Improved Optics in Monolithic Perovskite/Silicon Tandem Solar Cells with a Nanocrystalline Silicon Recombination Junction

Perovskite/silicon tandem solar cells are increasingly recognized as promi­sing candidates for next‐generation photovoltaics with performance beyond the single‐junction limit at potentially low production costs. Current designs for monolithic tandems rely on transparent conductive oxides as an intermediate recombination layer, which lead to optical losses and reduced shunt resistance. An improved recombination junction based on nanocrystalline silicon layers to mitigate these losses is demonstrated. When employed in monolithic perovskite/silicon heterojunction tandem cells with a planar front side, this junction is found to increase the bottom cell photocurrent by more than 1 mA cm^?2. In combination with a cesium‐based perovskite top cell, this leads to tandem cell power‐conversion efficiencies of up to 22.7% obtained from J–V measurements and steady‐state efficiencies of up to 22.0% during maximum power point tracking. Thanks to its low lateral conductivity, the nanocrystalline silicon recombination junction enables upscaling of monolithic perovskite/silicon heterojunction tandem cells, resulting in a 12.96 cm² monolithic tandem cell with a steady‐state efficiency of 18%.     

Structure is more important than physiology for estimating intracanopy distributions of leaf temperatures

Estimating leaf temperature distributions (LTDs) in canopies is crucial in forest ecology. Leaf temperature affects the exchange of heat, water, and gases, and it alters the performance of leaf‐dwelling species such as arthropods, including pests and invaders. LTDs provide spatial variation that may allow arthropods to thermoregulate in the face of long‐term changes in mean temperature or incidence of extreme temperatures. Yet, recording LTDs for entire canopies remains challenging. Here, we use an energy‐exchange model (RATP) to examine the relative roles of climatic, structural, and physiological factors in influencing three‐dimensional LTDs in tree canopies. A Morris sensitivity analysis of 13 parameters showed, not surprisingly, that climatic factors had the greatest overall effect on LTDs. In addition, however, structural parameters had greater effects on LTDs than did leaf physiological parameters. Our results suggest that it is possible to infer forest canopy LTDs from the LTDs measured or simulated just at the surface of the canopy cover over a reasonable range of parameter values. This conclusion suggests that remote sensing data can be used to estimate 3D patterns of temperature variation from 2D images of vegetation surface temperatures. Synthesis and applications. Estimating the effects of LTDs on natural plant–insect communities will require extending canopy models beyond their current focus on individual species or crops. These models, however, contain many parameters, and applying the models to new species or to mixed natural canopies depends on identifying the parameters that matter most. Our results suggest that canopy structural parameters are more important determinants of LTDs than are the physiological parameters that tend to receive the most empirical attention.     

Cerebral cortical blood flow in rabbits during parabolic flights (hypergravity and microgravity)

We studied the effect of gravity on cerebral cortical blood flow (CBF), mean arterial blood pressure () and heart rate in six rabbits exposed to parabolic flights. The CBF was obtained using a laser-Doppler probe fixed on to a cranial window. Before weightlessness, the animals were exposed to chest-to-back directed acceleration (1.8–2.0 g). The CBF values were expressed as a percentage of CBF_o (mean CBF during 60 s before the 1st parabola). Propranolol (1 mg · kg⁻¹ IV) was given after the 11th parabola and pentobarbital (12–15 mg · kg⁻¹ IV) after the 16th parabola. Before the administration of the drugs, CBF increased (P < 0.01) during hypergravity [i.e. maximal CBF 151 (SD 64)% CBF_o. Simultaneously increased [maximal , 119 (SD 11) mmHg (P < 0.01)]. At the onset of weightlessness, CBF and reached maximal values [194 (SD 96)% CBF_o (P < 0.01) and 127 (SD 19) mmHg, (P < 0.01) respectively]. The microgravity-induced increase in CBF was transient since CBF returned to its baseline value after 8 (SD 2) s of microgravity. After propranolol administration, CBF was not statistically different during hypergravity but an elevation of CBF was still observed in weightlessness. The increases in CBF and also persisted during weightlessness after pentobarbital administration. These data would indicate that CBF of nonanesthetized rabbits increases during the first seconds of weightlessness and demonstrate the involvement of rapid active regulatory mechanisms since CBF returned to control values within 8 (SD 2) s. We concluded that this elevation in blood flow was not related to stress because it persisted after the administration of propranolol and pentobarbital. Accepted: 6 November 1997     

Molecular cloning of two Solanum chacoense S-alleles and a hypothesis concerning their evolution

The polymerase chain reaction (PCR) has been used to clone two S-alleles (S13 and S14) from Solanum chacoense. The two alleles do not cross-hybridize on genomic Southern blots or on northern blots using stylar RNA. Although the S14 message was not detected in a stylar cDNA library prepared from mature flowers, a full-length copy of the S13 coding sequence was isolated by screening with the PCR fragment. We have analysed the sequences of the S13 cDNA and the S14 PCR fragment (60% of the mature protein coding sequence) in the context of S-RNase evolution, and propose that random point mutations may be sufficient to generate new S-alleles. Based on a phylogenetic tree composed of RNase sequences containing the conserved RNase motifs HGLWP and KHGXC, we suggest that gametophytic self-incompatibility genes are RNase genes that have acquired a new function in the gametophytic self-incompatibility system early in the evolution of flowering plants.     

Pour une approche psychosomatique de l’Andrologie

Through the opening offered by the psychosomatic approach, we encounter patients with all kinds of andrologic complaints, even quite unspecific ones. But we do know this mode of contact is particulary useful and fruitful when the troubles lean towards chronicity, or are linked to anxiety and/or depression, be that condition cause or consequence. As far as functional symptoms are involved, there is a specific value to this approach. The key-time of that consultant, i.e; psychosomatic andrology, will be described, with the particularity of a ?conversation” instead of the mandatory anamnesis, meanwhile in his life, the possibly perturbing psychological events, as well as an attempt to evaluate the patient’s behaviour. The richness of the clinical examination within this doctor’s induced environment of ?words” coupled to some therapeutic means will be summarized: drugs, somatic and psychological methods (meaning all kind of psychotherapic techniques: support, behaviourist, couple, psychoanalytic or psychoanalysis…) When symptom(s) tend towards chronicity, an emotional subjective life grafts itself on the anatomical substratum, thus creating the opening for psychoemotional affects. This is the core we try to attain and assess through the psychosomatic approach.     

Noninvasive Measurement of Vulnerability to Drought-Induced Embolism by X-Ray Microtomography

Hydraulic failure induced by xylem embolism is one of the primary mechanisms of plant dieback during drought. However, many of the methods used to evaluate the vulnerability of different species to drought-induced embolism are indirect and invasive, increasing the possibility that measurement artifacts may occur. Here, we utilize x-ray computed microtomography (microCT) to directly visualize embolism formation in the xylem of living, intact plants with contrasting wood anatomy (Quercus robur, Populus tremula × Populus alba, and Pinus pinaster). These observations were compared with widely used centrifuge techniques that require destructive sampling. MicroCT imaging provided detailed spatial information regarding the dimensions and functional status of xylem conduits during dehydration. Vulnerability curves based on microCT observations of intact plants closely matched curves based on the centrifuge technique for species with short vessels (P. tremula × P. alba) or tracheids (P. pinaster). For ring porous Q. robur, the centrifuge technique significantly overestimated vulnerability to embolism, indicating that caution should be used when applying this technique to species with long vessels. These findings confirm that microCT can be used to assess the vulnerability to embolism on intact plants by direct visualization.Theory describing the physiological mechanism that allows plants to extract water from the soil and transport it many tens of meters in height has often been the subject of intense debate (Tyree, 2003). Plants have evolved a water-transport system that relies on water sustaining a tensile force; as a result, xylem sap is at negative absolute pressures (Dixon and Joly, 1895; Melcher et al., 1998; Wei et al., 1999). However, this transport mechanism comes with its own set of problems. Most notably, water under tension is prone to cavitation, which results in the formation of gas bubbles (emboli) that block xylem conduits. Embolism reduces the capacity of the xylem tissue to deliver water to the canopy, where it is required to maintain adequate levels of cellular hydration (Tyree and Sperry, 1989). The probability of embolism occurring in the xylem increases during drought, with increasing tension in the xylem sap. During prolonged and severe droughts, xylem embolism can reach lethal levels, causing branch dieback and, ultimately, plant death (Davis et al., 2002; Brodribb and Cochard, 2009; Hoffmann et al., 2011; Choat, 2013; Urli et al., 2013). Water stress-induced embolism is now recognized as one of the principal causes of plant mortality in response to extreme drought events (Anderegg, 2015). In the face of increasingly severe droughts expected with rising global temperatures, hydraulic failure due to embolism has the potential to cause widespread dieback of trees across all major forest biomes (Choat et al., 2012).The majority of techniques used to estimate cavitation resistance are indirect and/or invasive, increasing the possibility of artifacts occurring during measurement (Cochard et al., 2013). Artifacts relating to invasive techniques are particularly relevant in this case, since xylem sap under tension is in a metastable state and may easily vaporize as a result of disturbance. Noninvasive imaging techniques offer the potential to make direct observations of xylem function in intact plants at high resolution and in real time. Noninvasive techniques include magnetic resonance imaging (MRI; Holbrook et al., 2001; Kaufmann et al., 2009; Choat et al., 2010) and, more recently, x-ray computed microtomography (microCT; Brodersen et al., 2010; Charra-Vaskou et al., 2012; McElrone et al., 2012). MicroCT provides superior spatial resolution to MRI, with resolutions below 2 μm attainable for a plant stem of 4 to 5 mm in diameter. This allows for detailed analysis of embolism formation and repair in the xylem, including spatial patterns of embolism spread between conduits (Brodersen et al., 2013; Dalla-Salda et al., 2014).However, noninvasive imaging techniques have seldom been used to validate indirect or invasive techniques used to estimate cavitation resistance. At this stage, only a handful of studies have utilized imaging technology to measure cavitation resistance in trees (Torres-Ruiz et al., 2014; Cochard et al., 2015), and these studies employed a destructive mode of the technique in which small branches were cut off the plant before scanning took place. Thus far, noninvasive imaging on intact plants has only been used to measure cavitation resistance in two species, grapevine (Vitis vinifera; Choat et al., 2010; Brodersen et al., 2013) and Sequoia sempervirens (Choat et al., 2015). Further measurement of cavitation resistance using noninvasive imaging on intact plants across a range of species, therefore, is a high priority.These comparisons are particularly important because of the current debate surrounding the invasive techniques (Cochard et al., 2013). Specifically, evidence from a variety of experiments suggests that centrifuge and air injection techniques underestimate cavitation resistance in species with long xylem vessels (Choat et al., 2010; Cochard et al., 2010; Ennajeh et al., 2011; Martin-StPaul et al., 2014; Torres-Ruiz et al., 2014; Wang et al., 2014). This artifact occurs when samples placed into centrifuge rotors or air injection collars have a large proportion of vessels that are cut open at both ends of the segment. A number of studies have disputed this open-vessel hypothesis and suggested that some versions of the centrifuge and air injection techniques provide reliable estimates of cavitation resistance (Jacobsen and Pratt, 2012; Sperry et al., 2012; Tobin et al., 2013). Because there will always be uncertainties associated with indirect measurements, noninvasive imaging using intact plants provides the best option for resolving these methodological issues.In this study, synchrotron-based microCT was utilized to investigate the formation of drought-induced embolism in the xylem of intact, potted plants. Three species were selected to provide a range of contrasting xylem structures: Quercus robur (ring porous), Populus tremula × Populus alba (diffuse porous), and Pinus pinaster (tracheid bearing). Visualizations of xylem embolism in the stems of these species during a sequence of natural dehydration were used to construct embolism vulnerability curves. We hypothesized that (1) vulnerability curves based on microCT observations would match vulnerability curves based on the centrifuge technique for species with short vessels (P. tremula × P. alba) or tracheid-based xylem (P. pinaster) and (2) the centrifuge technique would overestimate vulnerability to embolism in the long-vesseled species (Q. robur) due to the open-vessel artifact.     

Herbaceous Angiosperms Are Not More Vulnerable to Drought-Induced Embolism Than Angiosperm Trees

The water transport pipeline in herbs is assumed to be more vulnerable to drought than in trees due to the formation of frequent embolisms (gas bubbles), which could be removed by the occurrence of root pressure, especially in grasses. Here, we studied hydraulic failure in herbaceous angiosperms by measuring the pressure inducing 50% loss of hydraulic conductance (P₅₀) in stems of 26 species, mainly European grasses (Poaceae). Our measurements show a large range in P₅₀ from −0.5 to −7.5 MPa, which overlaps with 94% of the woody angiosperm species in a worldwide, published data set and which strongly correlates with an aridity index. Moreover, the P₅₀ values obtained were substantially more negative than the midday water potentials for five grass species monitored throughout the entire growing season, suggesting that embolism formation and repair are not routine and mainly occur under water deficits. These results show that both herbs and trees share the ability to withstand very negative water potentials without considerable embolism formation in their xylem conduits during drought stress. In addition, structure-function trade-offs in grass stems reveal that more resistant species are more lignified, which was confirmed for herbaceous and closely related woody species of the daisy group (Asteraceae). Our findings could imply that herbs with more lignified stems will become more abundant in future grasslands under more frequent and severe droughts, potentially resulting in lower forage digestibility.Terrestrial biomes provide numerous ecosystem services to humans, such as biodiversity refuges, forage supply, carbon sequestration, and associated atmospheric feedback (Bonan, 2008). Drought frequency and severity are predicted to increase across various ecosystems (Dai, 2013), and its impact on the fate of terrestrial biomes has aroused great concern for stakeholders over the past decade. For instance, worldwide forest declines have been associated with drought events (Allen et al., 2010), and the sustainability of grasslands, one of the most important agro-ecosystems representing 26% of the world land area, is threatened due to increasing aridity in the light of climate change (Tubiello et al., 2007; Brookshire and Weaver, 2015). Since the maintenance of grasslands is of prime importance for livestock, and several of the most valuable crops are grasses, herbaceous species deserve more attention from a hydraulic point of view to understand how they will cope with shifts in precipitation and temperature patterns.During water deficit, hydraulic failure in trees has been put forward as one of the primary causes of forest decline (Anderegg et al., 2015, 2016). Drought exacerbates the negative pressure inside the water conducting cells, making the liquid xylem sap more metastable, and thus more vulnerable, to air entry (i.e. gas embolism; Lens et al., 2013a). Extensive levels of embolisms may lead to desiccation, leaf mortality, branch sacrifice, and ultimately plant death (Barigah et al., 2013; Urli et al., 2013). Plant resistance to embolism is therefore assumed to represent a key parameter in determining the drought tolerance of trees and is estimated using so-called vulnerability curves (VCs), from which the P₅₀, i.e. the sap pressure inducing 50% loss of hydraulic conductivity, can be estimated (Cochard et al., 2013). P₅₀ values are therefore good proxies for drought stress tolerance in woody plants and have been published for hundreds of angiosperm and gymnosperm tree species (Delzon et al., 2010; Choat et al., 2012), illustrating a wide range from −0.5 to −19 MPa (Larter et al., 2015).Studies focusing on P₅₀ values of herbs are limited to stems of ∼14 angiosperm species (see Supplemental Table S1 and references cited therein). Half of the herbaceous angiosperms studied so far (Supplemental Table S1) have a stem P₅₀ between 0 and −2 MPa, indicating that many herbs are highly vulnerable to embolism. Moreover, positive root pressure has been reported in various herbs, including many grasses (Poaceae) with hydathodes in their leaves (Evert, 2006), and root pressure is hypothesized to refill embolized conduits overnight when transpiration is low (Miller, 1985; Neufeld et al., 1992; Cochard et al., 1994; Macduff and Bakken, 2003; Saha et al., 2009; Cao et al., 2012). This could suggest that embolism formation and repair follow a daily cycle in herbs. In other words, the midday water potential that herbs experience in the field may often be more negative than P₅₀, which would result in an extremely vulnerable hydraulic pipeline characterized by a negative hydraulic safety margin (expressed as the minimum midday water potential minus P₅₀). In contrast to herbs, most trees operate at a slightly positive hydraulic safety margin (Choat et al., 2012), and woody plants are often too tall to allow refilling by positive root and/or stem pressure in the upper stems (Ewers et al., 1997; Fisher et al., 1997). Therefore, it could be postulated that herbaceous species possess a hydraulic system that is more vulnerable to embolism than that of woody species. In this study, we want to underpin possible differences in embolism resistance between stems of herbaceous and woody angiosperms.The scarcity of P₅₀ measures in herbaceous angiosperms, including grasses and herbaceous eudicots, is mainly due to their fragile stems and low hydraulic conductivity, making VCs technically more challenging. Using minor adaptations to existing centrifuge techniques (Supplemental Text S1), we obtained a P₅₀ stem data set of 26 herbaceous angiosperm species (mainly grasses) from various collection sites in France and Switzerland. In addition, we compared our data set with published data from woody (gymnosperm and angiosperm) species, confronted some of our herbaceous eudicot measurements with original P₅₀ data from derived, woody relatives, and performed anatomical observations in grasses to investigate a possible link between stem anatomical characters and differences in P₅₀ among the species studied. Three main research questions are central in our article: (1) Are stems of herbaceous angiosperms more vulnerable to embolism than those of woody angiosperms? (2) Do grasses operate with highly vulnerable, negative hydraulic safety margins? (3) Do grasses show structure-function trade-offs in their stems with respect to embolism resistance?     

Allometry in Anisian (Middle Triassic) segminiplanate conodonts and its implications for conodont taxonomy

Conodonts are a clade of chordates and are valuable indicator fossils for biostratigraphy. The segminiplanate (neogondolelliform) conodonts represent a major morphological group ranging from upper Carboniferous to Upper Triassic marine sediments. However, the morphological similarity of segminiplanate P₁ elements generates problems for taxonomy, especially in the Permian and Triassic clades. This paper represents the first study of morphological variation in Triassic segminiplanate conodonts using a geometric morphometric approach. The laminar microstructures observed in conodont cross‐sections indicate that, within our analysed specimens, smaller conodonts with fewer laminae are generally from an earlier ontogenetic stage while larger conodonts with more laminae are from a later stage of ontogeny. Using linear regressions between relative warp scores from both upper and lateral views and conodont length, we demonstrate strongly allometric growth patterns for the species Paragondolella bifurcata Budurov & Stefanov. Our results indicate that the species‐group taxon Pg. praeszaboi bystrickyi (Kovacs et al.) is an early growth stage of Pg. bifurcata and thus synonymous. We suggest that the allometry of conodonts should be considered seriously, especially when there are numerous transitional morphologies between large‐ and small‐sized conodonts. Reconstructing the ontogenetic series and using larger‐sized conodonts within the numerous transitional morphologies in the population of a rock sample for the definition of new species are suggested for future studies.     

Old and unmowed saltmarsh patches provide attractive habitats for breeding passerines

Although the conservation stakes of saltmarshes are widely documented, these areas are still subjected to strong anthropic pressures, including land reclamation, leading to their conversion into arable lands, and agricultural exploitation (mainly cattle grazing and mowing), which modifies their floral and faunal composition. Through the example of one of the largest French saltmarshes, we first assessed how the age of the saltmarsh patches and the mowing intensity determined the spatial distribution of the different saltmarsh habitats. We then tested how the five commonest breeding passerines were distributed in accordance with the mowing activity and the distribution of these habitats. We found that the oldest and the unmowed patches promote the development of habitats dominated by Elymus pungens and Atriplex portulacoides, and also host the highest abundance of four of the five bird species studied. In the current context of an intense artificialization of the littoral area, this study highlights the importance of maintaining the oldest and the least human-impacted patches of natural habitats to conserve their associated biodiversity.