"Self-organizing Urban Hierarchy"

We have considered a general equilibrium model with monopolistically competitive markets, in which urban centers are service suppliers to all the agricultural regions as well as to the other urban centers. We have retained the forward and backward linkages of NEG to generate the agglomeration of firms and workers in cities. Our main result is that central places arise endogenously when transport costs take intermediate values.

"Competing for capital when labor is heterogeneous"

This paper investigates the impacts of capital mobility and tax competition in a setting with imperfect matching between firms and workers. The small country attracts less firms than the large one but accommodates a share of the industry that exceeds its capital share -a reverse home market effect. This allows the small country to be more aggressive and to set a higher tax rate than the large one, thus implying that tax competition reduces international inequalities. However, the large country always attains a higher utility than does the small country. Our model thus encapsulates both the "importance of being small" and the "importance of being large". Last, tax harmonization benefits to the small country but is detrimental to the large one.

"Labor Mobility and Economic Geography"

This paper investigates the impact of the heterogeneity of the labor force on the spatial distribution of activities. This goal is achieved by applying the tools of discrete choice theory to an economic geography model. We show that taste heterogeneity acts as a strong dispersion force. We also show that the relationship between the spatial distribution of the industry (the wage differential) and trade costs is smooth and inverted U-shaped. Finally, while Rawlsian equity leads to the dispersion of industry, our analysis reveals that efficiency leads to a solution close to the market outcome, although the latter is likely to involve too much agglomeration compared to the former.

"Regional Specialization, Urban Hierarchy, and Commuting Costs"

We consider an economic geography model of a new genre: all firms and workers are mobile and their agglomeration within a city generates rising urban costs through competition on a land market. When commuting costs are high (low), the industry tends to be agglomerated (dispersed). With two sectors, the same tendencies prevail for extreme commuting cost values, but richer patterns arise for intermediate values. When one good is perfectly mobile, the corresponding industry is partially dispersed and the other industry is agglomerated, thus showing regional specialization. When one sector supplies a nontradeable consumption good, this sector is more agglomerated than the other. The corresponding equilibrium involves an urban hierarchy: a larger array of varieties of each good is produced within the same city.

Motion of an Adhesive Gel in a Swelling Gradient: a Mechanism for Cell Locomotion

Motivated by the motion of nematode sperm cells, we present a model for the motion of an adhesive gel on a solid substrate. The gel polymerizes at the leading edge and depolymerizes at the rear. The motion results from a competition between a self-generated swelling gradient and the adhesion on the substrate. The resulting stress provokes the rupture of the adhesion points and allows for the motion. The model predicts an unusual force-velocity relation which depends in significant ways on the point of application of the force.Comment: 4 pages, 1 figur

"Is the regulation of the transport sector always detrimental to consumers?"

The aim of this paper is to qualify the claim that regulating a competitive transport sector is always detrimental to consumers. We show indeed that, although transport deregulation is beneficial to consumers as long as the location of economic activity is fixed, this is no longer true when, in the long run, firms and workers are freely mobile. The reason is that the static gains due to less monopoly power in the transport sector may well map into dynamic dead-weight losses because deregulation of the transport sector leads to more inefficient agglomeration. This latter change may, quite surprisingly, increase consumer prices in some regions, despite a more competitive transport sector. Transport deregulation is shown to map into aggregate consumer welfare losses and more inequality among consumers in the long run.

Casimir stresses in active nematic films

We calculate the Casimir stresses in a thin layer of active fluid with nematic order. By using a stochastic hydrodynamic approach for an active fluid layer of finite thickness $L$, we generalize the Casimir stress for nematic liquid crystals in thermal equilibrium to active systems. We show that the active Casimir stress differs significantly from its equilibrium counterpart. For contractile activity, the active Casimir stress, although attractive like its equilibrium counterpart, diverges logarithmically as $L$ approaches a threshold of the spontaneous flow instability from below. In contrast, for small extensile activity, it is repulsive, has no divergence at any $L$ and has a scaling with $L$ different from its equilibrium counterpart

On the Connectivity of Unions of Random Graphs

Graph-theoretic tools and techniques have seen wide use in the multi-agent systems literature, and the unpredictable nature of some multi-agent communications has been successfully modeled using random communication graphs. Across both network control and network optimization, a common assumption is that the union of agents' communication graphs is connected across any finite interval of some prescribed length, and some convergence results explicitly depend upon this length. Despite the prevalence of this assumption and the prevalence of random graphs in studying multi-agent systems, to the best of our knowledge, there has not been a study dedicated to determining how many random graphs must be in a union before it is connected. To address this point, this paper solves two related problems. The first bounds the number of random graphs required in a union before its expected algebraic connectivity exceeds the minimum needed for connectedness. The second bounds the probability that a union of random graphs is connected. The random graph model used is the Erd\H{o}s-R\'enyi model, and, in solving these problems, we also bound the expectation and variance of the algebraic connectivity of unions of such graphs. Numerical results for several use cases are given to supplement the theoretical developments made.Comment: 16 pages, 3 tables; accepted to 2017 IEEE Conference on Decision and Control (CDC

The actin cortex as an active wetting layer

Using active gel theory we study theoretically the properties of the cortical actin layer of animal cells. The cortical layer is described as a non-equilibrium wetting film on the cell membrane. The actin density is approximately constant in the layer and jumps to zero at its edge. The layer thickness is determined by the ratio of the polymerization velocity and the depolymerization rate of actin.Comment: submitted to Eur Phys Jour

Methods for multi-spectral image fusion: identifying stable and repeatable information across the visible and infrared spectra

Fusion of images captured from different viewpoints is a well-known challenge in computer vision with many established approaches and applications; however, if the observations are captured by sensors also separated by wavelength, this challenge is compounded significantly. This dissertation presents an investigation into the fusion of visible and thermal image information from two front-facing sensors mounted side-by-side. The primary focus of this work is the development of methods that enable us to map and overlay multi-spectral information; the goal is to establish a combined image in which each pixel contains both colour and thermal information. Pixel-level fusion of these distinct modalities is approached using computational stereo methods; the focus is on the viewpoint alignment and correspondence search/matching stages of processing. Frequency domain analysis is performed using a method called phase congruency. An extensive investigation of this method is carried out with two major objectives: to identify predictable relationships between the elements extracted from each modality, and to establish a stable representation of the common information captured by both sensors. Phase congruency is shown to be a stable edge detector and repeatable spatial similarity measure for multi-spectral information; this result forms the basis for the methods developed in the subsequent chapters of this work. The feasibility of automatic alignment with sparse feature-correspondence methods is investigated. It is found that conventional methods fail to match inter-spectrum correspondences, motivating the development of an edge orientation histogram (EOH) descriptor which incorporates elements of the phase congruency process. A cost function, which incorporates the outputs of the phase congruency process and the mutual information similarity measure, is developed for computational stereo correspondence matching. An evaluation of the proposed cost function shows it to be an effective similarity measure for multi-spectral information