Effect of spin-orbit coupling on the high harmonics from the topological Dirac semimetal Na3Bi

In this work, we performed extensive first-principles simulations of high-harmonic generation in the topological Diract semimetal Na3Bi using a time-dependent density functional theory framework, focusing on the effect of spin-orbit coupling (SOC) on the harmonic response. We also derived a general analytical model describing the microscopic mechanism of strong-field dynamics in presence of spin-orbit coupling, starting from a locally U(1)xSU(2) gauge-invariant Hamiltonian. Our results reveal that SOC: (i) affects the strong-field ionization by modifying the bandstructure of Na3Bi, (ii) modifies the electron velocity, making each spin channel to react differently to the pump laser field, (iii) changes the emission timing of the emitted harmonics. Moreover, we show that the SOC affects the harmonic emission by directly coupling the charge current to the spin currents, paving the way to the high-harmonic spectroscopy of spin currents in solids

Dynamics of the association between a long-lived understory myrmecophyte and its specific associated ants

Myrmecophytic symbioses are widespread in tropical ecosystems and their diversity makes them useful tools for understanding the origin and evolution of mutualisms. Obligate ant–plants, or myrmecophytes, provide a nesting place, and, often, food to a limited number of plant–ant species. In exchange, plant–ants protect their host plants from herbivores, competitors and pathogens, and can provide them with nutrients

Repetitions in infinite palindrome-rich words

Rich words are characterized by containing the maximum possible number of distinct palindromes. Several characteristic properties of rich words have been studied; yet the analysis of repetitions in rich words still involves some interesting open problems. We address lower bounds on the repetition threshold of infinite rich words over 2 and 3-letter alphabets, and construct a candidate infinite rich word over the alphabet $\Sigma_2=\{0,1\}$ with a small critical exponent of $2+\sqrt{2}/2$. This represents the first progress on an open problem of Vesti from 2017.Comment: 12 page

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

Detection of Mitochondrial COII DNA Sequences in Ant Guts as a Method for Assessing Termite Predation by Ants

Termites and ants contribute more to animal biomass in tropical rain forests than any other single group and perform vital ecosystem functions. Although ants prey on termites, at the community level the linkage between these groups is poorly understood. Thus, assessing the distribution and specificity of ant termitophagy is of considerable interest.We describe an approach for quantifying ant-termite food webs by sequencing termite DNA (cytochrome c oxidase subunit II, COII) from ant guts and apply this to a soil-dwelling ant community from tropical rain forest in Gabon. We extracted DNA from 215 ants from 15 species. Of these, 17.2% of individuals had termite DNA in their guts, with BLAST analysis confirming the identity of 34.1% of these termites to family level or better. Although ant species varied in detection of termite DNA, ranging from 63% (5/7; Camponotus sp. 1) to 0% (0/7; Ponera sp. 1), there was no evidence (with small sample sizes) for heterogeneity in termite consumption across ant taxa, and no evidence for species-specific ant-termite predation. In all three ant species with identifiable termite DNA in multiple individuals, multiple termite species were represented. Furthermore, the two termite species that were detected on multiple occasions in ant guts were in both cases found in multiple ant species, suggesting that anttermite food webs are not strongly compartmentalised. However, two ant species were found to consume only Anoplotermes-group termites, indicating possible predatory specialisation at a higher taxonomic level. Using a laboratory feeding test, we were able to detect termite COII sequences in ant guts up to 2 h after feeding, indicating that our method only detects recent feeding events. Our data provide tentative support for the hypothesis that unspecialised termite predation by ants is widespread and highlight the use of molecular approaches for future studies of ant-termite food webs

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

An unanticipated tumor-suppressive role of the SUMO pathway in the intestine unveiled by Ubc9 haploinsufficiency

Sumoylation is an essential posttranslational modification in eukaryotes that has emerged as an important pathway in oncogenic processes. Most human cancers display hyperactivated sumoylation and many cancer cells are remarkably sensitive to its inhibition, thus supporting application of chemical sumoylation inhibitors in cancer treatment. Here we show, first, that transformed embryonic fibroblasts derived from mice haploinsufficient for Ubc9, the essential and unique gene encoding the SUMO E2 conjugating enzyme, exhibit enhanced proliferation and transformed phenotypes in vitro and as xenografts ex vivo. To then evaluate the possible impact of loss of one Ubc9 allele in vivo, we used a mouse model of intestinal tumorigenesis. We crossed Ubc9+/− mice with mice harboring a conditional ablation of Apc either all along the crypt–villus axis or only in Lgr5+ crypt-based columnar (CBC) cells, the cell compartment that includes the intestinal stem cells proposed as cells-of-origin of intestinal cancer. While Ubc9+/− mice display no overt phenotypes and no globally visible hyposumoylation in cells of the small intestine, we found, strikingly, that, upon loss of Apc in both models, Ubc9+/− mice develop more (>2-fold) intestinal adenomas and show significantly shortened survival. This is accompanied by reduced global sumoylation levels in the polyps, indicating that Ubc9 levels become critical upon oncogenic stress. Moreover, we found that, in normal conditions, Ubc9+/− mice show a moderate but robust (15%) increase in the number of Lgr5+ CBC cells when compared to their wild-type littermates, and further, that these cells display higher degree of stemness and cancerrelated and inflammatory gene expression signatures that, altogether, may contribute to enhanced intestinal tumorigenesis. The phenotypes of Ubc9 haploinsufficiency discovered here indicate an unanticipated tumor-suppressive role of sumoylation, one that may have important implications for optimal use of sumoylation inhibitors in the clini

Linajes mitocondriales en muestras de Esquina de Huajra (Jujuy, Argentina) : Aportes al estudio de la ocupación incaica en la región y la procedencia de sus habitantes

El sitio arqueológico Esquina de Huajra (centrosur de la Quebrada de Humahuaca) corresponde a una instalación ubicada cronológicamente en la Fase Inca (ca. 500-420 AP) y la tradicionalmente asignada en el noroeste argentino como Hispano Indígena o de primeros contactos con el español (ca. 420-320 AP). Enmarcado en la política económica incaica, habría sido clave en la explotación y distribución de bienes procedentes de las Yungas Orientales. Además, su cultura material sugiere importantes redes de interacción con las tierras altas, planteando interrogantes sobre la conformación poblacional de sus habitantes.En este trabajo se analizan los linajes maternos de individuos de Esquina de Huajra en comparación con otros sitios del centro-sur andino para evaluar su posible origen foráneo, considerando que el reasentamiento de poblaciones fue una práctica imperial recurrente. El ADN fue extraído de piezas dentales de 6 individuos. Se secuenció la Región Hipervariable I del ADN mitocondrial en cuatro individuos hallándose dos A2 y dos C1. La ausencia de B2 discrepa con lo descripto para gran parte de los sitios andinos, donde este haplogrupo es mayoritario. Dos de los cuatro haplotipos se comparten únicamente con otros sitios de la Quebrada de Humahuaca del Período de Desarrollos Regionales (Los Amarillos y San José); pero una variante nodal C1 fue reportada tanto en Juella como en sitios peruanos preincaicos e incaicos. Estos resultados representan un primer aporte al estudio genético de los habitantes de Esquina de Huajra y una evidencia más de los complejos procesos poblacionales en la región andina.The archaeological site Esquina de Huajra (south-central area of the Quebrada de Humahuaca) is a location chronologically assigned to the Inca phase (ca. 500-420 AP) and to the Hispanic-indigenous phase or initial period of contact with the Spanish (ca. 420-320 AP). In the context of the Incaic economic system, Esquina de Huajra may have been a key settlement in the exploitation and distribution of goods from the eastern forests (Yungas). In addition, its material culture suggests major interaction networks with the highlands, raising questions about its inhabitants’ origin. In this work maternal lineages of individuals from Esquina de Huajra were analyzed in comparison to other sites in southcentral Andes to assess possible foreign origins, considering that population resettlement under Inca dominion was a common practice. DNA was extracted from the teeth of six individuals and mitochondrial hypervariable region I (HVRI) was successfully sequenced in four samples, resulting in two of them assigned to lineage A2 and the other two to C1. Absence of B2 disagrees with data from most Andean sites, where this lineage is the most frequent. Two of the four haplotypes are only shared with individuals from other sites located in Quebrada de Humahuaca (Los Amarillos and San Jose), and a nodal C1 variant was reported in samples from Juella and several pre-Inca and Inca Peruvian sites. These results represent the first contribution to genetic studies on the population of Esquina de Huajra and are also further evidence of the complex population processes in the Andean region.Asociación de Antropología Biológica de la República Argentina (AABRA