155 research outputs found
The Hubbard model with spin orbit coupling: a lattice gauge theory approach
We study the symmetry properties of the Hubbard model with spin-orbit
interactions of Rashba and Dresselhaus type. These interactions break the
rotational symmetry in spin space, so that the magnetic order cannot be
excluded by using the Bogoliubov inequality method. Nevertheless, we rigorously
show that the existence of the magnetic long-range orders may be ruled out when
the Rashba and Dresselhaus coupling constants are equal in modulus, whereas the
eta-pairing can be always ruled out, regardless of the microscopic parameters
of the model. These results are obtained by imposing locally the SU(2) gauge
symmetry on the lattice, and rewriting the spin-orbit interactions in such a
way that they are included in the path ordered of the gauge field on lattice.Comment: 7 page
The measurement problem in quantum mechanics
In this paper, we discuss the importance of measurement in quantum mechanics and the so-called measurement problem. Any quantum system can be described as a linear combination of eigenstates of an operator representing a physical quantity; this means that the system can be in a superposition of states that corresponds to different eigenvalues, i.e., different physical outcomes, each one incompatible with the others. The measurement process converts a state of superposition (not macroscopically defined) in a well-defined state. We show that, if we describe the measurement by the standard laws of quantum mechanics, the system would preserve its state of superposition even on a macroscopic scale. Since this is not the case, we assume that a measurement does not obey to standard quantum mechanics, but to a new set of laws that form a “quantum measurement theory”
Topological transition in Pb1-xSnxSe using Meta-GGA
We calculate the mirror Chern number (MCN) and the band gap for the alloy
Pb1-xSnxSe as a function of the concentration x by using virtual crystalline
approximation. We use the electronic structure from the relativistic density
functional theory calculations in the Generalized-Gradient- Approximation (GGA)
and meta-GGA approximation. Using the modified Becke-Johnson meta- GGA
functional, our results are comparable with the available experimental data for
the MCN as well as for the band gap. We advise to use modified Becke-Johnson
approximation with the parameter c=1.10 to describe the transition from trivial
to topological phase for this class of compounds.Comment: 5 pages, 5 figures, 1 table. arXiv admin note: text overlap with
arXiv:2302.0621
Intra-chain collinear magnetism and inter-chain magnetic phases in Cr3As3-K-based materials
We perform a comparative study of the KCr3As3 and the K2Cr3As3 quasi 1D
compounds, and show that the strong interplay between the lattice and the spin
degrees of freedom promotes a new collinear ferrimagnetic ground state within
the chains in presence of intrachain antiferromagnetic couplings. We propose
that the interchain antiferromagnetic coupling in KCr3As3 plays a crucial role
for the experimentally observed spin-glass phase with low critical temperature.
In the same region of the parameter space, we predict K2Cr3As3 to be
non-magnetic but on the verge of the magnetism, sustaining interchain
ferromagnetic spin fluctuations while the intrachain spin fluctuations are
antiferromagnetic.Comment: Accepted in Phys. Rev. B as a regular articl
Relationship between default mode network and resting-state electroencephalographic alpha rhythms in cognitively unimpaired seniors and patients with dementia due to alzheimer’s disease
Here we tested the hypothesis of a relationship between the cortical default mode network (DMN) structural integrity and the resting-state electroencephalographic (rsEEG) rhythms in patients with Alzheimer’s disease with dementia (ADD). Clinical and instrumental datasets in 45 ADD patients and 40 normal elderly (Nold) persons originated from the PDWAVES Consortium (www.pdwaves.eu). Individual rsEEG delta, theta, alpha, and fixed beta and gamma bands were considered. Freeware platforms served to derive (1) the (gray matter) volume of the DMN, dorsal attention (DAN), and sensorimotor (SMN) cortical networks and (2) the rsEEG cortical eLORETA source activities. We found a significant positive association between the DMN gray matter volume, the rsEEG alpha source activity estimated in the posterior DMN nodes (parietal and posterior cingulate cortex), and the global cognitive status in the Nold and ADD participants. Compared with the Nold, the ADD group showed lower DMN gray matter, lower rsEEG alpha source activity in those nodes, and lower global cognitive status. This effect was not observed in the DAN and SMN. These results suggest that the DMN structural integrity and the rsEEG alpha source activities in the DMN posterior hubs may be related and predict the global cognitive status in ADD and Nold persons.IRCCS San Raffaele Pisana of Rome ; Ministero della Salut
Tuning interchain ferromagnetic instability in A2Cr3As3 ternary arsenides by chemical pressure and uniaxial strain
We analyze the effects of chemical pressure induced by alkali metal
substitution and uniaxial strain on magnetism in the A2Cr3As3 (A = Na, K, Rb,
Cs) family of ternary arsenides with quasi-one dimensional structure. Within
the framework of the density functional theory, we predict that the
non-magnetic phase is very close to a 3D collinear ferrimagnetic state, which
realizes in the regime of moderate correlations, such tendency being common to
all the members of the family with very small variations due to the different
interchain ferromagnetic coupling. We uncover that the stability of such
interchain ferromagnetic coupling has a non-monotonic behavior with increasing
the cation size, being critically related to the degree of structural
distortions which is parametrized by the Cr-As-Cr bonding angles along the
chain direction. In particular, we demonstrate that it is boosted in the case
of the Rb, in agreement with recent experiments. We also show that uniaxial
strain is a viable tool to tune the non-magnetic phase towards an interchain
ferromagnetic instability. The modifcation of the shape of the Cr triangles
within the unit cell favors the formation of a net magnetization within the
chain and of a ferromagnetic coupling among the chains. This study can provide
relevant insights about the interplay between superconductivity and magnetism
in this class of materials.Comment: Accepted in Phys. Rev. Materials as a regular article. 13 pages, 23
figures, 3 table
An Encapsulated Juice Powder Concentrate Improves Markers of Pulmonary Function and Cardiovascular Risk Factors in Heavy Smokers
Cigarette smoking is associated with reduced pulmonary function and increased risk factors for cardiovascular disease. This randomized placebo-controlled double-blind study evaluated the effects of two different combinations of mixed fruit and vegetable juice powder concentrate (Juice Plus+, NSA, Collierville, TN) on heavy smokers
Resting state electroencephalographic rhythms are affected by immediately preceding memory demands in cognitively unimpaired elderly and patients with mild cognitive impairment
Experiments on event-related electroencephalographic oscillations in aged
people typically include blocks of cognitive tasks with a few minutes of
interval between them. The present exploratory study tested the effect of
being engaged on cognitive tasks over the resting state cortical arousal
after task completion, and whether it differs according to the level of the
participant’s cognitive decline. To investigate this issue, we used a local
database including data in 30 healthy cognitively unimpaired (CU) persons
and 40 matched patients with amnestic mild cognitive impairment (aMCI).
They had been involved in 2 memory tasks for about 40 min and underwent
resting-state electroencephalographic (rsEEG) recording after 5 min from the
task end. eLORETA freeware estimated rsEEG alpha source activity as an
index of general cortical arousal. In the CU but not aMCI group, there was
a negative correlation between memory tasks performance and posterior
rsEEG alpha source activity. The better the memory tasks performance,
the lower the posterior alpha activity (i.e., higher cortical arousal). There
was also a negative correlation between neuropsychological test scores of
global cognitive status and alpha source activity. These results suggest that
engagement in memory tasks may perturb background brain arousal for
more than 5 min after the tasks end, and that this effect are dependent on participants global cognitive status. Future studies in CU and aMCI groups may
cross-validate and extend these results with experiments including (1) rsEEG
recordings before memory tasks and (2) post-tasks rsEEG recordings after 5,
15, and 30 minThis study was supported by grants from the Spanish Government, Ministerio de Ciencia e Innovación (PSI2017-
89389-C2-R and PID2020-114521RB-C21/C22); the Galician Government (Xunta de Galicia), Axudas para a Consolidación e Estruturación de Unidades de Investigación Competitivas do Sistema Universitario de Galicia: GRC (GI-1807- USC); Ref: ED431-2017/27 and ED431C-2021/04; all with ERDF/FEDER funds. DP was supported by the Fundação para a Ciência e a Tecnologia (FCT) grant with reference SFRH/BPD/120111/2016. AF was supported by an FPI grant from the Ministerio de Ciencia e Innovación with reference PRE2018-085514S
Poor reactivity of posterior electroencephalographic alpha rhythms during the eyes open condition in patients with dementia due to Parkinson's disease
Here, we hypothesized that the reactivity of posterior resting-state electroencephalographic (rsEEG) alpha rhythms during the transition from eyes-closed to -open condition might be lower in patients with Parkinson's disease dementia (PDD) than in patients with Alzheimer's disease dementia (ADD). A Eurasian database provided clinical-demographic-rsEEG datasets in 73 PDD patients, 35 ADD patients, and 25 matched cognitively unimpaired (Healthy) persons. The eLORETA freeware was used to estimate cortical rsEEG sources. Results showed substantial (greater than −10%) reduction (reactivity) in the posterior alpha source activities from the eyes-closed to the eyes-open condition in 88% of the Healthy seniors, 57% of the ADD patients, and only 35% of the PDD patients. In these alpha-reactive participants, there was lower reactivity in the parietal alpha source activities in the PDD group than in the healthy control seniors and the ADD patients. These results suggest that PDD patients show poor reactivity of mechanisms desynchronizing posterior rsEEG alpha rhythms in response to visual inputs. That neurophysiological biomarker may provide an endpoint for (non) pharmacological interventions for improving vigilance regulation in those patients.European Consortium of Dementia ; IRCCS San Raffaele Rome ; World Medical Association ; Ministero della Salute ; Sapienza Università di Rom
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