Marie-Andrée; Berteaux, Dominique; Lecomte, Nicolas; Gauthier, Gilles; Szor, Guillaume; Bêty, Joël

2012-05-01

318

Spatio-Temporal Evolution and Scaling Properties of Human Settlements (Invited)  

NASA Astrophysics Data System (ADS)

Growth and evolution of cities and smaller settlements is usually studied in the context of population and other socioeconomic variables. While this is logical in the sense that settlements are groups of humans engaged in socioeconomic processes, our means of collecting information about spatio-temporal distributions of population and socioeconomic variables often lack the spatial and temporal resolution to represent the processes at scales which they are known to occur. Furthermore, metrics and definitions often vary with country and through time. However, remote sensing provides globally consistent, synoptic observations of several proxies for human settlement at spatial and temporal resolutions sufficient to represent the evolution of settlements over the past 40 years. We use several independent but complementary proxies for anthropogenic land cover to quantify spatio-temporal (ST) evolution and scaling properties of human settlements globally. In this study we begin by comparing land cover and night lights in 8 diverse settings - each spanning gradients of population density and degree of land surface modification. Stable anthropogenic night light is derived from multi-temporal composites of emitted luminance measured by the VIIRS and DMSP-OLS sensors. Land cover is represented as mixtures of sub-pixel fractions of rock, soil and impervious Substrates, Vegetation and Dark surfaces (shadow, water and absorptive materials) estimated from Landsat imagery with > 94% accuracy. Multi-season stability and variability of land cover fractions effectively distinguishes between spectrally similar land covers that corrupt thematic classifications based on single images. We find that temporal stability of impervious substrates combined with persistent shadow cast between buildings results in temporally stable aggregate reflectance across seasons at the 30 m scale of a Landsat pixel. Comparison of night light brightness with land cover composition, stability and variability yields several consistent relationships that persist across a variety of settlement types and physical environments. We use the multiple threshold method of Small et al (2011) to represent a continuum of settlement density by segmenting both night light brightness and multi-season land cover characteristics. Rank-size distributions of spatially contiguous segments quantify scaling and connectivity of land cover. Spatial and temporal evolution of rank-size distributions is consistent with power laws as suggested by Zipf's Law for city size based on population. However, unlike Zipf's Law, the observed distributions persist to global scales in which the larger agglomerations are much larger than individual cities. The scaling relations observed extend from the scale of cities and smaller settlements up to vast spatial networks of interconnected settlements.

Small, C.; Milesi, C.; Elvidge, C.; Baugh, K.; Henebry, G. M.; Nghiem, S. V.

2013-12-01

319

The changing spatio-temporal dynamics of thaw lake development, Seward Peninsula, Alaska.  

NASA Astrophysics Data System (ADS)

Contemporary anthropogenic climatic warming is having an accelerated, and more pronounced effect upon Arctic regions than any other environment on Earth. Increased surface temperatures have led to widespread permafrost degradation and a shift in dynamics. One landscape manifestation of localised permafrost decay, seen to be ubiquitous across low-lying tundra regions of Alaska, Canada and Siberia, is the thermokarst lake - or 'thaw' lake. These features are seen to be truly dynamic, with a relatively rapid evolution and decay. The exact impacts of climatic perturbation on thaw lake development are in contention; however, recent studies have suggested an increased vulnerability of these features, owing to the susceptibility of the fundamental processes of initiation, expansion and drainage to climatic variation. It is often hypothesised that with current trends, thaw lakes will see a net increase in expansion rate, and areal extent, with a potential for increased drainage events. Increased permafrost thaw and thermokarst activity has also led to shifts in biogeochemical cycles, leading to an amplified release from large carbon reservoirs currently sequestered within permafrost. An example of carbon release exhibited from thaw lakes is that of methane ebullition (gas bubble formation); this has been theorised to have the potential to initiate a major positive climatic feedback leading to a continued rise in global temperatures. Due to the remote nature and large area over which these landforms occur, remotely sensed data has been widely used in order to both accurately classify features and measure change over spatially large and great temporal extents. As well as studies interpreting data collected in the visible and near-infrared spectra, studies have recently made use of radar or microwave products in order to capture imagery avoiding adverse atmospheric conditions, most notably cloud cover. Data from Envisat ASAR operating in Wide Swath Mode was acquired for this study region; however, the core of this research relied upon the analysis of the changing lake morphology using visible and near-infrared spectra from MODIS and Landsat products. This research explored: (1) intra-annual variability of freeze-thaw cycles and resultant effects on thaw lake development; and (2) the spatio-temporal trends and changing dynamism of thaw lake activity. Research presented here within suggests that although climatic trends do indeed influence widespread changes within thaw lake characteristics, site-specific phenomena of sediment type and ice-content and fluvial activity also play integral roles. Understanding and observing changing spatio-temporal dynamics, particularly on an intra-annual basis, has helped to gather more information concerning complex lake processes, and increase the understanding of permafrost decay and thaw lake development.

Cooper, Michael; Rees, Gareth; Bartsch, Annett

2014-05-01

320

Quantifying spatio-temporal variability of soil water storage and their controls at multiple scales  

NASA Astrophysics Data System (ADS)

Soil water is the primary limiting factor in semiarid ecosystems and determinant of environmental health. The distribution of soil water in space and time has important hydrologic applications. However, the spatio-temporal variability of soil water is a major challenge in hydrology as their distribution in the landscape is controlled many factors and processes acting in different intensities over a variety of scales. Quantification of these variability and their dominant controls at multiple scales can only lead to a better understanding on the soil water dynamics in space and time and on the underlying processes causing the variability. In order to quantify spatio-temporal variability, soil water content (later converted to soil water storage, SWS) was measured down to 1.4 m (0.2 m depth interval) at 128 regularly spaced locations along a transect of 576 m over a five-year period from the Hummocky landscape of central Canada. The spatial pattern of SWS was very similar (large values of Spearman's rank correlation coefficient) over the entire study period and was almost a mirror image of the spatial pattern of the relative elevation. The similarity was stronger within a season (intra-season) than the same season from different years (inter-annual) and between seasons (inter-season). The variability at multiple scales was quantified using the wavelet transform. The strongest large scale (>72 m) variability contributed from the macro-topography and a moderate medium scale (18-72 m) variability contributed from the landform elements were persistent over the entire measurement period (time stability). The locations and the scales of the most persistent spatial patterns over time and depth were quantified using the wavelet coherency. The changes in the persistent patterns indicated the changes in the scales and locations of underlying hydrological processes, which can be used to identify change in sampling domain. The similarities/dissimilarities in the spatial pattern between the surface and sub-surface measurements at different scales and locations were used to infer the whole profile hydrological dynamics (depth persistence). The variability in SWS spatial patterns was controlled by different factors at different scales. Scale specific dominant controls were identified after separating the variance contribution of each scale towards the overall variance using the Hilbert-Huang transform. The large scale macro-topographical control and medium scale landform control were much stronger than very large scale soil textural control on SWS. The scale-specific relationship with controlling factors improved the prediction of SWS.

Biswas, Asim

2014-05-01

321

Spatio-temporal analysis on enterovirus cases through integrated surveillance in Taiwan  

PubMed Central

Background Severe epidemics of enterovirus have occurred frequently in Malaysia, Singapore, Taiwan, Cambodia, and China, involving cases of pulmonary edema, hemorrhage and encephalitis, and an effective vaccine has not been available. The specific aim of this study was to understand the epidemiological characteristics of mild and severe enterovirus cases through integrated surveillance data. Methods All enterovirus cases in Taiwan over almost ten years from three main databases, including national notifiable diseases surveillance, sentinel physician surveillance and laboratory surveillance programs from July 1, 1999 to December 31, 2008 were analyzed. The Pearson’s correlation coefficient was applied for measuring the consistency of the trends in the cases between different surveillance systems. Cross correlation analysis in a time series model was applied for examining the capability to predict severe enterovirus infections. Poisson temporal, spatial and space-time scan statistics were used for identifying the most likely clusters of severe enterovirus outbreaks. The directional distribution method with two standard deviations of ellipse was applied to measure the size and the movement of the epidemic. Results The secular trend showed that the number of severe EV cases peaked in 2008, and the number of mild EV cases was significantly correlated with that of severe ones occurring in the same week [r?=?0.553, p?spatio-temporal clusters in June 2008, the mild cases had begun to rise since May 2008, and the outbreak spread from south to north. Conclusions Local public health professionals can monitor the temporal and spatial trends plus spatio-temporal clusters and isolation rate of EV-71 in mild and severe EV cases in a community when virus transmission is high, to provide early warning signals and to prevent subsequent severe epidemics. PMID:24400725

2014-01-01

322

The Critical Role of Golgi Cells in Regulating Spatio-Temporal Integration and Plasticity at the Cerebellum Input Stage  

PubMed Central

The discovery of the Golgi cell is bound to the foundation of the Neuron Doctrine. Recently, the excitable mechanisms of this inhibitory interneuron have been investigated with modern experimental and computational techniques raising renewed interest for the implications it might have for cerebellar circuit functions. Golgi cells are pacemakers with preferential response frequency and phase-reset in the theta-frequency band and can therefore impose specific temporal dynamics to granule cell responses. Moreover, through their connectivity, Golgi cells determine the spatio-temporal organization of cerebellar activity. Finally, Golgi cells, by controlling granule cell depolarization and NMDA channel unblock, regulate the induction of long-term synaptic plasticity at the mossy fiber – granule cell synapse. Thus, the Golgi cells can exert an extensive control on spatio-temporal signal organization and information storage in the granular layer playing a critical role for cerebellar computation. PMID:18982105

D'Angelo, Egidio

2008-01-01

323

Spatio-Temporal instabilities and an Intrinsic Feedback-like Mechanism in Nonlinear LiNbO3 crystals  

NASA Astrophysics Data System (ADS)

We have measured and analyzed the spatio-temporal behavior of the electro-optic (EO) responsivity of LiNbO3 single crystals. While there is no apparent feedback-loop circuit involved in the sensor system, very strong spatio-temporal instabilities appear in the EO responsivity of some LiNbO3 crystals. The temporal instability exhibits an intermittent bursting pattern, which is similar in nature to the results obtained by Grebogi et al (Phys. Rev A 36 , 5365, 1987) from numerical simulations using the Ikeda map. This intermittent bursting in our experiment is due to the interplay between the external fields and the screening fields, and stems from strong nonlinear photorefractive effects. These effects establish an intrinsic feedback-like mechanism in nonlinear LiNbO3 crystals.

Wu, Dong Ho; Wieting, Terence J.

2002-03-01

324

Spatio-temporal organization of vehicles in a cellular automata model of traffic with `slow-to-start' rule  

NASA Astrophysics Data System (ADS)

The spatio-temporal organizations of vehicular traffic in cellular-automata models with `slow-to-start' rules are qualitatively different from those in the Nagel-Schreckenberg (NaSch) model of highway traffic. Here we study the effects of such a slow-to-start rule, introduced by Benjamin, Johnson and Hui (BJH), on the distributions of the distance-headways, time-headways, jam sizes and sizes of the gaps between successive jams by a combination of approximate analytical calculations and extensive computer simulations. We compare these results for the BJH model with the corresponding results for the NaSch model and interpret the qualitative differences in the nature of the spatio-temporal organizations of traffic in these two models in terms of a phase separation of the traffic caused by the slow-to-start rule in the BJH model.

Chowdhury, Debashish; Santen, Ludger; Schadschneider, Andreas; Sinha, Shishir; Pasupathy, Abhay

1999-05-01

325

On the stochastic homogenization of fully nonlinear uniformly parabolic equations in stationary ergodic spatio-temporal media  

NASA Astrophysics Data System (ADS)

We study homogenization for fully nonlinear uniformly parabolic equations in stationary ergodic spatio-temporal media from the qualitative and quantitative perspectives. Under suitable hypotheses, solutions to fully nonlinear uniformly parabolic equations in spatio-temporal media homogenize almost surely. In addition, we obtain a logarithmic rate of convergence for this homogenization in measure, assuming that the environment is strongly mixing with a prescribed logarithmic rate. A general methodology to study the stochastic homogenization and rates of convergence for stochastic homogenization of uniformly elliptic equations was introduced by Caffarelli, Souganidis, and Wang [1], and Caffarelli and Souganidis [2]. We extend their approach to fully nonlinear uniformly parabolic equations, developing a number of new arguments to handle the parabolic structure of the problem.

Lin, Jessica

2015-02-01

326

Blind separation of delayed sources based on information maximization  

Microsoft Academic Search

Bell and Sejnowski (see Neural Computation, vol.7, no.6, p.1004-34, 1995) have presented an approach to blind source separation based on the information maximization principle. We extend this approach into more general cases where the sources may have been delayed with respect to each other. We present a network architecture capable of coping with such sources, and we derive the adaptation

Kari Torkkola

1996-01-01

327

Short-term growth (RNA\\/DNA ratio) of yellow perch ( Perca flavescens ) in relation to environmental influences and spatio-temporal variation in a shallow fluvial lake  

Microsoft Academic Search

Shallow fluvial lakes are heterogeneous ecosystems in which marked spatio-temporal variation renders diffi- cult the analysis of key ecological processes, such as growth. In this study, we used generalized additive modelling of the RNA\\/DNA ratio, an index of short-term growth, to investigate the influence of environmental variables and spatio- temporal variation on growth of yellow perch (Perca flavescens) in Lake

Hélène Glémet; Marco A. Rodríguez

2007-01-01

328

Spatio-temporal predictive model based on environmental factors for juvenile spotted seatrout in Texas estuaries using boosted regression trees  

Microsoft Academic Search

Long-term, fisheries-independent bag seine surveys conducted in TX, USA estuaries from 1977 to 2009 were used to develop a spatio-temporal species-environment model for juvenile spotted seatrout, Cynoscion nebulous. Relationships between environmental predictors and juvenile spotted seatrout distribution were investigated using boosted regression trees (BRTs). Results showed good model performance and suggested that, in relation to environmental factors, juvenile spotted seatrout

John T. Froeschke; Bridgette F. Froeschke

2011-01-01

329

Robust line-of-sight stability and jitter compensation using spatio- temporal-filtering based control approaches  

Microsoft Academic Search

A spatio-temporal filter (STF) based active vibration suppression technique is presented. The STF approach is intended for use for stability and jitter compensation for the UltraLITE Precision Deployable Experiment - a ground demonstration of a sparse array, deployable, large aperture, optical space telescope concept. This technique is well suited for control of complex, real-world structures because it requires little model

Stuart J. Shelley; Thomas D. Sharp; Keith K. Denoyer

330

Analysing Spatio-Temporal Clustering of Meningococcal Meningitis Outbreaks in Niger Reveals Opportunities for Improved Disease Control  

PubMed Central

Background Meningococcal meningitis is a major health problem in the “African Meningitis Belt” where recurrent epidemics occur during the hot, dry season. In Niger, a central country belonging to the Meningitis Belt, reported meningitis cases varied between 1,000 and 13,000 from 2003 to 2009, with a case-fatality rate of 5–15%. Methodology/Principal Findings In order to gain insight in the epidemiology of meningococcal meningitis in Niger and to improve control strategies, the emergence of the epidemics and their diffusion patterns at a fine spatial scale have been investigated. A statistical analysis of the spatio-temporal distribution of confirmed meningococcal meningitis cases was performed between 2002 and 2009, based on health centre catchment areas (HCCAs) as spatial units. Anselin's local Moran's I test for spatial autocorrelation and Kulldorff's spatial scan statistic were used to identify spatial and spatio-temporal clusters of cases. Spatial clusters were detected every year and most frequently occurred within nine southern districts. Clusters most often encompassed few HCCAs within a district, without expanding to the entire district. Besides, strong intra-district heterogeneity and inter-annual variability in the spatio-temporal epidemic patterns were observed. To further investigate the benefit of using a finer spatial scale for surveillance and disease control, we compared timeliness of epidemic detection at the HCCA level versus district level and showed that a decision based on threshold estimated at the HCCA level may lead to earlier detection of outbreaks. Conclusions/Significance Our findings provide an evidence-based approach to improve control of meningitis in sub-Saharan Africa. First, they can assist public health authorities in Niger to better adjust allocation of resources (antibiotics, rapid diagnostic tests and medical staff). Then, this spatio-temporal analysis showed that surveillance at a finer spatial scale (HCCA) would be more efficient for public health response: outbreaks would be detected earlier and reactive vaccination would be better targeted. PMID:22448297

Paireau, Juliette; Girond, Florian; Collard, Jean-Marc; Maïnassara, Halima B.; Jusot, Jean-François

2012-01-01

331

A molecular approach to combat spatio-temporal variation in insecticidal gene ( Cry1Ac ) expression in cotton  

Microsoft Academic Search

Spatio-temporal expression of an insecticidal gene (Cry1Ac) in pre existing transgenic lines of transgenic cotton was studied. Seasonal decline in expression of Cry1Ac differed significantly among different cotton lines tested in the field conditions. The leaves of the Bt cotton plants were found to have the highest levels of toxin expression followed by squares, bolls, anthers and petals. Expression\\u000a of

Allah Bakhsh; Saima Siddique; Tayyab Husnain

332

Spinodal decomposition and the emergence of dissipative transient periodic spatio-temporal patterns in acentrosomal microtubule multitudes of different morphology.  

PubMed

We have studied a spontaneous self-organization dynamics in a closed, dissipative (in terms of guansine 5'-triphosphate energy dissipation), reaction-diffusion system of acentrosomal microtubules (those nucleated and organized in the absence of a microtubule-organizing centre) multitude constituted of straight and curved acentrosomal microtubules, in highly crowded conditions, in vitro. Our data give experimental evidence that cross-diffusion in conjunction with excluded volume is the underlying mechanism on basis of which acentrosomal microtubule multitudes of different morphologies (straight and curved) undergo a spatial-temporal demix. Demix is constituted of a bifurcation process, manifested as a slow isothermal spinodal decomposition, and a dissipative process of transient periodic spatio-temporal pattern formation. While spinodal decomposition is an energy independent process, transient periodic spatio-temporal pattern formation is accompanied by energy dissipative process. Accordingly, we have determined that the critical threshold for slow, isothermal spinodal decomposition is 1.0 ± 0.05 mg/ml of microtubule protein concentration. We also found that periodic spacing of transient periodic spatio-temporal patterns was, in the overall, increasing versus time. For illustration, we found that a periodic spacing of the same pattern was 0.375 ± 0.036 mm, at 36 °C, at 155th min, while it was 0.540 ± 0.041 mm at 31 °C, and at 275th min after microtubule assembly started. The lifetime of transient periodic spatio-temporal patterns spans from half an hour to two hours approximately. The emergence of conditions of macroscopic symmetry breaking (that occur due to cross-diffusion in conjunction with excluded volume) may have more general but critical importance in morphological pattern development in complex, dissipative, but open cellular systems. PMID:23822485

Buljan, Vlado A; Holsinger, R M Damian; Brown, D; Bohorquez-Florez, J J; Hambly, B D; Delikatny, E J; Ivanova, E P; Banati, R B

2013-06-01

333

Spinodal decomposition and the emergence of dissipative transient periodic spatio-temporal patterns in acentrosomal microtubule multitudes of different morphology  

NASA Astrophysics Data System (ADS)

We have studied a spontaneous self-organization dynamics in a closed, dissipative (in terms of guansine 5'-triphosphate energy dissipation), reaction-diffusion system of acentrosomal microtubules (those nucleated and organized in the absence of a microtubule-organizing centre) multitude constituted of straight and curved acentrosomal microtubules, in highly crowded conditions, in vitro. Our data give experimental evidence that cross-diffusion in conjunction with excluded volume is the underlying mechanism on basis of which acentrosomal microtubule multitudes of different morphologies (straight and curved) undergo a spatial-temporal demix. Demix is constituted of a bifurcation process, manifested as a slow isothermal spinodal decomposition, and a dissipative process of transient periodic spatio-temporal pattern formation. While spinodal decomposition is an energy independent process, transient periodic spatio-temporal pattern formation is accompanied by energy dissipative process. Accordingly, we have determined that the critical threshold for slow, isothermal spinodal decomposition is 1.0 ± 0.05 mg/ml of microtubule protein concentration. We also found that periodic spacing of transient periodic spatio-temporal patterns was, in the overall, increasing versus time. For illustration, we found that a periodic spacing of the same pattern was 0.375 ± 0.036 mm, at 36 °C, at 155th min, while it was 0.540 ± 0.041 mm at 31 °C, and at 275th min after microtubule assembly started. The lifetime of transient periodic spatio-temporal patterns spans from half an hour to two hours approximately. The emergence of conditions of macroscopic symmetry breaking (that occur due to cross-diffusion in conjunction with excluded volume) may have more general but critical importance in morphological pattern development in complex, dissipative, but open cellular systems.

Buljan, Vlado A.; Damian Holsinger, R. M.; Brown, D.; Bohorquez-Florez, J. J.; Hambly, B. D.; Delikatny, E. J.; Ivanova, E. P.; Banati, R. B.

2013-06-01

334

Spatio-temporal stability analysis of the separated flow pa st a NACA 0015 airfoil with ZNMF jet control  

Microsoft Academic Search

The current paper presents the spatio-temporal stability a nalysis of an instance of laminar separation, with the intention of deter- mining the most appropriate forcing frequency to initiate fl ow reattachment. The flow configuration is a NACA 0015 airfoil at an angle of attack (?) where laminar separation occurs imme- diately downstream of the leading edge. A zero-net-mass-flu x (ZNMF)

V. Kitsios; A. Ooi; J. Soria

335

Blind Source Separation and the Analysis of Microarray Data  

Microsoft Academic Search

We develop an approach for the exploratory analysis of gene expression data, based upon blind source separation techniques. This approach exploits higher-order statistics to iden- tify a linear model for (logarithms of) expression profiles, described as linear combina- tions of \\

P. Chiappetta; M. C. Roubaud; Bruno Torrésani

2004-01-01

336

Spatio-temporal coherence mapping of few-cycle vortex pulses  

NASA Astrophysics Data System (ADS)

Light carrying an orbital angular momentum (OAM) displays an optical phase front rotating in space and time and a vanishing intensity, a so-called vortex, in the center. Beyond continuous-wave vortex beams, optical pulses with a finite OAM are important for many areas of science and technology, ranging from the selective manipulation and excitation of matter to telecommunications. Generation of vortex pulses with a duration of few optical cycles requires new methods for characterising their coherence properties in space and time. Here we report a novel approach for flexibly shaping and characterising few-cycle vortex pulses of tunable topological charge with two sequentially arranged spatial light modulators. The reconfigurable optical arrangement combines interferometry, wavefront sensing, time-of-flight and nonlinear correlation techniques in a very compact setup, providing complete spatio-temporal coherence maps at minimum pulse distortions. Sub-7 fs pulses carrying different optical angular momenta are generated in single and multichannel geometries and characterised in comparison to zero-order Laguerre-Gaussian beams. To the best of our knowledge, this represents the shortest pulse durations reported for direct vortex shaping and detection with spatial light modulators. This access to space-time coupling effects with sub-femtosecond time resolution opens new prospects for tailored twisted light transients of extremely short duration.

Grunwald, R.; Elsaesser, T.; Bock, M.

2014-11-01

337

Spatio-Temporal Variability in Fecal Indicator Bacteria Concentrations at Huntington Beach: Connections to Physical Forcing  

NASA Astrophysics Data System (ADS)

Two major factors determine the spatial and temporal distributions of fecal indicator bacteria (FIB) at a given beach: local circulation & mixing patterns, and bacterial inactivation rates. High frequency and spatial resolution bacterial sampling combined with measurements of physical processes can be used to infer inactivation rates, enabling differentiation between dilution & mortality as factors driving variability in nearshore FIB abundance. A FIB sampling experiment (HB06) took place on 16 October 2006, at Huntington State Beach, a site selected due to its persistent problems with FIB pollution. Water samples were taken at 20-minute intervals (from 6:50am to 11:50am) at ten locations; four in an alongshore transect spanning 1 km at the shoreline, and the remainder in a 300-m long cross-shore transect. All samples were analyzed for FIB concentration (Total Coliforms, E. coli & Enterococci) and, for a subset, species level Enterococcus composition was determined. As part of the HB06 experiment, currents, temperature, waves, and chlorophyll fluorescence were measured simultaneously in the cross-shore direction with rapid CTD casts 300 m offshore. Results indicate that E. coli and Enterococcus concentrations exhibit exponential decreases with time, with smaller decay rates associated with depth and with sites in the Talbert Marsh and Santa Ana River. FIB concentrations are also noticeably lower farther offshore (300 m). Spatio-temporal patterns in FIB concentration will be presented in conjunction with the nearshore physical data allowing the relationship between physical dynamics and biological variability to be addressed.

Rippy, M. A.; Feddersen, F.; Leichter, J.; Omand, M.; Moore, D. F.; McGee, C.; Franks, P. J.

2007-05-01

338

Hot spot detection and spatio-temporal dynamics of dengue in Queensland, Australia  

NASA Astrophysics Data System (ADS)

Dengue has been a major public health concern in Australia since it re-emerged in Queensland in 1992-1993. This study explored spatio-temporal distribution and clustering of locally-acquired dengue cases in Queensland State, Australia and identified target areas for effective interventions. A computerised locally-acquired dengue case dataset was collected from Queensland Health for Queensland from 1993 to 2012. Descriptive spatial and temporal analyses were conducted using geographic information system tools and geostatistical techniques. Dengue hot spots were detected using SatScan method. Descriptive spatial analysis showed that a total of 2,398 locally-acquired dengue cases were recorded in central and northern regions of tropical Queensland. A seasonal pattern was observed with most of the cases occurring in autumn. Spatial and temporal variation of dengue cases was observed in the geographic areas affected by dengue over time. Tropical areas are potential high-risk areas for mosquito-borne diseases such as dengue. This study demonstrated that the locally-acquired dengue cases have exhibited a spatial and temporal variation over the past twenty years in tropical Queensland, Australia. There is a clear evidence for the existence of statistically significant clusters of dengue and these clusters varied over time. These findings enabled us to detect and target dengue clusters suggesting that the use of geospatial information can assist the health authority in planning dengue control activities and it would allow for better design and implementation of dengue management programs.

Naish, S.; Tong, S.

2014-11-01

339

Drivers and Spatio-Temporal Extent of Hyporheic Patch Variation: Implications for Sampling  

PubMed Central

The hyporheic zone in stream ecosystems is a heterogeneous key habitat for species across many taxa. Consequently, it attracts high attention among freshwater scientists, but generally applicable guidelines on sampling strategies are lacking. Thus, the objective of this study was to develop and validate such sampling guidelines. Applying geostatistical analysis, we quantified the spatio-temporal variability of parameters, which characterize the physico-chemical substratum conditions in the hyporheic zone. We investigated eight stream reaches in six small streams that are typical for the majority of temperate areas. Data was collected on two occasions in six stream reaches (development data), and once in two additional reaches, after one year (validation data). In this study, the term spatial variability refers to patch contrast (patch to patch variance) and patch size (spatial extent of a patch). Patch contrast of hyporheic parameters (specific conductance, pH and dissolved oxygen) increased with macrophyte cover (r2?=?0.95, p<0.001), while patch size of hyporheic parameters decreased from 6 to 2 m with increasing sinuosity of the stream course (r2?=?0.91, p<0.001), irrespective of the time of year. Since the spatial variability of hyporheic parameters varied between stream reaches, our results suggest that sampling design should be adapted to suit specific stream reaches. The distance between sampling sites should be inversely related to the sinuosity, while the number of samples should be related to macrophyte cover. PMID:22860053

Braun, Alexander; Auerswald, Karl; Geist, Juergen

2012-01-01

340

Northern gannets anticipate the spatio-temporal occurrence of their prey.  

PubMed

Seabirds, as other marine top predators, are often assumed to forage in an unpredictable environment. We challenge this concept and test the hypothesis that breeding Northern gannets (Morus bassanus) anticipate the spatio-temporal occurrence of their prey in the English Channel. We analyzed 23 foraging tracks of Northern gannets breeding on Rouzic Island (Brittany) that were recorded using GPS loggers during 2 consecutive years. All birds commuted between the breeding colony and foraging areas located at a mean distance of 85 km and 72 km (in 2005 and 2006, respectively) from the colony. Mean linearity indices of the outbound and inbound trips were between 0.83 and 0.87, approaching a beeline path to and from the foraging area. Additional parameters (flight speed, and number and duration of stopovers at sea) for the outbound and inbound trip were not statistically different, indicating that birds are capable of locating these feeding areas in the absence of visual clues, and to pin-point their breeding site when returning from the sea. Our bearing choice analysis also revealed that gannets anticipate the general direction of their foraging area during the first 30 min and the first 10 km of the trip. These results strongly suggest that birds anticipate prey location, rather than head into a random direction until encountering a profitable area. Further investigations are necessary to identify the mechanisms involved in seabird resource localization, such as sensorial abilities, memory effects, public information or a combination of these factors. PMID:20581265

Pettex, E; Bonadonna, F; Enstipp, M R; Siorat, F; Grémillet, D

2010-07-15

341

Stability and dynamics of spatio-temporal structures. Progress report, September 15, 1992--September 15, 1993  

SciTech Connect

The main goal of the project supported in this grant is to contribute to the understanding of localized spatial and spatio-temporal structures far from thermodynamic equilibrium. Here we report on our progress in the study of two classes of systems. (1) We have started to investigate localized wave-pulses in binary-mixture convection. This work is based on our recently derived extension of the conventionally used complex Ginzburg-Landau equations. We are considering three regimes: Dispersion-less supercritical waves; strongly dispersive subcritical waves; and localized waves as bound states of fronts between dispersionless subcritical waves and the motionless conductive state. (2) We have completed our investigation of steady domain structures in which domains of structures with different wave numbers alternate, separated by domain walls. In particular, we have studied their regimes of existence and stability within the framework of a Ginzburg-Landau equation and have compared it to previous results. Those were based on a long-wavelength approximation, which misses certain aspects which turn out to be important for the stability of the domain structures in realistic situations. In addition, we give a description of our work on resonantly forced waves in two-dimensional anisotropic systems.

Riecke, H.

1993-03-01

342

Spatio-temporal activity in real time (STAR): Optimization of regional fMRI feedback  

PubMed Central

The use of real-time feedback has expanded fMRI from a brain probe to include potential brain interventions with significant therapeutic promise. However, whereas time-averaged blood oxygenation level-dependent (BOLD) signal measurement is usually sufficient for probing a brain state, the real-time (frame-to-frame) BOLD signal is noisy, compromising feedback accuracy. We have developed a new real-time processing technique (STAR) that combines noise-reduction properties of multi-voxel (e.g., whole-brain) techniques with the regional specificity critical for therapeutics. Nineteen subjects were given real-time feedback in a cognitive control task (imagining repetitive motor activity vs. spatial navigation), and were all able to control a visual feedback cursor based on whole-brain neural activity. The STAR technique was evaluated, retrospectively, for five a priori regions of interest in these data, and was shown to provide significantly better (frame-by-frame) classification accuracy than a regional BOLD technique. In addition to regional feedback signals, the output of the STAR technique includes spatio-temporal activity maps (movies) providing insight into brain dynamics. The STAR approach offers an appealing optimization for real-time fMRI applications requiring an anatomically-localized feedback signal. PMID:21232612

Magland, Jeremy F.; Tjoa, Christopher W.; Childress, Anna Rose

2011-01-01

343

Coexistence of productive and non-productive populations by fluctuation-driven spatio-temporal patterns.  

PubMed

Cooperative interactions, their stability and evolution, provide an interesting context in which to study the interface between cellular and population levels of organization. Here we study a public goods model relevant to microorganism populations actively extracting a growth resource from their environment. Cells can display one of two phenotypes - a productive phenotype that extracts the resources at a cost, and a non-productive phenotype that only consumes the same resource. Both proliferate and are free to move by diffusion; growth rate and diffusion coefficient depend only weakly phenotype. We analyze the continuous differential equation model as well as simulate stochastically the full dynamics. We find that the two sub-populations, which cannot coexist in a well-mixed environment, develop spatio-temporal patterns that enable long-term coexistence in the shared environment. These patterns are purely fluctuation-driven, as the corresponding continuous spatial system does not display Turing instability. The average stability of coexistence patterns derives from a dynamic mechanism in which the producing sub-population equilibrates with the environmental resource and holds it close to an extinction transition of the other sub-population, causing it to constantly hover around this transition. Thus the ecological interactions support a mechanism reminiscent of self-organized criticality; power-law distributions and long-range correlations are found. The results are discussed in the context of general pattern formation and critical behavior in ecology as well as in an experimental context. PMID:25058368

Behar, Hilla; Brenner, Naama; Louzoun, Yoram

2014-09-01

344

A Kinect based sign language recognition system using spatio-temporal features  

NASA Astrophysics Data System (ADS)

This paper presents a sign language recognition system that uses spatio-temporal features on RGB video images and depth maps for dynamic gestures of Turkish Sign Language. Proposed system uses motion differences and accumulation approach for temporal gesture analysis. Motion accumulation method, which is an effective method for temporal domain analysis of gestures, produces an accumulated motion image by combining differences of successive video frames. Then, 2D Discrete Cosine Transform (DCT) is applied to accumulated motion images and temporal domain features transformed into spatial domain. These processes are performed on both RGB images and depth maps separately. DCT coefficients that represent sign gestures are picked up via zigzag scanning and feature vectors are generated. In order to recognize sign gestures, K-Nearest Neighbor classifier with Manhattan distance is performed. Performance of the proposed sign language recognition system is evaluated on a sign database that contains 1002 isolated dynamic signs belongs to 111 words of Turkish Sign Language (TSL) in three different categories. Proposed sign language recognition system has promising success rates.

Memi?, Abbas; Albayrak, Songül

2013-12-01

345

Analysis of single-molecule mechanical measurements with high spatio-temporal resolution  

NASA Astrophysics Data System (ADS)

Optical tweezers allow recording mechanical data from single biological molecules such as molecular motors, DNA processing enzymes, nucleic acids. Such data consist of time series that are dominated by thermal noise and such noisy recordings require proper analysis to correctly extract kinetic and mechanical information. Several different analysis approaches have been established in the past years. Here, we propose an analysis method for optical trapping recordings of non-processive motor proteins. The method does not assume any particular interaction kinetics, allows detection of sub-millisecond interactions and quantification of the number of false and lost events. Precise alignment of interaction events and ensemble averaging allow the investigation of the stepping dynamics of non-processive motors with a temporal resolution of few tens of microseconds and a spatial resolution of few angstroms. Our analysis is applied to the study of the motor protein myosin from fast skeletal muscle. Thanks to the high spatio-temporal resolution, we can distinguish three mechanical pathways in the acto-myosin interaction, with several orders of magnitude different kinetics, which contribute in a load-dependent manner to the myosin working stroke.

Capitanio, Marco; Gardini, Lucia; Pavone, Francesco S.

2013-09-01

346

Spatio-temporal requirements for transposable element piRNA-mediated silencing during Drosophila oogenesis  

PubMed Central

During Drosophila oogenesis, transposable element (TE) repression involves the Piwi-interacting RNA (piRNA) pathway which ensures genome integrity for the next generation. We developed a transgenic model to study repression of the Idefix retrotransposon in the germline. Using a candidate gene KD-approach, we identified differences in the spatio-temporal requirements of the piRNA pathway components for piRNA-mediated silencing. Some of them (Aub, Vasa, Spn-E) are necessary in very early stages of oogenesis within the germarium and appear to be less important for efficient TE silencing thereafter. Others (Piwi, Ago3, Mael) are required at all stages of oogenesis. Moreover, during early oogenesis, in the dividing cysts within the germarium, Idefix anti-sense transgenes escape host control, and this is associated with very low piwi expression. Silencing of P-element-based transgenes is also strongly weakened in these cysts. This region, termed the ‘Piwiless pocket’ or Pilp, may ensure that new TE insertions occur and are transmitted to the next generation, thereby contributing to genome dynamics. In contrast, piRNA-mediated silencing is strong in germline stem cells in which TE mobilization is tightly repressed ensuring the continued production of viable germline cysts. PMID:24288375

Dufourt, Jérémy; Dennis, Cynthia; Boivin, Antoine; Gueguen, Nathalie; Théron, Emmanuelle; Goriaux, Coline; Pouchin, Pierre; Ronsseray, Stéphane; Brasset, Emilie; Vaury, Chantal

2014-01-01

347

Window of audio-visual simultaneity is unaffected by spatio-temporal visual clutter  

PubMed Central

In the present study we investigate the rules governing the perception of audiovisual synchrony within spatio-temporally cluttered visual environments. Participants viewed a ring of 19 discs modulating in luminance while hearing an amplitude modulating tone. Each disc modulated with a unique temporal phase (40?ms intervals), with only one synchronized to the tone. Participants searched for the synchronised disc whose spatial location varied randomly across trials. Square-wave modulation facilitated search: the synchronized disc was frequently chosen, with tight response distributions centred near zero-phase lag. In the sinusoidal condition responses were equally distributed over the 19 discs regardless of phase. To investigate whether subjective synchrony in the square-wave condition was limited by spatial or temporal factors we repeated the experiment with either reduced spatial density (9 discs) or temporal density (80?ms phase intervals). Reduced temporal density greatly facilitated synchrony perception but left the synchrony bandwidth unchanged, while no influence of spatial density was found. We conclude that audio-visual synchrony is not strongly constrained by the spatial or temporal density of the visual display, but by a temporal window within which audio-visual events are perceived as synchronous, with a full bandwidth of ~185?ms. PMID:24872325

Van der Burg, Erik; Cass, John; Alais, David

2014-01-01

348

Spatio-temporal coherence mapping of few-cycle vortex pulses.  

PubMed

Light carrying an orbital angular momentum (OAM) displays an optical phase front rotating in space and time and a vanishing intensity, a so-called vortex, in the center. Beyond continuous-wave vortex beams, optical pulses with a finite OAM are important for many areas of science and technology, ranging from the selective manipulation and excitation of matter to telecommunications. Generation of vortex pulses with a duration of few optical cycles requires new methods for characterising their coherence properties in space and time. Here we report a novel approach for flexibly shaping and characterising few-cycle vortex pulses of tunable topological charge with two sequentially arranged spatial light modulators. The reconfigurable optical arrangement combines interferometry, wavefront sensing, time-of-flight and nonlinear correlation techniques in a very compact setup, providing complete spatio-temporal coherence maps at minimum pulse distortions. Sub-7 fs pulses carrying different optical angular momenta are generated in single and multichannel geometries and characterised in comparison to zero-order Laguerre-Gaussian beams. To the best of our knowledge, this represents the shortest pulse durations reported for direct vortex shaping and detection with spatial light modulators. This access to space-time coupling effects with sub-femtosecond time resolution opens new prospects for tailored twisted light transients of extremely short duration. PMID:25413789

Grunwald, R; Elsaesser, T; Bock, M

2014-01-01

349

Evaluation of color spatio-temporal interest points for human action recognition.  

PubMed

This paper considers the recognition of realistic human actions in videos based on spatio-temporal interest points (STIPs). Existing STIP-based action recognition approaches operate on intensity representations of the image data. Because of this, these approaches are sensitive to disturbing photometric phenomena, such as shadows and highlights. In addition, valuable information is neglected by discarding chromaticity from the photometric representation. These issues are addressed by color STIPs. Color STIPs are multichannel reformulations of STIP detectors and descriptors, for which we consider a number of chromatic and invariant representations derived from the opponent color space. Color STIPs are shown to outperform their intensity-based counterparts on the challenging UCF sports, UCF11 and UCF50 action recognition benchmarks by more than 5% on average, where most of the gain is due to the multichannel descriptors. In addition, the results show that color STIPs are currently the single best low-level feature choice for STIP-based approaches to human action recognition. PMID:24577192

Everts, Ivo; van Gemert, Jan C; Gevers, Theo

2014-04-01

350

The influence of spatio-temporal resource fluctuations on insular rat population dynamics  

PubMed Central

Local spatio-temporal resource variations can strongly influence the population dynamics of small mammals. This is particularly true on islands which are bottom-up driven systems, lacking higher order predators and with high variability in resource subsidies. The influence of resource fluctuations on animal survival may be mediated by individual movement among habitat patches, but simultaneously analysing survival, resource availability and habitat selection requires sophisticated analytical methods. We use a Bayesian multi-state capture–recapture model to estimate survival and movement probabilities of non-native black rats (Rattus rattus) across three habitats seasonally varying in resource availability. We find that survival varies most strongly with temporal rainfall patterns, overwhelming minor spatial variation among habitats. Surprisingly for a generalist forager, movement between habitats was rare, suggesting individuals do not opportunistically respond to spatial resource subsidy variations. Climate is probably the main driver of rodent population dynamics on islands, and even substantial habitat and seasonal spatial subsidies are overwhelmed in magnitude by predictable annual patterns in resource pulses. Marked variation in survival and capture has important implications for the timing of rat control. PMID:21775327

Russell, James C.; Ruffino, Lise

2012-01-01

351

Geomagnetic imprinting predicts spatio-temporal variation in homing migration of pink and sockeye salmon.  

PubMed

Animals navigate using a variety of sensory cues, but how each is weighted during different phases of movement (e.g. dispersal, foraging, homing) is controversial. Here, we examine the geomagnetic and olfactory imprinting hypotheses of natal homing with datasets that recorded variation in the migratory routes of sockeye (Oncorhynchus nerka) and pink (Oncorhynchus gorbuscha) salmon returning from the Pacific Ocean to the Fraser River, British Columbia. Drift of the magnetic field (i.e. geomagnetic imprinting) uniquely accounted for 23.2% and 44.0% of the variation in migration routes for sockeye and pink salmon, respectively. Ocean circulation (i.e. olfactory imprinting) predicted 6.1% and 0.1% of the variation in sockeye and pink migration routes, respectively. Sea surface temperature (a variable influencing salmon distribution but not navigation, directly) accounted for 13.0% of the variation in sockeye migration but was unrelated to pink migration. These findings suggest that geomagnetic navigation plays an important role in long-distance homing in salmon and that consideration of navigation mechanisms can aid in the management of migratory fishes by better predicting movement patterns. Finally, given the diversity of animals that use the Earth's magnetic field for navigation, geomagnetic drift may provide a unifying explanation for spatio-temporal variation in the movement patterns of many species. PMID:25056214

Putman, Nathan F; Jenkins, Erica S; Michielsens, Catherine G J; Noakes, David L G

2014-10-01

352

Spatio-temporal dynamics of species richness in coastal fish communities.  

PubMed

Determining patterns of change in species richness and the processes underlying the dynamics of biodiversity are of key interest within the field of ecology, but few studies have investigated the dynamics of vertebrate communities at a decadal temporal scale. Here, we report findings on the spatio-temporal variability in the richness and composition of fish communities along the Norwegian Skagerrak coast having been surveyed for more than half a century. Using statistical models incorporating non-detection and associated sampling variance, we estimate local species richness and changes in species composition allowing us to compute temporal variability in species richness. We tested whether temporal variation could be related to distance to the open sea and to local levels of pollution. Clear differences in mean species richness and temporal variability are observed between fjords that were and were not exposed to the effects of pollution. Altogether this indicates that the fjord is an appropriate scale for studying changes in coastal fish communities in space and time. The year-to-year rates of local extinction and turnover were found to be smaller than spatial differences in community composition. At the regional level, exposure to the open sea plays a homogenizing role, possibly due to coastal currents and advection. PMID:12350265

Lekve, Kyrre; Boulinier, Thierry; Stenseth, Nils Chr; Gjøsaeter, Jakob; Fromentin, Jean-Marc; Hines, James E; Nichols, James D

2002-09-01

353

Spatio-temporal variability of richness estimators: coastal marine fish communities as examples.  

PubMed

We assessed the performance of two estimators of species richness, the Chao2 and the Coleman 'random placement curve'. Using a dataset of intertidal fish from the Norwegian Skagerrak coast, we found that Chao2 was effective for low sampling intensity, often reaching asymptotic values for few samples, but for higher sampling intensity the performance deteriorated. For large samples, the Coleman random placement curve was more effective than the Chao2 estimates when comparing spatio-temporal patterns of species richness. Spatial patterns were clearly and consistently identified by both methods, whereas the coastal fish communities displayed too much variability in the early summer for any sensible measure of temporal patterns of fish-species richness to be made. To control for spurious results due to systematic differences in mean abundance of the samples the analyses were performed also on data standardised by the number of individuals in the samples, without any significant change in the results. We conclude that modest sampling effort is sufficient to characterise spatial patterns of coastal fish-species richness, while a detailed and high-precision description of seasonal patterns could not be obtained with any reasonable sampling effort. PMID:15800740

Lekve, Kyrre; Ellingsen, Kari E; Lingjaerde, Ole Chr; Gjøsaeter, Jakob; Stenseth, Nils Chr

2005-06-01

354

Unification of Bell, Leggett-Garg and Kochen-Specker inequalities: Hybrid spatio-temporal inequalities  

NASA Astrophysics Data System (ADS)

The Bell-type (spatial), Kochen-Specker (contextuality) or Leggett-Garg (temporal) inequalities are based on classically plausible but otherwise quite distinct assumptions. For any of these inequalities, satisfaction is equivalent to a joint probability distribution for all observables in the experiment. This implies a joint distribution for all pairs of observables, and is indifferent to whether or not they commute in the theory. This indifference underpins a unification of the above inequalities into a general framework of correlation inequalities. When the physical scenario is such that the correlated pairs are all compatible, the resulting correlation is nonsignaling, which may be local or multi-particle, corresponding to contextuality or Bell-type inequalities. If the pairs are incompatible, the resulting correlation corresponds to Leggett-Garg (LG) inequalities. That quantum mechanics (QM) violates all these inequalities suggests a close connection between the local, spatial and temporal properties of the theory. As a concrete manifestation of the unification, we extend the method due to Roy and Singh (J. Phys. A, 11 (1978) L167) to derive and study a new class of hybrid spatio-temporal inequalities, where the correlated pairs in the experiment are both compatible or incompatible. The implications for cryptography and monogamy inequalities of the unification are briefly touched upon.

Das, Siddhartha; Aravinda, S.; Srikanth, R.; Home, Dipankar

2013-12-01

355

Spatio-temporal coherence mapping of few-cycle vortex pulses  

PubMed Central

Light carrying an orbital angular momentum (OAM) displays an optical phase front rotating in space and time and a vanishing intensity, a so-called vortex, in the center. Beyond continuous-wave vortex beams, optical pulses with a finite OAM are important for many areas of science and technology, ranging from the selective manipulation and excitation of matter to telecommunications. Generation of vortex pulses with a duration of few optical cycles requires new methods for characterising their coherence properties in space and time. Here we report a novel approach for flexibly shaping and characterising few-cycle vortex pulses of tunable topological charge with two sequentially arranged spatial light modulators. The reconfigurable optical arrangement combines interferometry, wavefront sensing, time-of-flight and nonlinear correlation techniques in a very compact setup, providing complete spatio-temporal coherence maps at minimum pulse distortions. Sub-7?fs pulses carrying different optical angular momenta are generated in single and multichannel geometries and characterised in comparison to zero-order Laguerre-Gaussian beams. To the best of our knowledge, this represents the shortest pulse durations reported for direct vortex shaping and detection with spatial light modulators. This access to space-time coupling effects with sub-femtosecond time resolution opens new prospects for tailored twisted light transients of extremely short duration. PMID:25413789

Grunwald, R.; Elsaesser, T.; Bock, M.

2014-01-01

356

Spatio-temporal animation of Army logistics, simulations, facilitating analysis of military deployments.  

SciTech Connect

Visualization techniques for simulations are often limited to statistical reports, graphs, and charts, but simulations can be enhanced through the use of animation. A spatio-temporal animation allows a viewer to observe a simulation operate, rather than deduce it from numerical output. The Route Viewer, developed by Argonne National Laboratory, is a two-dimensional animation model that animates the objects and events produced by a discrete event simulation. It operates in a playback mode, whereby a simulated scenario is animated after the simulation has completed. The Route Viewer is used to verify the simulation's processes and data, but it also benefits the simulation as an analytical tool by facilitating spatial and temporal analysis. By visualizing the events of a simulated scenario in two-dimensional space, it is possible to determine whether the scenario, or simulation model, is reasonable. Further, the Route Viewer provides an awareness of what happens in a scenario, when it happens, and the completeness and efficiency of the scenario and its processes. For Army deployments, it highlights utilization of resources and where bottlenecks are occurring. This paper discusses how the Route Viewer facilitates the analysis of military deployment simulation model results.

Love, R. J.; Horsthemke, W.; Macal, C. M.; Van Groningen, C.; Decision and Information Sciences

2004-01-01

357

Polynomial chaos representation of spatio-temporal random fields from experimental measurements  

SciTech Connect

Two numerical techniques are proposed to construct a polynomial chaos (PC) representation of an arbitrary second-order random vector. In the first approach, a PC representation is constructed by matching a target joint probability density function (pdf) based on sequential conditioning (a sequence of conditional probability relations) in conjunction with the Rosenblatt transformation. In the second approach, the PC representation is obtained by having recourse to the Rosenblatt transformation and simultaneously matching a set of target marginal pdfs and target Spearman's rank correlation coefficient (SRCC) matrix. Both techniques are applied to model an experimental spatio-temporal data set, exhibiting strong non-stationary and non-Gaussian features. The data consists of a set of oceanographic temperature records obtained from a shallow-water acoustics transmission experiment. The measurement data, observed over a finite denumerable subset of the indexing set of the random process, is treated as a collection of observed samples of a second-order random vector that can be treated as a finite-dimensional approximation of the original random field. A set of properly ordered conditional pdfs, that uniquely characterizes the target joint pdf, in the first approach and a set of target marginal pdfs and a target SRCC matrix, in the second approach, are estimated from available experimental data. Digital realizations sampled from the constructed PC representations based on both schemes capture the observed statistical characteristics of the experimental data with sufficient accuracy. The relative advantages and disadvantages of the two proposed techniques are also highlighted.

Das, Sonjoy [University of Southern California, Kaprielian Hall 210, Los Angeles, CA 90089 (United States)], E-mail: sdas@usc.edu; Ghanem, Roger [University of Southern California, Kaprielian Hall 210, Los Angeles, CA 90089 (United States)], E-mail: ghanem@usc.edu; Finette, Steven [Acoustics Division, Naval Research Laboratory, Washington, DC 20375 (United States)], E-mail: steve.finette@nrl.navy.mil

2009-12-10

358

Spatio-temporal analysis of soil erosion risk and runoff using AnnAGNPS  

NASA Astrophysics Data System (ADS)

Soil erosion is one form of land degradation in Ethiopia deteriorating the fertility and productivity of the land. This fact indicates the need to delineate high erosion risk areas for appropriate soil and conservation measures. Land use/cover change is one of the important factors in soil erosion. This study attempts test and implement AnnAGNPS model to estimate the spatio-temporal patterns of soil erosion and runoff associated with land use changes in the past 50 years in the 9900 ha upstream part of the Koga catchment. High erosion risk areas will then be delineated for simulation of the appropriate soil and water conservation measures that would reduce the soil loss. The study is based on two years high temporal resolution data on discharge, sediment, and rain fall accompanied by historical land use/cover data generated from satellite imagery. In addition, it uses several documented physical parameters of the study area. The Koga catchment is one of the agriculture dominated typical catchments in the North Western Ethiopian highlands with high population density that lead to increased pressure on natural resources.

Yeshaneh, Eleni; Wagner, Wolfgang; Blöschl, Günter

2014-05-01

359

Forecasting the Earth's Trapped Particle Distribution Using Hierarchical Bayesian Spatio Temporal Model  

NASA Astrophysics Data System (ADS)

We employed the Hierarchical Bayesian spatio temporal (HBST) Gaussian Process (GP) model for forecasting the distribution of the Earth's trapped particle. The model was applied in the South Atlantic Anomaly (SAA) region. Data from 1-30 January 2000 of >30 keV electron flux acquired by National Oceanic and Atmospheric (NOAA) 15 satellite was carried to model. The purpose was to forecast the flux value on 31 January 2000. Gridding process of 10x10 lot-lan was performed after cleaning and log transforming data. The HBST GP model was undertaken by implementing the Monte Carlo Markov Chain (MCMC) method. The forecasting result was interpolated by using Kriging technique to draw the distribution map of particle flux. Statistical validation represented by mean square error, root mean square error, mean absolute error, mean absolute percentage error, bias, relative bias, and mean relative separation shows good indicators. The visual validation also figured a quite similarity with NOAA's map that the model capable to forecast the particle flux.

Suparta, Wayan; Gusrizal

2014-04-01

360

Understanding the spatio-temporal variability of phytoplankton biomass distribution in a microtidal Mediterranean estuary  

NASA Astrophysics Data System (ADS)

Understanding the spatio-temporal variability of phytoplankton in aquaculture zones is necessary for the prevention and/or prediction of harmful algal bloom events. Synoptic cruises, time series analyses of physical and biological parameters, and 3D modeling were combined to investigate the variability of phytoplankton biomass in Alfacs Bay at basin scale. This microtidal estuary located in the NW Mediterranean is an important area of shellfish and finfish exploitation, which is regularly affected by toxic outbreaks. Observations showed the existence of a preferential phytoplankton accumulation area on the NE interior of the bay. This pattern can be observed throughout the year, and we show that it is directly linked to the physical forcing in the bay, in particular, the interplay between freshwater input and wind-induced turbulence. Both drivers affect the strength of the estuarine circulation, explaining nearly 75% of the variability in phytoplankton biomass. More cells are retained when stratification is weakened and the estuarine circulation reduced, while flushing rates are higher during times of increased stratification and stronger estuarine flow. This has been confirmed by using a 3D hydrodynamic model with Eulerian tracers. Nutrients, while important to support phytoplankton populations, have been found to play only a secondary role in explaining this variability at basin scale.

Artigas, M. L.; Llebot, C.; Ross, O. N.; Neszi, N. Z.; Rodellas, V.; Garcia-Orellana, J.; Masqué, P.; Piera, J.; Estrada, M.; Berdalet, E.

2014-03-01

361

Spatio-temporal distribution of interplate coupling in southwest Japan deduced from inversion analysis  

NASA Astrophysics Data System (ADS)

We obtain the spatio-temporal distribution of the slip on the subduction interface of the Nankai trough over an entire earthquake cycle, using geodetic data (including leveling, triangulation and trilateration, sea level, and GPS surveys) observed during the last 100 years in southwest Japan. We develop a new inversion method that can treat the long-term crustal deformations, the coseismic earthquake displacements and the stress relaxation of the viscoelastic asthenosphere. From this analysis, we obtain a model that shows postseismic afterslip on the deeper part of the plate interface following the 1946 Nankaido earthquake. The significant afterslip is found beneath central Shikoku and totals about 0.8m. The slip deficit rate during the interseismic period is 5 ˜6 cm/year in the N50oW ˜N60oW direction, which is consistent with the relative plate motion between the Philippine Sea and the Amurian plates. A strongly coupled region is found in the shallower portion (<30 km), and the slip deficit rate has a maximum at a depth of about 20 km. The interplate coupling is very weak on the plate interface deeper than 30 km. The amount of slip deficit reaches about 3.3m off Shikoku and about 2m off the Kii peninsula 50 years after the 1946 earthquake. This suggests that fault healing and full interplate coupling has occurred by this time along the Nankai trough.

Ito, T.; Hashimoto, M.

2003-12-01

362

Spatio-temporal evolution of shoreline changes along the coast between sousse- Monastir (Eastearn of Tunisia)  

NASA Astrophysics Data System (ADS)

Spatio-temporal evolution of shoreline Changes along the coast between Sousse-Monastir (Eastern of Tunisia). Safa Fathallah*, Rim Ben Amor and Moncef Gueddari Unit of Research of Geochemistry and Environmental Geology. Faculty of Science of Tunis, University of Tunis El Manar, 2092. (*) Corresponding author: safa_fathallah@yahoo.fr The coast of Sousse-Monastir in eastern of Tunisia, has undergone great changes, due to natural and anthropic factors. Increasing human use, the construction of two ports and coastal urbanization (hotels and industries) has accelerated the erosion process. The coastal defense structures (breakwaters and enrockment), built to protect the most eroded zone are efficient, but eroded zones appeared in the southern part of breakwaters. Recent and historic aerial photography was used to estimate, observe, and analyze past shoreline and bathymetric positions and trends involving shore evolution for Sousse-Monastir coast. All of the photographs were calibrated and mosaicked by Arc Map Gis 9.1, the years used are 1925, 1962, 1988, 1996, and 2001 for shoreline change analysis and 1884 and 2001 for bathymetric changes. The analyze of this photographs show that the zone located at the south of breakwater are mostly eroded with high speed process (2m/year). Another zone appears as eroded at the south part of Hamdoun River, with 1,5m/year erosion speed . Keywords: Shoreline evolution, defense structures, Sousse-Monastir coast, Tunisia.

Fathallah, S.; Ben Amor, R.; Gueddari, M.

2009-04-01

363

Minimal Spatio-Temporal Extent of Events, Neutrinos, and the Cosmological Constant Problem  

NASA Astrophysics Data System (ADS)

Chryssomalakos and Okon, through a uniqueness analysis, have strengthened the Vilela Mendes suggestion that the immunity to infinitesimal perturbations in the structure constants of a physically-relevant Lie algebra should be raised to the status of a physical principle. Since the Poincaré-Heisenberg algebra does not carry the indicated immunity, it is suggested that the Lie algebra for the interface of the gravitational and quantum realms (IGQR) is its stabilized form. It carries three additional parameters: a length scale pertaining to the Planck/unification scale, a second length scale associated with cosmos, and a new dimensionless constant. Here, we show that the adoption of the stabilized Poincaré-Heisenberg algebra (SPHA) for the IGQR has the immediate implication that a "point particle" ceases to be a viable physical notion. It must be replaced by objects which carry a well-defined, representation space-dependent, minimal spatio-temporal extent. The ensuing implications have the potential, without spoiling any of the successes of the Standard Model of particle physics, to resolve the cosmological constant problem while concurrently offering a first-principle hint as to why there exists a coincidence between cosmic vacuum energy density and neutrino masses. The main theses which the essay presents is the following: an extension of the present-day physics to a framework which respects SPHA should be seen as the most natural and systematic path towards gaining a deeper understanding of outstanding questions, if not providing answers to them.

Ahluwalia-Khalilova, D. V.

364

A stereoscopic video conversion scheme based on spatio-temporal analysis of MPEG videos  

NASA Astrophysics Data System (ADS)

In this article, an automatic stereoscopic video conversion scheme which accepts MPEG-encoded videos as input is proposed. Our scheme is depth-based, relying on spatio-temporal analysis of the decoded video data to yield depth perception cues, such as temporal motion and spatial contrast, which reflect the relative depths between the foreground and the background areas. Our scheme is shot-adaptive, demanding that shot change detection and shot classification be performed for tuning of algorithm or parameters that are used for depth cue combination. The above-mentioned depth estimation is initially block-based, followed by a locally adaptive joint trilateral upsampling algorithm to reduce the computing load significantly. A recursive temporal filter is used to reduce the possible depth fluctuations (and also artifacts in the synthesized images) resulting from wrong depth estimations. The traditional Depth-Image-Based-Rendering algorithm is used to synthesize the left- and right-view frames for 3D display. Subjective tests show that videos converted by our scheme provide comparable perceived depth and visual quality with those converted from the depth data calculated by stereo vision techniques. Also, our scheme is shown to outperform the well-known TriDef software in terms of human's perceived 3D depth. Based on the implementation by using "OpenMP" parallel programming model, our scheme is capable of executing in real-time on a multi-core CPU platform.

Lin, Guo-Shiang; Huang, Hsiang-Yun; Chen, Wei-Chih; Yeh, Cheng-Ying; Liu, Kai-Che; Lie, Wen-Nung

2012-12-01

365

Unveiling TRPV1 Spatio-Temporal Organization in Live Cell Membranes.  

PubMed

Transient Receptor Potential Vanilloid 1 (TRPV1) is a non-selective cation channel that integrates several stimuli into nociception and neurogenic inflammation. Here we investigated the subtle TRPV1 interplay with candidate membrane partners in live cells by a combination of spatio-temporal fluctuation techniques and fluorescence resonance energy transfer (FRET) imaging. We show that TRPV1 is split into three populations with fairly different molecular properties: one binding to caveolin-1 and confined into caveolar structures, one actively guided by microtubules through selective binding, and one which diffuses freely and is not directly implicated in regulating receptor functionality. The emergence of caveolin-1 as a new interactor of TRPV1 evokes caveolar endocytosis as the main desensitization pathway of TRPV1 receptor, while microtubule binding agrees with previous data suggesting the receptor stabilization in functional form by these cytoskeletal components. Our results shed light on the hitherto unknown relationships between spatial organization and TRPV1 function in live-cell membranes. PMID:25764349

Storti, Barbara; Di Rienzo, Carmine; Cardarelli, Francesco; Bizzarri, Ranieri; Beltram, Fabio

2015-01-01

366

Insight into others’ minds: spatio-temporal representations by intrinsic frame of reference  

PubMed Central

Recent research has seen a growing interest in connections between domains of spatial and social cognition. Much evidence indicates that processes of representing space in distinct frames of reference (FOR) contribute to basic spatial abilities as well as sophisticated social abilities such as tracking other’s intention and belief. Argument remains, however, that belief reasoning in social domain requires an innately dedicated system and cannot be reduced to low-level encoding of spatial relationships. Here we offer an integrated account advocating the critical roles of spatial representations in intrinsic frame of reference. By re-examining the results from a spatial task (Tamborello etal., 2012) and a false-belief task (Onishi and Baillargeon, 2005), we argue that spatial and social abilities share a common origin at the level of spatio-temporal association and predictive learning, where multiple FOR-based representations provide the basic building blocks for efficient and flexible partitioning of the environmental statistics. We also discuss neuroscience evidence supporting these mechanisms. We conclude that FOR-based representations may bridge the conceptual as well as the implementation gaps between the burgeoning fields of social and spatial cognition. PMID:24592226

Sun, Yanlong; Wang, Hongbin

2014-01-01

367

Spatio-temporal organization of a cellular automaton model for computer network  

NASA Astrophysics Data System (ADS)

It was unveiled by Ren et al. [Comput. Phys. Comm. (2001)] that congestion transition emerges in cellular automaton models for computer network and this NaSch network model with Q=1 has similar behaviours as the NaSch traffic model with maximum velocity vmax=1. For these two NaSch models, the main difference lies in a node cell contained in the NaSch network model. In this paper, we will focus on our further investigation on spatio-temporal organization of the NaSch network model. More interesting phenomena of phase transition are discovered. Firstly, fundamental diagram illustrates that when Q>1 for the NaSch network model it is significantly different from its counterpart, i.e. the NaSch traffic model in a road traffic system. The addition of a node cell, which is allowed to have more than one packets, will lead to generating a new phase. Secondly, in order to characterize phase transition occurred in the NaSch network model, an order parameter is presented with the use of the time average density of nearest-neighbor pairs m. The computational results obtained show that criticality will disappear in a strict sense if noise exists. Finally, two other numerical features, i.e. spatial correlation functions G( r) and relaxation times ?, are analyzed so as to deeply describe behaviours near critical points.

Ren, Zhiliang; Deng, Zhidong; Sun, Zengqi

2002-04-01

368

Spatio-temporal distribution of dengue fever under scenarios of climate change in the southern Taiwan  

NASA Astrophysics Data System (ADS)

Dengue fever has been recognized as the most important widespread vector-borne infectious disease in recent decades. Over 40% of the world's population is risk from dengue and about 50-100 million people are infected world wide annually. Previous studies have found that dengue fever is highly correlated with climate covariates. Thus, the potential effects of global climate change on dengue fever are crucial to epidemic concern, in particular, the transmission of the disease. This present study investigated the nonlinearity of time-delayed impact of climate on spatio-temporal variations of dengue fever in the southern Taiwan during 1998 to 2011. A distributed lag nonlinear model (DLNM) is used to assess the nonlinear lagged effects of meteorology. The statistically significant meteorological factors are considered, including weekly minimum temperature and maximum 24-hour rainfall. The relative risk and the distribution of dengue fever then predict under various climate change scenarios. The result shows that the relative risk is similar for different scenarios. In addition, the impact of rainfall on the incidence risk is higher than temperature. Moreover, the incidence risk is associated to spatially population distribution. The results can be served as practical reference for environmental regulators for the epidemic prevention under climate change scenarios.

Lee, Chieh-Han; Yu, Hwa-Lung

2014-05-01

369

Bayesian spatio-temporal discard model in a demersal trawl fishery  

NASA Astrophysics Data System (ADS)

Spatial management of discards has recently been proposed as a useful tool for the protection of juveniles, by reducing discard rates and can be used as a buffer against management errors and recruitment failure. In this study Bayesian hierarchical spatial models have been used to analyze about 440 trawl fishing operations of two different metiers, sampled between 2009 and 2012, in order to improve our understanding of factors that influence the quantity of discards and to identify their spatio-temporal distribution in the study area. Our analysis showed that the relative importance of each variable was different for each metier, with a few similarities. In particular, the random vessel effect and seasonal variability were identified as main driving variables for both metiers. Predictive maps of the abundance of discards and maps of the posterior mean of the spatial component show several hot spots with high discard concentration for each metier. We argue how the seasonal/spatial effects, and the knowledge about the factors influential to discarding, could potentially be exploited as potential mitigation measures for future fisheries management strategies. However, misidentification of hotspots and uncertain predictions can culminate in inappropriate mitigation practices which can sometimes be irreversible. The proposed Bayesian spatial method overcomes these issues, since it offers a unified approach which allows the incorporation of spatial random-effect terms, spatial correlation of the variables and the uncertainty of the parameters in the modeling process, resulting in a better quantification of the uncertainty and accurate predictions.

Grazia Pennino, M.; Muñoz, Facundo; Conesa, David; López-Quílez, Antonio; Bellido, José M.

2014-07-01

370

Differential spatio-temporal expression of carotenoid cleavage dioxygenases regulates apocarotenoid fluxes during AM symbiosis.  

PubMed

Apocarotenoids are a class of compounds that play important roles in nature. In recent years, a prominent role for these compounds in arbuscular mycorrhizal (AM) symbiosis has been shown. They are derived from carotenoids by the action of the carotenoid cleavage dioxygenase (CCD) enzyme family. In the present study, using tomato as a model, the spatio-temporal expression pattern of the CCD genes during AM symbiosis establishment and functioning was investigated. In addition, the levels of the apocarotenoids strigolactones (SLs), C13 ?-ionol and C14 mycorradicin (C13/C14) derivatives were analyzed. The results suggest an increase in SLs promoted by the presence of the AM fungus at the early stages of the interaction, which correlated with an induction of the SL biosynthesis gene SlCCD7. At later stages, induction of SlCCD7 and SlCCD1 expression in arbusculated cells promoted the production of C13/C14 apocarotenoid derivatives. We show here that the biosynthesis of apocarotenoids during AM symbiosis is finely regulated throughout the entire process at the gene expression level, and that CCD7 constitutes a key player in this regulation. Once the symbiosis is established, apocarotenoid flux would be turned towards the production of C13/C14 derivatives, thus reducing SL biosynthesis and maintaining a functional symbiosis. PMID:25480008

López-Ráez, Juan A; Fernández, Iván; García, Juan M; Berrio, Estefanía; Bonfante, Paola; Walter, Michael H; Pozo, María J

2015-01-01

371

Unveiling TRPV1 Spatio-Temporal Organization in Live Cell Membranes  

PubMed Central

Transient Receptor Potential Vanilloid 1 (TRPV1) is a non-selective cation channel that integrates several stimuli into nociception and neurogenic inflammation. Here we investigated the subtle TRPV1 interplay with candidate membrane partners in live cells by a combination of spatio-temporal fluctuation techniques and fluorescence resonance energy transfer (FRET) imaging. We show that TRPV1 is split into three populations with fairly different molecular properties: one binding to caveolin-1 and confined into caveolar structures, one actively guided by microtubules through selective binding, and one which diffuses freely and is not directly implicated in regulating receptor functionality. The emergence of caveolin-1 as a new interactor of TRPV1 evokes caveolar endocytosis as the main desensitization pathway of TRPV1 receptor, while microtubule binding agrees with previous data suggesting the receptor stabilization in functional form by these cytoskeletal components. Our results shed light on the hitherto unknown relationships between spatial organization and TRPV1 function in live-cell membranes. PMID:25764349

Storti, Barbara; Di Rienzo, Carmine; Cardarelli, Francesco; Bizzarri, Ranieri; Beltram, Fabio

2015-01-01

372

Spatio-Temporal Complexity analysis of the Sea Surface Temperature in the Philippines  

NASA Astrophysics Data System (ADS)

A spatio-temporal complexity (STC) measure which has been previously used to analyze data from terrestrial ecosystems is employed to analyse 21 years of remotely sensed sea-surface temperature (SST) data from the Philippines. STC on the Philippine wide SST showed the monsoonal variability of the Philippine waters. STC is correlated with the SST mean (R2 ? 0.7), and inversely correlated with the SST standard deviation (R2 ? 0.9). Both STC and SST are highest during the middle of the year, which coincides with the Southwest Monsoon, but with the STC values being higher towards the end of the monsoon until the start of the inter-monsoon. In order to determine if STC has the potential to define limits of bio-regions, the spatial domain was subsequently divided into six thermal regions computed via clustering of temperature means. STC and EOF of the STC values were computed for each thermal region. Our STC analysis of the SST data, and comparisons with SST values suggest that the STC measure may be useful for characterising environmental heterogeneity over space and time for many long-term remotely sensed data.

Botin, Z. T.; David, L. T.; Del Rosario, R. C. H.; Parrott, L.

2010-11-01

373

Sedimentological constraints to the spatio-temporal evolution of the first Cenozoic Antarctic glaciation  

NASA Astrophysics Data System (ADS)

Glacial Isostatic Adjustement (GIA) modeling of solid Earth and gravitational perturbations induced by the Antarctic glaciation across the Eocene/Oligocene transition (EOT; ~34 Ma) predicts a relative sea level (rsl) rise over-ice proximal marine marginal settings. Accordingly, available sedimentary records from the Ross Sea (CIROS1, CRP-3), Prydz Bay (ODP 739, 1166) and Wilkes Land (IOPD U1356, U1360) provide evidence for progressively deeper depositional environments across the late Eocene towards the Oligocene isotope event-1 (Oi-1; 33.7 Ma, which marks a major glacial advancement episode. Since bathymetric changes at these near-field sites are controlled by GIA, the analysis and inter-site comparison of their sedimentary records provide insights into the spatio-temporal evolution of the nascent Antarctic Ice Sheet. In this work we simulate the inception of the Antarctic glaciation by means of a thermomechanical ice sheet-shelf model dynamically coupled to a sea level model based on the gravitationally self-consistent Sea Level Equation (SLE). We generate a set of ice-sheet and rsl scenarios according to (i) different values for the Earth rheological parameters, (ii) initial topographic/bathymetric conditions and (iii) precipitation/temperature patterns. By comparing the observations with the modeling solutions we find that the initial undeformed topography/bathymetry, and consequently its deformations driven by the GIA described by the SLE, are important conditions for a realistic development of the Antarctic ice-sheet.

Stocchi, P.; Galeotti, S.; De Boer, B.; Escutia, C.; DeConto, R.; Houben, A. J.; Passchier, S.; Vermeersen, B. L.; Van de Wal, R.; Brinkhuis, H.

2012-12-01

374

Fish in a ring: spatio-temporal pattern formation in one-dimensional animal groups.  

PubMed

In this work, we study the collective behaviour of fish shoals in annular domains. Shoal mates are modelled as self-propelled particles moving on a discrete lattice. Collective decision-making is determined by information exchange among neighbours. Neighbourhoods are specified using the perceptual limit and numerosity of fish. Fish self-propulsion and obedience to group decisions are described through random variables. Spatio-temporal schooling patterns are measured using coarse observables adapted from the literature on coupled oscillator networks and features of the time-varying network describing the fish-to-fish information exchange. Experiments on zebrafish schooling in an annular tank are used to validate the model. Effects of group size and obedience parameter on coarse observables and network features are explored to understand the implications of perceptual numerosity and spatial density on fish schooling. The proposed model is also compared with a more traditional metric model, in which the numerosity constraint is released and fish interactions depend only on physical configurations. Comparison shows that the topological regime on which the proposed model is constructed allows for interpreting characteristic behaviours observed in the experimental study that are not captured by the metric model. PMID:20413559

Abaid, Nicole; Porfiri, Maurizio

2010-10-01

375

Spatio-temporal dynamics of species richness in coastal fish communities.  

PubMed Central

Determining patterns of change in species richness and the processes underlying the dynamics of biodiversity are of key interest within the field of ecology, but few studies have investigated the dynamics of vertebrate communities at a decadal temporal scale. Here, we report findings on the spatio-temporal variability in the richness and composition of fish communities along the Norwegian Skagerrak coast having been surveyed for more than half a century. Using statistical models incorporating non-detection and associated sampling variance, we estimate local species richness and changes in species composition allowing us to compute temporal variability in species richness. We tested whether temporal variation could be related to distance to the open sea and to local levels of pollution. Clear differences in mean species richness and temporal variability are observed between fjords that were and were not exposed to the effects of pollution. Altogether this indicates that the fjord is an appropriate scale for studying changes in coastal fish communities in space and time. The year-to-year rates of local extinction and turnover were found to be smaller than spatial differences in community composition. At the regional level, exposure to the open sea plays a homogenizing role, possibly due to coastal currents and advection. PMID:12350265

Lekve, Kyrre; Boulinier, Thierry; Stenseth, Nils Chr; Gjøsaeter, Jakob; Fromentin, Jean-Marc; Hines, James E; Nichols, James D

2002-01-01

376

Theoretical analysis of the spatio-temporal structure of bone multicellular units  

NASA Astrophysics Data System (ADS)

Bone multicellular units (BMUs) maintain the viability of the skeletal tissue by coordinating locally the sequence of bone resorption and bone formation performed by cells of the osteoclastic and osteoblastic lineage. Understanding the emergence and the net bone balance of such structured microsystems out of the complex network of biochemical interactions between bone cells is fundamental for many bone-related diseases and the evaluation of fracture risk. Based on current experimental knowledge, we propose a spatio-temporal continuum model describing the interactions of osteoblastic and osteoclastic cells. We show that this model admits travelling-wave-like solutions with well-confined cell profiles upon specifying external conditions mimicking the environment encountered in cortical bone remodelling. The shapes of the various cell concentration profiles within this travelling structure are intrinsically linked to the parameters of the model such as differentiation, proliferation, and apoptosis rates of bone cells. The internal structure of BMUs is reproduced, allowing for experimental calibration. The spatial distribution of the key regulatory factors can also be exhibited, which in diseased states could give hints as to the biochemical agent most accountable for the disorder.

Buenzli, P. R.; Pivonka, P.; Gardiner, B. S.; Smith, D. W.; Dunstan, C. R.; Mundy, G. R.

2010-06-01

377

Spatio-temporal dynamics of kind versus hostile intentions in the human brain: An electrical neuroimaging study.  

PubMed

Neuroscience research suggests that inferring neutral intentions of other people recruits a specific brain network within the inferior fronto-parietal action observation network as well as a putative social network including brain areas subserving theory of mind, such as the posterior superior temporal sulcus (pSTS), the temporo-parietal junction (TPJ), and also the anterior cingulate cortex (ACC). Recent studies on harmful intentions have refined this network by showing the specific involvement of the ACC, amygdala, and ventromedial prefrontal cortex (vmPFC) in early stages (within 200 ms) of information processing. However, the functional dynamics for kind intentions within and among these networks remains unclear. To address this question, we measured electrical brain activity from 18 healthy adult participants while they were performing an intention inference task with three different types of intentions: kind, hostile and non-interactive. Electrophysiological results revealed that kind intentions were characterized by significantly larger peak amplitudes of N2 over the frontal sites than those for hostile and non-interactive intentions. On the other hand, there were no significant differences between hostile and non-interactive intentions at N2. The source analysis suggested that the vicinity of the left cingulate gyrus contributed to the N2 effect by subtracting the kindness condition from the non-interactive condition within 250-350 ms. At a later stage (i.e., during the 270-500 ms epoch), the peak amplitude of the P3 over the parietal sites and the right hemisphere was significantly larger for hostile intentions compared to the kind and non-interactive intentions. No significant differences were observed at P3 between kind and non-interactive intentions. The source analysis showed that the vicinity of the left anterior cingulate cortex contributed to the P3 effect by subtracting the hostility condition from the non-interactive condition within 450-550 ms. The present study provides preliminary evidence of the spatio-temporal dynamics sustaining the dissociation between the understandings of different types of social intentions. PMID:25517193

Wang, Yiwen; Huang, Liang; Zhang, Wei; Zhang, Zhen; Cacioppo, Stephanie

2015-06-01

378

Blind Source Separation by Sparse Decomposition in a Signal Dictionary  

Microsoft Academic Search

IntroductionIn blind source separation an N-channel sensor signal x(t) arises fromM unknown scalar source signals s i (t), linearly mixed together by anunknown N M matrix A, and possibly corrupted by additive noise(t)x(t) = As(t) + (t) (1.1)We wish to estimate the mixing matrix A and the M-dimensional sourcesignal s(t). Many natural signals can be sparsely represented in a propersignal

M. Zibulevsky; B. a. Pearlmutter; P. Bofill; P. Kisilev

2000-01-01

379

Blindness  

MedlinePLUS

... Research at NEI Education Programs Training and Jobs Blindness Listen Blindness Defined Blindness as defined by the U.S. definition ... Ethnicity 2010 U.S. Age-Specific Prevalence Rates for Blindness by Age and Race/Ethnicity Age White Black ...

380

Extensive spatio-temporal analysis of surface ozone over South Korea for 1999-2010 considering meteorological factors  

NASA Astrophysics Data System (ADS)

Spatio-temporal variations of surface ozone are investigated using the KZ-filter considering meteorological factors based on measurement data at 124 air quality monitoring sites and 72 weather stations over South Korea for the time period of 1999-2010. We use hourly data of ozone (O3), nitrogen dioxide (NO2), temperature (°C), dew-point temperature (°C), sea-level pressure (hPa), wind speed (m/s) and direction (16 cardinal directions), relative humidity (%), and solar insolation (W/m²). Over the Korean peninsula, surface O3 levels at the coastal cities are generally high due to the dynamic effects of the sea breeze and short-lived chlorine species from the sea salt, while those at the Seoul metropolitan area and other inland cities are low due to the NOx titration by anthropogenic emissions. The concentrations of surface O3 have generally increased for the analyzed period with the nationwide average linear trend of +0.26 ppbv/yr (+1.15 %/yr). We also examine the meteorological influences on the surface O3 levels over South Korea using a combined analysis of KZ-filter and multiple linear regressions between surface O3 and meteorological variables. Time-series of surface O3 are decomposed into the short-term, seasonal, and long-term components by the KZ-filter and regressed on meteorological variables. Through probability distribution analysis of the decomposed O3 time-series classified by wind direction, the O3 short-term variation at monitoring sites shows transport effects from the source regions. Impacts of surface temperature on the surface O3 levels are found to be significantly high in the highly populated metropolitan area and inland cities. It implies that those regions will be experiencing more frequent high-ozone events in the future climate conditions with the increase of global temperature. Especially in Seoul, the most populated area in South Korea, the probability of high O3 exceeding air quality standard is almost doubled for the temperature increase of about 4°C. Additional SVD analysis between O3 and NO2 shows similar temporal evolution with spatial patterns of the long-term O3 and NO2 components. This study would provide a reference for appropriate ozone control policy and for the performance evaluation of chemistry climate models over East Asia.

Seo, Jihoon; Youn, Daeok; Kim, Jin Young; Choi, Wookap

2013-04-01

381

Spatio-temporal variability of aerosols in the tropics relationship with atmospheric and oceanic environments  

NASA Astrophysics Data System (ADS)

Earth's radiation budget is directly influenced by aerosols through the absorption of solar radiation and subsequent heating of the atmosphere. Aerosols modulate the hydrological cycle indirectly by modifying cloud properties, precipitation and ocean heat storage. In addition, polluting aerosols impose health risks in local, regional and global scales. In spite of recent advances in the study of aerosols variability, uncertainty in their spatio-temporal distributions still presents a challenge in the understanding of climate variability. For example, aerosol loading varies not only from year to year but also on higher frequency intraseasonal time scales producing strong variability on local and regional scales. An assessment of the impact of aerosol variability requires long period measurements of aerosols at both regional and global scales. The present dissertation compiles a large database of remotely sensed aerosol loading in order to analyze its spatio-temporal variability, and how this load interacts with different variables that characterize the dynamic and thermodynamic states of the environment. Aerosol Index (AI) and Aerosol Optical Depth (AOD) were used as measures of the atmospheric aerosol load. In addition, atmospheric and oceanic satellite observations, and reanalysis datasets is used in the analysis to investigate aerosol-environment interactions. A diagnostic study is conducted to produce global and regional aerosol satellite climatologies, and to analyze and compare the validity of aerosol retrievals. We find similarities and differences between the aerosol distributions over various regions of the globe when comparing the different satellite retrievals. A nonparametric approach is also used to examine the spatial distribution of the recent trends in aerosol concentration. A significant positive trend was found over the Middle East, Arabian Sea and South Asian regions strongly influenced by increases in dust events. Spectral and composite analyses of surface temperature, atmospheric wind, geopotential height, outgoing longwave radiation, water vapor and precipitation together with the climatology of aerosols provide insight on how the variables interact. Different modes of variability, especially in intraseasonal time scales appear as strong modulators of the aerosol distribution. In particular, we investigate how two modes of variability related to the westward propagating synoptic African Easterly Waves of the Tropical Atlantic Ocean affect the horizontal and vertical structure of the environment. The statistical significance of these two modes is tested with the use of two different spectral techniques. The pattern of propagation of aerosol load shows good correspondence with the progression of the atmospheric and oceanic conditions suitable for dust mobilization over the Atlantic Ocean. We present extensions to previous studies related with dust variability over the Atlantic region by evaluating the performance of the long period satellite aerosol retrievals in determining modes of aerosol variability. Results of the covariability between aerosols-environment motivate the use of statistical regression models to test the significance of the forecasting skill of daily AOD time series. The regression models are calibrated using atmospheric variables as predictors from the reanalysis variables. The results show poor forecasting skill with significant error growing after the 3 rd day of the prediction. It is hypothesized that the simplicity of linear models results in an inability to provide a useful forecast.

Zuluaga-Arias, Manuel D.

2011-12-01

382

Spatio-Temporal Dynamics of Cholera during the First Year of the Epidemic in Haiti  

PubMed Central

Background In October 2010, cholera importation in Haiti triggered an epidemic that rapidly proved to be the world's largest epidemic of the seventh cholera pandemic. To establish effective control and elimination policies, strategies rely on the analysis of cholera dynamics. In this report, we describe the spatio-temporal dynamics of cholera and the associated environmental factors. Methodology/Principal findings Cholera-associated morbidity and mortality data were prospectively collected at the commune level according to the World Health Organization standard definition. Attack and mortality rates were estimated and mapped to assess epidemic clusters and trends. The relationships between environmental factors were assessed at the commune level using multivariate analysis. The global attack and mortality rates were 488.9 cases/10,000 inhabitants and 6.24 deaths/10,000 inhabitants, respectively. Attack rates displayed a significantly high level of spatial heterogeneity (varying from 64.7 to 3070.9 per 10,000 inhabitants), thereby suggesting disparate outbreak processes. The epidemic course exhibited two principal outbreaks. The first outbreak (October 16, 2010–January 30, 2011) displayed a centrifugal spread of a damping wave that suddenly emerged from Mirebalais. The second outbreak began at the end of May 2011, concomitant with the onset of the rainy season, and displayed a highly fragmented epidemic pattern. Environmental factors (river and rice fields: p<0.003) played a role in disease dynamics exclusively during the early phases of the epidemic. Conclusion Our findings demonstrate that the epidemic is still evolving, with a changing transmission pattern as time passes. Such an evolution could have hardly been anticipated, especially in a country struck by cholera for the first time. These results argue for the need for control measures involving intense efforts in rapid and exhaustive case tracking. PMID:23593516

Gaudart, Jean; Rebaudet, Stanislas; Barrais, Robert; Boncy, Jacques; Faucher, Benoit; Piarroux, Martine; Magloire, Roc; Thimothe, Gabriel; Piarroux, Renaud

2013-01-01

383

Spatio-Temporal Variation of Stream Metabolism in a Managed River System  

NASA Astrophysics Data System (ADS)

Metabolism estimates (gross primary production, GPP and community respiration, CR) obtained through the continuous monitoring of physicochemical properties in managed rivers may be used to evaluate the effects of various disturbances on ecosystem function. This work highlights the development of a GPP/CR observational network on the human-dominated Lower Merced River, currently the southern-most extent of Chinook salmon habitat in the Central Valley of California. Our investigations include spatial (both longitudinal and transverse gradients) and temporal (daily, seasonal and interannual) variation of these metabolism estimates as we are interested in relating responses of this type of lotic system to disturbances such as short- or long-term reservoir operational changes for drought management, flood control, fish habitat enhancement, or alleviation of salinity and nutrient discharges due to land management practices. The observational network will be described in terms of: (1) design and installation of a reproducible infrastructure of GPP/CR monitoring stations, (2) analysis aimed at linking the spatio-temporal metabolic trends to natural factors such as the seasonal radiation availability or nutrient input from leaf decay, and (3) separating natural effects from the ones triggered by human disturbances in order to better inform water resources management decisions. Observations over the 2009-10 water year, demonstrate that the Lower Merced River behaves as a heterotrophic system, with large temporal changes in metabolism clearly observable by the monitoring network. For example, the GPP/CR ratio decreased from 0.6 to 0.2 as a consequence of a large flow disturbance associated with short-term reservoir releases mandated biannually to support salmon migration. This and other examples set at different temporal and spatial scales will be presented and discussed in terms of management implications.

Villamizar, S. R.; Pai, H.; Butler, C. A.; Barnes, P. A.; Harmon, T. C.

2010-12-01

384

Diffusive spatio-temporal noise in a first-passage time model for intracellular calcium release  

NASA Astrophysics Data System (ADS)

The intracellular release of calcium from the endoplasmic reticulum is controlled by ion channels. The resulting calcium signals exhibit a rich spatio-temporal signature, which originates at least partly from microscopic fluctuations. While stochasticity in the gating transition of ion channels has been incorporated into many models, the distribution of calcium is usually described by deterministic reaction-diffusion equations. Here we test the validity of the latter modeling approach by using two different models to calculate the frequency of localized calcium signals (calcium puffs) from clustered IP3 receptor channels. The complexity of the full calcium system is here limited to the basic opening mechanism of the ion channels and, in the mathematical reduction simplifies to the calculation of a first passage time. Two models are then studied: (i) a hybrid model, where channel gating is treated stochastically, while calcium concentration is deterministic and (ii) a fully stochastic model with noisy channel gating and Brownian calcium ion motion. The second model utilises the recently developed two-regime method [M. B. Flegg, S. J. Chapman, and R. Erban, "The two-regime method for optimizing stochastic reaction-diffusion simulations," J. R. Soc., Interface 9, 859-868 (2012)], 10.1098/rsif.2011.0574 in order to simulate a large domain with precision required only near the Ca2+ absorbing channels. The expected time for a first channel opening that results in a calcium puff event is calculated. It is found that for a large diffusion constant, predictions of the interpuff time are significantly overestimated using the model (i) with a deterministic non-spatial calcium variable. It is thus demonstrated that the presence of diffusive noise in local concentrations of intracellular Ca2+ ions can substantially influence the occurrence of calcium signals. The presented approach and results may also be relevant for other cell-physiological first-passage time problems with small ligand concentration and high cooperativity.

Flegg, Mark B.; Rüdiger, Sten; Erban, Radek

2013-04-01

385

Associations of Dragonflies (Odonata) to Habitat Variables within the Maltese Islands: A Spatio-Temporal Approach  

PubMed Central

Relatively little information is available on environmental associations and the conservation of Odonata in the Maltese Islands. Aquatic habitats are normally spatio-temporally restricted, often located within predominantly rural landscapes, and are thereby susceptible to farmland water management practices, which may create additional pressure on water resources. This study investigates how odonate assemblage structure and diversity are associated with habitat variables of local breeding habitats and the surrounding agricultural landscapes. Standardized survey methodology for adult Odonata involved periodical counts over selected water-bodies (valley systems, semi-natural ponds, constructed agricultural reservoirs). Habitat variables relating to the type of water body, the floristic and physiognomic characteristics of vegetation, and the composition of the surrounding landscape, were studied and analyzed through a multivariate approach. Overall, odonate diversity was associated with a range of factors across multiple spatial scales, and was found to vary with time. Lentic water-bodies are probably of high conservation value, given that larval stages were mainly associated with this habitat category, and that all species were recorded in the adult stage in this habitat type. Comparatively, lentic and lotic seminatural waterbodies were more diverse than agricultural reservoirs and brackish habitats. Overall, different odonate groups were associated with different vegetation life-forms and height categories. The presence of the great reed, Arundo donax L., an invasive alien species that forms dense stands along several water-bodies within the Islands, seems to influence the abundance and/or occurrence of a number of species. At the landscape scale, roads and other ecologically disturbed ground, surface water-bodies, and landscape diversity were associated with particular components of the odonate assemblages. Findings from this study have several implications for the use of Odonata as biological indicators, and for current trends with respect to odonate diversity conservation within the Maltese Islands. PMID:23427906

Balzan, Mario V.

2012-01-01

386

Spatio-temporal analysis of a long-term global soil moisture dataset  

NASA Astrophysics Data System (ADS)

It is a well known truth that soil moisture plays an essential role within the hydrological cycle and the climate system. Therefore a deeper knowledge and understanding of soil moisture behaviour, changes and pattern is of major interest. This contribution introduces a statistical approach to recognize spatio-temporal patterns within a long-term global soil moisture data set. The great potential of satellites to detect soil moisture on a global and continuous scale is well-known and in particular microwave remote sensing is recognized to work as the most efficient instrument for acquiring soil moisture information. The current study is based on a long-term global soil moisture data set, the ESA CCI soil moisture data set (http://www.esa-soilmoisturee-cci.org). It was developed by combining data derived from active and passive microwave satellite-based sensors, profiting from the advantages of both retrieval techniques. The ESA CCI soil moisture data set provides soil moisture information for more than three decades and can easily be extended with products from current and future satellite missions. Relative dynamics and long term changes of the original satellite derived retrievals are preserved in the CCI product, thus a valuable basis for long-term analysis is given. By applying a cluster algorithm to monthly and seasonal means of the combined CCI data regions with similar temporal soil moisture patterns are created. The plausibility of the resulting groups is verified by comparison with land cover classifications and climate classes. Besides, special care has been taken of the treatment of missing values as their existences causes difficulties when statistical methods are applied. In this study various methods for missing value imputation are discussed to provide as much meaningful data as input for the following cluster analysis as possible. Overall, the described analysis of soil moisture product is expected to improve our knowledge and understanding of soil moisture behaviour and the quality of the used product.

Xaver, Angelika; Dorigo, Wouter A.

2013-04-01

387

Major Shifts in the Spatio-Temporal Distribution of Lung Antioxidant Enzymes during Influenza Pneumonia  

PubMed Central

With the incessant challenge of exposure to the air we breathe, lung tissue suffers the highest levels of oxygen tension and thus requires robust antioxidant defenses. Furthermore, following injury or infection, lung tissue faces the additional challenge of inflammation-induced reactive oxygen and nitrogen species (ROS/RNS). Little is known about the identity or distribution of lung antioxidant enzymes under normal conditions or during infection-induced inflammation. Using a mouse model of influenza (H1N1 influenza virus A/PR/8/34 [PR8]) in combination with bioinformatics, we identified seven lung-abundant antioxidant enzymes: Glutathione peroxidase 3 (Gpx3), Superoxide dismutase 3 (Sod3), Transferrin (Tf), peroxyredoxin6 (Prdx6), glutathione S-transferase kappa 1 (Gstk1), Catalase (Cat), and Glutathione peroxidase 8 (Gpx8). Interestingly, despite the demand for antioxidants during inflammation, influenza caused depletion in two key antioxidants: Cat and Prdx6. As Cat is highly expressed in Clara cells, virus-induced Clara cell loss contributes to the depletion in Cat. Prdx6 is also reduced due to Clara cell loss, however there is a coincident increase in Prdx6 levels in the alveoli, resulting in only a subtle reduction of Prdx6 overall. Analogously, Gpx3 shifts from the basement membranes underlying the bronchioles and blood vessels to the alveoli, thus maintaining balanced expression. Taken together, these studies identify key lung antioxidants and reveal their distribution among specific cell types. Furthermore, results show that influenza depletes key antioxidants, and that in some cases there is coincident increased expression, consistent with compensatory expression. Given that oxidative stress is known to be a key risk factor during influenza infection, knowledge about the antioxidant repertoire of lungs, and the spatio-temporal distribution of antioxidants, contributes to our understanding of the underlying mechanisms of influenza-induced morbidity and mortality. PMID:22355371

Yamada, Yoshiyuki; Limmon, Gino V.; Zheng, Dahai; Li, Na; Li, Liang; Yin, Lu; Chow, Vincent T. K.; Chen, Jianzhu; Engelward, Bevin P.

2012-01-01

388

Spatio-temporal gait analysis in children with cerebral palsy using, foot-worn inertial sensors.  

PubMed

A child's natural gait pattern may be affected by the gait laboratory environment. Wearable devices using body-worn sensors have been developed for gait analysis. The purpose of this study was to validate and explore the use of foot-worn inertial sensors for the measurement of selected spatio-temporal parameters, based on the 3D foot trajectory, in independently walking children with cerebral palsy (CP). We performed a case control study with 14 children with CP aged 6-15 years old and 15 age-matched controls. Accuracy and precision of the foot-worn device were measured using an optical motion capture system as the reference system. Mean accuracy ± precision for both groups was 3.4 ± 4.6 cm for stride length, 4.3 ± 4.2 cm/s for speed and 0.5 ± 2.9° for strike angle. Longer stance and shorter swing phases with an increase in double support were observed in children with CP (p=0.001). Stride length, speed and peak angular velocity during swing were decreased in paretic limbs, with significant differences in strike and lift-off angles. Children with cerebral palsy showed significantly higher inter-stride variability (measured by their coefficient of variation) for speed, stride length, swing and stance. During turning trajectories speed and stride length decreased significantly (p<0.01) for both groups, whereas stance increased significantly (p<0.01) in CP children only. Foot-worn inertial sensors allowed us to analyze gait spatiotemporal data outside a laboratory environment with good accuracy and precision and congruent results with what is known of gait variations during linear walking in children with CP. PMID:24044970

Brégou Bourgeois, A; Mariani, B; Aminian, K; Zambelli, P Y; Newman, C J

2014-01-01

389

A method of estimating spatio-temporally distributed groundwater recharge using integrated surface-subsurface modelling  

NASA Astrophysics Data System (ADS)

In general, there have been various methods of estimating groundwater recharge such as baseflow separation approaches, water budget analyses based on lumped conceptual models, and the water table fluctuation method (WTF) by using data from groundwater monitoring wells. However, groundwater recharge rates show spatial-temporal variability due to climatic conditions, land use, and hydrogeological heterogeneity, so these methods have various limitations in dealing with these characteristics. To overcome these limitations, we present a novel application of estimating recharge based on water balance components from the combined SWAT-MODFLOW model, which is an integrated surface-ground water model. During the process of computing recharge, the time delay is very important factor. SWAT model uses single linear reservoir storage module with an exponential decay weighting function for accounting time delay through vadose zone. However, single reservoir module has limitation on the long delay time. So we suggest a multi-reservoir storage routing module instead of single one, which represents a more realistic time delay through the vadose zone. By using this module, the parameter related to the delay time could be optimized by checking the correlation between simulated recharge and observed groundwater levels. The final step of this procedure is to compare simulated groundwater levels as well as simulated watershed runoff with observed ones. This method is applied to several watersheds in Korea for the purpose of testing the procedure for proper estimation of spatio-temporal groundwater recharge distribution. As this application procedure of estimating recharge has the advantages of the effectiveness of a watershed model as well as the accuracy of the WTF method, the estimated daily recharge rate could be thought as an improved estimate reflecting the heterogeneity of hydrogeology, climatic conditions, land use, as well as the physical behavior of water in soil layers and aquifers.

Chung, Il Moon; Kim, Nam Won; Lee, Jeongwoo; Sophocleous, Marios

2010-05-01

390

Spatio-temporal variation in serum chemistry of the lobster, Homarus americanus Milne-Edwards.  

PubMed

Monthly variations in serum chemistry of the American lobster, Homarus americanus Milne-Edwards, were investigated at one location in Long Island Sound (LIS). Comparisons between three locations within and outside LIS were also made for a single time point. Most serum analytes displayed significant fluctuation over the study period and between locations. Temporal patterns could be classified as: low in cool months/high in warm months, i.e. Na, Cl, Na:K ratio, Ca, albumin:globulin ratio, percentage Fe saturation; high in cool months/low in warm months, i.e. pH, K, urea, total protein, albumin, globulin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), lipaemia; June spike, i.e. glucose, cholesterol, creatine kinase, iron, transferrin iron-binding capacity; other less obvious fluctuations, i.e. Mg, PO4; and no apparent fluctuation, i.e. HCO3, alkaline phosphatase. The proportion of samples correctly classified into month of collection by a subset of 13 analytes using discriminant analysis improved as the months progressed from May (0.75) to October (>0.95). Discriminant analysis also resolved 96.5% of samples by location. The significant depression of serum calcium at the eastern LIS site correlates with excretory calcinosis, a calcium storage disease described from lobsters at this site, but contrasts with a seasonal elevation in serum calcium recorded in the temporal component of the study. Serum proteins, the electrolytes Ca and K and the enzymes ALT and AST proved to have the strongest spatio-temporal patterns of variation. Serum chemistry is a useful research tool for lobster populations, but the dearth of information on the homology of analyte functions in this species with those in vertebrate species makes interpretation of the results challenging. Late summer/autumn water conditions appear to cause stress for lobsters in LIS. PMID:16303028

Dove, A D M; Sokolowski, M S; Bartlett, S L; Bowser, P R

2005-11-01

391

Spatio-temporal features of vegetation restoration and variation after the Wenchuan earthquake with satellite images  

NASA Astrophysics Data System (ADS)

The Wenchuan earthquake was a deadly earthquake that occurred on May 12, 2008, in Sichuan province of China. With the help of classic statistic methods, including arithmetic mean, standard deviation and linear trend estimation, vegetation restoration was recognized by analyzing spatio-temporal features of normalized difference vegetation index (NDVI) before and after this earthquake. Results indicate: (1) spatial distribution of NDVI mean values remains similar from 1998 to 2011. Higher values are mainly found in north, whereas lower values are mainly distributed over southeast, which is in good correlation with elevation and landform. Vegetation damage is at different levels in different seismic intensity (SI) regions: the higher SI is, the worse vegetation damage is. (2) Over the whole region, standard deviation is bigger after earthquake than before. Both absolute and relative changes in ecosystem stability increase with increasing SI. In different counties, variation of ecosystem stability is more obvious after earthquake, increase of standard deviation is approximately 6.5 times. Relatively, vegetation regionalization is the smallest analysis unit. Consequently, changes resulting from earthquake are unobvious. (3) Linear trend estimation coefficient increases from 0.0079 before the earthquake to 0.0359 after the earthquake in this whole region. This indicates that the plant ecosystem is rapidly restored between 2009 and 2011. The biggest linear trend is for the hill region, indicating good plant restoration and increase after earthquake. Fluctuation of linear trend estimation coefficient in different counties is more obvious after earthquake. Vegetation restoration after earthquake is most obvious in the regions that suffered the greatest SI (SI10 and SI11). In contrast, fluctuation in linear trend estimation coefficient of annual NDVI mean value for different classes of vegetation is more obvious before earthquake.

Peng, Hou; Qiao, Wang; Yipeng, Yang; Weiguo, Jiang; Bingfeng, Yang; Qiang, Chen; Lihua, Yuan; Fanming, Kong; Xi, Chen; Guanjie, Wang

2014-01-01

392

Spatio-temporal pattern of NPP and related analyses with terrain factors in Wuling mountainous area  

NASA Astrophysics Data System (ADS)

Based on the MODIS NPP data, terrain data, and land cover map, spatio-temporal pattern of NPP in Wuling mountainous area during 2001-2010 and its relationships with the elevation and slope were analyzed using regression analysis and classification statistics. Results showed that the average annual NPP of the study area from 2001 to 2010 was 590.72 g C m-2 yr-1. The mean NPP of forest, shrub/grassland, and cropland were 596.79 g C m-2 yr-1, 586.98 g C m-2 yr-1, and 563.31 g C m-2 yr-1, respectively. During 2001-2010, the average annual total NPP of Wuling mountainous area was 98.90 T g C yr-1, ranging from 92.79 T g C yr-1 to 106.99 T g C yr-1. Besides, the spatial pattern of interannual variability of NPP in the north of our study area presented a significant increase trend while in the south it displayed an opposite tendency. According to the relationships between mean NPP and elevation as well as slope at steps of 30m and 3°, respectively, NPP increased with the altitude and slope first, then decreased slowly, but when the elevation above 1500m or the slope greater than 50°, the mean NPP presented large fluctuations. However, on the whole, mean NPP increased with the altitude and slope first, then decreased again. Additionally, mean NPP within elevation range of 200m-1000m and slope range of 5°-25° were relatively high, but it decreased one after another in the zones above 500m and had a trend of increase when the slope zones greater than 50°, which reflected the erosion intensity was weakened when the slope greater than a certain threshold.

Sun, L. Qing; Xiao, Xiao; Feng, Feng X.

2014-11-01

393

Injectable system for spatio-temporally controlled delivery of hypoxia-induced angiogenic signalling.  

PubMed

While chronically ischaemic tissues are continuously exposed to hypoxia, the primary angiogenic stimulus, they fail to appropriately respond to it, as hypoxia-regulated angiogenic factor production gradually undergoes down-regulation, thus hindering adaptive angiogenesis. We have previously reported on two strategies for delivering on demand hypoxia-induced signalling (HIS) in vivo, namely, implanting living or non-viable hypoxic cell-matrix depots that actively produce factors or act as carriers of factors trapped within the matrix during in vitro pre-conditioning, respectively. This study aims to improve this approach through the development of a novel, injectable system for delivering cell-free matrix HIS-carriers. 3D spiral collagen constructs, comprising an inner cellular and outer acellular compartment, were cultured under hypoxia (5% O?). Cell-produced angiogenic factors (e.g. VEGF, FGF, PLGF, IL-8) were trapped within the nano-porous matrix of the acellular compartment as they radially diffused through it. The acellular matrix was mechanically fragmented into micro-fractions and added into a low temperature (5 °C) thermo-responsive type I collagen solution, which underwent a collagen concentration-dependent solution-to-gel phase transition at 37 °C. Levels of VEGF and IL-8, delivered from matrix fractions into media by diffusion through collagen sol-gel, were up-regulated by day 4 of hypoxic culture, peaked at day 8, and gradually declined towards the baseline by day 20, while FGF levels were stable over this period. Factors captured within matrix fractions were bioactive after 3 months freeze storage, as shown by their ability to induce tubule formation in an in vitro angiogenesis assay. This system provides a minimally invasive, and repeatable, method for localised delivery of time-specific, cell-free HIS factor mixtures, as a tool for physiological induction of spatio-temporally controlled angiogenesis. PMID:22634070

Hadjipanayi, E; Cheema, U; Hopfner, U; Bauer, A; Machens, H G; Schilling, A F

2012-08-10

394

Spatio-Temporal Diffusion Pattern and Hotspot Detection of Dengue in Chachoengsao Province, Thailand  

PubMed Central

In recent years, dengue has become a major international public health concern. In Thailand it is also an important concern as several dengue outbreaks were reported in last decade. This paper presents a GIS approach to analyze the spatial and temporal dynamics of dengue epidemics. The major objective of this study was to examine spatial diffusion patterns and hotspot identification for reported dengue cases. Geospatial diffusion pattern of the 2007 dengue outbreak was investigated. Map of daily cases was generated for the 153 days of the outbreak. Epidemiological data from Chachoengsao province, Thailand (reported dengue cases for the years 1999–2007) was used for this study. To analyze the dynamic space-time pattern of dengue outbreaks, all cases were positioned in space at a village level. After a general statistical analysis (by gender and age group), data was subsequently analyzed for temporal patterns and correlation with climatic data (especially rainfall), spatial patterns and cluster analysis, and spatio-temporal patterns of hotspots during epidemics. The results revealed spatial diffusion patterns during the years 1999–2007 representing spatially clustered patterns with significant differences by village. Villages on the urban fringe reported higher incidences. The space and time of the cases showed outbreak movement and spread patterns that could be related to entomologic and epidemiologic factors. The hotspots showed the spatial trend of dengue diffusion. This study presents useful information related to the dengue outbreak patterns in space and time and may help public health departments to plan strategies to control the spread of disease. The methodology is general for space-time analysis and can be applied for other infectious diseases as well. PMID:21318014

Jeefoo, Phaisarn; Tripathi, Nitin Kumar; Souris, Marc

2011-01-01

395

Swim-Training Changes the Spatio-Temporal Dynamics of Skeletogenesis in Zebrafish Larvae (Danio rerio)  

PubMed Central

Fish larvae experience many environmental challenges during development such as variation in water velocity, food availability and predation. The rapid development of structures involved in feeding, respiration and swimming increases the chance of survival. It has been hypothesized that mechanical loading induced by muscle forces plays a role in prioritizing the development of these structures. Mechanical loading by muscle forces has been shown to affect larval and embryonic bone development in vertebrates, but these investigations were limited to the appendicular skeleton. To explore the role of mechanical load during chondrogenesis and osteogenesis of the cranial, axial and appendicular skeleton, we subjected zebrafish larvae to swim-training, which increases physical exercise levels and presumably also mechanical loads, from 5 until 14 days post fertilization. Here we show that an increased swimming activity accelerated growth, chondrogenesis and osteogenesis during larval development in zebrafish. Interestingly, swim-training accelerated both perichondral and intramembranous ossification. Furthermore, swim-training prioritized the formation of cartilage and bone structures in the head and tail region as well as the formation of elements in the anal and dorsal fins. This suggests that an increased swimming activity prioritized the development of structures which play an important role in swimming and thereby increasing the chance of survival in an environment where water velocity increases. Our study is the first to show that already during early zebrafish larval development, skeletal tissue in the cranial, axial and appendicular skeleton is competent to respond to swim-training due to increased water velocities. It demonstrates that changes in water flow conditions can result into significant spatio-temporal changes in skeletogenesis. PMID:22529905

Fiaz, Ansa W.; Léon-Kloosterziel, Karen M.; Gort, Gerrit; Schulte-Merker, Stefan; van Leeuwen, Johan L.; Kranenbarg, Sander

2012-01-01

396

THE EFFECTS OF SPATIO-TEMPORAL RESOLUTION ON DEDUCED SPICULE PROPERTIES  

SciTech Connect

Spicules have been observed on the Sun for more than a century, typically in chromospheric lines such as H{alpha} and Ca II H. Recent work has shown that so-called 'type II' spicules may have a role in providing mass to the corona and the solar wind. In chromospheric filtergrams these spicules are not seen to fall back down, and they are shorter lived and more dynamic than the spicules that have been classically reported in ground-based observations. Observations of type II spicules with Hinode show fundamentally different properties from what was previously measured. In earlier work we showed that these dynamic type II spicules are the most common type, a view that was not properly identified by early observations. The aim of this work is to investigate the effects of spatio-temporal resolution in the classical spicule measurements. Making use of Hinode data degraded to match the observing conditions of older ground-based studies, we measure the properties of spicules with a semi-automated algorithm. These results are then compared to measurements using the original Hinode data. We find that degrading the data has a significant effect on the measured properties of spicules. Most importantly, the results from the degraded data agree well with older studies (e.g., mean spicule duration more than 5 minutes, and upward apparent velocities of about 25 km s{sup -1}). These results illustrate how the combination of spicule superposition, low spatial resolution and cadence affect the measured properties of spicules, and that previous measurements can be misleading.

Pereira, Tiago M. D. [NASA Ames Research Center, Moffett Field, CA 94035 (United States)] [NASA Ames Research Center, Moffett Field, CA 94035 (United States); De Pontieu, Bart [Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Bldg. 252, Palo Alto, CA 94304 (United States)] [Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. A021S, Bldg. 252, Palo Alto, CA 94304 (United States); Carlsson, Mats [Institute of Theoretical Astrophysics, P.O. Box 1029, Blindern, NO-0315 Oslo (Norway)] [Institute of Theoretical Astrophysics, P.O. Box 1029, Blindern, NO-0315 Oslo (Norway)

2013-02-10

397

Spatio-Temporal Expression Pattern of Frizzled Receptors after Contusive Spinal Cord Injury in Adult Rats  

PubMed Central

Background Wnt proteins are a large family of molecules that are critically involved in multiple central nervous system (CNS) developmental processes. Experimental evidences suggest a role for this family of proteins in many CNS disorders, including spinal cord injury (SCI), which is a major neuropathology owing to its high prevalence and chronic sensorimotor functional sequelae. Interestingly, most Wnt proteins and their inhibitors are expressed in the uninjured spinal cord, and their temporal expression patterns are dramatically altered after injury. However, little is known regarding the expression of their better-known receptors, the Frizzled family, after SCI. Thus, the aim of the present study was to evaluate the expression of Frizzled receptors in the damaged spinal cord. Findings Based on the evidence that Wnts are expressed in the spinal cord and are transcriptionally regulated by SCI in adulthood, we analysed the spatio-temporal mRNA and protein expression patterns of Frizzled receptors after contusive SCI using quantitative RT-PCR and single and double immunohistochemistry, respectively. Our results show that almost all of the 10 known Frizzled receptors were expressed in specific spatial patterns in the uninjured spinal cords. Moreover, the Frizzled mRNAs and proteins were expressed after SCI, although their expression patterns were altered during the temporal progression of SCI. Finally, analysis of cellular Frizzled 5 expression pattern by double immunohistochemistry showed that, in the uninjured spinal cord, this receptor was expressed in neurons, oligodendrocytes, astrocytes, microglia and NG2+ glial precursors. After injury, Frizzled 5 was not only still expressed in oligodendrocytes, astrocytes and NG2+ glial precursors but also in axons at all evaluated time points. Moreover, Frizzled 5 was expressed in reactive microglia/macrophages from 3 to 14 days post-injury. Conclusions Our data suggest the involvement of Frizzled receptors in physiological spinal cord function and in the cellular and molecular events that characterise its neuropathology. PMID:23251385

Arenas, Ernest; Rodriguez, Francisco Javier

2012-01-01

398

Gene structure and spatio-temporal expression of chicken LPIN2.  

PubMed

LPIN2 is one of the members of the Lipin family, which acts as a phosphatidate phosphatase enzyme. In this study, we identified the cDNA sequence and exonic variants of chicken LPIN2, and evaluated its spatio-temporal expression patterns. It indicated that chicken LPIN2 cDNA contained a 2,664-bp open reading frame flanked by a 176-bp 5' untranslated region and a 429-bp 3' untranslated region, predicted encoding one protein of 886 amino acids. Fourteen variants (three missense mutations) were detected from the coding region of chicken LPIN2. W265L was predicted to affect the gene function (p < 0.01) and eight synonymous mutations were predicted to affect the binding sites of SR proteins, which suggested the important functions of these variants. Real-time quantitative PCR revealed that LPIN2 in two genotypic chickens (LD and HB chickens, with difference in growth rate) presented similar tissue expression patterns, which was liver and ovary enriched with low abundance in skeleton muscles. Chicken LPIN2 exhibited tissue-specific temporal-expression patterns during postnatal development (0-16 weeks). Chicken cutaneous LPIN2 was in steady-state mRNA levels during postnatal development; chicken LPIN2 mRNA in pectoralis major had a prominent level at 0 week-old, then dropped dramatically at 4 week-old and maintained a relatively low level through 4-16 weeks; while chicken hepatic LPIN2 had a relatively high expression at 0 week-old, with a relatively low level through 4-12 weeks and a slight increase at 16 week-old. The studies about the basic gene features of chicken LPIN2 would lay the foundation for further exploring its biological function. PMID:24562627

Zhang, Caixia; Wang, Runzhi; Chen, Wen; Kang, Xiangtao; Huang, Yanqun; Walker, Richard; Mo, Juan

2014-06-01

399

PROPAGATION OF SEISMIC WAVES THROUGH A SPATIO-TEMPORALLY FLUCTUATING MEDIUM: HOMOGENIZATION  

SciTech Connect

Measurements of seismic wave travel times at the photosphere of the Sun have enabled inferences of its interior structure and dynamics. In interpreting these measurements, the simplifying assumption that waves propagate through a temporally stationary medium is almost universally invoked. However, the Sun is in a constant state of evolution, on a broad range of spatio-temporal scales. At the zero-wavelength limit, i.e., when the wavelength is much shorter than the scale over which the medium varies, the WKBJ (ray) approximation may be applied. Here, we address the other asymptotic end of the spectrum, the infinite-wavelength limit, using the technique of homogenization. We apply homogenization to scenarios where waves are propagating through rapidly varying media (spatially and temporally), and derive effective models for the media. One consequence is that a scalar sound speed becomes a tensorial wave speed in the effective model and anisotropies can be induced depending on the nature of the perturbation. The second term in this asymptotic two-scale expansion, the so-called corrector, contains contributions due to higher-order scattering, leading to the decoherence of the wave field. This decoherence may be causally linked to the observed wave attenuation in the Sun. Although the examples we consider here consist of periodic arrays of perturbations to the background, homogenization may be extended to ergodic and stationary random media. This method may have broad implications for the manner in which we interpret seismic measurements in the Sun and for modeling the effects of granulation on the scattering of waves and distortion of normal-mode eigenfunctions.

Hanasoge, Shravan M. [Department of Geosciences, Princeton University, Princeton, NJ 08544 (United States); Gizon, Laurent [Max-Planck-Institut fuer Sonnensystemforschung, D-37191 Katlenburg-Lindau (Germany); Bal, Guillaume [Department of Applied and Physical Mathematics, Columbia University, New York, NY 10027 (United States)

2013-08-20

400

Phlegra Montes - Spatio-Temporal Distribution of Ice and Debris at Martian Mid-Latitudes  

NASA Astrophysics Data System (ADS)

Mars hosts an abundance of landforms indicative of near-subsurface ice. Lobate debris aprons belong to a group of well-studied but still enigmatic ice-related landforms which have been identified at mid-latitudes between 30o and 50o in both hemispheres. While nature and origin of ice in these aprons are still controversially debated there is a general consensus that these features are sensitive to climate variability and, consequently, a potential indicator of past climate conditions, and potential water reservoirs today. The northern hemisphere hosts three populations of debris aprons: the Tempe Terra/Mareotis Fossae(TT) region [2, 5], the Deuteronilus/Protonilus Mensae (DPM) [1, 4, 9], and the Phlegra Montes region (PM) [3]. In southern latitudes the impact-basins rims of Argyre (AP) and Hellas Planitiae/Promethei Terra (HP) host a similar, albeit less well-pronounced set of features [1, 2, 6]. While most research is being concentrated on the HP, TT and DPM areas, studies discussing the population of the PM (located at 165o E, 30-50o N, see figure 1) are rather sparse [3, 14, 15, 16] although features are generally well-developed, representative due to their spatial distribution and wellimaged by high-resolution instruments. We performed an integrated spatio-temporal analysis of the PM population and focus on the age distribution of debris aprons in order to constrain their formation age. Our research is motivated by the assumption that if young-Amazonian climate variations have controlled formation and appearance of geomorphic landforms on Mars, we should observe traces of this process in PM as latitudinal trends and variations should provide measurable characteristics. If so, and if surface ages based on crater-frequency analysis are consistent with these assumptions, the exact timing of climate shifts may be assessable.

Schulz, J.; van Gasselt, S.; Orgel, C.

2014-04-01

401

Spatio-temporal PM and AOD estimations over Northeast Asia during DRAGON NE-Asia campaign  

NASA Astrophysics Data System (ADS)

Particulate matter (PM) is closely related to human health, air quality, and climate changes. It has been directly measured on the surface level. However, ground-based measurements have a limitation in spatial coverage of PM concentrations. In order to overcome this spatial limitation of ground measurements, AOD, which is considered as a proxy to PM concentration, was used in this study. AOD was first utilized to figure out the characteristics of PM and was then used to estimate the PM concentrations in Northeast Asia during the DRAGON Northeast-Asia campaign (March-May 2012), using CMAQ-estimated AOD, COMS/GOCI-retrieved AOD, and the AOD data from the DRAGON NE-Asia campaign. First of all, current emission inventories (MEIC and INTEX-B based emission inventories) were evaluated to improve CMAQ modeling results. Next, several algorithms to convert aerosol composition to AOD were evaluated using intensive measurement data from the DRAGON NE-Asia campaign. The accuracy of the CMAQ-estimated AOD was further evaluated with hourly observing GOCI-retrieved AOD. After the evaluation, CMAQ-calculated AOD was mathematically combined with GOCI-retrieved AOD via data assimilation. After this, AERONET AOD measured by the DRAGON NE-Asia campaign was again combined with the assimilated AOD from CMAQ and GOCI AODs to produce more accurate spatio-temporal AOD fields over Northeast Asia. Using several relationships between PM (PM10 and PM2.5) and AOD, the best surface-PM concentrations over the entire domain were calculated. It was then evaluated with ground-based PM2.5 measurements from the DRAGON NE-Asia campaign. A good agreement between estimated PM2.5 and measured PM2.5 over the domain was found. Finally, the PM and AOD information was used to investigate the effects of transboundary PM pollution from China to the Korean peninsula.

Park, M.; Song, C.; Kim, J.

2013-12-01

402

Spatio-temporal variability of groundwater nitrate concentration in Texas: 1960 to 2010.  

PubMed

Nitrate (NO) is a major contaminant and threat to groundwater quality in Texas. High-NO groundwater used for irrigation and domestic purposes has serious environmental and health implications. The objective of this study was to evaluate spatio-temporal trends in groundwater NO concentrations in Texas on a county basis from 1960 to 2010 with special emphasis on the Texas Rolling Plains (TRP) using the Texas Water Development Board's groundwater quality database. Results indicated that groundwater NO concentrations have significantly increased in several counties since the 1960s. In 25 counties, >30% of the observations exceeded the maximum contamination level (MCL) for NO (44 mg L NO) in the 2000s as compared with eight counties in the 1960s. In Haskell and Knox Counties of the TRP, all observations exceeded the NO MCL in the 2000s. A distinct spatial clustering of high-NO counties has become increasingly apparent with time in the TRP, as indicated by different spatial indices. County median NO concentrations in the TRP region were positively correlated with county-based area estimates of crop lands, fertilized croplands, and irrigated croplands, suggesting a negative impact of agricultural practices on groundwater NO concentrations. The highly transmissive geologic and soil media in the TRP have likely facilitated NO movement and groundwater contamination in this region. A major hindrance in evaluating groundwater NO concentrations was the lack of adequate recent observations. Overall, the results indicated a substantial deterioration of groundwater quality by NO across the state due to agricultural activities, emphasizing the need for a more frequent and spatially intensive groundwater sampling. PMID:23128738

Chaudhuri, Sriroop; Ale, Srinivasulu; Delaune, Paul; Rajan, Nithya

2012-01-01

403

Spatio-temporal pattern formation on spherical surfaces: numerical simulation and application to solid tumour growth.  

PubMed

In this paper we examine spatio-temporal pattern formation in reaction-diffusion systems on the surface of the unit sphere in 3D. We first generalise the usual linear stability analysis for a two-chemical system to this geometrical context. Noting the limitations of this approach (in terms of rigorous prediction of spatially heterogeneous steady-states) leads us to develop, as an alternative, a novel numerical method which can be applied to systems of any dimension with any reaction kinetics. This numerical method is based on the method of lines with spherical harmonics and uses fast Fourier transforms to expedite the computation of the reaction kinetics. Numerical experiments show that this method efficiently computes the evolution of spatial patterns and yields numerical results which coincide with those predicted by linear stability analysis when the latter is known. Using these tools, we then investigate the r?le that pre-pattern (Turing) theory may play in the growth and development of solid tumours. The theoretical steady-state distributions of two chemicals (one a growth activating factor, the other a growth inhibitory factor) are compared with the experimentally and clinically observed spatial heterogeneity of cancer cells in small, solid spherical tumours such as multicell spheroids and carcinomas. Moreover, we suggest a number of chemicals which are known to be produced by tumour cells (autocrine growth factors), and are also known to interact with one another, as possible growth promoting and growth inhibiting factors respectively. In order to connect more concretely the numerical method to this application, we compute spatially heterogeneous patterns on the surface of a growing spherical tumour, modelled as a moving-boundary problem. The numerical results strongly support the theoretical expectations in this case. Finally in an appendix we give a brief analysis of the numerical method. PMID:11419617

Chaplain, M A; Ganesh, M; Graham, I G

2001-05-01

404

A review of blind source separation in NMR spectroscopy.  

PubMed

Fourier transform is the data processing naturally associated to most NMR experiments. Notable exceptions are Pulse Field Gradient and relaxation analysis, the structure of which is only partially suitable for FT. With the revamp of NMR of complex mixtures, fueled by analytical challenges such as metabolomics, alternative and more apt mathematical methods for data processing have been sought, with the aim of decomposing the NMR signal into simpler bits. Blind source separation is a very broad definition regrouping several classes of mathematical methods for complex signal decomposition that use no hypothesis on the form of the data. Developed outside NMR, these algorithms have been increasingly tested on spectra of mixtures. In this review, we shall provide an historical overview of the application of blind source separation methodologies to NMR, including methods specifically designed for the specificity of this spectroscopy. PMID:25142734

Toumi, Ichrak; Caldarelli, Stefano; Torrésani, Bruno

2014-08-01

405

Recurrent Neural Networks For Blind Separation of Sources  

Microsoft Academic Search

In this paper, fully connected recurrent neural networksare investigated for blind separation of sources.For these networks, a new class of unsupervised on-linelearning algorithms are proposed. These algorithmsare the generalization of the Hebbian\\/anti-Hebbianrule. They are not only biologically plausible but alsotheoretically sound. An important property of thesealgorithms is that the performance of the networks isindependent of the mixing matrix and the

S. Amari; A. Cichocki; H. H. Yang

1995-01-01

406

Mapping the spatio-temporal structure of motor cortical LFP and spiking activities during reach-to-grasp movements  

PubMed Central

Grasping an object involves shaping the hand and fingers in relation to the object’s physical properties. Following object contact, it also requires a fine adjustment of grasp forces for secure manipulation. Earlier studies suggest that the control of hand shaping and grasp force involve partially segregated motor cortical networks. However, it is still unclear how information originating from these networks is processed and integrated. We addressed this issue by analyzing massively parallel signals from population measures (local field potentials, LFPs) and single neuron spiking activities recorded simultaneously during a delayed reach-to-grasp task, by using a 100-electrode array chronically implanted in monkey motor cortex. Motor cortical LFPs exhibit a large multi-component movement-related potential (MRP) around movement onset. Here, we show that the peak amplitude of each MRP component and its latency with respect to movement onset vary along the cortical surface covered by the array. Using a comparative mapping approach, we suggest that the spatio-temporal structure of the MRP reflects the complex physical properties of the reach-to-grasp movement. In addition, we explored how the spatio-temporal structure of the MRP relates to two other measures of neuronal activity: the temporal profile of single neuron spiking activity at each electrode site and the somatosensory receptive field properties of single neuron activities. We observe that the spatial representations of LFP and spiking activities overlap extensively and relate to the spatial distribution of proximal and distal representations of the upper limb. Altogether, these data show that, in motor cortex, a precise spatio-temporal pattern of activation is involved for the control of reach-to-grasp movements and provide some new insight about the functional organization of motor cortex during reaching and object manipulation. PMID:23543888

Riehle, Alexa; Wirtssohn, Sarah; Grün, Sonja; Brochier, Thomas

2013-01-01

407

Complex, dynamic combination of physical, chemical and nutritional variables controls spatio-temporal variation of sandy beach community structure.  

PubMed

Sandy beach ecological theory states that physical features of the beach control macrobenthic community structure on all but the most dissipative beaches. However, few studies have simultaneously evaluated the relative importance of physical, chemical and biological factors as potential explanatory variables for meso-scale spatio-temporal patterns of intertidal community structure in these systems. Here, we investigate macroinfaunal community structure of a micro-tidal sandy beach that is located on an oligotrophic subtropical coast and is influenced by seasonal estuarine input. We repeatedly sampled biological and environmental variables at a series of beach transects arranged at increasing distances from the estuary mouth. Sampling took place over a period of five months, corresponding with the transition between the dry and wet season. This allowed assessment of biological-physical relationships across chemical and nutritional gradients associated with a range of estuarine inputs. Physical, chemical, and biological response variables, as well as measures of community structure, showed significant spatio-temporal patterns. In general, bivariate relationships between biological and environmental variables were rare and weak. However, multivariate correlation approaches identified a variety of environmental variables (i.e., sampling session, the C?N ratio of particulate organic matter, dissolved inorganic nutrient concentrations, various size fractions of photopigment concentrations, salinity and, to a lesser extent, beach width and sediment kurtosis) that either alone or combined provided significant explanatory power for spatio-temporal patterns of macroinfaunal community structure. Overall, these results showed that the macrobenthic community on Mtunzini Beach was not structured primarily by physical factors, but instead by a complex and dynamic blend of nutritional, chemical and physical drivers. This emphasises the need to recognise ocean-exposed sandy beaches as functional ecosystems in their own right. PMID:21858213

Ortega Cisneros, Kelly; Smit, Albertus J; Laudien, Jürgen; Schoeman, David S

2011-01-01

408

Complex, Dynamic Combination of Physical, Chemical and Nutritional Variables Controls Spatio-Temporal Variation of Sandy Beach Community Structure  

PubMed Central

Sandy beach ecological theory states that physical features of the beach control macrobenthic community structure on all but the most dissipative beaches. However, few studies have simultaneously evaluated the relative importance of physical, chemical and biological factors as potential explanatory variables for meso-scale spatio-temporal patterns of intertidal community structure in these systems. Here, we investigate macroinfaunal community structure of a micro-tidal sandy beach that is located on an oligotrophic subtropical coast and is influenced by seasonal estuarine input. We repeatedly sampled biological and environmental variables at a series of beach transects arranged at increasing distances from the estuary mouth. Sampling took place over a period of five months, corresponding with the transition between the dry and wet season. This allowed assessment of biological-physical relationships across chemical and nutritional gradients associated with a range of estuarine inputs. Physical, chemical, and biological response variables, as well as measures of community structure, showed significant spatio-temporal patterns. In general, bivariate relationships between biological and environmental variables were rare and weak. However, multivariate correlation approaches identified a variety of environmental variables (i.e., sampling session, the C?N ratio of particulate organic matter, dissolved inorganic nutrient concentrations, various size fractions of photopigment concentrations, salinity and, to a lesser extent, beach width and sediment kurtosis) that either alone or combined provided significant explanatory power for spatio-temporal patterns of macroinfaunal community structure. Overall, these results showed that the macrobenthic community on Mtunzini Beach was not structured primarily by physical factors, but instead by a complex and dynamic blend of nutritional, chemical and physical drivers. This emphasises the need to recognise ocean-exposed sandy beaches as functional ecosystems in their own right. PMID:21858213

Ortega Cisneros, Kelly; Smit, Albertus J.; Laudien, Jürgen; Schoeman, David S.

2011-01-01

409

Combining physical-based models and satellite images for the spatio-temporal assessment of soil infiltration capacity  

Microsoft Academic Search

The performance of managed artificial recharge (MAR) facilities by means of surface ponds (SP) is controlled by the temporal\\u000a evolution of the global infiltration capacity I\\u000a \\u000a c\\u000a of topsoils. Cost-effective maintenance operations that aim to maintain controlled infiltration values during the activity\\u000a of the SP require the full knowledge of the spatio-temporal variability of I\\u000a \\u000a c\\u000a . This task is

Daniele Pedretti; Daniel Fernàndez-Garcia; Xavier Sanchez-Vila; Marco Barahona-Palomo; Diogo Bolster

410

Nonlinear spatio-temporal interactions and neural connections in human vision using transient and M-sequence stimuli  

SciTech Connect

Reciprocal connections, in essence, are the dynamic wiring (connections) of the neural network circuitry. Given the high complexity of the neural circuitry in the human brain, it is quite a challenge to study the dynamic wiring of highly parallel and widely distributed neural networks. The measurements of stimulus evoked coherent oscillations provide indirect evidence of dynamic wiring. In this study, in addition to the coherent oscillation measurements, two more techniques are discussed for testing possible dynamic wiring: measurements of spatio-temporal interactions beyond the classical receptive fields, and neural structural testing using nonlinear systems analysis.

Chen, H.W.; Aine, C.J.; Flynn, E.R.; Wood, C.C.

1996-02-01

411

Are the spatio-temporal parameters of gait capable of distinguishing a faller from a non-faller elderly?  

PubMed

Fall is a common and a major cause of injuries. It is important to find elderlies who are prone to falls. The majority of serious falls occur during walking among the older adults. Analyzing the spatio-temporal parameters of walking is an easy way of assessment in the clinical setting, but is it capable of distinguishing a faller from a non-faller elderly? Through a systematic review of the literature, the objective of this systematic review was to identify and summarize the differences in the spatio-temporal parameters of walking in elderly fallers and non-fallers and to find out if these parameters are capable of distinguishing a faller from a non-faller. All original research articles which compared any special or temporal walking parameters in faller and non-faller elderlies were systematically searched within the Scopus and Embase databases. Effect size analysis was also done to standardize findings and compare the gait parameters of fallers and non-fallers across the selected studies. The electronic search led to 5381 articles. After title and abstract screening 30 articles were chosen; further assessment of the full texts led to 17 eligible articles for inclusion in the review. It seems that temporal measurements are more sensitive to the detection of risk of fall in elderly people. The results of the 17 selected studies showed that fallers have a tendency toward a slower walking speed and cadence, longer stride time, and double support duration. Also, fallers showed shorter stride and step length, wider step width and more variability in spatio-temporal parameters of gait. According to the effect size analysis, step length, gait speed, stride length and stance time variability were respectively more capable of differentiating faller from non-faller elderlies. However, because of the difference of methodology and number of studies which investigated each parameter, these results are prone to imprecision. Spatio-temporal analysis of level walking is not sufficient and cannot act as a reliable predictor of falls in elderly individuals. PMID:24831570

Mortaza, N; Abu Osman, N A; Mehdikhani, N

2014-12-01

412

A novel right ventricle segmentation strategy using local spatio-temporal MRI information with a prior regularizer term  

NASA Astrophysics Data System (ADS)

In this work is presented a novel strategy that tracks the right ventricle (RV) shape during a whole cardiac cycle in magnetic resonance sequences (MRC). The proposed approach obtains a set of spatio-temporal observations from a bidirectional per pixel motion descriptor which are each time fused with prior learned edges. A main advantage of the proposed approach is a robust MRI heart characterization that is regularized by a prior information, obtaining in each cardiac state coherent results. The proposed approach achieves a Dice Score of 0.64 evaluated over 16 patients.

Atehortúa, Angélica; Martínez, Fabio; Romero, Eduardo

2013-11-01

413

The structure of spatio-temporal defects in a spiral pattern in the Couette-Taylor flow  

NASA Astrophysics Data System (ADS)

Disorder in spiral pattern arising in the counter-rotating Couette-Taylor flow has been investigated. It was revealed that in a certain range of flow control parameters, defects may be generated on the background of spirals periodically in time. Spatio-temporal structure of a single defect has been investigated in detail. A simple theoretical model based on asymptotic solution of the complex Ginzburg-Landau equation was proposed to explain characteristics of a defect. We found that, for a given super-criticality, defects appear at a definite value of the spiral wave phase.

Ezersky, A. B.; Abcha, N.; Mutabazi, I.

2010-07-01

414

Blind Source Separation of More Sources Than Mixtures Using Overcomplete Representations  

Microsoft Academic Search

Empirical results were obtained for the blind source separation of more sources than mixtures using a recently pro- posed framework for learning overcomplete representations. This technique assumes a linear mixing model with additive noise and involves two steps: 1) learning an overcomplete representation for the observed data and 2) inferring sources given a sparse prior on the coefficients. We demonstrate

Te-Won Lee; Michael S. Lewicki; Mark Girolami; Terrence J. Sejnowski

1998-01-01

4