Abstract
The bacterial and archaeal community structure was examined in two methanogenic anaerobic digestion processes degrading organic household waste at mesophilic (37°C) and thermophilic (55°C) ...temperatures. Analysis of bacterial clone libraries revealed a predominance of Bacteroidetes (34% of total clones) and Chloroflexi (27%) at the mesophilic temperature. In contrast, in the thermophilic clone library, the major group of clones were affiliated with Thermotogae (61%). Within the domain Archaea, the phyla Euryarchaeota and Crenarchaeota were both represented, the latter only at the mesophilic temperature. The dominating archaeons grouped with Methanospirillum and Methanosarcina species at the mesophilic and thermophilic temperature, respectively. Generally, there was a higher frequency of different sequences at the lower temperature, suggesting a higher diversity compared to the community present at the thermophilic temperature. Furthermore, it was not only the species richness that was affected by temperature, but also the phylogenetic distribution of the microbial populations.
Recent comparisons between anatomically modern humans and ancient genomes of other hominins have raised the tantalizing, and hotly debated, possibility of hybridization. Although several tests of ...hybridization have been devised, they all rely on the degree to which different modern populations share genetic polymorphisms with the ancient genomes of other hominins. However, spatial population structure is expected to generate genetic patterns similar to those that might be attributed to hybridization. To investigate this problem, we take Neanderthals as a case study, and build a spatially explicit model of the shared history of anatomically modern humans and this hominin. We show that the excess polymorphism shared between Eurasians and Neanderthals is compatible with scenarios in which no hybridization occurred, and is strongly linked to the strength of population structure in ancient populations. Thus, we recommend caution in inferring admixture from geographic patterns of shared polymorphisms, and argue that future attempts to investigate ancient hybridization between humans and other hominins should explicitly account for population structure.
Mars Express and Mars Atmosphere and Volatile Evolution (MAVEN) observations have demonstrated the influence of Mars's spatially variable crustal magnetic fields upon the configuration of the plasma ...in the ionosphere. This influence furthermore leads to variations in ionospheric escape, conceivably in part through the modification of the plasma density and electron temperature in the upper ionosphere. In this study, we examine MAVEN Langmuir Probe and Waves data, finding a clear correspondence between the structure of the crustal fields and both the measured electron temperatures and densities, by first constructing an “average” profile from which departures can be quantified. Electron temperatures are shown to be lower in regions of strong crustal fields over a wide altitude range. We extend previous analyses to cover the nightside ionosphere, finding the same effects present to a lesser degree, in contrast to previous studies where the opposite relationship was found between densities and crustal fields. We further determine the altitude range over which this coupling between both plasma density (and temperature) and crustal fields is effective and use measurements made by MAVEN in the solar wind to explore the dependence of this crustal field control on the coupling to the solar wind and the interplanetary magnetic field (IMF). Based on this, there is some suggestion that variations in the solar wind dynamic pressure are associated with modulation of the effects of the crustal fields on plasma density, whereas the strength of the IMF modulates the crustal fields effects on both electron densities and temperatures.
Plain Language Summary
Mars's atmosphere is exposed to ultra‐violet light from the Sun, forming a layer of plasma at high altitudes around the planet. This plasma layer, termed the ionosphere, is strongly affected in terms of its density and temperature, both by external factors like the solar wind and the interplanetary magnetic field (IMF), and internal factors, like Mars's crustal magnetic field. Here, we study how effective the crustal magnetic fields are at shaping the ionosphere in both density and temperature, by first determining the average structure of the ionosphere, and then examining departures from this average. We find that plasma densities are elevated and temperatures reduced in regions where the crustal field is stronger. We also find the same effect on the nightside. This result is in apparent opposition to previous related studies, now based on a much larger data set, which we suggest may be the result of poor seasonal sampling in earlier studies. We further investigate how this crustal field control varies with the solar wind and IMF, and see evidence for weak modulation according to both the dynamic pressure exerted by the solar wind, and the strength of the IMF.
Key Points
We present a statistical analysis of Mars Atmosphere and Volatile Evolution Langmuir Probe and Wave densities and temperatures at Mars
Densities are elevated and temperatures reduced in strong crustal field regions, on both the dayside and nightside
Variations in the driving solar wind conditions are able to affect these correlations to a modest degree
Wakes behind spacecraft caused by supersonic drifting positive ions are common in plasmas and disturb in situ measurements. We review the impact of wakes on observations by the Electric Field and ...Wave double‐probe instruments on the Cluster satellites. In the solar wind, the equivalent spacecraft charging is small compared to the ion drift energy and the wake effects are caused by the spacecraft body and can be compensated for. We present statistics of the direction, width, and electrostatic potential of wakes, and we compare with an analytical model. In the low‐density magnetospheric lobes, the equivalent positive spacecraft charging is large compared to the ion drift energy and an enhanced wake forms. In this case observations of the geophysical electric field with the double‐probe technique becomes extremely challenging. Rather, the wake can be used to estimate the flux of cold (eV) positive ions. For an intermediate range of parameters, when the equivalent charging of the spacecraft is similar to the drift energy of the ions, also the charged wire booms of a double‐probe instrument must be taken into account. We discuss an example of these effects from the MMS spacecraft near the magnetopause. We find that many observed wake characteristics provide information that can be used for scientific studies. An important example is the enhanced wakes used to estimate the outflow of ionospheric origin in the magnetospheric lobes to about
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cold (eV) ions/s, constituting a large fraction of the mass outflow from planet Earth.
Plain Language Summary
Wakes caused by spacecraft motion or drifting plasma are common behind spacecraft with scientific instruments and disturb in situ observations of space plasmas. We review the impact of wakes on observations by the Electric Field and Wave double‐probe instruments on the Cluster satellites. In the solar wind, the wake behind a Cluster spacecraft is caused by the spacecraft body, is narrow, and can partly be compensated for when analyzing data. In the regions above the Earth's polar regions, the wake behind a Cluster spacecraft is caused by an electrostatic structure around the positively charged spacecraft, causing an enhanced wake. The charging stops positive ions from reaching the spacecraft. Rather, this wake can be used to estimate the flux of cold (eV) positive ions escaping from the ionosphere. Above the poles the flux is about
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ions/s, constituting a large fraction of the mass outflow from planet Earth. For an intermediate range of parameters, when the drift energy of the ions is comparable to the equivalent charge of the spacecraft, also the charged wire booms of a double‐probe instrument must be taken into account. We discuss an example from the MMS spacecraft near the magnetopause.
Key Points
Plasma wakes are common behind scientific spacecraft
Wakes in the solar wind can be compensated for in data analysis
Enhanced wakes in the polar lobes can be used to detect cold outflowing ions
Whilst an African origin of modern humans is well established, the timings and routes of their expansions into Eurasia are the subject of heated debate, due to the scarcity of fossils and the lack of ...suitably old ancient DNA. Here, we use high-resolution palaeoclimate reconstructions to estimate how difficult it would have been for humans in terms of rainfall availability to leave the African continent in the past 300k years. We then combine these results with an anthropologically and ecologically motivated estimate of the minimum level of rainfall required by hunter-gatherers to survive, allowing us to reconstruct when, and along which geographic paths, expansions out of Africa would have been climatically feasible. The estimated timings and routes of potential contact with Eurasia are compatible with archaeological and genetic evidence of human expansions out of Africa, highlighting the key role of palaeoclimate variability for modern human dispersals.
In a cometary coma, the ion-neutral decoupling distance, sometimes referred to as the ion exobase or collisionopause, can be defined as the cometocentric distance, r(in), where ions, initially moving ...with the neutral outgassing speed, have a probability of 1/e of not colliding with neutrals on their subsequent journey radially outwards. We present an analytical model for calculating this decoupling distance in the presence of a static radial electric field. We show that for a logarithmically decaying potential, the value of r(in) can even decrease to similar to 15 per cent of its field-free case value. Moreover, already at this distance, the effective ion speed can be expected to markedly exceed the neutral expansion velocity. These analytical results are in line with previous numerical calculations, adapting similar but not identical field profiles. The presence of a non-negligible ambipolar electric field and limited importance of ion-neutral collisional coupling are further supported by observations in the diamagnetic cavity of comet 67P/Churyumov-Gerasimenko by plasma instruments onboard Rosetta that reveal ion speeds several times higher than the neutral expansion velocity.
•Isogeometric membrane formulations with wrinkling based on tension-field theory.•A new technique is proposed to meet Cn continuity across the symmetry plane.•A combined solution procedure using ...dynamic relaxation and Newton-Raphson iteration.•The proposed model can reproduce folding deformations of membrane.
An isogeometric membrane element based on the non-uniform rational basis spline (NURBS) model is presented that accounts for membrane wrinkling based on tension-field theory. First, the element is validated by means of a benchmark problem involving a partly wrinkled membrane. It is then applied to the large deformation of a thin membrane structure using a two-stage procedure that combines dynamic relaxation and Newton–Raphson iteration. A simple technique is introduced that takes advantage of the geometrical symmetry of an isogeometric analysis model by using a “one-sided” open knot vector to treat the continuity of the membrane surface with respect to the symmetry plane. Because NURBS has many suitable features for representing complex geometries, it enriches the function space of the membrane element. Consequently, the characteristic mechanical responses of membranes, such as deep folding, are captured appropriately by the present isogeometric membrane element. In addition, a numerical example demonstrates that the convergence rate of the isogeometric membrane analysis with respect to refinement of the discretization is much better when tension-field theory is introduced in the analysis.
Shaken baby syndrome has typically been associated with findings of subdural haematoma, retinal haemorrhages and encephalopathy, which are referred to as the triad. During the last decade, however, ...the certainty with which the triad can indicate that an infant has been violently shaken has been increasingly questioned. The aim of this study was to determine the diagnostic accuracy of the triad in detecting that an infant had been shaken. The literature search was performed using PubMed, Embase and the Cochrane Library up to October 15, 2015. Relevant publications were assessed for the risk of bias using the QUADAS tool and were classified as having a low, moderate or high risk of bias according to predefined criteria. The reference standards were confessions or witnessed cases of shaking or accidents. The search generated 3773 s, 1064 were assessed as possibly relevant and read as full texts, and 30 studies were ultimately included. Of these, 28 were assessed as having a high risk of bias, which was associated with methodological shortcomings as well as circular reasoning when classifying shaken baby cases and controls. The two studies with a moderate risk of bias used confessions and convictions when classifying shaken baby cases, but their different designs made a meta‐analysis impossible. None of the studies had a low risk of bias.
Conclusion: The systematic review indicates that there is insufficient scientific evidence on which to assess the diagnostic accuracy of the triad in identifying traumatic shaking (very low‐quality evidence). It was also demonstrated that there is limited scientific evidence that the triad and therefore its components can be associated with traumatic shaking (low‐quality evidence).
Tensegrities are cable-strut assemblies which find their stiffness and self-equilibrium states from the integrity between tension and compression. Low stiffness and coinciding natural frequencies are ...known issues. Their stiffness can be regulated and improved by changing the level of pre-stress. In vibration health monitoring, the first natural frequency is used as an indicator of better stiffness, but coinciding natural frequencies will be an obstacle in measuring and analysing the correct resonance. In this paper, the above two issues have been considered for modular tensegrity structures. The finite element model used considers not only the axial vibration of the components, but also the transversal vibration where non-linear Euler–Bernoulli beam elements are used for simulations. A genetic algorithm is used to solve the optimization problem, with a multi-objective criterion combination. The optimum self-stress of the tensegrity structures can be chosen such that their lowest natural frequency is high, and separated from others. Two approaches are used to find the optimal self-stress vector: scaling from a base module or considering all modules at once. Both approaches give the same optimum solutions.
We studied the distribution of cold electrons (<1 eV) around comet 67P/Churyumov-Gerasimenko with respect to the solar wind convective electric field direction. The cold plasma was measured by the ...Langmuir Probe instrument and the direction of the convective electric field conv = − × was determined from magnetic field ( ) measurements inside the coma combined with an assumption of a purely radial solar wind velocity . We found that the cold plasma is twice as likely to be observed when the convective electric field at Rosetta's position is directed toward the nucleus (in the − conv hemisphere) compared to when it is away from the nucleus (in the + conv hemisphere). Similarly, the diamagnetic cavity, in which previous studies have shown that cold plasma is always present, was also found to be observed twice as often when in the − conv hemisphere, linking its existence circumstantially to the presence of cold electrons. The results are consistent with hybrid and Hall magnetohydrodynamic simulations as well as measurements of the ion distribution around the diamagnetic cavity.
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