Exponential stabilization for a class of hybrid systems with mixed delays in state and control

This paper proposes a switching design for the exponential stabilization problem of hybrid systems with mixed time-delays in both the state and control. By using an improved Lyapunov–Krasovskii functional, a memoryless switching controller for the exponential stabilization of the system is designed in terms of linear matrix inequalities. The approach also allows us to compute simultaneously the two bounds that characterize the exponential stability rate of the solution.     

Material force method: theoretical and numerical aspects in nonlinear electro-elastostatics

Formulations of the spatial and material motion problem in nonlinear electroelastostatics are considered in this work by a virtual work approach. Based on these formulations, a finite element discretization is realized and a numerical example is presented to demonstrate possible uses of the material force method in studying the closing process of cracks. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Pressure effects on the thermodynamic and mechanical properties of zinc-blende ZnTe compound

In this paper, the moment method in statistical mechanics has been employed to study the pressure effects on thermodynamic and mechanical properties of zinc-blende zinc telluride using many-body potential. We have derived the analytical expressions of the pressure-dependent lattice parameter, volume compression as well as mean-square displacement of zinc-blende type compound. Numerical calculations performed for ZnTe compound up to 12 GPa are found to be in good and reasonable agreement with available experimental data as well as with previous theoretical studies. These results have been used to evaluate the bulk modulus and its first pressure derivative of ZnTe. The present moment method has taken into account the quantum zero-point vibrations at low temperature and the higher-order anharmonic terms in the atomic displacements. This research shows the advantage of moment method on extensively studying thermo-mechanical properties of materials under high pressures.     

Er3+/Yb3+-activated silica-hafnia planar waveguides for photonics fabricated by rf-sputtering

95.8SiO₂–4.2HfO₂ planar waveguide activated by 0.2 mol% Er and 0.2 mol% Yb was fabricated by multi-target rf-sputtering technique. The optical parameters were measured by an m-line apparatus operating at 543.5, 632.8, 1319 and 1542 nm. The waveguide compositions were investigated by energy dispersive spectroscopy. The waveguide exhibits a single propagation mode at 1.3 and 1.5 μm with an attenuation coefficient of 0.2 dB/cm at 1.5 μm. The emission of ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ ion, with a 42 nm bandwidth was observed upon TE₀ mode excitation at 980 and 514.5 nm. Photoluminescence excitation spectroscopy was used to obtain information about the effective excitation efficiency of Er³⁺ ions by co-doping with Yb³⁺ ions. Channel waveguide in rib configuration were fabricated by wet etching process in the active film.     

Rayleigh waves in an isotropic elastic half-space coated by a thin isotropic elastic layer with smooth contact

In the present paper, we are interested in the propagation of Rayleigh waves in an isotropic elastic half-space coated with a thin isotropic elastic layer. The contact between the layer and the half space is assumed to be smooth. The main purpose of the paper is to establish an approximate secular equation of the wave. By using the effective boundary condition method, an approximate, yet highly accurate secular equation of fourth-order in terms of the dimensionless thickness of the layer is derived. From the secular equation obtained, an approximate formula of third-order for the velocity of Rayleigh waves is established. The approximate secular equation and the formula for the velocity obtained in this paper are potentially useful in many practical applications.     

Periodic Motions of Stokes and Navier–Stokes Flows Around a Rotating Obstacle

We prove the existence and uniqueness of periodic motions to Stokes and Navier–Stokes flows around a rotating obstacle \({D \subset \mathbb{R}^3}\) with the complement \({\Omega = \mathbb{R}^3 \backslash D}\) being an exterior domain. In our strategy, we show the C _b -regularity in time for the mild solutions to linearized equations in the Lorentz space \({L^{3,\infty}(\Omega)}\) (known as weak-L ³ spaces) and prove a Massera-typed Theorem on the existence and uniqueness of periodic mild solutions to the linearized equations in weak-L ³ spaces. We then use the obtained results for such equations and the fixed point argument to prove such results for Navier–Stokes equations around a rotating obstacle. We also show the stability of such periodic solutions.     

Degradable conjugates from oxanorbornadiene reagents

Oxanorbornadienedicarboxylate (OND) reagents were explored for purposes of binding and releasing drugs from serum albumins as representative macromolecular carriers. Being highly reactive Michael acceptors, ONDs form adducts with thiols and amines, which then undergo retro-Diels-Alder fragmentation. A study of more than 30 model adducts revealed a number of modifications that can be used to influence adduct stability. For the most reactive OND linkers, the labeling of the single available bovine serum albumin (BSA) cysteine residue was complete within minutes at a mid-micromolar concentration of reactants. While a selectivity of greater than 1000-fold for thiol over amine was observed with model amino acids, the labeling of protein amines with ONDs is fast enough to be practical, as demonstrated by the reaction with thiol-depleted BSA. The OND-amine adducts were found to be up to 15 times more stable than OND-thiol adducts, and to be sensitive to acid by virtue of a stereochemically dependent acceleration of cycloreversion. The release rate of fluorescent cargo from serum albumins was tuned by selecting the coupling partners: the available half-lives ranged from 40 min to 7 days at 37 °C. Such versatility of release profiles from protein carriers, controlled by the nature of the OND linkage, is a useful addition to the drug delivery toolbox.     

Structural role of counterions adsorbed on self-assembled peptide nanotubes

Among noncovalent forces, electrostatic ones are the strongest and possess a rather long-range action. For these reasons, charges and counterions play a prominent role in self-assembly processes in water and therefore in many biological systems. However, the complexity of the biological media often hinders a detailed understanding of all the electrostatic-related events. In this context, we have studied the role of charges and counterions in the self-assembly of lanreotide, a cationic octapeptide. This peptide spontaneously forms monodisperse nanotubes (NTs) above a critical concentration when solubilized in pure water. Free from any screening buffer, we assessed the interactions between the different peptide oligomers and counterions in solutions, above and below the critical assembly concentration. Our results provide explanations for the selection of a dimeric building block instead of a monomeric one. Indeed, the apparent charge of the dimers is lower than that of the monomers because of strong chemisorption. This phenomenon has two consequences: (i) the dimer-dimer interaction is less repulsive than the monomer-monomer one and (ii) the lowered charge of the dimeric building block weakens the electrostatic repulsion from the positively charged NT walls. Moreover, additional counterion condensation (physisorption) occurs on the NT wall. We furthermore show that the counterions interacting with the NTs play a structural role as they tune the NTs diameter. We demonstrate by a simple model that counterions adsorption sites located on the inner face of the NT walls are responsible for this size control.     

Folding pentapeptides into left and right handed alpha helices

Left or right handed alpha helicity can be induced in a pentapeptide (ANGYG) by appending left or right handed helical cycles as chiral templates. This sequence corresponds to a rare left handed helix found in the protein alanine racemase. Circular dichroism spectra reveal that pentapeptide ANGYG has no detectable structure in aq phosphate buffer, that it is an ambidextrous peptide in that it can be directed to fold into either a left handed or right handed alpha helix in water, with greater propensity for the uncommon left handed than the normal right handed conformation. A helix-inducing cyclic peptide at both ends of this peptide was more effective at inducing alpha helicity than a single cyclic peptide at one end. The alpha helical cyclic peptides provide novel tools for folding short peptides into thermodynamically unstable helices in water, and for studying factors that control chirality and helix induction.     

Geometric rigidity for analytic estimates of Müller–?verák

In the paper Müller–?verák (J Differ Geom 42(2):229–258, 1995) conformally immersed surfaces with finite total curvature were studied. In particular it was shown that surfaces with total curvature ${\int_{\Sigma} |A|^2 < 8 \pi}$ in dimension three were embedded and conformal to the plane with one end. Here, using techniques from Kuwert–Li (W ^2,2-conformal immersions of a closed Riemann surface into R ⁿ . arXiv:1007.3967v2 [math.DG], 2010), we will show that if the total curvature ${ \int_{\Sigma}|A|^2\leq8\pi}$ , then we are either embedded and conformal to the plane, isometric to a catenoid or isometric to Enneper’s minimal surface. In fact the technique of our proof shows that if we are conformal to the plane, then if n?≥ 3 and ${ \int_{\Sigma} | A|^{2}\leq 16 \pi }$ then Σ is embedded or Σ is the image of a generalized catenoid inverted at a point on the catenoid. In order to prove these theorems, we prove a Gauss–Bonnet theorem for surfaces with complete ends and isolated finite area singularities which extends a theorem of Jorge-Meeks (Topology 22(2):203–221, 1983). Using this theorem, we then prove an inversion formula for the Willmore energy.