Probing the Coordinative Unsaturation and Local Environment of Ti3+ Sites in an Activated High‐Yield Ziegler–Natta Catalyst

The typical activation of a fourth generation Ziegler–Natta catalyst TiCl₄/MgCl₂/phthalate with triethyl aluminum generates Ti³⁺ centers that are investigated by multi‐frequency continuous wave and pulse EPR methods. Two families of isolated, molecule‐like Ti³⁺ species have been identified. A comparison of the experimentally derived g tensors and ^35,37Cl hyperfine and nuclear‐quadrupole tensors with DFT‐computed values suggests that the dominant EPR‐active Ti³⁺ species is located on MgCl₂(110) surfaces (or equivalent MgCl₂ terminations with tetra‐coordinated Mg). O₂ reactivity tests show that a fraction of these Ti sites is chemically accessible, an important result in view of the search for the true catalyst active site in olefin polymerization.     

An enriched damage-frictional cohesive-zone model incorporating stress multi-axiality

The paper presents an interphase cohesive zone model (CZM) incorporating stress multi-axiality devised to capture, by simplified micro-modeling, the influence of the in-plane strain and stress state in the mechanical response of the CZM. Moreover, the model is able to account for the Poisson-related effect in the interphase, which can play an important role in the modeling of heterogeneous masonry elements. From the constitutive point of view, the proposed formulation couples damage and friction by addressing a smooth transition from a quasi-brittle response to a residual frictional behavior described by a Coulomb law with unilateral contact. As in-plane stresses are accounted for, damage activation and evolution are governed by a Drucker–Prager law with linear softening. A predictor-corrector procedure based on a backward Euler scheme is detailed for integrating the nonlinear evolutive problem together with the related tangent operator which consistently linearizes the algorithmic strategy. This framework is embedded into a kinematically-enriched finite element interphase formulation incorporating stress multi-axiality. The modeling features of the resulting numerical tool are tested both at the local level, for the typical interphase point, and in meso-structural tests consisting of brick-mortar triplets, investigating the capability of the proposed model and numerical procedure to simulate the brick-mortar decohesion mechanism during confined slip tests.     

Quantification of micafungin in human plasma by liquid chromatography-tandem mass spectrometry

Micafungin (MCF) is an antifungal agent of the echinocandin class approved in Europe both in adults and in children for the treatment of invasive candidiasis. Few analytical methods for therapeutic drug monitoring (TDM) of this drug have been described so far. In this paper, we describe a rapid and validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for the measurement of MCF in plasma. MCF was analyzed in 100-μL plasma samples over a wide range of concentrations (0.1–20 μg/mL) by LC-MS/MS after protein precipitation. The suitability of the assay for TDM was evaluated by using plasma samples from pediatric patients who received MCF for the treatment of invasive candidiasis. The overall turnaround time for the assay was 20 min. The lower limit of quantification of the method was 0.1 ng/mL. No ion suppression due to matrix effects was found with different pre-analytical conditions, such as hemolysis, lipemia, and hyperuricemia. A simple and rapid LC-MS/MS method which provides high specificity, precision, and accuracy for quantification of MCF in plasma has been developed and validated.     

Tracking error: a multistage portfolio model

We study multistage tracking error problems. Different tracking error measures, commonly used in static models, are discussed as well as some problems which arise when we move from static to dynamic models. We are interested in dynamically replicating a benchmark using only a small subset of assets, considering transaction costs due to rebalancing and introducing a liquidity component in the portfolio. We formulate and solve a multistage tracking error model in a stochastic programming framework. We numerically test our model by dynamically replicating the MSCI Euro index. We consider an increasing number of scenarios and assets and show the superior performance of the dynamically optimized tracking portfolio over static strategies.     

Fractal fluctuations and quantum-like chaos in the brain by analysis of variability of brain waves: A new method based on a fractal variance function and random matrix theory: A link with El Naschie fractal Cantorian space–time and V. Weiss and H. Weiss golden ratio in brain

We develop a new method for analysis of fundamental brain waves as recorded by the EEG. To this purpose we introduce a Fractal Variance Function that is based on the calculation of the variogram. The method is completed by using Random Matrix Theory. Some examples are given. We also discuss the link of such formulation with H. Weiss and V. Weiss golden ratio found in the brain, and with El Naschie fractal Cantorian space–time theory.     

Phase modulation and ellipticity of the light transmitted through a smectic C* layer with short helix pitch

A chiral ferroelectric smectic C* liquid crystal (FLC) with the helix pitch p ₀?=?330 nm was developed to avoid any scattering of visible light when the helix is not unwound over a certain limit. Planar cells with different FLC layer thickness (16 and 44 μm) have been assembled with helix axis parallel to the glass plates and aligned along the rubbing direction. The ellipticity of the light passing through the cells vs. the electric field was investigated, and a method for evaluating the electrically controlled birefringence via ellipticity measurements has been established. We have found that the FLC cell is an optical retardation layer driven by the electric field, the effective birefringence being proportional to the square electric field. The physical origin of the electrically controlled phase shift of the light passing through the FLC layer has been analysed.     

Forbidden periodic Fréedericksz transition: An example

Summary A single domain nematic liquid crystal undergoes first- or second-order transitions when placed in an external field (Fréedericksz transition). A new type of transition, giving rise to a periodic distortion of the mean molecular direction, within particular ranges of the elastic-constant ratio, has been recently studied. In this paper we show that, in a particular situation involving an electric and a magnetic field, both perpendicular to the director, and nonsymmetric boundary conditions, the periodic Fréedericksz transition is forbidden for any value of the elastic-constant ratio.

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Riassunto Un cristallo liquido nematico orientato in modo uniforme subisce una transizione orientazionale del primo o del secondo ordine quando è sottoposto ad un campo esterno (transizione di Fréedericksz). Recentemente è stato studiato un nuovo tipo di transizione che, per particolari valori del rapporto delle costanti elastiche, consiste in una distorsione periodica della direzione molecolare media. In questo lavoro si mostra che quando sono presenti due campi, elettrico e magnetico, incrociati e perpendicolari all’orientazione indisturbata del nematico, e le condizioni al contorno non sono simmetriche (ancoraggio forte/debole), non si ha piú transizione periodica di Freédericksz, per qualunque valore del rapporto tra le costanti elastiche.

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Резюме Однодоменный нематический жидкий кристалл претерпевает переходы первого или второго порядка во внешнем поле (переход Фрпдерикса). Недавно был исследован новый тип перехода, вызывающий периодическую дисторсию среднего молекулярного направления в некоторых областях отношения упругих постоянных. В этой системе мы показываем, что для определен электрических и магнитных полей, перпендикулярных директоры, и несимметричных граничных условий периодический переход Фридерикса оказывается запрещенным для любых значений отношения упругих постоянных.