Renazzo‐type (CR) carbonaceous chondrites belong to one of the most pristine meteorite groups containing various early solar system components such as matrix and fine‐grained rims (FGRs), whose ...formation mechanisms are still debated. Here, we have investigated FGRs of three Antarctic CR chondrites (GRA 95229, MIL 07525, and EET 92161) by electron microscopy techniques. We specifically focused on the abundances and chemical compositions of the amorphous silicates within the rims and matrix by analytical transmission electron microscopy. Comparison of the amorphous silicate composition to a matrix area of GRA 95229 clearly shows a compositional relationship between the matrix and the fine‐grained rim, such as similar Mg/Si and Fe/Si ratios. This relationship and the abundance of the amorphous silicates in the rims strengthen a solar nebular origin and rule out a primary formation mechanism by parent body processes such as chondrule erosion. Moreover, our chemical analyses of the amorphous silicates and their abundance indicate that the CR rims experienced progressive alteration stages. According to our analyses, the GRA 95229 sample is the least altered one based on its high modal abundance of amorphous silicates (31%) and close‐to‐chondritic Fe/Si ratios, followed by MIL 07525 and finally EET 92161 with lesser amounts of amorphous silicates (12% and 5%, respectively) and higher Fe/Si ratios. Abundances and chemical compositions of amorphous silicates within matrix and rims are therefore suitable recorders to track different alteration stages on a submicron scale within variably altered CR chondrites.
Currently accepted mechanistic models describing aqueous corrosion of borosilicate glasses are based on diffusion-controlled hydrolysis, hydration, ion exchange reactions, and subsequent ...re-condensation of the hydrolyzed glass network, leaving behind a residual hydrated glass or gel layer. Here, we report results of novel oxygen and silicon isotope tracer experiments with ternary Na borosilicate glasses that can be better explained by a process that involves the congruent dissolution of the glass, which is spatially and temporally coupled to the precipitation and growth of an amorphous silica layer at an inwardly moving reaction interface. Such a process is thermodynamically driven by the solubility difference between the glass and amorphous silica, and kinetically controlled by glass dissolution reactions at the reaction front, which, in turn, are controlled by the transport of water and solute elements through the growing corrosion zone. Understanding the coupling of these reactions is the key to understand the formation of laminar or more complex structural and chemical patterns observed in natural corrosion zones of ancient glasses. We suggest that these coupled processes also have to be considered to realistically model the long-term performance of silicate glasses in aqueous environments.
Predators frequently compete with other species for prey but can also interact by preying on each other’s vulnerable stages. Because eggs and juveniles are more vulnerable to this intraguild ...predation than adults, their survival will depend on maternal strategies to reduce predation risk. Recently, we reported that adult female predatory mites Gynaeseius liturivorus Ehara (Acari: Phytoseiidae) reduce intraguild predation on their eggs by remaining at oviposition sites, thus deterring the egg predators. In addition, they avoid oviposition close to eggs laid by conspecific females. We therefore expected that adult female G. liturivorus protect their own eggs better against these egg predators than eggs of other females. This was tested using juveniles of the predatory mite Neoseiulus californicus McGregor (Acari: Phytoseiidae) as egg predators and the western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), as the shared prey. When G. liturivorus eggs were kept with their mothers, the presence of juvenile egg predators did not affect the survival of eggs. However, when G. liturivorus eggs were kept with females that were not their mothers, the mortality of eggs in the presence of juvenile egg predators increased. When adult female G. liturivorus were guarding their eggs, they killed a similar number of juvenile egg predators as females that were not kept with their eggs. Hence, adult female G. liturivorus protect their eggs by remaining close to their eggs.
Predators frequently compete with other species for prey but can also interact by preying on each other’s vulnerable stages. Previously, we showed that adult female predatory mites remain at oviposition sites, thus deterring juveniles of another predatory mite species, resulting in reduced intraguild predation on their eggs. We now show that this guarding behavior is more effective when adult females guard their own eggs than when guarding eggs of other females.
One important application of borosilicate glass is its use as a nuclear waste form to immobilize high-level nuclear waste. Understanding the corrosion mechanism of borosilicate glasses in aqueous ...solutions is essential to reliably predict their long-term behavior in the worst-case scenario of glass-groundwater contact in a geologic repository. Traditional models evaluate the long-term corrosion process on the basis of diffusion-controlled hydration and ion exchange reactions that are followed by solid-state reconstruction of the hydrolyzed glass network. Here we report textural, chemical, and
18O and
26Mg isotope tracer results from corrosion experiments with a borosilicate glass in an acidic aqueous solution (initial pH ≈
0,
T
=
150
°C, 6 to 336
h) that contradict such a paradigm. We propose a new mechanistic model for glass corrosion under acidic conditions that is based on congruent (stoichiometric) dissolution of the glass that is spatially and temporally coupled to the precipitation of amorphous silica at an inward moving reaction front. The model potentially provides a novel framework to understand apparently contradictory observations made under more moderate conditions and to evaluate the long-term aqueous durability of silicate glasses.
Several animal species are known to distinguish between their own eggs and eggs of unrelated conspecifics. However, the cues involved in this discrimination are often unknown. These cues were studied ...using the predatory mite Gynaeseius liturivorus Ehara.
Adult females of these predatory mites oviposit in clusters and avoid oviposition close to eggs laid by other females, resulting in reduced cannibalism between offspring. Because predatory mites are blind, it was tested whether volatiles of eggs were used as a cue for egg recognition.
Adult female predatory mites were offered volatile cues of their own eggs and of unrelated conspecific eggs, and females were prevented from contacting the eggs. Predatory mites oviposited closer to their own eggs than to unrelated eggs. This preference was observed even when one own and one unrelated egg were offered as a volatile source.
These results suggest that adult female predatory mites can determine kinship using volatiles released from the eggs.
The predatory mite Gynaeseius liturivorus Ehara is known to distinguish between their own eggs and eggs of conspecific females. We studied cues involved in this egg discrimination.
Adult female predatory mites were offered volatile cues of their own eggs and of eggs of other females, and females could not contact the eggs.
Predatory mites oviposited closer to their own eggs than to other eggs, suggesting that they can determine kinship using volatiles released from the eggs.
It is well known that Fe-N-C catalysts reach a significantly better ORR activity in alkaline compared to acidic electrolyte. This advantage makes the material of interest for application in alkaline ...fuel cells. Beside this, for Pt/C catalyst it is known that the performance in acid can be significantly enhanced through ionic liquid modification following the Solid Catalysts with Ionic Liquid Layer (SCILL) concept. In our current study we combine both advantages and investigate for two Fe-N-C catalysts prepared either with or without sulfur in the precursor mixture the effect of IL modification. The unmodified catalysts are characterized using X-ray induced photoelectron spectroscopy (XPS), 57Fe Mößbauer and Raman spectroscopy as well as N2 sorption. The electrochemical behavior of the unmodified catalyst and with different pore-filling degrees of ionic liquid (IL) is analysed with respect to double layer capacitance, ORR activity and stability in accelerated stress tests mimicking the load-cycle conditions.
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•Modification of two types of Fe-N-C catalysts by an ionic liquid.•IL modification leads to improved activity and stability for a sulfur-free catalyst.•Strong correlation between the double layer capacitance and the activity.
Because predators may interfere with each other, an important step towards the implementation of successful release of multiple predators in biocontrol programs requires resolving how predators ...respond to the presence of heterospecific competitors. Several species of predatory mites are important biocontrol agents and the species
Phytoseiulus macropilis
and
Neoseiulus californicus
are used to control the two-spotted spider mite,
Tetranychus urticae
, an important pest in agriculture worldwide. We investigated their compatibility showing that the two predators do not avoid plants on which the other species is present together with their common prey, and demonstrated that their oviposition rates are not affected by the presence of the other species. However, the distribution of the eggs on leaf discs was affected by the presence of the heterospecific predator. This behaviour might weaken possible interference between these two biocontrol agents, which, in turn, may enable their persistence on plants and favour pest suppression. The increased joint use of several natural enemies for biological control highlights the importance of studies on predator–predator interactions.
The aim of the current study was to test the validity of the Norwegian version of the Desire Thinking Questionnaire (DTQ). Three cross‐sectional surveys were conducted investigating the psychometric ...properties of the DTQ in alcohol use (N = 588), nicotine use (N = 446) and social media use (N = 359). Principal components and confirmatory factor analyses supported the original two‐factor solution consisting of verbal perseveration (VP) and imaginal prefiguration (IP); however, one item was removed to obtain good fit. Internal consistency was acceptable. Both IP and VP showed significant correlations with problem drinking, nicotine dependence and problematic social media use. Regression analyses, controlling for demographics and negative affect, found IP and VP to be significantly associated with all dependent variables. The results confirm that desire thinking is an important construct across different addictive behaviours.
This paper presents an investigation of the limitations and optimisation of energy dispersive X-ray (EDX) tomography within the scanning transmission electron microscope, focussing on application of ...the technique to characterising the 3D elemental distribution of bimetallic AgAu nanoparticles. The detector collection efficiency when using a standard tomography holder is characterised using a tomographic data set from a single nanoparticle and compared to a standard low background double tilt holder. Optical depth profiling is used to investigate the angles and origin of detector shadowing as a function of specimen field of view. A novel time-varied acquisition scheme is described to compensate for variations in the intensity of spectrum images at each sample tilt. Finally, the ability of EDX spectrum images to satisfy the projection requirement for nanoparticle samples is discussed, with consideration of the effect of absorption and shadowing variations.
•We investigate the methodology of STEM-EDX tomography of nanoparticles.•We present a time-varied acquisition scheme to compensate for detector shadowing.•The ability of STEM-EDX tomography to meet the projection requirement is discussed.
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