358 research outputs found
The Juridical Status of Privileged Combatants Under the Geneva Protocol of 1977 Concerning International Conflicts
Centralized control and coordination of the connections in a wireless network is not possible in practice. To keep the delay from measure-ment instants to actuating the decisions, distributed control is required. This paper focuses on the uplink (from mobiles to base stations) and dis-cusses distributing the decision of when and when not to transmit data (distributed scheduling) to the mobiles. The scheme, uplink transmission timing, utilizes mobile transmitter power control feedback from the base station receiver to determine whether the channel is favorable or not compared to the average channel condition. Thereby, the battery consumption and disturbing power to other connections are reduced. The algorithm can be described as a feedback control system. Some transient behaviors are analyzed using systems theory, and supported by wireless network simulations of a system with a WCDMA (Wideband Code Division Multiple Access) radio interface as in most 3G systems
Dielectric losses in multi-layer Josephson junction qubits
We have measured the excited state lifetimes in Josephson junction phase and
transmon qubits, all of which were fabricated with the same scalable
multi-layer process. We have compared the lifetimes of phase qubits before and
after removal of the isolating dielectric, SiNx, and find a four-fold
improvement of the relaxation time after the removal. Together with the results
from the transmon qubit and measurements on coplanar waveguide resonators,
these measurements indicate that the lifetimes are limited by losses from the
dielectric constituents of the qubits. We have extracted the individual loss
contributions from the dielectrics in the tunnel junction barrier, AlOx, the
isolating dielectric, SiNx, and the substrate, Si/SiO2, by weighing the total
loss with the parts of electric field over the different dielectric materials.
Our results agree well and complement the findings from other studies,
demonstrating that superconducting qubits can be used as a reliable tool for
high-frequency characterization of dielectric materials. We conclude with a
discussion of how changes in design and material choice could improve qubit
lifetimes up to a factor of four.Comment: 10 pages, 4 figures,and 4 table
Traceable Coulomb Blockade Thermometry
We present a measurement and analysis scheme for determining traceable
thermodynamic temperature at cryogenic temperatures using Coulomb blockade
thermometry. The uncertainty of the electrical measurement is improved by
utilizing two sampling digital voltmeters instead of the traditional lock-in
technique. The remaining uncertainty is dominated by that of the numerical
analysis of the measurement data. Two analysis methods are demonstrated:
numerical fitting of the full conductance curve and measuring the height of the
conductance dip. The complete uncertainty analysis shows that using either
analysis method the relative combined standard uncertainty (k = 1) in
determining the thermodynamic temperature in the temperature range from 20 mK
to 200 mK is below 0.5 %. In this temperature range, both analysis methods
produced temperature estimates that deviated from 0.39 % to 0.67 % from the
reference temperatures provided by a superconducting reference point device
calibrated against the Provisional Low Temperature Scale of 2000.Comment: 11 page
Vibronic spectroscopy of an artificial molecule
With advanced fabrication techniques it is possible to make nanoscale
electronic structures that have discrete energy levels. Such structures are
called artificial atoms because of analogy with true atoms. Examples of such
atoms are quantum dots in semiconductor heterostructures and Josephson-junction
qubits. It is also possible to have artificial atoms interacting with each
other. This is an artificial molecule in the sense that the electronic states
are analogous to the ones in a molecule. In this letter we present a different
type of artificial molecule that, in addition to electronic states, also
includes the analog of nuclear vibrations in a diatomic molecule. Some of the
earlier experiments could be interpreted using this analogy, including qubits
coupled to oscillators and qubits driven by an intense field. In our case the
electronic states of the molecule are represented by a Josephson-junction
qubit, and the nuclear separation corresponds to the magnetic flux in a loop
containing the qubit and an LC oscillator. We probe the vibronic transitions,
where both the electronic and vibrational states change simultaneously, and
find that they are analogous to true molecules. The vibronic transitions could
be used for sideband cooling of the oscillator, and we see damping up to
sidebands of order 10.Comment: 5 pages, 4 figure
Enhancing Tc in field-doped Fullerenes by applying uniaxial stress
Capitalizing on the two-dimensional nature of superconductivity in
field-effect doped C60, we show that it should be possible to increase the
transition temperature Tc by applying uniaxial stress perpendicular to the gate
electrode. This method not only holds the promise of substantially enhancing Tc
(by about 30 K per GPa), but also provides a sensitive check of the current
understanding of superconductivity in the doped Fullerenes.Comment: 3 pages RevTe
Integration techniques of pHEMTs and planar Gunn diodes on GaAs substrates
This work presents two different approaches for the implementation of pseudomorphic high electron mobility transistors (pHEMTs) and planar Gunn diodes on the same gallium arsenide substrate. In the first approach, a combined wafer is used where a buffer layer separates the active layers of the two devices. A second approach was also examined using a single wafer where the AlGaAs/InGaAs/GaAs heterostructures were designed for the realisation of pHEMTs. The comparison between the two techniques showed that the devices fabricated on the single pHEMT wafer presented superior performance over the combined wafer technique. The DC and small-signal characteristics of the pHEMTs on the single wafer were enhanced after the use of T-gates with 70 nm length. The maximum transconductance of the transistors was equal to 780 mS/mm with 200 GHz maximum frequency of oscillation (fmax). Planar Gunn diodes fabricated in the pHEMT wafer, with 1.3 μm anode-to-cathode separation (LAC) presented oscillations at 87.6 GHz with maximum power of oscillation equal to -40 dBm
Shot noise of a multiwalled carbon nanotube field effect transistor
We have investigated shot noise in a 6−nm-diameter, semiconducting multiwalled carbon nanotube field effect transistor at 4.2 K over the frequency range of 600–950 MHz. We find a transconductance of 3–3.5 μS for optimal positive and negative source-drain voltages V. For the gate referred input voltage noise, we obtain 0.2 and 0.3 μV/√Hz for V > 0 and V < 0, respectively. As effective charge noise, this corresponds to (2–3)×10 exp −5 e/√Hz.Peer reviewe
Temporal and Spatial Positioning of Service Crops in Cereals Affects Yield and Weed Control
Leguminous service crops (SCs) can provide multiple services to cropping systems, reducing the reliance on external resources if sufficient biomass is produced. However, rapid light and temperature reductions limit post-harvest cultivation of SCs in Northern Europe. A novel practice of intercropping SCs in two consecutive crops (spring-winter cereal) to extend the period of SCs growth, and hence improve yield and reduce weeds, was tested. Three spatial and temporal arrangements of SCs and cash crops were investigated, as well as three SC mixtures, characterized by their longevity and frost sensitivity. Compared to no SC, the best performing mixture, frost-tolerant annuals, increased grain and N yield of winter wheat by 10% and 19%, respectively, and reduced weed biomass by 15% and 26% in oats and winter wheat, respectively. These effects were attributed to high biomass production and winter survival. However, this SC reduced oat yields by 15% compared to no SC. Furthermore, SC growth and service provision varied largely between experiments, driven by the weather conditions. Extending the SC's growth period by intercropping in two consecutive cereal crops has potential, but locally adapted species choices and establishment strategies are needed to ensure SC vitality until termination
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