Fließspannung im Bereich der (γ → α)-Umwandlung von kohlenstoffarmen Stählen

Auswertung von Fließkurven aus den Warmflachstauchversuchen und quantitativer Gefügeanalyse. Anomalie auf der Fließspannung-Temperatur-Kurve im (γ → α)-Bereich bei Umformung während der anisothermischen Umwandlung. Bilanz der Einflußfaktoren.     

Supermolecular morphology of polypropylene filled with nanosized silica

The supermolecular morphology of injection‐molded SiO₂/polypropylene (PP) nanocomposites was investigated via thin sections analyzed under polarized light and the systematic development of an appropriate etching technique, which allowed the study of the supermolecular morphologies with light microscopy (LM) and high‐resolution field emission scanning electron microscopy (FESEM). In parallel, information regarding the dispersion, distribution state, and morphology of SiO₂ particles was investigated via transmission electron microscopy (TEM) and scanning electron microscopy (SEM) of the ion‐polished and fractured surfaces of SiO₂‐filled PP. The TEM/SEM results demonstrated an almost homogeneous dispersion and distribution of SiO₂ particle agglomerates in the PP matrix. With polarized transmitting LM, reflecting LM, and FESEM, the spherulitic structure of the nanocomposites could be visualized to obtain information on the nanoparticle influence on the crystallization and structural behavior. The size and size distribution of the spherulites analyzed with transmitting light (thin sections) and reflecting light (etched specimens) showed an excellent correlation. With increasing filler loading, the mean size of the spherulites decrease as did the degree of crystallinity. This was a clear indication that the particles acted as nucleation agents and, on the other hand, hindered the arrangement of the molecules during the crystallization. As a result, the particles were most likely located in three areas: the center of the spherulites, the areas between the highly crystalline branches, and the spherulite boundaries. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39655.     

Conversion of Fusaric Acid to Fusarinol by Aspergillus tubingensis: A Detoxification Reaction

The fungus Fusarium oxysporum causes wilt diseases of plants and produces a potent phytotoxin fusaric acid (FA), which is also toxic to many microorganisms. An Aspergillus tubingensis strain with high tolerance to FA was isolated from soil and designated as CDRAt01. HPLC analysis of culture filtrates from A. tubingensis isolate CDRAt01 grown with the addition of FA indicated the formation of a metabolite over time that was associated with a decrease of FA. Spectral analysis and chemical synthesis confirmed the compound as 5-butyl-2-pyridinemethanol, referred to here as fusarinol. The phytotoxicity of fusarinol compared to FA was measured by comparing necrosis induced in cotton (Gossypium hirsutum L. cv. Coker 312) cotyledons. Fusarinol was significantly less phytotoxic than FA. Therefore, the A. tubingensis strain provides a novel detoxification mechanism against FA which may be utilized to control Fusarium wilt.     

The promise and challenge of iron-catalyzed cross coupling

Transition metal catalysts, particularly those derived from the group VIII-X metals, display remarkable efficiency for the formation of carbon-carbon and carbon-heteroatom bonds through the reactions of suitable nucleophiles with organic electrophilic partners. Within this subset of the periodic table, palladium and nickel complexes offer the broadest utility, while additionally providing the deepest mechanistic insight into thus-termed "cross-coupling reactions". The mammoth effort devoted to palladium and nickel catalysts over the past 30 years has somewhat obscured reports of alternative metal complexes in this arena. As cross-coupling reactions have evolved into a critical support for modern synthetic chemistry, the search for alternative catalysts has been taken up with renewed vigor.When the current generation of synthetic chemists reflects back to the origins of cross coupling for inspiration, the well-documented effect of iron salts on the reactivity of Grignard reagents with organic electrophiles surfaces as a fertile ground for alternative catalyst development. Iron possesses the practical benefits more befitting an alkali or alkaline earth metal, while displaying the unique reactivity of a d-block element. Therefore the search for broadly applicable iron catalysts for cross coupling is an increasingly important goal in modern synthetic organic chemistry.This Account describes the evolution of iron-catalyzed cross coupling from its inception in the work of Kochi to the present. Specific emphasis is placed on reactivity and synthetic applications, with selected examples from acyl-, alkenyl-, aryl-, and alkyl halide/pseudohalide cross coupling included. The typical reaction partners are Grignard reagents, though organomanganese, -copper, and -zinc derivatives have also been used in certain cases. Such iron-catalyzed processes occur very rapidly even at low temperature and therefore are distinguished by broad functional group compatibility. Furthermore, recent advances in carbon-heteroatom bond formation and studies relevant to the general reactivity of in situ generated and structurally defined "low-valent" iron catalysts are presented.The preparative aspects of iron-catalyzed cross coupling are encouraging, but the inclination to classify these processes within the characteristic reaction manifold is premature, as mechanistic studies have evolved at a comparatively slow pace. A typical protocol for cross coupling employs an Fe(+2) or Fe(+3) precatalyst, which is reduced in situ by the organometallic nucleophile. The nature of the resulting active component(s) is still best described, more than 30 years later, in Kochi's original terms as a "reduced form of soluble iron". Despite huge gaps in our current knowledge, three distinct mechanisms have been formulated, largely based on empirical evidence: a "canonical" cross-coupling process, a manifold wherein alkylation of an organoiron intermediate replaces transmetalation as a key step, and finally a proposal reliant on the formation of nucleophilic ate complexes. Conjecture and speculation abound, but precisely what constitutes the catalytic cycle in iron-catalyzed cross coupling remains an extremely challenging unanswered question.     

Vascular regression during amphibian metamorphosis—A scanning electron microscope study of vascular corrosion casts of the ventral velum in tadpoles of Xenopus laevis Daudin

We used scanning electron microscopy and vascular casting to study gross arterial supply, venous drainage, and microvascular patterns of the fully developed ventral velum of tadpoles of Xenopus laevis Daudin and analyzed changes of the velar vascular bed from prometamorphosis to metamorphic climax in a qualitative and quantitative manner. The multilayered, highly secretory ventral velum is supplied bilaterally by an anterior and a posterior velar artery, branches of the external carotid artery. Velar arterioles branch mainly dichotomously and form a flat two-dimensional capillary meshwork overlying the tops of filterplates I-IV. Thymopharyngeal veins, dorsal branches of the filter plates veins, and the internal jugular veins drain the velum toward the venous sinus of the heart. Location, architecture, and the drainage of the velar microvascular bed into the venous sinus make a significant contribution of the velar capillaries to gas exchange unlikely. Instead, velar capillaries rather serve the nutrition of the secretory epithelium. The overall morphology of velar vessels from prometamorphosis to metamorphic climax—deduced from vascular corrosion casts—points to atonic vessels with increased leakage indicated by adhering globular extravasations, and to obstructed or blind ending vessels evidenced by the tapered and/or rounded blind ending cast vessels. The significant decrease in the size of the ventral velum during the metamorphic cycle was paralleled by a miniaturization of the velar vascular bed. We hypothetize that this miniaturization occurs by a shortening and fusion of capillary mesh elements. Our findings in corrosion casts, particularly the miniaturization of the velar microvascular bed and the morphology of the regressing capillaries, point to profound morphologic and ultrastructural changes in velar vessels; a study on the fine structure of the microvascular bed of the ventral velum in metamorphic tadpoles is in progress.     

Influence of milk on haloperidol pharmacokinetics.

Psychiatric patients try to alleviate the effects of the butyrophenone neuroleptic haloperidol (HAL) by concomitant intake of milk or other dairy products. To determine whether this corresponded to milk-induced changes in HAL pharmacokinetics, male nonsmoking volunteers ingested a 10 mg HAL tablet (Haldol?) with 250 ml tap water (n?=?10) or 250 ml milk (n?=?9). Plasma HAL levels were determined up to 24 hr. Coadministration of 250 ml milk delayed the initial increase in HAL plasma levels (time lag increased 1.6-fold). However, of all 9 time points compared, only the HAL level difference at 1.5 hr after ingestion reached statistical significance. Differences in time lag, HAL levels for times p from .07 to .18). Because of the severity and high incidence of acute HAL side effects (akathisia, dysphoria, and anxiety), the original crossover design was abandoned and the study discontinued. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

POLYMER MELT RHEOLOGY: ON THE EVALUATION OF THE REPTATION MODEL

The predicted additivity of the complex moduli of monodisperse components (anionic polystyrenes) has been tested with care fully-prepared mixtures. This additivity holds in the fluid range for G” and, approximately, for G'. In the transition region to the rubber plateau, however, both moduli are seriously underestimated. Implications for calculations using GPC-data are discussed.     

Three-dimensional finite element for analysing thin plate/shell structures

A three-dimensional (3-D) hexahedron finite element is presented for the analysis of thin plate/shell structures. The element employs an explicit algebraic definition of six uniform (continuum) strains, six rigid body modes and classical Lagrange-Germain-Kirchhoff thin plate bending modes. Nine additional stiffness factors are used to control higher-order hourglass modes. The element may be used for plate/shell analyses where the flat plate assumptions are appropriate. Also it can easily be adapted to form transition elements to lower order 2-D elements, or to higher-order 3-D continuum elements. The stiffness matrix satisfies the geometric isotropy requirement, passes the patch test, and gives essentially identical response to either applied transverse corner forces or to twisting moments applied on the corner, a requirement of Kirchhoff's corner conditions for a classical thin plate. Several examples are presented to demonstrate the performance of this finite element.     

Analytical and physical investigation of alkyd resin in the course of its preparation. II. Study of condensation reaction and molecular weight distribution of alkyd

During preparation of alkyd resin by reaction between isocaprylic acid, phthalic anhydride, glycerol, and pentaerythritol the samples were successively taken away from the batch at different stages of the process and evaluated by analytical and physical ways. Acid numbers, hydroxyl numbers, and saponification numbers were determined by analyses of the samples and number-average molecular weights of alkyds were determined from vapor pressure osmotic measurements of their solutions. The extent of intramolecular esterification reactions (4–5%) was determined from these values. Molecular weight polydispersities in alkyd samples prepared at higher degrees of conversion were estimated by means of GPC measurements, and weight-average molecular weight of the final alkyd resin was calculated by using theoretical relationships derived for nonlinear condensation polymers.