Depressive disorders are heterogeneous diseases, and the complexity of symptoms has led to the formulation of several aethiopathological hypotheses. This heterogeneity may account for the following ...open issues about antidepressant therapy: (i) antidepressants show a time lag between pharmacological effects, within hours from acute drug administration, and therapeutic effects, within two-four weeks of subchronic treatment; (ii) this latency interval is critical for the patient because of the possible further mood worsening that may result in suicide attempts for the seemingly ineffective therapy and for the apparent adverse effects; (iii) and only 60–70 % of treated patients successfully respond to therapy. In this review, the complexity of the biological theories that try to explain the molecular mechanisms of these diseases is considered, encompassing (i) the classic “monoaminergic hypothesis” alongside the updated hypothesis according to which long-term therapeutical action of antidepressants is mediated by intracellular signal transduction pathways and (ii) the hypothalamic–pituitary-adrenal axis involvement. Although these models have guided research efforts in the field for decades, they have not generated a compelling and conclusive model either for depression pathophysiology or for antidepressant drugs’ action. So, other emerging theories are discussed: (iii) the alterations of neuroplasticity and neurotrophins in selective vulnerable cerebral areas; (iv) the involvement of inflammatory processes; (v) and the alterations in mitochondrial function and neuronal bioenergetics. The focus is put on the molecular and theoretical links between all these hypotheses, which are not mutually exclusive but otherwise tightly correlated, giving an integrated and comprehensive overview of the neurobiology of depressive disorders.
Radiative corrections and Lorentz violation Ferrari, A. F.; Nascimento, J. R.; Petrov, A. Yu
European physical journal. C, Particles and fields,
05/2020, Volume:
80, Issue:
5
Journal Article
Peer reviewed
Open access
Radiative corrections in Lorentz violating (LV) models have already received a lot of attention in the literature in recent years, with many instances where a LV operator in one sector of the ...Standard Model Extension (SME) generates, via loop corrections, one of the LV coefficients in the photon sector, which is probably the most understood and well constrained part of the SME. In many of these works, however, the now standard notation of the SME is not used, which can obscure the comparison of different results, and their possible phenomenological relevance. In this work, we fill this gap, trying to build up a more general perspective on the topic, bringing many of the results to the SME conventional notation and commenting on their possible phenomenological relevance. We uncover one example where a result already presented in the literature can be used to place a stronger bound on the temporal component of the
b
μ
coefficient of the fermion sector of the SME.
Context.
Evidence supports the idea that asteroids are rubble piles, that is, gravitational aggregates of loosely consolidated material. This makes their dynamics subject not only to the complex
N
...-body gravitational interactions between its constituents, but also to the laws of granular mechanics, which is one of the main unsolved problems in physics.
Aims.
We aim to develop a new method to identify dynamical transitions and predict qualitative behavior in the granular
N
-body problem, in which the dynamics of individual bodies are driven both by mutual gravity, contact and collision interactions.
Methods.
The method has its foundation in the combination of two elements: a granular
N
-body simulation code that can resolve the dynamics of granular fragments to particle-scale precision, and a theoretical framework that can decode the nature of particle-scale dynamics and their transitions by means of ad hoc indicators.
Results.
We present here a proof-of-concept of the method, with application to the spinning rubble-pile asteroid problem. We investigate the density-spin parameter space and demonstrate that the approach can identify the breakup limit and reshape region for spinning rubble-pile aggregates.
Conclusions.
We provide the performance of several ad hoc indicators and discuss whether they are suitable for identifying and predicting the features of the dynamical problem.
Most studies on buoyant microplastics in the marine environment rely on sea surface sampling. Consequently, microplastic amounts can be underestimated, as turbulence leads to vertical mixing. Models ...that correct for vertical mixing are based on limited data. In this study we report measurements of the depth profile of buoyant microplastics in the North Atlantic subtropical gyre, from 0 to 5 m depth. Microplastics were separated into size classes (0.5-1.5 and 1.5-5.0 mm) and types ('fragments' and 'lines'), and associated with a sea state. Microplastic concentrations decreased exponentially with depth, with both sea state and particle properties affecting the steepness of the decrease. Concentrations approached zero within 5 m depth, indicating that most buoyant microplastics are present on or near the surface. Plastic rise velocities were also measured, and were found to differ significantly for different sizes and shapes. Our results suggest that (1) surface samplers such as manta trawls underestimate total buoyant microplastic amounts by a factor of 1.04-30.0 and (2) estimations of depth-integrated buoyant plastic concentrations should be done across different particle sizes and types. Our findings can assist with improving buoyant ocean plastic vertical mixing models, mass balance exercises, impact assessments and mitigation strategies.
For the past several decades, we have been able to directly probe the motion of atoms that is associated with chemical transformations and which occurs on the femtosecond (10−15-s) timescale. ...However, studying the inner workings of atoms and molecules on the electronic timescale has become possible only with the recent development of isolated attosecond (10−18-s) laser pulses. Such pulses have been used to investigate atomic photoexcitation and photoionization and electron dynamics in solids, and in molecules could help explore the prompt charge redistribution and localization that accompany photoexcitation processes. In recent work, the dissociative ionization of H2 and D2 was monitored on femtosecond timescales and controlled using few-cycle near-infrared laser pulses. Here we report a molecular attosecond pump-probe experiment based on that work: H2 and D2 are dissociatively ionized by a sequence comprising an isolated attosecond ultraviolet pulse and an intense few-cycle infrared pulse, and a localization of the electronic charge distribution within the molecule is measured that depends-with attosecond time resolution-on the delay between the pump and probe pulses. The localization occurs by means of two mechanisms, where the infrared laser influences the photoionization or the dissociation of the molecular ion. In the first case, charge localization arises from quantum mechanical interference involving autoionizing states and the laser-altered wavefunction of the departing electron. In the second case, charge localization arises owing to laser-driven population transfer between different electronic states of the molecular ion. These results establish attosecond pump-probe strategies as a powerful tool for investigating the complex molecular dynamics that result from the coupling between electronic and nuclear motions beyond the usual Born-Oppenheimer approximation.
The sensitivity to sea surface temperature (SST) of small‐scale, flood‐causing convective systems in Mediterranean coastal areas is analyzed by means of mesoscale numerical simulations. Two different ...SST initializations are considered: a coarse field provided by a global atmospheric model and a high‐resolution multisatellite analysis. Quantitative precipitation forecasts are evaluated for a number of recent severe rainfall episodes in Liguria (northwestern Italy). In several cases, using a higher‐resolution SST leads to more realistic precipitation estimates in the forecasting range 36–48 h. In the shorter range, the satellite SST has a limited, or even negative, impact, due to the relatively slow adjustment of initial atmospheric fields. In one case, the satellite SST is beneficial for the only run forced with accurate large‐scale initial conditions. The results of this work suggest that a potentially significant improvement in severe precipitation forecasting in the Mediterranean could be achieved using realistic small‐scale SST fields.
Key Points
The role of SST initial field in numerical simulations of flash floods in Liguria (Italy) is shown
Quantitative precipitation forecast is strongly sensitive to small‐scale SST inhomogeneities
The operational use of fully atmosphere‐ocean coupled modeling systems is strongly encouraged
Organelles juxtaposition has been detected for decades, although only recently gained importance due to a pivotal role in the regulation of cellular processes dependent on membrane contact sites. ...Endoplasmic reticulum (ER) and mitochondria interaction is a prime example of organelles contact sites. Mitochondria-associated membranes (MAM) are proposed to harbor ER-mitochondria tether complexes, mainly when these organelles are less than 30 nm apart. Dysfunctions of proteins located at the MAM are associated with neurodegenerative diseases such as Parkinson’s, Alzheimer’s and amyotrophic lateral sclerosis, as well as neurodevelopmental disorders; hence any malfunction in MAM can potentially trigger cell death. This review will focus on the role of ER-mitochondria contact sites, regarding calcium homeostasis, lipid metabolism, autophagy, morphology and dynamics of mitochondria, mainly in the context of neurodegenerative diseases. Approaches that have been employed so far to study organelles contact sites, as well as methods that were not used in neurosciences yet, but are promising and accurate ways to unveil the functions of MAM during neurodegeneration, is also discussed in the present review.
Here we report concentrations of pollutants in floating plastics from the North Pacific accumulation zone (NPAC). We compared chemical concentrations in plastics of different types and sizes, ...assessed ocean plastic potential risks using sediment quality criteria, and discussed the implications of our findings for bioaccumulation. Our results suggest that at least a fraction of the NPAC plastics is not in equilibrium with the surrounding seawater. For instance, “hard plastic” samples had significantly higher PBDE concentrations than “nets and ropes” samples, and 29% of them had PBDE composition similar to a widely used flame-retardant mixture. Our findings indicate that NPAC plastics may pose a chemical risk to organisms as 84% of the samples had at least one chemical exceeding sediment threshold effect levels. Furthermore, our surface trawls collected more plastic than biomass (180 times on average), indicating that some NPAC organisms feeding upon floating particles may have plastic as a major component of their diets. If gradients for pollutant transfer from NPAC plastic to predators exist (as indicated by our fugacity ratio calculations), plastics may play a role in transferring chemicals to certain marine organisms.
Bursting neurons fire rapid sequences of action potential spikes followed by a quiescent period. The basic dynamical mechanism of bursting is the slow currents that modulate a fast spiking activity ...caused by rapid ionic currents. Minimal models of bursting neurons must include both effects. We considered one of these models and its relation with a generalized Kuramoto model, thanks to the definition of a geometrical phase for bursting and a corresponding frequency. We considered neuronal networks with different connection topologies and investigated the transition from a non-synchronized to a partially phase-synchronized state as the coupling strength is varied. The numerically determined critical coupling strength value for this transition to occur is compared with theoretical results valid for the generalized Kuramoto model.
Ocean plastic can persist in sea surface waters, eventually accumulating in remote areas of the world's oceans. Here we characterise and quantify a major ocean plastic accumulation zone formed in ...subtropical waters between California and Hawaii: The Great Pacific Garbage Patch (GPGP). Our model, calibrated with data from multi-vessel and aircraft surveys, predicted at least 79 (45-129) thousand tonnes of ocean plastic are floating inside an area of 1.6 million km
; a figure four to sixteen times higher than previously reported. We explain this difference through the use of more robust methods to quantify larger debris. Over three-quarters of the GPGP mass was carried by debris larger than 5 cm and at least 46% was comprised of fishing nets. Microplastics accounted for 8% of the total mass but 94% of the estimated 1.8 (1.1-3.6) trillion pieces floating in the area. Plastic collected during our study has specific characteristics such as small surface-to-volume ratio, indicating that only certain types of debris have the capacity to persist and accumulate at the surface of the GPGP. Finally, our results suggest that ocean plastic pollution within the GPGP is increasing exponentially and at a faster rate than in surrounding waters.
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