2,659 research outputs found
The Long-Term Perspective of Human Impact on Landscape for Environmental Change (LoTEC) and Sustainability: From Botany to the Interdisciplinary Approach
The Long-Term Perspective of Human Impact on Landscape for Environmental Change—LoTEC is a special matter for environmental and ecological studies; it is an essential tool to sustainable development and better-informed landscape management decisions
Barbero-Immirzi field in canonical formalism of pure gravity
The Barbero-Immirzi (BI) parameter is promoted to a field and a canonical
analysis is performed when it is coupled with a Nieh-Yan topological invariant.
It is shown that, in the effective theory, the BI field is a canonical
pseudoscalar minimally coupled with gravity. This framework is argued to be
more natural than the one of the usual Holst action. Potential consequences in
relation with inflation and the quantum theory are briefly discussed.Comment: 10 page
Quantum realizations of Hilbert-Palatini second-class constraints
In a classical theory of gravity, the Barbero-Immirzi parameter ()
appears as a topological coupling constant through the Lagrangian density
containing the Hilbert-Palatini term and the Nieh-Yan invariant. In a quantum
framework, the topological interpretation of can be captured through a
rescaling of the wavefunctional representing the Hilbert-Palatini theory, as in
the case of the QCD vacuum angle. However, such a rescaling cannot be realized
for pure gravity within the standard (Dirac) quantization procedure where the
second-class constraints of Hilbert-Palatini theory are eliminated beforehand.
Here we present a different treatment of the Hilbert-Palatini second-class
constraints in order to set up a general rescaling procedure (a) for gravity
with or without matter and (b) for any choice of gauge (e.g. time gauge). The
analysis is developed using the Gupta-Bleuler and the coherent state
quantization methods.Comment: Published versio
Redox activity as a powerful strategy to tune magnetic and/or conducting properties in benzoquinone-based metal-organic frameworks
Multifunctional molecular materials have attracted material scientists for several years as they are promising materials for the future generation of electronic devices. Careful selection of their molecular building blocks allows for the combination and/or even interplay of different physical properties in the same crystal lattice. Incorporation of redox activity in these networks is one of the most appealing and recent synthetic strategies used to enhance magnetic and/or conducting and/or optical properties. Quinone derivatives are excellent redox-active linkers, widely used for various applications such as electrode materials, flow batteries, pseudo-capacitors, etc. Quinones undergo a reversible two-electron redox reaction to form hydroquinone dianions via intermediate semiquinone radical formation. Moreover, the possibility to functionalize the six-membered ring of the quinone by various substituents/functional groups make them excellent molecular building blocks for the construction of multifunctional tunable metal-organic frameworks (MOFs). An overview of the recent advances on benzoquinone-based MOFs, with a particular focus on key examples where magnetic and/or conducting properties are tuned/switched, even simultaneously, by playing with redox activity, is herein envisioned
The NorthStar Ambulatory Assessment in Duchenne muscular dystrophy: considerations for the design of clinical trials.
With the emergence of experimental therapies for Duchenne muscular dystrophy (DMD), it is fundamental to understand the natural history of this disorder to properly design clinical trials. The aims of this study were to assess the effects produced on motor function by different DMD genotypes and early initiation of glucocorticoids
Psychiatric profile of motor subtypes of de novo drug-naïve Parkinson's disease patients
Background: Parkinson's disease (PD) is a heterogeneous neurodegenerative disorder. It is well established that different motor subtypes of PD evolve with different clinical courses and prognoses. The complete psychiatric profile underlying these different phenotypes since the very early stage of the disease is debated. Aims of the study: We aimed at investigating the psychiatric profile of the three motor subtypes of PD (akinetic-rigid, tremor-dominant, and mixed) in de novo drug-naïve patients with PD. Methods: Sixty-eight patients with PD, divided into 39 akinetic-rigid (AR), seven mixed (MIX), and 22 tremor-dominant (TD) patients underwent a complete assessment of psychiatric, cognitive, and motor symptoms. Results: No significant differences were found among groups. Conclusions: Our results suggest that a differentiation of the psychiatric symptoms associated with specific motor subtypes of PD is not detectable in de novo drug-naïve patients. Previous evidence that emerges later along the disease progression may be a consequence of the dopaminergic and nondopaminergic damage increase
On the Generalized Einstein-Cartan Action with Fermions
From the freedom exhibited by the generalized Einstein action proposed in
[1], we show that we can construct the standard effective Einstein-Cartan
action coupled to the fermionic matter without the usual current-current
interaction and therefore an effective action which does not depend neither on
the Immirzi parameter nor on the torsion. This establishes the equivalence
between the Einstein-Cartan theory and the theory of the general relativity
minimally coupled to the fermionic matter.Comment: 8 pages, Added references, Corrected typos, Accepted in Class. Quant.
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Multiplicity of electron- and photon-seeded electromagnetic showers at multi-petawatt laser facilities
Electromagnetic showers developing from the collision of an ultra-intense
laser pulse with a beam of high-energy electrons or photons are investigated
under conditions relevant to future experiments on multi-petawatt laser
facilities. A semi-analytical model is derived that predicts the shower
multiplicity, i.e. the number of pairs produced per incident seed particle
(electron or gamma photon). The model is benchmarked against particle-in-cell
simulations and shown to be accurate over a wide range of seed particle
energies (100 MeV - 40 GeV), laser relativistic field strengths (), and quantum parameter (ranging from 1 to 40). It is shown
that, for experiments expected in the next decade, only the first generations
of pairs contribute to the shower while multiplicities larger than unity are
predicted. Guidelines for forthcoming experiments are discussed considering
laser facilities such as Apollon and ELI Beamlines. The difference between
electron- and photon seeding and the influence of the laser pulse duration are
investigated.Comment: 23 pages, 9 figure
Metal-Organic Framework vs. Coordination Polymer-Influence of the Lanthanide on the Nature of the Heteroleptic Anilate/Terephtalate 3D Network
Metal-organic frameworks (MOFs), whose definition has been regularly debated, are a sub-class of coordination polymers (CPs) which may feature both an overall 3D architecture and some degree of porosity. In this context, MOFs based on lanthanides (Ln-MOFs) could find many applications due to the combination of sorption properties and magnetic/luminescent behaviors. Here we report rare examples of 3D Ln-CPs based on anilate linkers, obtained under solvothermal conditions using a heteroleptic strategy. The three compounds of formula [Yb-2(mu-ClCNAn)(2)(mu-F4BDC)(H2O)(4)]center dot(H2O)(3) (1), [Er-2(mu-ClCNAn)(2)(mu-F4BDC)(H2O)(4)]center dot(H2O)(4) (2) and [Eu-2(mu-ClCNAn)(2)(mu-F4BDC)(H2O)(6)] (3) have been characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and optical measurements. Structural characterization revealed that compounds 1 and 2 present an interesting MOF architecture with extended rectangular cavities which are only filled with water molecules. On the other hand, compound 3 shows a much more complex topology with no apparent cavities. We discuss here the origins of such differences and highlight the crucial role of the Ln(III) ion nature for the topology of the CP. Compounds 1 and 2 now offer a playground to investigate the possible synergy between gas/solvent sorption and magnetic/luminescent properties of Ln-MOFs
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