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Abstract To explain how populations with distinct warning signals coexist in close parapatry, we experimentally assessed intrinsic mechanisms acting as reproductive barriers within three poison-frog species from the Peruvian Amazon belonging to a Müllerian mimetic ring (Ranitomeya variabilis, Ranitomeya imitator and Ranitomeya fantastica). We tested the role of prezygotic and postzygotic isolation barriers between phenotypically different ecotypes of each species, using no-choice mating experiments and offspring survival analysis. Our results show that prezygotic mating preference did not occur except for one specific ecotype of R. imitator, and that all three species were able to produce viable inter-population F1 hybrids. However, while R. variabilis and R. imitator hybrids were able to produce viable F2 generations, we found that for R. fantastica, every F1 hybrid males were sterile while females remained fertile. This unexpected result, echoing with Haldane’s rule of speciation, validated phylogenetic studies which tentatively diagnose these populations of R. fantastica as two different species. Our work suggests that postzygotic genetic barriers likely participate in the extraordinary phenotypic diversity observed within Müllerian mimetic Ranitomeya populations, by maintaining species boundaries.

Data analysis workflows in many scientific domains have become increasingly complex and flexible. Here we assess the effect of this flexibility on the results of functional magnetic resonance imaging by asking 70 independent teams to analyse the same dataset, testing the same 9 ex-ante hypotheses1. The flexibility of analytical approaches is exemplified by the fact that no two teams chose identical workflows to analyse the data. This flexibility resulted in sizeable variation in the results of hypothesis tests, even for teams whose statistical maps were highly correlated at intermediate stages of the analysis pipeline. Variation in reported results was related to several aspects of analysis methodology. Notably, a meta-analytical approach that aggregated information across teams yielded a significant consensus in activated regions. Furthermore, prediction markets of researchers in the field revealed an overestimation of the likelihood of significant findings, even by researchers with direct knowledge of the dataset2-5. Our findings show that analytical flexibility can have substantial effects on scientific conclusions, and identify factors that may be related to variability in the analysis of functional magnetic resonance imaging. The results emphasize the importance of validating and sharing complex analysis workflows, and demonstrate the need for performing and reporting multiple analyses of the same data. Potential approaches that could be used to mitigate issues related to analytical variability are discussed.

This study investigated preparatory processes involved in adapting to changing episodic memory retrieval demands. Event-related potentials (ERPs) were recorded while participants performed a general old/new recognition task and a specific task that also required retrieval of perceptual details. The relevant task remained either constant or changed (predictably or randomly) across trials. Responses were slowed when participants switched from the specific to the general task but not vice versa. Hence, asymmetrical switch costs were observed, suggesting that retrieval preparation is dependent not only on the current retrieval goal but also influenced by recent retrieval attempts. Consistently, over posterior scalp regions ERPs associated with advance preparation were modulated by the preceding task, reflecting increased attentional selection requirements for the general task, and by the foreknowledge about the task sequence. When retrieval demands remained constant, frontal slow-waves elicited by retrieval-cues were more positive going for the specific task, indicating full implementation of a retrieval orientation that allows more efficient retrieval of perceptual details. (Contains 5 figures and 3 tables.)

The oxidation of monoterpenes under atmospheric conditions has been the subject of numerous studies. They were motivated by the formation of oxidized organic molecules (OOMs), which, due to their low vapor pressure, contribute to the formation of secondary organic aerosols (SOA). Among the different reaction mechanisms proposed for the formation of these oxidized chemical compounds, it appears that the autoxidation mechanism, involving successive events of O 2 addition and H migration, common to both low-temperature-combustion and atmospheric conditions, leads to the formation of highly oxidized products (HOPs). However, cool-flame oxidation (∼500 –800 K) of terpenes has not received much attention even if it can contribute to atmospheric pollution through biomass burning and wildfires. Under such conditions, terpenes can be oxidized via autoxidation. In the present work, we performed oxidation experiments with limonene–oxygen–nitrogen and α -pinene–oxygen–nitrogen mixtures in a jet-stirred reactor (JSR) at 590 K, a residence time of 2 s, and atmospheric pressure. Oxidation products were analyzed by liquid chromatography, flow injection, and soft-ionization–high resolution mass spectrometry. H–D exchange and 2,4-dinitrophenyl hydrazine derivatization were used to assess the presence of OOH and C = O groups in oxidation products, respectively. We probed the effects of the type of ionization used in mass spectrometry analyses on the detection of oxidation products. Heated electrospray ionization (HESI) and atmospheric-pressure chemical ionization (APCI) in positive and negative modes were used. We built an experimental database consisting of literature data for atmospheric oxidation and presently obtained combustion data for the oxidation of the two selected terpenes. This work showed a surprisingly similar set of oxidation products' chemical formulas, including oligomers, formed under the two rather different conditions, i.e., cool-flame and simulated atmospheric oxidation. Data analysis (in HESI mode) indicated that a subset of chemical formulas is common to all experiments, independently of experimental conditions. Finally, this study indicates that more than 45 % of the detected chemical formulas in this full dataset can be ascribed to an autoxidation reaction. [ABSTRACT FROM AUTHOR]

The oxidation of monoterpenes under atmospheric conditions has been the subject of numerous studies. They were motivated by the formation of oxidized organic molecules (OOM) which, due to their low vapor pressure, contribute to the formation of secondary organic aerosols (SOA). Among the different reaction mechanisms proposed for the formation of these oxidized chemical compounds, it appears that the autoxidation mechanism, involving successive events of O2 addition and H-migration, common to both low-temperature combustion and atmospheric conditions, is leading to the formation of highly oxidized products (HOPs). However, cool flame oxidation (~500-800 K) of terpenes has not received much attention even if it can contribute to atmospheric pollution through biomass burning and wildfires. Under such conditions, terpenes can be oxidized via autoxidation. In the present work, we performed oxidation experiments with limonene-oxygen-nitrogen and a-pinene-oxygen19 rogen mixtures in a jet-stirred reactor (JSR) at 590 K, a residence time of 2 s, and atmospheric pressure. Oxidation products were analyzed by liquid chromatography, flow injection, and soft ionization-high resolution mass spectrometry. H/D exchange and 2,4-dinitrophenyl hydrazine derivatization were used to assess the presence of OOH and C=O groups in oxidation products, respectively. We probed the effects of the type of ionization used in mass spectrometry analyses on the detection of oxidation products. Heated electrospray ionization (HESI) and atmospheric pressure chemical ionization (APCI), in positive and negative modes were used. We built an experimental database consisting of literature data for atmospheric oxidation and presently obtained combustion data for the oxidation of the two selected terpenes. This work showed a surprisingly similar set of oxidation products chemical formulas, including oligomers, formed under the two rather different conditions, i.e., cool flame and simulated atmospheric oxidation. Data analysis indicated that a subset of chemical formulas is common to all experiments independently of experimental conditions. Finally, this study indicates that more than 45% of the detected chemical formulas in this full dataset can be ascribed to an autoxidation reaction. [ABSTRACT FROM AUTHOR]

A systematic XRD/FTIR/CHN/ICP investigation for the structural transformation of hydrotalcite-like compounds Mg(sub 1-x)Al(sub x)(OH)(sub 2)(NO3)(sub x).nH2O as a continuous function of nitrate anions is presented. The abrupt structural changes could be caused due to the drastic change in nitrate anion arrangement even though the nitrate anion maintains its D3h symmetry.

The synthesis and the associated structural, bonding and electrochemical properties of perfluorinated fullerene C70, at the molecular level and for the bulk material are described. Expansion of the carbon frame, the elongation of the resulting C-F bond, and the presence of an ionocovalent nature could be attributed to fluorination.

Aversive events sometimes turn into intrusive memories. However, prior evidence indicates that such memories can be controlled via a mechanism of retrieval suppression. Here, we test the hypothesis that suppression exerts a sustained influence on memories by deteriorating their neural representations. This deterioration, in turn, would hinder their subsequent reactivation and thus impoverish the vividness with which they can be recalled. In an fMRI study, participants repeatedly suppressed memories of aversive scenes. As predicted, this process rendered the memories less vivid. Using a pattern classifier, we observed that suppression diminished the neural reactivation of scene information both globally across the brain and locally in the parahippocampal cortices. Moreover, the decline in vividness was associated with reduced reinstatement of unique memory representations in right parahippocampal cortex. These results support the hypothesis that suppression weakens memories by causing a sustained reduction in the potential to reactivate their neural representations. [ABSTRACT FROM AUTHOR]

The oxidation of monoterpenes under atmospheric conditions has been the subject of numerous studies. They were motivated by the formation of oxidized organic molecules (OOM) which, due to their low vapor pressure, contribute to the formation of secondary organic aerosols (SOA). Among the different reaction mechanisms proposed for the formation of these oxidized chemical compounds, it appears that the autoxidation mechanism, involving successive events of H-migration and O[sub 2] addition, common to both low-temperature combustion and atmospheric conditions, is leading to the formation of highly oxidized molecules (HOM). In atmospheric chemistry, the importance of autoxidation compared to other oxidation pathways has been the topic of numerous studies. Conversely, in combustion, autoxidation under cool flame conditions is the main oxidation process commonly taken into account. An analysis of oxidation products detected in both conditions was performed, using the present combustion data and literature data from tropospheric oxidation studies, to investigate possible similarities in terms of observed chemical formulae of products. To carry out this study, we chose two terpenes, α-pinene and limonene (C10H16), among the most abundant biogenic components in the atmosphere, and considered in many previous studies. Also, these two isomers were selected for the diversity of their reaction sites (exo-and endo- carbon-carbon double bonds). We built an experimental database consisting of literature atmospheric oxidation data and presently obtained combustion data for the oxidation of the two selected terpenes. In order to probe the effects of the type of ionization used in mass spectrometry analyses on the detection of oxidation products, we used heated electrospray ionization (HESI) and atmospheric pressure chemical ionization (APCI), in positive and negative modes. The oxidation of limonene-oxygen-nitrogen and α-pinene-oxygen-nitrogen mixtures was performed using a jet-stirred reactor at elevated temperature (590 K), a residence time of 2 s, and atmospheric pressure. Samples of the reacting mixtures were collected in acetonitrile and analyzed by high-resolution mass spectrometry (Orbitrap Q-Exactive) after direct injection and soft ionization, i.e. (+/-) HESI and (+/-) APCI. This work shows a surprisingly similar set of chemical formulae of products, including oligomers, formed in cool flames and under simulated atmospheric conditions. Data analysis showed that a non-negligible subset of chemical formulae is common to all experiments independently of experimental parameters. Finally, this study indicates that more than 40% of the detected chemical formulae in this full dataset can be ascribed to an autoxidation mechanism. [ABSTRACT FROM AUTHOR]

Atmospheric oxidation chemistry and, more specifically, photooxidation show that the long-term oxidation of organic aerosol (OA) progressively erases the initial signature of the chemical compounds and can lead to a relatively uniform character of oxygenated organic aerosol (OOA). This uniformity character observed after a long reaction time seems to contrast with the great diversity of reaction mechanisms observed in the early stages of oxidation. The numerous studies carried out on the oxidation of terpenes, and more particularly on limonene for its diversity of reaction sites (endo- and oxocyclic), allow this evolution to be studied. We have selected, for their diversity of experimental conditions, nine studies of limonene oxidation at room temperature over long reaction times to be compared to the present data set obtained at elevated temperature and short reaction time in order to investigate the similarities in terms of reaction mechanisms and chemical species formed. Here, the oxidation of limonene–oxygen–nitrogen mixtures was studied using a jet-stirred reactor at elevated temperature and atmospheric pressure. Samples of the reacting mixtures were collected and analyzed by high-resolution mass spectrometry (Orbitrap) after direct injection or after separation by reverse-phase ultra-high-pressure liquid chromatography and soft ionization, i.e., (+/-) HESI and (+/-) APCI. Unexpectedly, because of the diversity of experimental conditions in terms of continuous-flow tank reactor, concentration of reactants, temperature, reaction time, mass spectrometry techniques, and analysis conditions, the results indicate that among the 1138 presently detected molecular formulae, many oxygenates found in earlier studies of limonene oxidation by OH and/or ozone are also produced under the present conditions. Among these molecular formulae, highly oxygenated molecules and oligomers were detected in the present work. The results are discussed in terms of reaction pathways involving the initial formation of peroxy radicals (RO2), isomerization reactions yielding keto-hydroperoxides, and other oxygenated intermediates and products up to C25H32O17 , products which could derive from RO2 autoxidation via sequential H shift and O2 addition (C10H14O3,5,7,9,11) and products deriving from the oxidation of alkoxy radicals (produced by RO2 self-reaction or reaction with HO2) through multiple H shifts and O2 additions (C10H14O2,4,6,8,10). The oxidation of RO2 , with possible occurrence of the Waddington mechanism and of the Korcek mechanism, involving H shifts is also discussed. The present work demonstrates similitude between the oxidation products and oxidation pathways of limonene under simulated atmospheric conditions and in those encountered during the self-ignition of hydrocarbons at elevated temperatures. These results complement those recently reported by Vereecken and Nozière and confirm for limonene the existence of an oxidative chemistry of the alkylperoxy radical beyond 450 K based on the H shift (Nozière and Vereecken, 2019; Vereecken and Nozière, 2020). [ABSTRACT FROM AUTHOR]

Whereas the kinetics of oxidation of limonene has been extensively studied and mechanisms for its oxidation by OH and/or ozone have been proposed, more studies are required for better understanding its oxidation pathways. The oxidation of limonene-oxygen-nitrogen mixtures was studied using a jet-stirred reactor at elevated temperature and atmospheric pressure. Samples of the reacting mixtures were collected and analyzed by high resolution mass spectrometry (Orbitrap) after direct injection or after separation by reverse-phase ultra-high-pressure liquid chromatography and soft ionization by (+/-) HESI and (+/-) APCI. The results indicate that among the 1138 detected products, many oxygenates found in earlier studies of limonene oxidation by OH and/or ozone are also produced under the present conditions. Other highly oxygenated products and oligomers were also detected in the present work. The results are discussed in terms of reaction pathways involving the initial formation of peroxy radicals, isomerization reactions yielding keto-hydroperoxides and other oxygenated intermediates and products up to C25H32O17. The possible occurrence of the Waddington mechanism and of the Korcek mechanism are also discussed. The present work demonstrates similarities between the oxidation products and oxidation pathways of limonene under simulated atmospheric conditions and in those encountered during the self-ignition of hydrocarbons at low temperatures, which should stimulate future interactions between communities of atmospheric chemistry and combustion chemistry to improve current chemical models. [ABSTRACT FROM AUTHOR]

The oxidation of di-n-propyl-ether (DPE) was performed in a jet-stirred reactor at 1 and 10 atm, at residence times of 1 and 0.7 s, respectively, and initial fuel concentrations of 5000 and 1000 ppm at 1 and 10 atm, respectively. Atmospheric pressure experiments were used for characterization of cool flame products. The 10 atm experiment provided KHPs profile vs. temperature and mole fraction profiles of stable species which were obtained through sonic probe sampling, gas chromatography, Fourier transform infrared spectrometry analyses. High resolution mass spectrometry analyses (HRMS) with syringe direct injection or ultra-high-pressure liquid chromatography coupling was used to characterize hydroperoxides (C 3 H 8 O 2 , C 6 H 14 O 3), diols (C 6 H 14 O 3), ketohydroperoxides (C 6 H 12 O 4), carboxylic acids, and highly oxygenated molecules (C 6 H 12 O 6 , C 6 H 12 O 8) resulting from up to four O 2 additions on fuel's radicals. Heated electrospray and atmospheric pressure chemical ionizations (HESI and APCI) were used in positive and negative mode. Whereas the CH 2 groups neighboring the ether function are the most favorable sites for H-atom abstraction reactions, speciation indicated that other sites can react by metathesis forming a large pool of intermediates. Our kinetic reaction mechanism represents the experimental data for most of the stable species but need to be expended for simulating the formation of newly detected species. [ABSTRACT FROM AUTHOR]

Abstract: RhL2 complexes of phosphonate‐derivatized 2,2′‐bipyridine (bpy) ligands L were immobilized on titanium oxide particles generated in situ. Depending on the structure of the bipy ligand—number of tethers (1 or 2) to which the phosphonate end groups are attached and their location on the 2,2′‐bipyridine backbone (4,4′‐, 5,5′‐, or 6,6′‐positions)—the resulting supported catalysts showed comparable chemoselectivity but different kinetics for the hydrogenation of 6‐methyl‐5‐hepten‐2‐one under hydrogen pressure. Characterization of the six supported catalysts suggested that the intrinsic geometry of each of the phosphonate‐derivatized 2,2′‐bipyridines leads to supported catalysts with different microstructures and different arrangements of the RhL2 species at the surface of the solid, which thereby affect their reactivity. [ABSTRACT FROM AUTHOR]

Abstract: Both the hippocampus and ventromedial prefrontal cortex (vmPFC) appear to be critical for episodic future simulation. Damage to either structure affects one's ability to remember the past and imagine the future, and both structures are commonly activated as part of a wider core network during future simulation. However, the precise role played by each of these structures and, indeed, the direction of information flow between them during episodic simulation, is still not well understood. In this study, we scanned participants using functional magnetic resonance imaging while they imagined future events in response to object cues. We then used dynamic causal modeling to examine effective connectivity between the left anterior hippocampus and vmPFC during the initial mental construction of the events. Our results show that while there is strong bidirectional intrinsic connectivity between these regions (i.e., irrespective of task conditions), only the hippocampus to vmPFC connection increases during the construction of episodic future events, suggesting that the hippocampus initiates event simulation in response to retrieval cues, driving activation in the vmPFC where episodic details may be further integrated. [ABSTRACT FROM AUTHOR]

The hippocampus has been consistently associated with episodic simulation (i.e., the mental construction of a possible future episode). In a recent study, we identified an anterior-posterior temporal dissociation within the hippocampus during simulation. Specifically, transient simulation-related activity occurred in relatively posterior portions of the hippocampus and sustained activity occurred in anterior portions. In line with previous theoretical proposals of hippocampal function during simulation, the posterior hippocampal activity was interpreted as reflecting a transient retrieval process for the episodic details necessary to construct an episode. In contrast, the sustained anterior hippocampal activity was interpreted as reflecting the continual recruitment of encoding and/or relational processing associated with a simulation. In the present study, we provide a direct test of these interpretations by conducting a subsequent memory analysis of our previously published data to assess whether successful encoding during episodic simulation is associated with the anterior hippocampus. Analyses revealed a subsequent memory effect (i.e., later remembered > later forgotten simulations) in the anterior hippocampus. The subsequent memory effect was transient and not sustained. Taken together, the current findings provide further support for a component process model of hippocampal function during simulation. That is, unique regions of the hippocampus support dissociable processes during simulation, which include the transient retrieval of episodic information, the sustained binding of such information into a coherent episode, and the transient encoding of that episode for later retrieval. [ABSTRACT FROM AUTHOR]

Remembering the past and imagining the future both involve the retrieval of details stored in episodic memory and rely on the same core network of brain regions. Given these parallels, one might expect similar component processes to be involved in remembering and imagining. While a strong case can be made for the role of inhibition in memory retrieval, few studies have examined whether inhibition is also necessary for future imagining and results to-date have been mixed. In the current study, we test whether related concepts are inhibited during future imagining using a modified priming approach. Participants first generated a list of familiar places and for each place, the people they most strongly associate with it. A week later, participants imagined future events involving recombinations of people and places, immediately followed by a speeded response task in which participants made familiarity decisions about people’s names. Across two experiments, our results suggest that related concepts arenotinhibited during future imagining, but rather are automatically primed. These results fit with recent work showing that autobiographically significant concepts (e.g., friends’ names) are more episodic than semantic in nature, automatically activating related details in memory and potentially fuelling the flexible simulation of future events. [ABSTRACT FROM AUTHOR]

Local p-type doping in GaN is a key issue for device development but it remains a challenge to be achieved. In this work, we studied the activation of Mg implanted in the GaN. Multi-energy implantations were performed to achieve a 'box-like' profile. SIMS measurements showed unexpected deep Mg profile due to defect-assisted channeling in the GaN. In addition, a high-density defect region induced by the implantation was evidenced by TEM characterization. To protect the GaN surface prior to high temperature annealing, an AlN cap-layer was deposited by reactive sputtering followed by SiO x deposition leading to a double cap-layer. Afterwards, the capped samples were RTA-annealed at high temperatures for several minutes under nitrogen. Two types of annealing processes were applied: a monocycle and a multicycle annealing. After annealing, the double cap-layer was etched using chemical solutions. AFM characterizations, after annealing and cap-layer etching, demonstrated that a GaN surface with similar roughness to as-grown samples and pit-free can be achieved after both monocycle and multicycle annealing steps. However, an AlGaN layer at the AlN/GaN interface is observed by ToF-SIMS and remained after the etching of the AlN layer. Finally, Schottky diodes were processed on the unimplanted and annealed samples, evidencing a double barrier, while P/N junction diodes are still being processed on the implanted and annealed samples. [ABSTRACT FROM AUTHOR]

Different routes for preparing zirconium phosphonate-modified surfaces for immobilizing biomolecular probes are compared. Two chemical-modification approaches were explored to form self-assembled monolayers on commercially available primary amine-functionalized slides, and the resulting surfaces were compared to well-characterized zirconium phosphonate monolayer-modified supports prepared using Langmuir-Blodgett methods. When using POCl3 as the amine phosphorylating agent followed by treatment with zirconyl chloride, the result was not a zirconium-phosphonate monolayer, as commonly assumed in the literature, but rather the process gives adsorbed zirconium oxide/hydroxide species and to a lower extent adsorbed zirconium phosphate and/or phosphonate. Reactions giving rise to these products were modeled in homogeneous-phase studies. Nevertheless, each of the three modified surfaces effectively immobilized phosphopeptides and phosphopeptide tags fused to an affinity protein. Unexpectedly, the zirconium oxide/hydroxide modified surface, formed by treating the amine-coated slides with POCl3/Zr4+, afforded better immobilization of the peptides and proteins and efficient capture of their targets. [ABSTRACT FROM AUTHOR]

Simulations of future experiences are often emotionally arousing, and the tendency to repeatedly simulate negative future outcomes has been identified as a predictor of the onset of symptoms of anxiety. Nonetheless, next to nothing is known about how the healthy human brain processes repeated simulations of emotional future events. In this study, we present a paradigm that can be used to study repeated simulations of the emotional future in a manner that overcomes phenomenological confounds between positive and negative events. The results show that pulvinar nucleus and orbitofrontal cortex respectively demonstrate selective reductions in neural activity in response to frequently as compared to infrequently repeated simulations of negative and positive future events. Implications for research on repeated simulations of the emotional future in both non-clinical and clinical populations are discussed. [ABSTRACT FROM AUTHOR]