Extreme self-organization in networks constructed from gene expression data

We study networks constructed from gene expression data obtained from many types of cancers. The networks are constructed by connecting vertices that belong to each others' list of K-nearest-neighbors, with K being an a priori selected non-negative integer. We introduce an order parameter for characterizing the homogeneity of the networks. On minimizing the order parameter with respect to K, degree distribution of the networks shows power-law behavior in the tails with an exponent of unity. Analysis of the eigenvalue spectrum of the networks confirms the presence of the power-law and small-world behavior. We discuss the significance of these findings in the context of evolutionary biological processes.Comment: 4 pages including 3 eps figures, revtex. Revisions as in published versio

Charge injection, electroluminescence, and ageing of an epoxy resin in high divergent fields

[INTRODUCTION]Most experimental studies of electrical ageing have concentrated on semi-crystalline polymers such as those used in cable insulation and capacitors (see for example [1]). Theoretical models [2-4] for electrical ageing have been developed on the basis of these studies. The consensus is that ageing involves the formation of low-density regions, though the mechanisms responsible are disputed. For example, bond scission by high-energy electrons [2,5], and mechanical deformation have both been suggested. Both of these mechanisms are related to charge injection and the subsequent formation of high local fields. The semi-crystalline polymers studied so far have similar chemistries and almost identical morphologies. They tend, therefore, to show many similarities in, for example, the size of the energy barriers for the ageing reaction, critical ageing levels, and field dependence of ageing [4]. These similarities make it difficult to discriminate between mechanisms. Epoxy resins, however, are network polymers with a different molecular chemistry to that of the semi-crystalline polymers and are thus ideal to evaluate the proposed ageing mechanisms. We have therefore studied an epoxy resin (CY1301) under both uniform field and high divergent field conditions. Uniform field conditions were used to gain baseline characteristics for the properties of the unaged epoxy resin, and also for the effects of electrical ageing in low fields. Studies in high divergent fields were made using an electrode arrangement adapted from that of [6]. A number of wires set approximately 0.5mm apart were embedded, parallel to the flat faces, in thin (290 m ) flat samples. The radius of the wires ranged from 5 m (gold plated tungsten) to 25 m (tungsten). Relatively small voltages applied to the wires (5 kV DC) therefore produced local fields up to 170 kV/mm depending upon the wire radius chosen. These field levels are high enough to inject space-charge [6] without leading to instantaneous failure. This geometry, therefore, may both inject charge and simulate local stress enhancements arising from charge accumulation. The number of wires is large (30) so that the volume affected is big enough to allow changes on ageing to be detectable

Dispersive diffusion controlled distance dependent recombination in amorphous semiconductors

The photoluminescence in amorphous semiconductors decays according to power law $t^{-delta}$ at long times. The photoluminescence is controlled by dispersive transport of electrons. The latter is usually characterized by the power $alpha$ of the transient current observed in the time-of-flight experiments. Geminate recombination occurs by radiative tunneling which has a distance dependence. In this paper, we formulate ways to calculate reaction rates and survival probabilities in the case carriers execute dispersive diffusion with long-range reactivity. The method is applied to obtain tunneling recombination rates under dispersive diffusion. The theoretical condition of observing the relation $delta = alpha/2 + 1$ is obtained and theoretical recombination rates are compared to the kinetics of observed photoluminescence decay in the whole time range measured.Comment: To appear in Journal of Chemical Physic

Estimação de vazão em bacias hidrográficas do Sul do Espírito Santo usando o SWAT

O aumento da atividade econômica e do número de habitantes no mundo, juntamente com o uso não sustentável dos recursos hídricos, os despejos de efluentes sem tratamento no ambiente e o manejo inadequado das bacias hidrográficas, têm contribuído para diminuição da disponibilidade de água no planeta. Apesar de ser um recurso natural renovável, a água que retorna da atmosfera não ocorre de maneira uniformemente distribuída, nem no espaço geográfico, nem no tempo, tornando a sua boa gestão essencial para diminuição das consequências desastrosas dos eventos extremos de cheia e de escassez. Mas, uma gestão exitosa requer, além de profissionais qualificados, o uso de ferramentas para suporte à tomada de decisão. Neste contexto, a utilização de modelos hidrológicos pode auxiliar no planejamento e avaliação de práticas conservacionistas de solo e água e de manejo de bacias hidrográficas. Do exposto, o presente estudo teve o objetivo de avaliar a aplicabilidade do SWAT para a estimação de vazões em bacias hidrográficas no sul do Estado do Espírito Santo. Foram estudadas: a microbacia do córrego Jaqueira (MBJ), com aproximadamente 22,6 ha, e a sub-bacia do rio Itapemirim, à montante da estação fluviométrica de Rive (BIMR), com aproximadamente 2.237 km². Devido ao alto número de falhas e ao curto período de monitoramento hidrológico, não foi possível calibrar e verificar a aplicabilidade do modelo para a MBJ. Para a BIMR, na análise das vazões médias, estimou-se 45,5 m³ s-1 antes da calibração, e 32,6 m³ s-1 após a calibração, muito próxima da vazão média monitorada de 36,9 m³ s-1. Para o período de validação, a vazão média monitorada foi 22% maior (45,0 m³ s-1), enquanto a estimada foi de 33,9 m³ s-1, permanecendo próxima da vazão média estimada calibrada. Em análise gráfica, observou-se que, antes da calibração, as vazões mínimas estimadas ficaram abaixo das observadas, porém as vazões de pico eram superestimadas. Após a calibração, as vazões mínimas tiveram melhores correlações, enquanto as vazões de pico foram subestimadas. Na análise dos índices estatísticos, o R² passou de 0,74 para 0,76 após a calibração, mas foi reduzido para 0,63 no período de validação. Para o coeficiente de Nash Sufcliffe, houve uma melhora significativa do valor após a calibração, passando de -0,38 para 0,75, permanecendo com um valor aceitável de 0,57 no período de validação. O SWAT foi capaz de simular vazões em bacias hidrográficas do Sul do Espírito Santo, desde que não houvesse muitas falhas nos dados monitorados, sendo capaz inclusive de simular dados de outros períodos para os quais os parâmetros não foram ajustados

Time-domain imaging system in the terahertz range for immovable cultural heritage materials

In the field of cultural heritage science, the use of non‐destructive and contact‐free techniques has increased sharply over the past 10 years. Compared with conventional spectroscopic and imaging techniques such as X‐ray, ultraviolet, infrared, and laser spectroscopy, terahertz time‐domain imaging (THz‐TDI) is an innovative, non‐invasive, and safe technique, which provides good penetration depth (~1 cm) and broad spectral bandwidth (0.1–10 THz). This paper sets out the protocol and methodology for the application of THz‐TDI to immovable cultural heritage, illustrated by a series of case studies. The case studies demonstrate the efficacy of the technique in providing structural and material information for conservators

On composite laminates with extensional anisotropy

The definite list of extensionally (membrane) anisotropic composite laminates with up to 21 plies is presented. The listings comprise of individual stacking sequences, which are characterized in terms of angle- and cross-ply sub-sequence relationships as well as the blend-ratio of unbalanced angle-plies. Dimensionless parameters, including lamination parameters, are provided, from which the extensional and bending stiffness terms are readily calculated and an assessment of the bending stiffness efficiency made for angle- and cross-ply sub-sequences. Comparisons are made between the structural response of extensionally-anisotropic laminates and laminates with both extensional- and bending-anisotropy; Initial- and post-buckling responses are considered at the panel level together with the static response of a complete wing-box structure

Fast odour dynamics are encoded in the olfactory system and guide behaviour

Odours are transported in turbulent plumes, which result in rapid concentration fluctuations1,2 that contain rich information about the olfactory scenery, such as the composition and location of an odour source2,3,4. However, it is unclear whether the mammalian olfactory system can use the underlying temporal structure to extract information about the environment. Here we show that ten-millisecond odour pulse patterns produce distinct responses in olfactory receptor neurons. In operant conditioning experiments, mice discriminated temporal correlations of rapidly fluctuating odours at frequencies of up to 40 Hz. In imaging and electrophysiological recordings, such correlation information could be readily extracted from the activity of mitral and tufted cells—the output neurons of the olfactory bulb. Furthermore, temporal correlation of odour concentrations5 reliably predicted whether odorants emerged from the same or different sources in naturalistic environments with complex airflow. Experiments in which mice were trained on such tasks and probed using synthetic correlated stimuli at different frequencies suggest that mice can use the temporal structure of odours to extract information about space. Thus, the mammalian olfactory system has access to unexpectedly fast temporal features in odour stimuli. This endows animals with the capacity to overcome key behavioural challenges such as odour source separation5, figure–ground segregation6 and odour localization7 by extracting information about space from temporal odour dynamics

Clustering data by inhomogeneous chaotic map lattices

A new approach to clustering, based on the physical properties of inhomogeneous coupled chaotic maps, is presented. A chaotic map is assigned to each data-point and short range couplings are introduced. The stationary regime of the system corresponds to a macroscopic attractor independent of the initial conditions. The mutual information between couples of maps serves to partition the data set in clusters, without prior assumptions about the structure of the underlying distribution of the data. Experiments on simulated and real data sets show the effectiveness of the proposed algorithm.Comment: 8 pages, 6 figures. Revised version accepted for publication on Physical Review Letter