Tuning the metamagnetism of an antiferromagnetic metal

We describe a `disordered local moment' (DLM) first-principles electronic structure theory which demonstrates that tricritical metamagnetism can arise in an antiferromagnetic metal due to the dependence of local moment interactions on the magnetisation state. Itinerant electrons can therefore play a defining role in metamagnetism in the absence of large magnetic anisotropy. Our model is used to accurately predict the temperature dependence of the metamagnetic critical fields in CoMnSi-based alloys, explaining the sensitivity of metamagnetism to Mn-Mn separations and compositional variations found previously. We thus provide a finite-temperature framework for modelling and predicting new metamagnets of interest in applications such as magnetic cooling

Metabolism And The Rise Of Fungus Cultivation By Ants

Most ant colonies are comprised of workers that cooperate to harvest resources and feed developing larvae. Around 50 million years ago (MYA), ants of the attine lineage adopted an alternative strategy, harvesting resources used as compost to produce fungal gardens. While fungus cultivation is considered a major breakthrough in ant evolution, the associated ecological consequences remain poorly understood. Here, we compare the energetics of attine colony-farms and ancestral hunter-gatherer colonies using metabolic scaling principles within a phylogenetic context. We find two major energetic transitions. First, the earliest lower-attine farmers transitioned to lower mass-specific metabolic rates while shifting significant fractions of biomass from ant tissue to fungus gardens. Second, a transition 20 MYA to specialized cultivars in the higher-attine clade was associated with increased colony metabolism (without changes in garden fungal content) and with metabolic scaling nearly identical to hypometry observed in hunter-gatherer ants, although only the hunter-gatherer slope was distinguishable from isometry. Based on these evolutionary transitions, we propose that shifting living-tissue storage from ants to fungal mutualists provided energetic storage advantages contributing to attine diversification and outline critical assumptions that, when tested, will help link metabolism, farming efficiency, and colony fitness.Integrative Biolog

Sistema de recomendações de fertilizantes para o coqueiro (Cocos nucifera L.) com base na análise foliar.

Base de utilização da análise foliar para recomendar fertilizantes, nível critico, interações, amostragem das folhas para análises, base teórica da amostragem, limitações práticas, folha a ser amostrada, filotaxia do coqueiro, métodos práticos para reconhecimento da folha a ser mostrada, coleta, identificação e preparação da amostra, métodos a serem utilizados na análise, fatores envolvidos na iterpretação dos resultados.bitstream/item/44715/1/CPATC-DOCUMENTOS-7-SISTEMA-DE-RECOMENDACOES-DE-FERTILIZANTES-PARA-O-COQUEIRO-COCOS-NUCIFERA-L-COM.pd

Laser cooling of a trapped two-component Fermi gas

The collective Raman cooling of a trapped two-component Fermi gas is analyzed. We develop the quantum master equation that describes the collisions and the laser cooling, in the festina lente regime, where the heating due to photon reabsorption can be neglected. The numerical results based on Monte Carlo simulations show, that three-dimensional temperatures of the order of 0.008 T_F can be achieved. We analyze the heating related to the background losses, and conclude that our laser-cooling scheme can maintain the temperature of the gas without significant additional losses. Finally we derive an analytic expression for the temperature of a trapped Fermi gas heated by background collisions, that agrees very well with the data obtained from the numerical simulation.Comment: 5 pages, 3 figure

Two-dimensional conical dispersion in ZrTe5 evidenced by optical spectroscopy

Zirconium pentatelluride was recently reported to be a 3D Dirac semimetal, with a single conical band, located at the center of the Brillouin zone. The cone's lack of protection by the lattice symmetry immediately sparked vast discussions about the size and topological/trivial nature of a possible gap opening. Here we report on a combined optical and transport study of ZrTe5, which reveals an alternative view of electronic bands in this material. We conclude that the dispersion is approximately linear only in the a-c plane, while remaining relatively flat and parabolic in the third direction (along the b axis). Therefore, the electronic states in ZrTe5 cannot be described using the model of 3D Dirac massless electrons, even when staying at energies well above the band gap 6 meV found in our experiments at low temperatures.Comment: Physical Review Letters 122, 217402 (2019). Corrected acknowledgment

Decoherence induced spontaneous symmetry breaking

We study time dependence of exchange symmetry properties of Bell states when two qubits interact with local baths having identical parameters. In case of classical noise, we consider a decoherence Hamiltonian which is invariant under swapping the first and second qubits. We find that as the system evolves in time, two of the three symmetric Bell states preserve their qubit exchange symmetry with unit probability, whereas the symmetry of the remaining state survives with a maximum probability of 0.5 at the asymptotic limit. Next, we examine the exchange symmetry properties of the same states under local, quantum mechanical noise which is modeled by two identical spin baths. Results turn out to be very similar to the classical case. We identify decoherence as the main mechanism leading to breaking of qubit exchange symmetry.Comment: 12 page

Counting Majorana zero modes in superconductors

A counting formula for computing the number of (Majorana) zero modes bound to topological point defects is evaluated in a gradient expansion for systems with charge-conjugation symmetry. This semi-classical counting of zero modes is applied to some examples that include graphene and a chiral p-wave superconductor in two-dimensional space. In all cases, we explicitly relate the counting of zero modes to Chern numbers.Comment: 21 pages, 3 figure

Efeito de jenipapo sobre o crescimento micelial do agente causal da Sigatoka amarela da bananeira.

A Sigatoka amarela da bananeira, causada por Mycosphaerella musicola / Pseudocercospora musae, é um dos mais graves problemas da bananicultura brasileira, provocando severas perdas na produção. O manejo convencional da doença requer a aplicação de fungicidas, ação incompatível com as normas do sistema de produção orgânica. A busca de alternativas de controle que sejam passíveis de uso na produção orgânica de banana passou a ser uma ação necessária, para viabilização desse sistema. Assim, neste trabalho, o objetivo foi avaliar o efeito do suco de jenipapo (Genipa americana) sobre o crescimento de M. musicola em meio de cultura. O teste foi realizado mediante adição, ao meio de cultura BDA, do suco do genipapo em diferentes concentrações: testemunha (0%); 2%; 4%; B%; 16% e 32% de suco, em substituição ao volume de água. O fungo foi inoculado ao meio via suspensão de fragmentos de micélio, seguindo-se a incubação a 25°C e luz constante por 10 dias. Os resultados demonstraram que o produto paralisou totalmente o crescimento de M. musicola a partir da concentração de 16%, demonstrando alto potencial para utilização no controle da Sigatoka amarela