The effect of mean stress and stress biaxiality in high‐cycle fatigue

This article presents a review of selected multiaxial high‐cycle fatigue criteria with an emphasis on their ability to take into account the mean stress effect and the effect of a biaxial stress state. It is shown that the predictions of the various criteria are very different for the case of biaxial tensile loads. This is in contrast to the case of combined tension‐torsion loads, where the predictions are very similar. The second part of the article investigates which mechanical parameter (eg, the hydrostatic stress or the normal stress) is the most appropriate to take into account these cyclic stress states.     

Treadmilling and dynamic protrusions in fire ant rafts

Fire ants (Solenopsis invicta) are exemplary for their formation of cohered, buoyant and dynamic structures composed entirely of their own bodies when exposed to flooded environments. Here, we observe tether-like protrusions that emerge from aggregated fire ant rafts when docked to stationary, vertical rods. Ant rafts comprise a floating, structural network of interconnected ants on which a layer of freely active ants walk. We show here that sustained shape evolution is permitted by the competing mechanisms of perpetual raft contraction aided by the transition of bulk structural ants to the free active layer and outward raft expansion owing to the deposition of free ants into the structural network at the edges, culminating in global treadmilling. Furthermore, we see that protrusions emerge as a result of asymmetries in the edge deposition rate of free ants. Employing both experimental characterization and a model for self-propelled particles in strong confinement, we interpret that these asymmetries are likely to occur stochastically owing to wall accumulation effects and directional motion of active ants when strongly confined by the protrusions'' relatively narrow boundaries. Together, these effects may realize the cooperative, yet spontaneous formation of protrusions that fire ants sometimes use for functional exploration and to escape flooded environments.     

Delay and state observation for SISO nonlinear systems with input delay

This paper deals with the problem of state and delay estimation for SISO nonlinear systems with an unknown time‐varying delay in the input. The main idea is to approximate the delayed input by using Taylor's theorem and to create an extended system with the delay as part of the extended state. Then, the construction of an observer is proposed to estimate both state and delay. The results are illustrated by simulations.     

Impulsive second‐order sliding mode control in reduced information environment

The perturbed system with input‐output dynamics of arbitrary and well‐defined relative degree is considered in a reduced information environment. A novel impulsive second‐order sliding mode control in the reduced information environment is proposed. The almost instantaneous convergence to the origin is achieved via impulsive control acting in a concert with second‐order sliding mode control, specifically supertwisting and twisting algorithms. The impulsive actions are implemented in a piecewise constant format. Numerical examples illustrate the efficiency of the proposed control algorithms.     

On the use of formal methods to model and verify neuronal archetypes

Having a formal model of neural networks can greatly help in understanding and verifying their properties, behavior, and response to external factors such as disease and medicine. In this paper, we adopt a formal model to represent neurons, some neuronal graphs, and their composition. Some specific neuronal graphs are known for having biologically relevant structures and behaviors and we call them archetypes. These archetypes are supposed to be the basis of typical instances of neuronal information processing. In this paper we study six fundamental archetypes (simple series, series with multiple outputs, parallel composition, negative loop, inhibition of a behavior, and contralateral inhibition), and we consider two ways to couple two archetypes: (i) connecting the output(s) of the first archetype to the input(s) of the second archetype and (ii) nesting the first archetype within the second one. We report and compare two key approaches to the formal modeling and verification of the proposed neuronal archetypes and some selected couplings. The first approach exploits the synchronous programming language Lustre to encode archetypes and their couplings, and to express properties concerning their dynamic behavior. These properties are verified thanks to the use of model checkers. The second approach relies on a theorem prover, the Coq Proof Assistant, to prove dynamic properties of neurons and archetypes.     

Encoding Information on the Excited State of a Molecular Spin Chain

The quantum states of nano-objects can drive electrical transport properties across lateral and local-probe junctions. This raises the prospect, in a solid-state device, of electrically encoding information at the quantum level using spin-flip excitations between electron spins. However, this electronic state has no defined magnetic orientation and is short-lived. Using a novel vertical nanojunction process, these limitations are overcome and this steady-state capability is experimentally demonstrated in solid-state spintronic devices. The excited quantum state of a spin chain formed by Co phthalocyanine molecules coupled to a ferromagnetic electrode constitutes a distinct magnetic unit endowed with a coercive field. This generates a specific steady-state magnetoresistance trace that is tied to the spin-flip conductance channel, and is opposite in sign to the ground state magnetoresistance term, as expected from spin excitation transition rules. The experimental 5.9 meV thermal energy barrier between the ground and excited spin states is confirmed by density functional theory, in line with macrospin phenomenological modeling of magnetotransport results. This low-voltage control over a spin chain's quantum state and spintronic contribution lay a path for transmitting spin wave-encoded information across molecular layers in devices. It should also stimulate quantum prospects for the antiferromagnetic spintronics and oxides electronics communities.     

Claramines: A New Class Of Broad‐Spectrum Antimicrobial Agents With Bimodal Activity

The emergence of multidrug‐resistant bacteria and pathogens has created an urgent need for the development of new antibiotics. Herein we report our investigations into the broad‐spectrum activity of an easily prepared water‐soluble polyaminosterol compound, namely claramine A1, against both drug‐sensitive and drug‐resistant Gram‐negative and Gram‐positive bacterial strains. We also report its peculiar mechanism of action, which differs from that of all the other well‐known classes of antibiotics, toward Gram‐negative and Gram‐positive bacteria. Given their low cytotoxicity, this class of compounds based on claramine A1 could constitute an effective response to combat the emergence of multidrug‐resistant bacteria and nosocomial diseases.     

Imaging of P-glycoprotein of H69/VP small-cell lung cancer lines by scanning near-field optical microscopy and confocal laser microspectrofluorometer

Chemoresistance remains the major obstacle to successful therapy of the lung cancer. The multi-drug resistance (MDR) is generally associated with altered expression of drug transporter proteins, such as P-glycoprotein (P-gp). So the distribution of P-gp on the membrane is of great importance to further study the interaction between drug and P-gp. In the present work, the P-gp of the H69/VP small-lung cancer cells was detected using monoclonal antibody UIC2. A secondary goat-anti mouse antibody coupled with biotin was used. The fluorescence emission was detected from a streptavidin-Texas Red. Results were investigated by a homemade scanning near-field optical microscope (SNOM) coupled to a confocal laser microspectrofluorometer (CLMF). Topographical images and localized spectra were obtained at the level of one cell membrane. It was found that the distribution of P-gp is not homogeneous and this observation is basically in accord with the fluorescent images obtained by classical microscopy. The distribution of P-gp would be localized in a higher region on a cell surface. This methodology would also enhance our understanding of MDR under physiological conditions.     

MIL-53 and its Isoreticular Analogues: a Review of the Chemistry and Structure of a Prototypical Flexible Metal-Organic Framework

We present a review of the structural chemistry of metal-organic framework materials with the MIL-53 type structure. This family of materials is well-known for its structural flexibility, and also the wide variety of metal cations and functional ligands that can be included. This gives rise to a set of multivariate materials and isoreticular analogues, to which isoreticular functionalisation can also be applied. Starting from the parent structure, containing infinite chains of octahedral trivalent metal cations cross-linked by benzene-1,4-dicarboxylate, we illustrate the compositional variety possible: this includes materials that contain tetravalent and divalent cations, mixtures of metal cations, functionalised ligands, expanded structures from extended linkers and inclusion of pendant ligands. We emphasise the crystal chemistry of this group of materials, but will give some examples of properties, particularly those associated with the structural breathing effect of relevance to molecular sieving, and also discuss emerging practical applications.     

Cover Image,Volume 92, Issue 9

The cover image, by José Antonio Díaz et al., is based on the Research Article Kinetic modelling of the glycerol oxidation in the liquid phase: comparison of Pt, Au and Ag AS active phases, DOI: 10.1002/jctb.5296 . Photo Credit: CNRS Photothèque / Cyril FRESILLON.