High repetition-rate and quasi-cw operation of a waveguide CO2 TE laser

We report operation of a waveguide CO₂ TE laser at excitation pulse repetition frequencies as high as 40 kHz. Quasi-continuous laser output was obtained yielding an average output power of 1.5 W from an active volume of 0.1 cc. Details of laser construction and excitation circuitry are given.     

The effect of substrate work function on work function reduction of Re/W alloy-coated impregnated cathodes

The work function reduction at a metal surface caused by adsorbed barium and oxygen is already known with the resulting expression for the overall work function being =_S–_R. Results from the Re/W alloy-coated cathodes exhibit that _R increases with substrate work function with a slope of 1.09 by linear regression. A qualitative explanation of the above results comes from considering the arrangement of barium and oxygen on the surfaces. A charge transfer model is proposed for two-dimensional barium and oxygen lying on a flat non-interacting substrate. Calculation shows that the dipole strength increases with the charge transfer below the intermediate states.     

Bio-based materials for nonwovens

Cellulose - The nonwoven industry is one of the most innovative and important branches of the global fiber products industry. However, the use of petrochemical-based materials in many nonwoven...     

Five-Step Enantioselective Synthesis of Islatravir via Asymmetric Ketone Alkynylation and an Ozonolysis Cascade

A 5-step enantioselective synthesis of the potent anti-HIV nucleoside islatravir is reported. The highly efficient route was enabled by a novel enantioselective alkynylation of an α,β-unsaturated ketone, a unique ozonolysis-dealkylation cascade in water, and an enzymatic aldol-glycosylation cascade.     

Hecke Algebras of Group Extensions

Abstract

We describe the Hecke algebra ?(Γ,Γ₀) of a Hecke pair (Γ,Γ₀) in terms of the Hecke pair (N,Γ₀) where N is a normal subgroup of Γ containing Γ₀. To do this, we introduce twisted crossed products of unital *-algebras by semigroups. Then, provided a certain semigroup S ? Γ/N satisfies S ^?1 S = Γ/N, we show that ? (Γ,Γ₀) is the twisted crossed product of ? (N,Γ₀) by S. This generalizes a recent theorem of Laca and Larsen about Hecke algebras of semidirect products.     

Synthesis of a novel analytical reagent for the determination of active sites for conjugation on a catalytic aldolase monoclonal antibody

An optimized and scalable synthesis of a novel analytical reagent for the determination of the number of active sites available for conjugation on a catalytic aldolase monoclonal antibody (mAb) is described. The original conditions suffered from lack of reproducibility, incomplete reactions, and required several chromatographies and lyophilizations that afforded material of low purity. A redesigned route and optimized protocols have been developed that eliminate the use of toxic and unsafe reagents such as HMPA and HATU. In addition, the number of chromatographies has been reduced to only one and time-consuming and energy-intensive lyophilizations are no longer required. The overall yield has been considerably improved from the original 4% to 20% after telescoping the last two steps of the synthesis and this new approach allowed for the preparation of material with higher chemical purity (?99% vs the initial 90%) to meet specifications.     

Comparing behavioral and physiological measures of combination tones: Sex and race differences

Both distortion-product otoacoustic emissions (DPOAEs) and performance in an auditory-masking task involving combination tones were measured in the same frequency region in the same ears. In the behavioral task, a signal of 3.6?kHz (duration 300?ms, rise/fall time 20?ms) was masked by a 3.0-kHz tone (62?dB SPL, continuously presented). These two frequencies can produce a combination tone at 2.4?kHz. When a narrowband noise (2.0-2.8?kHz, 17?dB spectrum level) was added as a second masker, detection of the 3.6-kHz signal worsened by 6-9?dB (the Greenwood effect), revealing that listeners had been using the combination tone at 2.4?kHz as a cue for detection at 3.6?kHz. Several outcomes differed markedly by sex and racial background. The Greenwood effect was substantially larger in females than in males, but only for the White group. When the magnitude of the Greenwood effect was compared with the magnitude of the DPOAE measured in the 2.4?kHz region, the correlations typically were modest, but were high for Non-White males. For many subjects, then, most of the DPOAE measured in the ear canal apparently is not related to the combination-tone cue that is masked by the narrowband noise.     

Ionic liquid extraction method for upgrading eucalyptus kraft pulp to high purity dissolving pulp

High purity cellulose from wood is an important raw material for many applications such as cellulosic fibers, films or the manufacture of various cellulose acetate products. Hitherto, multi-step refining processes are needed for an efficient hemicellulose removal, most of them suffering from severe cellulose losses. Recently, a novel method for producing high purity cellulose from bleached paper grade birch kraft pulp was presented. In this so called IONCELL process, hemicelluloses are extracted by an ionic liquid–water mixture and both fractions can be recovered without yield losses or polymer degradation. Herein, it is demonstrated that bleached Eucalyptus urograndis kraft pulp can be refined to high purity acetate grade pulp via the IONCELL process. The hemicellulose content could be reduced from initial 16.6 to 2.4 wt% while persevering the cellulose I crystal form by using an optimized 1-ethyl-3-methylimidazolium dimethylphosphate-water mixture as the extraction medium. The degree of polymerization was then reduced by a sulfuric acid treatment for subsequent acetylation of the pulp, resulting in a final hemicellulose content of 2.2 wt%. When pre-treating the pulp enzymatically with endoxylanase, the final hemicellulose content could be reduced even to 1.7 wt%. For comparison, the eucalyptus kraft pulp was also subjected to cold caustic extraction and the same subsequent acid treatment which led to 3.9 wt% of residual hemicelluloses. The performance in acetylation of all produced pulps was tested and compared to commercial acetate grade pulp. The endoxylanase-IONCELL-treated pulp showed superior properties. Thus, an ecologically and economically efficient alternative for the production of highest value cellulose pulp is presented.     

Influence on Pore Structure of Micro/Nanofibrillar Cellulose in Pigmented Coating Formulations

Nano and microfibrillated cellulose (NFC and MFC, respectively, collectively termed MNFC) is known to interact strongly with water, related to its high polarity and surface area. The swelling behaviour acts to form a gel with high water retention properties. The observation that nanocellulose could possibly be used in paper or other coating formulations, as a co-binder, for example, raises a question about the possible effects it could have on coating pore structure. In this study, we analyse the pore structure of pigmented coatings, liquid absorption and permeability, in respect to the influence of partially substituting traditional co-binder carboxymethyl cellulose with MNFC. The contrast between polar water and non-polar liquid, such as alkane, is used to probe the water interactive and extractable in-coating (internal) gel-formation properties of the nanocellulosic materials. These contrasting liquids are important in many processes, such as offset printing, but also in respect to exposure of coatings in general to environmental factors in application. Results show that permeability to liquid water is dramatically reduced when nanocellulosic material is present, though water can permeate by diffusion through the nanocellulose gel network. Long timescale exposure to water during absorption leads to extraction of any soluble salts remaining after the chemical treatment of the fibrillar material during production. Inert alkane, on the other hand, can absorb and permeate freely without interactive hindrance from the nanocellulose, with no extractive effect. Such a construct could in principle be considered for use as an oil-water differential membrane or for slow release concepts in aqueous systems by loading soluble deliverable materials within the nanocellulosic gel.