Optimal system size for complex dynamics in random neural networks near criticality

In this Letter, we consider a model of dynamical agents coupled through a random connectivity matrix, as introduced in [Sompolinsky et. al, 1988] in the context of random neural networks. It is known that increasing the disorder parameter induces a phase transition leading to chaotic dynamics. We observe and investigate here a novel phenomenon in the subcritical regime : the probability of observing complex dynamics is maximal for an intermediate system size when the disorder is close enough to criticality. We give a more general explanation of this type of system size resonance in the framework of extreme values theory for eigenvalues of random matrices.Comment: 11 pages, 2 figure

Multi-agent simulations for emergency situations in an airport scenario

This paper presents a multi-agent framework using Net- Logo to simulate humanand collective behaviors during emergency evacuations. Emergency situationappears when an unexpected event occurs. In indoor emergency situation, evacuation plans defined by facility manager explain procedure and safety ways tofollow in an emergency situation. A critical and public scenario is an airportwhere there is an everyday transit of thousands of people. In this scenario theimportance is related with incidents statistics regarding overcrowding andcrushing in public buildings. Simulation has the objective of evaluating buildinglayouts considering several possible configurations. Agents could be based onreactive behavior like avoid danger or follow other agent, or in deliberative behaviorbased on BDI model. This tool provides decision support in a real emergencyscenario like an airport, analyzing alternative solutions to the evacuationprocess.Publicad

Time evolution of decay of two identical quantum particles

An analytical solution for the time evolution of decay of two identical non interacting quantum particles seated initially within a potential of finite range is derived using the formalism of resonant states. It is shown that the wave function, and hence also the survival and nonescape probabilities, for factorized symmetric and entangled symmetric/antisymmetric initial states evolve in a distinctive form along the exponentially decaying and nonexponential regimes. Our findings show the influence of the Pauli exclusion principle on decay. We exemplify our results by solving exactly the s-wave delta shell potential model.Comment: 14 pages, 3 figures, added references and discussio

Teachers and day labourers. The state school in Extremadura at the end of the 18th century

El presente trabajo estudia la situación social y económica de las escuelas públicas y los maestros de Extremadura a finales del siglo XVIII, en el contexto histórico de la Ilus­tración Para ello, se compara la situación económica de los maestros y las escuelas con la del sector más humilde de la sociedad: los jornaleros del campo. Para realizar este estudio, se han revisado todas las contestaciones a las preguntas formuladas acerca de la situación de la educación y los maestros en los pueblos, así como las relativas a la de otros trabajadores, incluidas en los "Interrogatorios de la Real Audiencia de Extremadura". Presentamos, en primer lugar, un extracto de la información contenida en ellos, que nos muestra la configuración de la población en Extremadura, la extensión de la escolari­dad pública, la atención a niños y niñas o la situación económica de escuelas y maestros, comparadas con otros sectores de la población. Los resultados obtenidos muestran una alta valoración social por parte de las clases ilustradas, pero a la vez, una elevada demanda por parte de todos los estamentos sociales, aunque la realidad del momento, como la de muchos años después, fuera la de una escasa ayuda económica a la educación, reflejada en el bajo reconocimiento económico de los maestros.The present study examines the social and economic situation of the state schools and teachers in Extremadura in the late 18th century, in the historical context of the Enlightenment. To this end, we compare the economic status of teachers and schools with the poorest sectors of society: the day labourers. For this study, we have reviewed all the answers to questions about the status of education and teachers in the villages, as well as those related to other workers, included in the "Questionings of the Royal High Court in Extremadura". Firstly, we will introduce an extract of the information contained therein, which shows the configuration of the population in Extremadura, the extension of public schooling, attention to boys and girls or the economic situation of schools and teachers, compared with other sectors of the population. The results show a high social value on the part of the enlightened classes, yet a high demand from all social strata, although the reality of the moment, like many years later, was that of a little financial aid to education, reflected in lower economic recognition of teachers.peerReviewe

Optimization of Nanoparticle-Based SERS Substrates through Large-Scale Realistic Simulations

Surface-enhanced Raman scattering (SERS) has become a widely used spectroscopic technique for chemical identification, providing unbeaten sensitivity down to the singlemolecule level. The amplification of the optical near field produced by collective electron excitations plasmons in nanostructured metal surfaces gives rise to a dramatic increase by many orders of magnitude in the Raman scattering intensities from neighboring molecules. This effect strongly depends on the detailed geometry and composition of the plasmonsupporting metallic structures. However, the search for optimized SERS substrates has largely relied on empirical data, due in part to the complexity of the structures, whose simulation becomes prohibitively demanding. In this work, we use state-of-the-art electromagnetic computation techniques to produce predictive simulations for a wide range of nanoparticle-based SERS substrates, including realistic configurations consisting of random arrangements of hundreds of nanoparticles with various morphologies. This allows us to derive rules of thumb for the influence of particle anisotropy and substrate coverage on the obtained SERS enhancement and optimum spectral ranges of operation. Our results provide a solid background to understand and design optimized SERS substrates.Peer ReviewedPostprint (published version

Coupling single molecule magnets to quantum circuits

In this work we study theoretically the coupling of single molecule magnets (SMMs) to a variety of quantum circuits, including microwave resonators with and without constrictions and flux qubits. The main results of this study is that it is possible to achieve strong and ultrastrong coupling regimes between SMM crystals and the superconducting circuit, with strong hints that such a coupling could also be reached for individual molecules close to constrictions. Building on the resulting coupling strengths and the typical coherence times of these molecules (of the order of microseconds), we conclude that SMMs can be used for coherent storage and manipulation of quantum information, either in the context of quantum computing or in quantum simulations. Throughout the work we also discuss in detail the family of molecules that are most suitable for such operations, based not only on the coupling strength, but also on the typical energy gaps and the simplicity with which they can be tuned and oriented. Finally, we also discuss practical advantages of SMMs, such as the possibility to fabricate the SMMs ensembles on the chip through the deposition of small droplets.Comment: 23 pages, 12 figure

Hypoxic Cell Waves around Necrotic Cores in Glioblastoma: A Biomathematical Model and its Therapeutic Implications

Glioblastoma is a rapidly evolving high-grade astrocytoma that is distinguished pathologically from lower grade gliomas by the presence of necrosis and microvascular hiperplasia. Necrotic areas are typically surrounded by hypercellular regions known as "pseudopalisades" originated by local tumor vessel occlusions that induce collective cellular migration events. This leads to the formation of waves of tumor cells actively migrating away from central hypoxia. We present a mathematical model that incorporates the interplay among two tumor cell phenotypes, a necrotic core and the oxygen distribution. Our simulations reveal the formation of a traveling wave of tumor cells that reproduces the observed histologic patterns of pseudopalisades. Additional simulations of the model equations show that preventing the collapse of tumor microvessels leads to slower glioma invasion, a fact that might be exploited for therapeutic purposes.Comment: 29 pages, 9 figure

Associations between sedentary time, physical activity and bone health among older people using compositional data analysis

Introduction : Aging is associated with a progressive decrease in bone mass (BM), and being physical active is one of the main strategies to combat this continuous loss. Nonetheless, because daily time is limited, time spent on each movement behavior is co-dependent. The aim of this study was to determine the relationship between BM and movement behaviors in elderly people using compositional data analysis. Methods : We analyzed 871 older people [395 men (76.9 +/- 5.3y) and 476 women (76.7 +/- 4.7y)]. Time spent in sedentary behavior (SB), light physical activity (LPA) and moderate-to-vigorous physical activity (MVPA), was assessed using accelerometry. BM was determined by bone densitometry (DXA). The sample was divided according to sex and bone health indicators. Results : The combined effect of all movement behaviors (PA and SB) was significantly associated with whole body, leg and femoral region BM in the whole sample (p<0.05), with leg and pelvic BM (p<0.05) in men and, with whole body, arm and leg BM (p<0.05) in women. In men, arm and pelvic BM were negatively associated with SB and whole body, pelvic and leg BM were positively associated with MVPA (p<0.05). In women, whole body and leg BM were positively associated with SB. Arm and whole body BM were positively associated and leg BM was negatively associated with LPA and arm BM was negatively associated with MVPA (p<0.05). Women without bone fractures spent less time in SB and more in LPA and MVPA than the subgroup with bone fractures. Conclusion : We identified that the positive effect of MVPA relative to the other behaviors on bone mass is the strongest overall effect in men. Furthermore, women might decrease bone fracture risk through PA increase and SB reduction, despite the fact that no clear benefits of PA for bone mass were found