The spatial Solow model

in Economics Bulletin (2004)

In this paper, we solve a Solow model in continuous time and space. We prove the existence of a solution to the problem and its convergence to a stationary solution. The simulations of various scenario in ... [more ▼]

In this paper, we solve a Solow model in continuous time and space. We prove the existence of a solution to the problem and its convergence to a stationary solution. The simulations of various scenario in the last section of the paper illustrates the convergence issue. [less ▲]

Spatial Sparsity Based Direct Positioning for IR-UWB in IEEE 802.15.4a Channels

in IEEE Int. Conf. UltraWide-Band (ICUWB) (2014)

Spatial- and Range- ISLR Trade-off in MIMO Radar Systems via Waveform Design

in IEEE Transactions on Signal Processing (2021)

This paper aims to design a set of transmit waveforms in cognitive colocated Multi-Input Multi-Output (MIMO) radar systems considering the simultaneous minimization of the contradictory objectives of ... [more ▼]

This paper aims to design a set of transmit waveforms in cognitive colocated Multi-Input Multi-Output (MIMO) radar systems considering the simultaneous minimization of the contradictory objectives of spatial- and the range- Integrated Sidelobe Level Ratio (ISLR). The design problem is formulated as a bi-objective Pareto optimization under practical constraints on the waveforms, namely total transmit power, peak-to-average-power ratio (PAR), constant modulus, and discrete phase alphabet. A Coordinate Descent (CD) based approach is proposed where the solution in each iteration is handled through novel methodologies designed in the paper. The simultaneous optimization leads to a trade-off between the two ISLRs and the simulation results illustrate significantly improved trade-off offered by the proposed methodologies. [less ▲]

A spatially constrained generative model and an EM algorithm for image segmentation

in IEEE Transactions on Neural Networks (2007), 18(3), 798-808

In this paper, we present a novel spatially constrained generative model and an expectation-maximization (EM) algorithm for model-based image segmentation. The generative model assumes that the unobserved ... [more ▼]

In this paper, we present a novel spatially constrained generative model and an expectation-maximization (EM) algorithm for model-based image segmentation. The generative model assumes that the unobserved class labels of neighboring pixels in the image are generated by prior distributions with similar parameters, where similarity is defined by entropic quantities relating to the neighboring priors. In order to estimate model pa rameters from observations, we derive a spatially constrained EM algorithm that iteratively maximizes a lower bound on the data log-likelihood, where the penalty term is data-dependent. Our algorithm is very easy to implement and is similar to the standard EM algorithm for Gaussian mixtures with the main difference that the labels posteriors are "smoothed" over pixels between each E-and M-step by a standard image filter. Experiments on synthetic and real images show that our algorithm achieves competitive segmentation results compared to other Markov-based methods, and is in general faster. [less ▲]

A Spatially explicit ABM of Central Place Foraging Theory and its explanatory power for hunter-gatherers settlement patterns formation processes

in Adaptive Behavior (2020)

The behavioural ecological approach to anthropology states that the density and distribution of resources determine optimal patterns of resource use and also sets its constraints to grouping, mobility and ... [more ▼]

The behavioural ecological approach to anthropology states that the density and distribution of resources determine optimal patterns of resource use and also sets its constraints to grouping, mobility and settlement choice. Central Place Foraging (CPF) models have been used for analysing foraging behaviours of hunter-gatherers and to draw a causal link from the volume of available resources in the environment to the mobility decisions of hunter-gatherers. In this study we propose a spatially explicit agent-based CPF mode. We explore its potential for explaining formation of settlement patterns and test its robustness to the configuration of space. Building on a model assuming homogeneous energy distributions we had to add several new parameters and an adaptation mechanism for foragers to predict the length of their stay, together with a heterogeneous environment configuration. The validation of the model shows that the spatially explicit CPF is generally robust to spatial configuration of energy resources. The total volume of energy has a significant effect on constraining sedentism as predicted by aspatial model and thus can be used on different environmental conditions. Still the spatial autocorrelation of resource distribution has a linear effect on optimal mobility decisions and needs to be considered in predictive models. The effect on settlement choice is not substantial and is more determined by other characteristics of settlement location. This limits the CPF models in analysing settlement pattern formation processes. [less ▲]

Spatially resolved raman spectroscopy of single- and few-layer graphene

in Nano Letters (2007), 7(2), 238-242

We present Raman spectroscopy measurements on single- and few-layer graphene flakes. By using a scanning confocal approach, we collect spectral data with spatial resolution, which allows us to directly ... [more ▼]

We present Raman spectroscopy measurements on single- and few-layer graphene flakes. By using a scanning confocal approach, we collect spectral data with spatial resolution, which allows us to directly compare Raman images with scanning force micrographs. Single-layer graphene can be distinguished from double- and few-layer by the width of the D' line: the single peak for single-layer graphene splits into different peaks for the double-layer. These findings are explained using the double-resonant Raman model based on ab initio calculations of the electronic structure and of the phonon dispersion. We investigate the D line intensity and find no defects within the flake. A finite D line response originating from the edges can be attributed either to defects or to the breakdown of translational symmetry. [less ▲]

Spatial–temporal variations of water vapor content over Ethiopia: a study using GPS observations and the ECMWF model

in GPS Solutions (2015)

We characterize the spatial–temporal variability of integrated water vapor (IWV) in Ethiopia from a network of global positioning system (GPS) stations and the European Center for Medium range Weather ... [more ▼]

We characterize the spatial–temporal variability of integrated water vapor (IWV) in Ethiopia from a network of global positioning system (GPS) stations and the European Center for Medium range Weather Forecasting (ECMWF) model. The IWV computed from the ECMWF model is integrated from the height of the GPS stations on 60 pressure levels to take both the actual earth surface and the model orography discrepancies into account. First, we compare the IWV estimated from GPS and from the model. The bias varies from site to site, and the correlation coefficients between the two data sets exceed 0.85 at different time scales. The results of this study show that the general ECMWF IWV trend is underestimation over highlands and overestimation over lowlands for wet periods, and overestimation over high- lands and underestimation over lowlands for dry periods with very few exceptional stations. Second, we observe the spatial variation of the IWV. High values are obtained in those stations that are located in the north-eastern (Afar depression) sites and the south-western part of the country. This distribution is related to the spatial variability of the climate in Ethiopia. Finally, we study the seasonal cycle and inter-annual variability of IWV for all stations over Ethiopia. The main result is the strong inter-annual vari- ability observed for the dry seasons. [less ▲]

The spatio-temporal correlates of holistic face perception

Poster (2007, May)

It is well known that faces are perceived holistically: their parts are integrated into a global or so-called holistic individual representation. Here we clarify where and how early in time individual ... [more ▼]

It is well known that faces are perceived holistically: their parts are integrated into a global or so-called holistic individual representation. Here we clarify where and how early in time individual holistic representations are extracted from the visual stimulus, by means of an event-related identity adaptation paradigm in fMRI (study 1; 10 subjects) and ERPs (study 2; 16 subjects). During blocks, subjects were presented with trials made of two sequentially presented faces and performed a same/different judgement on the top parts of each pair of faces. Face parts were presented either aligned or misaligned. For each face pair, the identity of top and bottom parts could be (a) both identical, (b) both different, (c) different only for the bottom part. The latter manipulation resulted in a strong face composite illusion behaviourally, i.e. the perception of identical top parts as being different, only in the aligned format. In the face-sensitive area of the middle fusiform gyrus (‘fusiform face area’) we observed a stronger response to the top part perceived as being different (release from adaptation), but only when the top and the bottom parts were aligned. It is consistent with the illusion of viewing different top parts of faces, and this release from fMR-adaptation is similar to the one observed in the ‘different’ condition for both aligned and misaligned parts. The same observations were made in ERPs as early as 150 ms, the amplitude of the electrophysiological response at occipito-temporal sites to the second face stimulus being reduced for identical relative to different top face parts, and to identical top parts perceived as different (aligned - bottom different). With both methods, the effects were stronger in the right hemisphere. Altogether, these observations indicate that individual faces are perceived holistically as early as 150 ms in the occipito-temporal cortex. [less ▲]

Spatio-Temporal Rainfall Estimation from Communication Satellite Data using Graph Neural Networks

Scientific Conference (2022, May)

Spatio-temporal ToF data enhancement by fusion

in Proceedings - International Conference on Image Processing, ICIP (2012)

We propose an extension of our previous work on spatial domain Time-of-Flight (ToF) data enhancement to the temporal domain. Our goal is to generate enhanced depth maps at the same frame rate of the 2-D ... [more ▼]

We propose an extension of our previous work on spatial domain Time-of-Flight (ToF) data enhancement to the temporal domain. Our goal is to generate enhanced depth maps at the same frame rate of the 2-D camera that, coupled with a ToF camera, constitutes a hybrid ToF multi-camera rig. To that end, we first estimate the motion between consecutive 2-D frames, and then use it to predict their corresponding depth maps. The enhanced depth maps result from the fusion between the recorded 2-D frames and the predicted depth maps by using our previous contribution on ToF data enhancement. The experimental results show that the proposed approach overcomes the ToF camera drawbacks; namely, low resolution in space and time and high level of noise within depth measurements, providing enhanced depth maps at video frame rate. © 2012 IEEE. [less ▲]