1,422 research outputs found
Observation of asymmetric solitons in waveguide arrays with refractive index gradient
We study light propagation in waveguide arrays made in Kerr nonlinear media
with a transverse refractive index gradient, and we find that the presence of
the refractive index gradient leads to the appearance of a number of new
soliton families. The effective coupling between the solitons and the localized
linear eigenmodes of the lattice induces a drastic asymmetry in the soliton
shapes and the appearance of long tails at the soliton wings. Such unusual
solitons are found to be completely stable under propagation, and we report
their experimental observation in fs-laser written waveguide arrays with
focusing Kerr nonlinearity.Comment: 4 pages, 5 figures, to appear in Optics Letter
Superconducting Electrometer Based on the Resistively Shunted Bloch Transistor
We have fabricated the Bloch transistor shunted on-chip by a small-sized Cr
resistor with Rs about 1 kOhm. The Bloch transistor normally consists of two
small Josephson junctions connected in series, which in our case have been
replaced by two superconducting interferometer loops, each with two junctions
in parallel. A capacitively coupled gate is supplied to control the induced
charge of the small intermediate electrode (island) of the transistor. The
measured I-V curves show no hysteresis and correspond to the operation of a
effective Josephson junction at the high-damping and strong-noise limits. The
critical current of the system was found to be close to its nominal value, that
is in accordance with the electromagnetic environment theory. The I-V curves
were modulated by the gate with a period of e and a maximum swing of about 2
/mu_V. Such rather moderate modulation results from the Josephson-to- charging
energies ratio, Ej/Ec about 9, in our sample being far from its optimum value
of 0.3 up to 1.Comment: To be published in IEEE Transactions on Applied Superconductivity,
June 199
Synchronized single electron emission from dynamical quantum dots
We study synchronized quantized charge pumping through several dynamical
quantum dots (QDs) driven by a single time modulated gate signal. We show that
the main obstacle for synchronization being the lack of uniformity can be
overcome by operating the QDs in the decay cascade regime. We discuss the
mechanism responsible for lifting the stringent uniformity requirements. This
enhanced functionality of dynamical QDs might find applications in
nanoelectronics and quantum metrology.Comment: 4 pages, 3 figures, submitted to AP
Impact of loss on the wave dynamics in photonic waveguide lattices
We analyze the impact of loss in lattices of coupled optical waveguides and
find that in such case, the hopping between adjacent waveguides is necessarily
complex. This results not only in a transition of the light spreading from
ballistic to diffusive, but also in a new kind of diffraction that is caused by
loss dispersion. We prove our theoretical results with experimental
observations.Comment: Accepted for publication in PRL, 5+8 pages (Paper + Supplemental
material), 4 figure
Characterization of All-Chromium Tunnel Junctions and Single Electron Tunneling Devices Fabricated by Direct-Writing Multilayer Technique
We report about the fabrication and analysis of the properties of Cr/CrO_x/Cr
tunnel junctions and SET transistors, prepared by different variants of
direct-writing multilayer technique. In all cases, the CrO_x tunnel barriers
were formed in air under ambient conditions. From the experiments on single
junctions, values for the effective barrier height and thickness were derived.
For the Cr/CrO_x/Cr SET transistors we achieved minimal junction areas of 17 x
60 nm^2 using a scanning transmission electron microscope for the e-beam
exposure on Si_3N_4 membrane substrate. We discuss the electrical performance
of the transistor samples as well as their noise behavior.Comment: 19 pages, 9 figure
The effect of thermal annealing on the properties of Al-AlOx-Al single electron tunneling transistors
The effect of thermal annealing on the properties of Al-AlOx-Al single
electron tunneling transistors is reported. After treatment of the devices by
annealing processes in forming gas atmosphere at different temperatures and for
different times, distinct and reproducible changes of their resistance and
capacitance values were found. According to the temperature regime, we observed
different behaviors as regards the resistance changes, namely the tendency to
decrease the resistance by annealing at T = 200 degree C, but to increase the
resistance by annealing at T = 400 degree C. We attribute this behavior to
changes in the aluminum oxide barriers of the tunnel junctions. The good
reproducibility of these effects with respect to the changes observed allows
the proper annealing treatment to be used for post-process tuning of tunnel
junction parameters. Also, the influence of the annealing treatment on the
noise properties of the transistors at low frequency was investigated. In no
case did the noise figures in the 1/f-regime show significant changes.Comment: 6 pages, 7 eps-figure
A stringent yeast two-hybrid matrix screening approach for protein-protein interaction discovery
The yeast two-hybrid (Y2H) system is currently one of the most important techniques for protein-protein interaction (PPI) discovery. Here, we describe a stringent three-step Y2H matrix interaction approach that is suitable for systematic PPI screening on a proteome scale. We start with the identification and elimination of autoactivating strains that would lead to false-positive signals and prevent the identification of interactions. Nonautoactivating strains are used for the primary PPI screen that is carried out in quadruplicate with arrayed preys. Interacting pairs of baits and preys are identified in a pairwise retest step. Only PPI pairs that pass the retest step are regarded as potentially biologically relevant interactions and are considered for further analysis
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Health through human settlements: Investigating policymakers’ perceptions of human settlement action for population health improvement in urban South Africa
Magnetization reversal of an individual exchange biased permalloy nanotube
We investigate the magnetization reversal mechanism in an individual
permalloy (Py) nanotube (NT) using a hybrid magnetometer consisting of a
nanometer-scale SQUID (nanoSQUID) and a cantilever torque sensor. The Py NT is
affixed to the tip of a Si cantilever and positioned in order to optimally
couple its stray flux into a Nb nanoSQUID. We are thus able to measure both the
NT's volume magnetization by dynamic cantilever magnetometry and its stray flux
using the nanoSQUID. We observe a training effect and temperature dependence in
the magnetic hysteresis, suggesting an exchange bias. We find a low blocking
temperature K, indicating the presence of a thin
antiferromagnetic native oxide, as confirmed by X-ray absorption spectroscopy
on similar samples. Furthermore, we measure changes in the shape of the
magnetic hysteresis as a function of temperature and increased training. These
observations show that the presence of a thin exchange-coupled native oxide
modifies the magnetization reversal process at low temperatures. Complementary
information obtained via cantilever and nanoSQUID magnetometry allows us to
conclude that, in the absence of exchange coupling, this reversal process is
nucleated at the NT's ends and propagates along its length as predicted by
theory.Comment: 8 pages, 4 figure
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