In the eighteenth century, Bridgetown, Barbados, was heavily populated by both enslaved and free women. Marisa J. Fuentes creates a portrait of urban Caribbean slavery in this colonial town from the ...perspective of these women whose stories appear only briefly in historical records. Fuentes takes us through the streets of Bridgetown with an enslaved runaway; inside a brothel run by a freed woman of color; in the midst of a white urban household in sexual chaos; to the gallows where enslaved people were executed; and within violent scenes of enslaved women's punishments. In the process, Fuentes interrogates the archive and its historical production to expose the ongoing effects of white colonial power that constrain what can be known about these women.
Combining fragmentary sources with interdisciplinary methodologies that include black feminist theory and critical studies of history and slavery,Dispossessed Livesdemonstrates how the construction of the archive marked enslaved women's bodies, in life and in death. By vividly recounting enslaved life through the experiences of individual women and illuminating their conditions of confinement through the legal, sexual, and representational power wielded by slave owners, colonial authorities, and the archive, Fuentes challenges the way we write histories of vulnerable and often invisible subjects.
Context.
Open clusters are key targets for studies of Galaxy structure and evolution, and stellar physics. Since the
Gaia
data release 2 (DR2), the discovery of undetected clusters has shown that ...previous surveys were incomplete.
Aims.
Our aim is to exploit the Big Data capabilities of machine learning to detect new open clusters in
Gaia
DR2, and to complete the open cluster sample to enable further studies of the Galactic disc.
Methods.
We use a machine-learning based methodology to systematically search the Galactic disc for overdensities in the astrometric space and identify the open clusters using photometric information. First, we used an unsupervised clustering algorithm, DBSCAN, to blindly search for these overdensities in
Gaia
DR2 (
l
,
b
,
ϖ
,
μ
α
*
,
μ
δ
), and then we used a deep learning artificial neural network trained on colour–magnitude diagrams to identify isochrone patterns in these overdensities, and to confirm them as open clusters.
Results.
We find 582 new open clusters distributed along the Galactic disc in the region |
b
| < 20°. We detect substructure in complex regions, and identify the tidal tails of a disrupting cluster
UBC 274
of ∼3 Gyr located at ∼2 kpc.
Conclusions.
Adapting the mentioned methodology to a Big Data environment allows us to target the search using the physical properties of open clusters instead of being driven by computational limitations. This blind search for open clusters in the Galactic disc increases the number of known open clusters by 45%.
Heat dissipation still remains an unsolved problem in dynamic plasticity, where nearly adiabatic conditions prevail during high-rate loading scenarios. It is well known that the mechanical energy ...that is not dissipated as heat during material straining remains stored in the lattice as microstructural defects, and thus, a one-to-one relationship can be expected between the stored energy, the materials microstructure, and its mechanical characteristics. This work demonstrates that this is not so straightforward. High-rate experiments on a Kolsky bar, combined with in situ thermal measurements, were performed on two well-studied materials: pure nickel and aluminum. A dislocation-based constitutive model was used to estimate the mechanical and thermomechanical material behavior. For both materials, the thermal response was observed to be strongly strain rate sensitive, while the mechanical flow, and microstructural characteristics (as characterized by transmission electron microscopy at similar strains), were not. This apparent discrepancy between mechanical and microstructural vs thermal results is discussed, and the concept of thermomechanical conversion is reassessed.
The objective of this study is to analyse the impact of perceived risk on intention to travel in the Covid-19 pandemic situation. Applying the Theory of Planned Behaviour, the study addresses the ...modulating effects of risk on the antecedents of intention; additionally, the resulting model includes the impact of this intention on the willingness to pay (WTP) more to benefit from additional safety measures at the destination. Furthermore, this paper addresses respondents belonging to an at-risk group for Covid-19 as a source of heterogeneity that may exert an effect on the results of the model. The model is tested using PLS-SEM, and the empirical results can contribute to the development of safety measures in tourism services and the design of effective actions to restore tourism.
Hydropeaking is the rapid change in the water flow downstream of a hydropower plant, driven by changes in daily electricity demand. These fluctuations may produce negative effects in freshwater fish. ...To minimize these impacts, previous studies have proposed habitat enhancement structures as potential mitigation measures for salmonids. However, the recommendation of these mitigation measures for cyprinids remains scarce and their effects unknown. In this study, the effects of potential habitat mitigation structures under simulated hydropeaking and base-flow conditions are examined for Iberian barbel (Luciobarbus bocagei) in an indoor flume. Solid triangular pyramids and v-shaped structures were evaluated as potential flow-refuging areas and compared with a configuration without structures. A novel, interdisciplinary approach is applied to investigate individual and group responses to rapidly changing flows, by assessing physiological (glucose and lactate), movement behaviour (structure use, sprints and drifts) and the pressure distribution using a fish-inspired artificial lateral line flow sensor. The major findings of this study are four-fold: 1) Under hydropeaking conditions, the v-shaped structures triggered a lactate response and stimulated individual structure use, whereas solid structures did not elicit physiological adjustments and favoured individual and group structure use. Overall, both solid structures and their absence stimulated sprints and drifts. 2) The hydrodynamic conditions created in hydropeaking did not always reflect increased physiological responses or swimming activity. 3) Each event-structure combination resulted in unique hydrodynamic conditions which were reflected in the different fish responses. 4) The most relevant flow variable measured was the pressure asymmetry, which is caused by the vortex size and shedding frequency of the structures. Considering the non-uniform nature of hydropeaking events, and the observation that the fish responded differently to specific flow event-structure combinations, a diverse set of instream structures should be considered for habitat-based hydropeaking mitigation measures for Iberian barbel.
Abstract
We investigate heat transport associated with compositionally driven convection driven by crystallization at the ocean–crust interface in accreting neutron stars, or growth of the solid core ...in cooling white dwarfs. We study the effect of thermal diffusion and rapid rotation on the convective heat transport, using both mixing length theory and numerical simulations of Boussinesq convection. We determine the heat flux, composition gradient, and Péclet number, Pe (the ratio of thermal diffusion time to convective turnover time) as a function of the composition flux. We find two regimes of convection with a rapid transition between them as the composition flux increases. At small Pe, the ratio between the heat flux and composition flux is independent of Pe, because the loss of heat from convecting fluid elements due to thermal diffusion is offset by the smaller composition gradient needed to overcome the reduced thermal buoyancy. At large Pe, the temperature gradient approaches the adiabatic gradient, saturating the heat flux. We discuss the implications for cooling of neutron stars and white dwarfs. Convection in neutron stars spans both regimes. We find rapid mixing of neutron star oceans, with a convective turnover time of the order of weeks to minutes depending on rotation. Except during the early stages of core crystallization, white dwarf convection is in the thermal-diffusion-dominated fingering regime. We find convective velocities much smaller than recent estimates for crystallization-driven dynamos. The small fraction of energy carried as kinetic energy calls into question the effectiveness of crystallization-driven dynamos as an explanation for observed magnetic fields in white dwarfs.
Predictive Control of AC-AC Modular Multilevel Converters Perez, Marcelo A.; Rodriguez, J.; Fuentes, E. J. ...
IEEE transactions on industrial electronics (1982),
2012-July, 2012-07-00, 20120701, Letnik:
59, Številka:
7
Journal Article
Recenzirano
Multilevel converters can reach medium-voltage operation increasing the efficiency of high-power applications. Among the existing multilevel converter topologies, the modular multilevel converter ...(MMC) provides the advantages of high modularity, availability, and high power quality. Moreover, the main advantage compared to cascaded multilevel converters is the lack of an input transformer which results in a reduction of cooling requirements, size, and cost. One of the drawbacks of this topology when used as an ac-ac converter is the input and output frequency components in the control loop, resulting in a more complex controller design. In this paper, a single-phase ac-ac MMC predictive control approach is proposed. The controller minimizes the input, output, and circulating current errors and balances the dc voltages. Experimental results show the performance of the proposed predictive control scheme.
Abstract We investigate crystallization-driven convection in carbon–oxygen white dwarfs. We present a version of the mixing length theory that self-consistently includes the effects of thermal ...diffusion and composition gradients, and provides solutions for the convective parameters based on the local heat and composition fluxes. Our formulation smoothly transitions between the regimes of fast adiabatic convection at large Peclet number and slow thermohaline convection at low Peclet number. It also allows for both thermally driven and compositionally driven convection, including correctly accounting for the direction of heat transport for compositionally driven convection in a thermally stable background. We use the MESA stellar evolution code to calculate the composition and heat fluxes during crystallization in different models of cooling white dwarfs, and determine the regime of convection and the convective velocity. We find that convection occurs in the regime of slow thermohaline convection during most of the cooling history of the star. However, at the onset of crystallization, the composition flux is large enough to drive fast overturning convection for a short time (∼10 Myr). We estimate the convective velocities in both of these phases and discuss the implications for explaining observed white dwarf magnetic fields with crystallization-driven dynamos.
Context. Glitches are rare spin-up events that punctuate the smooth slow-down of the rotation of pulsars. For the Vela pulsar and PSR J0537−6910, their large glitch sizes and the times between ...consecutive events have clear preferred scales (Gaussian distributions), contrary to the handful of other pulsars with enough glitches for such a study. Moreover, PSR J0537−6910 is the only pulsar that shows a strong positive correlation between the size of each glitch and the waiting time until the following one. Aims. We attempt to understand this behaviour through a detailed study of the distributions and correlations of glitch properties for the eight pulsars with at least ten detected glitches. Methods. We modelled the distributions of glitch sizes and of the times between consecutive glitches for the eight pulsars with at least ten detected events. We also looked for possible correlations between these parameters and used Monte Carlo simulations to explore two hypotheses that could explain why the correlation so clearly seen in PSR J0537−6910 is absent in other pulsars. Results. We confirm the above results for Vela and PSR J0537−6910, and verify that the latter is the only pulsar with a strong correlation between glitch size and waiting time to the following glitch. For the remaining six pulsars, the waiting time distributions are best fitted by exponentials, and the size distributions are best fitted by either power laws, exponentials, or log-normal functions. Some pulsars in the sample yield significant Pearson and Spearman coefficients (rp and rs) for the aforementioned correlation, confirming previous results. Moreover, for all except the Crab pulsar, both coefficients are positive. For each coefficient taken separately, the probability of this happening is 1/16. Our simulations show that the weaker correlations in pulsars other than PSR J0537−6910 cannot be due to missing glitches that are too small to be detected. We also tested the hypothesis that each pulsar may have two kinds of glitches, namely large, correlated ones and small, uncorrelated ones. The best results are obtained for the Vela pulsar, which exhibits a correlation with rp = 0.68 (p-value = 0.003) if its two smallest glitches are removed. The other pulsars are harder to accommodate under this hypothesis, but their glitches are not consistent with a pure uncorrelated population either. We also find that all pulsars in our sample, except the Crab pulsar, are consistent with the previously found constant ratio between glitch activity and spin-down rate, ν̇g/|ν̇| = 0.010±0.001 ν ˙ g / | ν ˙ | = 0.010 ± 0.001 $ \dot\nu_{\mathrm{g}}/|\dot\nu|=0.010\pm 0.001 $ , even though some of them have not shown any large glitches. Conclusions. To explain these results, we speculate except in the case of the Crab pulsar, that all glitches draw their angular momentum from a common reservoir (presumably a neutron superfluid component containing ≈1% of the star’s moment of inertia). However, two different trigger mechanisms could be active, a more deterministic one for larger glitches and a more random one for smaller ones.
Summary
Background
Psoriasis vulgaris is an inflammatory immune‐mediated disease, with lesional skin characterized by sharply demarcated, erythematous scaly plaques. Uninvolved psoriatic skin appears ...clinically similar to normal skin. However, it has been hypothesized that inflammatory cytokines, e.g. interleukin (IL)‐17, may affect any organ or tissue having a vascular supply; thus, distant uninvolved skin could be exposed to increased circulating IL‐17.
Objectives
To establish comparative genomic profiles between noninvolved skin and normal skin, in particular, determining immune abnormalities in distant uninvolved skin.
Methods
We performed a meta‐analysis on three gene array studies, comparing the nonlesional (NL) psoriatic skin transcriptome with normal gene expression. We investigated immunological features of noninvolved skin, particularly linked to IL‐17 signalling.
Results
We detected 252 differentially expressed gene transcripts in uninvolved skin compared with normal skin; multiple immune‐related genes, including IL‐17‐downstream genes, were upregulated. Increased expression of IL‐17‐signature genes (e.g. DEFB4 and S100A7) was associated with an increased number of CD3+, CD8+ and DC‐LAMP+ cells in NL skin vs. normal controls. Inducible T‐cell costimulator (ICOS) expression was detected only in a few T‐cells within NL skin.
Conclusions
Our data described the genomic profile in NL skin, characterizing the immune activation that was mainly attributed to IL‐17 signalling.
What's already known about this topic?
Classically, uninvolved psoriatic skin has been considered approximately similar to normal skin, though a few studies have shown some alterations compared with normal skin.
To our knowledge, only one study has described the transcriptomic profile in nonlesional vs. normal skin, showing altered gene expression related to lipid biosynthesis, innate immunity and keratinocyte differentiation.
What does this study add?
Complex immunologic activation is detectable in uninvolved psoriatic skin.
We report upregulation of key signalling pathways in psoriasis, in particular the interleukin (IL)‐17, IL‐22 and interferon‐γ signalling pathways, which has not been described previously.
Linked Comment: Johnston, et al. Br J Dermatol 2016; 174: 19–20.
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