Sliding modes of two interacting frictional interfaces

In the context of rate-and-state friction, we report an extensive analysis of stability of the quasi-static frictional sliding of two parallel interfaces dividing a linear elastic solid sheared at a constant rate. One possibility for the frictional sliding is that the interfaces slip at equal rates, a steady state described as symmetric. However a steady-state friction law that is non-monotonic allows the competing possibility of an asymmetric steady state in which the interfaces slide at different rates. A rate-and-state law that delivers such behaviour and agrees with the experimental results of Heslot et al. [1994. Creep, stick-slip, and dry-friction dynamics: experiments and a heuristic model. Phys. Rev. E 49, 4973-4988] is proposed. Analytical results combined with numerical investigations performed with the continuation package Auto and direct time integration are used to compile the complete picture of the many bifurcations that exist between the diverse steady and oscillatory sliding modes. In addition to the control parameters corresponding to the driving velocity and the stiffness of the medium, we find that the geometrical details of the steady-state friction law determine the occurrence and nature of bifurcations. Pitchfork bifurcations from the symmetric to asymmetric steady states coincide with the extrema of the friction law; Hopf bifurcations occur in the velocity weakening regime of the friction law. Torus and period-doubling bifurcations of periodic orbits also occur, and lead to complicated dynamics. We also present results of numerical computations that illustrate the complex and versatile dynamics of the two-interface system. We anticipate that the dynamics found in our model should be verifiable by experiments.     

Photophysical Properties of Ruthenium(II) Polypyridyl DNA Intercalators: Effects of the Molecular Surroundings Investigated by Theory

The environmental effects on the structural and photophysical properties of [Ru(L)₂(dppz)]²⁺ complexes (L=bpy=2,2′‐bipyridine, phen=1,10‐phenanthroline, tap=1,4,5,8‐tetraazaphenanthrene; dppz=dipyrido[3,3‐a:2′,3′‐c]phenazine), used as DNA intercalators, have been studied by means of DFT, time‐dependent DFT, and quantum mechanics/molecular mechanics calculations. The electronic characteristics of the low‐lying triplet excited states in water, acetonitrile, and DNA have been investigated to decipher the influence of the environment on the luminescent behavior of this class of molecules. The lowest triplet intra‐ligand (IL) excited state calculated at λ≈800 nm for the three complexes and localized on the dppz ligand is not very sensitive to the environment and is available for electron transfer from a guanine nucleobase. Whereas the lowest triplet metal‐to‐ligand charge‐transfer (³MLCT) states remain localized on the ancillary ligand (tap) in [Ru(tap)₂(dppz)]²⁺, regardless of the environment, their character is drastically modified in the other complexes [Ru(phen)₂(dppz)]²⁺ and [Ru(bpy)₂(dppz)]²⁺ upon going from acetonitrile (MLCT_dppz/phen or MLCT_dppz/bpy) to water (MLCT_dppz) and DNA (MLCT_phen and MLCT_bpy). The change in the character of the low‐lying ³MLCT states accompanying nuclear relaxation in the excited state controls the emissive properties of the complexes in water, acetonitrile, and DNA. The light‐switching effect has been rationalized on the basis of environment‐induced control of the electronic density distributed in the lowest triplet excited states.     

Synthesis of protected α-alkyl lanthionine derivatives

Protected α-alkyl lanthionine derivatives were synthesized in five steps starting from a known phenyloxazoline precursor. This approach involved the synthesis of a family of substituted cyclic sulfamidates and their regioselective opening by nucleophilic attack with a protected cysteine. This efficient multistep strategy affords various α-alkylated lanthionine derivatives in high yields.     

Characterisation of electrochemical immunosensor for detection of viable not-culturable forms of <Emphasis Type="Italic">Legionella pneumophila</Emphasis> in water samples

Legionella pneumophila may cause a fatal pneumonia in humans known as Legionnaires’ disease (LD). The strategies of L. pneumophila to adapt to and resist stressful environmental conditions include the ability to enter into a VBNC (viable but not culturable) state. The detection of L. pneumophila in environmental samples benefits from the use of standardised methods: for detection and enumeration following membrane filtration (AFNOR T90-431, ISO 11731) and detection and quantification by polymerase chain reaction PCR (AFNOR T90-471, ISO 12869). Culture is hampered by its inability to detect VBNC forms and PCR is unable to discriminate between live and dead bacteria. The present immunosensor was obtained by the immobilisation of a monoclonal anti-L. pneumophila antibody (MAb) on an indium-tin oxide (ITO) electrode by the self-assembled monolayers (SAMs) method using an aminosilane. The immunosensor was characterised by wettability (contact angle measurement), atomic force microscopy (AFM), confocal laser scanning microscopy (CLSM), and electrochemical impedance spectroscopy (EIS). A limit of detection of 10 bacteria per mL was observed on artificial samples.     

Active Esters as Pseudostoppers for Slippage Synthesis of [2]Pseudorotaxane Building Blocks: A Straightforward Route to Multi‐Interlocked Molecular Machines

The efficient synthesis and very easy isolation of dibenzo[24]crown‐8‐based [2]pseudorotaxane building blocks that contain an active ester motif at the extremity of the encircled molecular axle and an ammonium moiety as a template for the dibenzo[24]crown‐8 is reported. The active ester acts both as a semistopper for the [2]pseudorotaxane species and as an extensible extremity. Among the various investigated active ester moieties, those that allow for the slippage process are given particular focus because this strategy produces fewer side products. Extension of the selected N‐hydroxysuccinimide ester based pseudorotaxane building block by using either a mono‐ or a diamino compound, both containing a triazolium moiety, is also described. These provide a pH‐dependent two‐station [2]rotaxane molecular machine and a palindromic [3]rotaxane molecular machine, respectively. Molecular machinery on both interlocked compounds through variation of pH was studied and characterized by means of NMR spectroscopy.     

Thermal and light-induced spin-crossover in salts of the heptadentate complex [tris(4-{pyrazol-3-yl}-3-aza-3-butenyl)amine]iron(ii)

The syntheses of [FeL][BF(4)](2).H(2)O, [FeL][ClO(4)](2).H(2)O, [FeL][NO(3)](2).CH(3)NO(2) and [FeL][CF(3)SO(3)](2) (L = tris(4-{pyrazol-3-yl}-3-aza-3-butenyl)amine) are described. The isostructural BF(4)(-) and ClO(4)(-) salts are high-spin between 5-300 K, while the other two compounds are high-spin at room temperature but undergo gradual high-->low spin transitions upon cooling. For [FeL][NO(3)](2) this transition is centred at 139 K and proceeds to near-completeness, while for [FeL][CF(3)SO(3)](2) it is centred at 144 K and only proceeds to 50% conversion. The CF(3)SO(3)(-) salt also undergoes spin-crossover centred at 200 K in (CD(3))(2)CO solution, and exhibits dynamic inversion of its helical ligand conformation. All these compounds except the triflate salt have been crystallographically characterised, and show capped trigonal antiprismatic [6 + 1] coordination geometries. The NO(3)(-) and CF(3)SO(3)(-) salts undergo quantitative conversion to trapped, high-spin excited states upon irradiation with a green laser at 10 K (the LIESST effect; LIESST = Light-Induced Excited Spin State Trapping). The thermal stabilities of their LIESST excited states (T(LIESST) = 80-82 K) resemble those found for iron(ii) complexes of bidentate N-heterocyclic ligands. Hence, the LIESST properties of [FeL](2+) are those of a complex of three rigid bidentate domains linked by a flexible spacer, rather than of a single encapsulating podand.     

Guided acoustic wave Brillouin scattering in photonic crystal fibers

We experimentally investigate guided acoustic wave Brillouin scattering in several photonic crystal fibers by use of the so-called fiber loop mirror technique and show a completely different dynamics with respect to standard all-silica fibers. In addition to the suppression of most acoustic phonons, we show that forward Brillouin scattering in photonic crystal fibers is substantially enhanced only for the fundamental acoustic phonon because of efficient transverse acousto-optic field overlap. The results of our numerical simulations reveal that this high-frequency phonon is indeed trapped within the fiber core by the air-hole microstructure, in good agreement with experimental measurements.     

Nanoparticles of [Fe(NH2‐trz)3]Br2⋅3 H2O (NH2‐trz=2‐Amino‐1,2,4‐triazole) Prepared by the Reverse Micelle Technique: Influence of Particle and Coherent Domain Sizes on Spin‐Crossover Properties

By changing the surfactant/water ratio , nanoparticles of the iron(II) spin crossover material, [Fe(NH₂‐trz)₃]Br₂ ? 3 H₂O (with NH₂‐trz=4‐amino‐1,2,4‐triazole), have been synthesised from 1 μm down to 30 nm (see figure). Magnetic and reflectivity experiments indicate that the critical size for observing a thermal hysteresis in this 1D polymer family is around 50 nm, and powder X‐ray diffraction shows that particles of about 30 nm are constituted by about one coherent domain.

     

A simple and effective metaheuristic for the Minimum Latency Problem

The Minimum Latency Problem (MLP) is a variant of the Traveling Salesman Problem which aims to minimize the sum of arrival times at vertices. The problem arises in a number of practical applications such as logistics for relief supply, scheduling and data retrieval in computer networks. This paper introduces a simple metaheuristic for the MLP, based on a greedy randomized approach for solution construction and iterated variable neighborhood descent with random neighborhood ordering for solution improvement. Extensive computational experiments on nine sets of benchmark instances involving up to 1000 customers demonstrate the good performance of the method, which yields solutions of higher quality in less computational time when compared to the current best approaches from the literature. Optimal solutions, known for problems with up to 50 customers, are also systematically obtained in a fraction of seconds.     

Existence and conservation laws for the Boltzmann–Fermi–Dirac equation in a general domain

We prove an existence theorem for the Boltzmann–Fermi–Dirac equation for integrable collision kernels in possibly bounded domains with specular reflection at the boundaries, using the characteristic lines of the free transport. We then obtain that the solution satisfies the local conservations of mass, momentum and kinetic energy thanks to a dispersion technique.