scholarly journals A simplified analysis of the Chernobyl accident

2021 ◽  
Vol 7 ◽  
pp. 1
Author(s):  
Bertrand Mercier ◽  
Di Yang ◽  
Ziyue Zhuang ◽  
Jiajie Liang
Keyword(s):  
Numerical Models ◽  
List Type ◽  
Flash Evaporation ◽  
The Core ◽  
Large Size ◽  
Reaction Coefficient ◽  
Pressure Tubes ◽  
Void Effect ◽  
Reactivity Coefficient ◽  
Reactivity Increase

We show with simplified numerical models, that for the kind of RBMK operated in Chernobyl: The core was unstable due to its large size and to its weak power counter-reaction coefficient, so that the power of the reactor was not easy to control even with an automatic system. Xenon oscillations could easily be activated. When there was xenon poisoning in the upper half of the core, the safety rods were designed in such a way that, at least initially, they were increasing (and not decreasing) the core reactivity. This reactivity increase has been sufficient to lead to a very high pressure increase in a significant amount of liquid water in the fuel channels thus inducing a strong propagating shock wave leading to a failure of half the pressure tubes at their junction with the drum separators. The depressurization phase (flash evaporation) following this failure has produced, after one second, a significant decrease of the water density in half the pressure tubes and then a strong reactivity accident due to the positive void effect reactivity coefficient. We evaluate the fission energy released by the accident

scholarly journals Large Bent Jets in the Inner Region of CSS

1996 ◽  
Vol 175 ◽  
pp. 71-72
Author(s):  
F. Mantovani ◽  
W. Junor ◽  
M. Bondi ◽  
L. Padrielli ◽  
W. Cotton ◽  
...  
Keyword(s):  
Velocity Structure ◽  
Radio Sources ◽  
Ambient Media ◽  
The Core ◽  
Gaseous Environment ◽  
Radio Jets ◽  
Large Size ◽  
Superluminal Motion ◽  
Inner Region ◽  
Quasars And Radio Galaxies

Recently we focussed our attention on a sample of Compact Steep-spectrum Sources (CSSs) selected because of the large bent radio jets seen in the inner region of emission. The largest distortions are often seen in sources dominated by jets, and there are suggestions that this might to some extent be due to projection effects. However, superluminal motion is rare in CSSs. The only case we know of so far is 3C147 (Alef at al. 1990) with a mildly superluminal speed of ≃ 1.3v/c. Moreover, the core fractional luminosity in CSSs is ≃ 3% and ≤ 0.4% for quasars and radio galaxies respectively. Similar values are found for large size radio sources i.e. both boosting and orientations in the sky are similar for the two classes of objects. An alternative possibility is that these bent-jet sources might also be brightened by interactions with the ambient media. There are clear indications that intrinsic distortions due to interactions with a dense inhomogeneous gaseous environment play an important role. Observational support comes from the large RMs found in CSSs (Taylor et al. 1992; Mantovani et al. 1994; Junor et al. these proc.) and often associated with strong depolarization (Garrington & Akujor, t.p.). The CSSs also have very luminous Narrow Line Regions emission, with exceptional velocity structure (Gelderman, t.p.).

scholarly journals Can evolutionary thinking shed light on gender diversity?

2019 ◽  
Vol 25 (6) ◽  
pp. 351-362 ◽  
Author(s):  
Bernadette Wren ◽  
John Launer ◽  
Michael J. Reiss ◽  
Annie Swanepoel ◽  
Graham Music
Keyword(s):  
Gender Identity ◽  
Gender Diversity ◽  
Medical Intervention ◽  
List Type ◽  
Sex And Gender ◽  
Medical Interventions ◽  
The Core ◽  
Causal Pathways ◽  
And Gender ◽  
Shed Light

SUMMARYIssues of sexual reproduction lie at the core of evolutionary thinking, which often places an emphasis on how individuals attempt to maximise the number of successful offspring that they can produce. At first sight, it may therefore appear that individuals who opt for gender-affirming medical interventions are acting in ways that are evolutionarily disadvantageous. However, there are persuasive hypotheses that might make sense of such choices in evolutionary terms and we explore these here. It is premature to claim knowledge of the extent to which evolutionary arguments can usefully be applied to issues of gender identity, although worth reflecting on the extent to which nature tends towards diversity in matters of sex and gender. The importance of acknowledging and respecting different views in this domain, as well as recognising both the uncertainty and likely multiplicity of causal pathways, has implications for clinicians. We make some suggestions about how clinicians might best respond when faced with requests from patients in this area.LEARNING OBJECTIVESAfter reading this article you will be able to:•understand evolutionary arguments about diversity in human gender identity•identify strengths and weaknesses in evolutionary arguments applied to transgender issues•appreciate the range and diversity of gender experience and gender expression among people who present to specialist gender services, as well as the likely complexities of their reasons for requesting medical intervention.

scholarly journals CORE-Kids: a protocol for the development of a core outcome set for childhood fractures

BMJ Open ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. e036224 ◽  
Author(s):  
Ben Arthur Marson ◽  
Joseph C Manning ◽  
Marilyn James ◽  
Simon Craxford ◽  
Sandeep R Deshmukh ◽  
...  
Keyword(s):  
Core Outcome Set ◽  
Significant Heterogeneity ◽  
List Type ◽  
Core Outcome ◽  
The Core ◽  
Outcome Set ◽  
Study Results ◽  
Orthopaedic Literature ◽  
Registration Number ◽  
Limb Fractures

IntroductionLimb fractures in children are common yet there are few trials that compare treatments for these injuries. There is significant heterogeneity in the outcomes reported in the paediatric orthopaedic literature, which limits the ability to compare study results and draw firm conclusions. The aim of the CORE-Kids Study is to develop a core outcome set for use in research studies of childhood limb fractures. A core outcome set will provide a minimum set of outcomes to be measured in all trials to minimise the heterogeneity of outcomes reported and minimise reporting bias. A core outcome set ensures that outcomes are reported that are relevant to families as well as clinicians. The core outcome set will include additional upper and lower limb modules.MethodsThe development of the core outcome set will require four phases to evaluate:What are the outcomes that are relevant to professionals?What are the outcomes that are relevant to families?What are the most important of these outcomes?Which outcomes should be included in the core outcome set?This will be completed through a systematic review of trials to identify the outcomes domains that are relevant to trialists. A series of semi-structured interviews will be completed with families to identify the outcome domains that are relevant to families. These outcome domains will be used in a three-round Delphi Study to analyse the importance of these outcome domains to a range of stakeholders including parents, clinicians and researchers. Following this, the core outcome set will be decided at a consensus meeting.Ethics and disseminationEthical approval has been awarded HRA/REC IRAS number 262503. Date of approval 06/08/2019. Dissemination will be through scientific literature and international societies.Trial registrationCore Outcome Measures in Effectiveness Trials Initiative, registration number: 1274. Date of registration 13/12/2018.PROSPERO registration numberCRD42018106605.

scholarly journals On the existence of Kobayashi and Bergman metrics for Model domains

2020 ◽  
Author(s):  
Nikolay Shcherbina
Keyword(s):  
Entire Function ◽  
Continuous Function ◽  
Pseudoconvex Domain ◽  
Plurisubharmonic Function ◽  
Holomorphic Curves ◽  
List Type ◽  
Bergman Metric ◽  
The Core ◽  
Bounded Smooth ◽  
Bergman Metrics

Abstract We prove that for a pseudoconvex domain of the form $${\mathfrak {A}} = \{(z, w) \in {\mathbb {C}}^2 : v > F(z, u)\}$$ A = { ( z , w ) ∈ C 2 : v > F ( z , u ) } , where $$w = u + iv$$ w = u + i v and F is a continuous function on $${\mathbb {C}}_z \times {\mathbb {R}}_u$$ C z × R u , the following conditions are equivalent: The domain $$\mathfrak {A}$$ A is Kobayashi hyperbolic. The domain $$\mathfrak {A}$$ A is Brody hyperbolic. The domain $$\mathfrak {A}$$ A possesses a Bergman metric. The domain $$\mathfrak {A}$$ A possesses a bounded smooth strictly plurisubharmonic function, i.e. the core $$\mathfrak {c}(\mathfrak {A})$$ c ( A ) of $$\mathfrak {A}$$ A is empty. The graph $$\Gamma (F)$$ Γ ( F ) of F can not be represented as a foliation by holomorphic curves of a very special form, namely, as a foliation by translations of the graph $$\Gamma ({\mathcal H})$$ Γ ( H ) of just one entire function $${\mathcal {H}} : {\mathbb {C}}_z \rightarrow {\mathbb {C}}_w$$ H : C z → C w .

Integrated Analysis of Mechanical and Thermal Hydraulic Behavior of Graphite Stack in Channel-Type Reactors in Case of a Fuel Channel Rupture Accident

2002 ◽  
Author(s):  
Sergei L. Soloviev ◽  
Boris A. Gabaraev ◽  
Leonid M. Parafilo ◽  
Dmitry V. Kruchkov ◽  
Oleg Yu. Novoselsky ◽  
...  
Keyword(s):  
Computational Analysis ◽  
Pressure Tube ◽  
Integrated Analysis ◽  
The Core ◽  
Pressure Tubes ◽  
Confinement System ◽  
Integrated Code ◽  
Channel Type ◽  
Graphite Stack ◽  
Fluid Parameters

The paper discusses the methodology and a computational exercise analyzing the processes taking place in the graphite stack of an RBMK reactor in case of a pressure tube rupture caused by overheating. The methodology of the computational analysis is implemented in integrated code U_STACK which models thermal-hydraulic and mechanical processes in the stack with a varying geometry, coupled with the processes going on in the circulation loop and accident localization (confinement) system. Coolant parameters, cladding and pressure tube temperatures, pressure tube ballooning and rupture, coolant outflow are calculated for a given accident scenario. Fluid parameters, movement of graphite blocks and adjacent pressure tubes bending after the tube rupture are calculated for the whole volume of the core. Calculations also cover additional loads on adjacent fuel channels in the rupture zone, reactor shell, upper and lower plates. Impossibility of an induced pressure tube rupture is confirmed.

scholarly journals The Effects of Grout Curtain Parameters on Uplift and Piping Phenomenon; Case Study: Sattarkhan Dam

Hydrology ◽  
2019 ◽  
Vol 6 (3) ◽  
pp. 71
Author(s):  
Kambiz Meshkabadi ◽  
Yousef Zandi
Keyword(s):  
Numerical Models ◽  
Grout Curtain ◽  
Hydraulic Structures ◽  
Uplift Pressure ◽  
The Core ◽  
Horizontal Drainage ◽  
Potential Risks ◽  
Dam Core ◽  
Water Seal

Design of earth dams and their issues during and after construction is very important for residents downstream of the dam because of the potential risks and possible breakdowns. In the design of dams, various forces influence the dam body, including uplift pressure and piping phenomenon which should be considered in order to ensure the safety of the dam. Among the measures taken to prevent the washing away phenomenon, the reduction of the output gradient, and the leakage discharge from beneath the hydraulic structures, construction of the grout curtain and installation of the drainage are applicable. Therefore, in order to investigate the effect of various parameters such as the gradient angle of the grout curtain, length, and distance and the number of grout curtains, as well as the length of the drainage on the pressure and output gradient of the numerical models, were considered in current study. For this purpose, the SEEP/W software was used for modeling on Sattarkhan Dam as a case study. The results of the analysis showed that the use of the Qa’im grout curtain at the upstream of the dam has the highest resistance against the pressure and piping phenomenon. The results also showed that increase in the length of the curtain of the water seal increases safety against uplift and piping phenomenon. The use of further spacing between the two grout curtains under the core of the dam led to increase in overall pressure or reduction in safety against uplift pressure. Increase in the length of the horizontal drainage reduced the effects of uplift pressure and output gradient. Results show that period of 70 to 110 degree is appropriate for curtain angle and setting curtain in upstream of dam core with angle of 70 to 80 degree is optimum and economic. A length of 30 m is optimum for curtain. The number of 2 curtains is also optimum. Studying various scenarios of distance of 2 curtains in dam core indicates that distance of 6 m is optimum and also length of 18 m for horizontal drainage is optimum.

scholarly journals White Dwarfs

1994 ◽  
Vol 146 ◽  
pp. 71-78
Author(s):  
Peter Thejll
Keyword(s):  
Mass Loss ◽  
White Dwarfs ◽  
Main Sequence ◽  
Asymptotic Giant Branch ◽  
List Type ◽  
Stellar Core ◽  
The Core ◽  
Long Time ◽  
Red Giant ◽  
Carbon Burning

It is the intention of this review to explain what white dwarfs are and why it is interesting to study them, and why the H+2molecule is of special interest.The evolution, from start to finish, of a star of mass less than about 2 solar masses (M⊙), can roughly be summarized as follows:–A cloud of gas contracts from the interstellar medium until hydrogen ignites at the center and amain sequence(MS) star forms. H is transformed to He and the MS phase continues until H is exhausted in the stellar core.–H continues burning in a shell outside the He core while the core contracts. He “ashes” are added to the core, and ared giantstar is formed as the envelope expands. The star evolves up the Red Giant Branch (RGB) (i.e. it becomes more and more luminous and the surface cools).–Towards the end of the RGB phase, mass-loss from the upper layers increases until helium to carbon burning in the core ignites suddenly under degenerate conditions – this is called theHelium Flash(HF). The HF terminates the RGB evolution, and therefore also the mass-loss and the growth of the stellar core.–The star readjusts its structure and the He-core burns steadily on thehorizontal branch(HB) (a phase of nearly-constant luminosity) until fuel is exhausted in the He-core.–Then the C/O core contracts anew and the expansion of the envelope, and the growth of the core, during He-shell burning, mimics RGB evolution but relatively little mass is added to the core this time.–The second ascent of the giant branch (the so-called Asymptotic Giant Branch, or AGB) continues with increased mass loss towards the end–Rapid detachment of a considerable fraction of the remaining envelope and the hot core takes place, sometimes observable as thePlanetary Nebulae(PN) phase.–The PN is dispersed as the core contracts to a white dwarf (WD).–The WD cools for a long time, as internal kinetic energy and latent heat is released.

scholarly journals DATeS: a highly extensible data assimilation testing suite v1.0

2019 ◽  
Vol 12 (2) ◽  
pp. 629-649 ◽  
Author(s):  
Ahmed Attia ◽  
Adrian Sandu
Keyword(s):  
Data Assimilation ◽  
Linear Algebra ◽  
Numerical Models ◽  
Object Oriented ◽  
Time Discretization ◽  
Third Party ◽  
Great Flexibility ◽  
Testing Environment ◽  
The Core ◽  
Main Components

Abstract. A flexible and highly extensible data assimilation testing suite, named DATeS, is described in this paper. DATeS aims to offer a unified testing environment that allows researchers to compare different data assimilation methodologies and understand their performance in various settings. The core of DATeS is implemented in Python and takes advantage of its object-oriented capabilities. The main components of the package (the numerical models, the data assimilation algorithms, the linear algebra solvers, and the time discretization routines) are independent of each other, which offers great flexibility to configure data assimilation applications. DATeS can interface easily with large third-party numerical models written in Fortran or in C, and with a plethora of external solvers.

A NOVEL CRM PFC CONTROL METHOD FOR REDUCING INDUCTOR

2014 ◽  
Vol 23 (03) ◽  
pp. 1450038 ◽  
Author(s):  
LING-FENG SHI ◽  
HUI-LI GUAN ◽  
QIN-QIN LI ◽  
XIN-QUAN LAI
Keyword(s):  
Control System ◽  
Control Method ◽  
Input Voltage ◽  
The Novel ◽  
Voltage Range ◽  
Low Input ◽  
The Core ◽  
Large Size ◽  
Control Circuits ◽  
Conduction Mode

A novel control method for the critical conduction mode (CRM) power factor correction (PFC) converter is presented, which reduces the size of the boost inductor in the system with wide input-voltage range and improves the efficiency of the system with low input voltage. By introducing the following boost circuit, the output voltage in the application circuit varies with the input root mean square (RMS) voltage to reduce the demand for the large size of the inductor and the efficiency of the system keeps high under the low input voltage. A novel CRM PFC control system with smaller size inductor and higher efficiency is achieved by applied the following boost method to the core control circuits. Experiment results show that the inductance value of the boost inductor is 430 μH using the presented PFC control system and 700 μH using the traditional PFC control system when the input voltage varies from 85 V to 265 V. The novel control method decreases the inductor's value at 38.2%, and the efficiency of the system improves at 1.62% under the input voltage of 85 V.

Sign in / Sign up

Export Citation Format

Share Document