608 research outputs found
Habitat requirements and ecological niche of two cryptic amphipod species at landscape and local scales
Cryptic species are phylogenetically diverged taxa that are morphologically indistinguishable
and may differ in their ecological and behavioral requirements. This may have important implications for
ecosystem services and conservation of biodiversity. We investigated whether two ecologically important
cryptic species of the freshwater amphipod Gammarus fossarum (types A and B) are associated with different
habitats. We collected data on their occurrence at both the landscape scale (large watersheds) and at the
local scale (river reach) to compare macro- and microscale environmental parameters associated with their
presence. Analysis of the landscape scale data showed that occurrence of types A and B differ with respect
to watershed and river size and, interestingly, human impact on river ecomorphology. Whereas type B was
mainly found in less forested areas with higher human impact, type A showed the opposite occurrence
pattern. Analyses of the local scale data suggested that habitats occupied by type A were characterized by
larger gravel, larger stones and less macrophytes than habitats occupied by type B. The landscape and local
data set showed contradicting patterns with regard to stream size. Overall, the observed differences between
the two types of G. fossarum most likely reflect ecological differences between them, but alternative
explanations (e.g., historical colonization processes) cannot be completely ruled out. Our study underlines
that common cryptic species can differ in their ecology and response to anthropogenic influence. Such
differences in habitat requirements among difficult-to-identify taxa present a challenge for biodiversity
and ecosystem management. Our results emphasize the importance of conservative and precautionary
approaches in maintenance of habitat diversity and environmental heterogeneity
One-Dimensional Approximation of Viscous Flows
Attention has been paid to the similarity and duality between the
Gregory-Laflamme instability of black strings and the Rayleigh-Plateau
instability of extended fluids. In this paper, we derive a set of simple
(1+1)-dimensional equations from the Navier-Stokes equations describing thin
flows of (non-relativistic and incompressible) viscous fluids. This
formulation, a generalization of the theory of drop formation by Eggers and his
collaborators, would make it possible to examine the final fate of
Rayleigh-Plateau instability, its dimensional dependence, and possible
self-similar behaviors before and after the drop formation, in the context of
fluid/gravity correspondence.Comment: 17 pages, 3 figures; v2: refs & comments adde
Air entrainment through free-surface cusps
In many industrial processes, such as pouring a liquid or coating a rotating
cylinder, air bubbles are entrapped inside the liquid. We propose a novel
mechanism for this phenomenon, based on the instability of cusp singularities
that generically form on free surfaces. The air being drawn into the narrow
space inside the cusp destroys its stationary shape when the walls of the cusp
come too close. Instead, a sheet emanates from the cusp's tip, through which
air is entrained. Our analytical theory of this instability is confirmed by
experimental observation and quantitative comparison with numerical simulations
of the flow equations
Hydrodynamic theory of de-wetting
A prototypical problem in the study of wetting phenomena is that of a solid
plunging into or being withdrawn from a liquid bath. In the latter, de-wetting
case, a critical speed exists above which a stationary contact line is no
longer sustainable and a liquid film is being deposited on the solid.
Demonstrating this behavior to be a hydrodynamic instability close to the
contact line, we provide the first theoretical explanation of a classical
prediction due to Derjaguin and Levi: instability occurs when the outer, static
meniscus approaches the shape corresponding to a perfectly wetting fluid
The Two Fluid Drop Snap-off Problem: Experiments and Theory
We address the dynamics of a drop with viscosity breaking up
inside another fluid of viscosity . For , a scaling theory
predicts the time evolution of the drop shape near the point of snap-off which
is in excellent agreement with experiment and previous simulations of Lister
and Stone. We also investigate the dependence of the shape and
breaking rate.Comment: 4 pages, 3 figure
Management of Technology Focused on the Water Analysis Results in Artesians Wells
The water is an universal soluble, fundamental to every living being. The main component to the human body and indispensable for any form of life, however, there is an increasing preocupation within the quality of their providers, which are the rivers, strands and springs, but as the time passes by are threatened by anthropogenic activities, main causer of the contamination and destruction of the local fauna and habitat. The principal objetictive of this research was to generate necessary information to further make use of this water, specifically located in Porto Velho, RondĂ´nia, in Jamari\u27s River\u27s hidrographic basin sided with Green River\u27s, one affluent and one subfluent of Madeira\u27s River, which is one of the most important hidrographic basins of Amazon\u27s River, yet, lots of physical, chemicals and microbiological parameters were effected, like pH, turbidity, overall alkalinity, overall toughness, iron, chloride, color, fecal coliforms, that are capable of identify the contamination by anthropic action, obtaining the characteristics of the containing waters in the studied area, which in turn had favorable results, following the collected results we could confirm that all them were under acceptable and expectable parameters required by legislation in force of bathing, aquatic community preservation and human consumption, being the last one dependable of a simple threatment (chlorination)
Making Atomic-Level Magnetism Tunable with Light at Room Temperature
The capacity to manipulate magnetization in two-dimensional dilute magnetic
semiconductors (2D-DMSs) using light, specifically in magnetically doped
transition metal dichalcogenide (TMD) monolayers (M-doped TX2, where M = V, Fe,
Cr; T = W, Mo; X = S, Se, Te), may lead to innovative applications in
spintronics, spin-caloritronics, valleytronics, and quantum computation. This
Perspective paper explores the mediation of magnetization by light under
ambient conditions in 2D-TMD DMSs and heterostructures. By combining magneto-LC
resonance (MLCR) experiments with density functional theory (DFT) calculations,
we show that the magnetization can be enhanced using light in V-doped TMD
monolayers (e.g., V-WS2, V-WSe2, V-MoS2). This phenomenon is attributed to
excess holes in the conduction and valence bands, as well as carriers trapped
in magnetic doping states, which together mediate the magnetization of the
semiconducting layer. In 2D-TMD heterostructures such as VSe2/WS2 and
VSe2/MoS2, we demonstrate the significance of proximity, charge-transfer, and
confinement effects in amplifying light-mediated magnetism. This effect is
attributed to photon absorption at the TMD layer (e.g., WS2, MoS2) that
generates electron-hole pairs mediating the magnetization of the
heterostructure. These findings will encourage further research in the field of
2D magnetism and establish a novel direction for designing 2D-TMDs and
heterostructures with optically tunable magnetic functionalities, paving the
way for next-generation magneto-optic nanodevices
A Continuum Description of Vibrated Sand
The motion of a thin layer of granular material on a plate undergoing
sinusoidal vibrations is considered. We develop equations of motion for the
local thickness and the horizontal velocity of the layer. The driving comes
from the violent impact of the grains on the plate. A linear stability theory
reveals that the waves are excited non-resonantly, in contrast to the usual
Faraday waves in liquids. Together with the experimentally observed continuum
scaling, the model suggests a close connection between the neutral curve and
the dispersion relation of the waves, which agrees quite well with experiments.
For strong hysteresis we find localized oscillon solutions.Comment: paper has been considerably extended (11 instead of 6 pages; 6
instead of 4 figures) much better agreement with experiment. obtain now
oscillons in 1 dimensio
Pioglitazone Prevents Capillary Rarefaction in Streptozotocin-Diabetic Rats Independently of Glucose Control and Vascular Endothelial Growth Factor Expression
Background/Aims: Reduction of capillary network density occurs early in the development of metabolic syndrome and may be relevant for the precipitation of diabetes. Agonists of the peroxisome proliferator-activated receptor (PPAR)-gamma transcription factor are vasculoprotective, but their capacity for structural preservation of the microcirculation is unclear. Methods: Male Wistar rats were rendered diabetic by streptozotocin and treated with pioglitazone in chow for up to 12 weeks. Capillary density was determined in heart and skeletal muscle after platelet endothelial cell adhesion molecule-1 (PECAM-1) immunostaining. Hallmarks of apoptosis and angiogenesis were determined. Results: Capillary density deteriorated progressively in the presence of hyperglycemia (from 971/mm(2) to 475/mm(2) in quadriceps muscle during 13 weeks). Pioglitazone did not influence plasma glucose, left ventricular weight, or body weight but nearly doubled absolute and relative capillary densities compared to untreated controls (1.2 vs. 0.6 capillaries/myocyte in heart and 1.5 vs. 0.9 capillaries/myocyte in quadriceps muscle) after 13 weeks of diabetes. No antiapoptotic or angiogenic influence of pioglitazone was detected while a reduced expression of hypoxia-inducible factor-3 alpha and PPAR coactivator-1 alpha (PGC-1 alpha) mRNA as well as vascular endothelial growth factor (VEGF) protein possibly occurred as a consequence of improved vascularization. Conclusion: Pioglitazone preserves microvascular structure in diabetes independently of improvements in glycemic control and by a mechanism unrelated to VEGF-mediated angiogenesis. Copyright (C) 2012 S. Karger AG, Base
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