Dynamical Study of Adsorbate-Induced Restructuring Kinetics in Bimetallic Catalysts Using the PdAu(111) Model System.

Dynamic restructuring of bimetallic catalysts plays a crucial role in their catalytic activity and selectivity. In particular, catalyst pretreatment with species such as carbon monoxide and oxygen has been shown to be an effective strategy for tuning the surface composition and morphology. Mechanistic and kinetic understanding of such restructuring is fundamental to the chemistry and engineering of surface active sites but has remained challenging due to the large structural, chemical, and temporal degrees of freedom. Here, we combine time-resolved temperature-programmed infrared reflection absorption spectroscopy, ab initio thermodynamics, and machine-learning molecular dynamics to uncover previously unidentified timescale and kinetic parameters of in situ restructuring in Pd/Au(111), a highly relevant model system for dilute Pd-in-Au nanoparticle catalysts. The key innovation lies in utilizing CO not only as a chemically sensitive probe of surface Pd but also as an agent that induces restructuring of the surface. Upon annealing in vacuum, as-deposited Pd islands became encapsulated by Au and partially dissolved into the subsurface, leaving behind isolated Pd monomers on the surface. Subsequent exposure to 0.1 mbar CO enabled Pd monomers to repopulate the surface up to 373 K, above which complete Pd dissolution occurred by 473 K, with apparent activation energies of 0.14 and 0.48 eV, respectively. These restructuring processes occurred over the span of ∼1000 s at a given temperature. Such a minute-timescale dynamics not only elucidates the fluxional nature of alloy catalysts but also presents an opportunity to fine-tune the surface under moderate temperature and pressure conditions.

Modeling of Twin Screw Extrusion of Polymeric Materials.

An issue of modeling of twin-screw extrusion of polymeric materials is reviewed. The paper is written in honor of Prof. James L. White who was a pioneer in studying this issue. A global approach to process modeling is presented which includes solid polymer transport, polymer plasticating, and the flow of molten polymer. The methodology of CFD modeling of twin-screw extrusion is presented as well as the examples of this modeling which show the details of the process. Optimization and scaling of twin-screw extrusion are also covered. And finally, the future prospects of developments and research of twin screw extrusion is discussed.

Rheological Basics for Modeling of Extrusion Process of Wood Polymer Composites.

Wood polymer composites are materials with pseudoplastic and viscoelastic properties. They have yield stress and exhibit slip during flow. Studies on extrusion and rheology, as well as on process modeling of these highly filled materials are limited. Extensive rheological and extrusion modeling studies on the wood polymer composite based on the polypropylene matrix were performed. Viscous and slip flow properties were determined (with Rabinowitsch, Bagley, and Mooney corrections) at broad (extrusion) range of shear rate and temperature, using a high-pressure capillary rheometer. Rheological models of Klein and power-law were used for flow modeling, and Navier model was applied for slip modeling. A novel global computer model of WPC extrusion with slip effects has been developed, and process simulations were performed to compute the extrusion parameters (throughput, power consumption, pressure, temperature, etc.), and to study the effect of the material rheological characteristics on the process flow. Simulations were validated experimentally, and were discussed with respect to both rheological and process modeling aspects. It was concluded that the location of the operating point of extrusion process, which defines the thermo-mechanical process conditions, is fundamentally dependent on the rheological materials characteristics, including slip effects.

Growth and Atomic-Scale Characterization of Ultrathin Silica and Germania Films: The Crucial Role of the Metal Support.

The present review reports on the preparation and atomic-scale characterization of the thinnest possible films of the glass-forming materials silica and germania. To this end state-of-the-art surface science techniques, in particular scanning probe microscopy, and density functional theory calculations have been employed. The investigated films range from monolayer to bilayer coverage where both, the crystalline and the amorphous films, contain characteristic XO4 (X=Si,Ge) building blocks. A side-by-side comparison of silica and germania monolayer, zigzag phase and bilayer films supported on Mo(112), Ru(0001), Pt(111), and Au(111) leads to a more general comprehension of the network structure of glass former materials. This allows us to understand the crucial role of the metal support for the pathway from crystalline to amorphous ultrathin film growth.

Fundamentals of Global Modeling for Polymer Extrusion.

A review paper is presented on modeling for polymer extrusion for both single screw and twin-screw extrusion. An issue of global modeling is discussed, which includes modeling for solid conveying, melting, melt flow, and co-operation of the screw/die system. The classical approach to global modeling of the extrusion process, which is based on separate models for each section of the screw, i.e., solid transport section, melting and pre-melting sections, and the melt flow section is presented. In this case, the global model consists of the elementary models. A novel continuous concept of global modeling based on CFD (Computational Fluids Dynamics) computations is also presented, and a concept of using the DEM (Discrete Element Method) computation coupled with CFD computations is discussed.

From Crystalline to Amorphous Germania Bilayer Films at the Atomic Scale: Preparation and Characterization.

A new two-dimensional (2D) germanium dioxide film has been prepared. The film consists of interconnected germania tetrahedral units forming a bilayer structure, weakly coupled to the supporting Pt(111) metal-substrate. Density functional theory calculations predict a stable structure of 558-membered rings for germania films, while for silica films 6-membered rings are preferred. By varying the preparation conditions the degree of order in the germania films is tuned. Crystalline, intermediate ordered and purely amorphous film structures are resolved by analysing scanning tunnelling microscopy images.

A Two-Dimensional 'Zigzag' Silica Polymorph on a Metal Support.

We present a new polymorph of the two-dimensional (2D) silica film with a characteristic 'zigzag' line structure and a rectangular unit cell which forms on a Ru(0001) metal substrate. This new silica polymorph may allow for important insights into growth modes and transformations of 2D silica films as a model system for the study of glass transitions. Based on scanning tunneling microscopy, low energy electron diffraction, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy measurements on the one hand, and density functional theory calculations on the other, a structural model for the 'zigzag' polymorph is proposed. In comparison to established monolayer and bilayer silica, this 'zigzag' structure system has intermediate characteristics in terms of coupling to the substrate and stoichiometry. The silica 'zigzag' phase is transformed upon reoxidation at higher annealing temperature into a SiO2 silica bilayer film which is chemically decoupled from the substrate.

Computer Modeling for Single-Screw Extrusion of Wood⁻Plastic Composites.

Experimental and theoretical studies have been performed on the single-screw extrusion of wood⁻plastics composites. Experimental research has been carried out on the flow and melting of polypropylene (PP)-based composites with different wood flour (WF) content in the single-screw extruder. Based on these experimental observations, elementary models of the process phenomena have been proposed and a global model of the process has been developed. This global computer model includes the models of solid conveying, melting dependent on the wood flour content, melt flow in the screw, and melt flow in the die. 3-D non-Newtonian finite element method (FEM) screw pumping characteristics have been applied to model the melt flow in the metering section of the screw. The model predicts the extrusion output, pressure and temperature profiles, melting profile, and power consumption. The model has been validated experimentally. An effect of material slip on the extruder operation has been discussed including both slipping in the screw/barrel surfaces and in the extruding die.

[Patient with sudden cardiac arrest, peripartum cardiomyopathy and pulmonary embolism]. / Nagle zatrzymanie krazenia u pacjentki z kardiomiopatia okoloporodowa i zatorowoscia plucna

Peripartum cardiomyopathy is a type of dilatated cardiomyopathy, occuring with symptoms of heart failure (HF) during last month of pregnancy or within 5 months after labour. Authors are presenting the case of patient admitted to hospital primary with diagnosis of non-high risk pulmonary embolism 6 weeks after delivery, who developed episode of sudden cardiac death followed by symptoms of cardiogenic shock. Peripartum cardiomyopathy was additionally diagnosed. After HF treatment with bromocriptine supply, gradual clinical improvement was achieved. The patient was discharged after 15 days of hospitalisation with diagnosis of peripartum cardiomyopathy with non-high risk pulmonary embolism.

Evaluation of the relations between the presence of the metabolic syndrome and the degree of visceral obesity and the severity of coronary artery disease by coronary angiography.

BACKGROUND: The prevalence of the metabolic syndrome (MetSy) steadily increases worldwide. AIM: To evaluate the relation between the presence of MetSy and visceral obesity and the presence of coronary lesions, and to assess correlations between waist circumference and body mass index (BMI) and coronary lesions. METHODS: We studied 105 patients who underwent elective coronary angiography. The study population was divided into four groups depending on the presence of MetSy and visceral obesity. Coronary angiographic evaluation was performed by an invasive cardiologist. For ultimate objective evaluation of the degree of coronary stenoses, quantitative coronary angiography was performed. Based upon coronary angiography results, patients were divided into four groups depending on the severity of coronary artery disease (CAD): with no coronary lesions, with haemodynamically insignificant lesions (1-69% stenosis), with haemodynamically significant lesions (> 70%) in 1 or 2 vessels, and with multivessel disease (> 70% stenoses in 3 vessels or a > 50% stenosis in the left main coronary artery). RESULTS: Normal coronary arteries were significantly more commonly found in patients without obesity and MetSy (50% of patients). Haemodynamically significant lesions were most frequently found among obese patients with MetSy (40% of patients) and among obese patients without MetSy (38.1% of patients). Concomitant presence of obesity among patients with MetSy (i.e., MetSy with obesity as compared to MetSy without obesity) was not found to be significantly related to the severity of CAD. In addition, advanced CAD was significantly more frequent in obese patients with MetSy compared to the other groups. Isolated visceral obesity in patients without MetSy (i.e., obese patients without MetSy as compared to non-obese patients without MetSy) was found to correlate with haemodynamically significant coronary lesions. When we evaluated nonparametric correlations between waist circumference, BMI; and the severity of CAD, BMI did not correlate with coronary lesions (r = 0.08, p = 0.37). In contrast, a significant correlation was found between waist circumference and the severity of CAD (r = 0.55, p < 0.001). Haemodynamically significant lesions were more significantly more frequent in patients with MetSy compared to patients without MetSy (76% vs. 24%, p < 0.001). Haemodynamically significant lesions were found in 67.7% of patients with isolated visceral obesity compared to 23.2% of non-obese patients without MetSy. In multivariate analysis, CAD was significantly more likely among patients with MetSy regardless of the analysed model (OR 5.3, 95% CI 1.1-25.8, p < 0.05). CONCLUSIONS: 1. The presence of MetSy significantly correlates with haemodynamically significant coronary lesions. 2. The degree of visceral obesity significantly correlates with the severity of CAD. 3. BMI does not correlate with the severity of CAD. 4. Isolated visceral obesity is a weaker determinant of haemodynamically significant coronary lesions compared to MetSy with associated obesity. 5. MetSy is associated with significantly more advanced coronary lesions, i.e. multivessel disease.

[Pulmonary embolism suspicion in a young female patient with the Paget-von Schrötter syndrome]. / Podejrzenie zatorowosci plucnej u mlodej kobiety z zespolem Pageta i Schröttera.

Deep upper limbs veins thrombosis is a relatively rare condition in comparison to the lower limbs thrombosis. Most commonly occurs as a complication of major veins catheterisation. It may also be caused by stenosis of axillar or subclavian veins due to neoplastic infiltration, enlarged lymph nodes or congenital thrombophilia. The Paget-von Schrötter syndrome caused by exercise-induced thrombosis described in this case report is very infrequent.

[From chest pain to cardioverter-defibrillator implantation--a case report]. / Od bólu za mostkiem do wszczepienia kardiowertera-defibrylatora - opis przypadku.

A case of a 48-year-old male admitted to the hospital because of recurrent chest pain, is described. Further diagnostic tests did not confirm ischemia, but revealed the presence of arrhythmogenic right ventricular cardiomyopathy. During hospital stay, the patient developed syncopal episode due to ventricular tachycardia. A cardioverter-defibrillator was implanted.