Search results for " polymers"

An investigation of photo- and pressure-induced effects in a pair of isostructural two-dimensional spin-crossover framework materials

2014

International audience; Two new isostructural iron(II) spin-crossover (SCO) framework (SCOF) materials of the type [Fe(dpms)2 (NCX)2 ] (dpms=4,4'-dipyridylmethyl sulfide; X=S (SCOF-6(S)), X=Se (SCOF-6(Se))) have been synthesized. The 2D framework materials consist of undulating and interpenetrated rhomboid (4,4) nets. SCOF-6(S) displays an incomplete SCO transition with only approximately 30 % conversion of high-spin (HS) to low-spin iron(II) sites over the temperature range 300-4 K (T1/2 =75 K). In contrast, the NCSe(-) analogue, SCOF-6(Se), displays a complete SCO transition (T1/2 =135 K). Photomagnetic characterizations reveal quantitative light- induced excited spin-state trapping (LIES…

Superiority of Optimized Portfolios to Naive Diversification: Fact or Fiction?

2017

Abstract DeMiguel, Garlappi, and Uppal (2009) conducted a highly influential study where they demonstrated that none of the optimized portfolios consistently outperformed the naive diversification. This result triggered a heated debate within the academic community on whether portfolio optimization adds value. Nowadays several studies claim to defend the value of portfolio optimization. The commonality in all these studies is that various portfolio optimization methods are implemented using the datasets generously provided by Kenneth French and the performance is measured by means of the Sharpe ratio. This paper aims to provide a cautionary note regarding the use of Kenneth French datasets …

Optimal Dynamic Portfolio Risk Management

2016

Numerous econometric studies report that financial asset volatilities and correlations are time-varying and predictable. Over the past decade, this knowledge has stimulated increasing interest in various dynamic portfolio risk control techniques. The two basic types of risk control techniques are: risk control across assets and risk control over time. At present, the two types of risk control techniques are not implemented simultaneously. There has been surprisingly little theoretical study of optimal dynamic portfolio risk management. In this paper, the author fills this gap in the literature by formulating and solving the multi-period portfolio choice problem. In terms of dynamic portfoli…

Research Regarding the Physical-Mechanical Properties of Knits for Garments – Abrasion Resistance

2017

Abstract During wear, the fabric is subjected to a complex combination of forces acting at various rates, in various intensities, in various directions and for various periods. This is one of the main causes of a fabric and garment becoming unacceptable for further wear. The main goal of this research paper is to improve the physical-mechanical properties of knits for garments by choosing the right fabric structure and raw material. The abrasion resistance is a mechanical deterioration and progressive loss of substance from a fabric, resulting from the fabric rubbing against itself or another surface. Tests was done on weft knitted fabric for garments using cotton, wool and mixed yarns, thr…

Rigid Closed‐Cell PUR Foams Containing Polyols Derived from Renewable Resources: The Effect of Polymer Composition, Foam Density, and Organoclay Fill…

2017

Die lebende anionische Polymerisation

2017

Zusammenfassung Vor sechzig Jahren entdeckte Michael Szwarc die lebende anionische Polymerisation. Trotz ihrer hohen synthetischen Anforderungen ist sie bis heute die praziseste Methode zur Herstellung von wohldefinierten Polymeren und inspirierte zahlreiche neue Polymerisationsmethoden. Masgeschneiderte Blockcopolymere finden sich in den verschiedensten Anwendungen von High-End-Verpackungsmaterialien uber die Elektronik bis hin zu Nanomedizin.

A delamination test for structural wood adhesives used in thick joints

2001

A test method was developed for the measurement of delamination of structural wood adhesives applied in thick joints. Large differences were observed within a range of 8 commercial epoxy-based products.

Theoretical study on the decomposition mechanism of bisphenol A polycarbonate induced by the combined effect of humidity and UV irradiation.

2020

Polycarbonate (PC) is a good material for covering and protecting cultural heritage sites because of its durability, mechanical properties, and transparency. When bisphenol A polycarbonate is subjected to weathering conditions this polymer shows several degradation processes depending on the irradiation wavelength, humidity and temperature. In particular, the combined effects of humidity and UV irradiation speed up the PC molecular weight reduction. In this work, the decomposition mechanisms associated to the hydrolysis process are scrutinized and the effects of UV irradiation on the hydrolysis process are evaluated throughout the Density Functional Theory (DFT) approach. It was found that …

Effect of different concentrations of specific inhibitor of matrix metalloproteinases on the shear bond strength of self-adhesive resin cements to de…

2017

Background Considering the probability of chemical and enzymatic reactions between matrix metalloproteinases (MMPs) in the dentin structure and their specific inhibitors, the aim of the present study was to evaluate the effect of different concentrations of specific inhibitor of MMPs (galardin) on the shear bond strength of self-adhesive resin cements to dentin. Material and Methods Forty-eight sound human premolars were mounted in self-cured acrylic resin after removal of the enamel on the buccal and lingual surfaces. The dentin surfaces achieved were polished and prepared with 600-grit silicon carbide paper. The samples were divided into 3 groups (n=16) based on the concentration of galar…

The effect of bone marrow-derived stem cells associated with platelet-rich plasma on the osseointegration of immediately placed implants

2020

Background Stem cells associated with growth factors have been shown to improve bone healing and the osseointegration of dental implants. A Brazilian miniature pig model was used to evaluate the effect of autologous bone marrow-derived mesenchymal stem cells (BM-MSCs) associated with platelet-rich plasma (PRP) on the osseointegration of immediately placed dental implants. Material and methods A total of four male adult miniature pigs were used in this study. BM-MSCs from each pig were isolated from the iliac crest and expanded in vitro. The undifferentiated BM-MSCs were mixed with autologous PRP and implanted in the post-extraction sockets at the experimental sites before implant placement …