3,695 research outputs found
Autocatalytic and cooperatively-stabilized dissociation of water on a stepped platinum surface
Water-metal interfaces are ubiquitous and play a key role in many chemical
processes, from catalysis to corrosion. Whereas water adlayers on atomically
flat transition metal surfaces have been investigated in depth, little is known
about the chemistry of water on stepped surfaces, commonly occurring in
realistic situations. Using first-principles simulations we study the
adsorption of water on a stepped platinum surface. We find that water adsorbs
preferentially at the step edge, forming linear clusters or chains, stabilized
by the cooperative effect of chemical bonds with the substrate and hydrogen
bonds. In contrast with flat Pt, at steps water molecules dissociate forming
mixed hydroxyl/water structures, through an autocatalytic mechanism promoted by
hydrogen bonding. Nuclear quantum effects contribute to stabilize partially
dissociated cluster and chains. Together with the recently demonstrated
attitude of water chains adsorbed on stepped Pt surfaces to transfer protons
via thermally activated hopping, these findings candidate these systems as
viable proton wires.Comment: 19 pages, 4 figure
Development of an Ex Vivo Organ Culture Technique to Evaluate Probiotic Utilization in IBD
The consistent technical and conceptual progress in the study of the microbiota has led novel impulse to the research for therapeutical application of probiotic bacteria in human pathologies, such as inflammatory bowel disease (IBD). Considering the heterogenous results of probiotics in clinical studies, the model of translational medicine may lead to a more specific and efficacious utilization of probiotic bacteria in IBD. In this regard, the selection and utilization of appropriate experimental models may drive the transition from pure in vitro systems to practical clinical application. We developed a simple and reproducible ex vivo organ culture method with potential utilization for the evaluation of probiotic bacteria efficacy in IBD patients
Application of clinical indexes in ulcerative colitis patients in regular follow-up visit. correlation with endoscopic 'mucosal healing' and implication for management
OBJECTIVE: Ulcerative Colitis (UC) is a chronic inflammatory disease of the colon of unknown etiology. Several clinical indexes have been proposed for UC disease activity evaluation, but none have been properly validated. Moreover, the reference parameter for the scores and their prognostic value is not clear. Mucosal healing has been recently proposed as an important end-point. Aim of the present study was to evaluate the correlation of four clinical indexes with objective diagnostic tools for UC evaluation, the discriminative ability in identifying patients with endoscopic mucosal healing, and to analyze the possible prognostic indication for disease course in 1 year of follow-up. PATIENTS AND METHODS: We analyzed data of 75 patients recorded in regular follow-up visit in IBD clinic at S. Andrea Hospital, Rome, between 2007-2011. We recorded clinical data and lab tests at the time of the visit, and endoscopic/ histological repor ts performed within 1 month. Clinical indexes (Seo' activity index, Simple Clinical Colitis Activity Index, partial Mayo score and Endoscopic-Clinical Correlation Index) were calculated and correlation to endoscopic and histologic activity, and to C-reactive protein increment, was assessed by mean of Spearman's rank correlation. Discriminative ability of the indexes for patients with and without endoscopic mucosal healing was tested by calculation of area under ROC curve (AUC). Patients with low and high clinical scores were compared for number of flares and increment of therapy during 1 year of follow-up. RESULTS: Clinical indexes had a good correlation with endoscopic activity (mean r = 0.73 ± 0.06), a fair correlation with CRP-increment (mean r = 0.55 ± 0.01) and a poor one with histologic activity (mean r = 0.35 ± 0.01). The discriminatory ability of the indexes for endoscopic mucosal healing was good for all the indexes (mean AUC = 0.87 ± 0.05). Patients with high clinical score had more flares and required more frequently increase of therapy at 1 year of follow up compared with patients with low score. CONCLUSIONS: Clinical indexes have a good correlation with endoscopic activity and can discriminate patients with and without mucosal healing. Patients with low and high score have different risk of disease flare and of need to increase therapy at 1 year. Clinical indexes may represent a useful tool for disease assessment in clinical practice in UC outpatients with mildmoderate disease
Transformations of Logic Programs on Infinite Lists
We consider an extension of logic programs, called \omega-programs, that can
be used to define predicates over infinite lists. \omega-programs allow us to
specify properties of the infinite behavior of reactive systems and, in
general, properties of infinite sequences of events. The semantics of
\omega-programs is an extension of the perfect model semantics. We present
variants of the familiar unfold/fold rules which can be used for transforming
\omega-programs. We show that these new rules are correct, that is, their
application preserves the perfect model semantics. Then we outline a general
methodology based on program transformation for verifying properties of
\omega-programs. We demonstrate the power of our transformation-based
verification methodology by proving some properties of Buechi automata and
\omega-regular languages.Comment: 37 pages, including the appendix with proofs. This is an extended
version of a paper published in Theory and Practice of Logic Programming, see
belo
Classical-path integral adaptive resolution in molecular simulation: towards a smooth quantum-classical coupling
Simulations that couple different classical molecular models in an adaptive
way by changing the number of degrees of freedom on the fly, are available
within reasonably consistent theoretical frameworks. The same does not occur
when it comes to classical-quantum adaptivity. The main reason for this is the
difficulty in describing a continuous transition between the two different kind
of physical principles: probabilistic for the quantum and deterministic for the
classical. Here we report the basic principles of an algorithm that allows for
a continuous and smooth transition by employing the path integral description
of atoms.Comment: 8 pages 4 figure
Path Integral Molecular Dynamics within the Grand Canonical-like Adaptive Resolution Technique: Simulation of Liquid Water
Quantum effects due to the spatial delocalization of light atoms are treated
in molecular simulation via the path integral technique. Among several methods,
Path Integral (PI) Molecular Dynamics (MD) is nowadays a powerful tool to
investigate properties induced by spatial delocalization of atoms; however
computationally this technique is very demanding. The abovementioned limitation
implies the restriction of PIMD applications to relatively small systems and
short time scales. One possible solution to overcome size and time limitation
is to introduce PIMD algorithms into the Adaptive Resolution Simulation Scheme
(AdResS). AdResS requires a relatively small region treated at path integral
level and embeds it into a large molecular reservoir consisting of generic
spherical coarse grained molecules. It was previously shown that the
realization of the idea above, at a simple level, produced reasonable results
for toy systems or simple/test systems like liquid parahydrogen. Encouraged by
previous results, in this paper we show the simulation of liquid water at room
conditions where AdResS, in its latest and more accurate Grand-Canonical-like
version (GC-AdResS), is merged with two of the most relevant PIMD techniques
available in literature. The comparison of our results with those reported in
literature and/or with those obtained from full PIMD simulations shows a highly
satisfactory agreement
Can Mesoporous Silica Speed Up Degradation of Benzodiazepines? Hints from Quantum Mechanical Investigations
This work reports for the first time a quantum mechanical study of the interactions of a model benzodiazepine drug, i.e., nitrazepam, with various models of amorphous silica surfaces, differing in structural and interface properties. The interest in these systems is related to the use of mesoporous silica as carrier in drug delivery. The adopted computational procedure has been chosen to investigate whether silica–drug interactions favor the drug degradation mechanism or not, hindering the beneficial pharmaceutical effect. Computed structural, energetics, and vibrational properties represent a relevant comparison for future experiments. Our simulations demonstrate that adsorption of nitrazepam on amorphous silica is a strongly exothermic process in which a partial proton transfer from the surface to the drug is observed, highlighting a possible catalytic role of silica in the degradation reaction of benzodiazepines
Water on Pt(111): the importance of proton disorder
The structure of a water adlayer on Pt(111) surface is investigated by
extensive first principle calculations. Only allowing for proton disorder the
ground state energy can be found. This results from an interplay between
water/metal chemical bonding and the hydrogen bonding of the water network. The
resulting short O-Pt distance accounts for experimental evidences. The novelty
of these results shed a new light on relevant aspects of water-metal
interaction.Comment: 10 pages 4 figures (color
Be Decay Anomaly and Light
In this proceedings, we discuss a light (17 MeV) solution to the anomaly
observed in the decay of Beryllium-8 by the Atomki collaboration. We detail an
anomaly free model with minimal particle content which can satisfy all other
experimental constraints with gauge couplings .Comment: Prepared for the 2019 EW session of the 54th Rencontres de Moriond,
talk presented by Simon Kin
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