1,226 research outputs found
Dualism between Physical Frames and Time in Quantum Gravity
In this work we present a discussion of the existing links between the
procedures of endowing the quantum gravity with a real time and of including in
the theory a physical reference frame. More precisely, as first step, we
develop the canonical quantum dynamics, starting from the Einstein equations in
presence of a dust fluid and arrive to a Schroedinger evolution. Then, by
fixing the lapse function in the path integral of gravity, we get a
Schroedinger quantum dynamics, of which eigenvalues problem provides the
appearance of a dust fluid in the classical limit. The main issue of our
analysis is to claim that a theory, in which the time displacement invariance,
on a quantum level, is broken, is indistinguishable from a theory for which
this symmetry holds, but a real reference fluid is included.Comment: 9 pages, submitted to Mod. Phys. Lett. A, major replacements in
section 3 and
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
Dystonia: sparse synapses for D2 receptors in striatum of a DYT1 knock-out mouse model
Dystonia pathophysiology has been partly linked to downregulation and dysfunction of dopamine D2 receptors in striatum. We aimed to investigate the possible morpho-structural correlates of D2 receptor downregulation in the striatum of a DYT1 Tor1a mouse model. Adult control Tor1a+/+ and mutant Tor1a+/â mice were used. The brains were perfused and free-floating sections of basal ganglia were incubated with polyclonal anti-D2 antibody, followed by secondary immune-fluorescent antibody. Confocal microscopy was used to detect immune-fluorescent signals. The same primary antibody was used to evaluate D2 receptor expression by western blot. The D2 receptor immune-fluorescence appeared circumscribed in small disks (~0.3â0.5 ÎŒm diameter), likely representing D2 synapse aggregates, densely distributed in the striatum of Tor1a+/+ mice. In the Tor1a+/â mice the D2 aggregates were significantly smaller (ÎŒm2 2.4 ± SE 0.16, compared to ÎŒm2 6.73 ± SE 3.41 in Tor1a+/+) and sparse, with ~30% less number per microscopic field, value correspondent to the amount of reduced D2 expression in western blotting analysis. In DYT1 mutant mice the sparse and small D2 synapses in the striatum may be insufficient to âgateâ the amount of presynaptic dopamine release diffusing in peri-synaptic space, and this consequently may result in a timing and spatially larger nonselective sphere of influence of dopamine action
Psychiatric profile of motor subtypes of de novo drug-naĂŻve 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-naĂŻve 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-naĂŻve patients. Previous evidence that emerges later along the disease progression may be a consequence of the dopaminergic and nondopaminergic damage increase
Generating functional for the gravitational field: implementation of an evolutionary quantum dynamics
We provide a generating functional for the gravitational field, associated to
the relaxation of the primary constraints as extended to the quantum sector.
This requirement of the theory, relies on the assumption that a suitable time
variable exist, when taking the T-products of the dynamical variables. More
precisely, we start from the gravitational field equations written in the
Hamiltonian formalism and expressed via Misner-like variables; hence we
construct the equation to which the T-products of the dynamical variables obey
and transform this paradigm in terms of the generating functional, as taken on
the theory phase-space. We show how the relaxation of the primary constraints
(which correspond to break down the invariance of the quantum theory under the
4-diffeomorphisms) is summarized by a free functional taken on the Lagrangian
multipliers, accounting for such constraints in the classical theory. The issue
of our analysis is equivalent to a Gupta-Bleuler approach on the quantum
implementation of all the gravitational constraints; in fact, in the limit of
small , the quantum dynamics is described by a Schr\"odinger equation,
as soon as the mean values of the momenta, associated to the lapse function and
the shift vector, are not vanishing. Finally we show how, in the classical
limit, the evolutionary quantum gravity reduces to General Relativity in the
presence of an Eckart fluid, which corresponds to the classical counterpart of
the physical clock, introduced in the quantum theory.Comment: 23 pages, no figures, to appear on International Journal of Modern
Physics
Gravity from a fermionic condensate of a gauge theory
The most prominent realization of gravity as a gauge theory similar to the
gauge theories of the standard model comes from enlarging the gauge group from
the Lorentz group to the de Sitter group. To regain ordinary Einstein-Cartan
gravity the symmetry must be broken, which can be accomplished by known
quasi-dynamic mechanisms. Motivated by symmetry breaking models in particle
physics and condensed matter systems, we propose that the symmetry can
naturally be broken by a homogenous and isotropic fermionic condensate of
ordinary spinors. We demonstrate that the condensate is compatible with the
Einstein-Cartan equations and can be imposed in a fully de Sitter invariant
manner. This lends support, and provides a physically realistic mechanism for
understanding gravity as a gauge theory with a spontaneously broken local de
Sitter symmetry.Comment: 16 page
Cognitive and neuropsychiatric profiles in idiopathic rapid eye movement sleep behavior disorder and Parkinson's disease
Rapid eye movement (REM) sleep behavior disorder (RBD) is a risk factor for developing Parkinson's disease (PD) and may represent its prodromal state. We compared neuropsychological and neuropsychiatric phenotypes of idiopathic (i) RBD, PD and healthy comparators (HC) in order to identify iRBD specific characteristics. Thirty-eight patients with iRBD, 38 PD patients with RBD (PD + RBD), 38 PD patients without RBD (PD-RBD) and 38 HC underwent a comprehensive neurological, neuropsychological and neuropsychiatric evaluation. iRBD, PD + RBD and PD-RBD performed worse than HC in short-term verbal memory, praxia, language and executive functions. iRBD had higher levels of anxiety, depression, apathy and alexithymia than HC. iRBD had higher levels of apathy than PD + RBD. Both PD groups had higher levels of anxiety and depression than HC. Surprisingly, iRBD performed better than all groups in long-term verbal memory. Patients diagnosed with iRBD are characterized by poor global cognitive performance, but better long-term memory and higher levels of depression, anxiety, alexithymia and apathy. Alexithymia and apathy in patients diagnosed with iRBD may be the expression of precocious derangement of emotional regulation, subsequently observed also in PD. Cognitive and neuropsychiatric symptoms of iRBD are early clinical manifestations of widespread neurodegeneration
Corrigendum to âPollen-based paleoenvironmental and paleoclimatic change at Lake Ohrid (south-eastern Europe) during the past 500 kaâ published in Biogeosciences, 13, 1423â1437, 2016
In this corrigendum we report an updated pollen record from the Lake Ohrid DEEP site spanning the past 500 ka whereby we have reprocessed and re-analyzed 104 samples affected by chemical procedure problems that occurred in one palynological laboratory. Firstly, these samples were affected by the use of wrong containers, causing in- adequate settling of particles at the set centrifuging speed. Secondly, HCl and HF treatments were combined without the prescribed intermediate centrifuging and decanting steps. The inaccuracy in the protocol resulted in the loss of smaller pollen grains and in the overrepresentation of bisaccate ones in most of the re-analyzed samples. We therefore provide an updated set of figures with the new data and have revised the description of the results, discussion and conclusions re- ported in Sadori et al. (2016) where necessary. We stress that the majority of the original results and conclusions remain valid, while the recordsâ reliability and resolution have improved as 12 samples that had been omitted in the original study because of low count sums are now included in the revised dataset (Sadori et al., 2018)
Is autonomic nervous system involved in restless legs syndrome during wakefulness?
OBJECTIVE: To investigate cardiovascular autonomic function in patients with restless leg syndrome (RLS) by means of cardiovascular reflexes and heart rate variability (HRV) during wakefulness.METHODS: Twelve RLS patients and 14 controls underwent cardiovascular function tests including head-up tilt test (HUTT), Valsalva maneuver, deep breathing, hand grip, and cold face. HRV analysis was performed in the frequency domain using both autoregressive (AR) and fast Fourier transform algorithms in rest supine condition and during HUTT.RESULTS: There was a significant increase in systolic blood pressure values in supine rest condition and a trend toward a lower Valsalva ratio in RLS patients with respect to controls. The significant and physiological changes of HRV at HUTT detected in healthy subjects were not found in RLS patients. CONCLUSION: RLS patients exhibit a tendency toward hypertension, reduced amplitude of both sympathetic and parasympathetic responses at HUTT, as well as blunted parasympathetic drive to blood pressure changes. These findings, if confirmed by more controlled studies, might support the hypothesis of auonomic nervous system involvement during wakefulness and consequently an enhanced cardiovascular risk in RLS
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