Matter Configurations Research Articles

ON NEGATIVE MASS

The Schwarzschild solution to the matter free, spherically symmetric Einstein equations has one free parameter, the mass. But the mass can be of any sign. What is the meaning of the negative mass solutions? The answer to this question for the case of a pure Schwarzschild negative mass black solution is still elusive, however, in this essay, we will consider negative mass solutions within a Schwarzschild–de Sitter geometry. We show that there exist reasonable configurations of matter, bubbles of distributions of matter, that satisfy the dominant energy condition everywhere, that are nonsingular and well behaved everywhere, but correspond to the negative mass Schwarzschild–de Sitter geometry outside the matter distribution. These negative mass bubbles could occur as the end state of a quantum tunneling transition.

Modeling the quantum evolution of the universe through classical matter

It is well known that the canonical quantization of the Friedmann-Lema\^itre-Robertson-Walker (FLRW) filled with a perfect fluid leads to nonsingular universes which, for later times, behave as their classical counterpart. This means that the expectation value of the scale factor $<a>(t)$ never vanishes and, as $t\to\infty$, we recover the classical expression for the scale factor. In this paper, we show that such universes can be reproduced by classical cosmology given that the universe is filled with an exotic matter. In the case of a perfect fluid, we find an implicit equation of state (EoS). We then show that this single fluid with an implict EoS is equivalent to two non-interacting fluids, one of them representing stiff matter with negative energy density. In the case of two non-interacting scalar fields, one of them of the phantom type, we find their potential energy. In both cases we find that quantum mechanics changes completely the configuration of matter for small values of time, by adding a fluid or a scalar field with negative energy density. As time passes, the density of negative energy decreases and we recover the ordinary content of the classical universe. The more the initial wave function of the universe is concentrated around the classical big bang singularity, the more it is necessary to add negative energy, since this type of energy will be responsible for the removal of the classical singularity.

Plausible families of compact objects with a nonlocal equation of state

We present the plausibility of some models emerging from an algorithm devised to generate a one-parameter family of interior solutions for the Einstein equations. We explore how their physical variables change as the family parameter varies. The models studied correspond to anisotropic spherical matter configurations having a nonlocal equation of state. This particular type of equation of state, with no causality problems, provides at a given point the radial pressure not only as a function of the density but as a functional of the enclosed matter distribution. We have found that there are several model-independent tendencies as the parameter increases: the equation of state tends to be stiffer and the total mass becomes half of its external radius. Profiting from the concept of cracking of materials in general relativity, we obtain that these models become more potentially stable as the family parameter increases.

Rotating regular black holes

The formation of spacetime singularities is a quite common phenomenon in General Relativity and it is regulated by specific theorems. It is widely believed that spacetime singularities do not exist in Nature, but that they represent a limitation of the classical theory. While we do not yet have any solid theory of quantum gravity, toy models of black hole solutions without singularities have been proposed. So far, there are only non-rotating regular black holes in the literature. These metrics can be hardly tested by astrophysical observations, as the black hole spin plays a fundamental role in any astrophysical process. In this Letter, we apply the Newman–Janis algorithm to the Hayward and to the Bardeen black hole metrics. In both cases, we obtain a family of rotating solutions. Every solution corresponds to a different matter configuration. Each family has one solution with special properties, which can be written in Kerr-like form in Boyer–Lindquist coordinates. These special solutions are of Petrov type D, they are singularity free, but they violate the weak energy condition for a non-vanishing spin and their curvature invariants have different values at r=0 depending on the way one approaches the origin. We propose a natural prescription to have rotating solutions with a minimal violation of the weak energy condition and without the questionable property of the curvature invariants at the origin.

A new spherical harmonics scheme for multi-dimensional radiation transport I. Static matter configurations

Recent work by McClarren and Hauck (2010) [31] suggests that the filtered spherical harmonics method represents an efficient, robust, and accurate method for radiation transport, at least in the two-dimensional (2D) case. We extend their work to the three-dimensional (3D) case and find that all of the advantages of the filtering approach identified in 2D are present also in the 3D case. We reformulate the filter operation in a way that is independent of the timestep and of the spatial discretization. We also explore different second- and fourth-order filters and find that the second-order ones yield significantly better results. Overall, our findings suggest that the filtered spherical harmonics approach represents a very promising method for 3D radiation transport calculations.

Conformal Mappings in Relativistic Astrophysics

We describe the use of conformal mappings as a mathematical mechanism to obtain exact solutions of the Einstein field equations in general relativity. The behaviour of the spacetime geometry quantities is given under a conformal transformation, and the Einstein field equations are exhibited for a perfect fluid distribution matter configuration. The field equations are simplified and then exact static and nonstatic solutions are found. We investigate the solutions as candidates to represent realistic distributions of matter. In particular, we consider the positive definiteness of the energy density and pressure and the causality criterion, as well as the existence of a vanishing pressure hypersurface to mark the boundary of the astrophysical fluid.

Classifying bases for 6D F-theory models

Abstract We classify six-dimensional F-theory compactifications in terms of simple features of the divisor structure of the base surface of the elliptic fibration. This structure controls the minimal spectrum of the theory. We determine all irreducible configurations of divisors (“clusters”) that are required to carry nonabelian gauge group factors based on the intersections of the divisors with one another and with the canonical class of the base. All 6D F-theory models are built from combinations of these irreducible configurations. Physically, this geometric structure characterizes the gauge algebra and matter that can remain in a 6D theory after maximal Higgsing. These results suggest that all 6D supergravity theories realized in F-theory have a maximally Higgsed phase in which the gauge algebra is built out of summands of the types su(3), so(8), f4, e6, e8, e8, (g2 ⊕ su(2)); and su(2) ⊕ so(7) ⊕ su(2), with minimal matter content charged only under the last three types of summands, corresponding to the non-Higgsable cluster types identified through F-theory geometry. Although we have identified all such geometric clusters, we have not proven that there cannot be an obstruction to Higgsing to the minimal gauge and matter configuration for any possible F-theory model. We also identify bounds on the number of tensor fields allowed in a theory with any fixed gauge algebra; we use this to bound the size of the gauge group (or algebra) in a simple class of F-theory bases.

Three-Dimensional Structural Analysis of Lipid and DNA Complex using Zernike Phase Contrast Transmission Electron Microscope Tomography

Lipids and DNA complex, so called lipoplex, is a promising materials for gene (for example si-RNA) delivery. The lipoplex were thought to be randomly agglomerated. But the first article written by C. R. Safinya et al. (Science 1998, 128, 78-81) suggested an model of orderly aligned lamellar layers proved by small angle x-ray scattering (SAXS).In this study, we observe the lipoplex by transmission electron microscope (TEM). Samples are the lipoplex made from cationic lipid: DOTAP (1,2-Dioleoyl-3-Trimethylammonium-Propane), zwitter ionic lipid: DOPC (1,2-Doleoyl-sn-Glycero-3-Phosphocholine), and plasmid DNA. Newly developed Zernike phase contrast TEM is used in order to get more contrast, and cryo-transfer is used in order to preserve configuration of bio matter into ice by the quick freezing.In addition, we use a new observation method; TEM tomography. If we use transmission images from conventional TEM, it is difficult to know the conformational structures of complicated arranged object. To solve this problem, we take dozens of TEM images with be tilted from −70 to 70 degree by 2 degree steps, and reconstructed to the conformational structure.Due to the tomography treatment, the conformational structure of the complex can be analyzed. We can analyze not only the boundary structure of the complex agglomeration, but also inside structure. Moreover, we want to discuss about the production process of the lamellar structure based on the results of the TEM tomography observation.

The influence of complex white matter architecture on the mean diffusivity in diffusion tensor MRI of the human brain

In diffusion tensor magnetic resonance imaging (DT-MRI), limitations concerning complex fiber architecture (when an image voxel contains fiber populations with more than one dominant orientation) are well-known. Fractional anisotropy (FA) values are lower in such areas because of a lower directionality of diffusion on the voxel-scale, which makes the interpretation of FA less straightforward. Moreover, the interpretation of the axial and radial diffusivities is far from trivial when there is more than one dominant fiber orientation within a voxel. In this work, using (i) theoretical considerations, (ii) simulations, and (iii) experimental data, it is demonstrated that the mean diffusivity (or the trace of the diffusion tensor) is lower in complex white matter configurations, compared with tissue where there is a single dominant fiber orientation within the voxel. We show that the magnitude of this reduction depends on various factors, including configurational and microstructural properties (e.g., the relative contributions of different fiber populations) and acquisition settings (e.g., the b-value). These results increase our understanding of the quantitative metrics obtained from DT-MRI and, in particular, the effect of the microstructural architecture on the mean diffusivity. More importantly, they reinforce the growing awareness that differences in DT-MRI metrics need to be interpreted cautiously.

Regular black holes: Electrically charged solutions, Reissner-Nordström outside a de Sitter core

To have the correct picture of a black hole as a whole, it is of crucial importance to understand its interior. The singularities that lurk inside the horizon of the usual Kerr-Newman family of black hole solutions signal an endpoint to the physical laws and, as such, should be substituted in one way or another. A proposal that has been around for sometime is to replace the singular region of the spacetime by a region containing some form of matter or false vacuum configuration that can also cohabit with the black hole interior. Black holes without singularities are called regular black holes. In the present work, regular black hole solutions are found within general relativity coupled to Maxwell's electromagnetism and charged matter. We show that there are objects which correspond to regular charged black holes, whose interior region is de Sitter, whose exterior region is Reissner-Nordstr\"om, and the boundary between both regions is made of an electrically charged spherically symmetric coat. There are several types of solutions: regular nonextremal black holes with a null matter boundary, regular nonextremal black holes with a timelike matter boundary, regular extremal black holes with a timelike matter boundary, and regular overcharged stars with a timelike matter boundary. The main physical and geometrical properties of such charged regular solutions are analyzed.

Waste Treatment by Supercritical Water Oxidation

Supercritical water oxidation (SCWO) is a new oxidation technology that utilizes supercritical water reaction to destroy the configuration of matter. Organic waste is converted to harmless gaseous or liquid substances such as CO2 and H2O. Thanks to its unique technology advantage, it has a rapid development in the recent years, and becoming a potential and green technology of wastewater and organic waste treatment. This paper focused on SCWO technology and apparatus, and reviewed achievements on patents of wastewater and organic waste treatment by SCWO. Eventually, this article prospected the development trend of this new oxidation technology.

A moving mirror in AdS space as a toy model for holographic thermalization

It is expected that thermalization may be described within gauge/gravity duality by considering time-dependent configurations on the gravity side of the correspondence, for instance a gravitational collapse of a matter configuration in Anti-de Sitter space. As a step towards the ambitious goal of describing such a configuration, we investigate a simple time-dependent toy model in which a mirror moves in the radial direction of Anti-de Sitter space. For this configuration, we establish a procedure for calculating two-point functions of scalar fluctuations, based on a WKB approximation. We test our method on two sample trajectories for the mirror, and find that the singularity structure of the two-point functions is in agreement with geometric optics.

The relativistic fluid ball as a stratified model of an astrophysical object

A relativistic fluid ball with an inhomogeneous static stratified matter configuration is considered. A model of an astrophysical object with this structure of matter is constructed.

Charged annular disks and Reissner-Nordström type black holes from extremal dust

We present the first analytical superposition of a charged black hole with an annular disk of extremal dust. In order to obtain the solutions, we first solve the Einstein-Maxwell field equations for sources that represent disklike configurations of matter in confomastatic spacetimes by assuming a functional dependence among the metric function, the electric potential, and an auxiliary function, which is taken as a solution of the Laplace equation. We then employ the Lord Kelvin inversion method applied to models of finite extension in order to obtain annular disks. The structures obtained extend to infinity, but their total masses are finite and all the energy conditions are satisfied. Finally, we observe that the extremal Reissner-Nordstr\"om black hole can be embedded into the center of the disks by adding a boundary term in the inversion.

Preliminary study of MR imaging in rat with series coil

Objective To investigate the effect of MR imaging in rats with series coil. Methods MR scanning was performed on the self-made aqueous solution phantom with the series coil and other three coils respectively, using the same FRFSE- XL pulse sequence. SNR of the same image was obtained in the same position slice for all four coils. Twelve SD rats were divided into three model groups and one normal group. FRFSE-XL FSPGR and Probe-SI pulse sequence were respectively used to show the brain injury,1H-MRS, spinal cord injury (SCI) and abdomen with series coils. Results The SNR of series coil (39. 7)was over six times higher than the SNR of knee joint coil (6. 41 ), which was the best in other three coils.Grey matter and white matte; the brain structure and hematomas were clearly depicted in the rats'brain on T1WI and T2WI. From the second week after injection of 6-OHDA into the rats brain, the ratio of NAA/Cr decreased (before injection 1.24 ,two weeks after injection 0. 781 ). The spinal cord and the configuration of the white matter were clearly showed on T2WI image, and the location and degree of SCI in the rat thoracic spinal cord were also well defined on T2 WI image. The pulse sequence of FSPGR T1 WI was used for rat abdomen scanning. The scan time was only eight seconds. It is helpful to overcome the breathing movement effect and show the structure of rat abdomen. Conclusion It provided a good means for the rat MR in vivo to make use of 3.0T MR combined with series coils. Key words: Magnetic resonance imaging; Magnetic resonance spectroscopy; Spinal cord injury; Animal experimentation

Towards the unification of gravity and other interactions: What has been Missed?

Faced with the persisting problem of the unification of gravity with other fundamental interactions we investigate the possibility of a new paradigm, according to which the basic space of physics is a multidimensional space C associated with matter configurations. We consider general relativity in C. In spacetime, which is a 4-dimensional subspace of C, we have not only the 4-dimensional gravity, but also other interactions, just as in Kaluza-Klein theories. We then consider a finite dimensional description of extended objects in terms of the center of mass, area, and volume degrees of freedom, which altogether form a 16-dimensional manifold whose tangent space at any point is Clifford algebra Cl(1,3). The latter algebra is very promising for the unification, and it provides description of fermions.

Surplus solid angle as an imprint of Hořava-Lifshitz gravity

We consider the electrostatic field of a point charge coupled to Horava-Lifshitz gravity and find an exact solution describing the space with a surplus (or deficit) solid angle. Although, theoretically in general relativity, a surplus angle is hardly to be obtained in the presence of ordinary matter with positive energy distribution, it seems natural in Horava-Lifshitz gravity. We present the sudden disappearance and reappearance of a star image as an astrophysical effect of a surplus angle. We also consider matter configurations of all possible power law behaviors coupled to Horava-Lifshitz gravity and obtain a series of exact solutions.

Validating the Tensor Distribution Function for Fiber Reconstruction in HARDI (High-Angular Resolution Diffusion Imaging)

Introduction: Diffusion tensor imaging (DTI) reveals white matter microstructure and fiber pathways in the living brain by examining the 3D diffusion profile of water molecules in brain tissue. Even so, DTI-derived measures will be incorrect where fibers cross or mix, as the single tensor model cannot resolve these more complicated white matter configurations. High-angular resolution diffusion imaging (HARDI) addresses this problem by applying more than 6 independent diffusion-sensitized gradients. Many HARDI reconstruction methods (e.g., q-ball imaging, DOT, PAS) impose restrictive assumptions on fibers, e.g., all fiber tracts must have the same anisotropy profile. Here we model the HARDI signal more flexibly, as in [1], as a unit-mass probability density on the 6D manifold of symmetric positive definite tensors, yielding a Tensor Distribution Function (TDF), or continuous mixture of tensors, at each point in the brain. The TDF can model fiber crossing and non-Gaussian diffusion. From the TDF, one can derive analytic formulae for the water displacement probability function, orientation distribution function (ODF), tensor orientation distribution function (TOD), and their corresponding anisotropy measures. Here we further develop the TDF framework, verifying its accuracy in revealing fiber crossings in human brain HARDI data.

The Revenge of the Still

The Revenge of the Still

Effective field theory, large number of particle species, and holography

An effective quantum field theory (QFT) with a manifest UV/IR connection, so as to be valid for arbitrarily large volumes, can successfully be applied to the cosmological dark energy problem as well as the cosmological constant (CC) problem. Motivated by recent approaches to the hierarchy problem, we develop such a framework with a large number of particle species. When applying to systems on the brink of experiencing a sudden collapse to a black hole, we find that the entropy, unlike the total energy, now becomes an increasing function of the number of field species. An internal consistency of the theory is then used to infer the upper bound on the number of particle species, showing consistency with the holographic Bekenstein–Hawking bound. This may thus serve to fill in a large gap in entropy of any non-black hole configuration of matter and the black holes. In addition, when the bound is saturated the entanglement entropy matches the black hole entropy, thus solving the multiplicity of species problem. In a cosmological setting, the maximum allowable number of species becomes a function of cosmological time, reaching its minimal value in a low-entropy post-reheating epoch.