170 research outputs found
Structural change in the dairy sectors of Germany and the Netherlands - A markov analysis
With the milk quota announced to be abolished in the future, the dairy sector is going to face a significant policy regime shift. This paper sets out to analyze the impact of milk quotas on the dairy farm structure of two important milk producing member states: Germany and the Netherlands. Based on proper behavioral assumptions, non stationary Markov chain models are specified and estimated using a generalized cross entropy procedure, which takes into account both sample and prior information. Moreover four mobility indicators characterizing structural change are developed and calculated. Structural change in the dairy sector as measured by the mobility measures is faster in West Germany than in the Netherlands. However, in the transition region East Germany structural change outpaces that of the traditional German and Dutch dairy sectors by a factor two or more. The introduction of milk quotas as of April 1, 1984 reduced overall farm mobility for the Netherlands, but increased mobility in West Germany. However, in both cases the milk quotas lead to an increase in upward mobility
Liquid-induced damping of mechanical feedback effects in single electron tunneling through a suspended carbon nanotube
In single electron tunneling through clean, suspended carbon nanotube devices
at low temperature, distinct switching phenomena have regularly been observed.
These can be explained via strong interaction of single electron tunneling and
vibrational motion of the nanotube. We present measurements on a highly stable
nanotube device, subsequently recorded in the vacuum chamber of a dilution
refrigerator and immersed in the 3He/4He mixture of a second dilution
refrigerator. The switching phenomena are absent when the sample is kept in the
viscous liquid, additionally supporting the interpretation of dc-driven
vibration. Transport measurements in liquid helium can thus be used for finite
bias spectroscopy where otherwise the mechanical effects would dominate the
current.Comment: 4 pages, 3 figure
Magnetic damping of a carbon nanotube NEMS resonator
A suspended, doubly clamped single wall carbon nanotube is characterized at
cryogenic temperatures. We observe specific switching effects in dc-current
spectroscopy of the embedded quantum dot. These have been identified previously
as nano-electromechanical self-excitation of the system, where positive
feedback from single electron tunneling drives mechanical motion. A magnetic
field suppresses this effect, by providing an additional damping mechanism.
This is modeled by eddy current damping, and confirmed by measuring the
resonance quality factor of the rf-driven nano-electromechanical resonator in
an increasing magnetic field.Comment: 8 pages, 3 figure
Nuclear spin relaxation probed by a single quantum dot
We present measurements on nuclear spin relaxation probed by a single quantum
dot in a high-mobility electron gas. Current passing through the dot leads to a
spin transfer from the electronic to the nuclear spin system. Applying electron
spin resonance the transfer mechanism can directly be tuned. Additionally, the
dependence of nuclear spin relaxation on the dot gate voltage is observed. We
find electron-nuclear relaxation times of the order of 10 minutes
Optomechanical coupling and damping of a carbon nanotube quantum dot
Carbon nanotubes are excellent nano-electromechanical systems, combining high
resonance frequency, low mass, and large zero-point motion. At cryogenic
temperatures they display high mechanical quality factors. Equally they are
outstanding single electron devices with well-known quantum levels and have
been proposed for the implementation of charge or spin qubits. The integration
of these devices into microwave optomechanical circuits is however hindered by
a mismatch of scales, between typical microwave wavelengths, nanotube segment
lengths, and nanotube deflections. As experimentally demonstrated recently in
[Blien et al., Nat. Comm. 11, 1363 (2020)], coupling enhancement via the
quantum capacitance allows to circumvent this restriction. Here we extend the
discussion of this experiment. We present the subsystems of the device and
their interactions in detail. An alternative approach to the optomechanical
coupling is presented, allowing to estimate the mechanical zero point motion
scale. Further, the mechanical damping is discussed, hinting at hitherto
unknown interaction mechanisms.Comment: 17 pages, 13 figures, 3 table
A Component-oriented Framework for Autonomous Agents
The design of a complex system warrants a compositional methodology, i.e.,
composing simple components to obtain a larger system that exhibits their
collective behavior in a meaningful way. We propose an automaton-based paradigm
for compositional design of such systems where an action is accompanied by one
or more preferences. At run-time, these preferences provide a natural fallback
mechanism for the component, while at design-time they can be used to reason
about the behavior of the component in an uncertain physical world. Using
structures that tell us how to compose preferences and actions, we can compose
formal representations of individual components or agents to obtain a
representation of the composed system. We extend Linear Temporal Logic with two
unary connectives that reflect the compositional structure of the actions, and
show how it can be used to diagnose undesired behavior by tracing the
falsification of a specification back to one or more culpable components
Broken SU(4) symmetry in a Kondo-correlated carbon nanotube
Understanding the interplay between many-body phenomena and non-equilibrium
in systems with entangled spin and orbital degrees of freedom is a central
objective in nano-electronics. We demonstrate that the combination of Coulomb
interaction, spin-orbit coupling and valley mixing results in a particular
selection of the inelastic virtual processes contributing to the Kondo
resonance in carbon nanotubes at low temperatures. This effect is dictated by
conjugation properties of the underlying carbon nanotube spectrum at zero and
finite magnetic field. Our measurements on a clean carbon nanotube are
complemented by calculations based on a new approach to the non-equilibrium
Kondo problem which well reproduces the rich experimental observations in Kondo
transport.Comment: 8 pages, 6 figures; appendix of 14 pages, 7 figure
Single electron-phonon interaction in a suspended quantum dot phonon cavity
An electron-phonon cavity consisting of a quantum dot embedded in a
free-standing GaAs/AlGaAs membrane is characterized in Coulomb blockade
measurements at low temperatures. We find a complete suppression of single
electron tunneling around zero bias leading to the formation of an energy gap
in the transport spectrum. The observed effect is induced by the excitation of
a localized phonon mode confined in the cavity. This phonon blockade of
transport is lifted at magnetic fields where higher electronic states with
nonzero angular momentum are brought into resonance with the phonon energy.Comment: 4 pages, 4 figure
Homogeneous Gold Catalysis through Relativistic Effects: Addition of Water to Propyne
In the catalytic addition of water to propyne the Au(III) catalyst is not
stable under non-relativistic conditions and dissociates into a Au(I) compound
and Cl2. This implies that one link in the chain of events in the catalytic
cycle is broken and relativity may well be seen as the reason why Au(III)
compounds are effective catalysts.Comment: 12 pages, 3 figures, 1 tabl
A Mechanical Mass Sensor with Yoctogram Resolution
Nanoelectromechanical systems (NEMS) have generated considerable interest as
inertial mass sensors. NEMS resonators have been used to weigh cells,
biomolecules, and gas molecules, creating many new possibilities for biological
and chemical analysis [1-4]. Recently, NEMS-based mass sensors have been
employed as a new tool in surface science in order to study e.g. the phase
transitions or the diffusion of adsorbed atoms on nanoscale objects [5-7]. A
key point in all these experiments is the ability to resolve small masses. Here
we report on mass sensing experiments with a resolution of 1.7 yg (1 yg =
10^-24 g), which corresponds to the mass of one proton, or one hydrogen atom.
The resonator is made of a ~150 nm long carbon nanotube resonator vibrating at
nearly 2 GHz. The unprecedented level of sensitivity allows us to detect
adsorption events of naphthalene molecules (C10H8) and to measure the binding
energy of a Xe atom on the nanotube surface (131 meV). These ultrasensitive
nanotube resonators offer new opportunities for mass spectrometry,
magnetometry, and adsorption experiments.Comment: submitted version of the manuscrip
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