6,046 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
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
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
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
High-Temperature Superconducting Level Meter for Liquid Argon Detectors
Capacitive devices are customarily used as probes to measure the level of
noble liquids in detectors operated for neutrino studies and dark matter
searches. In this work we describe the use of a high-temperature
superconducting material as an alternative to control the level of a cryogenic
noble liquid. Lab measurements indicate that the superconductor shows a linear
behaviour, a high degree of stability and offers a very accurate determination
of the liquid volume. This device is therefore a competitive instrument and
shows several advantages over conventional level meters.Comment: 13 pages, 11 figures. Accepted for publication in JINS
On the bicrossproduct structures for the family of algebras
It is shown that the family of deformed algebras has a different bicrossproduct
structure for each in analogy to the undeformed case.Comment: Latex2e file. 14 page
Do borrão às aguadas: os engenheiros militares e a representação da Capitania de São Paulo
A análise do papel dos engenheiros militares perpassa as discussões sobre regiões específicas, mesmo quando eles, aparentemente, estão ausentes delas. Sua presença ou ausência sempre foi sinônimo de interesse e de projeto colonizador mais ou menos dirigido. Este ensaio tem como objeto de estudo a cartografia dos engenheiros militares atuantes na Capitania de São Paulo, território comumente visto como economicamente periférico e mais autônomo face aos desígnios da Coroa portuguesa. Com foco no corpus cartográfico de alguns profissionais que aqui atuaram, trata indiretamente da multifacetada atuação desses engenheiros, bem como do processo de feitura das cartas geográficas, corográficas e topográficas, do borrão às aguadas. Investigar a cartografia de alguns desses profissionais permite não apenas explorar a riqueza de suas biografias, como, também, acompanhar o processo de produção técnica dos mapas e os desígnios políticos envolvidos no devassamento e representação das terras descobertas no Novo Mundo.Analyzing the role of military engineers means venturing into discussions about specific regions, even those from which they are apparently absent. Their presence or absence has always been synonymous with interest and a more or less directed colonization project. This essay examines the maps produced by the military engineers working in the Captaincy of São Paulo, a territory often looked upon as one of little economic import and a rather autonomous area in light of the plans of the Portuguese Crown. By focusing on the cartographic corpus bequeathed by certain professionals serving in this region, we deal indirectly with the multifaceted role of these engineers as well as with the process of making geographic, chorographic and topographic charts - all the way from the sketch to watercolored maps. Perusing the charts constructed by some of these professionals enabled us not only to delve into the rich details of their biographies but also to observe the technical mapmaking process and to unravel the political designs behind the exploration and representation of the lands discovered in the New World
Dinâmica do potencial redox em condições de alagamento em amostras de latossolo amarelo, textura média do nordeste paraense.
Resumo: Os Latossolos Amarelos textura média é a classe de solo predominante no nordeste paraense aonde a atividade do cultivo da palma de óleo (dendezeiro) que é uma atividade tradicional e em expansão. Um dos desafios para a expansão da palmicultura é a elucidação da etiologia do agente causal da anomalia conhecida como amarelecimento fatal. Entre as hipóteses que estão sendo testada é estsão os distúrbios provocados na solução do solo devido a alteração do potencial redox em condições de alagamento e consequentemente redução do oxigênio no solo. O presente experimento teve como objetivo estudar a variação do potencial oxirredução em amostras de um Latossolo Amarelo, textura média, distrófico submetido a condições de alagamento por um período de 60 dias. Adicionalmente se testou o efeito da homogeneização da amostras na avaliação do potencial redox. As amostras de solo foram coletadas numa área de cultivo de palma de óleo no município de Moju - PA, com incidência de amarelecimento fatal. Estas amostras posteriormente foram alagadas por um período de 60 dias. Durante este período, o potencial redox foi medido semanalmente . Os resultados mostraram que o potencial redox se reduz com o tempo de alagamento, sendo limitado por deficiência de carbono. Não houve diferenças significativas nas leituras do potencial redox com e sem homogeneização das amostras.A adição de uma fonte adicional de carbono (glucose) levou o potencial a valores de – 350 mV, nestas condições e com baixo valor de pH típico destes solos predominam as formas reduzidas de Fe, Mn e N que podem causar distúrbios fisiológicos a palma de óleo e outros cultivos
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