A general geomorphological recession flow model for river basins

Recession flows in a basin are controlled by the temporal evolution of its active drainage network (ADN). The geomorphological recession flow model (GRFM) assumes that both the rate of flow generation per unit ADN length (q) and the speed at which ADN heads move downstream (c) remain constant during a recession event. Thereby, it connects the power law exponent of -dQ/dt versus Q (discharge at the outlet at time t) curve, , with the structure of the drainage network, a fixed entity. In this study, we first reformulate the GRFM for Horton-Strahler networks and show that the geomorphic ((g)) is equal to D/(D-1), where D is the fractal dimension of the drainage network. We then propose a more general recession flow model by expressing both q and c as functions of Horton-Strahler stream order. We show that it is possible to have = (g) for a recession event even when q and c do not remain constant. The modified GRFM suggests that is controlled by the spatial distribution of subsurface storage within the basin. By analyzing streamflow data from 39 U.S. Geological Survey basins, we show that is having a power law relationship with recession curve peak, which indicates that the spatial distribution of subsurface storage varies across recession events. Key Points The GRFM is reformulated for Horton-Strahler networks. The GRFM is modified by allowing its parameters to vary along streams. Sub-surface storage distribution controls recession flow characteristics.

Chaotic dynamic analysis of viscoelastic plates

The dynamic buckling of viscoelastic plates with large deflection is investigated in this paper by using chaotic and fractal theory. The material behavior is given in terms of the Boltzmann superposition principle. in order to obtain accurate computation results, the nonlinear integro-differential dynamic equation is changed into an autonomic four-dimensional dynamical system. The numerical time integrations of equations are performed by using the fourth-order Runge-Kutta method. And the Lyapunov exponent spectrum, the fractal dimension of strange attractors and the time evolution of deflection are obtained. The influence of geometry nonlinearity and viscoelastic parameter on the dynamic buckling of viscoelastic plates is discussed.

Detection and Characterization of Long-Pulse Low-Velocity Impact Damage in Plastic Bonded Explosives

Damage not only degrades the mechanical properties of explosives, but also influences the shock sensitivity, combustion and even detonation behavior of explosives. The study of impact damage is crucial in the vulnerability evaluation of explosives. A long-pulse low-velocity gas gun with a gas buffer was developed and used to induce impact damage in a hot pressed plastic bonded explosive. Various methods were used to detect and characterize the impact damage of the explosive. The microstructure was examined by use of polarized light microscopy. Fractal analysis of the micrographs was conducted by use of box counting method. The correlation between the fractal dimensions and microstructures was analyzed. Ultrasonic testing was conducted using a pulse through-transmission method to obtain the ultrasonic velocity and ultrasonic attenuation. Spectra analyses were carried out for recorded ultrasonic signals using fast Fourier transform. The correlations between the impact damage and ultrasonic parameters including ultrasonic velocities and attenuation coefficients were also analyzed. To quantitatively assess the impact induced explosive crystal fractures, particle size distribution analyses of explosive crystals were conducted by using a thorough etching technique, in which the explosives samples were soaked in a solution for enough time that the binder was totally removed. Impact induces a large extent of explosive crystal fractures and a large number of microcracks. The ultrasonic velocity decreases and attenuation coefficients increase with the presence of impact damage. Both ultrasonic parameters and fractal dimension can be used to quantitatively assess the impact damage of plastic bonded explosives.

分形图像压缩方法研究的新进展

分形图像压缩是一种利用迭代函数系统理论(IFs)、基于自相似特征的有损编码方法。它以其高压缩比的潜在性能而在近年来倍受重视，但目前实现自动IFs编码仍有相当难度，该领域仍存在许多问题亟待解决。笔者对分形图像压缩的理论基础、自动分形图像压缩的实现以及分形图像序列压缩等进行了全面的综述，介绍了各种具有代表性的改进算法，阐明了各个算法的原理和特点，最后对目前研究中存在的问题及可能的对策和研究方向进行了讨论。

Mechanics of Adhesion in MEMS-a Review

A review is presented of the mechanics of microscale adhesion in microelectromechanical systems (MEMS). Some governing dimensionless numbers such as Tabor number, adhesion parameter and peel number for microscale elastic adhesion contact are discussed in detail. The peel number is modified for the elastic contact between a rough surface in contact with a smooth plane. Roughness ratio is introduced to characterize the relative importance of surface roughness for microscale adhesion contact, and three kinds of asperity height distributions are discussed: Gaussian, fractal, and exponential distributions. Both Gaussian and exponential distributions are found to be special cases of fractal distribution. Casimir force induced adhesion in MEMS, and adhesion of carbon nanotubes to a substrate are also discussed. Finally, microscale plastic adhesion contact theory is briefly reviewed, and it is found that the dimensionless number, plasticity index of various forms, can be expressed by the roughness ratio.

Identificación de habitats potenciales, efectivos y conectividad para la fauna silvestre, Nandaime, Nicaragua

El presente estudio surge a partir de monitoreos previos en la zona en los cuales se determinaron muy pocas especies principalmente de Mamíferos, así que se propuso conocer si los hábitats en el parche tiene la capacidad para albergar suficientes especies y si el parche se encontraba aislado de otros para que se diera un flujo de animales desde otras partes del paisaje hasta el sitio de interés. Se identificaron los hábitats efectivos y potenciales y la existencia de conexión de ésta área con otra área natural (estudio de paisaje) que sirva de corredor a la fauna silvestre en la comunidad La Chipopa, Nandaime. Los tipos de hábitats se seleccionaron según criterios florísticos: formas de vida predominantes, composición y densidad de especies. Para el estudio de conectividad y fragmentación se realizó un análisis con imágenes de satélite para determinar las clases de cobertura de la zona y se utilizaron como firmas espectrales las clases de cobertura vegetal 2011 del Ministerio de Agropecuario y Forestal (MAGFOR), la herramienta V_LATE 1.1 y la herramienta Corridor Designer . Se determinaron siete tipos de hábitat. El hábitat de mayor tamaño fue el Área de árboles con poca lianas (AAPL) (3.25 ha) la cual representa el 76 % del área total. En registro bibliográfico se determinaron 270 especies en el paisaje, de éstas el 22 % no encontrarían hábitat dentro del área. El hábitat efectivo el cual alberga más especies (12 ) fue AAPL. Dentro de los hábitats potenciales se encuentran: AAP L (25 ) y Área de árboles con mucha infección por lianas (AAML) (12 ), sin embargo, se determinaron que 67 especies (32 %) prefieren cualquier hábitat como potencial dentro del mosaico. El análisis de estructura del paisaje indica que el área se divide en 17 clases de cobertura, de éstas, las áreas de tacotal cubren el 48% del total mientras que las áreas de cultivos y pastos cubren en 34%. Dentro de la matriz del paisaje el uso que se encuentra más fragmentado es el área de bosque cerrado ya que la distancia mínima que una especie debería de recorrer para encontrar esa clase es de 4,184 m, las clases de cobertura menos fragmentadas fueron las áreas agrícolas y pastos. Existe una relación entre los índices de diversidad de formas , dimensión fractal y proximidad en relación a los usos cultivos, pasto y bosque latifoliado cerrado. Dentro del paisaje se crean dos tipos de corredores uno se localiza al noroeste y otro al sureste, a pesar de formarse corredores el paisaje se encuentra muy fragmentado para permitir la conectividad de Nandarola con otros parches cercanos.

Fractals and Scaling in Fracture Induced by Microcrack Coalescence

A numerical model is proposed to simulate fracture induced by the coalescence of numerous microcracks, in which the condition for coalescence between two randomly nucleated microcracks is determined in terms of a load-sharing principle. The results of the simulation show that, as the number density of nucleated microcracks increases, stochastic coalescence first occurs followed by a small fluctuation, and finally a newly nucleated microcrack triggers a cascade coalescence of microcracks resulting in catastrophic failure. The fracture profiles exhibit self-affine fractal characteristics with a universal roughness exponent, but the critical damage threshold is sensitive to details of the model. The spatiotemporal distribution of nucleated microcracks in the vicinity of critical failure follows a power-law behaviour, which implies that the microcrack system may evolve to a critical state.

Identificación de habitats potenciales, efectivos y conectividad para la fauna silvestre, Nandaime, Nicaragua

El presente estudio se propone determinar los hábitats efectivos y potenciales dentro de un parche de bosque seco secundario de 4.26 ha y la existencia de conexión de ésta área con otra área natural (estudio de paisaje) que sirva de corredor a la fauna silvestre en la comunidad La Chipopa, Nandaime. Los tipos de hábitats se seleccionaron según criterios florísticos. Para el estudio de conectividad y fragmentación se realizó un análisis con imágenes de satélite para determinar las clases de cobertura de la zona y se utilizaron como firmas espectrales las clases de cobertura vegetal 2011 del Ministerio de Agropecuario y Forestal (MAGFOR), la herramienta V_LATE 1.1 y la herramienta corridor desinger. Se determinaron siete tipos de hábitat. El hábitat de mayor tamaño fue el Área de árboles con poca infección con lianas (AAPL) (3.05 ha) la cual representa el 72 % del área total. En registro bibliográfico se determinaron 271 especies en el paisaje, de éstas, 102 (38 %) no encontrarían hábitat dentro del área. Los hábitats efectivos se determinaron por medio de muestreos anteriores, la mayor cantidad de especies (11 o el 33%) se asocia con AAPL. Dentro de los hábitats potenciales se encuentran: AAPL (23 o el 17 %) y Área de árboles con mucha infección por lianas (AAML) (12 o el 9%), sin embargo se determinaron que 26 especies (19%) prefieren toda el área como hábitat potencial. El análisis de estructura del paisaje indica que el área se divide en 17 clases de cobertura, de éstas, las áreas de tacotal cubren el 48% del total mientras que las áreas de cultivos y pastos cubren en 34%. Dentro de la matriz del paisaje el uso que se encuentra más fragmentado es el área de bosque cerrado ya que la distancia mínima que una especie de fauna silvestre debería de recorrer para encontrar esa clase es de 4,184 m, las clases de cobertura menos fragmentadas fueron las áreas agrícolas y pastos. Existe una relación entre las variables forma, dimensión fractal y proximidad en relación a los usos cultivos, pasto y bosque latifoliado cerrado. El paisaje se encuentra muy fragmentado para permitir la existencia de corredores por donde fluya la fauna silvestre.

Avalanche behavior and statistical properties in a microcrack coalescence process

Fracture owing to the coalescence of numerous microcracks can be described by a simple statistical model, where a coalescence event stochastically occurs as the number density of nucleated microcracks increases. Both numerical simulation and statistical analysis reveal that a microcrack coalescence process may display avalanche behavior and that the final failure is catastrophic. The cumulative distribution of coalescence events in the vicinity of critical fracture follows a power law and the fracture profile has self-affine fractal characteristic. Some macromechanical quantities may be traced back and extracted from the mesoscopic process based on the statistical analysis of coalescence events.

Statistical analysis of synthetic earthquake catalogs generated by models with various levels of fault zone disorder

The stress release model, a stochastic version of the elastic rebound theory, is applied to the large events from four synthetic earthquake catalogs generated by models with various levels of disorder in distribution of fault zone strength (Ben-Zion, 1996) They include models with uniform properties (U), a Parkfield-type asperity (A), fractal brittle properties (F), and multi-size-scale heterogeneities (M). The results show that the degree of regularity or predictability in the assumed fault properties, based on both the Akaike information criterion and simulations, follows the order U, F, A, and M, which is in good agreement with that obtained by pattern recognition techniques applied to the full set of synthetic data. Data simulated from the best fitting stress release models reproduce, both visually and in distributional terms, the main features of the original catalogs. The differences in character and the quality of prediction between the four cases are shown to be dependent on two main aspects: the parameter controlling the sensitivity to departures from the mean stress level and the frequency-magnitude distribution, which differs substantially between the four cases. In particular, it is shown that the predictability of the data is strongly affected by the form of frequency-magnitude distribution, being greatly reduced if a pure Gutenburg-Richter form is assumed to hold out to high magnitudes.

A generalized model for the effective thermal conductivity of porous media based on self-similarity

A generalized model for the effective thermal conductivity of porous media is derived based on the fact that statistical self-similarity exists in porous media. The proposed model assumes that porous media consist of two portions: randomly distributed non-touching particles and self-similarly distributed particles contacting each other with resistance. The latter are simulated by Sierpinski carpets with side length L = 13 and cutout size C = 3, 5, 7 and 9, respectively, depending upon the porosity concerned. Recursive formulae are presented and expressed as a function of porosity, ratio of areas, ratio of component thermal conductivities and contact resistance, and there is no empirical constant and every parameter has a clear physical meaning. The model predictions are compared with the existing experimental data, and good agreement is found in a wide range of porosity of 0.14-0.80, and this verifies the validity of the proposed model.

Enfoque de los Modelos de Ruptura Dieléctrica desde la Termodinámica Estadística

Resumen: El modelado del proceso de ruptura dieléctrica de aislantes sometidos a un campo eléctrico intenso es importante para el desarrollo de nuevos materiales en las industrias eléctrica y electrónica. Información experimental generada en el laboratorio muestra que el proceso de ruptura dieléctrica involucra la transferencia de energía con la consecuente acumulación progresiva de carga y daño en el material. Ésta, produce finalmente la ruptura macroscópica, creando un camino conductor que inutiliza al material aislante. A partir de experimentos de simulación se han calculado los parámetros característicos (dos y tres parámetros) de la función de distribución de fallas (distribución de Weibull), para distintas familias de árboles. También se ha estudiado la relación intrínseca entre las distintas familias de árboles, mediante una distribución generalizada de Weibull con un índice entrópico q. Este índice q es representativo de la estructura fractal de los distintos árboles.

Collective evolution characteristics and computer simulation of short fatigue cracks

Fatigue testing was conducted using a kind of triangular isostress specimen to obtain the short-fatigue-crack behaviour of a weld low-carbon steel. The experimental results show that short cracks continuously initiate at slip bands within ferrite grain domains and the crack number per unit area gradually increases with increasing number of fatigue cycles. The dispersed short cracks possess an orientation preference, which is associated with the crystalline orientation of the relevant slip system. Based on the observed collective characteristics, computer modelling was carried out to simulate the evolution process of initiation, propagation and coalescence of short cracks. The simulation provides progressive displays which imitate the appearance of experimental observations. The results of simulation indicate that the crack path possesses a stable value of fractal dimension whereas the critical value of percolation covers a wide datum band, suggesting that the collective evolution process of short cracks is sensitive to the pattern of crack site distribution.

Numerical simulation of evolution-induced catastrophe

A numerical simulation of damage evolution in a two-dimensional system of micocracks is presented. It reveals that the failure is induced by a cascade of coalescences of microcracks, and the fracture surface appears fractal. A model of evolution-induced catastrophe is introduced. The fractal dimension is found to be a function of evolution rule only. This result could qualitatively explain the correlation of fractal dimension and fracture toughness discovered in experiments.

Evolution induced catastrophe

Fracture due to coalescence of microcracks seems to be catalogued in a new model of evolution induced catastrophe (EIC). The key underlying mechanism of the EIC is its automatically enlarging interaction of microcracks. This leads to an explosively evolving catastrophe. Most importantly, the EIC presents a fractal dimension spectrum which appears to be dependent on the interaction.