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López RA, Shaaban SM, Lazar M, Poedts S, Yoon PH, Micera A, Lapenta G. Particle-in-cell Simulations of the Whistler Heat-flux Instability in Solar Wind Conditions. Astrophys J Lett 2019; 882:10.3847/2041-8213/ab398b. [PMID: 32042401 PMCID: PMC7008930 DOI: 10.3847/2041-8213/ab398b] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In collision-poor plasmas from space, e.g., solar wind or stellar outflows, the heat flux carried by the strahl or beaming electrons is expected to be regulated by the self-generated instabilities. Recently, simultaneous field and particle observations have indeed revealed enhanced whistler-like fluctuations in the presence of counter-beaming populations of electrons, connecting these fluctuations to the whistler heat-flux instability (WHFI). This instability is predicted only for limited conditions of electron beam-plasmas, and has not yet been captured in numerical simulations. In this Letter we report the first simulations of WHFI in particle-in-cell setups, realistic for the solar wind conditions, and without temperature gradients or anisotropies to trigger the instability in the initiation phase. The velocity distributions have a complex reaction to the enhanced whistler fluctuations conditioning the instability saturation by a decrease of the relative drifts combined with induced (effective) temperature anisotropies (heating the core electrons and pitch-angle and energy scattering the strahl). These results are in good agreement with a recent quasilinear approach, and support therefore a largely accepted belief that WHFI saturates at moderate amplitudes. In the anti-sunward direction the strahl becomes skewed with a pitch-angle distribution decreasing in width as electron energy increases, which seems to be characteristic of self-generated whistlers and not to small-scale turbulence.
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Affiliation(s)
- R A López
- Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
| | - S M Shaaban
- Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
- Theoretical Physics Research Group, Physics Department, Faculty of Science, Mansoura University, 35516, Mansoura, Egypt
| | - M Lazar
- Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
- Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany
| | - S Poedts
- Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
| | - P H Yoon
- Institute for Physical Science and Technology, University of Maryland, College Park, MD, USA
- School of Space Research, Kyung Hee University, Republic of Korea
- Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea
| | - A Micera
- Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
- Solar-Terrestrial Centre of Excellence-SIDC, Royal Observatory of Belgium, B-1180 Brussels, Belgium
| | - G Lapenta
- Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium
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Lindner A, López RA, Durante E, Hernandez H, Botta V, Sadaba S, Boffi FM. Effect of conditioning horses every third day at v10 on measures of fitness. J Anim Physiol Anim Nutr (Berl) 2010; 95:286-93. [PMID: 20880285 DOI: 10.1111/j.1439-0396.2010.01053.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This study examined the effect of exercising horses five times per fortnight with two bouts of 5 min duration at their v(10) with 2 days between consecutive exercise sessions. Five Anglo-Arabian horses were treadmill-conditioned for 6 weeks. A standardized exercise test (SET) was performed at the beginning of the conditioning period (CP) to determine the blood lactate-running speed (BLRS) and the heart rate-running speed (HRRS) relationship and the SET was repeated every 2 weeks. After each SET, the BLRS relation was used to calculate the horse's speed (v = velocity), which produced a blood lactate concentration (LA) of 10 mmol/l (v(10) ) and 4 mmol/l (v(4) ). From the HRRS was calculated the speed at which the horses had a heart rate of 180 b/min (v(180) ). Each horse was then conditioned for the next 2 weeks five times at its individual v(10) for two 5-min bouts. Exercise speed was individually adapted to the new v(10) every 2 weeks. In addition, horses were submitted to another SET prescription to determine the peak oxygen consumption (VO(2 peak) ) before, after 3 weeks and at the end of CP. The v(4) of horses increased during the CP (p < 0.05). v(180) did not change (p > 0.05). VO(2 peak) increased in the first 3 weeks of CP (p < 0.05) and levelled off afterwards (p > 0.05). The conclusion drawn was that exercising horses five times per fortnight at their v(10) for two 5-min bouts with 2 days between consecutive exercise sessions improved v(4) and VO(2 peak) but not v(180).
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Affiliation(s)
- A Lindner
- Arbeitsgruppe Pferd, Juelich, Germany.
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Lacorazza HD, López RA, Venera GD, Biscoglio De Jiménez Bonino M. Localization of histidine residues relevant for the binding of alpha-bungarotoxin to the acetylcholine receptor alpha-subunit in V8-proteolytic fragments. Neurochem Int 1996; 28:557-67. [PMID: 8792337 DOI: 10.1016/0197-0186(95)00113-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Histidine residues have been shown to be critical for alpha-BgTx binding to the acetylcholine receptor (Lacorazza et al., 1992; Bouzat et al., 1993; Lacorazza et al., 1995). Receptor subunits from Discopyge tschudii were modified with diethylpyrocarbonate (DEP). DEP treatment produces a concentration-dependent decrease of [125I] alpha-BgTx binding to the alpha-subunit. The neurotoxin binding capacity was fully restored by adding the nucleophile hydroxylamine. By proteolytic mapping of the alpha-subunit with V8-protease, we determined that the binding capacity to the fragment alpha V8-19 decreased 80% by DEP treatment. In addition, the [125I] alpha-BgTx binding to the same fragment decreased by 70% when the subunits were reduced and affinity-alkylated. We report the N-terminal sequence of both subunits and V8-fragments (alpha V8-10, alpha V8-13, and alpha V8-18), which constitute a first contribution to the knowledge of the primary structure of the Discopyge tschudii receptor. We propose that the fragment alpha V8-19 contains one or more of the histidine residues involved in the alpha-BgTx binding and probably includes the Cys alpha 192-193 disulfide bond. Only two histidine residues are present in the extracellular sequence of Torpedo californica for such fragments: His alpha 186 and alpha 204.
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Affiliation(s)
- H D Lacorazza
- Instituto de Química y Fisicoquímica Biológicas (UBA-CONICET) Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Argentina
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