Trees as Islands: Canopy Ant Species Richness Increases with the Size of Liana-Free Trees in a Neotropical Forest

The physical characteristics of habitats shape local community structure; a classic example is the positive relationship between the size of insular habitats and species richness. Despite the high density and proximity of tree crowns in forests, trees are insular habitats for some taxa. Specifically, crown isolation (i.e. crown shyness) prevents the movement of small cursorial animals among trees. Here, we tested the hypothesis that the species richness of ants (Sa) in individual, isolated trees embedded within tropical forest canopies increases with tree size. We predicted that this pattern disappears when trees are connected by lianas (woody vines) or when strong interactions among ant species determine tree occupancy. We surveyed the resident ants of 213 tree crowns in lowland tropical forest of Panama. On average, 9.2 (range = 2–20) ant species occupied a single tree crown. Average (± SE) Sa was ca 25% higher in trees with lianas (10.2 ± 0.26) than trees lacking lianas (8.0 ± 0.51). Sa increased with tree size in liana‐free trees (Sa = 10.99A0.256), but not in trees with lianas. Ant species composition also differed between trees with and without lianas. Specifically, ant species with solitary foragers occurred more frequently in trees with lianas. The mosaic‐like pattern of species co‐occurrence observed in other arboreal ant communities was not found in this forest. Collectively, the results of this study indicate that lianas play an important role in shaping the local community structure of arboreal ants by overcoming the insular nature of tree crowns

Ultrafast Light-Induced Lifshitz Transition

Fermi surface is at the heart of our understanding of metals and strongly correlated many-body systems. An abrupt change in the Fermi surface topology, also called Lifshitz transition, can lead to the emergence of fascinating phenomena like colossal magnetoresistance and superconductivity. While Lifshitz transitions have been demonstrated for a broad range of materials and using different types of static external perturbations such as strain, doping, pressure and temperature, a non-equilibrium route toward ultrafast and transient modification of the Fermi surface topology has not been experimentally demonstrated. Combining time-resolved multidimensional photoemission spectroscopy with state-of-the-art TDDFT+U simulations, we introduce a scheme for driving an ultrafast Lifshitz transition in the correlated Weyl semimetal Td-MoTe2. We demonstrate that this non-equilibrium topological electronic transition finds its microscopic origin in the dynamical modification of the effective electronic correlations. These results shed light on a novel ultrafast and all-optical scheme for controlling the Fermi surface topology in correlated quantum materials

Optically-Induced Symmetry Breaking via Nonlinear Phononics

Optical nonlinearities in solids reveal information about both the in-plane rotational and out-of-plane inversion symmetries of a crystal. In the van der Waals material hexagonal boron nitride (hBN) both these symmetries and the linear vibrational properties have led to the rich physics of mid-infrared phonon-polaritons. However, the role of strong electron-phonon nonlinearities requires further study. In this work, we investigate both theoretically and experimentally the rich interplay of phonon anharmonicity and symmetry in phonon-polariton mediated nonlinear optics. We show that large enhancements (>30x) of third-harmonic generation occur for incident femtosecond pulses that are resonant with the hBN transverse optical phonons. In addition, we predict and observe large transient sub-picosecond duration second-harmonic signals during resonant excitation, which in equilibrium is forbidden by symmetry. This surprising result indicates that instantaneous crystal inversion symmetry breaking can be optically induced and controlled via phonon interactions by both the power and polarization of the pump laser

Linajes mitocondriales amerindios en una muestra poblacional de la Región Metropolitana de Buenos Aires

En trabajos previos se evaluó el aporte aborígen, utilizando marcadores genéticos proteicos, en la Región Metropolitana de Buenos Aires. En este estudio nos proponemos estimar el grado de contribución de los linajes maternos amerindios mediante el análisis del ADNmt (haplogrupos A, B, C y D) en individuos que residen en esa región. Las muestras provienen de dadores del Hospital Italiano de Buenos Aires. El ADN extraído se amplificó mediante la técnica de PCR y luego se realizó la digestión enzimática para caracterizar los distintos haplogrupos: HaeIII para ganancia de un sitio en 663 (A), Hinc II, pérdida de un sitio en posición 13259 (C) y pérdida de un sitio Alu I en 5176 (D), y la deleción de 9pb típica del haplogrupo B de la región V. El 50% (25/50) de las muestras estudiadas fueron de origen amerindio, detectándose un 28% de A, 16% de B, 44% de C y 12% de D. Los resultados obtenidos indican alta participación de linajes maternos amerindios en la muestra estudiada que se corresponden con los datos genealógicos relevados.Asociación de Antropología Biológica de la República Argentin

Exploring the challenges faced by frontline workers in health and social care amid the COVID-19 pandemic: experiences of frontline workers in the English Midlands region, UK

The first cases of Coronavirus (COVID-19) were reported in Wuhan, China in December 2019. Globally millions of people have been diagnosed with the virus whilst thousands have died. As the virus kept spreading health and social care frontline workers (HSCFW) were faced with difficulties when discharging their duties. This paper was set out to explore the challenges faced by different frontline workers in health and social care during the COVID-19 pandemic. The research utilized an explorative qualitative approach. A total of forty (N = 40) in-depth one-to-one semi-structured interviews were undertaken with HSCFW who included support workers (n = 15), nurses (n = 15), and managers (N = 10). Health and social care workers were drawn from domiciliary care and care homes (with and without nursing services). All the interviews were done online. The data were thematically analyzed, and the emergent themes were supported by quotes from the interviews held with participants. Following data analysis the research study found that lack of pandemic preparedness, shortage of Personal Protective Equipment (PPE), anxiety and fear amongst professionals, challenges in enforcing social distancing, challenges in fulfilling social shielding responsibility, anxiety and fear amongst residents and service users, delay in testing, evolving PPE guidance and shortage of staff were challenges faced by frontline health and social care workers during COVID-19 pandemic. The results of the current study point to a need for adequate pandemic preparedness within the health and social care sector to protect both frontline workers and the individuals they look after

Enhanced tunable second harmonic generation from twistable interfaces and vertical superlattices in boron nitride homostructures

Broken symmetries induce strong even-order nonlinear optical responses in materials and at interfaces. Unlike conventional covalently bonded nonlinear crystals, van der Waals (vdW) heterostructures feature layers that can be stacked at arbitrary angles, giving complete control over the presence or lack of inversion symmetry at a crystal interface. Here, we report highly tunable second harmonic generation (SHG) from nanomechanically rotatable stacks of bulk hexagonal boron nitride (BN) crystals and introduce the term twistoptics to describe studies of optical properties in twistable vdW systems. By suppressing residual bulk effects, we observe SHG intensity modulated by a factor of more than 50, and polarization patterns determined by moiré interface symmetry. Last, we demonstrate greatly enhanced conversion efficiency in vdW vertical superlattice structures with multiple symmetry-broken interfaces. Our study paves the way for compact twistoptics architectures aimed at efficient tunable frequency conversion and demonstrates SHG as a robust probe of buried vdW interfaces

Spatial Distribution of Dominant Arboreal Ants in a Malagasy Coastal Rainforest: Gaps and Presence of an Invasive Species

We conducted a survey along three belt transects located at increasing distances from the coast to determine whether a non-random arboreal ant assemblage, such as an ant mosaic, exists in the rainforest on the Masoala Peninsula, Madagascar. In most tropical rainforests, very populous colonies of territorially dominant arboreal ant species defend absolute territories distributed in a mosaic pattern. Among the 29 ant species recorded, only nine had colonies large enough to be considered potentially territorially dominant; the remaining species had smaller colonies and were considered non-dominant. Nevertheless, the null-model analyses used to examine the spatial structure of their assemblages did not reveal the existence of an ant mosaic. Inland, up to 44% of the trees were devoid of dominant arboreal ants, something not reported in other studies. While two Crematogaster species were not associated with one another, Brachymyrmex cordemoyi was positively associated with Technomyrmex albipes, which is considered an invasive species—a non-indigenous species that has an adverse ecological effect on the habitats it invades. The latter two species and Crematogaster ranavalonae were mutually exclusive. On the other hand, all of the trees in the coastal transect and at least 4 km of coast were occupied by T. albipes, and were interconnected by columns of workers. Technomyrmex albipes workers collected from different trees did not attack each other during confrontation tests, indicating that this species has formed a supercolony along the coast. Yet interspecific aggressiveness did occur between T. albipes and Crematogaster ranavalonae, a native species which is likely territorially dominant based on our intraspecific confrontation tests. These results suggest that the Masoala rainforest is threatened by a potential invasion by T. albipes, and that the penetration of this species further inland might be facilitated by the low density of native, territorially dominant arboreal ants normally able to limit its progression

Towards Electrical, Integrated Implementations of SIMPL Systems

International audienceThis paper discusses strategies for the electrical, integrated implementation of a novel security tool termed SIMPL system, which was introduced in [1]. SIMPL systems are a public key version of Physical Unclonable Functions (PUFs). Like a PUF, each SIMPL system S is physically unique and non-reproducible, and implements an individual function FS. In opposition to a PUF, every SIMPL system S possesses a publicly known numerical description D(S), which allows its digital simulation and prediction. However, any such simulation must work at a detectably lower speed than the real-time behavior of S. As argued in [1], SIMPL systems have practicality and security advantages over PUFs, Certificates of Authenticity (COAs), Physically Obfuscated Keys (POKs), and also over standard mathematical cryptotechniques. This manuscript focuses on electrical, integrated realizations of SIMPL systems, and proposes two potential candidates: SIMPL systems derived from special SRAM-architectures (so-called "skew designs" of SRAM cells), and implementations based on analog computing arrays called Cellular Non-Linear Networks (CNNs)

Climate Change Impact on Neotropical Social Wasps

Establishing a direct link between climate change and fluctuations in animal populations through long-term monitoring is difficult given the paucity of baseline data. We hypothesized that social wasps are sensitive to climatic variations, and thus studied the impact of ENSO events on social wasp populations in French Guiana. We noted that during the 2000 La Niña year there was a 77.1% decrease in their nest abundance along ca. 5 km of forest edges, and that 70.5% of the species were no longer present. Two simultaneous 13-year surveys (1997–2009) confirmed the decrease in social wasps during La Niña years (2000 and 2006), while an increase occurred during the 2009 El Niño year. A 30-year weather survey showed that these phenomena corresponded to particularly high levels of rainfall, and that temperature, humidity and global solar radiation were correlated with rainfall. Using the Self-Organizing Map algorithm, we show that heavy rainfall during an entire rainy season has a negative impact on social wasps. Strong contrasts in rainfall between the dry season and the short rainy season exacerbate this effect. Social wasp populations never recovered to their pre-2000 levels. This is probably because these conditions occurred over four years; heavy rainfall during the major rainy seasons during four other years also had a detrimental effect. On the contrary, low levels of rainfall during the major rainy season in 2009 spurred an increase in social wasp populations. We conclude that recent climatic changes have likely resulted in fewer social wasp colonies because they have lowered the wasps' resistance to parasitoids and pathogens. These results imply that Neotropical social wasps can be regarded as bio-indicators because they highlight the impact of climatic changes not yet perceptible in plants and other animals