Example of a stable wormhole in general relativity

We study a static, spherically symmetric wormhole model whose metric coincides with that of the so-called Ellis wormhole but the material source of gravity consists of a perfect fluid with negative density and a source-free radial electric or magnetic field. For a certain class of fluid equations of state, it has been shown that this wormhole model is linearly stable under both spherically symmetric perturbations and axial perturbations of arbitrary multipolarity. A similar behavior is predicted for polar nonspherical perturbations. It thus seems to be the first example of a stable wormhole model in the framework of general relativity (at least without invoking phantom thin shells as wormhole sources).Comment: 6 pages, no figure

New analytic models of traversable wormholes

The analytic solution of the general relativity equations for spherically symmetric wormholes are given. We investigate the special case of a "traversable" wormhole i.e., one allowing the signal to pass through it. The energy-momentum tensor of wormhole matter is represented as a superposition of a spherically symmetric magnetic field and dust matter with negative matter density. The dynamics of the model are investigated. We discuss both the solution of the equation with a Lambda-term and without it. Superposing enough dust matter, a magnetic field, and a Lambda-term can produce a static solution, which turns out to be a spherical Multiverse model with an infinite number of wormholes connected spherical universes. Corresponding solution can be static and dynamic.Comment: 15 pages, 2 figure

Homogeneous singularities inside collapsing wormholes

We analyze analytically and numerically the origin of the singularity in the course of the collapse of a wormhole with the exotic scalar field Psi with negative energy density, and with this field Psi together with the ordered magnetic field H. We do this under the simplifying assumptions of the spherical symmetry and that in the vicinity of the singularity the solution of the Einstein equations depends only on one coordinate (the homogeneous approximation). In the framework of these assumptions we found the principal difference between the case of the collapse of the ordinary scalar field Phi with the positive energy density together with an ordered magnetic field H and the collapse of the exotic scalar field Psi together with the magnetic field H. The later case is important for the possible astrophysical manifestation of the wormholes.Comment: 10 pages, 5 figures each of which has a),b),c),and d) sub-figures. To be published in "Physical review. D, Particles, fields, gravitation, and cosmology

Thermal equation of state and thermodynamic properties of iron carbide Fe 3 C to 31 GPa and 1473 K

Resent experimental and theoretical studies suggested preferential stability of Fe 3 C over Fe 7 C 3 at the condition of the Earth's inner core. Previous studies showed that Fe 3 C remains in an orthorhombic structure with the space group Pnma to 250 GPa, but it undergoes ferromagnetic (FM) to paramagnetic (PM) and PM to nonmagnetic (NM) phase transitions at 6–8 and 55–60 GPa, respectively. These transitions cause uncertainties in the calculation of the thermoelastic and thermodynamic parameters of Fe 3 C at core conditions. In this work we determined P‐V‐T equation of state of Fe 3 C using the multianvil technique and synchrotron radiation at pressures up to 31 GPa and temperatures up to 1473 K. A fit of our P‐V‐T data to a Mie‐Gruneisen‐Debye equation of state produce the following thermoelastic parameters for the PM‐phase of Fe 3 C: V 0  = 154.6 (1) Å 3 , K T 0 = 192 (3) GPa, K T ′ = 4.5 (1), γ 0 = 2.09 (4), θ 0  = 490 (120) К, and q  = −0.1 (3). Optimization of the P‐V‐T data for the PM phase along with existing reference data for thermal expansion and heat capacity using a Kunc‐Einstein equation of state yielded the following parameters: V 0  = 2.327 cm 3 /mol (154.56 Å 3 ), K T 0  = 190.8 GPa, K T ′ = 4.68, Θ E10  = 305 K (which corresponds to θ 0  = 407 K), γ 0  = 2.10, e 0  = 9.2 × 10 −5 K −1 , m  = 4.3, and g  = 0.66 with fixed parameters m E 1  = 3 n  = 12, γ ∞  = 0, β  = 0.3, and a 0  = 0. This formulation allows for calculations of any thermodynamic functions of Fe 3 C versus T and V or versus T and P . Assuming carbon as the sole light element in the inner core, extrapolation of our equation of state of the NM phase of Fe 3 C suggests that 3.3 ± 0.9 wt % С at 5000 К and 2.3 ± 0.8 wt % С at 7000 К matches the density at the inner core boundary. Key Points We present a P‐V‐T EOS for PM‐Fe 3 C with support from thermodynamic analyses We discuss uncertainties in magnetic transitions We applied EOS data for modeling carbon content in the corePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/101805/1/jgrb50396.pd

Dynamical formation and evolution of (2+1)-dimensional charged black holes

In this paper, we investigate the dynamical formation and evolution of 2 + 1-dimensional charged black holes. We numerically study dynamical collapses of charged matter fields in an anti de Sitter background and note the formation of black holes using the double-null formalism. Moreover, we include re-normalized energy-momentum tensors assuming the S-wave approximation to determine thermodynamical back-reactions to the internal structures. If there is no semi-classical effects, the amount of charge determines the causal structures. If the charge is sufficiently small, the causal structure has a space-like singularity. However, as the charge increases, an inner Cauchy horizon appears. If we have sufficient charge, we see a space-like outer horizon and a time-like inner horizon, and if we give excessive charge, black hole horizons disappear. We have some circumstantial evidences that weak cosmic censorship is still satisfied, even for such excessive charge cases. Also, we confirm that there is mass inflation along the inner horizon, although the properties are quite different from those of four-dimensional cases. Semi-classical back-reactions will not affect the outer horizon, but they will affect the inner horizon. Near the center, there is a place where negative energy is concentrated. Thus, charged black holes in three dimensions have two types of curvature singularities in general: via mass inflation and via a concentration of negative energy. Finally, we classify possible causal structures.Comment: 40 pages, 15 figure

Prompt, early, and afterglow optical observations of five gamma-ray bursts (GRBs 100901A, 100902A, 100905A, 100906A, and 101020A)

We present results of the prompt, early, and afterglow optical observations of five gamma-ray bursts, GRBs 100901A, 100902A, 100905A, 100906A, and 101020A, made with the Mobile Astronomical System of TElescope-Robots in Russia (MASTER-II net), the 1.5-m telescope of Sierra-Nevada Observatory, and the 2.56-m Nordic Optical Telescope. For two sources, GRB 100901A and GRB 100906A, we detected optical counterparts and obtained light curves starting before cessation of gamma-ray emission, at 113 s and 48 s after the trigger, respectively. Observations of GRB 100906A were conducted with two polarizing filters. Observations of the other three bursts gave the upper limits on the optical flux; their properties are briefly discussed. More detailed analysis of GRB 100901A and GRB 100906A supplemented by Swift data provides the following results and indicates different origins of the prompt optical radiation in the two bursts. The light curves patterns and spectral distributions suggest a common production site of the prompt optical and high-energy emission in GRB 100901A. Results of spectral fits for GRB 100901A in the range from the optical to X-rays favor power-law energy distributions with similar values of the optical extinction in the host galaxy. GRB 100906A produced a smoothly peaking optical light curve suggesting that the prompt optical radiation in this GRB originated in a front shock. This is supported by a spectral analysis. We have found that the Amati and Ghirlanda relations are satisfied for GRB 100906A. An upper limit on the value of the optical extinction on the host of GRB 100906A is obtained.Comment: 18 pages, 14 figures, 14 tables, 5 machine readable tables; accepted for publication in MNRA

The MASTER-II network of robotic optical telescopes. First results

The main stages in the creation of the Russian segment of the MASTER network of robotic telescopes is described. This network is designed for studies of the prompt optical emission of gammaray bursts (GRBs; optical emission synchronous with the gamma-ray radiation) and surveys of the sky aimed at discovering uncataloged objects and photometric studies for various programs. The first results obtained by the network, during its construction and immediately after its completion in December 2010, are presented. Eighty-nine alert pointings at GRBs (in most cases, being the first ground telescopes to point at the GRBs) were made from September 2006 through July 2011. The MASTER network holds first place in the world in terms of the total number of first pointings, and currently more than half of first pointings at GRBs by ground telescopes are made by the MASTER network. Photometric light curves of GRB 091020, GRB 091127, GRB 100901A, GRB 100906A, GRB 10925A, GRB 110106A, GRB 110422A, and GRB 110530A are presented. It is especially important that prompt emission was observed for GRB 100901A and GRB 100906A, and thar GRB 091127, GRB 110422A, and GRB 110106A were observed from the first seconds in two polarizations. Very-wide-field cameras carried out synchronous observations of the prompt emission of GRB 081102, GRB 081130B, GRB 090305B, GRB 090320B, GRB 090328, and GRB 090424. Discoveries of Type Ia supernovae are ongoing (among them the brightest supernova in 2009): 2008gy, 2009nr, 2010V, and others. In all, photometry of 387 supernovae has been carried out, 43 of which were either discovered or first observed with MASTER telescopes; more than half of these are Type Ia supernovae. Photometric studies of the open clusters NGC 7129 and NGC 7142 have been conducted, leading to the discovery of 38 variable stars. Sixty-nine optical transients have been discovered. © 2013 Pleiades Publishing, Ltd

Актуализация формы федерального государственного статистического наблюдения № 3-ДОЗ «Сведения o дозах облучения пациентов при проведении медицинских рентгенорадиологических исследований». Предпосылки к переработке

Analysis of levels of exposure of public of the Russian Federation by sources of ionizing exposure is one of main parts of the activities conducted by the Federal Service for Surveillance on Consumer Rights Protection and Human Wellbeing. Data on the doses of public of the Russian Federation from medical exposure on facility, regional and federal levels is collected using the form of federal governmental statistical surveillance № 3-DOZ “Data on patient doses from medical X-ray examinations”, that is active since 2000. For the last 20 years there were no significant updates of the form № 3-DOZ. According to the decision of the Board of the Rospotrebnadzor from 11.09.2020, a complex program on update and modernization of form № 3-DOZ was initiated, that has resulted in the approvement of new form № 3-DOZ by the order of Rosstat № 880. The form has been significantly changed to reflect the modern condition of X-ray diagnostics in the Russian Federation. The aim of the current study was to analyze main components of medical exposure dose data collection system that required update and modernization. The study was performed based on the results of assessment of the forms № 3-DOZ from different medical facilities and regions in 2015-2020. The results of the study allowed developing main approaches to the update of the form № 3-DOZ that were implemented in a new edition of the form.Анализ уровней облучения населения Российской Федерации источниками ионизирующего излучения является важной частью мероприятий, проводимых Федеральной службой по надзору в сфере защиты прав потребителей и благополучия человека. Информация о дозах облучения населения Российской Федерации при медицинском облучении на объектовом, региональном и федеральном уровнях собирается с использованием формы федерального статистического наблюдения № 3-ДОЗ «Сведения о дозах облучения пациентов при проведении медицинских рентгенорадиологических исследований», действующей с 2000 г. За 20 лет использования формы № 3-ДОЗ она существенно не модернизировалась. В рамках решения коллегии Роспотребнадзора от 11.09.2020 г. проводилась комплексная программа по актуализации и модернизации формы № 3-ДОЗ, которая завершилась утверждением новой формы № 3-ДОЗ приказом Росстата № 880 от 30 ноября 2022 г., при этом форма № 3-ДОЗ претерпела значительные изменения, направленные на учет современного состояния лучевой диагностики в Российской Федерации. Целью данной работы являлся анализ основных компонентов системы сбора данных по уровням медицинского облучения, которые нуждались в доработке и актуализации в рамках переработки формы № 3-ДОЗ. Работа была выполнена с учетом результатов анализа объектовых и региональных форм № 3-ДОЗ за период 2015–2020 гг. По результатам работы были сформированы основные направления актуализации формы № 3-ДОЗ, реализованные в новом варианте формы