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

Model of Managed Self-Education in Postgraduate Training

Модель управляемого самообразования апробирована в учебном процессе аспирантуры в инженерном университете. Мониторинг процесса знакомства обучающихся с содержанием онлайн-курса, динамики представления отчетных материалов и результаты опроса аспирантов показали достаточную готовность данных субъектов образования к самостоятельной учебной активности без непосредственного участия преподавателя.The model of managed self-education has been tested in the educational process of postgraduate studies at the Engineering University. Monitoring of the process of students acquaintance with the content of the online course, the dynamics of the presentation of reporting materials and the results of the survey of graduate students showed sufficient readiness of these subjects for independent educational activity without the direct participation of the teacher

Kinematics of a relativistic particle with de Sitter momentum space

We discuss kinematical properties of a free relativistic particle with deformed phase space in which momentum space is given by (a submanifold of) de Sitter space. We provide a detailed derivation of the action, Hamiltonian structure and equations of motion for such free particle. We study the action of deformed relativistic symmetries on the phase space and derive explicit formulas for the action of the deformed Poincare' group. Finally we provide a discussion on parametrization of the particle worldlines stressing analogies and differences with ordinary relativistic kinematics.Comment: RevTeX, 12 pages, no figure

Radiation Tolerance of Single-Sided Microstrip Detector with Si3N4Si_{3}N_{4} 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

Permeability of Magnetic Cores with Air Gaps

The influence of the geometric dimensions of the cut core and the number and size of air gaps on the effective permeability was investigated. Using dimensional analysis, an equation was obtained that relates the permeability of the cut core to the simplest dimensionless combination of the mean magnetic flux length l, single air gap length lg1, the cross-sectional area S of the core, and gap number ng . Permeability calculated from the geometric parameters of the cut core was compared with the effective permeability obtained using a two-dimensional FEMM simulation. Simulation has shown that the equation derived from dimensional analysis provides the best fit. The influence of each significant parameters l, lg1, ng, and S on cut core permeability is demonstrated. Experimental results have shown that an equation derived from dimensional analysis can be used to predict cut core permeability. In this case, one should take into account the residual air gap that forms after cutting the core. A method for assessing the residual air gap is proposed. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

A Method for Magma Viscosity Assessment by Lava Dome Morphology

Lava domes form when a highly viscous magma erupts on the surface. Several types of lava dome morphology can be distinguished depending on the flow rate and the rheology of magma: obelisks, lava lobes, and endogenic structures. The viscosity of magma nonlinearly depends on the volume fraction of crystals and temperature. Here we present an approach to magma viscosity estimation based on a comparison of observed and simulated morphological forms of lava domes. We consider a two-dimensional axisymmetric model of magma extrusion on the surface and lava dome evolution, and assume that the lava viscosity depends only on the volume fraction of crystals. The crystallization is associated with a growth of the liquidus temperature due to the volatile loss from the magma, and it is determined by the characteristic time of crystal content growth (CCGT) and the discharge rate. Lava domes are modeled using a finite-volume method implemented in Ansys Fluent software for various CCGTs and volcanic vent sizes. For a selected eruption duration a set of morphological shapes of domes (shapes of the interface between lava dome and air) is obtained. Lava dome shapes modeled this way are compared with the observed shape of the lava dome (synthesized in the study by a random modification of one of the calculated shapes). To estimate magma viscosity, the deviation between the observed dome shape and the simulated dome shapes is assessed by three functionals: the symmetric difference, the peak signal-to-noise ratio, and the structural similarity index measure. These functionals are often used in the computer vision and in image processing. Although each functional allows to determine the best fit between the modeled and observed shapes of lava dome, the functional based on the structural similarity index measure performs it better. The viscosity of the observed dome can be then approximated by the viscosity of the modeled dome, which shape fits best the shape of the observed dome. This approach can be extended to three-dimensional case studies to restore the conditions of natural lava dome growth

Magnetizing of Finemet-type alloys by magnetization rotation in weak fields

Magnetic properties of functional magnetic materials depend on the magnetization processes nature. Creation of amorphous and nanocrystalline alloys using the rapid quenching technology is the result of the latest advances in magnetic materials area. Although significantly different in structure, they show excellence properties. In this paper we will investigate the magnetization properties of the Finemet-type nanocrystalline alloys in the range of their initial permeability formation. We will show that due to low level of effective magnetic anisotropy, even in weak fields, magnetization can occur through reversible, hysteresis-free rotation of the domain's magnetization vector. © Published under licence by IOP Publishing Ltd.Ministry of Science and Higher Education of the Russian Federation: 3.6121.2017/8.9, 4.9541.2017/8.9This work was supported by the Ministry of Science and higher Education and of the Russian Federation in the framework of state tasks No. 3.6121.2017/8.9 and No. 4.9541.2017/8.9

Kinematic Viscosity of Melt Prepared from an Amorphous Fe72.5Cu1Nb2Mo1.5Si14B9Ribbon

In this work, the viscosity of a melt prepared by melting an amorphous ribbon of Fe72.5Cu1Nb2Mo1.5Si14B9 alloy was studied. The amorphous ribbon was produced by rapid quenching of the melt, which was preheated at a temperature above (overheated mode) and below (not overheated mode) critical temperature Tk . A hysteresis loop was found in the temperature dependence of viscosity, the widest part of which falls on a temperature from 1670 K to Tk = 1760 K. In this temperature range, the melt has the highest activation energy and the largest cluster size. It has been proven that the melt viscosity increases with decreasing cluster size. In the low-temperature region, an overheated melt has the highest viscosity and the smallest cluster size comparable to the atomic size. It is shown that the heredity of the structure is preserved in the melt from the amorphous ribbon despite a number of structural transitions. © Published under licence by IOP Publishing Ltd

РОЛЬ УЧЕБНО-МАТЕРИАЛЬНОЙ БАЗЫ В ПОДГОТОВКЕ ВОЛОНТЕРОВ-СПАСАТЕЛЕЙ

The authors see the development of professional competencies of applied bachelor possible by means of further training and professional training on educational basis of volunteer organization; this is considered to be a promising direction in the training of engineers. The paper is aimed at making the grounds and application of educational basis of volunteer organizations for efficient Bachelor training on various courses as well as motivating the teachers for conducting seminars and applying the elements of educational basis. Many years’ experience of volunteer activity and chiefs of student clubs define the stages of educational base formation, pedagogical conditions of the base development, creation and implementation the program intended to create the facility for training process in the profession-oriented volunteer organizations. Guidance and experience of the Student Volunteer Club, organized by educational institution, allowed to define the stages of educational basis foundation, pedagogical conditions of its development, creation and constant updating during training. The research outlines the opportunities of professional competencies building while training Bachelors on the programme «Technosphere Safety” by means of further training on the basis of educational base of the volunteer organization. This base includes professional tests and guidance on supporting the educational base of volunteers –rescuers. The outlines insufficient number of classroom studies in Undegraduate that results in the fact that current educational base of university volunteer organizations enhances training and contributes to application of professional theoretical knowledge on the objects of educational base of volunteer organization.Развитие профессиональных компетенций студентов прикладного бакалавриата посредством дополнительного обучения и профессиональных проб на учебно-материальной базе профессионально ориентированной волонтерской организации является перспективным направлением в подготовке инженерных кадров. Целью работы является педагогическое обоснование и реализация программы создания учебно-материальной базы в профессионально ориентированных волонтерских организациях для повышения эффективности подготовки бакалавров по различным дисциплинам и мотивации преподавателей к проведению практических занятий с использованием объектов учебно-материальной базы. На многолетнем опыте деятельности волонтеров и руководителей студенческого клуба, организованного при образовательном учреждении, определены этапы формирования учебно-материальной базы, педагогические условия ее проектирования, создания и постоянной актуализации во время учебного процесса. Показана необходимость предоставления участникам волонтерских организаций возможности ее усовершенствования. В ходе работы определены возможности развития профессиональных компетенций студентов бакалавриата направления «Техносферная безопасность» посредством дополнительного обучения на учебно- материальной базе волонтерской организации по технологии профессиональных проб, разработаны рекомендации по созданию и поддержанию в актуальном состоянии учебно-материальной базы волонтеров-спасателей. Показано, что в связи с недостаточным количеством аудиторных практических занятий в основной образовательной программе бакалавриата актуальная учебно-материальная база волонтерских организаций вузов способствует реализации учебного процесса с большей результативностью, позволяя применить теоретические знания по специальности на объектах материальной базы волонтерской организации