Quasilinear approach of the cumulative whistler instability in fast solar winds: Constraints of electron temperature anisotropy

Context. Solar outflows are a considerable source of free energy which accumulates in multiple forms like beaming (or drifting) components and/or temperature anisotropies. However, kinetic anisotropies of plasma particles do not grow indefinitely and particle-particle collisions are not efficient enough to explain the observed limits of these anisotropies. Instead, the self-generated wave instabilities can efficiently act to constrain kinetic anisotropies, but the existing approaches are simplified and do not provide satisfactory explanations. Thus, small deviations from isotropy shown by the electron temperature ($T$) in fast solar winds are not explained yet. Aims. This paper provides an advanced quasilinear description of the whistler instability driven by the anisotropic electrons in conditions typical for the fast solar winds. The enhanced whistler-like fluctuations may constrain the upper limits of temperature anisotropy $A \equiv T_\perp /T_\parallel > 1$, where $\perp, \parallel$ are defined with respect to the magnetic field direction. Methods. Studied are the self-generated whistler instabilities, cumulatively driven by the temperature anisotropy and the relative (counter)drift of the electron populations, e.g., core and halo electrons. Recent studies have shown that quasi-stable states are not bounded by the linear instability thresholds but an extended quasilinear approach is necessary to describe them in this case. Results. Marginal conditions of stability are obtained from a quasilinear theory of the cumulative whistler instability, and approach the quasi-stable states of electron populations reported by the observations.The instability saturation is determined by the relaxation of both the temperature anisotropy and the relative drift of electron populations.Comment: Accepted for publication in A&

Dual Maxwellian-Kappa modelling of the solar wind electrons: new clues on the temperature of Kappa populations

Context. Recent studies on Kappa distribution functions invoked in space plasma applications have emphasized two alternative approaches which may assume the temperature parameter either dependent or independent of the power-index $\kappa$. Each of them can obtain justification in different scenarios involving Kappa-distributed plasmas, but direct evidences supporting any of these two alternatives with measurements from laboratory or natural plasmas are not available yet. Aims. This paper aims to provide more facts on this intriguing issue from direct fitting measurements of suprathermal electron populations present in the solar wind, as well as from their destabilizing effects predicted by these two alternating approaches. Methods. Two fitting models are contrasted, namely, the global Kappa and the dual Maxwellian-Kappa models, which are currently invoked in theory and observations. The destabilizing effects of suprathermal electrons are characterized on the basis of a kinetic approach which accounts for the microscopic details of the velocity distribution. Results. In order to be relevant, the model is chosen to accurately reproduce the observed distributions and this is achieved by a dual Maxwellian-Kappa distribution function. A statistical survey indicates a $\kappa$-dependent temperature of the suprathermal (halo) electrons for any heliocentric distance. Only for this approach the instabilities driven by the temperature anisotropy are found to be systematically stimulated by the abundance of suprathermal populations, i.e., lowering the values of $\kappa$-index.Comment: Submitted to A&

The relationship between the dimensions of the internal auditory canal and the anomalies of the vestibulocochlear nerve

Background: Internal auditory canal (IAC) stenosis and vestibulocochlear nerve (VCN) abnormalities have been reported to be associated with sensorineural hearing loss. Previous studies classified the normal dimensions of the IAC and its anomalies with no consideration of the VCN. Other studies categorised the VCN development in only stenotic canals. In the present study, an anatomical classification of the normal dimensions of the IAC and its anomalies and their association with malformations of the VCN and its subdivisions were described. Materials and methods: Retrospective review was undertaken for children ranged from 1 to 10 years. A total of 764 canals were investigated for pre-operative assessment of cochlear implantation. Other 100 canals of normal hearing ears were included as the control group. The maximum anteroposterior diameter, considered the width of the canal, was measured in axial plane and the length of the canal was identified in coronal plane. The canals were categorised normal: if they are from 3 to 8 mm, patulous: if they are more than 8 mm, stenotic: if they are less than 3 mm and atretic if absent, using multislice computed tomography. The VCN trunks and their subdivisions were investigated using magnetic resonance imaging. Results: Internal auditory canals were found normal in 66% with a mean width: 5.27 ± ± 0.68, patulous in 17% with a mean width 113% more than that of the control group (p = 0.000), stenotic in 13% with a mean width 73% less as compared to that of the control group (p = 0.000) and atretic in 4% of the experimental canals. The VCN trunks were found normal with well-developed subdivisions in 77.8% of the normal canals, 98.4% of the patulous canals, and 19.2% of the stenotic canals. The VCN trunks were normal with hypoplastic subdivisions in 11.3% of the normal canals, 1.6% in the patulous canals, and 61.6% in the stenotic canals with a mean width 52% less than that of the normal trunk with developed subdivisions. Hypoplastic VCN trunks with absent subdivisions were reported in 7.3% of the normal canals, 11.1% of the stenotic canals and in 3.2% of the atretic canals. The VCN trunks were not found in 3.6% of the normal canals, in 8.1% of the stenotic canals and in 96.8% of the atretic canals. Conclusions: Internal auditory canal formation was dependent on the process of development and growth of the eighth cranial nerve and its subdivisions that greatly affected the completion of IAC canalisation. This paper could serve as a reference providing a quantitative classification of the relationship between the dimensions of the IAC and the development of the VCN trunk and its subdivisions

Pyran-Squaraine as Photosensitizers for Dye-Sensitized Solar Cells: DFT/TDDFT Study of the Electronic Structures and Absorption Properties

In an effort to provide, assess, and evaluate a theoretical approach which enables designing efficient donor-acceptor dye systems, the electronic structure and optical properties of pyran-squaraine as donor-acceptor dyes used in dye-sensitized solar cells were investigated. Ground state properties have been computed at the B3LYP/6-31+G** level of theory. The long-range corrected density functionals CAM-B3LYP, PBEPBE, PBE1PBE (PBE0), and TPSSH with 6-311++G** were employed to examine absorption properties of the studied dyes. In an extensive comparison between experimental results and ab initio benchmark calculations, the TPSSH functional with 6-311++G** basis set was found to be the most appropriate in describing the electronic properties for the studied pyran and squaraine dyes. Natural transition orbitals (NTO), frontier molecular orbitals (FMO), LUMO, HOMO, and energy gaps, of these dyes, have been analyzed to show their effect on the process of electron injection and dye regeneration. Interaction between HOMO and LUMO of pyran and squaraine dyes was investigated to understand the recombination process and charge-transfer process involving these dyes. Additionally, we performed natural bond orbital (NBO) analysis to investigate the role of charge delocalization and hyperconjugative interactions in the stability of the molecule