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Recent Submissions
Resolving the puzzle of sound propagation in liquid helium at low temperatures
(AIP Publishing, 2019-12) Scott, Tony C.; Zloshchastiev, Konstantin G.
Experimental data suggests that, at temperatures below 1 K, the pressure in liquid helium has a cubic dependence on density. Thus the speed of sound scales as a cubic root of pressure. Near a critical pressure point, this speed approaches zero whereby the critical pressure is negative, thus indicating a cavitation instability regime. We demonstrate that to explain this dependence, one has to view liquid helium as a mixture of three quantum Bose liquids: dilute (Gross–Pitaevskii-type) Bose–Einstein condensate, Ginzburg–Sobyanin-type fluid, and logarithmic superfluid. Therefore, the dynamics of such a mixture is described by a quantum wave equation, which contains not only the polynomial (Gross–Pitaevskii and Ginzburg–Sobyanin) nonlinearities with respect to a condensate wavefunction, but also a non-polynomial logarithmic nonlinearity. We derive an equation of state and speed of sound in our model, and show their agreement with the experiment.
Developing a data lakehouse for a South African government-sector training authority : implementing quality control for incremental extract-load-transform pipelines in the ingestion layer
(IGI Global, 2024-12) Govender, Priyanka; Naicker, Nalindren; Patel, Sulaiman Saleem; Joseph, Seena; Moonsamy, Devraj; Akinola, Ayotuyi Tosin; Madamshetty, Lavanya; Govender, Thamotharan Prinavin; Ogunleye, Olalekan Samuel
The Durban University of Technology is undertaking a project to develop a data lakehouse system for a South African government-sector training authority. This system is considered critical to enhance the monitoring and evaluation capabilities of the training authority and ensure service delivery. Ensuring the quality of data ingested into the lakehouse is critical, as poor data quality deteriorates the efficiency of the lakehouse solution. This chapter studies quality control for ingestion-layer pipelines to propose a data quality framework. Metrics considered for data quality were completeness, accuracy, integrity, correctness, and timeliness. The framework was evaluated by practically applying it to a sample semi-structured dataset to gauge its effectiveness. Recommendations for future work include expanded integration, such as incorporating data from more varied sources and implementing incremental data ingestion triggers.
Resolving the puzzle of sound propagation in a dilute Bose-Einstein condensate
(World Scientific Pub Co Pte Ltd, 2022-08-10) Zloshchastiev, Konstantin G.
A unified model of a dilute Bose–Einstein condensate is proposed, combining the logarithmic and Gross–Pitaevskii (GP) nonlinear terms in a wave equation, where the GP term describes two-body interactions, as suggested by the standard perturbation theory; while the logarithmic term is essentially nonperturbative, and takes into account quantum vacuum effects. The model is shown to have excellent agreement with sound propagation data in the condensate of cold sodium atoms known since the now classic works by Andrews and collaborators. The data also allowed us to place constraints on two of the unified model’s parameters, which describe the strengths of the logarithmic and GP terms. Additionally, we suggest an experiment constraining the value of the third parameter (the characteristic density scale of the logarithmic part of the model), using the conjectured attraction–repulsion transition of many-body interaction inside the condensate.
Sound propagation in cigar-shaped Bose liquids in the Thomas-Fermi approximation : a comparative study between Gross-Pitaevskii and logarithmic models
(MDPI AG, 2022-11) Zloshchastiev, Konstantin G.
A comparative study is conducted of the propagation of sound pulses in elongated Bose liquids and Bose-Einstein condensates in Gross-Pitaevskii and logarithmic models, by means of the Thomas-Fermi approximation. It is demonstrated that in the linear regime the propagation of small density fluctuations is essentially one-dimensional in both models, in the direction perpendicular to the cross section of a liquid’s lump. Under these approximations, it is demonstrated that the speed of sound scales as a square root of particle density in the case of the Gross-Pitaevskii liquid/condensate, but it is constant in a case of the homogeneous logarithmic liquid.
Temperature-driven dynamics of quantum liquids : logarithmic nonlinearity, phase structure and rising force
(World Scientific Pub Co Pte Ltd, 2019-07-10) Zloshchastiev, Konstantin G.
We study a large class of strongly interacting condensate-like materials, which can be characterized by a normalizable complex-valued function. A quantum wave equation with logarithmic nonlinearity is known to describe such systems, at least in a leading-order approximation, wherein the nonlinear coupling is related to temperature. This equation can be mapped onto the flow equations of an inviscid barotropic fluid with intrinsic surface tension and capillarity; the fluid is shown to have a nontrivial phase structure controlled by its temperature. It is demonstrated that in the case of a varying nonlinear coupling an additional force occurs, which is parallel to a gradient of the coupling. The model predicts that the temperature difference creates a direction in space in which quantum liquids can flow, even against the force of gravity. We also present arguments explaining why superfluids, be it superfluid components of liquified cold gases or Cooper pairs inside superconductors, can affect closely positioned acceleration-measuring devices.