Thermal nonlinear effects in hybrid silica/polymer microdisks

The linear and thermal nonlinear spectral responses of silica and hybrid silica/polymer microdisk resonators are investigated. Both types of resonators can be fabricated using the same technological procedure with only slight modification. An extra polymer layer results in opposite sign of the nonlinear thermal optical response of the hybrid microdisks compared to the pure silica ones, which can be explained by the different thermorefractive coefficients of silica and polymer. A full compensation of eigen frequency shift, caused by thermal nonlinearity, has been demonstrated experimentally.     

Robust optimization – methodology and applications

Robust Optimization (RO) is a modeling methodology, combined with computational tools, to process optimization problems in which the data are uncertain and is only known to belong to some uncertainty set. The paper surveys the main results of RO as applied to uncertain linear, conic quadratic and semidefinite programming. For these cases, computationally tractable robust counterparts of uncertain problems are explicitly obtained, or good approximations of these counterparts are proposed, making RO a useful tool for real-world applications. We discuss some of these applications, specifically: antenna design, truss topology design and stability analysis/synthesis in uncertain dynamic systems. We also describe a case study of 90 LPs from the NETLIB collection. The study reveals that the feasibility properties of the usual solutions of real world LPs can be severely affected by small perturbations of the data and that the RO methodology can be successfully used to overcome this phenomenon. Received: May 24, 2000 / Accepted: September 12, 2001?Published online February 14, 2002     

Difluoro complexes of platinum(II) and -(IV) with monodentate phosphine ligands: an exceptional stability of d6 octahedral organometallic fluorides

Complexes (R3P)2PtF2 were prepared by reaction of the corresponding diiodo precursors with AgF in dichloromethane. The intermediate formation of trans- and cis-(R3P)2Pt(I)F was also observed. All fluoro complexes demonstrate a strong preference for the cis-configuration (R = Ph or Et) unless a bulky phosphine ligand is used (R = i-Pr), in which case the trans complex was observed. The Pt(IV) difluoro compounds (R3P)2Ar2PtF2 were obtained by reacting the Pt(II) diaryl precursors with XeF2. The fluoro ligands are located in the trans-position relative to the aryl groups in the overall octahedral environment. The representative Pt(II) and Pt(IV) difluoro complexes were characterized by X-ray crystallography. All fluoro compounds react rapidly with chlorotrimethylsilane to give the corresponding chloro complexes. The Pt(IV) difluorides are remarkably stable in the C-C reductive elimination reaction, relative to their dichloro analogs which reductively eliminate diaryl within several hours at 45 degrees C in N-methylpyrrolidone. It was found that phosphine dissociation from the octahedral Pt(IV) complex is essential for the reductive elimination reaction to take place, the difluoro complex being kinetically stable even at 60 degrees C.     

Determination of coagulation coefficients and aggregation kinetics for charged aerosols

A new method has been developed which allows determination of the coagulation coefficient of two oppositely charged particles experimentally. For this purpose, quasi-monodisperse particles of different sizes and morphology were used to study the influence of different parameters on the coagulation coefficient. A good agreement between experimental results and the classic Fuchs' theory was obtained when including a method accounting for particle nonsphericity. In experiments with polydisperse bipolarly charged aerosols, no principal differences to uncharged aerosols were found when a dimensionless representation was used. Changes in particle number concentration and geometric mean diameter can be described by simple empirical expressions.     

Transformations of chloroethylenes in the presence of aprotonic acids

The cationic polymerization of vinyl chloride, vinylidene chloride, and cis- and trans- 1,2-dichloroethylenes with the use of Lewis acid-type catalysts has been studied. Vinylidene chloride is smoothly polymerized in the presence of ZnCl₂ at 40°C to form the dimer, 1,1,3,3-tetrachlorobutene-1, and poly(vinylidene chloride) having somewhat increased crystallinity (45%). Vinyl chloride is polymerized very slowly in the presence of AlCl₃ and TiCl₄ to give dimeric, trimeric, tetrameric, and low molecular weight polymer products. The polymerization is followed by carbonium ion isomerization that leads to reaction products of branched structure. The cis- and trans-1,2-dichloroethylenes react in the presence of AlCl₃ only at 50–60°C, and their polymerization is terminated at the stage of dimer and cyclic trimer formation. A mechanism of carbonium ion-initiated polymerization of chloroethylenes is proposed, and the causes which lead to early termination of polymerization are discussed.     

Fiber‐reinforced composite hydrogels for bioadhesive and sealant applications

The use of bioadhesives and sealants for wound closure and healing applications is becoming more and more popular, particularly when other techniques, such as stapling or suturing, are impractical or inefficient. Loading adhesives with fibers has tremendous potential for improving their mechanical properties. The concept of fiber‐reinforced bioadhesives and sealants is novel and has not been investigated to date. In the present study, natural cellulose fibers were selected for enhancement of bioadhesive properties. A bioadhesive formulation based on a combination of gelatin and alginate crosslinked with water‐soluble carbodiimide was used as a generic formulation for this study, on the basis of our previous studies. The polymeric matrix and the cellulose fibers showed high affinity, which resulted in a dramatic increase in the viscosity and in the burst strength. They moderately affected the curing time, swelling, and weight loss. A mixed response was found in the compression modulus and the bonding strength in lap shear. We demonstrated that fiber‐reinforced bioadhesives have a great potential for surgical sealant applications because of improvement in the cohesive strength of the composite hydrogel. This study presents proof of the concept of using fibers for the enhancement of bioadhesive properties as a result of fiber‐reinforcement and may comprise the basis for future studies in this field. Copyright © 2017 John Wiley & Sons, Ltd.     

Robust solutions of Linear Programming problems contaminated with uncertain data

Optimal solutions of Linear Programming problems may become severely infeasible if the nominal data is slightly perturbed. We demonstrate this phenomenon by studying 90 LPs from the well-known NETLIB collection. We then apply the Robust Optimization methodology (Ben-Tal and Nemirovski [1–3]; El Ghaoui et al. [5, 6]) to produce “robust” solutions of the above LPs which are in a sense immuned against uncertainty. Surprisingly, for the NETLIB problems these robust solutions nearly lose nothing in optimality. Received: July 1999 / Accepted: May 2000?Published online July 20, 2000     

On the wave dispersion in microstructured solids

Continuum Mechanics and Thermodynamics - In this paper, elastic wave propagation in a one-dimensional micromorphic medium characterized by two internal variables is investigated. The evolution...