13,170 research outputs found
Non-local transport and the hydrodynamic shear viscosity in graphene
Motivated by recent experimental progress in preparing encapsulated graphene
sheets with ultra-high mobilities up to room temperature, we present a
theoretical study of dc transport in doped graphene in the hydrodynamic regime.
By using the continuity and Navier-Stokes equations, we demonstrate
analytically that measurements of non-local resistances in multi-terminal Hall
bar devices can be used to extract the hydrodynamic shear viscosity of the
two-dimensional (2D) electron liquid in graphene. We also discuss how to probe
the viscosity-dominated hydrodynamic transport regime by scanning probe
potentiometry and magnetometry. Our approach enables measurements of the
viscosity of any 2D electron liquid in the hydrodynamic transport regime.Comment: 12 pages, 4 multi-panel figure
Electron hydrodynamics dilemma: whirlpools or no whirlpools
In highly viscous electron systems such as, for example, high quality
graphene above liquid nitrogen temperature, a linear response to applied
electric current becomes essentially nonlocal, which can give rise to a number
of new and counterintuitive phenomena including negative nonlocal resistance
and current whirlpools. It has also been shown that, although both effects
originate from high electron viscosity, a negative voltage drop does not
principally require current backflow. In this work, we study the role of
geometry on viscous flow and show that confinement effects and relative
positions of injector and collector contacts play a pivotal role in the
occurrence of whirlpools. Certain geometries may exhibit backflow at
arbitrarily small values of the electron viscosity, whereas others require a
specific threshold value for whirlpools to emerge
Wearable flexible lightweight modular RFID tag with integrated energy harvester
A novel wearable radio frequency identification (RFID) tag with sensing, processing, and decision-taking capability is presented for operation in the 2.45-GHz RFID superhigh frequency (SHF) band. The tag is powered by an integrated light harvester, with a flexible battery serving as an energy buffer. The proposed active tag features excellent wearability, very high read range, enhanced functionality, flexible interfacing with diverse low-power sensors, and extended system autonomy through an innovative holistic microwave system design paradigm that takes antenna design into consideration from the very early stages. Specifically, a dedicated textile shorted circular patch antenna with monopolar radiation pattern is designed and optimized for highly efficient and stable operation within the frequency band of operation. In this process, the textile antenna's functionality is augmented by reusing its surface as an integration platform for light-energy-harvesting, sensing, processing, and transceiver hardware, without sacrificing antenna performance or the wearer's comfort. The RFID tag is validated by measuring its stand-alone and on-body characteristics in free-space conditions. Moreover, measurements in a real-world scenario demonstrate an indoor read range up to 23 m in nonline-of-sight indoor propagation conditions, enabling interrogation by a reader situated in another room. In addition, the RFID platform only consumes 168.3 mu W, when sensing and processing are performed every 60 s
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A Novel Reporter Mouse Uncovers Endogenous Brn3b Expression.
Brn3b (Pou4f2) is a class-4 POU domain transcription factor known to play central roles in the development of different neuronal populations of the Central Nervous System, including retinal ganglion cells (RGCs), the neurons that connect the retina with the visual centers of the brain. Here, we have used CRISPR-based genetic engineering to generate a Brn3b-mCherry reporter mouse without altering the endogenous expression of Brn3b. In our mouse line, mCherry faithfully recapitulates normal Brn3b expression in the retina, the optic tracts, the midbrain tectum, and the trigeminal ganglia. The high sensitivity of mCherry also revealed novel expression of Brn3b in the neuroectodermal cells of the optic stalk during early stages of eye development. Importantly, the fluorescent intensity of Brn3b-mCherry in our reporter mice allows for noninvasive live imaging of RGCs using Scanning Laser Ophthalmoscopy (SLO), providing a novel tool for longitudinal monitoring of RGCs
Sequentializing Parameterized Programs
We exhibit assertion-preserving (reachability preserving) transformations
from parameterized concurrent shared-memory programs, under a k-round
scheduling of processes, to sequential programs. The salient feature of the
sequential program is that it tracks the local variables of only one thread at
any point, and uses only O(k) copies of shared variables (it does not use extra
counters, not even one counter to keep track of the number of threads).
Sequentialization is achieved using the concept of a linear interface that
captures the effect an unbounded block of processes have on the shared state in
a k-round schedule. Our transformation utilizes linear interfaces to
sequentialize the program, and to ensure the sequential program explores only
reachable states and preserves local invariants.Comment: In Proceedings FIT 2012, arXiv:1207.348
Internal Time Formalism for Spacetimes with Two Killing Vectors
The Hamiltonian structure of spacetimes with two commuting Killing vector
fields is analyzed for the purpose of addressing the various problems of time
that arise in canonical gravity. Two specific models are considered: (i)
cylindrically symmetric spacetimes, and (ii) toroidally symmetric spacetimes,
which respectively involve open and closed universe boundary conditions. For
each model canonical variables which can be used to identify points of space
and instants of time, {\it i.e.}, internally defined spacetime coordinates, are
identified. To do this it is necessary to extend the usual ADM phase space by a
finite number of degrees of freedom. Canonical transformations are exhibited
that identify each of these models with harmonic maps in the parametrized field
theory formalism. The identifications made between the gravitational models and
harmonic map field theories are completely gauge invariant, that is, no
coordinate conditions are needed. The degree to which the problems of time are
resolved in these models is discussed.Comment: 36 pages, Te
Effects of No-Tillage Production Practices on Crop Yields as Influenced by Crop and Growing Environment Factors
This paper evaluated differences between yields of no-tillage compared to conventional or reduced tillage and their associated downside risk. Six crops were evaluated along with how those yields and risks differed by various environmental factors such geographic location, precipitation, soil type and how long the practice had been used.no-tillage, conservation, conventional tillage, downside-risk, yield, Agribusiness, Environmental Economics and Policy, Farm Management, Land Economics/Use, Production Economics, Risk and Uncertainty,
Orographic and convective gravity waves above the Alps and Andes mountains during GPS radio occultation events – a case study
The significant distortions introduced in the measured atmospheric gravity wavelengths by soundings other than in vertical and horizontal directions, are discussed as a function of elevation angle of the sounding path and the gravity waves aspect ratio. Under- or overestimation of real vertical wavelengths during the measurement process depends basically on the value of these two parameters. The consequences of these distortions on the calculation of the energy and vertical flux of horizontal momentum are analyzed and discussed in the context of two experimental limb satellite setups: GPS-LEO radio occultations and TIMED/SABER measurements. Possible discrepancies previously found between the momentum flux calculated from satellite temperature profiles, on site and from model simulations, may, to a certain degree, be attributed to these distortions. A recalculation of previous momentum flux climatologies based on these considerations seems to be a difficult goal.Fil: Hierro, Rodrigo Federico. Universidad Austral. Facultad de IngenierĂa. Departamento de Ciencias Básicas; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Steiner, Andrea K.. Universidad de Graz; AustriaFil: de la Torre, Alejandro. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Austral. Facultad de IngenierĂa. Departamento de Ciencias Básicas; ArgentinaFil: Alexander, Pedro Manfredo. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de FĂsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FĂsica de Buenos Aires; ArgentinaFil: Llamedo Soria, Pablo Martin. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Austral. Facultad de IngenierĂa. Departamento de Ciencias Básicas; ArgentinaFil: Cremades, Pablo Gabriel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentin
On Unitary Time Evolution in Gowdy Cosmologies
A non-perturbative canonical quantization of Gowdy polarized models
carried out recently is considered. This approach profits from the equivalence
between the symmetry reduced model and 2+1 gravity coupled to a massless real
scalar field. The system is partially gauge fixed and a choice of internal time
is performed, for which the true degrees of freedom of the model reduce to a
massless free scalar field propagating on a 2-dimensional expanding torus. It
is shown that the symplectic transformation that determines the classical
dynamics cannot be unitarily implemented on the corresponding Hilbert space of
quantum states. The implications of this result for both quantization of fields
on curved manifolds and physically relevant questions regarding the initial
singularity are discussed.Comment: 16 pages, no figures, latex file; references added, a proof included.
Final version to appear in IJMP
Antiproton modulation in the Heliosphere and AMS-02 antiproton over proton ratio prediction
We implemented a quasi time-dependent 2D stochastic model of solar modulation
describing the transport of cosmic rays (CR) in the heliosphere. Our code can
modulate the Local Interstellar Spectrum (LIS) of a generic charged particle
(light cosmic ions and electrons), calculating the spectrum at 1AU. Several
measurements of CR antiparticles have been performed. Here we focused our
attention on the CR antiproton component and the antiproton over proton ratio.
We show that our model, using the same heliospheric parameters for both
particles, fit the observed anti-p/p ratio. We show a good agreement with
BESS-97 and PAMELA data and make a prediction for the AMS-02 experiment
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