Field line distribution of density at \u3ci\u3eL\u3c/i\u3e=4.8 inferred from observations by CLUSTER

For two events observed by the CLUSTER space- craft, the field line distribution of mass density ρ was inferred from Alfve ́n wave harmonic frequencies and compared to the electron density ne from plasma wave data and the oxy- gen density nO+ from the ion composition experiment. In one case, the average ion mass M≡ρ/ne was about 5amu (28 October 2002), while in the other it was about 3 amu (10 September 2002). Both events occurred when the CLUSTER 1 (C1) spacecraft was in the plasmatrough. Nevertheless, the electron density ne was significantly lower for the first event (ne =8 cm−3 ) than for the second event (ne =22 cm−3 ), and this seems to be the main difference leading to a dif- ferent value of M. For the first event (28 October 2002), we were able to measure the Alfve ́n wave frequencies for eight harmonics with unprecedented precision, so that the er- ror in the inferred mass density is probably dominated by factors other than the uncertainty in frequency (e.g., mag- netic field model and theoretical wave equation). This field line distribution (at L=4.8) was very flat for magnetic lati- tude |MLAT|20◦ but very steeply increasing with respect to |MLAT| for |MLAT|40◦. The total variation in ρ was about four orders of magnitude, with values at large |MLAT| roughly consistent with ionospheric values. For the second event (10 September 2002), there was a small local maxi- mum in mass density near the magnetic equator. The in- ferred mass density decreases to a minimum 23% lower than the equatorial value at |MLAT|=15.5◦, and then steeply in- creases as one moves along the field line toward the iono- sphere. For this event we were also able to examine the spa- tial dependence of the electron density using measurements of ne from all four CLUSTER spacecraft. Our analysis in- dicates that the density varies with L at L∼5 roughly like L−4, and that ne is also locally peaked at the magnetic equa- tor, but with a smaller peak. The value of ne reaches a den- sity minimum about 6% lower than the equatorial value at |MLAT|=12.5◦, and then increases steeply at larger values of |MLAT|. This is to our knowledge the first evidence for a local peak in bulk electron density at the magnetic equa- tor. Our results show that magnetoseismology can be a useful technique to determine the field line distribution of the mass density for CLUSTER at perigee and that the distribution of electron density can also be inferred from measurements by multiple spacecraft

A quantitative test of Jones NTC beaming theory using CLUSTER constellation

Non-thermal continuum (NTC) radiation is, with auroral kilometric radiation (AKR), one of the two electromagnetic emissions generated within the Earth's magnetosphere and radiated into space. The location of the source of NTC has been sought for several decades, with only limited success. The constellation formed by the four CLUSTER spacecraft provides the possibility of triangulation in the vicinity of the source, thus allowing progress in source localisation, while simultaneously revealing the beaming properties of NTC radio sources. <br><br> We present a case event showing two beams localised on opposite sides of the magnetic equator. At any selected frequency, triangulation points to a single region source of small size. Its position is compatible with the range of possible loci of sources predicted by the radio window theory of Jones (1982) in a frame of constraints relaxed from the simple sketch proposed in early works. The analysis of similar observations from the Dynamics Explorer 1 by Jones et al. (1987) enabled the authors to claim validation of the radio window theory. CLUSTER observations, however, reveal a large beaming cone angle projected onto the ecliptic plane, a feature unobservable by Dynamics Explorer which had a different spin axis orientation. According to the radio window theory, such a large observed cone angle can only be formed by a series of point sources, each beaming in a narrow cone angle. This study demonstrates the difficulty of validating NTC linear generation mechanisms using global beaming properties alone

The Evolution of Respiratory Chain Complex I from a Smaller Last Common Ancestor Consisting of 11 Protein Subunits

The NADH:quinone oxidoreductase (complex I) has evolved from a combination of smaller functional building blocks. Chloroplasts and cyanobacteria contain a complex I-like enzyme having only 11 subunits. This enzyme lacks the N-module which harbors the NADH binding site and the flavin and iron–sulfur cluster prosthetic groups. A complex I-homologous enzyme found in some archaea contains an F420 dehydrogenase subunit denoted as FpoF rather than the N-module. In the present study, all currently available whole genome sequences were used to survey the occurrence of the different types of complex I in the different kingdoms of life. Notably, the 11-subunit version of complex I was found to be widely distributed, both in the archaeal and in the eubacterial kingdoms, whereas the 14-subunit classical complex I was found only in certain eubacterial phyla. The FpoF-containing complex I was present in Euryarchaeota but not in Crenarchaeota, which contained the 11-subunit complex I. The 11-subunit enzymes showed a primary sequence variability as great or greater than the full-size 14-subunit complex I, but differed distinctly from the membrane-bound hydrogenases. We conclude that this type of compact 11-subunit complex I is ancestral to all present-day complex I enzymes. No designated partner protein, acting as an electron delivery device, could be found for the compact version of complex I. We propose that the primordial complex I, and many of the present-day 11-subunit versions of it, operate without a designated partner protein but are capable of interaction with several different electron donor or acceptor proteins