2,052 research outputs found
On a Gromoll-Meyer type theorem in globally hyperbolic stationary spacetimes
Following the lines of the celebrated Riemannian result of Gromoll and Meyer,
we use infinite dimensional equivariant Morse theory to establish the existence
of infinitely many geometrically distinct closed geodesics in a class of
globally hyperbolic stationary Lorentzian manifolds.Comment: 39 pages, LaTeX2e, amsar
Impact of COVID-19 on maxillofacial surgery practice: a worldwide survey
The outbreak of coronavirus disease 2019 (COVID-19) is rapidly changing our habits. To date, April 12, 2020, the virus has reached 209 nations, affecting 1.8 million people and causing more than 110,000 deaths. Maxillofacial surgery represents an example of a specialty that has had to adapt to this outbreak, because of the subspecialties of oncology and traumatology. The aim of this study was to examine the effect of this outbreak on the specialty of maxillofacial surgery and how the current situation is being managed on a worldwide scale. To achieve this goal, the authors developed an anonymous questionnaire which was posted on the internet and also sent to maxillofacial surgeons around the globe using membership lists from various subspecialty associations. The questionnaire asked for information about the COVID-19 situation in the respondent's country and in their workplace, and what changes they were facing in their practices in light of the outbreak. The objective was not only to collect and analyse data, but also to highlight what the specialty is facing and how it is handling the situation, in the hope that this information will be useful as a reference in the future, not only for this specialty, but also for others, should COVID-19 or a similar global threat arise again
Neonatal Brain MRI and Motor Outcome at School Age in Children with Neonatal Encephalopathy: A Review of Personal Experience
The aim of this paper is to review (i) the
spectrum of neuromotor function at school age in
children who had been born full-term and
presented with neonatal encephalopathy (NE) and
low Apgar scores and (ii) the relation between the
presence/absence of such difficulties and neonatal
brain MRI. Motor outcome appears to be mainly
related to the severity of basal ganglia and
internal capsule involvement. Severe basal ganglia
lesions were always associated with the most
severe outcome, microcephaly, tetraplegia, and
severe global delay, whereas more discrete basal
ganglia lesions were associated with athetoid
cerebral palsy, with normal cognitive development
or minor neuro-motor abnormalities. White
matter lesions were associated with abnormal
motor outcome only if the internal capsule was
involved. Children with moderate white matter
changes but normal internal capsule, had normal
motor outcome at school age
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
Chirality of tensor perturbations for complex values of the Immirzi parameter
In this paper we generalise previous work on tensor perturbations in a de
Sitter background in terms of Ashtekar variables to cover all complex values of
the Immirzi parameter gamma (previous work was restricted to imaginary gamma).
Particular attention is paid to the case of real gamma. Following the same
approach as in the imaginary case, we can obtain physical graviton states by
invoking reality and torsion free conditions. The Hamiltonian in terms of
graviton states has the same form whether gamma has a real part or not; however
changes occur for the vacuum energy and fluctuations. Specifically, we observe
a gamma dependent chiral asymmetry in the vacuum fluctuations only if gamma has
an imaginary part. Ordering prescriptions also change this asymmetry. We thus
present a measurable result for CMB polarisation experiments that could shed
light on the workings of quantum gravity.Comment: 6 pages, 1 figur
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.
Gra
Generalized Chern-Simons Modified Gravity in First-Order Formalism
We propose a generalization of Chern-Simons (CS) modified gravity in
first-order formalism. CS modified gravity action has a term that comes from
the chiral anomaly which is Pontryagin invariant. First-order CS modified
gravity is a torsional theory and in a space-time with torsion the chiral
anomaly includes a torsional topological term called Nieh-Yan invariant. We
generalize the CS modified gravity by adding the Nieh-Yan term to the action
and find the effective theory. We compare the generalized theory with the
first-order CS modified gravity and comment on the similarities and
differences.Comment: 8 pages, an author added, new paragraphs, comments and references
added, published in Gen. Relativ. Gravi
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
Option pricing in an exponential MixedTS Lévy process
In this paper we present an option pricing model based on the assumption that the underlying asset price is an exponential Mixed Tempered Stable L\ue9vy process. We also introduce a new R package called PricingMixedTS that allows the user to calibrate this model using procedures based on loss or likelihood functions
- …