Flat Sector Research Articles

Axialgravisolitons at infinite corner

Abstract Gravitational solitons (gravisolitons) are particular exact solutions of Einstein field equation in vacuum build on a given background solution. Their interpretation is not yet fully clear but they contain many of the physically relevant solutions low N-solitons solutions. 
However, a systematic study and characterization of gravisolitons solution for every N is lacking and their relevance in a theory of quantum gravity is not fully understood. This work aims to investigate and characterize some properties of N-axialsoliton solutions such as their asymptotically behaviour and asymptotic symmetries given minimal assumptions on the background metric. We develop an explicit systematic asymptotically expansion for the N-axialsoliton solution and we compute the leading order of the asymptotic killing vectors. Moreover, in the perspective to better understand the role of gravisolitons in quantum gravity we make a link, and a one of the first explicit test, to the corner symmetry proposal deriving which subalgebra of the universal corner symmetry algebra is generated by the asymptotic Killing vectors of N-axialsoliton solution. In the spirit of the corner proposal, the axialgravisoliton corner symmetry algebra (agcsa) can be useful for the quantization of the non-asymptotically flat sector of gravity while, in the spirit of IR triangle, new soft theorems and memory effects could emerge.

Bouncing Universe in loop quantum gravity: full theory calculation

In loop quantum gravity mathematically rigorous models of full quantum gravity were proposed. In this paper we will study a cosmological sector of one of the models describing quantum gravity with positive cosmological constant coupled to massless scalar field. In our previous research we introduced a method to reduce the model to homogeneous-isotropic sector at the quantum level. In this paper we propose a method to restrict our homogeneous-isotropic model to the spatially flat sector. After this restriction the number of degrees of freedom gets substantially reduced. This allows us to make numerical and analytical calculations. Remarkably, the resulting model shares some structural similarities with the loop quantum cosmological models and therefore sheds some new light on the relation between loop quantum gravity and loop quantum cosmology. According to our model the evolution of the Universe is periodic. The quantum gravity effects resolve the Big Bang singularity leading to a Big Bounce and cause the Universe to contract after a classical expansion phase.

Problem of environmental remediation of the river runoff of basin geosystem of the small river Alma (Republic of Crimea)

An assessment of the ecological state of the small river basin Alma of the Republic of Crimea has been carried out. Due to intensive nature management in the 20th century, the primary natural environment was transformed into a natural-engineering system (NES). The critical components of the NES are the lowland sector and surface waters basin. The flat sector turned into an agricultural landscape with a low coefficient of natural protection, it needs transformation based on landscape planning. Runoff the Alma River is almost completely regulated by reservoirs and ponds, as a result of which the channel is deprived of water for most of the year. It is proposed to restore the natural flow of the river by redistributing the reserves of the Partizansky reservoir and establishing Western European water consumption standards for Simferopol.

Flow around a corner in the water impact problem

In this work, we study the local flow in the vicinity of a flat sector of arbitrary angle α in the water impact problem as motivated by recent experimental observations in the author's laboratory. The key question is as to why the ejecta formed during the impact at zero deadrise angle is considerably higher along a straight edge of the sector compared to that near a sharp corner α < π, e.g., if the impacting body is a rectangular plate. Resolving this question is made possible by the discovered here mathematical equivalence of the problem to electromagnetic diffraction phenomena. The main result of the present study is the revealed and quantified influence of the geometry of a flat plate corner on the fluid flow around it, which also contributes to the understanding of certain three-dimensional effects in the water impact problem and provides a generalization of the classical two-dimensional results on the impact at zero deadrise angle. The offered theoretical solution is also qualitatively supported with the help of particle image velocimetry measurements.

Cosmological sector for localized mass and spin in 2+1 dimensional topologically massive gravity

Abstract The cosmological sector to the full non-linear topologically massive gravity (TMG) is obtained for localized sources of mass m and spin σ besides the asymptotically spinning conical flat sector previously obtained [A. Edery, M.B. Paranjape, gr-qc/9606029, to be published]. In a small region near but outside the sources, the metric resembles the spinning conical flat metric but we find that the mass m creates a negative deficit angle of 3 m as opposed to m . Furthermore, it is not possible to recover the results of pure Einstein gravity in the limit μ →∞ unlike the flat sector.

Asymptotic Analysis of a Narrow Gas-Lubricated, Flat Sector Thrust Bearing

The method of matched expansions is employed to analyze the steady state operation of a finite gas-lubricated flat sector bearing for the case where the ratio of radial to circumferential dimensions is small and the relevant bearing number, Λ, is moderate. This technique yields general expressions for the pressure distribution, load bearing capacity, power loss and center of pressure location that are valid for a significant and continuous range of bearing dimensions, orientations and operating conditions. Comparisons are made, where possible, with the existing results from the literature obtained by numerical methods.

Electric singularity near the tip of a sharp cone

The singularity of the electric fields, proportional to the radial coordinate value R/sup nu -1/, is investigated for a very sharp, perfectly conducting cone of arbitrary cross section. It is shown that, in the limit of a very small cone, the exponent nu tends to zero in proportion with the inverse of the logarithm of the maximum opening angle. Results are shown for the circular and elliptic cone, with the flat sector as a special case, and for the pyramid with n equal faces. An expression, valid for arbitrary opening angles, is presented in the case of a flat sector. >

Closure to “Discussion of ‘An Accurate Solution of the Gas Lubricated, Flat Sector Thrust Bearing’” (1977, ASME J. Lubr. Technol., 99, p. 307)

Closure to “Discussion of ‘An Accurate Solution of the Gas Lubricated, Flat Sector Thrust Bearing’” (1977, ASME J. Lubr. Technol., 99, p. 307)

An Accurate Solution of the Gas Lubricated, Flat Sector Thrust Bearing

A flat sector shaped pad geometry for gas lubricated thrust bearings is analyzed considering both pitch and roll angles of the pad and the true film thickness distribution. Maximum load capacity is achieved when the pad is tilted so as to create a uniform minimum film thickness along the pad trailing edge. Performance characteristics for various geometries and operating conditions of gas thrust bearings are presented in the form of design curves. A comparison is made with the rectangular slider approximation. It is found that this approximation is unsafe for practical design, since it always overestimates load capacity.

A Cantilever Mounted Resilient Pad Gas Thrust Bearing

A gas thrust bearing consisting of flat sector shaped pads mounted on resilient metallic cantilever beams is described and analyzed. Compliance and stiffness of the bearing assembly are discussed and the effects of bearing design parameters on performance are shown. A design example is presented and a special case where zero axial movement of the runner can be obtained is pointed out.

The Dual Action Gas Thrust Bearing—A New High Load Bearing Concept

The principle of utilizing hydrodynamic effects in diverging films for improving load capacity in gas thrust bearings is discussed. A new concept of dual action bearing based on that principle is described and analyzed. The potential of the new bearing is demonstrated both analytically for an infinitely long slider and by numerical solution for a flat sector shaped thrust bearing. It is shown that the dual action bearing can extend substantially the range of load carrying capacity in gas lubricated thrust bearings and improve their efficiency.