306 research outputs found
Hamiltonian analysis of SO(4,1) constrained BF theory
In this paper we discuss canonical analysis of SO(4,1) constrained BF theory.
The action of this theory contains topological terms appended by a term that
breaks the gauge symmetry down to the Lorentz subgroup SO(3,1). The equations
of motion of this theory turn out to be the vacuum Einstein equations. By
solving the B field equations one finds that the action of this theory contains
not only the standard Einstein-Cartan term, but also the Holst term
proportional to the inverse of the Immirzi parameter, as well as a combination
of topological invariants. We show that the structure of the constraints of a
SO(4,1) constrained BF theory is exactly that of gravity in Holst formulation.
We also briefly discuss quantization of the theory.Comment: 9 page
MacDowell-Mansouri gravity and Cartan geometry
The geometric content of the MacDowell-Mansouri formulation of general
relativity is best understood in terms of Cartan geometry. In particular,
Cartan geometry gives clear geometric meaning to the MacDowell-Mansouri trick
of combining the Levi-Civita connection and coframe field, or soldering form,
into a single physical field. The Cartan perspective allows us to view physical
spacetime as tangentially approximated by an arbitrary homogeneous "model
spacetime", including not only the flat Minkowski model, as is implicitly used
in standard general relativity, but also de Sitter, anti de Sitter, or other
models. A "Cartan connection" gives a prescription for parallel transport from
one "tangent model spacetime" to another, along any path, giving a natural
interpretation of the MacDowell-Mansouri connection as "rolling" the model
spacetime along physical spacetime. I explain Cartan geometry, and "Cartan
gauge theory", in which the gauge field is replaced by a Cartan connection. In
particular, I discuss MacDowell-Mansouri gravity, as well as its more recent
reformulation in terms of BF theory, in the context of Cartan geometry.Comment: 34 pages, 5 figures. v2: many clarifications, typos correcte
THE NUMERICAL MODELING OF LAVA DOME EVOLUTION AT VOLCÁN DE COLIMA USING VOF AND SPH METHODS
Lava flows from extrusive volcanic eruptions can have catastrophic consequences both for human life and the environment. Modeling such situations is an important scientific problem. The main driving forces in the evolution of the mentioned lava flows are gravitational forces, viscous friction forces on the surface of the spill, and the processes of crystallization of molten rocks into lava plateau, tubes, and domes. In this paper, the mathematical model of an extrusive volcanic eruption includes the Navier–Stokes equation, the incompressibility equation, the viscous phase transfer equation, as well as the corresponding initial and boundary conditions. Mathematical models of volcanic lava flows are considered and compared within the Euler (Volume Of Fluid – VOF) and Lagrange (Smooth Particle Hydrodynamic – SPH) formulations. ANSYS Fluent, OpenFOAM, and SPlisHSPlasH packages were used for computer simulation. Computer simulation algorithms for the problem are implemented in C++ language. Numerical modeling of the evolution of a real lava dome formed at the Colima volcano (Mexico) in February–March 2013 was carried out. For this experiment, information about the dynamics of lava dome growth, collected during the eruption, was used. It is shown how the computer simulation approach makes it possible to establish the dependence of the lava dome morphology on the rheology of a highly viscous fluid and the intensity of lava outflow. © 2022 Chinese Journal of Dermatology. All rights reserved
NMDB database and global survey method
The method of a global survey developed in the 1970s allows using a world-wide network of neutron monitor
stations as a single multidirectional device. Wherein, receiving characteristics of each device, which reflects
their geometries and geographical positions, are taken into account. Such an approach makes it possible to
define the first two angular moments of the distribution function of cosmic rays in the interplanetary space
at each hour of observation. With the creation in 2008/2009 and subsequent development of an international
database of neutron monitors NMDB, for the first time it appeared an opportunity to use the global survey
method in real-time mode. Such a situation creates a unique possibility to use the results not only for scienti-
fic researches but also for space weather forecasting. To use the data of the world-wide network of neutron
monitors it is necessary to carry preliminary preparations. Thereby, in the current work, the main attention is
attracted to a solution to some practical questions that arise when using the NMDB in real-time
NMDB and space weather forecasting
From the creation of NMDB in 2007 and through the growth in the number of stations and the data accumulation, the ShICRA SB RAS group continuously have used its facilities. For the last years we have created a method for short-term forecasting of intense geomagnetic storms with an advance time 1-2 days. The probability of forecasting is around 80%. We have reported about the method in the previous NMDB: virtual symposium on cosmic ray studies with neutron detectors in 2020. The method is based on the global survey method that was developed in Yakutsk in 1960s and uses the world network of neutron monitors as a single multidirectional device. The method is intended to estimate hourly dynamics of cosmic ray anisotropy in free-space. Note that only with the NMDB creation we managed to implement it in real time mode. Now we started work on creating another method for space weather forecasting by measurements of cosmic ray fluctuations. For this purpose, we use 1-min data of NMDB. In the current report we present the first results of our investigation on forecasting of intense geomagnetic storms with Dst < -50 nT. The results obtained indicate the possibility of developing and implementing in real time a method for predicting strong geophysical manifestations of space weather on the basis of ground-based cosmic ray measurements
Neuroimmunological mechanisms of chronic pain syndrome
The article considers the mechanisms of chronic low back pain. Three pathophysiological mechanisms: nociceptive, neurogenic (neuropathic), and psychogenic are noted to be involved in the development of pain syndrome. The role of cellular and molecular changes in the posterior horn and in the somatosensory dysregulated mechanism of neuropathic pain is shown. Immunological processes, including neurohumoral (serotoninergic) and hormonal (sex hormones and specific proteins) ones, play an important role in the development of pain. The generalization and further study of these mechanisms are embodied in approaches to therapy for pain syndromes and hence these require analysis and further investigation
Radiation Tolerance of Single-Sided Microstrip Detector with Insulator
The ALICE Collaboration is investigating the radiation tolerance and operation of silicon microstrip detectors for the inner tracking system. Detectors with and without an additional layer of Si3N4 insulator were made in one set, using the same thickness of SiO2 insulator. Measurements were made on both types of detectors after irradiation with 20 MeV electrons, using doses up to 2Mrad. The additional Si3N4 layer allows a coupling capacitor breakdown voltage larger than 100 V and capacitor yield larger than 99 percent. However, the leakage current for detectors with double layer insulator is about 20 nA per strip while the leakage current for the single layer SiO2 insulated detectors is only 0.5 nA. The 20 nA leakage current leads to 450 electrons noise when the ALICE 128C electronics with a peaking time of 1.4 microseconds is used. At a 1 nA leakage current the noise is 100 electrons. The ENC for an input capacitance of 5 pF is 300 electrons. Since all detectors show an increased leakage current after irradiation, the difference between the single and duoble layer insulation detectors becomes negligible when doses of the order of several hundreds of krad are applied
Interstrip resistance of a semiconductor microstrip detector
In this work the interelement (interstrip) resistance of the microstrip detector is studied. A few detectors with a different construction are investigated. The dependence of the interstrip resistance on the dose of detector irradiation with electrons is obtained. The possibility of application interstrip resistance measurement for the determination of the good strip yield is shown
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