440 research outputs found
Slippage of water past superhydrophobic carbon nanotube forests in microchannels
We present in this letter an experimental characterization of liquid flow
slippage over superhydrophobic surfaces made of carbon nanotube forests,
incorporated in microchannels. We make use of a micro-PIV (Particule Image
Velocimetry) technique to achieve the submicrometric resolution on the flow
profile necessary for accurate measurement of the surface hydrodynamic
properties. We demonstrate boundary slippage on the Cassie superhydrophobic
state, associated with slip lengths of a few microns, while a vanishing slip
length is found in the Wenzel state, when the liquid impregnates the surface.
Varying the lateral roughness scale L of our carbon nanotube forest-based
superhydrophobic surfaces, we demonstrate that the slip length varies linearly
with L in line with theoretical predictions for slippage on patterned surfaces.Comment: under revie
Is the availability of substrate for the tricarboxylic acid cycle a limiting factor for uncoupled respiration in sycamore (Acer pseudoplatanus) cells?
van der Waals interaction in nanotube bundles : consequences on vibrational modes
We have developed a pair-potential approach for the evaluation of van der
Waals interaction between carbon nanotubes in bundles.
Starting from a continuum model, we show that the intertube modes range from
to . Using a non-orthogonal tight-binding approximation
for describing the covalent intra-tube bonding in addition, we confirme a
slight chiral dependance of the breathing mode frequency and we found that this
breathing mode frequency increase by 10 % if the nanotube lie inside a
bundle as compared to the isolated tube.Comment: 5 pages, 2 figure
High-field 1/f noise in hBN-encapsulated graphene transistors
Low-frequency 1/f noise in electronics is a conductance fluctuation, that has
been expressed in terms of a mobility "-noise" by Hooge and
Kleinpenning. Understanding this noise in graphene is a key towards
high-performance electronics. Early investigations in diffusive graphene have
pointed out a deviation from the standard Hooge formula, with a modified
expression where the free-carrier density is substituted by a constant density
. We investigate hBN-encapsulated
graphene transistors where high mobility gives rise to the non-linear
velocity-saturation regime. In this regime, the -noise is accounted for
by substituting conductance by differential conductance , ressulting in a
bell-shape dependence of flicker noise with bias voltage . The same analysis
holds at larger bias in the Zener regime, with two main differences: the first
one is a strong enhancement of the Hooge parameter reflecting the hundred-times
larger coupling of interband excitations to the hyperbolic phonon-polariton
(HPhP) modes of the mid-infrared Reststrahlen (RS) bands of hBN. The second is
an exponential suppression of this coupling at large fields, which we attribute
to decoherence effects. We also show that the HPhP bands control the amplitude
of flicker noise according to the graphene-hBN thermal coupling estimated with
microwave noise thermometry. The phenomenology of -noise in graphene
supports a quantum-coherent bremsstrahlung interpretation of flicker noise.Comment: v2, main + SI, added reference to open data on Zenodo repositor
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Modeling the global emission, transport and deposition of trace elements associated with mineral dust
Trace element deposition from desert dust has important impacts on ocean primary productivity, the quantification of which could be useful in determining the magnitude and sign of the biogeochemical feedback on radiative forcing. However, the impact of elemental deposition to remote ocean regions is not well understood and is not currently included in global climate models. In this study, emission inventories for eight elements primarily of soil origin, Mg, P, Ca, Mn, Fe, K, Al, and Si are determined based on a global mineral data set and a soil data set. The resulting elemental fractions are used to drive the desert dust model in the Community Earth System Model (CESM) in order to simulate the elemental concentrations of atmospheric dust. Spatial variability of mineral dust elemental fractions is evident on a global scale, particularly for Ca. Simulations of global variations in the Ca / Al ratio, which typically range from around 0.1 to 5.0 in soils, are consistent with observations, suggesting that this ratio is a good signature for dust source regions. The simulated variable fractions of chemical elements are sufficiently different; estimates of deposition should include elemental variations, especially for Ca, Al and Fe. The model results have been evaluated with observations of elemental aerosol concentrations from desert regions and dust events in non-dust regions, providing insights into uncertainties in the modeling approach. The ratios between modeled and observed elemental fractions range from 0.7 to 1.6, except for Mg and Mn (3.4 and 3.5, respectively). Using the soil database improves the correspondence of the spatial heterogeneity in the modeling of several elements (Ca, Al and Fe) compared to observations. Total and soluble dust element fluxes to different ocean basins and ice sheet regions have been estimated, based on the model results. The annual inputs of soluble Mg, P, Ca, Mn, Fe and K associated with dust using the mineral data set are 0.30 Tg, 16.89 Gg, 1.32 Tg, 22.84 Gg, 0.068 Tg, and 0.15 Tg to global oceans and ice sheets
Modeling the global emission, transport and deposition of trace elements associated with mineral dust
Trace element deposition from desert dust has important impacts on ocean primary productivity, the quantification of which could be useful in determining the magnitude and sign of the biogeochemical feedback on radiative forcing. However, the impact of elemental deposition to remote ocean regions is not well understood and is not currently included in global climate models. In this study, emission inventories for eight elements primarily of soil origin, Mg, P, Ca, Mn, Fe, K, Al, and Si are determined based on a global mineral data set and a soil data set. The resulting elemental fractions are used to drive the desert dust model in the Community Earth System Model (CESM) in order to simulate the elemental concentrations of atmospheric dust. Spatial variability of mineral dust elemental fractions is evident on a global scale, particularly for Ca. Simulations of global variations in the Ca / Al ratio, which typically range from around 0.1 to 5.0 in soils, are consistent with observations, suggesting that this ratio is a good signature for dust source regions. The simulated variable fractions of chemical elements are sufficiently different; estimates of deposition should include elemental variations, especially for Ca, Al and Fe. The model results have been evaluated with observations of elemental aerosol concentrations from desert regions and dust events in non-dust regions, providing insights into uncertainties in the modeling approach. The ratios between modeled and observed elemental fractions range from 0.7 to 1.6, except for Mg and Mn (3.4 and 3.5, respectively). Using the soil database improves the correspondence of the spatial heterogeneity in the modeling of several elements (Ca, Al and Fe) compared to observations. Total and soluble dust element fluxes to different ocean basins and ice sheet regions have been estimated, based on the model results. The annual inputs of soluble Mg, P, Ca, Mn, Fe and K associated with dust using the mineral data set are 0.30 Tg, 16.89 Gg, 1.32 Tg, 22.84 Gg, 0.068 Tg, and 0.15 Tg to global oceans and ice sheets
Atmospheric aerosols at the Pierre Auger Observatory and environmental implications
The Pierre Auger Observatory detects the highest energy cosmic rays.
Calorimetric measurements of extensive air showers induced by cosmic rays are
performed with a fluorescence detector. Thus, one of the main challenges is the
atmospheric monitoring, especially for aerosols in suspension in the
atmosphere. Several methods are described which have been developed to measure
the aerosol optical depth profile and aerosol phase function, using lasers and
other light sources as recorded by the fluorescence detector. The origin of
atmospheric aerosols traveling through the Auger site is also presented,
highlighting the effect of surrounding areas to atmospheric properties. In the
aim to extend the Pierre Auger Observatory to an atmospheric research platform,
a discussion about a collaborative project is presented.Comment: Regular Article, 16 pages, 12 figure
The camera of the fifth H.E.S.S. telescope. Part I: System description
In July 2012, as the four ground-based gamma-ray telescopes of the H.E.S.S.
(High Energy Stereoscopic System) array reached their tenth year of operation
in Khomas Highlands, Namibia, a fifth telescope took its first data as part of
the system. This new Cherenkov detector, comprising a 614.5 m^2 reflector with
a highly pixelized camera in its focal plane, improves the sensitivity of the
current array by a factor two and extends its energy domain down to a few tens
of GeV.
The present part I of the paper gives a detailed description of the fifth
H.E.S.S. telescope's camera, presenting the details of both the hardware and
the software, emphasizing the main improvements as compared to previous
H.E.S.S. camera technology.Comment: 16 pages, 13 figures, accepted for publication in NIM
Fabrication and electrical integration of robust carbon nanotube micropillars by self-directed elastocapillary densification
Vertically-aligned carbon nanotube (CNT) "forest" microstructures fabricated
by chemical vapor deposition (CVD) using patterned catalyst films typically
have a low CNT density per unit area. As a result, CNT forests have poor bulk
properties and are too fragile for integration with microfabrication
processing. We introduce a new self-directed capillary densification method
where a liquid is controllably condensed onto and evaporated from CNT forests.
Compared to prior approaches, where the substrate with CNTs is immersed in a
liquid, our condensation approach gives significantly more uniform structures
and enables precise control of the CNT packing density and pillar
cross-sectional shape. We present a set of design rules and parametric studies
of CNT micropillar densification by this method, and show that self-directed
capillary densification enhances the Young's modulus and electrical
conductivity of CNT micropillars by more than three orders of magnitude. Owing
to the outstanding properties of CNTs, this scalable process will be useful for
the integration of CNTs as functional material in microfabricated devices for
mechanical, electrical, thermal, and biomedical applications
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