Local Front Research Articles

Experimental study of stable imbibition displacements in a model open fracture. II. Scale-dependent avalanche dynamics.

We report the results of an experimental investigation of the spatiotemporal dynamics of stable imbibition fronts in a disordered medium, in the regime of capillary disorder, for a wide range of experimental conditions. We have used silicone oils of various viscosities μ and nearly identical oil-air surface tension, and forced them to slowly invade a model open fracture at very different flow rates v. In this second part of the study we have carried out a scale-dependent statistical analysis of the front dynamics. We have specifically analyzed the influence of μ and v on the statistical properties of the velocity V_{ℓ}, the spatial average of the local front velocities over a window of lateral size ℓ. We have varied ℓ from the local scale defined by our spatial resolution up to the lateral system size L. Even though the imposed flow rate is constant, the signals V_{ℓ}(t) present very strong fluctuations which evolve systematically with the parameters μ, v, and ℓ. We have verified that the non-Gaussian fluctuations of the global velocity V_{ℓ}(t) are very well described by a generalized Gumbel statistics. The asymmetric shape and the exponential tail of those distributions are controlled by the number of effective degrees of freedom of the imbibition fronts, given by N_{eff}=ℓ/ℓ_{c} (the ratio of the lateral size of the measuring window ℓ to the correlation length ℓ_{c}∼1/sqrt[μv]). The large correlated excursions of V_{ℓ}(t) correspond to global avalanches, which reflect extra displacements of the imbibition fronts. We show that global avalanches are power-law distributed, both in sizes and durations, with robustly defined exponents-independent of μ, v, and ℓ. Nevertheless, the exponential upper cutoffs of the distributions evolve systematically with those parameters. We have found, moreover, that maximum sizes ξ_{S} and maximum durations ξ_{T} of global avalanches are not controlled by the same mechanism. While ξ_{S} are also determined by ℓ/ℓ_{c}, like the amplitude fluctuations of V_{ℓ}(t), ξ_{T} and the temporal correlations of V_{ℓ}(t) evolve much more strongly with imposed flow rate v than with fluid viscosity μ.

A Geometric Approach to Stationary Defect Solutions in One Space Dimension

In this manuscript, we consider the impact of a small jump-type spatial heterogeneity on the existence of stationary localized patterns in a system of partial differential equations in one spatial dimension, i.e., defined on $\mathbb{R}$. This problem corresponds to analyzing a discontinuous and non-autonomous $n$-dimensional system, $\scriptsize\dot{u}=\left\{ \begin{array}{ll} f(u),& t\leq0,\\ f(u)+\varepsilon g(u),& t>0, \end{array}\right.$ under the assumption that the unperturbed system, i.e., the $\varepsilon \to 0$ limit system, possesses a heteroclinic orbit $\Gamma$ that connects two hyperbolic equilibrium points (plus several additional nondegeneracy conditions). The unperturbed orbit $\Gamma$ represents a localized structure in the PDE setting. We define the (pinned) defect solution $\Gamma_\varepsilon$ as a heteroclinic solution to the perturbed system such that $\lim_{\varepsilon \to 0} \Gamma_\varepsilon = \Gamma$ (as graphs). We distinguish between three types of defect solutions: trivial, local, and global defect solutions. The main goal of this manuscript is to develop a comprehensive and asymptotically explicit theory of the existence of local defect solutions. We find that both the dimension of the problem as well as the nature of the linearized system near the endpoints of the heteroclinic orbit $\Gamma$ have a remarkably rich impact on the existence of these local defect solutions. We first introduce the various concepts in the setting of planar systems $(n=2)$ and---for reasons of transparency of presentation---consider the three-dimensional problem in full detail. Then, we generalize our results to the $n$-dimensional problem, with special interest for the additional phenomena introduced by having $n \geq 4$. We complement the general approach by working out two explicit examples in full detail: (i) the existence of pinned local defect kink solutions in a heterogeneous Fisher--Kolmogorov equation ($n=4$) and (ii) the existence of pinned local defect front and pulse solutions in a heterogeneous generalized FitzHugh--Nagumo system $(n=6)$.

Three-dimensional crack growth modelling of a Ni-based superalloy at elevated temperature and sustained loading

High temperature materials subjected to elevated temperature have been shown to be sensitive to dwell times, giving an increased crack growth rate. The interaction between these dwell times and rapid cyclic loads have been shown to constitute a complex problem. Many models have been developed for 1D conditions, but the application to general 3D conditions has seldom been seen, although this is the most common case in most structures. In this paper a model for taking care of the interaction between these load modes in general 3D crack growth has been developed. The model uses 1D results for extension to general 3D, thus providing for local crack front evolution with a minimum of numerical simulations. Consequently, a history dependent crack growth law in 3D is given in this paper, which is capable of tracking the damage from the sustained load, and the interaction with rapid cyclic loading. The model has been implemented for usage with finite element calculations and several different tests are simulated and compared with experimental results for the nickel based superalloy Inconel 718 at 550°C. The simulation results show crack shapes in agreement with experimental fracture surfaces and time to failure.

Baseline monitoring of organic sunscreen compounds along South Carolina's coastal marine environment

Organic ultraviolet filters (UV-F) are increasingly being used in personal care products to protect skin and other products from the damaging effects of UV radiation. In this study, marine water was collected monthly for approximately one year from six coastal South Carolina, USA sites and analyzed for the occurrence of seven organic chemicals used as UV filters (avobenzone, dioxybenzone, octocrylene, octinoxate, oxybenzone, padimate-o and sulisobenzone). The results were used to examine the relationship between beach use and the distribution of UV-F compounds along coastal South Carolina, USA. Five of the seven target analytes were detected in seawater along coastal South Carolina during this study. Dioxybenzone and sulisobenzone were not detected. The highest concentrations measured were >3700ng octocrylene/L and ~2200ng oxybenzone/L and beach use was greatest at this site; a local beach front park. Patterns in concentrations were assessed based on season and a measure of beach use.

Heavy ion acceleration at dipolarization fronts in planetary magnetotails

Transient reconnection events in planetary magnetotails give rise to fast plasma jets, whose leading edges are called dipolarization fronts. We perform a test particle simulation of the acceleration of several ion species (H+, He+, and O+) in a 2-D model of dipolarization fronts. We study the dependence of the acceleration on parameters of the model, finding, e.g., that the average ion energy increases with the front velocity and with the initial injection energy. When the ion species are initially cold, O+ ions get the largest amount of average energy. Conversely, when the injection energy of O+ ions is increased, their average energy gain does not exceed that of the lighter species, suggesting that ion energization at local dipolarization fronts strongly depends on the initial particle gyroradius. Further, the energy gained by the most energetic fraction of particles scales approximately as the square root of the mass ratio.

Dynamics of non-circular finite-release gravity currents

The present work reports some new aspects of non-axisymmetric gravity currents obtained from laboratory experiments, fully resolved simulations and box models. Following the earlier work of Zgheib et al. (Theor. Comput. Fluid Dyn., vol. 28, 2014, pp. 521–529) which demonstrated that gravity currents initiating from non-axisymmetric cross-sectional geometries do not become axisymmetric, nor do they retain their initial shape during the slumping and inertial phases of spreading, we show that such non-axisymmetric currents eventually reach a self-similar regime during which (i) the local front propagation scales as $t^{1/2}$ as in circular releases and (ii) the non-axisymmetric front has a self-similar shape that primarily depends on the aspect ratio of the initial release. Complementary experiments of non-Boussinesq currents and top-spreading currents suggest that this self-similar dynamics is independent of the density ratio, vertical aspect ratio, wall friction and Reynolds number $\mathit{Re}$, provided the last is large, i.e. $\mathit{Re}\geqslant O(10^{4})$. The local instantaneous front Froude number obtained from the fully resolved simulations is compared to existing models of Froude functions. The recently reported extended box model is capable of capturing the dynamics of such non-axisymmetric flows. Here we use the extended box model to propose a relation for the self-similar horizontal aspect ratio ${\it\chi}_{\infty }$ of the propagating front as a function of the initial horizontal aspect ratio ${\it\chi}_{0}$, namely ${\it\chi}_{\infty }=1+(\ln {\it\chi}_{0})/3$. The experimental and numerical results are in good agreement with the proposed relation.

Topology and burning rates of turbulent, lean, H2/air flames

Improved understanding of turbulent flames characterized by negative consumption speed-based Markstein lengths is necessary to develop better models for turbulent lean combustion of high hydrogen content fuels. In this paper we investigate the topology and burning rates of turbulent, lean (ϕ = 0.31), H2/air flames obtained from a recently published DNS database (Aspden et al., 2011). We calculate local flame front curvatures, strain rates, thicknesses, and burning velocities and compare these values to reference quantities obtained from stretched laminar flames computed numerically in three model geometrical configurations—a counterflow twin flame, a tubular counterflow flame and an expanding cylindrical flame. We compare and contrast the DNS with these model laminar flame calculations, and show both where they closely correlate with each other, as well as where they do not. These results in the latter case are shown to result from non-flamelet behaviors, unsteady effects, and curvature-strain correlations. These insights are derived from comparisons conditioned on different topological features, such as portions of the flame front with a spherical/cylindrical shape, the leading edge of the flame, and portions of the flame front with low mean curvature. We also show that reference time scales vary appreciably over the flame, and characterizing the relative values of fluid mechanic and kinetic time scales by a single value leads to erroneous conclusions. For example, there is a two order of magnitude decrease in chemical time scales at the leading edge of the front relative to its unstretched value. For this reason, the leading edge of the front quite closely tracks quasi-steady calculations, even in the lowest Damköhler number case, DaF∼0.005.

Effects of mixture composition and turbulence intensity on flame front structure and burning velocities of premixed turbulent hydrocarbon/air Bunsen flames

The influences of the equivalence ratio, turbulence intensity, and different thermo-diffusive characteristics on the flame brush characteristics, instantaneous flame front structures, and burning velocities of premixed turbulent methane/–, ethane/–, and propane/air Bunsen flames were investigated systematically. Particle image velocimetry and Mie scattering techniques were utilized to measure the turbulence statistics and to visualize flame front corrugations, respectively. All experiments were performed under a constant bulk flow velocity of 21.0 m/s. The equivalence ratio range was from 0.7 to 1.35 for methane/air flames, 0.7–1.45 for ethane/air flames, and 0.8–1.35 for propane/air flames. Two perforated plates were used to produce different turbulence levels. A series of comprehensive parameters including the characteristic flame height, mean flame brush thickness, mean volume of the turbulent flame region, mean fuel consumption rate, two-dimensional flame front curvature, local flame front angle, two-dimensional flame surface density, wrinkled flame surface area, turbulent burning velocity, mean flamelet consumption velocity, and mean turbulent flame stretch factor were obtained. The mean turbulent flame stretch factor displayed a dependence on the equivalence ratio and turbulence intensity. Results show that the mean turbulent flame stretch factors for lean/stoichiometric and rich mixtures were not equal when the unstrained premixed laminar burning velocity, non-dimensional bulk flow velocity, non-dimensional turbulence intensity, and non-dimensional longitudinal integral length scale were kept constant.

Combined positron emission tomography and computed tomography to visualize and quantify fluid flow in sedimentary rocks

Here we show for the first time the combined positron emission tomography (PET) and computed tomography (CT) imaging of flow processes within porous rocks to quantify the development in local fluid saturations. The coupling between local rock structure and displacement fronts is demonstrated in exploratory experiments using this novel approach. We also compare quantification of 3-D temporal and spatial water saturations in two similar CO2 storage tests in sandstone imaged separately with PET and CT. The applicability of each visualization technique is evaluated for a range of displacement processes, and the favorable implementation of combining PET/CT for laboratory core analysis is discussed. We learn that the signal-to-noise ratio (SNR) is over an order of magnitude higher for PET compared with CT for the studied processes.

Mechanical origin of b-value changes during stimulation of deep geothermal reservoirs

The distribution of induced-earthquake magnitudes in deep geothermal reservoirs is a classical tool for monitoring reservoirs. It typically shows some important fluctuations through time and space. Despite being a very crude information (i.e., a scalar quantity) of very complex mechanical stress evolution, understanding these variations could still give us insights into the mechanics of the reservoir. Here, we analyze the output of a simple quasi-static physical model of a single fault and propose a new way to describe bursts that could be compared to seismic events. Our model is an elastic fiber bundle model describing multiple ruptures along a single major fault of the reservoir. It consists of a set of fibers with various strengths, arranged in a planar L×L two-dimensional array, linking together two elastic half-spaces. It mimics a fault zone with various asperities. During load, the fibers break quasi-statically according to a stress threshold distribution. Contrary to classical fiber bundle model, here, when a fiber breaks, it redistributes the load on the surviving fibers through long range elastic interactions. Interestingly, the elasticity of the half-spaces which changes the range of the stress distribution, characterizes two distinct regimes. In a stiff regime, we find an effective ductile deformation regime at large scale since the damage distribution is very difuse. Conversely in softer systems, the distance between two consecutive breaking fibers gets smaller and failure of the interface is localized, exhibiting an effective brittle regime. We analyze two types of burst distributions: a classical one built from the statistics of the broken bonds during each failure step and a new one defines from a waiting time matrix of the fracture front propagation. The first one reproduces several known results for this type of model. The new one evidences the existence of effective creeping advances of the front with statistics that follow a Gutenberg-Richter distribution, in particular, in the ductile regime (stiff systems). We proposed a new definition of bursts in a fault model, based on the local fracture front velocity. We find that b v -values for the distribution of the velocity clusters are very consistent with Gutenberg-Richter distribution of induced seismicity. We link the b v -value fluctuations in the reservoirs to the influence of the velocity threshold level that could be related to recording limitation. b b -values obtained from the broken bond statistics are hardly comparable to seismic events because of the lack of space contiguousness of broken fibers during bursts. In the light of our results, we discuss the implications of b-value changes in geothermal reservoir in terms of fault asperities and normal stress evolution.

Multi-Objective Fish School Search

The authors propose in this paper a very first version of the Fish School Search (FSS) algorithm for Multi-Objective Optimization. The proposal allows the optimization of problems with two or more conflicting objectives. The authors incorporated the dominance concept within the traditional FSS operators, creating a new approach called Multi-objective Fish School Search, MOFSS. They also adapted the barycenter concept deployed in the original FSS, which was replaced by the set of existing solutions in an external archive created to store the non-dominated solutions found during the search process. From their results in the DTLZ set of benchmark functions, the authors observed that the MOFSS obtained a similar performance when compared to well-known and well-established multi-objective swarm-based optimization algorithms. They detected some convergence problems in functions with a high number of local Pareto fronts. However, adaptive schemes can be used in future work to overcome this weakness.

Climatology ofCyclones and TheirTracking over Southern Coasts ofCaspian Sea

The southern coasts of Caspian Sea is subjected to synoptic/mesoscale weather systemsranging from locally enhanced sea breeze formation and small local front systems to synoptic scale cyclones.This study presents climatology of cyclones over the southern coasts of Caspian Sea covering a ten year period1996-2005. Altogether 57 cyclones were formed during the ten year period. Anoticeable seasonality is observedin evolution of cyclones over the entire Caspian region, a majority of the 57 cyclones (73.7%) were developedduring winter and fall seasons while the remaining (26.3%) occurred during spring and summer seasons.Most ofthe cyclones were of low intensity, out of 57 cyclones observed during the ten year period 16 (28%) were deepdepressions and 24 (42.1%) were cyclonic storms. Altogether 5 super cyclonic storms were observed during theperiod, out of which 4 were observed during winter and fall seasons. Mid-tropospheric, large-scale processes andlocal features were responsible for the initial development of all weather systems. The Mediterranean Sea playsa significant role in cyclogenesis and propagation of the systems the Caspian region. Further, a Mediterraneancyclonic system formed during October 2001 was studied in detail using backward trajectory Lagrangian model:Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT). The HYSPLIT model outputs confirmedthe observed synoptic features for the weather system of the case study.

Curvature Effects in Turbulent Premixed Flames of H2/Air: a DNS Study with Reduced Chemistry

Data from a three-dimensional Direct Numerical Simulation of a turbulent premixed Bunsen flame at a low global Lewis number are analyzed to address the effects of the curvature on the local flame front. For this purpose, the chemical kinetics is modeled according to a reduced scheme, involving 5 reactions and 7 species, to mimic a H$_{2}$/Air flame at equivalence ratio $\phi=0.5$. An increase of the local temperature and reaction rate is found for fronts elongated into the fresh gases (concave), while local quenching is observed for fronts elongated in the opposite direction (convex), i.e. towards the burnt mixture. Data show that the occurrence in the reaction region of these super-reactive (concave fronts) and quenched zones (convex fronts) is predominant compared to a behavior compatible with the corresponding unstretched laminar flame. In particular, well inside the reaction region, the probability density function of the OH radical concentration shows a bi-modal shape with peaks corresponding to negative (concave) and positive (convex) curvatures, while a locally flat front is less frequently detected. The two states are associated with a higher and lower chemical activity with respect the laminar case. Additional statistics conditioned to the local hydrogen concentration provide further information on this dual-state dynamics and on the differences with respect to the corresponding laminar unstretched flame when moving from the fresh to the burnt gas regions. Finally we discuss the effects of the turbulence on the thermo-diffusive instability showing that the turbulent fluctuations, increasing the flame front corrugations, are essentially responsible of the local flame quenching.

Modeling multi-scale processes in hydraulic fracture propagation using the implicit level set algorithm

In this paper we describe an implicit level set algorithm (ILSA) (Peirce and Detournay, 2008) suitable for modeling multi-scale behavior in planar hydraulic fractures propagating in three dimensional elastic media. This multi-scale behavior is typically encountered when multiple physical processes compete to determine the location of the fracture free boundary. Instead of having to match the mesh size to the finest active length scale, or having to re-mesh as the dominant length scales change in space and time, the novel ILSA scheme is able to represent the required multi-scale behavior on a relatively coarse rectangular mesh. This is achieved by using the local front velocity to construct, for each point of a set of control points, a mapping that adaptively identifies the dominant length scale at which the appropriate multi-scale universal asymptotic solution needs to be sampled. Finer-scale behavior is captured in a weak sense by integrating the universal asymptotic solution for the fracture width over partially filled tip elements and using these integrals to set the average values of the widths in all tip elements. The ILSA solution shows good agreement with a multi-scale reference solution comprising a radial solution that transitions from viscosity to toughness dominated propagation regimes. The ILSA scheme is also used to model blade-like hydraulic fractures that break through stress barriers located symmetrically with respect to the injection point. For the zero toughness case, the ILSA solution shows close agreement to experimental results. The multi-scale ILSA scheme is also used to provide results when the material toughness KIc is non-zero. In this case different parts of the fracture-free-boundary can be propagating in different regimes. It is hoped that the multi-scale ILSA solutions presented here will form a set of reference results that can be used to benchmark simulators that use a propagation criterion based on only one dissipative process (either toughness or viscosity). The multi-scale ILSA solutions at larger times (for which plane strain conditions develop in vertical cross sections) are compared with and show close agreement to plane strain exact solutions for height-growth and the fracture width in vertical cross sections. This comparison provides some measure of the accuracy of the multi-scale ILSA scheme. The multi-scale ILSA solutions are also used to identify the regimes of applicability of pseudo 3D (P3D) approximate solutions. These ILSA solutions can also be used to design improved P3D models.

A DNS study of self-accelerating cylindrical hydrogen–air flames with detailed chemistry

The self-accelerating expanding cylindrical stoichiometric hydrogen–air flames at eight atmospheres were studied via two-dimensional direct numerical simulation (DNS) of the full compressible Navier–Stokes equations with detailed chemistry. The flame morphology and propagation were finely resolved by the application of a time step of 2.5ns and a grid size of 4μm. Temporally, the intermittent propagation of the flame front is captured through examining its propagation velocity. Spatially, the flame front is found to be comprised of segments exhibiting similar propagation properties, i.e. the intermittent instantaneous propagation of the flame front is attributed to the development of cellular structures induced by hydrodynamic instability. The long-term average propagation velocity of the flame front is described by a power law, with a self-acceleration exponent of 1.22 for the flame radius with respect to time. The increase in the global flame velocity is shown to be primarily a consequence of increased flame surface area, with the local front propagation velocity remaining largely at the constant laminar flame speed for the near-unity Lewis number mixture studied herein.

Leading edge statistics of turbulent, lean, H2–air flames

Several studies have utilized leading points concepts to explain the sensitivity of turbulent burning rates to fuel/oxidizer composition, especially in negative Markstein length mixtures. Leading point theories suggest that the premixed turbulent flame speed is controlled by the flame front characteristics at the flame brush leading edge, or, in other words, by the flamelets that advance farthest into the unburned mixture (the so-called leading points). Furthermore, several authors have postulated that these leading edge flamelets have an inner structure similar to a critically perturbed laminar flame, i.e., the local stretch rate approaches the extinction value, near where the maximum possible laminar burning velocity is reached.In order to investigate these hypotheses for leading points burning rates, this paper analyzes the flame front structure at the leading edge of turbulent, lean (ϕ=0.31) premixed H2/Air flames, utilizing a database of direct numerical simulations (DNS) previously reported by Aspden et al. (2011). We calculate local flame front curvature, thickness, and burning velocity and compare these values to reference quantities obtained from stretched laminar flames computed numerically in different geometrical configurations (a counterflow twin flame, a tubular counterflow flame and an expanding cylindrical flame). These comparisons show that curvatures and burning velocities approach those of “critically” stretched laminar flames for the highest turbulent intensity case, but not for the lower turbulence intensity cases. In all cases, however, the structure of the flame front at the leading edge seems to closely mirror laminar flame calculations.

New Electrocardiographic Criteria to Differentiate Acute Pericarditis and Myocardial Infarction: Rossello X, Wiegerinck RF, Alguiersuari J, et al. Am J Med 2014;127:233–9.

Accurately diagnosing ST-segment elevation myocardial infarctions (STEMIs) in the emergency department can prove to be a challenging task, and misdiagnosis can lead to unnecessary coronary angiography. This article from four tertiary hospitals in Spain sought to improve the distinction between pericarditis and STEMI by examining the duration of the QRS complex and QT interval. The authors hypothesized that the QRS interval would be prolonged in acute MI due to slowed propagation of the local activation front by transmural ischemia; the QT interval was expected to be shortened in the acute period. They performed a multi-centric case-control study examining 150 patients with acute chest pain associated with ST elevation: 71 who presented with STEMIs and 79 who had acute pericarditis. Admission electrocardiograms (ECGs) were manually analyzed for deviation of the PR segment from baseline, ST-segment deviation from the J-point, QRS duration, and QT interval. Each ECG was analyzed using one of three models: Model A included the duration of the QRS complex and QT interval; Model B utilized the classic ECG criteria of PR deviation and J-point level in aVR, as well as the number of leads with ST-segment elevation, ST-segment depression, and PR depression; and Model C tested all of the above variables. Receiver operating characteristic curves (ROCs) were constructed for each model, and the ROCs were compared using the DeLong method. Overall, patients with acute pericarditis were younger with fewer cardiac risk factors. Additionally, these patients showed greater upright PR deviation and deeper J-point in aVR, as well as a higher number of ECG leads with ST elevation and PR depression and a lower number of leads with reciprocal ST depression compared to STEMI ECGs. In patients with pericarditis, the QRS and QT intervals were the same in leads with and without ST elevation, whereas patients diagnosed with STEMIs showed a longer duration of the QRS complex and shorter QT interval length in leads with ST elevation compared to isoelectric leads. Comparison of the aforementioned models showed improvement in the ROC when QRS and QT interval duration were included in the analysis, with the ROC for model A being 0.807, model B 0.863, and model C 0.914. This study demonstrates that factoring the QRS duration and QT interval in your analysis of an ECG can help the clinician identify pericarditis and acute STEMI. The authors note that the study was limited by a lack of randomization, and that the ECG findings significantly influenced the ultimate diagnosis for patients at discharge.

Sufism and Politics in Contemporary Egypt: A Study of Sufi Political Engagement in the Pre and Post-revolutionary Reality of January 2011

Experts on Sufi movements relegate a rather significant and critical role for Sufism in the formation of redefined political forces on the new post-Arab Spring political map. This is particularly true for one of the most vibrant Sufi capitals of the Muslim world, Egypt, holding a record sum of more than 10 million Sufi members. In spite of this, however, one year after the Revolution in Egypt, political developments exhibited a pattern of failure of Sufis gaining political ground in the post-Mubarak political arena. This paper discusses contentions and problematic issues Sufis faced with respect to politics in Egypt, with particular focus given to their political experience in Egypt. This study seeks to explore the Sufi experience throughout the process of political struggle, while examining their contributions to the November 2011 elections in an attempt to unveil the factors culminating in their political setback in spite of their massive membership base, and the official favored support of the state, both on the local and international fronts. The study concludes that the nature of the Sufi practice itself contributed to a restraining of their political presence, in addition to their lack of political awareness, poor organization and populism, all of which acted critically toward creating a failed political journey for the Sufi orders in modern Egypt.

Climate-driven range shifts explain the distribution of extant gene pools and predict future loss of unique lineages in a marine brown alga.

The climate-driven dynamics of species ranges is a critical research question in evolutionary ecology. We ask whether present intraspecific diversity is determined by the imprint of past climate. This is an ongoing debate requiring interdisciplinary examination of population genetic pools and persistence patterns across global ranges. Previously, contrasting inferences and predictions have resulted from distinct genomic coverage and/or geographical information. We aim to describe and explain the causes of geographical contrasts in genetic diversity and their consequences for the future baseline of the global genetic pool, by comparing present geographical distribution of genetic diversity and differentiation with predictive species distribution modelling (SDM) during past extremes, present time and future climate scenarios for a brown alga, Fucus vesiculosus. SDM showed that both atmospheric and oceanic variables shape the global distribution of intertidal species, revealing regions of persistence, extinction and expansion during glacial and postglacial periods. These explained the distribution and structure of present genetic diversity, consisting of differentiated genetic pools with maximal diversity in areas of long-term persistence. Most of the present species range comprises postglacial expansion zones and, in contrast to highly dispersive marine organisms, expansions involved only local fronts, leaving distinct genetic pools at rear edges. Besides unravelling a complex phylogeographical history and showing congruence between genetic diversity and persistent distribution zones, supporting the hypothesis of niche conservatism, range shifts and loss of unique genetic diversity at the rear edge were predicted for future climate scenarios, impoverishing the global gene pool.

High-temperature crack growth in a Ni-base superalloy during sustained load

The high-temperature sustained load crack growth behaviour of a Ni-base superalloy was investigated using a combination of mechanical testing in controlled atmosphere, fractographical and microanalytical investigations, and finite element modelling. The results show that the local crack front geometry is un-even on two scales – jaggedness on the scale of 100μm was observed in all specimens, whereas mm-scale waviness could occasionally be observed. The jaggedness can be explained by a percolation-type crack growth along weaker grain boundaries, whereas the large-scale waviness is presumably due to larger regions of the material having specific grain texture with high crack growth resistance. The un-even crack front is shown to potentially have considerable effects on the loading conditions at the crack tip, whereas ligaments of un-cracked material in the crack wake are deemed to have less effect on the crack tip loading due to their low area fraction. The ligaments fail intergranularly in the wake as the crack grows in the present case, as opposed to by creep fracture as previously proposed. Finally, the plastically deformed regions about the crack and crack tip are shown not to exhibit any elevated oxygen levels, implying that the damage in these regions is purely mechanical.