Dirac points merging and wandering in a model Chern insulator

We present a model for a Chern insulator on the square lattice with complex first and second neighbor hoppings and a sublattice potential which displays an unexpectedly rich physics. Similarly to the celebrated Haldane model, the proposed Chern insulator has two topologically non-trivial phases with Chern numbers $\pm1$. As a distinctive feature of the present model, phase transitions are associated to Dirac points that can move, merge and split in momentum space, at odds with Haldane's Chern insulator where Dirac points are bound to the corners of the hexagonal Brillouin zone. Additionally, the obtained phase diagram reveals a peculiar phase transition line between two distinct topological phases, in contrast to the Haldane model where such transition is reduced to a point with zero sublattice potential. The model is amenable to be simulated in optical lattices, facilitating the study of phase transitions between two distinct topological phases and the experimental analysis of Dirac points merging and wandering

Efficiency wage and union effects in labor demand and wage structure in Mexico - An application of quantile analysis

Applying quantile analysis to detailed firm-level data from Mexico, the authors study determinants of demand and wages for two classes of labor. Unions appear to have a strong impact on how much unskilled labor is employed but not on wages. This suggests an extreme example of"monopoly union"behavior. The impact on productivity is, by definition, negative, but unions could also be said to be forcing firms to use"appropriate technology"(less capital and more workers), increasing the total amount of labor employed in the economy. The only impact on wages appears for the tenth (lowest) quantile of unskilled workers, suggesting that unions prevent workers from being paid too far below the median for their skill level. The authors identify significant efficiency wage effects where firms pay above market clearing to prevent labor turnover both in labor demand and in the wage equations. Since minimum wages are not binding and the union impact on wages is small, this suggests that whatever segmentation exists emerges endogenously and is not due to union - or government - induced distortions. The authors offer the first use of quantile analysis to analyze labor demand at the firm level, and one of the first uses of correct standard errors in two-stage least-squares quantile regression.Labor Policies,Banks&Banking Reform,Public Health Promotion,Environmental Economics&Policies,Economic Theory&Research,Labor Management and Relations,Health Monitoring&Evaluation,Economic Theory&Research,Banks&Banking Reform,Environmental Economics&Policies

The strong global dimension of piecewise hereditary algebras

Let T be a tilting object in a triangulated category equivalent to the bounded derived category of a hereditary abelian category with finite dimensional homomorphism spaces and split idempotents. This text investigates the strong global dimension, in the sense of Ringel, of the endomorphism algebra of T. This invariant is expressed using the infimum of the lengths of the sequences of tilting objects successively related by tilting mutations and where the last term is T and the endomorphism algebra of the first term is quasi-tilted. It is also expressed in terms of the hereditary abelian generating subcategories of the triangulated category.Comment: Final published version. After refereeing, historical considerations were added and the length of the article was reduced: Introduction and Section 1 were reformulated; Subsection 2.1 was moved to Section 1 (with an abridged proof); Subsection 3.2 was reformulated (with an abridged proof); The proof in A.5 was rewritten (now shorter); And minor rewording was processed throughout the articl

Molecular modeling of drug delivery systems based on carbon nanostructures: structure, function, and potential applications for anticancer complexes of Pt(II)

The medication with Pt(II) drugs (cisplatin, carboplatin, and oxaliplatin) has been an effective alternative for treating cancers due to their notable inhibition of cancer cells growth and the prevention of metastasis. Nevertheless, the low selectivity of these metallodrugs for malignant cells produces severe side effects, which limit this chemotherapy. In this context, carbon nanohorns (CNHs) have been considered potential nanovectors for drugs, since they present low toxicity, drug-loading capacity, biodegradation routes, and biocompatibility when oxidized. However, there is still a lack of studies regarding the molecular behavior of these nanocarriers on cell membranes. The present work aims to characterize the interactions between inclusion complexes drug@CNH, which are formed by platinum drugs encapsulated in CNHs, and plasma membranes by using molecular dynamics simulations. The results demonstrated that the van der Waals contribution played a primary role (∼74%) for the complex stability, which explain the confined dynamics of drugs inside the CNHs. The free energy profiles revealed an endergonic character of the drug release processes from CNHs, in which the energy barrier for oxaliplatin release (~24 kcal mol–1 ) was ~30% larger than those for carboplatin and cisplatin (~18 kcal mol-1 ). The simulations also showed four stages of the interaction mechanism CNH--membrane: approach, insertion, permeation, and internalization. Despite the low structural disturbance of the membranes, the free energy barrier of ∼55 kcal mol-1 for the CNHs translocation indicated that this transport is kinetically unfavorable by passive process. The in silico experiments evidenced that the most likely mechanism of cisplatin delivery from CNHs involve the approach and insertion stages, where the nanovector adheres on the surface of cancer cells, as reported in in vitro studies. After this retention, the drug load may be slowly released in the tumor site. Finally, simulations of the cellular uptake of Pt(II) drugs also pointed out significant energy barriers (~30 kcal mol-1 ) for this process, which reflects their low permeability in membranes as discussed in experimental studies. In addition to reinforcing the potential of CNH as nanovector of Pt(II) drugs, the results presented in this thesis may assist and drive new experimental studies with CNHs, focusing on the development of less aggressive formulations for cancer treatments.A medicação com fármacos a base de Pt(II) (cisplatina, carboplatina e oxaliplatina) tem sido uma alternativa efetiva para tratar cânceres devido à sua notável inibição do crescimento de células cancerosas e a prevenção de metástases. No entanto, a baixa seletividade dessas metalodrogas por células cancerosas gera severos efeitos colaterais. Nesse contexto, nanohorns de carbono (CNHs) têm sido considerados potenciais nanovetores de fármacos, devido a baixa toxicidade, capacidade de carreamento de fármacos, rotas de biodegradação, e biocompatibilidade quando oxidados. Porém, existe uma carência de estudos tratando o comportamento desses nanocarreadores em biomembranas. Esse trabalho tem como objetivo caracterizar as interações entre complexos de inclusão fármaco@CNH, formados por fármacos de Pt(II) encapsulados em CNHs, e membranas usando simulações por dinâmica molecular. Os resultados demonstraram que a contribuição de van der Waals teve um papel primário (∼74%) na estabilidade dos complexos, o que explica a dinâmica confinada dos fármacos dentro dos CNHs. Os perfis de energia livre revelaram o caráter endergônico da liberação dos fármacos a partir de CNHs, nos quais a barreira de energia para a liberação da oxaliplatina (~24 kcal mol– 1 ) é ~30% maior do que aquelas para carboplatina e cisplatina. As simulações mostraram quatro estágios do mecanismo de interação CNH-membrana: aproximação, inserção, permeação e internalização. Apesar do baixo distúrbio estrutural das membranas, a barreira de energia livre de ∼55 kcal mol-1 para a translocação de CNHs indicou que esse transporte é desfavorável cineticamente via o processo passivo. Os experimentos in silico evidenciam que o mecanismo mais provável de entrega de cisplatina a partir de CNHs envolve a aproximação e inserção, onde o nanovetor adere na superfície de células cancerosas, como reportado em estudos in vitro. Após essa retenção, a carga de fármaco deve ser ligeiramente liberada no tumor. As simulações de captação celular de fármacos de Pt(II) também apontaram barreiras de energia significativas (∼30 kcal mol-1 ) para esse processo, o que reflete a baixa permeabilidade deles em membranas como discutido em estudos experimentais. Além de reforçar o potencial de CNHs como nanovetores de fármacos de Pt(II), os resultados apresentados nessa tese podem auxiliar e impulsionar novos estudos com CNHs, focando no desenvolvimento de formulações menos agressivas para tratamentos de câncer.FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerai