7,396 research outputs found
Graphene Squeeze-Film Pressure Sensors
The operating principle of squeeze-film pressure sensors is based on the
pressure dependence of a membrane's resonance frequency, caused by the
compression of the surrounding gas which changes the resonator stiffness. To
realize such sensors, not only strong and flexible membranes are required, but
also minimization of the membrane's mass is essential to maximize responsivity.
Here, we demonstrate the use of a few-layer graphene membrane as a squeeze-film
pressure sensor. A clear pressure dependence of the membrane's resonant
frequency is observed, with a frequency shift of 4 MHz between 8 and 1000 mbar.
The sensor shows a reproducible response and no hysteresis. The measured
responsivity of the device is 9000 Hz/mbar, which is a factor 45 higher than
state-of-the-art MEMS-based squeeze-film pressure sensors while using a 25
times smaller membrane area
Visualizing the motion of graphene nanodrums
Membranes of suspended two-dimensional materials show a large variability in
mechanical properties, in part due to static and dynamic wrinkles. As a
consequence, experiments typically show a multitude of nanomechanical resonance
peaks, which makes an unambiguous identification of the vibrational modes
difficult. Here, we probe the motion of graphene nanodrum resonators with
spatial resolution using a phase-sensitive interferometer. By simultaneously
visualizing the local phase and amplitude of the driven motion, we show that
unexplained spectral features represent split degenerate modes. When taking
these into account, the resonance frequencies up to the eighth vibrational mode
agree with theory. The corresponding displacement profiles however, are
remarkably different from theory, as small imperfections increasingly deform
the nodal lines for the higher modes. The Brownian motion, which is used to
calibrate the local displacement, exhibits a similar mode pattern. The
experiments clarify the complicated dynamic behaviour of suspended
two-dimensional materials, which is crucial for reproducible fabrication and
applications
Colorimetry technique for scalable characterization of suspended graphene
Previous statistical studies on the mechanical properties of
chemical-vapor-deposited (CVD) suspended graphene membranes have been performed
by means of measuring individual devices or with techniques that affect the
material. Here, we present a colorimetry technique as a parallel, non-invasive,
and affordable way of characterizing suspended graphene devices. We exploit
Newton rings interference patterns to study the deformation of a double-layer
graphene drum 13.2 micrometer in diameter when a pressure step is applied. By
studying the time evolution of the deformation, we find that filling the drum
cavity with air is 2-5 times slower than when it is purged
The influence of coronal EUV irradiance on the emission in the He I 10830 A and D3 multiplets
Two of the most attractive spectral windows for spectropolarimetric
investigations of the physical properties of the plasma structures in the solar
chromosphere and corona are the ones provided by the spectral lines of the He I
10830 A and 5876 A (or D3) multiplets, whose polarization signals are sensitive
to the Hanle and Zeeman effects. However, in order to be able to carry out
reliable diagnostics, it is crucial to have a good physical understanding of
the sensitivity of the observed spectral line radiation to the various
competing driving mechanisms. Here we report a series of off-the-limb non-LTE
calculations of the He I D3 and 10830 A emission profiles, focusing our
investigation on their sensitivity to the EUV coronal irradiation and the model
atmosphere used in the calculations. We show in particular that the intensity
ratio of the blue to the red components in the emission profiles of the He I
10830 A multiplet turns out to be a good candidate as a diagnostic tool for the
coronal irradiance. Measurements of this observable as a function of the
distance to the limb and its confrontation with radiative transfer modeling
might give us valuable information on the physical properties of the solar
atmosphere and on the amount of EUV radiation at relevant wavelengths
penetrating the chromosphere from above.Comment: 19 pages, 11 figures (pre-print format). Accepted for publication in
Ap
Anomalous response of superconducting titanium nitride resonators to terahertz radiation
We present an experimental study of KIDs fabricated of atomic layer deposited
TiN films, and characterized at radiation frequencies of ~GHz. The
responsivity to radiation is measured and found to increase with increasing
radiation powers, opposite to what is expected from theory and observed for
hybrid niobium titanium nitride / aluminium (NbTiN/Al) and all-aluminium
(all-Al) KIDs. The noise is found to be independent of the level of the
radiation power. The noise equivalent power (NEP) improves with higher
radiation powers, also opposite to what is observed and well understood for
hybrid NbTiN/Al and all-Al KIDs. We suggest that an inhomogeneous state of
these disordered superconductors should be used to explain these observations
Production and Downstream Integration of 5-(Chloromethyl)furfural from Lignocellulose
The importance of reducing the strong dependence of the chemical industry on fossil feedstock is no longer a debate. Above-the-ground carbon is abundant, but scalable technologies to supply alternatives to fossil-fuel-derived chemicals and/or materials at the world scale are still not available. Lignocellulosic biomass is the most available carbon source, and a first requirement for its valorization is the complete saccharification of its sugar-bearing components. HCl-based technologies can achieve this at 20 °C and ambient pressure. These principles were disclosed in the 1920s, but the inability to economically separate sugars from acids impeded its commercialization. Avantium Chemicals B.V. developed a modern version of this “Bergius” highly concentrated acid hydrolysis, in which the saccharides in HCl are transformed into furanics without any prior purification, in particular, to 5-(chloromethyl)furfural (CMF). Saccharide conversion to CMF was developed by Mascal in the early 2000s. CMF is extracted in situ using immiscible organic solvents, allowing for an easy product separation. This study not only targets to investigate the viability and optimization of this integrated process but also aims to predict the outcome of the CMF formation reaction by applying design of experiment techniques from the hydrolyzed saccharides varying a broad range of reaction parameters
Divergência entre acessos de arroz irrigado brasileiro utilizando o método de Ward.
O objetivo do trabalho foi caracterizar a parecença entre 27 acessos de linhagens e cultivares brasileiras de sistema de cultivo irrigado da coleção nuclear de arroz da Embrapa, reunindo-os em grupos por meio da técnica de agrupamento de Ward aplicada a caracteres agronômicos
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