4,735 research outputs found
Macroscopic electrostatic potentials and interactions in self-assembled molecular bilayers: the case of Newton black films
We propose a very simple but 'realistic' model of amphiphilic bilayers,simple
enough to be able to include a large number of molecules in the sample, but
nevertheless detailed enough to include molecular charge distributions,
flexible amphiphilic molecules and a reliable model of water. All these
parameters are essential in a nanoscopic scale study of intermolecular and long
range electrostatic interactions. We also propose a novel, simple and more
accurate macroscopic electrostatic field for model bilayers. This model goes
beyond the total dipole moment of the sample, which on a time average is zero
for this type of symmetrical samples, i. e., it includes higher order moments
of this macroscopic electric field. We show that by representing it with a
superposition of gaussians it can be 'analytically' integrated, and therefore
its calculation is easily implemented in a MD simulation (even in simulations
of non-symmetrical bi- or multi-layers). In this paper we test our model by
molecular dynamics simulations of Newton black films
Octonic Electrodynamics
In this paper we present eight-component values "octons", generating
associative noncommutative algebra. It is shown that the electromagnetic field
in a vacuum can be described by a generalized octonic equation, which leads
both to the wave equations for potentials and fields and to the system of
Maxwell's equations. The octonic algebra allows one to perform compact combined
calculations simultaneously with scalars, vectors, pseudoscalars and
pseudovectors. Examples of such calculations are demonstrated by deriving the
relations for energy, momentum and Lorentz invariants of the electromagnetic
field. The generalized octonic equation for electromagnetic field in a matter
is formulated.Comment: 12 pages, 1 figur
Analytical Strategies for Fingerprinting of Antioxidants, Nutritional Substances, and Bioactive Compounds in Foodstuffs Based on High Performance Liquid Chromatography-Mass Spectrometry: An Overview
New technology development and globalisation have led to extreme changes in the agri-food sector in recent years that need an important food supply chain characterisation from plant materials to commercial productions. Many analytical strategies are commonly utilised in the agri-food industry, often using complementary technologies with different purposes. Chromatography on-line coupled to mass spectrometry (MS) is one of the most selective and sensitive analytical methodologies. The purpose of this overview is to present the most recent MS-based techniques applied to food analysis. An entire section is dedicated to the recent applications of high-resolution MS. Covered topics include liquid (LC)– and gas chromatography (GC)–MS analysis of natural bioactive substances, including carbohydrates, flavonoids and related compounds, lipids, phenolic compounds, vitamins, and other different molecules in foodstuffs from the perspectives of food composition, food authenticity and food adulteration. The results represent an important contribution to the utilisation of GC–MS and LC–MS in the field of natural bioactive compound identification and quantification
Reduction of the cyanide content during fermentation of cassava roots and leaves to produce bikedi and ntoba mbodi, two food products from Congo
Cassava roots and leaves constitute energy-rich and protein-rich foods, respectively, for the populations in Central Africa, where they are consumed as staple foods. But cassava roots and leaves contain some cyanide in the form of cyanogenic glucosides, notably the linamarine, which can constitute a poison for the consumers when roots or leaves are processed improperly. Cassava roots and leaves processing in Congo, as in most central African countries, involve fermentation. The fermentation of the cassava roots is a lactic fermentation (pH 3.8) with Lactobacillus as dominant microflora whereas that of the cassava leaves is an alkaline fermentation (pH 8.5) where Bacillus constitute the main microflora. The hydrolysis of cyanogenic glucosides takes place as well in acid medium during the cassava tubers fermentation as in basic medium with the cassava leaves fermentation. The cyanide content decreases during the fermentation of cassava roots and leaves by more than 70% through the activities of the bacterial produced linamarase, allowing the hydrolysis of cyanogenic glucosides. Certain lactic bacteria present in the environment of fermentation are resistant to the strong cyanide concentrations of between 200 and 800 ppm.African Journal of Biotechnology Vol. 4 (7), pp. 689-696, 200
Ritual displays by a parasitic cuckoo: nuptial gifts or territorial warnings?
In the sexual selection framework, nuptial gifts are materials a donor provides to a receiver that can increase the donor's fitness. In specific cases, sharing crucial information may be a nonmaterial nuptial gift. To investigate this hypothesis, we focused on the common cuckoo, Cuculus canorus, an obligate avian brood parasite whose reproduction costs of females are mainly related to finding host nests needed to lay their eggs. Nest searching is assumed to be conducted only by females. We hypothesized that males could contribute by transferring information on nest locations to females as a nonmaterial nuptial gift. Here, we show the results of a first step in this direction, in which we identified any behaviour potentially conveying information on nest abundance in the surrounding area, that is, behaviours whose frequency varied with host nest density. We conducted our investigation in a marshland area within the Po Plain (Italy), where we recorded both visual displays of cuckoos at perching sites, by using camera traps, and nest abundance of two of the most parasitized cuckoo host species, the reed warbler, Acrocephalus scirpaceus, and great reed warbler, Acrocephalus arundinaceus, by systematic nest monitoring. We found that male cuckoos adopted a certain posture, wing drooping, and tended to keep their tails up more frequently in areas with the highest versus lowest host nest densities. This is consistent with these behaviours acting as potential signals codifying information on nest abundance in the area. We finally discuss the implications of our findings for the mating choices of female cuckoos and the study directions warranted to reveal whether these displays and information transfer may be included as new elements of the sexual selection framework. (c) 2023 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/)
An intramolecular oxa-Michael reaction on α,β-unsaturated α-amino-δ-hydroxycarboxylic acid esters. Synthesis of functionalized 1,3-dioxanes
A highly diastereoselective intramolecular oxa-Michael reaction on α,β-unsaturated α-amino-δ-hydroxycarboxylic acid esters is presented; 1,3-dioxanes functionalized in positions 2,4 and 6 were obtained in good yields and with excellent selectivities; an experimental and computational study was carried out to understand the reaction course in terms of yields and selectivities. This reaction proceeds under mild reaction conditions using highly electrophilic aldehydes and ketones
Universal features of cell polarization processes
Cell polarization plays a central role in the development of complex
organisms. It has been recently shown that cell polarization may follow from
the proximity to a phase separation instability in a bistable network of
chemical reactions. An example which has been thoroughly studied is the
formation of signaling domains during eukaryotic chemotaxis. In this case, the
process of domain growth may be described by the use of a constrained
time-dependent Landau-Ginzburg equation, admitting scale-invariant solutions
{\textit{\`a la}} Lifshitz and Slyozov. The constraint results here from a
mechanism of fast cycling of molecules between a cytosolic, inactive state and
a membrane-bound, active state, which dynamically tunes the chemical potential
for membrane binding to a value corresponding to the coexistence of different
phases on the cell membrane. We provide here a universal description of this
process both in the presence and absence of a gradient in the external
activation field. Universal power laws are derived for the time needed for the
cell to polarize in a chemotactic gradient, and for the value of the smallest
detectable gradient. We also describe a concrete realization of our scheme
based on the analysis of available biochemical and biophysical data.Comment: Submitted to Journal of Statistical Mechanics -Theory and Experiment
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