178 research outputs found
Comparative Study on Pantothenic Acid Separation by Reactive Extraction with Tri-n-octylamine and Di-(2-ethylhexyl) Phosphoric Acid
The mechanism of reactive extraction of pantothenic acid with tri-n-octylamine and di-(2-ethylhexyl) phosphoric acid was analysed for three solvents in the presence or absence of 1-octanol. In the absence of 1-octanol, the stoichiometric ratio between the solute and tri-n-octylamine was 1:1 for dichloromethane, 1:2 for butyl acetate, and 1:4 for n-heptane. In the presence of 1-octanol, the formation of aminic adducts was restricted, the stoichiometries for the interfacial reaction between the acid and tri-n-octylamine becoming 1:1 for dichloromethane and butyl acetate, 1:2 for n-heptane. A similar effect has been observed for extraction with di-(2-ethylhexyl) phosphoric acid, the structure of the interfacial compound being changed for n-heptane and butyl acetate from HAE2 in the absence of 1-octanol to HAE by addition of this alcohol. The highest extraction constants were obtained when extractant associates were formed. However, when the extraction mechanism was the same, the increase in organic phase polarity influenced positively the value of extraction constant
Inelastic scattering of broadband electron wave packets driven by an intense mid-infrared laser field
Intense, 100 fs laser pulses at 3.2 and 3.6 um are used to generate, by
multi-photon ionization, broadband wave packets with up to 400 eV of kinetic
energy and charge states up to Xe+6. The multiple ionization pathways are well
described by a white electron wave packet and field-free inelastic cross
sections, averaged over the intensity-dependent energy distribution for (e,ne)
electron impact ionization. The analysis also suggests a contribution from a 4d
core excitation in xenon
Eco-friendly Production of Chemicals 1. Improvement of Enzymatic Production of Acetophenone by Direct Extraction
Acetophenone can be enzymatically produced by conversion of methylbenzylamine using transaminase. The enzymatic process
is strongly affected by the product inhibition, thus requiring the acetophenone removal from the media during its synthesis. In
this purpose, the individual and selective extraction of acetophenone and methylbenzylamine with the biocompatible solvent nheptane containing 1-octanol, D2EHPA or TOA has been analyzed at three values of pH (5, 7, and 9). Regardless of the solvent
used and pH-value, the highest efficiency has been reached for extraction of acetophenone, the difference between the extraction
yields of acetophenone and methylbenzylamine being amplified during the separation of these compounds from their mixture. On
the basis of the experimental selectivity factors and taking into consideration both the possible loss of substrate from the media
and the pH required for enzymatic reaction, pH = 7, it has been concluded that the optimum solvent combination is the mixture
between n-heptane and 1-octanol. This solvent mixture allowed reaching high selectivity factor of 315, corresponding to the
extraction yield of acetophenone of 94.5 % and of methylbenzylamine of only 0.3 %
Irreducible holonomy algebras of Riemannian supermanifolds
Possible irreducible holonomy algebras \g\subset\osp(p,q|2m) of Riemannian
supermanifolds under the assumption that \g is a direct sum of simple Lie
superalgebras of classical type and possibly of a one-dimensional center are
classified. This generalizes the classical result of Marcel Berger about the
classification of irreducible holonomy algebras of pseudo-Riemannian manifolds.Comment: 27 pages, the final versio
The Effect of Polyphenols, Minerals, Fibers, and Fruits on Irritable Bowel Syndrome: A Systematic Review
Background: Irritable bowel syndrome (IBS) is a chronic gastrointestinal disorder characterized by abdominal pain, bloating, and changes in bowel habits. Various dietary factors have been implicated in the pathogenesis and management of IBS symptoms. This systematic review aims to evaluate the effects of polyphenols, minerals, fibers, and fruits on the symptoms and overall well-being of individuals with IBS. Materials and Methods: A comprehensive literature search was conducted in several electronic databases, including PubMed, Scopus, and Web of Science. Studies published up until July 2023 were included. Results: The selected studies varied in terms of study design, participant characteristics, intervention duration, and outcome measures. Overall, the findings suggest that dietary interventions involving polyphenols, minerals, fibers, and fruits can have a positive impact on IBS symptoms. Dietary fiber supplementation, particularly soluble fiber, has been associated with reduced bloating and enhanced stool consistency. Conclusions: This systematic review provides evidence supporting the beneficial effects of polyphenols, minerals, fibers, and fruits in IBS patients. These dietary components hold promise as complementary approaches for managing IBS symptoms. However, due to the heterogeneity of the included studies and the limited number of high-quality randomized controlled trials, further well-designed trials are warranted to establish the optimal dosages, duration, and long-term effects of these interventions. Understanding the role of specific dietary components in IBS management may pave the way for personalized dietary recommendations and improve the quality of life for individuals suffering from this complex disorder
Algebraic structure of gravity in Ashtekar variables
The BRST transformations for gravity in Ashtekar variables are obtained by
using the Maurer-Cartan horizontality conditions. The BRST cohomology in
Ashtekar variables is calculated with the help of an operator
introduced by S.P. Sorella, which allows to decompose the exterior derivative
as a BRST commutator. This BRST cohomology leads to the differential invariants
for four-dimensional manifolds.Comment: 19 pages, report REF. TUW 94-1
Clocking Auger electrons
Intense X-ray free-electron lasers (XFELs) can rapidly excite matter, leaving it in inherently unstable states that decay on femtosecond timescales. The relaxation occurs primarily via Auger emission, so excited-state observations are constrained by Auger decay. In situ measurement of this process is therefore crucial, yet it has thus far remained elusive in XFELs owing to inherent timing and phase jitter, which can be orders of magnitude larger than the timescale of Auger decay. Here we develop an approach termed ‘self-referenced attosecond streaking’ that provides subfemtosecond resolution in spite of jitter, enabling time-domain measurement of the delay between photoemission and Auger emission in atomic neon excited by intense, femtosecond pulses from an XFEL. Using a fully quantum-mechanical description that treats the ionization, core-hole formation and Auger emission as a single process, the observed delay yields an Auger decay lifetime of 2.2_−0.3^+0.2 fs for the KLL decay channel
Clocking Auger Electrons
Intense X-ray free-electron lasers (XFELs) can rapidly excite matter, leaving
it in inherently unstable states that decay on femtosecond timescales. As the
relaxation occurs primarily via Auger emission, excited state observations are
constrained by Auger decay. In situ measurement of this process is therefore
crucial, yet it has thus far remained elusive at XFELs due to inherent timing
and phase jitter, which can be orders of magnitude larger than the timescale of
Auger decay. Here, we develop a new approach termed self-referenced attosecond
streaking, based upon simultaneous measurements of streaked photo- and Auger
electrons. Our technique enables sub-femtosecond resolution in spite of jitter.
We exploit this method to make the first XFEL time-domain measurement of the
Auger decay lifetime in atomic neon, and, by using a fully quantum-mechanical
description, retrieve a lifetime of fs for the KLL
decay channel. Importantly, our technique can be generalised to permit the
extension of attosecond time-resolved experiments to all current and future FEL
facilities.Comment: Main text: 20 pages, 3 figures. Supplementary information: 17 pages,
6 figure
On Some Geometric Structures Associated to a k-Symplectic Manifold
A canonical connection is attached to any k-symplectic manifold. We study the
properties of this connection and its geometric applications to k-symplectic
manifolds. In particular we prove that, under some natural assumption, any
ksymplectic manifold admits an Ehresmann connection, discussing some
corollaries of this result, and we find vanishing theorems for characteristic
classes on a k-symplectic manifold.Comment: To appear on J. Phys. A: Math. Theo
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