Thin Halo Research Articles

МОЖНО ЛИ ИДЕНТИФИЦИРОВАТЬ ВЫСОКОДИФФЕРЕНЦИРОВАННЫЙ РАК УЖЕ ПРИ СОНОГРАФИЧЕСКОМ ИССЛЕДОВАНИИ ЩИТОВИДНОЙ ЖЕЛЕЗЫ?

Primary diagnostics of thyroid neoplasms remains actual issue of modern endocrinology. Comprehensive clinical examination, ultrasound, and fine needle biopsy enable to make a conclusion about thyroid nodule properties but with a lot of mistakes, and take much time. Aims: assessment of diagnostic value of ultrasound criteria those may direct at papillary thyroid cancer. Materials and methods: one carried out observation multicenter retrospective continuous research among patients undergone for thyroid nodules surgery. It included adult patients (18-78) of both sexes. Patients’ case reports within 2013-2019 were sampled. Patients were shared into 2 groups according to final histological results. Results: the objects of research were 124 in-patients’ case reports. 32 of them were diagnosed thyroid cancer (24 - papillary, 8 – follicular), and 92 – benign nodules. Among searched criteria all (except hypoechogenicity) evidently differed between benign nodules and papillary cancer. In comparison criterion «absence of thin halo» reached the upper border of evidence of suspicion for papillary cancer. Multiple comparison indicated statistical difference between benign nodules (p<0,001) and follicular cancer (p<0,05). 2 of 24 papillary cancer patients (9%) in ultrasound did not demonstrate any criterion; all after this were arranged to benign nodules. 21 of 24 patients (88%) with 2 and more positive criteria were assessed correctly, but 51 of 92 benign nodules (56%) in ultrasound were assessed as papillary cancer. Conclusions: ultrasound imaging accuracy in thyroid papillary cancer is approximately equal in presence of 2 to 4 criteria; maximum accuracy (74%) is reached in presence of 3 criteria. In presence of 1 or 5 criteria is significantly lower: in 1 criterion due to low specificity, in 5 criteria – due to rarity of simultaneous combination. Follicular cancer can’t be identified in ultrasound imaging.

Sonographic Features of Estrogen-Negative Breast Cancers: A Correlation Study With Human Epidermal Growth Factor Type II Overexpression

The purpose of this study was to retrospectively review sonographic imaging features of estrogen-negative breast cancers and compare tumors with and without human epidermal growth factor type II (HER2) overexpression. Breast sonography findings from a sample of 54 patients with estrogen-negative breast cancer as well as pathological data and HER2 status were reviewed. Sonographic features including size, depth shapes, margin, location, patterns of internal echoes, posterior echoes, orientation, and presence of halo and clinicopathologic data and imaging features were correlated with tumor HER2 status. Based on these 54 patients with estrogen-negative breast cancers, 21 patients were positive for HER2 receptor, and 33 patients were negative for HER2 receptor. Among HER2 positive cancers, irregular shape, microlobulation, indistinct margins, posterior shadowing, a thin halo, heterogeneous internal echoes, and parallel orientation were the most frequent sonographic features. No associations were found between HER-2 status and tumor size, shape, margins, posterior feature, halo, internal echoes, or orientation on sonography.

Quantitative Analysis of Immature Secretory Granules in Beta Cells of Mouse Pancreatic Islets by Serial Block-Face Scanning Electron Microscopy

Serial block-face scanning electron microscopy (SBF-SEM) can provide high-resolution structural information from large volumes of biological tissue at the nanometer scale. By using SBF-SEM with a ∼1 kV electron probe that is scanned across the surface of a plastic embedded block of tissue, it is possible to image tissue volumes as large as 100,000 cubic micrometers with 5 nanometer voxel size in the plane of the block face and 25 nanometer normal to the block face. A sensitive detector collects backscattered electrons from heavy atoms staining ultrastructure near the surface of the block, and a microtome built in to the specimen stage cuts a thin layer from block face to expose a surface for imaging. Repetition of these steps produces an image stack that can be aligned, analyzed, and segmented. We have used SBF-SEM to study immature secretory granules in beta cells of mouse islets. Secretory granules contain insulin that is released in response to elevated blood glucose levels. Our objective was to use granule morphology to define their state of maturity. Immature granules contain proinsulin, and have lightly stained cores surrounded by thin halos, in contrast to mature granules that have more densely stained insulin cores surrounded by wide halos. From the SBF-SEM image stacks, we identified mature and immature secretory granules and measured the ratio of core volume to total granule volume. We also measured the relative abundances of immature granules and mature granules, which enabled us to estimate the maturation time for the beta granules by considering the measured release times of isotopically labeled insulin.

Reconstructing the star formation history of the Solar neighbourhood with Gaia

AbstractTaking advantage of the Gaia DR1, we combined TGAS parallaxes with the Tycho-2 and APASS photometry to calculate the star formation history (SFH) of the solar neighbourhood within 250 pc using the colour-magnitude diagram fitting technique. Our dynamically-evolved SFH is in excellent agreement with that calculated from the Hipparcos catalogue within 80 pc of the Sun, showing an enhanced star formation rate (SFR) in the past ~4 Gyr. We then correct the SFR for the disc thickening with age to obtain a SFR that is representative of the whole solar cylinder, and show that even with an extreme correction our results are not consistent with an exponentially decreasing SFR as found by recent studies. Finally, we discuss how this technique can be applied out to ~5 kpc thanks to the next Gaia data releases, which will allow us to quantify the SFH of the thin disc, thick disc and halo in situ.

RADIATION HYDRODYNAMICS MODELS OF THE INNER RIM IN PROTOPLANETARY DISKS

ABSTRACT Many stars host planets orbiting within a few astronomical units (AU). The occurrence rate and distributions of masses and orbits vary greatly with the host star’s mass. These close planets’ origins are a mystery that motivates investigating protoplanetary disks’ central regions. A key factor governing the conditions near the star is the silicate sublimation front, which largely determines where the starlight is absorbed, and which is often called the inner rim. We present the first radiation hydrodynamical modeling of the sublimation front in the disks around the young intermediate-mass stars called Herbig Ae stars. The models are axisymmetric and include starlight heating; silicate grains sublimating and condensing to equilibrium at the local, time-dependent temperature and density; and accretion stresses parameterizing the results of MHD magnetorotational turbulence models. The results compare well with radiation hydrostatic solutions and prove to be dynamically stable. Passing the model disks into Monte Carlo radiative transfer calculations, we show that the models satisfy observational constraints on the inner rim’s location. A small optically thin halo of hot dust naturally arises between the inner rim and the star. The inner rim has a substantial radial extent, corresponding to several disk scale heights. While the front’s overall position varies with the stellar luminosity, its radial extent depends on the mass accretion rate. A pressure maximum develops near the location of thermal ionization at temperatures of about 1000 K. The pressure maximum is capable of halting solid pebbles’ radial drift and concentrating them in a zone where temperatures are sufficiently high for annealing to form crystalline silicates.

A nodal discontinuous Galerkin method for reverse-time migration on GPU clusters

Improving both accuracy and computational performance of numerical tools is a major challenge for seismic imaging and generally requires specialized implementations to make full use of modern parallel architectures. We present a computational strategy for reverse-time migration (RTM) with accelerator-aided clusters. A new imaging condition computed from the pressure and velocity fields is introduced. The model solver is based on a high-order discontinuous Galerkin time-domain (DGTD) method for the pressure-velocity system with unstructured meshes and multi-rate local time-stepping. We adopted the MPI+X approach for distributed programming where X is a threaded programming model. In this work we chose OCCA, a unified framework that makes use of major multi-threading languages (e.g. CUDA and OpenCL) and offers the flexibility to run on several hardware architectures. DGTD schemes are suitable for efficient computations with accelerators thanks to localized element-to-element coupling and the dense algebraic operations required for each element. Moreover, compared to high-order finite-difference schemes, the thin halo inherent to DGTD method reduces the amount of data to be exchanged between MPI processes and storage requirements for RTM procedures. The amount of data to be recorded during simulation is reduced by storing only boundary values in memory rather than on disk and recreating the forward wavefields. Computational results are presented that indicate that these methods are strong scalable up to at least 32 GPUs for a three-dimensional RTM case.

Usefulness of ultrasonography in the differential diagnosis of thyroidal follicular tumor

To evaluate the usefulness of ultrasonography in distinguishing follicular carcinoma from adenoma. The ultrasound data of 37 patients with histopathologically confirmed follicular carcinomas who were treated in PUMC Hospital from January 2000 to November 2012 were retrospectively studied. In addition, 74 sex-and age-matched patients with histopathologically confirmed adenomas during the same period were enrolled as the control group. The pathologic results were regarded as the gold standard. Irregular shape (32.4% of follicular carcinoma vs 5.4% of adenoma), absence of thin halo (67.6% vs 36.5%), indistinct margin (21.6% vs 1.4%), hypoechoic appearance (64.9% vs 39.2%), punctuate calcification(40.5% vs 13.5%), absence of cystic change (78.4% vs 54.1%), and being complicated with other thyroid disease (56.8% vs 28.4%) were more frequently associated with follicular carcinoma than with benign adenoma (P<0.05). No significant difference in the echotexture and internal flow was observed between the two groups (P>0.05). Although follicular carcinoma and adenoma share many sonographic features, irregular shape, absence of thin halo, indistinct margin, hypoechoic appearance, punctuate calcification, absence of cystic change, and being complicated with other thyroid disease favor a follicular carcinoma diagnosis.

The Topography of White Mater Peri-Ventricular Hyperintensities on Brain Magnetic Resonance Imagings (MRI) Among Cameroonians

Background: Peri-Ventricular Hyperintensity (PVH) refers to bright signal adjacent to lateral ventricles on T2 weighted (T2W) and Fluid Attenuated Inversion Recovery (FLAIR) brain MR images. It is a qualitative evaluation of white mater lesions. Aim: Evaluating the incidence and topographic distribution of cerebral periventricular hyperintensities among Cameroonians using FLAIR and T2W brain MR images. Materials and methods: Prospective study of patients who came for brain MRI from June 2009 to Febuary 2010. Patients were scanned after data documentation with AIRIS 11 0.3 Tesla imager starting from medullo-cervical cord junction. Axial T2W and FLAIR images were acquired using 6-8mm slice tissue thickness and 0.5-1 mm intersection gap. Images were evaluated qualitatively into absent, type 1-3 PVH. Type 1-peri-ventricular frontal capping, rimming or thin smooth halo. Type 2-PVH extends into deep white mater. Type 3-PVH extends into sub-cortical white mater. Inclusion criteria included reportable quality images. Results were analysed with Computer statistical package SPSS 13 Results: Ninety seven patients with 60 (61.86%), males and 37 (38.14%) females were studied. Age range was 0- 89 with mean of 44.5. 75.26% of all cases, 70% of all males and 83.78% of all females had absent PVH. 24.74% (n=24, M: F=3:1) of studied population had PVH, shared into 33.33% type 1 PVH, 58.33% type 2 and 8.33% type 3. Peaks of type 2 PVH in males and females were 60-69 and 70-79 respectively. The commonest association of type 2 PVH in males and females were CVD (62%) and cerebral atrophy (50%) respectively. Conclusion: The incidence rate of PVH among Cameroonians without population bias is 24.74% with male earlier onset and predominance. PVH is common and severer among elderly (50 years and above). The predominant type of PVH in both sexes is type 2 with commonest association in males being CVD but cerebral atrophy in females.

Identification of &amp;lt;i&amp;gt;Alternaria&amp;lt;/i&amp;gt; spp. as Pathogenic on the Native Species &amp;lt;i&amp;gt;Terminalia australis&amp;lt;/i&amp;gt; and &amp;lt;i&amp;gt;Salvia guaranitica&amp;lt;/i&amp;gt;

This work is the result of activities included in the cooperative project between Asociacion Ribera Norte (ARN) and the Department of Plant Pathology, School of Agronomy, University of Buenos Aires. ARN is a non-governmental organization created in 1993 mainly for the management of the Reserva Ecologica Municipal Ribera Norte, a preservation area located in San Isidro (North of Buenos Aires), within the Provincia Paranaense region. The aims were to identify diseases in native plant species growing there. Light brown leaf spots with thin brown margins and narrow yellow halos were observed on Terminalia australis (mean disease severity: 25%). The pathogen was isolated, inoculated on healthy plants, reisolated from infected leaves and identified as Alternaria tenuissima. Similarly, another leaf-spot disease was observed on Salvia guaranitica, characterized by reddish brown large spots developed from the apexes and margins towards the centre of the leaves, reaching the veins in some cases (mean severity: 20%). Pathogen isolation, inoculation and reisolation led to the identification of A. alternata as the causal agent of the disease. Unusual heavy rain is analyzed as disease conductive.

The risk of malignancy of the thyroid nodule/focal lesion – an assessment by ultrasound, based on our own scoring system

Ultrasonography (US) is the most commonly performed test used to visualize the thyroid. This examination is safe and readily available, hence it is very often carried out. Ultrasound observations allow the description of structural abnormalities of the thyroid gland evaluated in whole, or of nodules/focal lesions present in the thyroid. An ultrasound examination measures the acoustic density of tissues. The image is displayed on the apparatus screen in grayscale (B-mode). An assessment of blood flow, showing the location and intensity of thyroid vascularity is a newer US technique that uses the Doppler effect for measurements. In turn, elastography is the latest application of US, i.e. the examination which is based on the assessment of the, so-called, stiffness of lesions in comparison with the stiffness of normal thyroid tissue (i.e., the tissue of morphologically normal appearance). A common performance of US of the neck region, often carried out because of the indications that are not related to the thyroid gland (e.g., evaluation of salivary glands, assessment of blood flows in carotid and vertebral arteries) leads to the disclosure of a number of lesions detected incidentally in the thyroid gland itself. In turn, it results in the need for proper interpretation of US images in order to optimize further diagnostic and therapeutic procedures. Previous studies on the use of US to determine the nature of focal lesions/thyroid nodules in terms of their vs. character did not allowed to give a clear answer. These studies have not led to the general acceptance of cancer risk US patterns. Thus, at the present stage of knowledge, it is not possible to accept the categorical and definitive determination of the nature of lesions in terms of malignant vs. benign – on the basis of US image only. However, the studies have helped to determine the characteristics of a group of US image features, the presence of which is associated with a higher risk of cancer diagnosis. Endocrinologists diagnosing the patients with thyroid diseases are expecting to have exact guidelines and recommendations that would make easier to decide on the appropriate management. This applies in particular to answer the question: what is a greater risk to the patient - whether to undergo a surgical treatment, or abandon it? Analysis of data from the medical literature and our personal experience indicate the possibility of assigning certain patterns of US appearance to the risk of lesion malignancy. The multiplicity of possible combinations of co-occurrence of different US characteristics indicates that the most appropriate way of an objective assessment of the image is the introduction of an appropriate scoring system which reflects the accumulation of suspicious US features and the of US risk of malignancy expressed by a number of assigned points. This is precisely our issue that we have decided to propose; our scale divides the patterns of US image risk into 3 levels: high, intermediate and low risk. In our scoring system, the finding of pathologically altered lymph nodes (usually enlarged) and/or a confirmation of the fast growing lesions/thyroid nodules (augmentation) is equal to granting 3 points for each of these characteristics. Hypoechogenicity, the presence of microcalcifications, shape of lesion - close to the rotational ellipsoid with the longest axis of a vertical (shape of an egg in upright position), as well as the presence of abnormal vascular flows (the increased and chaotic blood flows centrally located in the lesion, or totally absent blood flows in hypoechogenic lesions) is equal to the grant 1 point for each of the features. The absence of a regular thin halo, solid structure (composition) of the lesion, the focus/nodule diameter of 3 cm and more and its uneven, blurred outlines (margins) are associated with granting 0.5 points for each of the features. The sum of granted points, resulting from the presence of US features specified above, is the basis of qualification for US risk levels. The score ranging from 0 to 4 points, awarded on the basis of thyroid US, speaks for a low risk of thyroid cancer, the score from 4 to 7 points – corresponds to intermediate risk, and the granting of 7 points or more qualifies to the group of US high-risk of malignancy. The use of this scoring system can help make the right clinical decisions, especially in patients with non-diagnostic smears (category I of The Bethesda System for Reporting Thyroid Cytopathology - TBSRTC), also in patients with the smears, in case of which it is impossible to determine the exact nature of the smear (category III TBSRTC, being also called category of exclusion), as well as in patients with lesions (category II TBSRTC) when such a cytological diagnosis seems unlikely in combination with the US image indicating a high risk of malignancy.

Breast Hamartoma: Mammographic Findings

Breast Hamartoma: Mammographic Findings

Galactic magnetic turbulence from radio data

Fluctuations in the Galactic synchrotron emission can be traced by the angular power spectrum of radio maps at low multipoles. At frequencies below few GHz, large-scale anisotropies are mainly induced by magnetic field turbulence, since non-thermal electrons radiating at these frequencies are uniformly distributed over the scales of magnetic field inhomogeneities. By performing an analysis of five radio maps, we extract constraints on turbulence spectral index and halo scale. Results favour a power spectrum significantly flatter than for 3D Kolmogorov-like turbulence, and a thin halo. This can be interpreted as an indication supporting non-conventional models of propagation of cosmic-ray particles in the Galaxy, or as a suggestion of a spectral-index break in the observed magnetic turbulence power spectrum.

Luminosity-colour relations for thin-disc main-sequence stars

In this study we present the absolute magnitude calibrations of thin-disc main-sequence stars in the optical (M V ), and in the near-infrared (Mj). Thin-disc stars are identified by means of Padova isochrones, and absolute magnitudes for the sample are evaluated via the newly reduced Hipparcos data. The obtained calibrations cover a large range of spectral types: from A0 to M4 in the optical and from A0 to M0 in the near-infrared. Also, we discuss the effects of binary stars and evolved stars on the absolute magnitude calibrations. The usage of these calibrations can be extended to the estimation of galactic model parameters for the thin disc individually, in order to compare these parameters with the corresponding ones estimated by Χ 2 min statistics (which provides galactic model parameters for thin and thick discs and halo simultaneously) to test any degeneracy between them. The calibrations can also be used in other astrophysical researches where distance plays an important role in that study.

Chromogranin A: Immunocytochemical localization in secretory granules of frog atrial cardiomyocytes

Chromogranin A (CgA) is a member of the granin family of acidic proteins that present in the secretory granules (SGs) of many endocrine, neuroendocrine and neuronal cells. Atrial natriuretic peptide (ANP)-storing SGs in atrial cardiomyocytes of rat heart also contain CgA. Cardiosuppressive effect of CgA-derived peptides (vasostatins) on in vitro isolated and perfused working frog and rat hearts has been shown under both basal conditions and beta-adrenergic stimulation. More recently it has been revealed that rat heart produces and processes CgA-derived vasostatin-containing peptides. Until now nothing has been known about the presence of CgA in an amphibian heart. We have investigated the subcellular localization of CgA in atrial myocytes of adult frog Rana temporaria heart using ultraimmunocytochemical method. Immunocytochemical staining of the frog atrial tissue for CgA and ANP has shown that out of three morphologically different types (A, B and D) of specific cytoplasmic granules (SCGs) present in myocytes only two (A and B)--large (120-200 nm in diameter) granules with more and with less electron dense core--exhibit immunoreactivity (IR) to these two antigens. The third type (D) of granules (80-100 nm in diameter) are small membrane bound granules characterized by highly electron dense core surrounded with a thin halo. These granules revealed negative reaction on immunostaining for both CgA and ANP. The presence of CgA- and ANP-IR in the same SCGs in frog atrial myocytes is consistent with the endocrine nature of these granules. Taking into account our and literature data we propose that CgA present in frog atrial cardiomyocite SCGs might be a precursor of vasostatin-containing peptides, as it takes place in rat heart. It is possible that these CgA-derived peptides together with ANP exert their regulatory function through the autocrine and/or paracrine mechanisms and play important cardioprotective role in frog heart under stress condition.

Galactic structure studies from the Beijing-Arizona-Taiwan-Connecticut survey

We present an analysis of the photometric parallaxes of stars in 21 of the Beijing-Arizona-Taiwan-Connecticut Survey fields carried out with the National Astronomical Observatories (NAOC) 60/90 cm Schmidt Telescope in 15 intermediate-band filters from 3000 to 10000 A. In this study, we have adopted a three-component (thin disc, thick disc and halo) model to analyse star count information. By calculating the stellar space density as a function of distance from the Galactic plane, we determine that the range of scaleheight for the thin disc varies from 220 to 320 pc. Although 220 pc seems an extreme value, it is close to the lower limit in the literature. The range of scaleheight for the thick disc is from 600 to 1100 pc, and the corresponding space number density normalization is 7.0-1.0 per cent of the thin disc. We find that the scaleheight of the disc may be variable with the observed direction, which cannot simply be attributed to statistical errors. Possibly the main reasons can be attributed to the disc (mainly the thick disc) being flared, with a scaleheight increasing with radius. The structure is consistent with the merger origin for the thick disc formation. Adopting a de Vaucouleurs r 1/4 law halo, we also find that the axis ratio towards the Galactic Centre is somewhat flatter (∼0.4), while the shape of the halo in the anticentre and antirotation direction is rounder with c/a > 0.4. Our results show that star counts in different lines of sight can be used directly to obtain a rough estimate of the shape of the stellar halo. Our solutions support the Galactic models with a flattened inner halo, possibly formed by an early merger in the Galaxy's history.

Discs and haloes in pre-main-sequence stars

A B S T R A C T We study the infrared (IR) emission from flared discs with and without additional optically thin haloes. Flux calculations of a flared disc in vacuum can be considered a special case of the more general family of models in which the disc is imbedded in an optically thin halo. In the absence of such a halo, flux measurements can never rule out its existence because the disc flaring surface defines a mathematically equivalent halo that produces the exact same flux at all IR wavelengths. When a flared disc with height H at its outer radius R is imbedded in a halo whose optical depth at visual wavelengths is τhalo, the system IR flux is dominated by the halo whenever τhalo > (1/4)H/R. Even when its optical depth is much smaller, the halo can still have a significant effect on the disc temperature profile. Imaging is the only way to rule out the existence of a potential halo, and we identify a decisive test that extracts a signature unique to flared discs from imaging observations.

VLA observations at 7 mm of the planetary nebula IC 4997

We present high angular resolution (0.1 arcsec) VLA observations at 7-mm wavelength towards the bipolar planetary nebula IC 4997. The 7-mm emission in IC 4997 is dominated by a bright, compact core, the flux density of which at this wavelength is about six times brighter than at 2.0 and 3.6 cm. We model the centimetre and millimetre continuum spectrum in terms of free–free emission from an ionized core–halo source. In this model a dense (2.6 × 106 cm−3), optically thick inner core dominates the millimetre emission, while a low-density (1 × 104 cm−3), optically thin halo dominates the centimetre emission. The spectral index of the core (between 2 cm and 7 mm) is α≃ 1.6 ± 0.1(Sν∝να), which is consistent with optically thick free–free emission. An upper limit for the mass-loss rate that created this inner core is ∼ 3 × 10−6 M⊙ yr−1, suggesting that this core may have been formed at the end of the superwind phase.

Isolation, characterization and diuron transformation capacities of a bacterial strain Arthrobacter sp. N2

A bacterial strain able to transform diuron was isolated from a soil by enrichment procedures. Strain isolation was realized by plating on minimal-agarose medium spread with this herbicide and selecting the colonies surrounded by a clear thin halo. One strain was characterized and identified as an Arthrobacter sp. It metabolized diuron and the final transformation product, 3,4-dichloroaniline, was produced in stoichiometric amounts. The transformation of diuron at different concentrations was more efficient in the presence of alternative sources of carbon and nitrogen. The bacterial activity was also evaluated in soil microcosms with a consequent disappearance of diuron and concomitant appearance of 3,4-dichloroaniline, of which the concentration decreased thereafter. Bacterial cells inoculated in the microcosms survived as viable but eventually nonculturable cells.

A vein occurrence of co-existing talc, saponite, and corrensite, Builth Wells, Wales

AbstractUnique phyllosilicate assemblages occur in quartz-calcite veins cutting altered andesite at Builth Wells, UK. These veins show: (1) a central talc-dominated assemblage, grading into a saponite/corrensite/chlorite-dominated assemblage near their walls; (2) talc replacing calcite and quartz; and (3) closely associated blocky and fibrous saponite. Fibrous saponite occurs in narrow (&lt;1 cm) fractures that extend for up to 1 m from major (⩽ 50 cm wide) talc-bearing veins. A thin halo (&lt;5 mm) of wall-rock alteration, containing blocky saponite and minor corrensite, borders the fibrous saponite. These minerals may have originated when cooling, low-pH, quartz-saturated, Mg-rich fluid invaded pre-existing quartz/calcite veins. Quartz is replaced by talc where calcite dissolution caused the pH to increase. Wallrock alteration liberated Fe and Al to the fluid causing blocky saponite and corrensite to form. Fibrous saponite formed where lithostatic pressures were directed across hydraulic fractures.

Spectral Properties of Accretion Disks around Galactic and Extragalactic Black Holes

view Abstract Citations (556) References (66) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectral Properties of Accretion Disks around Galactic and Extragalactic Black Holes Chakrabarti, Sandip ; Titarchuk, Lev G. Abstract We study the spectral properties of a very general class of accretion disks which can be decomposed into three distinct components apart from a shock at r = rs: (1) An optically thick Keplerian disk on the equatorial plane (r > rs); (2) a sub-Keplerian optically thin halo above and below this disk r > rs and (3) a hot, optically slim τ ∼ 1 postshock region r < rs ∼ 5-10rg where rg is the Schwarzschild radius. The postshock halo intercepts soft photons from the Keplerian component and reradiates them as hard X-rays and γ rays after Comptonization. We solve two-temperature equations in the postshock region with Coulomb energy exchange between protons and electrons, and incorporating radiative processes such as bremsstrahlung and Comptonization. We also present the exact prescription to compute the reflection of the hard X-rays from the cool disk. We produce radiated spectra from both the disk components as functions of the accretion rates and compare them with the spectra of Galactic and extragalactic black hole candidates. We find that the transition from hard state to soft state is smoothly initiated by a single parameter, namely the mass accretion rate of the disk. In the soft state, when the postshock region is very optically thick and cooled down, bulk motion of the converging flow determines the spectral index to be about 1.5 in agreement with observations. Publication: The Astrophysical Journal Pub Date: December 1995 DOI: 10.1086/176610 arXiv: arXiv:astro-ph/9510005 Bibcode: 1995ApJ...455..623C Keywords: ACCRETION; ACCRETION DISKS; BLACK HOLE PHYSICS; RADIATION MECHANISMS: NONTHERMAL; SHOCK WAVES; STARS: NEUTRON; Astrophysics E-Print: 45 pages of Latex file + 10 figures (Misprints in Description and Caption of Figure 2 are corrected) full text sources arXiv | ADS | data products SIMBAD (10) Related Materials (1) Erratum: 1996ApJ...467..474C