701 research outputs found
Polarization and long-term variability of Sgr A* X-ray echo
We use a model of the molecular gas distribution within ~100 pc from the
center of the Milky Way (Kruijssen, Dale & Longmore) to simulate time evolution
and polarization properties of the reflected X-ray emission, associated with
the past outbursts from Sgr A*. While this model is too simple to describe the
complexity of the true gas distribution, it illustrates the importance and
power of long-term observations of the reflected emission. We show that the
variable part of X-ray emission observed by Chandra and XMM from prominent
molecular clouds is well described by a pure reflection model, providing strong
support of the reflection scenario. While the identification of Sgr A* as a
primary source for this reflected emission is already a very appealing
hypothesis, a decisive test of this model can be provided by future X-ray
polarimetric observations, that will allow placing constraints on the location
of the primary source. In addition, X-ray polarimeters (like, e.g., XIPE) have
sufficient sensitivity to constrain the line-of-sight positions of molecular
complexes, removing major uncertainty in the model.Comment: 17 pages, 10 figures, accepted for publication in MNRA
Can Sgr A* flares reveal the molecular gas density PDF?
Illumination of dense gas in the Central Molecular Zone (CMZ) by powerful
X-ray flares from Sgr A* leads to prominent structures in the reflected
emission that can be observed long after the end of the flare. By studying this
emission we learn about past activity of the supermassive black hole in our
Galactic Center and, at the same time, we obtain unique information on the
structure of molecular clouds that is essentially impossible to get by other
means. Here we discuss how X-ray data can improve our knowledge of both sides
of the problem. Existing data already provide: i) an estimate of the flare age,
ii) a model-independent lower limit on the luminosity of Sgr A* during the
flare and iii) an estimate of the total emitted energy during Sgr A* flare. On
the molecular clouds side, the data clearly show a voids-and-walls structure of
the clouds and can provide an almost unbiased probe of the mass/density
distribution of the molecular gas with the hydrogen column densities lower than
few . For instance, the probability distribution
function of the gas density can be measured this way. Future high
energy resolution X-ray missions will provide the information on the gas
velocities, allowing, for example a reconstruction of the velocity field
structure functions and cross-matching the X-ray and molecular data based on
positions and velocities.Comment: 13 pages, 7 figures; Accepted for publication in MNRA
Not that long time ago in the nearest galaxy: 3D slice of molecular gas revealed by a 110 years old flare of Sgr A*
A powerful outburst of X-ray radiation from the supermassive black hole Sgr
A* at the center of the Milky Way is believed to be responsible for the
illumination of molecular clouds in the central ~100 pc of the Galaxy (Sunyaev
et al., 1993, Koyama et al., 1996). The reflected/reprocessed radiation comes
to us with a delay corresponding to the light propagation time that depends on
the 3D position of molecular clouds with respect to Sgr A*. We suggest a novel
way of determining the age of the outburst and positions of the clouds by
studying characteristic imprints left by the outburst in the spatial and time
variations of the reflected emission. We estimated the age of the outburst that
illuminates the Sgr A molecular complex to be ~110 yr. This estimate implies
that we see the gas located ~10 pc further away from us than Sgr A*. If the Sgr
B2 complex is also illuminated by the same outburst, then it is located ~130 pc
closer than our Galactic Center. The outburst was short (less than a few years)
and the total amount of emitted energy in X-rays is erg, where is the mean hydrogen density of the
cloud complex in units of . Energetically, such fluence can
be provided by a partial tidal disruption event or even by a capture of a
planet. Further progress in more accurate positioning and timing of the
outburst should be possible with future X-ray polarimetric observations and
long-term systematic observations with Chandra and XMM-Newton. A few
hundred-years long X-ray observations would provide a detailed 3D map of the
gas density distribution in the central pc region.Comment: 10 pages, 7 figures, accepted for publication in MNRA
Geotechnical conditions contributing to negative geological process development in urban areas (the case of Kemerovo-city)
The paper addresses the issue of intensive urban development in the area of Kemerovo-city. Underestimation of geotechnical conditions of the area at the project and construction stages results in negative geological processes such as erosion, waterlogging, soil subsidence, and underflooding. These processes can lead to deformation and failure of buildings and constructions
Self-force of a point charge in the space-time of a symmetric wormhole
We consider the self-energy and the self-force for an electrically charged
particle at rest in the wormhole space-time. We develop general approach and
apply it to two specific profiles of the wormhole throat with singular and with
smooth curvature. The self-force for these two profiles is found in manifest
form; it is an attractive force. We also find an expression for the self-force
in the case of arbitrary symmetric throat profile. Far from the throat the
self-force is always attractive.Comment: 18 pages, 3 figures Comments: corrected pdf, enlarged pape
Probing 3D Density and Velocity Fields of ISM in Centers of Galaxies with Future X-Ray Observations
Observations of bright and variable "reflected" X-ray emission from molecular
clouds located within inner hundred parsec of our Galaxy have demonstrated that
the central supermassive black hole, Sgr A*, experienced short and powerful
flares in the past few hundred years. These flares offer a truly unique
opportunity to determine 3D location of the illuminated clouds (with ~10 pc
accuracy) and to reveal their internal structure (down to 0.1 pc scales). Short
duration of the flare(s), combined with X-rays high penetration power and
insensitivity of the reflection signal to thermo- and chemo-dynamical state of
the gas, ensures that the provided diagnostics of the density and velocity
fields is unbiased and almost free of the projection and opacity effects. Sharp
and sensitive snapshots of molecular gas accessible with aid of future X-ray
observatories featuring large collecting area and high angular (arcsec-level)
and spectral (eV-level) resolution cryogenic bolometers will present invaluable
information on properties of the supersonic turbulence inside the illuminated
clouds, map their shear velocity field and allow cross-matching between X-ray
data and velocity-resolved emission of various molecular species provided by
ALMA and other ground-based facilities. This will highlight large and
small-scale dynamics of the dense gas and help uncovering specifics of the ISM
lifecycle and high-mass star formation under very extreme conditions of
galactic centers. While the former is of particular importance for the SMBH
feeding and triggering AGN feedback, the latter might be an excellent test case
for star formation taking place in high-redshift galaxies.Comment: White paper submitted to the Astro2020 Decadal Surve
Drilling Through Gas Hydrates Formations: Managing Wellbore Stability Risks
As hydrocarbon exploration and development moves into deeper water and
onshore arctic environments, it becomes increasingly important to quantify the drilling
hazards posed by gas hydrates.
To address these concerns, a 1D semi-analytical model for heat and fluid transport
in the reservoir was coupled with a numerical model for temperature distribution along
the wellbore. This combination allowed the estimation of the dimensions of the hydratebearing
layer where the initial pressure and temperature can dynamically change while
drilling. These dimensions were then used to build a numerical reservoir model for the
simulation of the dissociation of gas hydrate in the layer. The bottomhole pressure
(BHP) and formation properties used in this workflow were based on a real field case.
The results provide an understanding of the effects of drilling through hydratebearing
sediments and of the impact of drilling fluid temperature and BHP on changes in
temperature and pore pressure within the surrounding sediments. It was found that the
amount of gas hydrate that can dissociate will depend significantly on both initial
formation characteristics and bottomhole conditions, namely mud temperature and pressure. The procedure outlined suggested in this work can provide quantitative results
of the impact of hydrate dissociation on wellbore stability, which can help better design
drilling muds for ultra deep water operations
Rare case of type II glycogen storage disease
The article presents information about a rare case of Pompe disease. It is a glycogen storage disease. During the third screening of a pregnant woman, the ultrasonography of the fetus’s heart revealed the myocardial hypertrophy of the left ventricle perceived as posthypoxic. After delivery, the newborn underwent the ultrasound examination and molecular genetic studies. Firstly, the hepatomegaly and cardiomegaly were diagnosed. Then an infantile form of Pompe disease was found. The patient got enzyme replacement therapy without positive result. The death occurred at the age of 2 years and 5 months as a result of cardiovascular disease failure. Macroscopically, the sizes of the internal organs were increased. The microscopic examination demonstrated glycogen deposition in the myocardium, skeletal muscles, mucous membranes of the organs of the gastrointestinal tract, liver, kidney, spleen and adrenal gland
Integrable boundary conditions for classical sine-Gordon theory
The possible boundary conditions consistent with the integrability of the
classical sine-Gordon equation are studied. A boundary value problem on the
half-line with local boundary condition at the origin is considered.
The most general form of this boundary condition is found such that the problem
be integrable. For the resulting system an infinite number of involutive
integrals of motion exist. These integrals are calculated and one is identified
as the Hamiltonian. The results found agree with some recent work of Ghoshal
and Zamolodchikov.Comment: 10 pages, DTP/94-3
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