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Thermal transpiration flow
This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Thermal transpiration is the macroscopic movement of rarefied gas induced by a temperature gradient. The gas moves from the lower to the higher temperature zone. An original method is proposed here to measure the mean macroscopic movement of gas in the case of a long circular cross-section glass microtube on to which a gradient of temperature is applied. The mass flow rate and the thermo-molecular pressure difference have been measured by monitoring the absolute pressure evolution in time at both ends of the capillary using high-speed response pressure gauges. Two gases Nitrogen and Helium are studied and three different temperature differences of 50, 60 and 70 Celsius degrees are applied to the tube. The analysed gas rarefaction conditions vary from transitional to slip regime.The European Community’s Seventh Framework Program (FP7/2007-2013 under grant agreement no 215504
Magnon valley Hall effect in CrI3-based vdW heterostructures
Magnonic excitations in the two-dimensional (2D) van der Waals (vdW)
ferromagnet CrI3 are studied. We find that bulk magnons exhibit a non-trivial
topological band structure without the need for Dzyaloshinskii-Moriya (DM)
interaction. This is shown in vdW heterostructures, consisting of single-layer
CrI3 on top of different 2D materials as MoTe2, HfS2 and WSe2. We find
numerically that the proposed substrates modify substantially the out-of-plane
magnetic anisotropy on each sublattice of the CrI3 subsystem. The induced
staggered anisotropy, combined with a proper band inversion, leads to the
opening of a topological gap of the magnon spectrum. Since the gap is opened
non-symmetrically at the K+ and K- points of the Brillouin zone, an imbalance
in the magnon population between these two valleys can be created under a
driving force. This phenomenon is in close analogy to the so-called valley Hall
effect (VHE), and thus termed as magnon valley Hall effect (MVHE). In linear
response to a temperature gradient we quantify this effect by the evaluation of
the temperature-dependence of the magnon thermal Hall effect. These findings
open a different avenue by adding the valley degrees of freedom besides the
spin, in the study of magnons
The use of ecosystem-based adaptation practices by smallholder farmers in Central America
There is growing interest in promoting the use of Ecosystem-based Adaptation (EbA) practices to help smallholder farmers adapt to climate change, however there is limited information on how commonly these practices are used by smallholder farmers and what factors influence their use. Using participatory mapping and field surveys, we examined the prevalence and characteristics of EbA practices on 300 smallholder coffee and maize farmers in six landscapes in Central America and explored the socioeconomic and biophysical factors associated with their use. The prevalence of individual EbA practices varied across smallholder farms. Common EbA practices included live fences, home gardens, shade trees in coffee plantations, and dispersed trees in maize fields. We found a mean of 3.8 EbA practices per farm. Factors that were correlated with the total number of EbA practices on farms included the mean area of coffee plantations, farmer age, farmer experience, the farm type and the landscape in which farms were located. Factors associated with the presence or characteristics of individual EbA practices included the size of coffee plantations, farmer experience, farmer education, land tenure, landscape and farm type. Our analysis suggests that many smallholder farmers in Central America are already using certain EbA practices, but there is still scope for greater implementation. Policy makers, donors and technicians can encourage the broader use of EbA by smallholder farmers by facilitating farmer-to-farmer exchanges to share knowledge on EbA implementation, assessing the effectiveness of EbA practices in delivering adaptation benefits, and tailoring EbA policies and programs for smallholder farmers in different socioeconomic and biophysical contexts. (Résumé d'auteur
Quinstant Dark Energy Predictions for Structure Formation
We explore the predictions of a class of dark energy models, quinstant dark
energy, concerning the structure formation in the Universe, both in the linear
and non-linear regimes. Quinstant dark energy is considered to be formed by
quintessence and a negative cosmological constant. We conclude that these
models give good predictions for structure formation in the linear regime, but
fail to do so in the non-linear one, for redshifts larger than one.Comment: 9 pages, 14 figures, "Accepted for publication in Astrophysics &
Space Science
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