58 research outputs found
Direct electronic measurement of Peltier cooling and heating in graphene
Thermoelectric effects allow the generation of electrical power from waste
heat and the electrical control of cooling and heating. Remarkably, these
effects are also highly sensitive to the asymmetry in the density of states
around the Fermi energy and can therefore be exploited as probes of distortions
in the electronic structure at the nanoscale. Here we consider two-dimensional
graphene as an excellent nanoscale carbon material for exploring the
interaction between electronic and thermal transport phenomena, by presenting a
direct and quantitative measurement of the Peltier component to electronic
cooling and heating in graphene. Thanks to an architecture including nanoscale
thermometers, we detected Peltier component modulation of up to 15 mK for
currents of 20 A at room temperature and observed a full reversal between
Peltier cooling and heating for electron and hole regimes. This fundamental
thermodynamic property is a complementary tool for the study of nanoscale
thermoelectric transport in two-dimensional materials.Comment: Final version published in Nature Communications under a Creative
Commons Attribution 4.0 International Licens
Modulation of magnon spin transport in a magnetic gate transistor
We demonstrate a modulation of up to 18% in the magnon spin transport in a
magnetic insulator (YFeO, YIG) using a common ferromagnetic
metal (permalloy, Py) as a magnetic control gate. A Py electrode, placed
between two Pt injector and detector electrodes, acts as a magnetic gate in our
prototypical magnon transistor device. By manipulating the magnetization
direction of Py with respect to that of YIG, the transmission of magnons
through the Py|YIG interface can be controlled, resulting in a modulation of
the non-equilibrium magnon density in the YIG channel between the Pt injector
and detector electrodes. This study opens up the possibility of using the
magnetic gating effect for magnon-based spin logic applications
Colloquium: Spintronics in graphene and other two-dimensional materials
After the first unequivocal demonstration of spin transport in graphene
(Tombros et al., 2007), surprisingly at room temperature, it was quickly
realized that this novel material was relevant for both fundamental spintronics
and future applications. Over the decade since, exciting results have made the
field of graphene spintronics blossom, and a second generation of studies has
extended to new two-dimensional (2D) compounds. This Colloquium reviews recent
theoretical and experimental advances on electronic spin transport in graphene
and related 2D materials, focusing on emergent phenomena in van der Waals
heterostructures and the new perspectives provided by them. These phenomena
include proximity-enabled spin-orbit effects, the coupling of electronic spin
to light, electrical tunability, and 2D magnetism.Comment: 30 pages, 12 figure
Spin dependent quantum interference in non-local graphene spin valves
Spin dependent electron transport measurements on graphene are of high
importance to explore possible spintronic applications. Up to date all spin
transport experiments on graphene were done in a semi-classical regime,
disregarding quantum transport properties such as phase coherence and
interference. Here we show that in a quantum coherent graphene nanostructure
the non-local voltage is strongly modulated. Using non-local measurements, we
separate the signal in spin dependent and spin independent contributions. We
show that the spin dependent contribution is about two orders of magnitude
larger than the spin independent one, when corrected for the finite
polarization of the electrodes. The non-local spin signal is not only strongly
modulated but also changes polarity as a function of the applied gate voltage.
By locally tuning the carrier density in the constriction we show that the
constriction plays a major role in this effect and indicates that it can act as
a spin filter device. Our results show the potential of quantum coherent
graphene nanostructures for the use in future spintronic devices
Thermoelectric spin voltage in graphene
In recent years, new spin-dependent thermal effects have been discovered in
ferromagnets, stimulating a growing interest in spin caloritronics, a field
that exploits the interaction between spin and heat currents. Amongst the most
intriguing phenomena is the spin Seebeck effect, in which a thermal gradient
gives rise to spin currents that are detected through the inverse spin Hall
effect. Non-magnetic materials such as graphene are also relevant for spin
caloritronics, thanks to efficient spin transport, energy-dependent carrier
mobility and unique density of states. Here, we propose and demonstrate that a
carrier thermal gradient in a graphene lateral spin valve can lead to a large
increase of the spin voltage near to the graphene charge neutrality point. Such
an increase results from a thermoelectric spin voltage, which is analogous to
the voltage in a thermocouple and that can be enhanced by the presence of hot
carriers generated by an applied current. These results could prove crucial to
drive graphene spintronic devices and, in particular, to sustain pure spin
signals with thermal gradients and to tune the remote spin accumulation by
varying the spin-injection bias
Bright 30 THz Impulsive Solar Bursts
Impulsive 30 THz continuum bursts have been recently observed in solar
flares, utilizing small telescopes with a unique and relatively simple optical
setup concept. The most intense burst was observed together with a GOES X2
class event on October 27, 2014, also detected at two sub-THz frequencies,
RHESSI X-rays and SDO/HMI and EUV. It exhibits strikingly good correlation in
time and in space with white light flare emission. It is likely that this
association may prove to be very common. All three 30 THz events recently
observed exhibited intense fluxes in the range of 104 solar flux units,
considerably larger than those measured for the same events at microwave and
sub-mm wavelengths. The 30 THz burst emission might be part of the same
spectral burst component found at sub-THz frequencies. The 30 THz solar bursts
open a promising new window for the study of flares at their originComment: 11 pages, 4 Figures J. Geophys. Res - Space Physics, accepted, May
21, 201
The Structural Evolution of Milky-Way-Like Star-Forming Galaxies zeta is approximately 1.3
We follow the structural evolution of star-forming galaxies (SFGs) like the Milky Way by selecting progenitors to zeta is approx. 1.3 based on the stellar mass growth inferred from the evolution of the star-forming sequence. We select our sample from the 3D-HT survey, which utilizes spectroscopy from the HST-WFC3 G141 near-IR grism and enables precise redshift measurements for our sample of SFGs. Structural properties are obtained from Sersic profile fits to CANDELS WFC3 imaging. The progenitors of zeta = 0 SFGs with stellar mass M = 10(exp 10.5) solar mass are typically half as massive at zeta is approx. 1. This late-time stellar mass grow is consistent with recent studies that employ abundance matching techniques. The descendant SFGs at zeta is approx. 0 have grown in half-light radius by a factor of approx. 1.4 zeta is approx. 1. The half-light radius grows with stellar mass as r(sub e) alpha stellar mass(exp 0.29). While most of the stellar mass is clearly assembling at large radii, the mass surface density profiles reveal ongoing mass growth also in the central regions where bulges and pseudobulges are common features in present day late-type galaxies. Some portion of this growth in the central regions is due to star formation as recent observations of H() maps for SFGs at zeta approx. are found to be extended but centrally peaked. Connecting our lookback study with galactic archeology, we find the stellar mass surface density at R - 8 kkpc to have increased by a factor of approx. 2 since zeta is approx. 1, in good agreement with measurements derived for the solar neighborhood of the Milky Way
Fabrication of cell container arrays with overlaid surface topographies
This paper presents cell culture substrates in the form of microcontainer arrays with overlaid surface topographies, and a technology for their fabrication. The new fabrication technology is based on microscale thermoforming of thin polymer films whose surfaces are topographically prepatterned on a micro- or nanoscale. For microthermoforming, we apply a new process on the basis of temporary back moulding of polymer films and use the novel concept of a perforated-sheet-like mould. Thermal micro- or nanoimprinting is applied for prepatterning. The novel cell container arrays are fabricated from polylactic acid (PLA) films. The thin-walled microcontainer structures have the shape of a spherical calotte merging into a hexagonal shape at their upper circumferential edges. In the arrays, the cell containers are arranged densely packed in honeycomb fashion. The inner surfaces of the highly curved container walls are provided with various topographical micro- and nanopatterns. For a first validation of the microcontainer arrays as in vitro cell culture substrates, C2C12 mouse premyoblasts are cultured in containers with microgrooved surfaces and shown to align along the grooves in the three-dimensional film substrates. In future stem-cell-biological and tissue engineering applications, microcontainers fabricated using the proposed technology may act as geometrically defined artificial microenvironments or niches
Inter-relações entre as propriedades fÃsicas e os coeficientes da curva de retenção de água de um latossolo sob diferentes sistemas de uso
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