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This paper presents a stochastic analysis of the size effect on the nominal strength of quasibrittle structures with a large preexisting notch. This type of scaling behavior has been extensively studied within a deterministic framework. Little attention is paid to stochastic analysis, which is essential for reliability-based analysis and design of engineering structures. Stochastic finite element simulations are performed to study the failure of geometrically similar beams of different sizes. The numerical analysis uses a continuum damage model, in which the tensile strength and fracture energy are modeled by homogeneous random fields. Different correlation lengths are considered as a parametric study. The analysis yields the size effects on the mean and coefficient of variation (CoV) of the nominal structural strength. It is shown that the size effect on the mean strength agrees well with the Bazant size effect model. The simulation predicts a strong size effect on the CoV of the nominal strength. Small-, intermediate-, and large-size asymptotes are derived analytically for the scaling behavior of the strength CoV. Based on these asymptotes, an approximate scaling equation is proposed for the CoV of nominal strength. The effect of the correlation length on the simulated failure behavior is discussed. [ABSTRACT FROM AUTHOR]

It is worth understanding the potentials of zero charge (PZCs) and structures of stepped metal/water interfaces, because for many electrocatalytic reactions, stepped surfaces are more active than atomically flat surfaces. Herein, a series of stepped Pt/water interfaces are modeled at different step densities with ab initio molecular dynamics. It is found that the structures of Pt/water interfaces are significantly influenced by the step density, particularly in regard to the distribution of chemisorbed water. The step sites of metal surfaces are more preferred for water chemisorption than terrace sites, and until the step density is very low, water will chemisorb on the terrace. In addition, it is revealed that the PZCs of stepped Pt/water interfaces are generally smaller than that of Pt(111), and the difference is mainly attributed to the difference in their work function, providing a simple way to estimate the PZCs of stepped metal surfaces. Finally, it is interesting to see that the Volta potential difference is almost the same for Pt/water interfaces with different step densities, although their interface structures and magnitude of charge transfer clearly differ. [ABSTRACT FROM AUTHOR]

Helicostoa sinensis E. Lamy, 1926 is a unique freshwater gastropod species with a sessile habit. This enigmatic species was first found cemented on river limestones from China about 120 years ago and described together with the genus. It was never collected again and has been considered monotypic. Here, we report the rediscovery of Helicostoa from several rivers in China, and describe a second species of this genus based on a comprehensive study. In addition to the unique sessile habit of both species, the new Helicostoa species presents one of the most remarkable cases of sexual dimorphism within molluscs. Only the adult female is sessile and the original aperture of the female is sealed by shell matter or rock, while an opening on the body whorl takes the function of the original aperture. The male is vagile, with a normal aperture. Our results confirm the recently suggested placement of Helicostoa within the family Bithyniidae. The sessility of Helicostoa species is considered as an adaption to the limestone habitat in large rivers. The extreme sexual dimorphism and secondary aperture of females are considered as adaptations to overcome the obstacles for mating and feeding that come with a sessile life style. [ABSTRACT FROM AUTHOR]

The field density of as-constructed asphalt pavements usually exhibits considerable variability. Understanding and quantifying this variability is of crucial importance for building more reliable and durable pavements. This study investigates the probability distribution of the field density based on an analytical model of gyratory compaction. The model is derived from mass balance and the transition state theory for the process of aggregate rearrangement. Meanwhile, the variability in the compaction effort is also taken into account. The model is first calibrated by the laboratory gyratory compaction experiments, and is then used to predict the probability distribution of the field density, which is compared with field measurements. It is shown that the probabilistic model can capture the left-skewed and leptokurtic features of the field density distribution. The present model surpasses the commonly used Gaussian distribution for characterising the field density distribution. A parametric study is performed to investigate the effects of the compaction properties of mixture and field compaction effort on the probability distribution of the field density. The model can potentially be used to guide the asphalt mix design for achieving the desired field density. [ABSTRACT FROM AUTHOR]

Cation effects have been shown in numerous experiments to play a significant role in electrocatalysis. To understand these effects at the molecular level, we systematically investigate the structures and capacitances of electric double layers with a variety of cations as counter charges at Pt(111)-COad/water interfaces with ab initio molecular dynamics. It is encouraging to find that the computed Helmholtz capacitances for different cations are in quantitative agreement with experiments, and that the trend of cation effects on capacitances shows clear correlation with the structures of interface cations of differing sizes and hydration energies. More importantly, we demonstrate the Helmholtz capacitance as the key descriptor for measuring the activity of CO-CO dimerization, the rate-determining step for C2+ formation in electroreduction of CO and CO2. Our work provides atomistic insights into cation effects on electric double layers and electrocatalysis that are crucial for optimizing electrode and electrolyte materials. [ABSTRACT FROM AUTHOR]

An extinct freshwater molluscan fauna has been discovered from Quaternary lacustrine deposits of a recently vanished group of lakes and surrounding lacustrine deposits in the Luliang Basin, Yunnan Province, China. Three species of Tchangmargarya He, 2013 are dominant and distributed sympatrically here. One of them is new to science. Here we describe the three Tchangmargarya species from the Luliang Basin, including the new species, Tchangmargarya cuan n. sp., and compare the species composition of this fauna with the other extant lacustrine mollusc fauna of Yunnan. The vanished lakes group in Luliang is the first case of sympatric distribution within Tchangmargarya. It is considered to have once been a diversity hotspot of Tchangmargarya and represents a vanished Quaternary lacustrine habitat in Yunnan. [ABSTRACT FROM AUTHOR]

A new genus of viviparid snail, Dalipaludina gen. nov., from the Yunnan Plateau of China is described within an integrative taxonomic framework based on data from the mitochondrial COI marker and morphology. Dalipaludina can be distinguished from all other viviparid genera by a unique combination shell, operculum and radula characters. Four species are assigned here to the new genus, Dalipaludina delavayana comb. nov., Dalipaludina oxytropoides comb. nov., Dalipaludina occidentalis comb. nov., and Dalipaludina pyramidella comb. nov., and one species is newly assigned to Margarya, Margarya dianchiensis comb. nov. The four species of Dalipaludina are allopatrically distributed in shallow water lentic habitats at high altitude regions of the Yunnan Plateau. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the effect of nimodipine combined with atorvastatin calcium on the micro inflammation and oxidative stress levels in patients with cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH) and its clinical implications. Methods: A total of 80 patients with CVS caused by SAH who had been admitted to Baoding First Central Hospital from August 2021 to August 2022 were selected and randomly divided into two groups. The control group underwent conventional symptomatic treatment, while the experimental group was administered nimodipine combined with atorvastatin calcium on the basis of conventional treatment. The changes in the micro inflammatory cytokines and oxidative stress factors in the two groups were compared, as well as the differences in clinical efficacy and incidence of adverse drug reactions. Results: After treatment, the levels of inflammatory cytokines in the experimental group decreased more significantly than those in the control group (p=0.00). After treatment, the serum levels of oxidative stress factors were obviously higher in the experimental group than in the control group (p=0.00). After treatment, the total efficacy was 77.5% in the experimental group and 55% in the control group, and the difference was statistically significant (p=0.04). Conclusions: Nimodipine combined with atorvastatin calcium could significantly improve the clinical symptoms in patients with CVS after SAH, which would be beneficial, safe, and effective for the patient's recovery. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of time-dependent bond slip on the delayed failure of RC frames. The time-dependent model of bond slip is formulated based on the mechanism of subcritical damage accumulation along the steel–concrete interface. A kinetic model of the time dependence of slip under sustained loading is developed through numerical simulations. The model is incorporated into a recently developed reduced-order numerical model for simulations of the progressive collapse of RC frames. It is shown that the present model captures the essential deformation mechanisms of the frame under both monotonic loading and sustained loading, and that the time dependence of bond slip has a profound influence on the delayed failure of RC frames, especially under moderate sustained loading. This finding highlights the importance of understanding and accounting for the time dependence of bond slip for future study of the delayed progressive collapse of RC structures. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of the failure behavior of SiC fiber-reinforced SiC matrix (SiC/SiC) composite tubes under multiaxial loading. A new testing apparatus is designed to independently apply axial stress and internal pressure to SiC/SiC tubes. Acoustic emission (AE) is used to monitor the damage growth in the specimen. Based on the measured stress–strain response, a strain-based criterion is proposed to determine the proportional limit stress (PLS). The proposed strain-based criterion is compared with the PLS determined by the AE measurement. The PLS is determined for different loading ratios to form a multiaxial failure surface. By testing multiple replicates, the statistical variations of the PLS are determined. Based on the experimental results, a mathematical model is developed to characterize the probability distribution of the PLS of SiC/SiC composites under multiaxial loading. [ABSTRACT FROM AUTHOR]

The collapse of the World Trade Center (WTC) Towers during the terrorist attacks on September 11, 2001, remains one of the most tragic catastrophes in the field of structural engineering. This paper first reviews a mathematical model that explains the process of the total collapse of the Twin Towers and shows that the downward collapse progression below the impacted floors was spontaneous. The model is based on a continuum description of the motion of the crush front and captures various types of energy dissipation during the collapse. The predictions of this model match all the observations, including the video records of the first few seconds of motion of both towers, the seismic records of the collapse durations for both towers, the mass and size distributions of comminuted concrete particles, and the fast expansion of dust clouds during collapse with the booms generated. This catastrophe provoked general interest in other types of progressive collapse of buildings. This is the subject of the second part of this paper, in which a three-dimensional stochastic computational model for the collapse of RC frame buildings is presented. The occurrence probabilities of different collapse patterns are predicted. The model is further extended to investigate the delayed collapse behavior of RC frames. The results of the analysis shed light on the emerging trend of probabilistic analysis and design of structures against progressive collapse. [ABSTRACT FROM AUTHOR]

This paper presents a discrete element model for simulations of the compaction process of hot mixed asphalt (HMA). The model is anchored by the concept of a fine aggregate matrix (FAM), which consists of the binder and fine aggregates. In the simulation, the coarse aggregates are explicitly modeled as composite particles. Meanwhile, the FAM is considered as the thick coating of the coarse aggregates with complex constitutive laws. Interparticle interactions include influences of (1) particle properties via Hertz–Mindlin relations; and (2) FAM properties via lubrication relationships. The lubrication relationships include a variable for viscosity for which we derive normal and tangential rate-dependent forms using rheology theory of dense granular-fluid systems, verified reasonable for our systems with the discrete element simulations and experiments with FAM. We assimilate these elements into gyratory compaction simulations of HMA of different aggregate size distributions. We compare these with experiments and find that this model is capable of capturing the measured effects of grain size distribution on the overall compaction behavior of HMA. We conclude by highlighting the advantages of this discrete element model for HMA compaction problems. [ABSTRACT FROM AUTHOR]

The morphological identification of many groups of gastropods is mostly based on shell morphology and genital structures. The value of opercular characters as taxonomic characters has so far been barely studied and evaluated. Here, the opercular characters of river snails (Viviparidae) have been revised systematically for the first time. Based on a morphological study of the opercula of 38 species of 25 viviparid genera, 16 newly defined opercular characters are shown to be useful for genus and species identification. A detailed diagnosis and description of opercular characters for each genus/species is given. One new generic assignment of a viviparid species is proposed based on this study, namely Cipangopaludina nagaensis n. comb. [ABSTRACT FROM AUTHOR]

In shear failure, reinforced concrete (RC) beams always develop, in a stable manner, a finite length crack before the maximum load is reached. Thus, the crack tip location cannot sample a large volume of material with random strength because a small region in which the crack tip can lie is fixed by fracture mechanics. Consequently, the size effect on the mean strength cannot be statistical. It must be predominantly energetic or deterministic and, thus, must follow the Type-2 size effect law. What has not yet been clarified is the size effect on the coefficient of variation (CoV) of beam strength, which is important for anchoring the probability distribution of shear strength and choosing the safety factor. In this study, we run thousands of explicit finite element simulations using Abaqus-Explicit version 6.14 with microplane model M7, each with a random input of material strength and Young's modulus for each finite element in the structure. The CoV of beam strength is found to decrease with the structure size when geometrically similar beams are compared, although the CoV tends to a constant for large sizes. This size effect on the CoV is similar to that in ductile failure governed by a Gaussian distribution of strength and contrasts with that in brittle failures following the Weibull distribution, for which the CoV is size independent. To characterize the size dependence of the strength CoV, an analytical formula is developed based on the statistics of the sample quantiles of a series of random variables. [ABSTRACT FROM AUTHOR]

There has been ever-increasing interest over the past decade in improving understanding of the mechanisms responsible for the progressive collapse of structures. Existing design recommendations and analyses are largely limited to instantaneous (time-independent) collapse. However, recent experiments revealed that reinforced concrete (RC) structures may be susceptible to delayed collapse, prompting the consideration of time-dependent material behavior as part of progressive collapse analysis and design. A reduced-order computational model for delayed collapse behavior of RC structures is introduced here in which the potential damage zones that evolve within a structure are treated as cohesive elements. The constitutive model of the cohesive element accounts for viscoelastic deformation and time-dependent damage accumulation of the concrete and hardening plasticity of the steel reinforcement. The remaining part of the structure is treated as a viscoelastic continuum. The model is first applied to simulate a pushdown experiment on a RC frame subassemblage under displacement-controlled loading. The deformation and failure mechanisms are in good agreement with experimental observations. The model is then used to investigate the behavior of the subassemblage in a "static fatigue scenario" in which the load is monotonically increased to a prescribed level and is then held constant until ultimate structural failure resulting from the assumed time-dependent response of the concrete material. The corresponding timescale of the delayed failure is on the order of hours, a result that has important implications not only for the analysis and design of RC structures against progressive collapse but also for the safety of first responders who enter structures that may collapse within that period of time. [ABSTRACT FROM AUTHOR]

A general framework for analyzing the failure probability of concrete specimens with the mean strength sampled from a large database is presented. The framework explicitly takes into account the level of uncertainty of the existing strength database involving different concretes tested in different labs. This uncertainty strongly influences the probability distribution of the nominal strength of each structure. The energetic (nonstatistical) size effect on structural strength is also incorporated into the analysis. The proposed framework is demonstrated by analyzing the reliability of reinforced concrete beams against diagonal shear failure. The analysis considers four different levels of uncertainty of the mean strength database, with coefficients of variation 5%, 10%, 25%, and 40%. It is shown that the overall failure probability strongly depends on the structure size, and that this size effect is also influenced by the uncertainty level of the database. In addition, an approximate solution procedure is developed for calculating the failure probability in the spirit of the first-order reliability method. Compared to the existing procedure, the proposed model is shown to yield a more realistic estimate of the structural failure risk and to lead to an analytical solution of the safety factor that can be used for reliability-based structural design. [ABSTRACT FROM AUTHOR]

Nowadays, plastic forming technology for micro-scale parts is booming. Kinds of microstructures with high-precision, multi-function are required by modern manufacturing industry. Laser shock imprinting, as a high-efficient, high-precision, and low-cost micro-forming technology, has been widely studied. But at present, the precision of microstructure fabricated by the method was not enough, and the microstructure cannot completely replicate from micro-mold. This paper defined filling rate and vertical degree to measure the forming precision of microstructures and realized microstructure complete forming with high precision (filling rate reach to 100% and vertical degree reach to 90°). According to stress modes and forming precision, the forming process was divided into three stages (elastic deformation, plastic stretching, and plastic compression) in this paper. Through experiment and simulation, the surface profile, stress distribution, thinning of metallic thickness, and roughness were analyzed in each stage. Besides, grain refinement degree and refinement mechanism was explained in the paper. Therefore, by changing the micro-mold, laser shock imprinting could fabricate complex microstructure with high precision. [ABSTRACT FROM AUTHOR]

The species of Satsuma are mostly endemic to East Asia except for one species distributed in Batan Island of the Philippines. More than 99% of the known species of this genus are endemic to the island environment. Only three species are currently known to occur on the mainland. Here we describe a new sinistral Satsuma species from China, Satsuma guandi n. sp. We studied the shell morphology and genital anatomy of the new species and reconstructed the molecular phylogeny of the genus based on partial nucleotide sequences of the mitochondrial gene cytochrome c oxidase subunit I and nuclear markers from the ribosomal RNA cistrons (the internal transcribed spacer and the external transcribed spacer regions). The new species differs from other sinistral Satsuma species by having a strongly angulated shell and an open dark brownish-red umbilicus. The new species also differed from all other sinistral congeners in details of its reproductive anatomy. The molecular analysis supports the validity of the new species within the genus Satsuma. [ABSTRACT FROM AUTHOR]

It is vital to understand the oxygen reduction reaction (ORR) mechanism at the molecular level for the rational design and synthesis of high activity fuel‐cell catalysts. Surface enhanced Raman spectroscopy (SERS) is a powerful technique capable of detecting the bond vibrations of surface species in the low wavenumber range, however, using it to probe practical nanocatalysts remains extremely challenging. Herein, shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) was used to investigate ORR processes on the surface of bimetallic Pt3Co nanocatalyst structures. Direct spectroscopic evidence of *OOH suggests that ORR undergoes an associative mechanism on Pt3Co in both acidic and basic environments. Density functional theory (DFT) calculations show that the weak *O adsorption arise from electronic effect on the Pt3Co surface accounts for enhanced ORR activity. This work shows SHINERS is a promising technique for the real‐time observation of catalytic processes. [ABSTRACT FROM AUTHOR]

It is vital to understand the oxygen reduction reaction (ORR) mechanism at the molecular level for the rational design and synthesis of high activity fuel‐cell catalysts. Surface enhanced Raman spectroscopy (SERS) is a powerful technique capable of detecting the bond vibrations of surface species in the low wavenumber range, however, using it to probe practical nanocatalysts remains extremely challenging. Herein, shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) was used to investigate ORR processes on the surface of bimetallic Pt3Co nanocatalyst structures. Direct spectroscopic evidence of *OOH suggests that ORR undergoes an associative mechanism on Pt3Co in both acidic and basic environments. Density functional theory (DFT) calculations show that the weak *O adsorption arise from electronic effect on the Pt3Co surface accounts for enhanced ORR activity. This work shows SHINERS is a promising technique for the real‐time observation of catalytic processes. [ABSTRACT FROM AUTHOR]

It is vital to understand the oxygen reduction reaction (ORR) mechanism at the molecular level for the rational design and synthesis of high activity fuel‐cell catalysts. Surface enhanced Raman spectroscopy (SERS) is a powerful technique capable of detecting the bond vibrations of surface species in the low wavenumber range, however, using it to probe practical nanocatalysts remains extremely challenging. Herein, shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) was used to investigate ORR processes on the surface of bimetallic Pt3Co nanocatalyst structures. Direct spectroscopic evidence of *OOH suggests that ORR undergoes an associative mechanism on Pt3Co in both acidic and basic environments. Density functional theory (DFT) calculations show that the weak *O adsorption arise from electronic effect on the Pt3Co surface accounts for enhanced ORR activity. This work shows SHINERS is a promising technique for the real‐time observation of catalytic processes. [ABSTRACT FROM AUTHOR]

In recent years, advanced manufacturing techniques, such as high-definition plasma, water jet, and laser cutting, have opened up an opportunity to create a new class of steel connections that rely on intermeshed (i.e. interlocked) components. The main advantage of this type of connection is that they do not require either welding or bolting, which allows faster construction. Although the interest in intermeshed connections has increased in recent years, the mechanical behavior of these connections has not been fully understood. This paper presents a numerical study on the ultimate load capacity failure modes of intermeshed connections under mixed-mode loading. The experimental behavior of the connection components is also investigated through a series of tests. The study considers a recently developed intermeshed connection for beams and columns. The numerical simulations were performed by using a commercially available 3D finite element software package. By considering different types of mixed mode loading, interaction diagrams of axial, shear, and moment capacities of the intermeshed connection were obtained. The results indicated that there exists an intricate interaction among axial, shear, and moment capacities, which arises from the intermeshed configuration of the flanges and web. For each interaction diagram, the corresponding failure mechanism was analyzed. The simulated interaction between axial, shear, and moment capacities were further compared with the provision of the current design codes. While the intermeshed connection studied here showed promise for gravity loading, further study is needed to ensure alignment of the flanges so as to avoid axial and/or flexural failures. • The intermeshed steel connection exhibits excellent shear resistance. • Axial and flexural behavior are affected by the alignment of the intermeshed flanges. • The presence of shear has a significant influence on axial and moment capacities. • P-M-V interactions in existing codes are not applicable to the intermeshed connection. • This connection could serve in gravity frames if flange alignment could be maintained. [ABSTRACT FROM AUTHOR]

The two-parameter Weibull distribution has been widely adopted to model the lifetime statistics of dielectric breakdown under constant voltage, but recent lifetime testing for high-k gate dielectrics has revealed a systematic departure from Weibull statistics, evocative of lifetime statistics for small quasibrittle structures under constant stress. Here we identify a mathematical analogy between the dielectric breakdown in semiconductor electronic devices and the finite-size weakest-link model for mechanical strength of quasibrittle structures and adapt a recently developed probabilistic theory of structural failure to gate dielectrics. Although the theory is general and does not rely on any particular model of local breakdown events, we show how its key assumptions can be derived from the classical dielectric breakdown model, which predicts certain scaling exponents. The theory accurately fits the observed kinked shape of the histograms of lifetime plotted in Weibull scale, as well as the measured dependence of the median lifetime on the gate area (or size), including its deviation from a power law. The theory also predicts that the Weibull modulus for breakdown lifetime increases in proportion to the thickness of the oxide layer and suggests new ideas for more effective reliability testing. [ABSTRACT FROM AUTHOR]

Understanding the tail behavior of the probability distribution of structural strength is of paramount importance for reliability-based design of engineering structures. For brittle and quasibrittle structures, the tail distribution not only determines the design strength at a low failure probability, but also governs the functional form of the strength distribution of large-size structures. There exists clear evidence that the Weibull distribution is applicable to brittle structures. Based on the theory of extreme value statistics, the applicability of Weibull distribution suggests that the tail distribution must follow a power law. The justification of the power-law tail distribution was first proposed by Freudenthal based on an assumed type of flaw statistics and linear elastic fracture mechanics of non-interacting flaws. A series of recent studies suggested that the power-law tail can be explained by the transition rate theory governing the statistics of material failure at the nano-scale. In this study, we investigate the tail distribution by considering the randomness in both material strength and applied stress field. The present analysis adopts a nonlocal strength-based failure criterion, in which the spatial variability of the material strength is represented by an autocorrelated random field. The failure statistics of the structure is calculated as a first passage probability. We analyze this problem in 1D, 2D and 3D settings, and the results indicate that in all cases the tail distribution of the nominal structural strength follows a power law. It is shown that the power-law tail behavior of strength distribution stems from the tail distribution of material strength. The flaw statistics introduces additional randomness to the nominal structural strength, but does not dictate the power-law form of its tail distribution. [ABSTRACT FROM AUTHOR]

Anchored by the theory of extreme value statistics, Weibull distribution is the most widely used mathematical model for strength distribution of brittle structures. In a series of recent studies, a finite weakest-link model was developed for strength distribution of quasi-brittle structures, and the classical Weibull distribution was shown to represent the large-size asymptote of the model. By employing a length scale, the finite weakest-link model is capable of capturing correctly the size effects on both the probability distribution and the mean value of structural strength. However, the connection of this length scale with the basic material properties is still missing. This study investigates the relationship between the length scale of the finite weakest-link model and the material length scales by analyzing the size effect on the mean structural strength. The mathematical form of this relationship is derived through dimensional analysis. To validate the model, a set of mean size effect curves is obtained through stochastic simulations, which use a nonlinear constitutive model involving both the Irwin characteristic length and the crack band width. The internal length scale of the weakest-link model is determined by optimum fitting of the benchmark size effect curves in the small-size range. Furthermore, the effect of stress field on this internal length scale is studied by considering three different loading configurations. The present analysis reveals the importance of the mean size effect analysis for the calibration of finite weakest-link model. [ABSTRACT FROM AUTHOR]

Habitat loss poses a grave threat to endemic species with narrow distributions. Some species become extinct even before scientific identification due to habitat destruction. Here, a probable example is reported based on some recent and subfossil shells from an almost disappeared wetland lake in Yunnan Province, China. A new ornamented freshwater snail species,Tchangmargarya ziyin. sp., is recognised and described based on morphological comparison with the otherTchangmargaryaspecies. The subfossil specimens of the new species show a great similarity toTchangmargrya yangtsunghaiensis(Tchang & Tsi, 1949), indicating their potentially close relationship. The discovery of the new species demonstrates that the plateau lakes of Yunnan, even the small ones, have a high biodiversity and endemism. Furthermore, it enriches the knowledge of the distribution ofTchangmargaryaand provides further evidence that the Liangwang Mountains are a significant biogeographic barrier to three endemic viviparid genera (Margarya,Anularya andTchangmargarya) of Yunnan. Since the only known habitat of this species has been mostly landfilled due to the construction of a golf course and villas, this species possibly has already gone extinct. In order to implement conservation measures more efficiently, more comprehensive surveys should be conducted in all plateau lakes of Yunnan, including those that might seem insignificant. [ABSTRACT FROM PUBLISHER]

The previously formulated model of the gravity-driven collapse of the twin towers of the World Trade Center (WTC) on September 11, 2011 was shown to match all the existing observations, including the video record of the crush-down motion of the top part of tower during the first few seconds, the seismically recorded duration of collapse, the size distribution of particles caused by impact comminution of concrete floor slabs, the loud booms due to near-sonic lateral ejection velocity of air and dust, and precedence of the crush-down collapse mode before the crush-up. Nevertheless, different degrees of ductility, fracturing and end support flexibility of WTC columns could lead to an equally good match of these observations and remained uncertain, due to lack of test data. Recently, Korol and Sivakumaran reported valuable experiments that allow clarifying this uncertainty. They revealed that, under the simplifying assumptions of rigid end supports and unlimited ductility (or no fracturing) of unheated columns, the energy dissipation of the WTC columns would have been at maximum 3.5-times as large as that calculated by the plastic hinge mechanism normally considered for small-deflection buckling. This increase would still allow close match of all the aforementioned observations except for the first two seconds of the video. The proper conclusion from Korol and Sivakumaran's tests, based on close matching of the video record, is that the fracturing of unheated columns and the flexibility of their end restraints must have significantly reduced the energy dissipation in columns calculated under the assumptions of no fracture and no end restraint flexibility. [ABSTRACT FROM AUTHOR]

This paper presents a critical comparison of the existing code provisions for the shear strength of concrete beams. The comparison is based on the computerized filtering-out of the inevitable statistical bias from the available multivariate database on shear strength, on an examination of the predicted size effects on shear strength and their underlying hypotheses and on the results of recent high-fidelity numerical simulations of shear failure. In addition to examining the existing models, the present comparison also provides several key considerations for testing the scientific soundness of any model of shear failure in concrete beams, which is necessary for future revisions to the design code provisions. [ABSTRACT FROM AUTHOR]

This paper presents a simplified method for evaluating the risk of progressive collapse of reinforced concrete (RC) buildings. The method is formulated based on a recently developed two-scale numerical model for RC structures. In this model, all structural members are modeled by a set of coarse-scale cohesive elements representing the potential damage zones (PDZs). The cohesive constitutive behavior is determined by fine-scale finite element (FE) simulations of the corresponding PDZs. In the present study, a new energy-equivalent linear elastic cohesive model is developed for RC buildings. The damage status of the PDZ is determined by comparing the elastic energy stored in the cohesive element with the actual energy dissipation capacity of the PDZ. This model is applied to analyze the behavior of a two-dimensional frame subassemblage under a column removal scenario, and it is shown the model is capable of capturing the total energy dissipation of the entire failure process. This cohesive model is combined with a sequential analysis method to identify different possible failure paths leading to collapse initiation. The present model is applied to analyze the collapse initiation risk of a prototype RC building, where the randomness in both gravity loads and material properties is taken into account. The results are compared with the recent simulations using a nonlinear dynamic model. It is shown that the present analysis is much more efficient than the conventional nonlinear dynamic analysis, and it yields a reasonable upper bound of the collapse probability. [ABSTRACT FROM AUTHOR]

Zinc (Zn) metal anodes are badly troubled by the challenges of notorious dendrites and corrosion reactions from H 2 O and I 3 − ions during stripping/plating processes, impeding the commercial application of Zn-iodine (I 2) batteries. In this work, we report a novel strategy for the in-situ construction of uniform silicon-based anticorrosion films on Zn metal anodes (Zn@Ts) through the treatment of tetraethyl orthosilicate (TEOS) steam on Zn disks for different times. TEOS can be decomposed into three-dimensional (3D) porous inorganic frameworks (SiO x C y) filled with organic polymers (SiC x O y H z) on Zn metal at 180 °C in autoclave. On the one hand, silicon-based composite layers can protect Zn metal from direct contact with aqueous electrolyte and stabilize the electrode/electrolyte interface, which hinders the occurrence of hydrogen evolution as well as corrosion reactions. On the other hand, 3D macroporous structure not only provides strong mechanical framework but also guides Zn2+ flux to homogenize Zn2+ concentration and realize uniform Zn nucleation/deposition, which contributes to suppress the growth of Zn dendrites. Zn@Ts symmetric batteries exhibit better cycling life of 5000 h comparing with bare Zn at 2 mA cm−2 and 2 mA h cm−2. Zn–I 2 full-cells can achieve 89 mA h g−1 and 93% capacity retention after 20000 cycles. [Display omitted] • TEOS steam was used to treat Zn metal to form silicon-based anticorrosion films. • Silicon-based films suppress the corrosion of H 2 O and I 3 − in aqueous electrolyte. • Inorganic/organic components in anticorrosion films restrain Zn dendrite growth. • The protected Zn metal anodes can achieve ultra-long lifespan of 5000 h. • Zn–I 2 full-cells can reach 93% capacity retention after 20000 cycles. [ABSTRACT FROM AUTHOR]

This paper reports the results of scratch tests on three rocks (Bonne Terre Dolomite, Alabama Marble and Dunnville Sandstone) conducted at depths of cut ranging from 0.2 mm to 2.6 mm. The experiments were performed on slabs of thickness slightly smaller than the cutter width, with a camera recording the entire cutting process. The test results reveal the existence of three cutting regimes: ductile, fragmentation, and brittle with increasing depth of cut. The regimes differ by the failure mode, the dependence of the specific energy ϵ on the depth of cut d , and the fragment shapes. In the ductile regime, ϵ ∼ d 0 and the fragments are constitutive grains of the rock or powder as a result of intense shearing. In the fragmentation regime, ϵ ∼ d − 1 / 2 and the fragments is a mix of ductile-type particles and flake-like chips also the product of shear failure. Finally, the brittle regime is characterized by ϵ ∼ d − 1 and is essentially associated with chip-like fragments that come in two varieties depending on whether they are created by shear or by tension. The d − 1 -dependence of the specific energy can only be observed if the rock is sufficiently homogeneous at the scale of the experiment. The distinction between different modes of failure is based on evidence from video recording and fractography with a Scanning Electron Microscope. It is shown that the dominance of tensile over shear fracture is intimately related to the existence of a crushed zone, which acts as a wedge to initiate a tensile macrocrack in a compressive stress field. Finally, an analysis of the energy partitioning in the brittle regime indicates that the energy dissipated in creating new surfaces with a tensile crack is actually negligible compared to the energy expended in the formation of the wedge. This result indicates that the mode I toughness cannot be determined from the specific energy in the brittle regime, on the basis of a model of a crack parallel to the free surface, in contradiction with published claims to that effect. Finally, this experimental investigation clarifies some confusion in the literature, rooted on assuming the existence of only two modes of failure, ductile and brittle. • Scratch tests on rock slabs reveal ductile, fragmentation, and brittle regimes. • The scaling of the specific energy with depth of cut depends on the cutting regime. • Flake-like chips produced in the fragmentation regime are created by shear. • The crushed zone acts as a wedge to initiate tensile cracks in brittle regime. • The energy dissipated in the propagation of a tensile crack is negligible. [ABSTRACT FROM AUTHOR]

A unified chemo-mechanical model is developed to simulate stress corrosion cracking (SCC) of high density polyethylene (HDPE) in a chlorinated environment. The model consists of three components, each of which captures a critical aspect of SCC. A chemical kinetics–diffusion model is used to simulate the reactions and migration of chemical substances. The fracture behavior of HDPE is captured by a cohesive crack model, in which the cohesive properties are considered to be dependent on the extent of the chemical degradations. The time-dependent creep behavior of the bulk HDPE material is described by an elastic–viscoplastic constitutive model. This chemo-mechanical model is numerically implemented for finite element (FE) analysis of SCC of HDPE structures. The simulations show two different failure mechanisms depending on the applied stress level: at high stresses, the failure is primarily due to the excessive plastic deformation whereas at low stresses the chemical reactions and diffusion are the dominant factors leading to failure. In addition, examination of detailed crack growth kinetics reveals that at low stress levels the disinfectant concentration has a significant effect on the crack growth behavior through the relative dominance between the chemical reaction and diffusion processes. [ABSTRACT FROM AUTHOR]

We develop a two-scale numerical model to simulate the response of reinforced concrete (RC) frame structures under thermomechanical loading. In this model, the nonlinear behavior of structural members is captured by a set of nonlinear cohesive elements, which represents the potential damage zones that could form under the given loading. The thermo-dependent constitutive behavior of each cohesive element is determined through finite element (FE) simulations of its corresponding potential damage zone at different elevated temperatures. For the FE simulations, the thermo-dependent material properties are determined based on the existing literature in conjunction with a set of experiments on concrete at elevated temperatures. The proposed two-scale model is used to simulate the behavior of a RC frame subassemblage under thermomechanical loading and the simulation results are compared with the predictions by the standard FE analysis. It is shown that the present model can well capture the thermomechanical behavior of RC frame structures. Finally, the model is applied to analyze the global behavior of a prototype RC frame subjected to compartment fires. [ABSTRACT FROM AUTHOR]

The systematics of the viviparid freshwater snail genus Margarya endemic to the ancient lakes of Yunnan, China, is revised based on comparative analyses of morphological features, including shell, operculum, radula, and genital anatomy, and molecular phylogenetic analyses of partial sequences of the mitochondrial 16 S rDNA ( 16 S) and cytochrome c oxidase subunit I ( COI) genes, as well as the nuclear Internal Transcribed Spacer 2 ( ITS2). The taxonomic utility of key anatomical and morphological features in this group is evaluated. The genus Margarya as delimited previously is split into three genera in order to retain monophyletic taxa: (1) Margarya s.s., consisting of four species, i.e. the type species Margarya melanioides plus Margarya francheti, Margarya oxytropoides, and Margarya monodi; (2) the previously introduced subgenus Tchangmargarya is elevated to an independent genus containing two species, Tchangmargarya yangtsunghaiensis and the new species T changmargarya multilabiata sp. nov.; and (3) a new genus, A nularya gen. nov., is described, also containing two species, i.e. Anularya mansuyi and Anularya bicostata. Molecular phylogenies based on analyses of three gene fragments have identical topologies, supporting the monophyly of these genera. The sister group of Margarya s.s. is Cipangopaludina, whereas the sister group of Anularya is Sinotaia; Tchangmargarya is sister to a clade containing all the aforementioned groups. Features of the operculum and the right male tentacle (penis) are particularly informative on the generic level, whereas shell and radular characters are especially useful to differentiate species. The phylogenetic relationships recovered here are consistent with orogenic patterns of the Yunnan Mountains. Changes in the river system and water area of ancient lakes caused by tectonic activities probably play an important role in speciation and shaping the current pattern of species distribution in Yunnan. © 2015 The Linnean Society of London [ABSTRACT FROM AUTHOR]

Microelectromechanical Systems (MEMS) devices typically need to be designed against a very low failure probability, which is on the order of [ABSTRACT FROM AUTHOR]

Novel dendron encapsulated conjugated organic molecular wire (Den-OPE)–CdSe quantum dot (QD) nanostructures have been designed. By tailoring the size of dendrimers, different amounts of Den-OPEs could be attached to CdSe, which forms different sizes of core–shell Den-OPE–CdSe composites. With an increase in the size of dendrimers, the emission intensity of CdSe QDs increased due to the higher Förster energy transfer (FRET) efficiency from the bigger size Den-OPEs to CdSe QDs. [ABSTRACT FROM AUTHOR]

Many modern engineering structures are made of brittle heterogenous (quasibrittle) materials, such as concrete, composites, and tough ceramics. Recent studies have shown that the strength distribution of quasibrittle structures varies from a Gaussian distribution modified by a power-law tail to a Weibull distribution as the structure size increases, and such size dependence can be well captured by a finite weakest link model. This paper investigates the implication of the size-dependent strength distribution on the reliability-based analysis and design of quasibrittle structures by considering a linear failure limit state. The size effect on the statistical properties of structural strength directly leads to a size-dependent Cornell index, which could give a reasonable estimation of the failure risk in some cases. To improve the prediction of the structural failure risk, the size dependence of the strength distribution is further incorporated into the computation of the Hasofer–Lind index, where it is shown that the transformation method for the non-Gaussian random structural strength is dependent on the structure size and geometry. By assuming that the applied load follows a Gaussian distribution, approximate size effect equations are developed for the central and nominal safety factors through asymptotic matching. The proposed formulation of the size effect on reliability indices and safety factors is applied to analyze the failure of the Malpasset arch dam. [ABSTRACT FROM AUTHOR]

This study investigates the use of Graphene Nanoplatelets (GNP) in cement composite to quantify the material damage extent. The damage sensing capability of this new cement composite is demonstrated by experimentally measuring the electric potential across prisms with a known notch depth and comparing it with the finite element simulations. Meanwhile, the damage extent is directly related to the change in electric potential based on a mathematical analogy between the electrostatic field and the elastostatic field under anti-plane shear loading. It is shown that the fractional change in electric potential arising from damage is equivalent to the fractional change in elastic compliance, which can be exploited for structural health evaluation. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive set of size effect experiments on fatigue crack kinetics for Berea sandstone. It is observed that for all specimens the Paris-Erdogan law is applicable for a wide range of amplitudes of the stress intensity factor. The fatigue tests also indicate that there is a small-crack growth regime at the beginning stage of cyclic loading, where the growth rate decreases as the crack initiates from the notch tip. It is shown that the fracture kinetics for both the small-crack growth and the Paris regimes is subjected to a strong size effect. Meanwhile, a series of size effect tests on monotonic strength of Berea sandstone is also performed in order to investigate the difference in fracture process between fatigue and monotonic loading scenarios. By using the digital image correlation method, it is found that the fracture process zone (FPZ) length under cyclic loading is about 60% larger than that under monotonic loading. In parallel with the experimental investigation, it is shown that the observed effect of the specimen size on the fracture kinetics can be explained by a size effect model for the critical energy dissipation for fatigue crack growth, which is analogous to the size effect on the apparent fracture energy for monotonic loading. [ABSTRACT FROM AUTHOR]

This paper presents a two-scale numerical model for assessing the risk of progressive collapse of reinforced concrete (RC) frame structures. In this model, the potential damage zones in various structural components, such as beams, columns and joint panels, are represented by a set of coarse-scale cohesive elements. The constitutive behavior of the cohesive elements is formulated in the effective traction–separation space, where the general mixed-mode failure can be well represented. The model parameters for the cohesive elements with their corresponding probability distributions are calibrated from the fine-scale stochastic finite element simulations of the potential damage zones. With incremental Latin Hypercube sampling of both random cohesive properties and external loads, the model is used to investigate the probabilistic collapse behavior of a two-dimensional 30 story RC structural frame under different column removal scenarios, where the occurrence probabilities of various possible collapse extents are calculated. Finally, the present probabilistic approach is compared with the conventional deterministic analysis method. [ABSTRACT FROM AUTHOR]

To overcome the safety hazard and poor cyclability resulting from the formation of lithium (Li) dendrites and "dead Li", we report a facile strategy to control the growth of Li and stabilize the interface by covering the surface of metallic Li with three-dimensional networked carboxymethylcellulose sodium/thiourea (CMC/SN) polymers with abundant heteroatoms. The strong adsorption energy of heteroatoms with Li and the high elasticity of CMC/SN films can limit longitudinal growth and facilitate lateral growth of Li to form flat pie-type morphology and decrease the contact of Li with electrolyte, which avoid the formation of Li dendrites and excessive solid electrolyte interphase (SEI) layers. Metallic Li electrodes with CMC/SN protective layers possess high coulombic efficiency even after 210 cycles and sustain stable plating and stripping processes for 1500 h at the current density of 2 mA cm−2. This study provides an effective method to construct polymeric layers with rich heteroatoms on Li surface for suppressing the growth of Li dendrites and improving the interfacial stability and contributes to the practical application of Li metal anodes. [Display omitted] • The growth of Li metal was controlled by the confined effect of CMC/SN films. • CMC/SN with rich S, N, and O atoms possesses high adsorption energy with Li metal. • The pie-type morphology was formed through restraining longitudinal growth of Li. • The Li prestored Cu@CMC/SN electrodes display a superior cycle stability (1500 h). [ABSTRACT FROM AUTHOR]

The combination of subcritical damage growth and creep deformation can cause delayed failure of concrete materials. Such a time-dependent failure behavior adds a new consideration in design of concrete structures. To investigate this behavior, a time-dependent constitutive model for concrete is proposed. The model is anchored by integration of the continuum damage mechanics and nonlinear creep theory. It captures several essential mechanisms responsible for delayed failure behavior of concrete, which include instantaneous softening damage, plasticity, subcritical damage growth, and nonlinear creep. The model is calibrated by the creep experiments on concrete specimens under uniaxial compression and three-point bending. It is shown that the model can well capture the time-dependent deformation and failure of concrete structures under a wide range of loading levels. The contributions of different individual mechanisms to the overall structural response are investigated. The calibrated model is then used to simulate the response of a reinforced concrete frame under sustained loading. The simulation yields the stress-life curve, which is an essential metric describing the delayed failure behavior of concrete structures. • A time-dependent constitutive model for concrete is developed. • The proposed model considers instantaneous softening damage, plasticity, subcritical damage growth and nonlinear creep. • Systematic calibration of concrete creep experiments at different loading levels is performed. • The simulation of delayed failure of reinforced concrete frame yields the stress-life curve. • The time-dependent effect of Vierendeel frame action is investigated. [ABSTRACT FROM AUTHOR]

The design of various engineering structures, such as buildings, infrastructure, aircraft, ships, as well as microelectronic components and medical implants, must ensure an extremely low probability of failure during their service lifetime. Since such a low probability is beyond the means of histogram testing, we must rely on some physically based probabilistic model for the statistics of structural lifetime. Attention is focused on structures consisting of quasibrittle materials. These are brittle materials with inhomogeneities that are not negligible compared with the structure size, as exemplified by concrete, fiber composites, tough ceramics, rocks, sea ice, bone, wood, and many more at the micro- or nano-scale. This paper presents a finite weakest-link model of the fatigue lifetime of quasibrittle structures that fail at the fracture of one representative volume element (RVE). In this model, the probability distribution of critical stress amplitude is first derived by assuming a prescribed number of loading cycles and a fixed stress ratio. The probability distribution of fatigue lifetime is then deduced from the probability distribution of critical stress amplitude through the Paris law for fatigue crack growth. It is shown that the present theory matches well with the experimentally measured lifetime histograms of various engineering and dental ceramics, which systematically deviate from the two-parameter Weibull distribution. The theory indicates that the mean fatigue lifetime of quasibrittle structures must strongly depend on the structure size and geometry. Finally, the present model indicates that the probability distribution of fatigue lifetime can be determined from the mean size effect analysis. [ABSTRACT FROM PUBLISHER]

Highlights: [•] We present an indirect method to determine the strength distribution of quasibrittle structures. [•] The method is verified by a set of experiments on asphalt mixture at a low temperature. [•] The finite weakest link model agrees well with the measured strength histograms of specimens of different sizes. [ABSTRACT FROM AUTHOR]

Solving big data must deal with three crucial problems; big data storage, big data analysis and big data management. Firstly, the definitions of big data and Hadoop ecosystem are summarized respectively. Secondly, how to face big data is discussed from the two aspects of commercial products and Hadoop ecosystem. The paper focuses on reviewing the big data solution based on Hadoop ecosystem; (1) HDFS, HBase and OpenTSDB are used to deal with storage problems; (2) Hadoop MapReduce (Hive) and HadoopDB do analytical problems; and (3) Sqoop and Ganglia solve management problems. For each partner, its architecture, principles and features are analyzed. And for some defects or problems existing in some key partners, we propose some solutions, ideas and viewpoints based on our research progress. It is predicted that Hadoop ecosystem is the preferable solution for the small and medium-sized enterprises. [ABSTRACT FROM AUTHOR]