Fluid Collapse Research Articles

Numerical Verification of the Solution to the Problem of Empty Cavity Collapse in a Viscous Fluid

Numerical Verification of the Solution to the Problem of Empty Cavity Collapse in a Viscous Fluid

Emergent modified gravity: The perfect fluid and gravitational collapse

Emergent modified gravity: The perfect fluid and gravitational collapse

Antibacterial activity and mechanism of chelerythrine against Streptococcus agalactiae.

Streptococcus agalactiae (S.agalactiae), also known as group B Streptococcus (GBS), is a highly infectious pathogen. Prolonged antibiotic usage leads to significant issues of antibiotic residue and resistance. Chelerythrine (CHE) is a naturally occurring benzophenidine alkaloid and chelerythrine chloride (CHEC) is its hydrochloride form with diverse biological and pharmacological activities. However, the antibacterial mechanism of CHEC against GBS remains unclear. Thus, this study aims to investigate the in vitro antibacterial activity of CHEC on GBS and elucidate its underlying mechanism. The antibacterial effect of CHEC on GBS was assessed using inhibitory zone, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) assays, as well as by constructing a time-kill curve. The antibacterial mechanism of CHEC was investigated through techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM), measurement of alkaline phosphatase (AKP) activity, determination of Na+ K+, Ca2+ Mg2+-adenosine triphosphate (ATP) activity, observation of membrane permeability, and analysis of intracellular reactive oxygen species (ROS) and mRNA expression levels of key virulence genes. The results demonstrated that the inhibition zone diameters of CHEC against GBS were 14.32 mm, 12.67 mm, and 10.76 mm at concentrations of 2 mg/mL, 1 mg/mL, and 0.5 mg/mL, respectively. The MIC and MBC values were determined as 256 μg/mL and 512 μg/mL correspondingly. In the time-kill curve, 8 × MIC, 4 × MIC and 2 × MIC CHEC could completely kill GBS within 24 h. SEM and TEM analyses revealed significant morphological alterations in GBS cells treated with CHEC including shrinkage, collapse, and leakage of cellular fluids. Furthermore, the antibacterial mechanism underlying CHEC's efficacy against GBS was attributed to its disruption of cell wall integrity as well as membrane permeability resulting in extracellular release of intracellular ATP, AKP, Na+ K+, Ca2+ Mg2+. Additionally CHEC could increase the ROS production leading to oxidative damage and downregulating mRNA expression levels of key virulence genes in GBS cells. In conclusion, CHEC holds potential as an antimicrobial agent against GBS and further investigations are necessary to elucidate additional molecular mechanisms.

Power law singularity for cavity collapse in a compressible Euler fluid with Tait–Murnaghan equation of state

Motivated by the high energy focusing found in rapidly collapsing bubbles, which is relevant to implosion processes that concentrate energy density, such as sonoluminescence, we consider a calculation of an empty cavity collapse in a compressible Euler fluid. We review and then use the method based on similarity theory that was previously used to compute the power law exponent n for the collapse of an empty cavity in water during the late stage of the collapse. We extend this calculation by considering different fluids surrounding the cavity, all of which are parametrized by the Tait–Murnaghan equation of state through parameter γ. As a result, we obtain the dependence of n on γ for a wide range of γ, and indeed see that the collapse is sensitive to the equation of state of an outside fluid.

Discussion of Acute Deficiency Syndrome Theory and its Clinical Application

Discussion of Acute Deficiency Syndrome Theory and its Clinical Application

Erratum: Strong curvature naked singularities in spherically symmetric perfect fluid collapse [Phys. Rev. D 101 , 044052 (2020)

Received 21 February 2023DOI:https://doi.org/10.1103/PhysRevD.107.069903© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasGeneral relativityGravitationSingularities In general relativityGravitation, Cosmology & Astrophysics

Разработка математической модели акустического источника, сопровождающего распад кавитационной каверны на схлопывающиеся пузырьки

Object and purpose of research. This paper is intended to develop a mathematical model of cavitation void fragmentation into separate collapsing bubbles as an acoustic source for further implementation in Logos software package. The study was performed on propeller models in cavitating environment. Subject matter and methods. Volume and quantity of bubbles appearing after fragmentation of a cavitation void on propellers, as well as amplitude and frequency properties of a single bubble collapse are studied as per CFD methods. Viscous flow properties are found from finite-volume (FVM) solution to unsteady Reynolds equations (RANS) closed by a biparametric semi-empirical turbulence model. The coefficients in the mathematical model of acoustic source thus obtained were calibrated through validation that included noise measurements at KSRC Cavitation Tunnel. Main results. This work included numerical simulation of collapse dynamics for a single cavitation bubble at different initial conditions, with approximation of the pressure impact created by bubble collapse in the infinite fluid and near a solid wall. The study estimated volume and quantity of the bubbles created by the fragmentation of cavitation void on propellers (3 propellers of different shape operating at different advance ratios and cavitation numbers). The mathematical model representing above-mentioned process could be further implemented in Logos software as a finite-volume algorithm with k-ω SST turbulence model. The study also created a validation base for further testing and calibration of the mathematical model thus developed. Conclusion. The study was performed as part of project Mathematical simulation on exa- and zetaflops class supercomputers launched by National Centre for Physics and Mathematics (Russia). The analysis of obtained results has shown that the mathematical model suggested in this paper does have practical potential, but it needs additional empirical data for greater flexibility and more accurate estimates. Without this model, these practical tasks still could be handled but at a cost of considerable and, most importantly, unnecessary increase in required hardware resources.

Energy condition and cosmic censorship conjecture in the perfect fluid collapse

The hypothesis of cosmic censorship plays a crucial role in classical general relativity, as an aspect of the strong version it expresses that naked singularities would never occur from the black hole singularity. In this paper, we will present how energy conditions prohibit forming the local naked singularity in the spherical perfect fluid collapse, and thus we get one step closer to the strong cosmic censorship conjecture proof. We also show that this result can be extended to the cosmological constant background.

Micromechanical simulations of the collapse of a submerged granular column

In this work, we present a numerical study of a granular collapse in a viscous fluid adopting a DEM-PFV (Pore Finite Volume) coupled model. We analyze the time evolution of the collapse and the final morphology of the deposit (triangular or trapezoidal) as a function of the initial solid fraction and column aspect ratio. Finally, we discuss the role of the initial packing fraction of the granular material on the time evolution of the pore pressure. The numerical results are consistent with experimental observation [3] showing the capability of the DEM-PFV coupled model to simulate saturated granular media from triggering to flowing and stopping conditions.

Effect of electric field on string-oriented perfect fluid collapse in f (R) gravity

This work investigates the nature of singularity formed from string-oriented charged perfect fluid collapse in theory of f (R) gravity. The spherically symmetric spacetime is assumed to be filled with a string-oriented charged perfect fluid. The gravitational collapse of the fluid is analyzed to understand the effects of electric field on the time and radii of apparent horizons and singularity formation. The presence of an electric field was discovered to increase the mass of the collapsing system, the radii of apparent horizon development, and the time gap between the event horizon and singularity. The term [Formula: see text] acts as an anti-gravity term. However, the presence of electric field accelerates the gravitational collapse.

Collapsing scenario for the k-essence emergent generalized Vaidya spacetime in the context of massive gravity's rainbow

In this study, we investigate the collapsing scenario for the k-essence emergent Vaidya spacetime in the context of massive gravity's rainbow. For this study, we consider that the background metric is Vaidya spacetime in massive gravity's rainbow. We show that the k-essence emergent gravity metric closely resembles the new type of generalized Vaidya massive gravity metric with the rainbow deformations for null fluid collapse, where we consider the k-essence scalar field as a function solely of the advanced or the retarded time. The k-essence emergent Vaidya massive gravity rainbow mass function is also different. This new type k-essence emergent Vaidya massive gravity rainbow metric satisfies the required energy conditions. The existence of a locally naked central singularity and the strength and strongness of the singularities for the rainbow deformations of the k-essence emergent Vaidya massive gravity metric are the interesting outcomes of the present work.

The effect of pH and electrical conductivity of the soaking fluid on the collapse of a silty clay

Different fluids can permeate the soil collapsing at various levels of severity depending on their physicochemical characteristics. This work evaluated the effect of pH and electrical conductivity (ECf) of different soaking fluids on the collapsible behavior of a lateritic silty clay. Double and single oedometer tests were performed using four chemically distinct soaking fluids (water, leachate and two laboratory solutions, one alkaline and one acid). The collapse index (I) was evaluated according to two criteria. In addition, physical-chemical analysis of the soil and measurements of pH and ECf were done. According to the results, the soil is collapsible for the four soaking fluids. No single relationship was found between fluid pH and collapse index, although, the highest values of collapse index were found in the tests soaked with alkaline and acid solutions. Finally, a unique direct relationship was found between the collapse index and the ECf, that is, the higher this parameter, the higher the collapse index value.

Homogeneous perfect fluid collapse in five-dimensional spherically symmetric spacetime

In this paper, the higher-dimensional collapse of homogeneous isotropic perfect fluid is studied by considering the geometry of five-dimensional spherically symmetric metric. Using equations of state for different fields like dust, radiation and stiff fluid with and without cosmological constant [Formula: see text], the gravitational collapse is studied. The results are compared with the usual four-dimensional study in [A. V. Astashenok, K. Mosani, S. D. Odintsov and G. C. Samanta, Int. J. Geom. Methods Mod. Phys. 16, 1950035 (2019)]. It is found that the collapse rate is faster in five-dimensional spacetime as compared to four-dimensional case supporting the cosmic censorship hypothesis.

Analysis of a charged unidirectional perfect fluid gravitational collapse in cylindrical spacetime

The gravitational collapse of charged imperfect fluids (including the presence of strings) models the structural evolution of the Universe. The dynamics of a charged cylindrically symmetric spacetime investigates the effects of charge on the rate of gravitational collapse. In this respect, the Einstein–Maxwell equations are formed and solved to obtain the values of the dynamical parameters of the fluid including density, pressure and electric field. These parameters are graphically presented. It was concluded that the string tension effects all the physical parameters of the fluid. Moreover, the density and electric field intensity increases while the fluid’s pressure decreases near the time of singularity formation.

One-Step Exfoliation/Etching Method to Produce Chitosan-Stabilized Holey Graphene Nanosheets for Superior DNA Adsorption.

Holey graphene (HG) features universal applications in adsorption because of the large surface areas and the abundant active sites across the nanopores, but it is difficult to produce HG nanosheets straightforwardly from bulk graphite with current etching methods. Herein, for the first time, we developed a one-step sonication-assisted liquid-phase exfoliation/etching method to produce HG nanosheets from bulk graphite by taking advantage of chitosan for stabilization. With the cavitation bubble collapse stress during the intense sonication, the graphite powders were exfoliated and nanopores of tunable diameters from 40 to 200 nm were generated across the graphene nanosheets. Importantly, with chitosan as the stabilizing agent to reduce the fluid collapse stress transferred onto the graphene nanosheets, the lateral size of HG could be as large as 30 μm. Using this approach, several holey layered crystals (graphite, hexagonal boron nitride, and tungsten disulfide) were fabricated with adequate nanostructures, including lateral size, nanosheet thickness, and nanopore size. Notably, the nanoporous structure endowed the graphene nanosheets with superior high double-stranded DNA adsorption (1253 μg/mg, the highest until now) and excellent DNA protection capacity. Based on this, the HG nanosheets were developed for the surface-mediated reversal gene transfection, displaying appreciable efficiency with the traditional methods.

Swim Bladder Disorders in Koi Carp (Cyprinus carpio).

Simple SummaryPhysostomous fish like cyprinids possess a swim bladder with a pneumatic duct in connection with the foregut, permitting the gas to enter into or be released through the alimentary canal. Due to this peculiar anatomic structure, bacteria and mycetes can potentially ascend the duct and colonize the swim-bladder. Besides inflammatory reactions, other swim bladder disorders include fluid accumulation, collapse, overinflation, and herniation. These swim bladder disorders and consequent buoyancy problems can be encountered in ornamental fish. Nonetheless, details about comprehensive disease management are poorly represented in the koi carp (Cyprinus carpio) literature. A clinical–pathological and microbiological investigation was performed in nine koi carp presenting abdominal swelling and abnormal swimming behavior. Swim bladder deformation, accumulation of clear fluid within the swim bladder, chronic aerocystitis, and bacteria identified as Aeromonas hydrophila/caviae group and Shewanella xiamenensis were the main findings. A wide range of sensitivity was shown to antimicrobials for isolated S. xiamemensis strains. Accordingly, antibiotic treatment succeeded in the full recovery of three cases in which S. xiamemensis infection was detected. Along with these results, the contribution of this study to the scientific field is to document a multidisciplinary clinical–pathological and microbiological investigation of these animals, which are rightly considered pets and should be similarly approached.Swim bladder disorders and consequent buoyancy problems are encountered in ornamental fish, including koi carp. Nevertheless, beyond clinical and pharmacological management, they are largely underdiagnosed. In this study, nine koi carp showing abdominal swelling and abnormal swimming behavior were investigated. Clinical approach, varying from case to case, included ultrasonographic and X-ray investigations, bacteriological analysis of the collected fluid, antimicrobial susceptibility pattern, and possibly histological analysis. Diagnostic imaging, corroborating gross examination, documented swim bladder deformation/dislocation and serous fluid within the swim bladder chambers of most animals. Bacteria belonging to the Aeromonas hydrophila/caviae group and Shewanella xiamenensis were identified. S. xiamenensis strains showed a sensibility to all tested molecules except for one strain, which was resistant to tetracycline and cyprofloxacin. Antibiotic treatment succeeded in the full recovery of three cases in which S. xiamemensis infection was detected. Chronic aerocystitis was histologically documented where tissue was available. The swim bladder histopathological findings highlighted a chronic process that had compromised the quality of life of the animals. A multidisciplinary clinical–pathological and microbiological approach is highly suggested to recognize swim bladder conditions as early as possible, aiming to drive medical intervention and raising the chances of fish survival.

Marginally trapped surfaces in spherical gravitational collapse

This paper deals with a detail study of gravitational collapse of dust and viscous fluids under the assumptions of spherical symmetry. Our main goal is to closely analyze the horizons which arise during this gravitational phenomenon. To this end, we examine the formation and evolution of trapped surfaces in these spacetimes, with special attention to trapped regions and cylinders foliated by marginally trapped surfaces. The time evolution of trapped surfaces, collapsing shell as well as the event horizon are identified analytically as well as numerically. Using different density profiles of matter, we analyze, how the nature of the marginally trapped surfaces modify as we change the energy momentum tensor. These studies reveal that depending on the mass function and the mass profile, it is possible to envisage situations where dynamical horizons, timelike tubes or isolated horizons may arise.

Gravitational collapse for the K-essence emergent Vaidya spacetime

In this paper, we study the gravitational collapse in the k-essence emergent gravity using a generalized Vaidya-type metric as a background. We also analyze the cosmic censorship hypothesis for this system. We show that the emergent gravity metric resembles closely to the new type of the generalized Vaidya metrics for null fluid collapse with the k-essence emergent mass function, where we consider the k-essence scalar field being a function solely of the advanced or the retarded time. This new type of k-essence emergent Vaidya metric has satisfied the required energy conditions. The existence of the locally naked central singularity, the strength and the strongness of the singularities for the k-essence emergent Vaidya metric are the interesting outcomes of the present work.

Final fate of charged anisotropic fluid collapse in f(R) gravity

In this paper, the spherically symmetric gravitational collapse of anisotropic fluid in the presence of charge in metric [Formula: see text] theory is analyzed. We consider the static and non static spherically symmetric spacetimes for outer and inner regions of collapsing object respectively. For the smooth matching of inner and outer regions, the Senovilla as well as Darmois matching conditions are utilized. The closed form solutions are obtained from field equations. Moreover, we examine the apparent horizons and their physical significance. The effect of cosmological constant and [Formula: see text] term is same and the collapsing rate speeds up as compared to that of anisotropic fluid case when the electromagnetic field is introduced. Electromagnetic charge also affects the time interval of singularities and cosmological horizons.

K -essence emergent spacetime as a generalized Vaidya geometry

We establish a formal connection between the {\bf K}-essence emergent gravity scenario and generalizations of Vaidya spacetime. Choosing the {\bf K}-essence action to be of the Dirac-Born-Infeld variety, the physical spacetime to be a general static spherically symmetric black hole and restricting the {\bf K}-essence scalar field to be a function solely of the advanced or the retarded time, we show that the emergent gravity metric resembles closely the generalized Vaidya metrics for null fluid collapse proposed by Husain. Imposing null energy conditions on the emergent energy-momentum tensor derived from the emergent Einstein equation, restrictions are obtained on the functions characterizing the emergent metric for consistent identification with generalized Vaidya spacetimes. We discuss the possibility of dynamical horizons in the {\bf K-}essence emergent Vaidya spacetime. Admissible explicit black hole background metrics are discussed as examples.