241 research outputs found
Cellulases for oligosaccharide synthesis : a preliminary study
Crude cellulases, cellobiohydrolase I and endoglucanase I from Trichoderma reesei, were used for preliminary analysis of the potential of
cellulases for oligosaccharide synthesis. The reaction products were analysed by ionic chromatography. Synthesis activity could be detected in concentrated aqueous solutions of glucose, cellobiose, maltose and raffinose. CBH I and EG I showed similar activity, with the exception
of the case where cellobiose was the substrate. In this case, CBH I originated more ligosaccharides and in higher yields. For the best case among the studied experimental conditions (enzyme: CBH I; substrate: cellubiose; temperature: 4ºC), yields in the order of 40% oligosaccharides were obtained. The effect of the temperature on the reaction yield and kinetics was also studied
Observational constraints on Rastall's cosmology
Rastall's theory is a modification of General Relativity, based on the
non-conservation of the stress-energy tensor. The latter is encoded in a
parameter such that restores the usual law. We test Rastall's theory in cosmology, on a flat
Robertson-Walker metric, investigating a two-fluid model and using the type Ia
supernovae Constitution dataset. One of the fluids is pressureless and obeys
the usual conservation law, whereas the other is described by an equation of
state , with constant. The Bayesian analysis of the
Constitution set does not strictly constrain the parameter and prefers
values of close to -1. We then address the evolution of small
perturbations and show that they are dramatically unstable if and
, i.e. General Relativity is the favored configuration. The only
alternative is , for which the dynamics becomes independent from
.Comment: Latex file, 14 pages, 6 figures in eps format. Substantial
modifications performed, main conclusions change
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Recent development of prebiotic research — statement from an expert workshop
A dietary prebiotic is defined as ‘a substrate that is selectively utilized by host microorganisms conferring a health benefit’. Although this definition evolved concomitantly with the knowledge and technological developments that accrued in the last twenty years, what qualifies as prebiotic continues to be a matter of debate. In this statement, we report the outcome of a workshop where academic experts working in the field of prebiotic research met with scientists from industry. The workshop covered three main topics: (i) evolution of the prebiotic concept/definition; (ii) the gut modeling in vitro technology PolyFermS to study prebiotic effects; and (iii) the potential novel microbiome-modulating effects associated with vitamins. The future of prebiotic research is very promising. Indeed, the technological developments observed in recent years provide scientists with powerful tools to investigate the complex ecosystem of gut microbiota. Combining multiple in vitro approaches with in vivo studies is key to understanding the mechanisms of action of prebiotics consumption and their potential beneficial effects on the host
Gravitomagnetism in Metric Theories: Analysis of Earth Satellites Results, and its Coupling with Spin
Employing the PPN formalism the gravitomagnetic field in different metric
theories is considered in the analysis of the LAGEOS results. It will be shown
that there are several models that predict exactly the same effect that general
relativity comprises. In other words, these Earth satellites results can be
taken as experimental evidence that the orbital angular momentum of a body does
indeed generate space--time geometry, notwithstanding they do not endow general
relativity with an outstanding status among metric theories. Additionally the
coupling spin--gravitomagnetic field is analyzed with the introduction of the
Rabi transitions that this field produces on a quantum system with spin 1/2.
Afterwards, a continuous measurement of the energy of this system is
introduced, and the consequences upon the corresponding probabilities of the
involved gravitomagnetic field will be obtained. Finally, it will be proved
that these proposals allows us, not only to confront against future experiments
the usual assumption of the coupling spin--gravotimagnetism, but also to
measure some PPN parameters and to obtain functional dependences among them.Comment: 10 page
Quantum-classical transition in Scale Relativity
The theory of scale relativity provides a new insight into the origin of
fundamental laws in physics. Its application to microphysics allows us to
recover quantum mechanics as mechanics on a non-differentiable (fractal)
spacetime. The Schrodinger and Klein-Gordon equations are demonstrated as
geodesic equations in this framework. A development of the intrinsic properties
of this theory, using the mathematical tool of Hamilton's bi-quaternions, leads
us to a derivation of the Dirac equation within the scale-relativity paradigm.
The complex form of the wavefunction in the Schrodinger and Klein-Gordon
equations follows from the non-differentiability of the geometry, since it
involves a breaking of the invariance under the reflection symmetry on the
(proper) time differential element (ds - ds). This mechanism is generalized
for obtaining the bi-quaternionic nature of the Dirac spinor by adding a
further symmetry breaking due to non-differentiability, namely the differential
coordinate reflection symmetry (dx^mu - dx^mu) and by requiring invariance
under parity and time inversion. The Pauli equation is recovered as a
non-relativistic-motion approximation of the Dirac equation.Comment: 28 pages, no figur
Scalar models for the generalized Chaplygin gas and the structure formation constraints
The generalized Chaplygin gas model represents an attempt to unify dark
matter and dark energy. It is characterized by a fluid with an equation of
state . It can be obtained from a generalization of the
DBI action for a scalar, tachyonic field. At background level, this model gives
very good results, but it suffers from many drawbacks at perturbative level. We
show that, while for background analysis it is possible to consider any value
for , the perturbative analysis must be restricted to positive values
of . This restriction can be circumvented if the origin of the
generalized Chaplygin gas is traced back to a self-interacting scalar field,
instead of the DBI action. But, in doing so, the predictions coming from
formation of large scale structures reduce the generalized Chaplygin gas model
to a kind of quintessence model, and the unification scenario is lost, if the
scalar field is the canonical one. However, if the unification condition is
imposed from the beginning as a prior, the model may remain competitive. More
interesting results, concerning the unification program, are obtained if a
non-canonical self-interacting scalar field, inspired by Rastall's theory of
gravity, is imposed. In this case, an agreement with the background tests is
possible.Comment: Latex file, 25 pages, 33 figures in eps format. New section on scalar
models. Accepted for publication in Gravitation&Cosmolog
Note on the Evolution of the Gravitational Potential in Rastall Scalar Field Theories
We investigate the evolution of the gravitational potential in Rastall scalar
field theories. In a single component model a consistent perturbation theory,
formulated in the newtonian gauge, is possible only for , which is
the General Relativity limit. On the other hand, the addition of another
canonical fluid component allows also to consider the case .Comment: 16 pages, 3 figures, Sections 2 and 5 enlarged, accepted for
publication in Physics Letters
Analyzing three-player quantum games in an EPR type setup
We use the formalism of Clifford Geometric Algebra (GA) to develop an
analysis of quantum versions of three-player non-cooperative games. The quantum
games we explore are played in an Einstein-Podolsky-Rosen (EPR) type setting.
In this setting, the players' strategy sets remain identical to the ones in the
mixed-strategy version of the classical game that is obtained as a proper
subset of the corresponding quantum game. Using GA we investigate the outcome
of a realization of the game by players sharing GHZ state, W state, and a
mixture of GHZ and W states. As a specific example, we study the game of
three-player Prisoners' Dilemma.Comment: 21 pages, 3 figure
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Prebiotic effects: metabolic and health benefits
The different compartments of the gastrointestinal tract are inhabited by populations of micro-organisms. By far the most important predominant populations are in the colon where a true symbiosis with the host exists that is a key for well-being and health. For such a microbiota, 'normobiosis' characterises a composition of the gut 'ecosystem' in which micro-organisms with potential health benefits predominate in number over potentially harmful ones, in contrast to 'dysbiosis', in which one or a few potentially harmful micro-organisms are dominant, thus creating a disease-prone situation. The present document has been written by a group of both academic and industry experts (in the ILSI Europe Prebiotic Expert Group and Prebiotic Task Force, respectively). It does not aim to propose a new definition of a prebiotic nor to identify which food products are classified as prebiotic but rather to validate and expand the original idea of the prebiotic concept (that can be translated in 'prebiotic effects'), defined as: 'The selective stimulation of growth and/or activity(ies) of one or a limited number of microbial genus(era)/species in the gut microbiota that confer(s) health benefits to the host.' Thanks to the methodological and fundamental research of microbiologists, immense progress has very recently been made in our understanding of the gut microbiota. A large number of human intervention studies have been performed that have demonstrated that dietary consumption of certain food products can result in statistically significant changes in the composition of the gut microbiota in line with the prebiotic concept. Thus the prebiotic effect is now a well-established scientific fact. The more data are accumulating, the more it will be recognised that such changes in the microbiota's composition, especially increase in bifidobacteria, can be regarded as a marker of intestinal health. The review is divided in chapters that cover the major areas of nutrition research where a prebiotic effect has tentatively been investigated for potential health benefits. The prebiotic effect has been shown to associate with modulation of biomarkers and activity(ies) of the immune system. Confirming the studies in adults, it has been demonstrated that, in infant nutrition, the prebiotic effect includes a significant change of gut microbiota composition, especially an increase of faecal concentrations of bifidobacteria. This concomitantly improves stool quality (pH, SCFA, frequency and consistency), reduces the risk of gastroenteritis and infections, improves general well-being and reduces the incidence of allergic symptoms such as atopic eczema. Changes in the gut microbiota composition are classically considered as one of the many factors involved in the pathogenesis of either inflammatory bowel disease or irritable bowel syndrome. The use of particular food products with a prebiotic effect has thus been tested in clinical trials with the objective to improve the clinical activity and well-being of patients with such disorders. Promising beneficial effects have been demonstrated in some preliminary studies, including changes in gut microbiota composition (especially increase in bifidobacteria concentration). Often associated with toxic load and/or miscellaneous risk factors, colon cancer is another pathology for which a possible role of gut microbiota composition has been hypothesised. Numerous experimental studies have reported reduction in incidence of tumours and cancers after feeding specific food products with a prebiotic effect. Some of these studies (including one human trial) have also reported that, in such conditions, gut microbiota composition was modified (especially due to increased concentration of bifidobacteria). Dietary intake of particular food products with a prebiotic effect has been shown, especially in adolescents, but also tentatively in postmenopausal women, to increase Ca absorption as well as bone Ca accretion and bone mineral density. Recent data, both from experimental models and from human studies, support the beneficial effects of particular food products with prebiotic properties on energy homaeostasis, satiety regulation and body weight gain. Together, with data in obese animals and patients, these studies support the hypothesis that gut microbiota composition (especially the number of bifidobacteria) may contribute to modulate metabolic processes associated with syndrome X, especially obesity and diabetes type 2. It is plausible, even though not exclusive, that these effects are linked to the microbiota-induced changes and it is feasible to conclude that their mechanisms fit into the prebiotic effect. However, the role of such changes in these health benefits remains to be definitively proven. As a result of the research activity that followed the publication of the prebiotic concept 15 years ago, it has become clear that products that cause a selective modification in the gut microbiota's composition and/or activity(ies) and thus strengthens normobiosis could either induce beneficial physiological effects in the colon and also in extra-intestinal compartments or contribute towards reducing the risk of dysbiosis and associated intestinal and systemic pathologies
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