Direct Photoredox‐Catalyzed Reductive Difluoromethylation of Electron‐Deficient Alkenes

Photoredox‐catalyzed reductive difluoromethylation of electron‐deficient alkenes was achieved in one step under tin‐free, mild and neutral conditions. This protocol affords a facile method to introduce RCF₂ (R=H, Ph, Me, and CH₂N₃) groups at sites β to electron‐withdrawing groups. It was found that TTMS (tris(trimethylsilyl)silane) served nicely as both the H‐atom donor and the electron donor in the catalytic cycle. Experimental and DFT computational results provided evidence that RCF₂ (R=H, Ph, Me) radicals are nucleophilic in nature.     

An extension of the concept of material symmetry

Summary The nature of a material is in large part described by its symmetry group. It is proposed to extend this concept to a more general type of symmetry transformation, and the use of such an extension is illustrated by using it to define several classes of materials and presenting the corresponding representation theorems.

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Sommario La natura di un materiale è in gran parte descritta dal suo gruppo di simmetria. Si propone di estendere questo concetto a un tipo più generale di trasformazione simmetrica, e l'uso di questa estensione è illustrato nel definire parecchie classi di materiali e nel formulare i corrispondenti teoremi di rappresentazione.

     

A new method of representation of fiber creep data tensile creep behavior of some acrylic fibers

Summary Fiber creep data are usually represented as plots of extension versus time at constant stress and temperature. Fiber samples, however, exhibit some degree of variability in structure from filament to filament. Consequently, even when initial applied stresses are nominally equivalent (as determined by measurement of cross-sectional area, and load), the creep of individual fibers can differ significantly, and the creep behavior of a sample can only be characterized statistically.Structural parameters such as orientation, which affect fiber properties greatly, and therefore creep, are not considered in the conventional representation of creep data. Orientation, in turn, is associated with stretch or extension. On this basis, creep, i. e. creep rate, can be expected to depend on extension.In the proposed method for representing creep data, the rate of creep is related to the extension at a constant time and temperature. In these so-called isochronal creep rate curves, the use of stress as an independent variable is omitted, and is replaced by extension. This method of representation discloses common creep characteristics in fibers, which, though taken from the same sample, exhibit widely different creep behavior when treated conventionally. In this way, the creep behavior of the whole sample can be conveniently represented. These plots reveal more detail than the ordinary creep curves, and indicate different creep mechanisms within certain extension regions as well as the stretch-relaxation history of the particular fiber sample. In this paper, the aspects and limitations of these two methods of representation of creep data are discussed, and their relative merits are demonstrated using experimental acrylic fibers.     

In search of physical parameters influenced by flow patterns in a heterogeneous two-phase mixture in microchannels using concomitant measurements

Space transportation systems require high-performance thermal protection and fluid management for systems ranging from cryogenic fluid devices to primary structures, and for propulsion systems exposed to extremely high temperatures, and other space systems, e.g., integrated circuits and cooling/environment control devices for advanced space suits. Although considerable developmental effort is underway to bring promising technologies to a readiness level for practical use, new and innovative methods are still needed. One such method is the Advanced Micro Cooling Module (AMCM), essentially a compact two-phase heat exchanger constructed of microchannels and designed to rapidly remove large quantities of heat from critical systems by incorporating phase transition. This paper describes the results of experimental research in two-phase flow phenomena, encompassing both an experimental and an analytical approach to the incorporation of flow patterns for air–water mixtures flowing in microchannels. Specifically addressed are: (1) design and construction of a sensitive two-phase experimental system which measures both ac and dc components of in situ physical mixture parameters including spatial concentration, using concomitant methods; (2) data acquisition and analysis in the amplitude, time, and frequency domains; and (3) analysis of results including evaluation of in situ physical parameters, and assessment of their validity for application in flow pattern determination.     

Graph Theory Applied to Plasma Chemical Reaction Engineering

Plasma Chemistry and Plasma Processing - This work explores the following applications of graph theory to plasma chemical reaction engineering: assembly of a weighted directional graph with the key...