Investigating short-time-scale variations in cometary ions around comet 67P

The highly varying plasma environment around comet 67P/Churyumov–Gerasimenko inspired an upgrade of the ion mass spectrometer (Rosetta Plasma Consortium Ion Composition Analyzer) with new operation modes, to enable high time resolution measurements of cometary ions. Two modes were implemented, one having a 4 s time resolution in the energy range 0.3–82 eV/q and the other featuring a 1 s time resolution in the energy range 13–50 eV/q. Comparing measurements made with the two modes, it was concluded that 4 s time resolution is enough to capture most of the fast changes of the cometary ion environment. The 1462 h of observations done with the 4 s mode were divided into hour-long sequences. It is possible to sort 84 per cent of these sequences into one of five categories, depending on their appearance in an energy–time spectrogram. The ion environment is generally highly dynamic, and variations in ion fluxes and energies are seen on time-scales of 10 s to several minutes

Spatial distribution of low-energy plasma around 2 comet 67P/CG from Rosetta measurements

International audienceWe use measurements from the Rosetta plasma consortium (RPC) Langmuir probe (LAP) and mutual impedance probe (MIP) to study the spatial distribution of low-energy plasma in the near-nucleus coma of comet 67P/Churyumov-Gerasimenko. The spatial distribution is highly structured with the highest density in the summer hemisphere and above the region connecting the two main lobes of the comet, i.e. the neck region. There is a clear correlation with the neutral density and the plasma to neutral density ratio is found to be ∼1-2·10 −6 , at a cometocentric distance of 10 km and at 3.1 AU from the sun. A clear 6.2 h modulation of the plasma is seen as the neck is exposed twice per rotation. The electron density of the collisonless plasma within 260 km from the nucleus falls of with radial distance as ∼1/r. The spatial structure indicates that local ionization of neutral gas is the dominant source of low-energy plasma around the comet

Lower hybrid waves at comet 67P/Churyumov–Gerasimenko

We investigate the generation of waves in the lower hybrid frequency range by density gradients in the near plasma environment of comet 67P/Churyumov–Gerasimenko. When the plasma is dominated by water ions from the comet, a situation with magnetized electrons and unmagnetized ions is favourable for the generation of lower hybrid waves. These waves can transfer energy between ions and electrons and reshape the plasma environment of the comet. We consider cometocentric distances out to a few hundred km. We find that when the electron motion is not significantly interrupted by collisions with neutrals, large average gradients within tens of km of the comet, as well as often observed local large density gradients at larger distances, are often likely to be favourable for the generation of lower hybrid waves. Overall, we find that waves in the lower hybrid frequency range are likely to be common in the near plasma environment

Cancer cell differentiation heterogeneity and aggressive behavior in solid tumors

The differentiation stage of tumors is a central aspect in the histopathological classification of solid malignancies. The differentiation stage is strongly associated with tumor behavior, and generally an immature tumor is more aggressive than the more differentiated counterpart. While this is common knowledge in surgical pathology, the contribution of differentiation-related gene expression and functions to tumor behavior is often overlooked in the experimental, tumor biological setting. The mechanisms by which tumor cell differentiation stages are perturbed or affected are poorly explored but have recently come into focus with the introduction.of the tumor stem cell concept. While developmental biologists view the differentiation as a unidirectional event, pathologists and tumor biologists have introduced the concept of dedifferentiation to explain phenotypic changes occurring in solid tumors. In this review we discuss the impact of the tumor cell differentiation stage as used in surgical pathology. We further discuss knowledge gained from exploring the molecular basis of the differentiation and dedifferentiation processes in neuroblastoma and breast cancer, two tumor forms where the tumor cell differentiation concept is used in the clinical diagnostic work and where the tumor stem cell theory has been applied

Effective ion speeds at ~200–250 km from comet 67P/Churyumov–Gerasimenko near perihelion

In 2015 August, comet 67P/Churyumov–Gerasimenko, the target comet of the ESA Rosetta mission, reached its perihelion at ~1.24 au. Here, we estimate for a three-day period near perihelion, effective ion speeds at distances ~200–250 km from the nucleus. We utilize two different methods combining measurements from the Rosetta Plasma Consortium (RPC)/Mutual Impedance Probe with measurements either from the RPC/Langmuir Probe or from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)/Comet Pressure Sensor (COPS) (the latter method can only be applied to estimate the effective ion drift speed). The obtained ion speeds, typically in the range 2–8 km s⁻¹, are markedly higher than the expected neutral outflow velocity of ~1 km s⁻¹. This indicates that the ions were de-coupled from the neutrals before reaching the spacecraft location and that they had undergone acceleration along electric fields, not necessarily limited to acceleration along ambipolar electric fields in the radial direction. For the limited time period studied, we see indications that at increasing distances from the nucleus, the fraction of the ions’ kinetic energy associated with radial drift motion is decreasing