Note on the optical appearance of a star collapsing through its gravitational radius

1979 ◽  
Vol 232 ◽  
pp. 277 ◽  
Author(s):  
K. Lake ◽  
R. C. Roeder
Keyword(s):  
Gravitational Radius ◽  
Optical Appearance

scholarly journals Addressing the missing matter problem in galaxies through a new fundamental gravitational radius

2017 ◽  
Vol 2017 (06) ◽  
pp. 044-044 ◽  
Author(s):  
S. Capozziello ◽  
P. Jovanović ◽  
V. Borka Jovanović ◽  
D. Borka
Keyword(s):  
Gravitational Radius

scholarly journals Protecting ultra- and hyperhydrophilic implant surfaces in dry state from loss of wettability

2016 ◽  
Vol 2 (1) ◽  
pp. 557-560 ◽  
Author(s):  
Steffen Lüers ◽  
Markus Laub ◽  
Herbert P. Jennissen
Keyword(s):  
Dental Implants ◽  
Phosphate Buffer ◽  
Potassium Phosphate ◽  
Optimal System ◽  
Potassium Phosphate Buffer ◽  
Long Time ◽  
Optical Appearance

AbstractUltrahydrophilic titanium miniplates with sandblasted and acid etched (SLA) surfaces were protected from loss of hydrophilicity by an exsiccation layer of salt and stored in a dry state. Various salts in different concentrations were tested in respect to their conservation capacity and optical appearance. Potassium phosphate buffer in a specified composition appeared to be optimal. This optimal system was applied in a long time storage experiment showing no loss of hydrophilicity over years. It was also transferred with success to hyperhydrophilic dental implants.

scholarly journals How the Limit Values Work

2021 ◽  
Keyword(s):  
Cosmological Constant ◽  
Gravitational Radius ◽  
Limit Values ◽  
Event Horizons ◽  
Dirac Type ◽  
Large Numbers ◽  
Spatio Temporal ◽  
The Universe ◽  
Limiting Values ◽  
Physical Principles

The efficiency of limiting quantities as a tool for describing physics at various spatio-temporal scales is shown. Due to its universality, limit values allow us to establish relationships between, at first glance, distant from each other's characteristics. The article discusses specific examples of the use of limit values to establish such relationships between quantities at different scales. Based on the principle of reaching the limiting values on the event horizons, a connection was obtained between the Planck values and the values of the Universe. The resulting relation can be attributed to relations of the Dirac type - the coincidence of large numbers that emerged from empirical observations. In the article, the relationships between large numbers of the Dirac type are established proceeding, in a certain sense, from physical principles - the existence of limiting values. It is shown that this ratio is observed throughout the evolution of the Universe. An alternative way of solving the problem of the cosmological constant using limiting values and its relation to the minimum spatial scale is discussed. In addition, a one-parameter family of masses was introduced, including the mass of the Universe, the Planck mass and the mass of the graviton, which also establish relationships between quantities differing by 120 orders of magnitude. It is shown that entropic forces also obey the same universal limiting constraints as ordinary forces. Thus, the existence of limiting values extends to informational limitations in the Universe. It is fundamentally important that on any event horizon, regardless of its scale (i.e., its gravitational radius), the universal value of limit force c4/4G is realized. This allows you to relate the characteristics of the Universe related to various stages of its evolution.

scholarly journals Light scattering of glass-particle filled matrices with similar refractive index

2018 ◽  
Vol 52 (30) ◽  
pp. 4231-4246 ◽  
Author(s):  
Wolfgang Wildner ◽  
Dietmar Drummer
Keyword(s):  
Refractive Index ◽  
Light Source ◽  
White Light ◽  
Scattered Light ◽  
Glass Particle ◽  
Refractive Indices ◽  
Mechanical And Thermal Properties ◽  
White Light Source ◽  
Transmission Measurements ◽  
Optical Appearance

If fillers can be added to transparent materials without losing transparency, then advantages like enhanced mechanical and thermal properties can be integrated. The investigated specimens consist of glass particles and refractive index oil as a model for transparent matrices with a very similar refractive index. Their optical properties and resulting limitations are described. Potential uses are also demonstrated by application-oriented optical testing. Besides a standard spectrometer, additional spectrometer setups were used. These include a diffuse as well as a collimated illumination and different sample positioning. Furthermore, the scattered light intensity was measured at different angles. This analysis reveals that composites with smaller particles transmit more light directly. In contrast, standard spectrometers indicate an increasing direct transmittance of composites with larger particles. They collect significant amounts of scattered light and, therefore, are not suitable for transmission measurements of such composites. The different positioning shows that all specimens exhibit very little scattering when placed directly on a diffuse light source. With a greater distance between specimen and light source, the scattering increases strongly. To display the composites' optical appearance, the light-dark-contrast of the diffuse white light source photographed behind the composite was analyzed. Both long and short distances between composite and light source lead to a precise image of the light source. Nevertheless, the white light source appears in the color of the wavelength with matching refractive indices at long distances.

scholarly journals High frequency pulse anodising of aluminium: Anodising kinetics and optical appearance

2019 ◽  
Vol 360 ◽  
pp. 222-231 ◽  
Author(s):  
Flemming Jensen ◽  
Visweswara Chakravarthy Gudla ◽  
Ib Kongstad ◽  
Rajan Ambat
Keyword(s):  
High Frequency ◽  
Optical Appearance ◽  
Frequency Pulse

scholarly journals A Conceptual Model for the Origin of the Cutoff Parameter in Exotic Compact Objects

Symmetry ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 2072
Author(s):  
Wilson Alexander Rojas Castillo ◽  
Jose Robel Arenas Salazar
Keyword(s):  
Black Hole ◽  
Conceptual Model ◽  
Initial Position ◽  
Compact Objects ◽  
Field Equations ◽  
Gravitational Radius ◽  
Cutoff Parameter ◽  
Gravitational Field Equations ◽  
Dynamic Quantity ◽  
The Difference

A Black Hole (BH) is a spacetime region with a horizon and where geodesics converge to a singularity. At such a point, the gravitational field equations fail. As an alternative to the problem of the singularity arises the existence of Exotic Compact Objects (ECOs) that prevent the problem of the singularity through a transition phase of matter once it has crossed the horizon. ECOs are characterized by a closeness parameter or cutoff, ϵ, which measures the degree of compactness of the object. This parameter is established as the difference between the radius of the ECO’s surface and the gravitational radius. Thus, different values of ϵ correspond to different types of ECOs. If ϵ is very big, the ECO behaves more like a star than a black hole. On the contrary, if ϵ tends to a very small value, the ECO behaves like a black hole. It is considered a conceptual model of the origin of the cutoff for ECOs, when a dust shell contracts gravitationally from an initial position to near the Schwarzschild radius. This allowed us to find that the cutoff makes two types of contributions: a classical one governed by General Relativity and one of a quantum nature, if the ECO is very close to the horizon, when estimating that the maximum entropy is contained within the material that composes the shell. Such entropy coincides with the Bekenstein–Hawking entropy. The established cutoff corresponds to a dynamic quantity dependent on coordinate time that is measured by a Fiducial Observer (FIDO). Without knowing the details about quantum gravity, parameter ϵ is calculated, which, in general, allows distinguishing the ECOs from BHs. Specifically, a black shell (ECO) is undistinguishable from a BH.

scholarly journals New Solution of a Spherically Symmetric Static Problem of General Relativity

2017 ◽  
Vol 9 (5) ◽  
pp. 29
Author(s):  
Valery Vasiliev
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Classical Solution ◽  
Critical Radius ◽  
Static Problem ◽  
Critical Value ◽  
Relativity Theory ◽  
Spherically Symmetric ◽  
General Relativity Theory ◽  
Gravitational Radius

The paper is concerned with the spherically symmetric static problem of the General Relativity Theory. The classical solution of this problem found in 1916 by K. Schwarzschild for a particular metric form results in singular space metric coefficient and provides the basis of the objects referred to as Black Holes. A more general metric form applied in the paper allows us to obtain the solution which is not singular. The critical radius of the fluid sphere, following from this solution does not coincide with the traditional gravitational radius. For the spheres with radii that are less than the critical value, the solution of GRT problem does not exist.

scholarly journals Accretion into Black Hole, and Formation of Magnetically Arrested Accretion Disks

Universe ◽  
2019 ◽  
Vol 5 (6) ◽  
pp. 146 ◽  
Author(s):  
Gennady Bisnovatyi-Kogan
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Large Scale ◽  
Symmetry Plane ◽  
Stationary Flow ◽  
Gravitational Radius ◽  
Radiative Efficiency ◽  
Disk Structure ◽  
Large Scale Magnetic Field ◽  
Infrared Star

The exact time-dependent solution is obtained for a magnetic field growth during a spherically symmetric accretion into a black hole (BH) with a Schwarzschild metric. Magnetic field is increasing with time, changing from the initially uniform into a quasi-radial field. Equipartition between magnetic and kinetic energies in the falling gas is supposed to be established in the developed stages of the flow. Estimates of the synchrotron radiation intensity are presented for the stationary flow. The main part of the radiation is formed in the relativistic region r ≤ 7 r g , where r g is a BH gravitational radius. The two-dimensional stationary self-similar magnetohydrodynamic solution is obtained for the matter accretion into BH, in a presence of a large-scale magnetic field, under assumption, that the magnetic field far from the BH is homogeneous and its influence on the flow is negligible. At the symmetry plane perpendicular to the direction of the distant magnetic field, the dense quasi-stationary disk is formed around BH, which structure is determined by dissipation processes. Solutions of the disk structure have been obtained for a laminar disk with Coulomb resistivity and for a turbulent disk. Parameters of the shock forming due to matter infall onto the disk are obtained. The radiation spectrum of the disk and the shock are obtained for the 10 M ⊙ BH. The luminosity of such object is about the solar one, for a characteristic galactic gas density, with possibility of observation at distances less than 1 kpc. The spectra of a laminar and a turbulent disk structure around BH are very different. The laminar disk radiates mainly in the ultraviolet, the turbulent disk emits a large part of its flux in the infrared. It may occur that some of the galactic infrared star-like sources are a single BH in the turbulent accretion state. The radiative efficiency of the magnetized disk is very high, reaching ∼ 0.5 M ˙ c 2 . This model of accretion was called recently as a magnetically arrested disk (MAD). Numerical simulations of MAD and its appearance during accretion into neutron stars, are considered and discussed.

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