Dinâmica de carbono e nitrogênio em um sistema agroflorestal sucessional na região neotropical

The present study aimed to assess the effect of fourteen years of implementation of a successional and biodiverse agroforestry system (AFS) in a degraded agricultural field located in the Cerrado region of Central Brazil on the carbon and nitrogen dynamics. To track short term soil N dynamics we sampled instantaneous soil N rates in four seasonal periods (wet-dry, dry, dry-wet, wet) and to track long term C and N dynamics we measured C and N stable isotopes in the plant-litter-soil system. As additional data we determined the aboveground biomass; resorption rates of foliar and, soil C and N stocks.  The measured aboveground biomass was 19.2 Mg C ha-1. The mean resorption rate of foliar N was 49.3%. C:N ratio was 20.4 ± 1.4 and 14.2 ± 0.32 in the litter layer and the topsoil, respectively. Soil N-NH4+ was predominant over N-NO3-. After 40 days, the cumulative N-N2O emission was 0.33 kg ha-1. The mean C and N stocks were 3.8 Mg N ha-1 and 43.6 Mg C ha-1, respectively. The averaged soil δ15N was 6.8‰. Soil δ13C was -20.3‰. After 14 years of implementation, approximately 40% of the total C in the topsoil (0-20 cm depth) was derived from the AFS biomass input, predominantly from the C3 photosynthetic pathway. The studied biodiverse AFS that replaced a degraded agricultural field in the Cerrado region showed to be responsive both in terms of soil and plant C and N pools and fluxes.O presente estudo teve como objetivo avaliar o efeito de quatorze anos de implementação de um sistema agroflorestal (SAF) sucessional e biodiverso em uma área agrícola degradada localizada na região de Cerrado do Brasil Central sobre a dinâmica de carbono e nitrogênio. Para verificar a dinâmica de N no curto prazo foram feitas medidas das taxas de transformação de N no solo em quatro períodos sazonais (chuva-seca, seca, seca-chuva e chuva) e para determinar a dinâmica de C e N no longo prazo foram analisadas as razões isotópicas de C e N no sistema planta-serapilheira-solo. Além disso, os seguintes parâmetros foram medidos: biomassa acima do solo, taxas de retranslocação de N foliar, e estoques de C e N no solo. A biomassa acima do solo foi de 19,2 Mg C ha-1. A taxa média de reabsorção de N foliar foi de 49,3%. A relação C:N foi de 20,4 ± 1,4 e 14,2 ± 0,32 na camada de serapilheira e na camada superficial do solo, respectivamente. O N-NH4 + do solo foi predominante sobre o N-NO3-. Após 40 dias, a emissão cumulativa de N-N2O foi de 0,33 kg ha-1. Os estoques médios de C e N foram de 3,8 Mg N ha-1 e 43,6 Mg C ha-1, respectivamente. O valor médio de δ15N do solo foi de 6,8‰, enquanto o valor médio de δ13C no solo foi de -20,3‰. Após 14 anos de implementação, aproximadamente 40% do C total na camada superficial do solo (0-20 cm de profundidade) mostrou ser derivado da entrada de biomassa oriunda do SAF, que é predominantemente do tipo fotossintético C3. O SAF estudado, que substituiu um campo agrícola degradado na região do Cerrado, mostrou-se responsivo tanto em termos de estoques e fluxos de C e N do solo e da planta

Global disparities in surgeons’ workloads, academic engagement and rest periods: the on-calL shIft fOr geNEral SurgeonS (LIONESS) study

: The workload of general surgeons is multifaceted, encompassing not only surgical procedures but also a myriad of other responsibilities. From April to May 2023, we conducted a CHERRIES-compliant internet-based survey analyzing clinical practice, academic engagement, and post-on-call rest. The questionnaire featured six sections with 35 questions. Statistical analysis used Chi-square tests, ANOVA, and logistic regression (SPSS® v. 28). The survey received a total of 1.046 responses (65.4%). Over 78.0% of responders came from Europe, 65.1% came from a general surgery unit; 92.8% of European and 87.5% of North American respondents were involved in research, compared to 71.7% in Africa. Europe led in publishing research studies (6.6 ± 8.6 yearly). Teaching involvement was high in North America (100%) and Africa (91.7%). Surgeons reported an average of 6.7 ± 4.9 on-call shifts per month, with European and North American surgeons experiencing 6.5 ± 4.9 and 7.8 ± 4.1 on-calls monthly, respectively. African surgeons had the highest on-call frequency (8.7 ± 6.1). Post-on-call, only 35.1% of respondents received a day off. Europeans were most likely (40%) to have a day off, while African surgeons were least likely (6.7%). On the adjusted multivariable analysis HDI (Human Development Index) (aOR 1.993) hospital capacity > 400 beds (aOR 2.423), working in a specialty surgery unit (aOR 2.087), and making the on-call in-house (aOR 5.446), significantly predicted the likelihood of having a day off after an on-call shift. Our study revealed critical insights into the disparities in workload, access to research, and professional opportunities for surgeons across different continents, underscored by the HDI

Influence of quasi-particle density over polaron mobility in armchair graphene nanoribbons

An important aspect concerning the performance of armchair graphene nanoribbons (AGNRs) as materials for conceiving electronic devices is related to the mobility of charge carriers in these systems. When several polarons are considered in the system, a quasi-particle wave function can be affected by that of its neighbor provided the two are close enough. As the overlap may affect the transport of the carrier, the question concerning how the density of polarons affect its mobility arises. In this work, we investigate such dependence for semiconducting AGNRs in the scope of nonadiabatic molecular dynamics. Our results unambiguously show an impact of the density on both the stability and average velocity of the quasi-particles. We have found a phase transition between regimes where increasing density stops inhibiting and starts promoting mobility; densities higher than 7 polarons per 45 angstrom present increasing mean velocity with increasing density. We have also established three different regions relating electric field and average velocity. For the lowest electric field regime, surpassing the aforementioned threshold results in overcoming the 0.3 angstrom fs(-1) limit, thus representing a transition between subsonic and supersonic regimes. For the highest of the electric fields, density effects alone are responsible for a stunning difference of 1.5 angstrom fs(-1) in the mean carrier velocity.Funding Agencies|CNPq; CAPES; FAP-DF; CENAPAD-SP; Brazilian Ministry of Planning, Development and Management [005/2016, 11/2016]; DPGU - Brazilian Union Public Defender [066/2016]; FAP-DF [0193.000.942/2015, 193.001.511/2017]</p

Bipolaron Dynamics in Graphene Nanoribbons

Graphene nanoribbons (GNRs) are two-dimensional structures with a rich variety of electronic properties that derive from their semiconducting band gaps. In these materials, charge transport can occur via a hopping process mediated by carriers formed by self-interacting states between the excess charge and local lattice deformations. Here, we use a two-dimensional tight-binding approach to reveal the formation of bipolarons in GNRs. Our results show that the formed bipolarons are dynamically stable even for high electric field strengths when it comes to GNRs. Remarkably, the bipolaron dynamics can occur in acoustic and optical regimes concerning its saturation velocity. The phase transition between these two regimes takes place for a critical field strength in which the bipolaron moves roughly with the speed of sound in the material.Funding Agencies|CNPq; CAPES; FAP-DF; CENAPAD-SP; Brazilian Ministry of Planning, Development and Management [005/2016, 11/2016]; DPGU - Brazilian Union Public Defender [066/2016]; FAP-DF grants [0193.001.511/2017, 0193.001343/2016, 0193.001766/2017]</p

Spin-Orbit Effects on the Dynamical Properties of Polarons in Graphene Nanoribbons

The dynamical properties of polarons in armchair graphene nanoribbons (GNR) is numerically investigated in the framework of a two-dimensional tight-binding model that considers spin-orbit (SO) coupling and electron-lattice (e-l) interactions. Within this physical picture, novel polaron properties with no counterparts to results obtained from conventional tight-binding models are obtained. Our findings show that, depending on the systems width, the presence of SO coupling changes the polarons charge localization giving rise to different degrees of stability for the charge carrier. For instance, the joint action of SO coupling and e-l interactions could promote a slight increase on the charge concentration in the center of the lattice deformation associated to the polaron. As a straightforward consequence, this process of increasing stability would lead to a depreciation in the polarons motion by decreasing its saturation velocity. Our finds are in good agreement with recent experimental investigations for the charge localization in GNR, mostly when it comes to the influence of SO coupling. Moreover, the contributions reported here provide a reliable method for future works to evaluate spin-orbit influence on the performance of graphene nanoribbons.Funding Agencies|CNPq; CAPES; FAP-DF; FINATEC; Brazilian Ministry of Planning, Development and Management [005/2016 DIPLA, 11/2016 SEST]; DPGU - Brazilian Union Public Defender [066/2016]; FAP-DF [0193.000.942/2015, 0193.001343/2016]; IFG</p