We perform 2.5D axisymmetric simulations of the pulsar magnetosphere (aligned dipole rotator) using the charge conservative, relativistic, electromagnetic particle in cell code picsar. Particle in ...cell codes are a powerful tool to use for studying the pulsar magnetosphere, because they can handle the force-free and vacuum limits and provide a self-consistent treatment of magnetic reconnection. In the limit of dense plasma throughout the magnetosphere, our solutions are everywhere in the force-free regime except for dissipative regions at the polar caps, in the current layers, and at the Y-point. These dissipative regions arise self-consistently, since we do not have any explicit dissipation in the code. A minimum of ≈15–20 per cent of the electromagnetic spin-down luminosity is transferred to the particles inside 5 light cylinder radii. However, the particles can carry as much as ≳ 50 per cent of the spin-down luminosity if there is insufficient plasma in the outer magnetosphere to screen the component of electric field parallel to the magnetic field. In reality, the component of the spin-down luminosity carried by the particles could be radiated as gamma-rays, but high-frequency synchrotron emission would need to be implemented as a sub-grid process in our simulations and is not present for the current suite of runs. The value of the spin-down luminosity in our simulations is within ≈10 per cent of the force-free value, and the structure of the electromagnetic fields in the magnetosphere is on the whole consistent with the force-free model.
Neutral sodium is a minority species in the atmospheres of late-type stars, and line formation in local thermodynamic equilibrium (LTE) is often a poor assumption, in particular for strong lines. We ...present an extensive grid of non-LTE calculations for several Na I lines in cool stellar atmospheres, including metal-rich and metal-poor dwarfs and giants. For the first time, we constructed a Na model atom that incorporates accurate quantum mechanical calculations for collisional excitation and ionisation by electrons as well as collisional excitation and charge exchange reactions with neutral hydrogen. Similar to Li I, the new rates for hydrogen impact excitation do not affect the statistical equilibrium calculations, while charge exchange reactions have a small but non-negligible influence. The presented LTE and non-LTE curves-of-growth can be interpolated to obtain non-LTE abundances and abundance corrections for arbitrary stellar parameter combinations and line strengths. The typical corrections for weak lines are −0.1... −0.2 dex, whereas saturated lines may overestimate the abundance in LTE by more than 0.5 dex. The non-LTE Na abundances appear very robust with respect to uncertainties in the input collisional data.
We performed the non-local thermodynamic equilibrium (non-LTE, NLTE) calculations for Ca i-ii with the updated model atom that includes new quantum-mechanical rate coefficients for Ca i + H i ...collisions from two recent studies and investigated the accuracy of calcium abundance determinations using the Sun, Procyon, and five metal-poor (MP, −2.6 ≤ Fe/H ≤−1.3) stars with well-determined stellar parameters. Including H i collisions substantially reduces over-ionisation of Ca i in the line formation layers compared with the case of pure electronic collisions and thus the NLTE effects on abundances derived from Ca i lines. We show that both collisional recipes lead to very similar NLTE results. As for Ca ii, the classical Drawinian rates scaled by SH = 0.1 are still applied. When using the subordinate lines of Ca i and the high-excitation lines of Ca ii, NLTE provides the smaller line-to-line scatter compared with the LTE case for each star. For Procyon, NLTE removes a steep trend with line strength among strong Ca i lines seen in LTE and leads to consistent Ca/H abundances from the two ionisation stages. In the MP stars, the NLTE abundance from Ca ii 8498 Å agrees well with the abundance from the Ca i subordinate lines, in contrast to LTE, where the abundance difference grows towards lower metallicity and reaches 0.46 dex in BD −13°3442 (Fe/H = −2.62). NLTE largely removes abundance discrepancies between the high-excitation lines of Ca ii and Ca ii 8498 Å obtained for our four Fe/H < −2 stars under the LTE assumption. We investigated the formation of the Ca i resonance line in the Fe/H < −2 stars. When the calcium abundance varies between Ca/H ≃ −1.8 and −2.3, photon loss in the resonance line itself in the uppermost atmospheric layers drives the strengthening of the line core compared with the LTE case, and this effect prevails over the weakening of the line wings, resulting in negative NLTE abundance correction and underestimation of the abundance derived from Ca i 4226 Å compared with that from the subordinate lines, by 0.08 to 0.32 dex. This problem may be related to the use of classical homogeneous (1D) model atmospheres. The situation is improved when the calcium abundance decreases and the Ca i 4226 Å line formation depths are shifted into deep atmospheric layers that are dominated by over-ionisation of Ca i. However, the departures from LTE are still underestimated for Ca i 4226 Å at Ca/H ≃ −4.4 (HE 0557-4840). Consistent NLTE abundances from the Ca i resonance line and the Ca ii lines are found for HE 0107-5240 and HE 1327-2326 with Ca/H ≤−5. Thus, the Ca i/Ca ii ionisation equilibrium method can successfully be applied to determine surface gravities of Ca/H ≾ −5 stars. We provide the NLTE abundance corrections for 28 lines of Ca i in a grid of model atmospheres with 5000 K ≤ Teff ≤ 6500 K, 2.5 ≤ log g ≤ 4.5, −4 ≤ Fe/H ≤ 0, which is suitable for abundance analysis of FGK-type dwarfs and subgiants.
We show that an electro-osmotic flow near the slippery hydrophobic surface depends strongly on the mobility of surface charges, which are balanced by counterions of the electrostatic diffuse layer. ...For a hydrophobic surface with immobile charges, the fluid transport is considerably amplified by the existence of a hydrodynamic slippage. In contrast, near the hydrophobic surface with mobile adsorbed charges, it is also controlled by an additional electric force, which increases the shear stress at the slipping interface. To account for this, we formulate electrohydrodynamic boundary conditions at the slipping interface, which should be applied to quantify electro-osmotic flows instead of hydrodynamic boundary conditions. Our theoretical predictions are fully supported by dissipative particle dynamics simulations with explicit charges. These results lead to a new interpretation of zeta potential of hydrophobic surfaces.
A
bstract
We suggest an explanation for and explore the consequences of the excess around 95 GeV in the di-photon and di-tau invariant mass distributions recently reported by the CMS collaboration at ...the Large Hadron Collider (LHC), together with the discrepancy that has long been observed at the Large Electron-Positron (LEP) collider in the
b
b
¯
invariant mass. Interestingly, the most recent findings announced by the ATLAS collaboration do not contradict, or even support, these intriguing observations. Their search in the di-photon final state similarly reveals an excess of events within the same mass range, albeit with a bit lower significance, thereby corroborating and somewhat reinforcing the observations made by CMS.
We demonstrate that the lightest CP-even Higgs boson in the general 2-Higgs Doublet Model (2HDM) Type-III can explain simultaneously the observed excesses at approximately 1.3
σ
C.L. while satisfying up-to-date theoretical and experimental constraints. Moreover, the 2HDM Type-III predicts an excess in the
pp
→
t
t
¯
H
SM
production channel of the 125 GeV Higgs boson,
H
SM
. This effect is caused by a up to 12% enhancement of the
H
SM
tt
Yukawa coupling in comparison to that predicted by the Standard Model. Such an effect can be tested at the High Luminosity LHC (HL-LHC), which can either discover or exclude the scenario we suggest. This unique characteristic of the 2HDM Type-III makes this scenario with the 95 GeV resonance very attractive for further theoretical and experimental investigations at the (HL-)LHC and future colliders.
Hemostasis is a complex physiological mechanism that functions to maintain vascular integrity under any conditions. Its primary components are blood platelets and a coagulation network that interact ...to form the hemostatic plug, a combination of cell aggregate and gelatinous fibrin clot that stops bleeding upon vascular injury. Disorders of hemostasis result in bleeding or thrombosis, and are the major immediate cause of mortality and morbidity in the world. Regulation of hemostasis and thrombosis is immensely complex, as it depends on blood cell adhesion and mechanics, hydrodynamics and mass transport of various species, huge signal transduction networks in platelets, as well as spatiotemporal regulation of the blood coagulation network. Mathematical and computational modeling has been increasingly used to gain insight into this complexity over the last 30 years, but the limitations of the existing models remain profound. Here we review state-of-the-art-methods for computational modeling of thrombosis with the specific focus on the analysis of unresolved challenges. They include: a) fundamental issues related to physics of platelet aggregates and fibrin gels; b) computational challenges and limitations for solution of the models that combine cell adhesion, hydrodynamics and chemistry; c) biological mysteries and unknown parameters of processes; d) biophysical complexities of the spatiotemporal networks' regulation. Both relatively classical approaches and innovative computational techniques for their solution are considered; the subjects discussed with relation to thrombosis modeling include coarse-graining, continuum versus particle-based modeling, multiscale models, hybrid models, parameter estimation and others. Fundamental understanding gained from theoretical models are highlighted and a description of future prospects in the field and the nearest possible aims are given.
•The state of the art in modeling thrombus formation is presented.•Models at all scales of thrombus formation, such as the coagulation cascade, blood flow and blood cells, are considered.•The obstacles, limitations and challenges involved in building the above models and integrating into a whole are discussed.•The importance of theoretical modelling for thrombosis therapy in a heterogeneous population is highlighted.
The loss of water from Mars to space is thought to result from the transport of water to the upper atmosphere, where it is dissociated to hydrogen and escapes the planet. Recent observations have ...suggested large, rapid seasonal intrusions of water into the upper atmosphere, boosting the hydrogen abundance. We use the Atmospheric Chemistry Suite on the ExoMars Trace Gas Orbiter to characterize the water distribution by altitude. Water profiles during the 2018-2019 southern spring and summer stormy seasons show that high-altitude water is preferentially supplied close to perihelion, and supersaturation occurs even when clouds are present. This implies that the potential for water to escape from Mars is higher than previously thought.
ABSTRACT
Cross-sections and rate coefficients for the partial inelastic processes in calcium–hydrogen collisions are calculated by means of the quantum reprojection method for nuclear dynamics based ...on the accurate ab initio electronic structure data. That is, the atomic data for the 110 inelastic processes of excitation, de-excitation, ion-pair formation, and mutual neutralization in Ca + H and Ca+ + H− collisions are computed for all transitions between the 11 low-lying CaH(2Σ+) molecular states including ionic one. The quantum chemical data are used in a hybrid diabatic representation, which is derived from the adiabatic representation. It is found that the largest rate coefficients correspond to the mutual neutralization processes. At the temperature 6000 K, the maximal rate is equal to $4.37 \times 10^{-8}\, \mathrm{cm}^{3}\,\mathrm{s}^{-1}$. It is shown that the large-valued rates are determined by long-range ionic–covalent interactions with final binding energies from the optimal window, while moderate- and low-valued rates by both long- and short-range non-adiabatic regions with final energies outside of the optimal window.
The formation mechanism of local pulsatile jet streams is considered. It may in general be reduced to the following sequence: (i) a breaking gravity wave produces a turbulent patch that “moves” with ...it; (ii) adiabatic mixing within the “moving” turbulent patch maintains a near-adiabatic lapse rate; and (iii) just after turbulence withdrawal, the buoyant forces initiate developing a pulsatile jet stream. The base of the associated mathematical model is a second-order nonlinear ordinary differential equation obtained from the set of the governing hydrodynamic equations under the Boussinesq approximation. It is demonstrated that such phenomena as ripples in airglow images and extremely large winds in the lower thermosphere may be related to local pulsatile jet streams, which, in turn, appear in the lower thermosphere as a result of gravity-wave breaking.
ABSTRACT
We present a new model atom of Zn i-Zn ii based on the most up-to-date photoionization cross-sections, electron-impact excitation rates, and rate coefficients for the Zn i + H i and Zn ii ... + H− collisions. The latter were calculated using the multichannel quantum asymptotic treatment based on the Born–Oppenheimer approach. Non-LTE analysis was performed for the first time for lines of Zn i and Zn ii in the ultraviolet (UV) spectra of two very metal-poor reference stars: HD 84937 and HD 140283. We found consistent non-LTE abundance from the resonance Zn i 2138 Å line, the subordinate lines, and the lines of Zn ii. In both stars, non-LTE leads to 0.17 dex higher average abundance from Zn i, while, for Zn ii lines, non-LTE corrections are minor and do not exceed 0.06 dex. Using lines of Zn i in the high-resolution spectra, we determined the non-LTE abundances for a sample of 80 stars in the −2.5 ≤ Fe/H ≤ 0.2 metallicity range. The Zn/Fe versus Fe/H diagram reveals a dip, with Zn/Fe ≃ 0.3 in the most metal-poor stars, a close-to-solar value for Fe/H ∼−1.2, and increasing Zn/Fe up to 0.3 in the thick disc stars. The close-to-solar metallicity stars have subsolar Zn/H ≃ −0.1, on average. Non-LTE abundances of zinc were derived for the first time for seven reference F- to B-type stars. We provide a grid of the non-LTE abundance corrections.
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