A generalization of the fractal/facies model

In order to generalize the fractal/facies concept, a new stochastic fractal model for ln(K) increment probability density functions (PDFs) is presented that produces non-Gaussian behavior at smaller lags and converges to Gaussian at larger lags. The model is based on the classical Laplace PDF. The new stochastic fractal family is called fractional Laplace motion (fLam) having stationary increments called fractional Laplace noise (fLan). This fractal is different from other fractals because the character of the underlying increment PDFs changes dramatically with lag size, which leads to lack of self-similarity. Data also appear to display this characteristic. In the larger lag size ranges, approximate self-affinity does hold. The basic field procedure for further testing of the fractional Laplace theory is to measure ln(K) increment distributions along transects, calculate frequency distributions from the data, and compare results to appropriate fLan family members. The variances of the frequency distributions should also change with lag size (scale) in a prescribed manner. There are mathematical reasons such as the geometric central limit theorem, for surmising that fLam/fLan may be more fundamental than other approaches that have been proposed for modeling ln(K) frequency distributions.     

Conditions for upscalability of bioclogging in pore network models

In this work, we model the biofilm growth at the microscale using a rectangular pore network model in 2D and a cubic network in 3D. For the 2D network, we study the effects of bioclogging on porosity and permeability when we change parameters like the number of nodes in the network, the network size, and the concentration of nutrients at the inlet. We use a 3D cubic network to study the influence of the number of nodes in the z direction on the biofilm growth and on upscalability. We show that the biofilm can grow uniformly or heterogeneously through the network. Using these results, we determine the conditions for upscalability of bioclogging for rectangular and cubic networks. If there is uniform biofilm growth, there is a unique relation between permeability and porosity, K ～ ?², this relation does not depend on the volume of the network, therefore the system is upscalable. However, if there is preferential biofilm growth, the porosity-permeability relation is not uniquely defined, hence upscalability is not possible. The Damköhler number is used to determine when upscalability is possible. If the Damköhler number is less than 10¹, the biofilm grows uniformly and therefore the system is upscalable. However, if the Damköhler number is greater than 10³, the biofilm growth exhibits a deviation from uniform biofilm growth and heterogeneous growth is observed, therefore upscalability is not possible. There is a transition from uniform growth to preferential growth if the Damköhler number is between 10¹ and 10³.     

http://www.sciencedirect.com/science/article/pii/S1674987114001133

A chronological study of seamount rocks in the South China Sea basin provides a great opportunity to understand the expansion and evolution history of the sea basin. In this paper, we analyzed the 40Ar...     

A Late Mesoproterozoic 40Ar/39Ar age for a melt breccia from the Keurusselkä impact structure,Finland

Field investigations in the eroded central uplift of the ≤30 km Keurusselkä impact structure, Finland, revealed a thin, dark melt vein that intersects the autochthonous shatter cone‐bearing target rocks near the homestead of Kirkkoranta, close to the center of the impact structure. The petrographic analysis of quartz in this melt breccia and the wall rock granite indicate weak shock metamorphic overprint not exceeding ~8–10 GPa. The mode of occurrence and composition of the melt breccia suggest its formation as some kind of pseudotachylitic breccia. ⁴⁰Ar/³⁹Ar dating of dark and clast‐poor whole‐rock chips yielded five concordant Late Mesoproterozoic miniplateau ages and one plateau age of 1151 ± 10 Ma [± 11 Ma] (2σ; MSWD = 0.11; P = 0.98), considered here as the statistically most robust age for the rock. The new ⁴⁰Ar/³⁹Ar age is incompatible with ~1.88 Ga Svecofennian tectonism and magmatism in south‐central Finland and probably reflects the Keurusselkä impact, followed by impact‐induced hydrothermal chloritization of the crater basement. In keeping with the crosscutting relationships in the outcrop and the possible influence of postimpact alteration, the Late Mesoproterozoic ⁴⁰Ar/³⁹Ar age of ~1150 Ma should be treated as a minimum age for the impact. The new ⁴⁰Ar/³⁹Ar results are consistent with paleomagnetic results that suggested a similar age for Keurusselkä, which is shown to be one of the oldest impact structures currently known in Europe and worldwide.     

Seismic design methodology for friction damped braced frames

This paper is concerned with the design of steel frames using friction damped slotted bolted connections (SBCs) in the diagonal braces. A dynamic model is developed to describe the behaviour of a single‐degree‐of‐freedom (SDOF) steel frame that uses bilinear hysteretic behaviour for the damper. This model is generalized to MDOF systems. A novel algorithm for displacement reversal in the transition from slip to stick is presented. It uses numerical noise for its success. A design procedure that attains the stiffness of the individual braces and their elongation at the threshold of activation is then applied to a 10‐storey steel frame. This design process is a two‐phase iterative procedure that converges quite fast. Copyright © 2000 John Wiley & Sons, Ltd.     

Episodic wood loading in a mountainous neotropical watershed

The Upper Rio Chagres drains 414 km² of steep, mountainous terrain in central Panama. A tropical air mass thunderstorm on 10 July 2007 produced a flood across the basin that peaked at 720 m³ s^− 1 at a headwaters gage draining 17.5 km² and 1710 m³ s^− 1 at a downstream gage draining 414 km². The storm also triggered numerous landslides in the upper basin, which facilitated the formation of large logjams along portions of the channel where transport capacity of wood was reduced by a change in channel geometry such as a bend or channel expansion. During field work in February 2008, we characterized three jams with surface areas of 400–2450 m²; two of these jams resulted in storage of substantial (1100–8200 m³) sediment wedges upstream. We returned to these sites in March 2009 to document changes in the logjams and sediment storage. Drawing on observations made in the basin since 2002, and site visits during 2008 and 2009, we suggest that jams such as these last two years or less. We propose that wood dynamics in the Upper Chagres alternate between brief periods of moderate wood load in the form of large logjams and much longer periods of essentially no wood load, a situation that contrasts with the more consistent wood loads in catchments of similar size in temperate environments and with limited studies of more consistent wood load in tropical catchments with no landslides.