224 research outputs found
Competitiveness of Broiler Producers in North America Under Alternative Free Trade Scenarios
International Relations/Trade,
Spatial Equilibrium Analysis of the World Durum Industry Under Alternative Export Policies
International Relations/Trade,
United States and Canadian Free Trade Agreement: Economic Implications
International Relations/Trade,
Ballistic transport and surface scattering in (In,Ga)As-InP heterostructure narrow channels
Narrow conduction channels are fabricated from an In0.75Ga0.25As-InP heterostructure using electron-beam lithography and dry etching. The etched surface is realized to be smooth by employing a reactive ion etching. The etching-induced surface conduction is eliminated by removing the damaged surface layer using a diluted HCl solution. The negligible surface depletion for the In-rich quantum well enables to create conducting channels in arbitrary geometries such as in a circular shape. We evidence the presence of a ballistic contribution in the electron transport by demonstrating a rectification of rf excitations that is achieved by the magnetic-field-tuned transmission asymmetry in the circularly-shaped channels. The absence of the surface depletion is shown to cause, on the other hand, a surface scattering for the electrons confined in the channels. An increase of the resistance, including its anomalous enhancement at low temperatures, is induced by the gas molecules attached to the sidewalls of the channels. We also report a large persistent photoconduction, which occurs as a parallel conduction in the undoped InP barrier layer.Peer Reviewe
Electron effective mass in Sn-doped monoclinic single crystal -gallium oxide determined by mid-infrared optical Hall effect
The isotropic average conduction band minimum electron effective mass in
Sn-doped monoclinic single crystal -GaO is experimentally
determined by mid-infrared optical Hall effect to be
combining investigations on () and () surface cuts. This result
falls within the broad range of values predicted by theoretical calculations
for undoped -GaO. The result is also comparable to recent
density functional calculations using the
Gaussian-attenuation-Perdue-Burke-Ernzerhof hybrid density functional, which
predict an average effective mass of (arXiv:1704.06711
[cond-mat.mtrl-sci]). Within our uncertainty limits we detect no anisotropy for
the electron effective mass, which is consistent with most previous theoretical
calculations. We discuss upper limits for possible anisotropy of the electron
effective mass parameter from our experimental uncertainty limits, and we
compare our findings with recent theoretical results
Arrival time and intensity binning at unprecedented repetition rates
Understanding dynamics on ultrafast timescales enables unique and new insights
into important processes in the materials and life sciences. In this respect,
the fundamental pump-probe approach based on ultra-short photon pulses aims at
the creation of stroboscopic movies. Performing such experiments at one of the
many recently established accelerator-based 4th-generation light sources such
as free-electron lasers or superradiant THz sources allows an enormous
widening of the accessible parameter space for the excitation and/or probing
light pulses. Compared to table-top devices, critical issues of this type of
experiment are fluctuations of the timing between the accelerator and external
laser systems and intensity instabilities of the accelerator-based photon
sources. Existing solutions have so far been only demonstrated at low
repetition rates and/or achieved a limited dynamic range in comparison to
table-top experiments, while the 4th generation of accelerator-based light
sources is based on superconducting radio-frequency technology, which enables
operation at MHz or even GHz repetition rates. In this article, we present the
successful demonstration of ultra-fast accelerator-laser pump-probe
experiments performed at an unprecedentedly high repetition rate in the few-
hundred-kHz regime and with a currently achievable optimal time resolution of
13 fs (rms). Our scheme, based on the pulse-resolved detection of multiple
beam parameters relevant for the experiment, allows us to achieve an excellent
sensitivity in real-world ultra-fast experiments, as demonstrated for the
example of THz-field-driven coherent spin precession
Ultrafast High-Field THz beamline at X-ray FEL
THz sources at FLASH utilize spent electron beam from a soft X-ray FEL to generate very intense (up to 150µJ), tunable frequency (1-300THz) and ultrafast narrowband (~10%) THz pulses, which are naturally synchronized to soft X-ray pulses [1]. This unique combination allows for wide range of element specific pump-probe experiments in physics, material science and biology. Here we discuss the unique features of the FLASH THz pulses and the accelerator source that bring along a set of challenges in the diagnostics of their key parameters: pulse energy, spectral, temporal and spatial profiles.VII International School and Conference on Photonics : PHOTONICA2019 : Abstracts of Tutorial, Keynote, Invited Lectures, Progress Reports and Contributed Papers; August 26-30; Belgrad
THz-Driven Coherent Magnetization Dynamics in a Labyrinth Domain State
Terahertz (THz) light pulses can be used for an ultrafast coherent
manipulation of the magnetization. Driving the magnetization at THz frequencies
is currently the fastest way of writing magnetic information in ferromagnets.
Using time-resolved resonant magnetic scattering, we gain new insights to the
THz-driven coherent magnetization dynamics on nanometer length scales. We
observe ultrafast demagnetization and coherent magnetization oscillations that
are governed by a time-dependent damping. This damping is determined by the
interplay of lattice heating and magnetic anisotropy reduction revealing an
upper speed limit for THz-induced magnetization switching. We show that in the
presence of nanometer-sized magnetic domains, the ultrafast magnetization
oscillations are associated with a correlated beating of the domain walls. The
overall domain structure thereby remains largely unaffected which highlights
the applicability of THz-induced switching on the nanoscale.Comment: 10 pages, 8 figures and 54 reference
[pain]Byte VR Storytelling & Classical Ballet
This initial stage paper focuses on the Virtual Reality (VR) experience of the [pain]Byte ballet. The live and VR experience debut October 1st 2017, as part of the Brighton digital festival. Specifically, the development of the VR environment to compliment live performance by using the same choreography to create an option capture element of the VR story telling experience. Reviewing Virtual & Alternative reality gaming & storytelling works and the use of VR for chronic pain management (Chen, Win). Does the VR experience compare to that of the live theatre for the audience?
The data visualisations and VR environment will be continuations of the Network Simulator, [data]Storm 2015. We are visualising and comparing the pain pathway system to that of a social network. Linking pain signals to viral/negative messaging for some of the visuals. The main purpose of the pieces links to how “we" present ourselves online, these better or veiled versions of ourselves. For chronic pain sufferers, this can be daily activity in the real world. The paper concludes by identifying some future directions for the research project.
The Ballet: [pain]Byte is a data driven dance classical ballet performance and VR (virtual reality) experience. [pain]Byte, is about chronic pain and biomedical engineering, in particular the use of implanted technology - neuromodulation (Al-Kaisey et al). Using data as a medium for storytelling, what it means to be in chronic pain. The live augmented theatre and VR experience research focuses on how an audience’s exposure and understanding are impacted by the difference mediums used for [pain]byte
High-field high-repetition-rate sources for the coherent THz control of matter
Ultrashort flashes of THz light with low photon energies of a few meV, but strong electric or magnetic field transients have recently been employed to prepare various fascinating nonequilibrium states in matter. Here we present a new class of sources based on superradiant enhancement of radiation from relativistic electron bunches in a compact electron accelerator that we believe will revolutionize experiments in this field. Our prototype source generates high-field THz pulses at unprecedented quasicontinuous-wave repetition rates up to the MHz regime. We demonstrate parameters that exceed state-of-the-art laser-based sources by more than 2 orders of magnitude. The peak fields and the repetition rates are highly scalable and once fully operational this type of sources will routinely provide 1 MV/cm electric fields and 0.3 T magnetic fields at repetition rates of few 100 kHz. We benchmark the unique properties by performing a resonant coherent THz control experiment with few 10 fs resolution
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