Facets for Art Gallery Problems

The Art Gallery Problem (AGP) asks for placing a minimum number of stationary guards in a polygonal region P, such that all points in P are guarded. The problem is known to be NP-hard, and its inherent continuous structure (with both the set of points that need to be guarded and the set of points that can be used for guarding being uncountably infinite) makes it difficult to apply a straightforward formulation as an Integer Linear Program. We use an iterative primal-dual relaxation approach for solving AGP instances to optimality. At each stage, a pair of LP relaxations for a finite candidate subset of primal covering and dual packing constraints and variables is considered; these correspond to possible guard positions and points that are to be guarded. Particularly useful are cutting planes for eliminating fractional solutions. We identify two classes of facets, based on Edge Cover and Set Cover (SC) inequalities. Solving the separation problem for the latter is NP-complete, but exploiting the underlying geometric structure, we show that large subclasses of fractional SC solutions cannot occur for the AGP. This allows us to separate the relevant subset of facets in polynomial time. We also characterize all facets for finite AGP relaxations with coefficients in {0, 1, 2}. Finally, we demonstrate the practical usefulness of our approach. Our cutting plane technique yields a significant improvement in terms of speed and solution quality due to considerably reduced integrality gaps as compared to the approach by Kr\"oller et al.Comment: 29 pages, 18 figures, 1 tabl

Gas rotation, shocks and outflow within the inner 3 kpc of the radio galaxy 3C 33

We present optical integral field spectroscopy $-$ obtained with the Gemini Multi-Object Spectrograph $-$ of the inner $4.0 \times 5.8$ kpc$^2$ of the narrow line radio galaxy 3C 33 at a spatial resolution of 0.58 kpc. The gas emission shows three brightest structures: a strong knot of nuclear emission and two other knots at $\approx 1.4$ kpc south-west and north-east of the nucleus along the ionization axis. We detect two kinematic components in the emission lines profiles, with a "broader component" (with velocity dispersion $\sigma > 150$ km s$^{-1}$) being dominant within a $\sim$ 1 kpc wide strip ("the nuclear strip") running from the south-east to the north-west, perpendicular to the radio jet, and a narrower component ($\sigma < 100$ km s$^{-1}$) dominating elsewhere. Centroid velocity maps reveal a rotation pattern with velocity amplitudes reaching $\sim \pm 350$ km s$^{-1}$ in the region dominated by the narrow component, while residual blueshifts and redshifts relative to rotation are observed in the nuclear strip, where we also observe the highest values of the [N II]/H{\alpha}, [S II]/H{\alpha} and [O I]/H{\alpha} line ratios, and an increase of the gas temperature ($\sim 18000$ K), velocity dispersion and electron density ($\sim 500$ cm$^{-3}$). We interpret these residuals and increased line ratios as due to a lateral expansion of the ambient gas in the nuclear strip due to shocks produced by the passage of the radio jet. The effect of this expansion in the surrounding medium is very small, as its estimated kinetic power represents only $2.6 - 3.0 \times 10^{-5}$ of the AGN bolometric luminosity. A possible signature of inflow is revealed by an increase in the [O I]/H{\alpha} ratio values and velocity dispersions in the shape of two spiral arms extending to 2.3 kpc north-east and south-west from the nucleus.Comment: 16 pages, 14 figures, accepted by MNRA

Experimental Realization of the Fuse Model of Crack Formation

In this work, we present an experimental investigation of the fuse model. Our main goal was to study the influence of the disorder on the fracture process. The experimental apparatus used consisted of an $L\times L$ square lattice with fuses placed on each bond of the lattice. Two types of materials were used as fuses: copper and steel wool wires. The lattice composed only by copper wires varied from a weakly disordered system to a strongly disordered one. The lattice formed only by steel wool wires corresponded to a strongly disordered one. The experimental procedure consisted of applying a potential difference V to the lattice and measuring the respective current I. The characteristic function $I(V)$ obtained was investigated in order to find the scaling law dependence of the voltage and the current on the system size $L$ when the disorder was changed. Our results show that the scaling laws are only verified for the disordered regime.Comment: 4 pages, 8 figures.ep

PAI-1 Expressa no Infiltrado Inflamatório Intratumoral em Pacientes com Carcinoma Epidermoide de Cavidade Oral

PAI-1 Expressa no Infiltrado Inflamatório Intratumoral em Pacientes com Carcinoma Epidermoide de Cavidade Ora

Introspection dynamics: a simple model of counterfactual learning in asymmetric games

Social behavior in human and animal populations can be studied as an evolutionary process.Individuals often make decisions between different strategies, and those strategies that yield afitness advantage tend to spread. Traditionally, much work in evolutionary game theory considerssymmetric games: individuals are assumed to have access to the same set of strategies, and theyexperience the same payoff consequences. As a result, they can learn more profitable strategies byimitation. However, interactions are oftentimes asymmetric. In that case, imitation may beinfeasible (because individuals differ in the strategies they are able to use), or it may be undesirable(because individuals differ in their incentives to use a strategy). Here, we consider an alternativelearning process which applies to arbitrary asymmetric games,introspection dynamics. Accordingto this dynamics, individuals regularly compare their present strategy to a randomly chosenalternative strategy. If the alternative strategy yields a payoff advantage, it is more likely adopted. Inthis work, we formalize introspection dynamics for pairwise games. We derive simple and explicitformulas for the abundance of each strategy over time and apply these results to severalwell-known social dilemmas. In particular, for the volunteer’s timing dilemma, we show that theplayer with the lowest cooperation cost learns to cooperate without delay

Inference Time Optimization Using BranchyNet Partitioning

Deep Neural Network (DNN) applications with edge computing presents a trade-off between responsiveness and computational resources. On one hand, edge computing can provide high responsiveness deploying computational resources close to end devices, which may be prohibitive for the majority of cloud computing services. On the other hand, DNN inference requires computational power to be executed, which may not be available on edge devices, but a cloud server can provide it. To solve this problem (trade-off), we partition a DNN between edge device and cloud server, which means the first DNN layers are processed at the edge and the other layers at the cloud. This paper proposes an optimal partition of DNN, according to network bandwidth, computational resources of edge and cloud, and parameter inherent to data. Our proposal aims to minimize the inference time, to allow high responsiveness applications. To this end, we show the equivalency between DNN partitioning problem and shortest path problem to find an optimal solution, using Dijkstra's algorithm.Comment: 8 pages, 11 figures, IEEE Symposium on Computers and Communications 202

Violence Against Drivers and Conductors in the Road Passenger Transport Sector in Maputo, Mozambique

This cross-sectional study examined the extent, nature and risk factors of workplace violence in the road passenger transport sector in Maputo, the capital city of Mozambique. A random sample of 504 participants was selected from a population of 2 618 registered bus, minibus, and taxi drivers/conductors. The results indicated that workplace violence, psychological as well as physical, is highly prevalent among drivers/conductors, with 77% reporting ever being abused and 64% reporting being abused during the past 12 months. Particularly vulnerable groups comprised illiterate employees, bus drivers/conductors, employees with long experience, and those holding a supervisory position. In addition, a high workload was associated with an increased likelihood of exposure to workplace violence in the road passenger transport sector. This article discusses the implications of the findings for possible interventions and further research

Violence Against Drivers and Conductors in the Road Passenger Transport Sector in Maputo, Mozambique

This cross-sectional study examined the extent, nature and risk factors of workplace violence in the road passenger transport sector in Maputo, the capital city of Mozambique. A random sample of 504 participants was selected from a population of 2 618 registered bus, minibus, andtaxi drivers/conductors. The results indicated that workplace violence, psychological as well as physical, is highly prevalent among drivers/conductors, with 77% reporting ever being abusedand 64% reporting being abused during the past 12 months. Particularly vulnerable groups comprised illiterate employees, bus drivers/conductors, employees with long experience, and those holding a supervisory position. In addition, a high workload was associated with an increased likelihood of exposure to workplace violence in the road passenger transport sector. This article discusses the implications of the findings for possible interventions and further research