scholarly journals Chromospheric Activity in 55 Cancri: I. Results from Theoretical Wave Studies

2021 ◽  
Author(s):  
Diaa E Fawzy ◽  
Manfred Cuntz
Keyword(s):  
Acoustic Waves ◽  
Theoretical Models ◽  
Forthcoming Paper ◽  
Time Dependent ◽  
Flux Tubes ◽  
Longitudinal Waves ◽  
Partial Redistribution ◽  
Self Consistent ◽  
Consistent Treatment ◽  
The Impact

Abstract We present theoretical models of chromospheric heating for 55 Cancri, an orange dwarf of relatively low activity. Self-consistent, nonlinear and time-dependent ab-initio numerical computations are pursued encompassing the generation, propagation, and dissipation of waves. We consider longitudinal waves operating among arrays of flux tubes as well as acoustic waves pertaining to nonmagnetic stellar regions. Additionally, flux enhancements for the longitudinal waves are also taken into account as supplied by transverse tube waves. The Ca II K fluxes are computed (multi-ray treatment) assuming partial redistribution as well as time-dependent ionization. The self-consistent treatment of time-dependent ionization (especially for hydrogen) greatly impacts the atmospheric temperatures and electron densities (especially behind the shocks); it also affects the emergent Ca II fluxes. Particularly, we focus on the influence of magnetic heating on the stellar atmospheric structure and the emergent Ca II emission, as well as the impact of nonlinearities. Our study shows that a higher photospheric magnetic filling factor entails a larger Ca II emission; however, an increased initial wave energy flux (e.g., associated with mode coupling) is of little difference. Comparisons of our theoretical results with observations will be conveyed in forthcoming Paper II.

scholarly journals Heating of Stellar Chromospheres and Transition Regions

2004 ◽  
Vol 219 ◽  
pp. 437-448
Author(s):  
Zdzislaw E. Musielak
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Acoustic Waves ◽  
Theoretical Models ◽  
Flux Tubes ◽  
Stellar Convection ◽  
Wave Heating ◽  
Active Stars ◽  
Magnetic Flux Tubes ◽  
Magnetic Waves

To explain the heating of stellar chromospheres and transition regions, two classes of heating mechanisms have been considered: dissipation of acoustic and magnetic waves generated in stellar convection zones; and dissipation of currents generated by photospheric motions of surface magnetic fields. The focus of this paper is on the wave heating mechanisms and on recent results which demonstrate that theoretical models of stellar chromospheres based on the wave heating can explain the “basal flux” and the observed Ca II emission in most stars but cannot account for the observed Mg II emission in active stars. The obtained results clearly show that the base of stellar chromospheres is heated by acoustic waves, the heating of the middle and upper chromospheric layers is dominated by magnetic waves associated with magnetic flux tubes, and that other non-wave heating mechanisms are required to explain the structure of the highest layers of stellar chromospheres and transition regions.

scholarly journals Time-dependent multi-zone radiation transfer modeling of fast blazar variability

2010 ◽  
Vol 6 (S275) ◽  
pp. 136-139
Author(s):  
Giovanni Fossati ◽  
Xuhui Chen
Keyword(s):  
Monte Carlo ◽  
Radiation Transfer ◽  
Time Dependent ◽  
Relativistic Electrons ◽  
Time Effects ◽  
X Ray ◽  
Self Consistent ◽  
Data Coverage ◽  
Consistent Treatment ◽  
First Time

AbstractWe present the first applications of a new time-dependent multi-zone jet radiation transfer code to the study the multiwavelength emission of the TeV Blazar Mrk 421. The code couples Fokker-Planck and Monte Carlo methods. For the first time all light travel time effects are fully considered as well as proper self-consistent treatment of Compton cooling, which depends on them. The first tests focus on the March 2001 observations of Mrk 421, still one of the best datasets available for phenomenology and X-ray/TeV data coverage. We summarize the results of scenarios of variability induced by injection of relativistic electrons in a blob encountering a shock, and with different combinations with a second component, either co-spatial or independent from the active region.

The Effects of Employment Protection legislationon Personnel Policies: A Review of Theoretical Modelsand Empirical results

2014 ◽  
pp. 126-140
Author(s):  
O. Mironenko
Keyword(s):  
Personnel Selection ◽  
Selection Criteria ◽  
Theoretical Models ◽  
Employment Protection ◽  
Empirical Results ◽  
Protection Legislation ◽  
Labour Contracts ◽  
Hiring And Firing ◽  
The Impact ◽  
Personnel Policies

Employers incur costs while fulfilling the requirements of employment protection legislation. The article contains a review of the core theoretical models and empirical results concerning the impact of these costs on firms’ practices in hiring, firing, training and remuneration. Overall, if wages are flexible or enforcement is weak, employment protection does not significantly influence employers’ behavior. Otherwise, stringent employment protection results in the reduction of hiring and firing rates, changes in personnel selection criteria, types of labour contracts and dismissal procedures, and, in some cases, it may lead to the growth of wages and firms’ investments to human capital.

The impact of statin therapy after surgical or endovascular treatment of cerebral aneurysms

2020 ◽  
Vol 133 (1) ◽  
pp. 182-189
Author(s):  
Tae-Jin Song ◽  
Seung-Hun Oh ◽  
Jinkwon Kim
Keyword(s):  
Statin Therapy ◽  
Coil Embolization ◽  
Primary Outcome ◽  
Cox Regression ◽  
Cerebral Aneurysms ◽  
Time Dependent ◽  
Lipid Lowering ◽  
Surgical Clipping ◽  
The Impact

OBJECTIVECerebral aneurysms represent the most common cause of spontaneous subarachnoid hemorrhage. Statins are lipid-lowering agents that may expert multiple pleiotropic vascular protective effects. The authors hypothesized that statin therapy after coil embolization or surgical clipping of cerebral aneurysms might improve clinical outcomes.METHODSThis was a retrospective cohort study using the National Health Insurance Service–National Sample Cohort Database in Korea. Patients who underwent coil embolization or surgical clipping for cerebral aneurysm between 2002 and 2013 were included. Based on prescription claims, the authors calculated the proportion of days covered (PDC) by statins during follow-up as a marker of statin therapy. The primary outcome was a composite of the development of stroke, myocardial infarction, and all-cause death. Multivariate time-dependent Cox regression analyses were performed.RESULTSA total of 1381 patients who underwent coil embolization (n = 542) or surgical clipping (n = 839) of cerebral aneurysms were included in this study. During the mean (± SD) follow-up period of 3.83 ± 3.35 years, 335 (24.3%) patients experienced the primary outcome. Adjustments were performed for sex, age (as a continuous variable), treatment modality, aneurysm rupture status (ruptured or unruptured aneurysm), hypertension, diabetes mellitus, household income level, and prior history of ischemic stroke or intracerebral hemorrhage as time-independent variables and statin therapy during follow-up as a time-dependent variable. Consistent statin therapy (PDC > 80%) was significantly associated with a lower risk of the primary outcome (adjusted hazard ratio 0.34, 95% CI 0.14–0.85).CONCLUSIONSConsistent statin therapy was significantly associated with better prognosis after coil embolization or surgical clipping of cerebral aneurysms.

COVID-19: Time-Dependent Effective Reproduction Number and Sub-notification Effect Estimation Modeling (Preprint)

2020 ◽  
Author(s):  
Eduardo Atem De Carvalho ◽  
Rogerio Atem De Carvalho
Keyword(s):  
New York ◽  
Reproduction Number ◽  
Moving Average ◽  
Real Data ◽  
Time Dependent ◽  
Initial Value ◽  
Health Authorities ◽  
Reproduction Numbers ◽  
Effect Estimation ◽  
The Impact

BACKGROUND Since the beginning of the COVID-19 pandemic, researchers and health authorities have sought to identify the different parameters that govern their infection and death cycles, in order to be able to make better decisions. In particular, a series of reproduction number estimation models have been presented, with different practical results. OBJECTIVE This article aims to present an effective and efficient model for estimating the Reproduction Number and to discuss the impacts of sub-notification on these calculations. METHODS The concept of Moving Average Method with Initial value (MAMI) is used, as well as a model for Rt, the Reproduction Number, is derived from experimental data. The models are applied to real data and their performance is presented. RESULTS Analyses on Rt and sub-notification effects for Germany, Italy, Sweden, United Kingdom, South Korea, and the State of New York are presented to show the performance of the methods here introduced. CONCLUSIONS We show that, with relatively simple mathematical tools, it is possible to obtain reliable values for time-dependent, incubation period-independent Reproduction Numbers (Rt). We also demonstrate that the impact of sub-notification is relatively low, after the initial phase of the epidemic cycle has passed.

scholarly journals Transport Properties of Natural and Artificial Smart Fabrics Impregnated by Graphite Nanomaterial Stacks

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 1018
Author(s):  
Carola Esposito Corcione ◽  
Francesca Ferrari ◽  
Raffaella Striani ◽  
Antonio Greco
Keyword(s):  
Electrical Conductivity ◽  
Transport Properties ◽  
Low Cost ◽  
Empirical Relationship ◽  
Theoretical Models ◽  
Expandable Graphite ◽  
Easy Method ◽  
Textile Materials ◽  
Fabric Materials ◽  
The Impact

In this work, we studied the transport properties (thermal and electrical conductivity) of smart fabric materials treated with graphite nanomaterial stacks–acetone suspensions. An innovative and easy method to produce graphite nanomaterial stacks–acetone-based formulations, starting from a low-cost expandable graphite, is proposed. An original, economical, fast, and easy method to increase the thermal and electrical conductivity of textile materials was also employed for the first time. The proposed method allows the impregnation of smart fabric materials, avoiding pre-coating of the fibers, thus reducing costs and processing time, while obtaining a great increase in the transport properties. Two kinds of textiles, cotton and Lycra®, were selected as they represent the most used natural and artificial fabrics, respectively. The impact of the dimensions of the produced graphite nanomaterial stacks–acetone-based suspensions on both the uniformity of the treatment and the transport properties of the selected textile materials was accurately evaluated using several experimental techniques. An empirical relationship between the two transport properties was also successfully identified. Finally, several theoretical models were applied to predict the transport properties of the developed smart fabric materials, evidencing a good agreement with the experimental data.

scholarly journals Many-impurity scattering on the surface of a topological insulator

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
José Luis Hernando ◽  
Yuriko Baba ◽  
Elena Díaz ◽  
Francisco Domínguez-Adame
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Topological Insulator ◽  
Disordered Systems ◽  
Spectral Properties ◽  
Random Distribution ◽  
Surface States ◽  
Impurity Scattering ◽  
Self Consistent ◽  
The Impact

AbstractWe theoretically address the impact of a random distribution of non-magnetic impurities on the electron states formed at the surface of a topological insulator. The interaction of electrons with the impurities is accounted for by a separable pseudo-potential method that allows us to obtain closed expressions for the density of states. Spectral properties of surface states are assessed by means of the Green’s function averaged over disorder realisations. For comparison purposes, the configurationally averaged Green’s function is calculated by means of two different self-consistent methods, namely the self-consistent Born approximation (SCBA) and the coherent potential approximation (CPA). The latter is often regarded as the best single-site theory for the study of the spectral properties of disordered systems. However, although a large number of works employ the SCBA for the analysis of many-impurity scattering on the surface of a topological insulator, CPA studies of the same problem are scarce in the literature. In this work, we find that the SCBA overestimates the impact of the random distribution of impurities on the spectral properties of surface states compared to the CPA predictions. The difference is more pronounced when increasing the magnitude of the disorder.

scholarly journals Evolution of the Kuiper Belt during the Accretion of the Outer Planets

2002 ◽  
Vol 12 ◽  
pp. 214-218
Author(s):  
A. Brunini ◽  
M.D. Melita
Keyword(s):  
Kuiper Belt ◽  
Resonance Capture ◽  
Orbital Structure ◽  
Outer Planets ◽  
Self Consistent ◽  
The Impact ◽  
Outward Migration

AbstractA set of self-consistent simulations of the formation of Uranus and Neptune are performed to study the evolution of the native KBOs in the process. Our main goal is to have a deeper understanding of the impact of the formation of the outer planets on the present orbital structure of the trans-neptunian region. We aim to understand if resonance capture driven by the outward migration of Neptune can actually occur and its interplay with the invasion of massive planetesimals expelled from the Uranus-Neptune region as a byproduct of their formation. Also the putative present existence in the Oort reservoir of a population of objects originated in the Kuiper belt is analyzed.

scholarly journals Diffusion in CP Stars: The Quest for Accuracy

1998 ◽  
Vol 11 (2) ◽  
pp. 671-673
Author(s):  
G. Alecian
Keyword(s):  
Computational Methods ◽  
Stellar Evolution ◽  
Diffusion Processes ◽  
Stellar Atmospheres ◽  
Time Dependent ◽  
Data Bases ◽  
Self Consistent ◽  
Stellar Envelopes ◽  
Better Than

We present a brief review about recent progresses concerning the study of diffusion processes in CP stars. The most spectacular of them concerns the calculation of radiative accelerations in stellar envelopes for which an accuracy better than 30% can now be reached for a large number of ions. This improvement is mainly due to huge and accurate atomic and opacity data bases available since the beginning of the 90’s. Developments of efficient computational methods have been carried out to take advantage of these new data. These progresses have, in turn, led to a better understanding of how the element stratification is building up with time. A computation of self-consistent stellar evolution models, including time-dependent diffusion, can now be within the scope of the next few years. However, the progresses previously mentioned do not apply for stellar atmospheres and upper layers of envelopes.

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