Probing Turbulence, Gravity, Supernovae, and Magnetic Field Effects with the 6D Kinematics of Young Stars in Milky Way Star-forming Regions

The paper is devoted to study the effect of gravity, magnetic field and laser pulse on the general model of the equations of generalized thermoelasticity for a homogeneous isotropic elastic half-space. The formulation is applied under four theories of generalized thermoelasticity: the coupled theory, Lord-Schulman theory, Green-Lindsay theory as well as Green-Naghdi theory. By employing normal mode analysis, the analytical expressions for the displacement components, temperature and the (mechanical and Maxwell’s) stresses distribution are obtained in the physical domain. These expressions are also calculated numerically and corresponding graphs are plotted to illustrate and compare the theoretical results. The effect of gravity, magnetic field and laser pulse are also studied and displayed graphically to show the physical meaning of the phenomena. A comparison has been made between the present results and the results obtained by the others. The results indicate that the effects of magnetic field, laser pulse and gravity field are very pronounced.

In this paper, we investigated the spreading of shear wave in an anisotropic non-homogeneous elastic medium under effect of dry sand, rotation, gravity, primary stress, and magnetic field. We have reached equation of variation of shear wave velocity c1 in an anisotropic incompressible medium according to sand, rotation, gravity, primary stress, and magnetic field, then we used graphs to illustrate to show the effect of direction of spreading of shear wave. The results indicate that the effect of dry sand, rotation, gravity, primary stress, and magnetic field on the spreading of shear wave in an anisotropic inhomogeneous elastic medium are very pronounced. The results have been obtained are discussed and presented visually, the results demonstrate that the effect of sand, gravity field, primary stress, magnetic field, anisotropy and rotation are noticeable.

The process of converting gas into stars underpins much of astrophysics, yet many fundamental questions surrounding this process remain unanswered. For example -- how sensitive is star formation to the local environmental conditions? How do massive and dense stellar clusters form, and how does this crowded environment influence the stars that form within it? How do the most massive stars form and is there an upper limit to the stellar initial mass function (IMF)? Answering questions such as these is crucial if we are to construct an end-to-end model of how stars form across the full range of conditions found throughout the Universe. The research described in this thesis presents a study that utilises a multi-scale approach to identifying and characterising the early precursors to young massive clusters and high-mass proto-stars, with a specific focus on the extreme environment in the inner few hundred parsecs of the Milky Way -- the Central Molecular Zone (CMZ). The primary sources of interest that are studied in detail belong to the Galactic centre dust ridge -- a group of six high-mass (M ~ 10^(4-5) Msun), dense (R ~ 1-3 pc, n > 10^(4) cm^(-3)), and quiescent molecular clouds. These properties make these clouds ideal candidates for representing the earliest stages of high-mass star and cluster formation. The research presented makes use of single-dish and interferometric far-infrared and (sub-)millimetre observations to study their global and small-scale properties. A comparison of the known young massive clusters (YMCs) and their likely progenitors (the dust ridge clouds) in the CMZ shows that the stellar content of YMCs is much more dense and centrally concentrated than the gas in the clouds. If these clouds are truly precursors to massive clusters, the resultant stellar population would have to undergo significant dynamical evolution to reach central densities that are typical of YMCs. This suggests that YMCs in the CMZ are unlikely to form monolithically. Extending this study to include YMCs in the Galactic disc again shows that the known population of YMC precursor clouds throughout the Galaxy are not sufficiently dense or central concentrated that they could form a cluster that then expands due to gas expulsion. The data also reveal an evolutionary trend, in which clouds contract and accrete gas towards their central regions along with concurrent star formation. This is argued to favour a conveyor-belt mode of YMC formation and is again not consistent with a monolithic formation event. High angular resolution observations of the dust ridge clouds with the Submillimeter Array are presented. They reveal an embedded population of compact and massive cores, ranging from ~ 50 - 2150 Msun within radii of ~ 0.1 - 0.25 pc. These are likely formation sites of high-mass stars and clusters, and are strong candidates for representing the initial conditions of extremely massive stars. Two of these cores are found to be young, high-mass proto-stars, while the remaining 13 are quiescent. Comparing these cores with high-mass proto-stars in the Galactic disc, along with models in which star formation is regulated by turbulence, shows that these cores are consistent with the idea that the critical density threshold for star formation is greater in the turbulent environment at the Galactic centre.

© La Fortune This article is distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and redistribution in any medium, provided that the original author and source are credited. This letter is inspired by the findings of M. Rabinowitz in his recent publication, “Why Observable Space Is Solely Three Dimensional” (Rabinowitz 2014). His paper provides coherent reasoning why our physical universe can only have one time and three spatial dimensions. He also states that “flux,” i.e., electrostatics and by analogy, gravitation, must remain consistent with threedimensional space with forces obeying the inverse-square law.

A comparison of star formation within the galactic centre and galactic disc

view Abstract Citations (9) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Effect of a Vertical Magnetic Field on the Propagation of Gravity Waves Along the Plane Surface of a Semi-Infinite Viscous, Electrically Conducting Fluid. Roberts, P. H. ; Boardman, A. D. Abstract The basic equations and boundary conditions governing the effect of vertical magnetic and gravitational fields on small-amplitude perturbations of the free equilibrium surface of a viscous, electrically conducting fluid are presented Normal modes are examined. A dispersion relationship is derived which relates the complex "frequency" n of the normal mode to the Allven velocity, V, the viscosity, , the magnetic diffusivity, X, and the horizontal wave number, k. This dispersion relationship is solved in nine extreme cases In six of these, the magnetic field is too weak to modify substantially the familiar gravity- wave solution holding in the absence of a magnetic field. The influence of the field is so strong in the remaining three cases that they have no parallel in the zero-field case One of these holds for any k if the magnetic field is sufficiently strong In this case n = gV-l(X/ l/2 i e, the effect of the magnetic field is so great that the disturbance is attenuated aperiodically as the Aliven waves radiate energy away from the free surface. Another interesting feature demonstrated is the existence (if V is sufficiently large) of a band of wave numbers k for which no normal-mode solution exists It is nevertheless demonstrated that the associated initial-value problem can be solved for such values of k. In addition to the nine extreme cases mentioned above, three special cases are solved for all k for particular values of V, namely, p = p = 0, and X = 0. Publication: The Astrophysical Journal Pub Date: March 1962 DOI: 10.1086/147291 Bibcode: 1962ApJ...135..552R full text sources ADS |

Galaxy evolution as a function of mass and environment: giant and dwarf galaxies in superclusters and in the field

In this paper the linear theory of the thermoelasticity has been employed to study the effect the reflection of plane harmonic waves from a semi-infinite elastic solid under the effect of the magnetic field , rotation, initial stress and gravity. The medium under consideration is traction free, homogeneous, isotropic, as well as with three-phase-lag. The normal mode analysis is used to solve the resulting non-dimensional coupled equations. The expressions for the reflection coefficients, which are the relations of the amplitudes of the reflected waves to the amplitude of the incident waves, are obtained similarly, the reflection coefficient ratio variations with the angle of incident under different conditions are shown graphically. Comparisons are made with the results predicted by different theories Lord-Shulman theory (L-S), the Green-Naghdi theory of type III (G-N III) and the three-phase-lag model in the absence and presence of a magnetic field, rotation, initial stress and gravity. The results indicate that the effect of rotation, magnetic field, initial stress and gravity field are very pronounced.

During directional solidification of binary alloy mixtures, instability in the solid/liquid interface appears due to constitutional undercooling. As a result of this instability, a reactive porous medium, namely mushy layer, is formed, and it separates the liquid phase from the solid phase completely. The intrinsic structure of the mushy layer is of fine-scale dendritic crystal that shelters solute in the interstitial fluid. In a gravitational field, the rejection of lighter solute components from an advancing solidification front brings about unstable density gradient. Ensuing convective motions in the mush are driven by a density difference. The convection can change the solid matrix of the mushy layer. Hence, the dynamic response of the mushy layer is driven by interaction among heat transfer, solute transport and convection. As a contactless control tool, external magnetic field can change the heat and solute transport, which has a significant effect on the phase change process. Therefore, when magnetic field, thermal diffusion, solute transport and buoyancy convection are considered simultaneously in the phase transformation process, the mechanism of mushy region will become more complex and interesting. In this paper, the effect of external magnetic field on the stability of mushy layer during binary alloy solidification is studied. The coupling effects of magnetic field, temperature field, concentration field and convection are considered in the model. Including the direct mode and the oscillation mode, the resulting dispersion relation reveals the influence of magnetic field on the stability of mushy layer through linear stability analysis. It is found that the Lorentz force can reduce the instability effect which is caused by buoyancy convection. In the oscillation mode, an external magnetic field brings about a stabilizing effect on the mushy layer, but in the direct mode, the effect of external magnetic field on stability of the mushy layer is uncertain. In conclusion, the finding in this paper provides an important theoretical reference for improving products quality by applying an external magnetic field in the metals processing industry.

Star formation in the Galactic disc is primarily controlled by gravity, turbulence, and magnetic fields. It is not clear that this also applies to star formation near the Galactic Centre. Here we determine the turbulence and star formation in the CMZ cloud G0.253+0.016. Using maps of 3 mm dust emission and HNCO intensity-weighted velocity obtained with ALMA, we measure the volume-density variance σρ /ρ 0=1.3±0.5 and turbulent Mach number $\mathcal{M}$ = 11±3. Combining these with turbulence simulations to constrain the plasma β = 0.34±0.35, we reconstruct the turbulence driving parameter b=0.22±0.12 in G0.253+0.016. This low value of b indicates solenoidal (divergence-free) driving of the turbulence in G0.253+0.016. By contrast, typical clouds in the Milky Way disc and spiral arms have a significant compressive (curl-free) driving component (b > 0.4). We speculate that shear causes the solenoidal driving in G0.253+0.016 and show that this may reduce the star formation rate by a factor of 7 compared to nearby clouds.

Stars form from molecular gas under complex conditions influenced by multiple competing physical mechanisms, such as gravity, turbulence, and magnetic fields. However, accurately identifying the fraction of gas actively involved in star formation remains challenging. Using dust continuum observations from the Herschel Space Observatory, we derived column density maps and their associated probability distribution functions (N-PDFs). Assuming that the power-law component in the N-PDFs corresponds to gravitationally bound (and thus star-forming) gas, we analyzed a diverse sample of molecular clouds spanning a wide range of mass and turbulence conditions. This sample included 21 molecular clouds from the solar neighborhood (d<500 pc) and 16 high-mass star-forming molecular clouds. For these two groups, we employed the counts of young stellar objects (YSOs) and mid to far-infrared luminosities as proxies for star formation rates (SFRs), respectively. Both groups revealed a tight linear correlation between the mass of the gravitationally bound gas and the SFR, suggesting a universally constant star formation efficiency in the gravitationally bound gas phase. The star-forming gas mass derived from threshold column densities (N_ threshold ) varies from cloud to cloud and is widely distributed over the range of ∼1--17times10^21 cm^-2 based on N-PDF analysis. However, in solar neighborhood clouds it is in rough consistency with the traditional approach using ge 8 mag. In contrast, in highly turbulent regions (e.g., the Galactic Central Molecular Zone) where the classical approach fails, the gravitationally bound gas mass and SFR still follow the same correlation as other high-mass star-forming regions in the Milky Way. Our findings also strongly support the interpretation that gas in the power-law component of the N-PDF is undergoing self-gravitational collapse to form stars.

Since the breakthrough enabling the mass production of single-walled carbon nanotubes (SWNTs) (Iijima 1993), many researchers in institutes and companies around the world have been developing efficient production methods for SWNTs (Harris, 1999). Various applications of this new and stable carbon nanomaterial with unique properties have been proposed (Jorio et al., 2008). However, insufficient control of the production of SWNTs is a major problem in developing applications of SWNTs. The mass production of long highquality, defect-free SWNTs such as those with a length of 10 cm and a diameter of 1 nm is a major research target. Quality control in the production of SWNTs in terms of their diameter, chirality and defect density is also an important research target. Through the development of SWNTs, it is hoped that they can be used in strong and lightweight carbon wires and lightweight but strong composite bodies for many types of vehicles. Therefore, a basic study on the production process of SWNTs is very important for establishing new methods of producing high-quality SWNTs. In this study, the production of SWNTs by the arc discharge method is investigated. This is one of most popular methods of producing SWNTs, and it is essential to carry out the reaction in a hot helium gas atmosphere. As the reaction is strongly affected by gravity (heat convection) (Mieno, 2004) and the applied magnetic field (Lorentz force), the effects of gravity, heat convection and magnetic field on the production of SWNTs were experimentally studied. The process was examined under zero gravity, normal gravity and high gravity. As there are large differences among them, the authors discusses experimental results in comparison with reaction models and fluid simulation results. An investigation of the effect of applied magnetic field on inducing the JxB force in the arc plasma is also reported, and the effect of such a field on the production of SWNTs is clarified. The effect of zero gravity was first examined using a vertical swing tower (VST), that repeatedly produces 1.1 s of zero gravity. Then, a series of parabolic-flight experiments were carried out with the support of Japan Space Forum, in which 10-20 periods of 20 s of zero gravity were obtained per flight. The results were compared with those of the laboratory experiment. A higher-gravity experiment was carried out using a rotating acceleration generator, which produces gravity of 1-3 g0 (g0: normal gravitational acceleration). The produced SWNTs were measured by TEM, Raman spectrometry and other methods.

The aim of this investigation is making mathematical model for the variation in laser pulse, rotational gravity, and magnetic fields on the generalized thermoelastic homogeneous isotropic half‐space. The governing dynamical system equations have been formulated considering the four thermoelastic models: coupled (CT) model, Lord and Shulman (LS) model, Green and Lindsay (GL) theory, and Green and Naghdi (GN III) model. Normal mode analysis technique is used to obtain the analytical expressions for the displacement components, temperature, and mechanical and Maxwell’s stresses distribution. The effect of laser pulse, gravity, and magnetic field is studied by numerical examples and displayed graphically. A comparison has been made between the theories as well as the present results and agreement with it as a special case from this study. The results predict the strong effect of magnetic field, laser pulse, and gravity field on the wave propagation phenomenon.

Context. Episodic accretion has been observed in short-period binaries, where bursts of accretion occur at periastron. The binary trigger hypothesis has also been suggested as a driver for accretion during protostellar stages. Aims. Our goal is to investigate how the strength of episodic accretion bursts depends on eccentricity. Methods. We investigate the binary trigger hypothesis in longer-period (> 20 yr) binaries by carrying out three-dimensional magnetohydrodynamical simulations of the formation of low-mass binary stars down to final separations of ∼10 AU, including the effects of gas turbulence and magnetic fields. We ran two simulations with an initial turbulent gas core of one solar mass each and two different initial turbulent Mach numbers, ℳ = σv/cs = 0.1 and ℳ = 0.2, for 6500 yr after protostar formation. Results. We observe bursts of accretion at periastron during the early stages when the eccentricity of the binary system is still high. We find that this correlation between bursts of accretion and passing periastron breaks down at later stages because of the gradual circularisation of the orbits. For eccentricities greater than e = 0.2, we observe episodic accretion triggered near periastron. However, we do not find any strong correlation between the strength of episodic accretion and eccentricity. The strength of accretion is defined as the ratio of the burst accretion rate to the quiescent accretion rate. We determine that accretion events are likely triggered by torques between the rotation of the circumstellar disc and the approaching binary stars. We compare our results with observational data of episodic accretion in short-period binaries and find good agreement between our simulations and the observations. Conclusions. We conclude that episodic accretion is a universal mechanism operating in eccentric young binary-star systems, independent of separation, and it should be observable in long-period binaries as well as in short-period binaries. Nevertheless, the strength depends on the torques and hence the separation at periastron.

Background: Expansion of the use of magnetic fields in metals, mining, transport, research, and medicine industries has led to a discussion about the effects of magnetic fields and whether their strength is negligible. The aim of this study was to investigate the effects of magnetic field on the viability and proliferation rate of HeLa cells. Materials and Methods: We studied the effects of magnetic field on the viability, proliferation rate and membrane lipid peroxidation of cells, thus, HeLa cells (cancer cells) and human fibroblast cells (normal cells) were used. Initially, the cells were cultured in DMEM and to determine the impact of the magnetic field, the cells were treated with magnetic field at 4 specific intensity levels (0, 7, 14 and 21 mT) and 2 exposure times (24 h and 48 h). The viability percentage and inhibition of cell proliferation were calculated by MTT assay and Trypan blue staining, respectively. Results: Lipid peroxidation of the cell membrane was examined by malondialdehyde (MDA) method. As the intensity and exposure time of the static magnetic field (SMF) increased, the viability percentage and proliferation rate decreased and the lipid peroxidation levels increased in the Hela cells. Conclusion: In this study, we have shown the anticancer effects of static magnetic field and propose a suitable intensity range that can be effective for the treatment of cancer.