23,544 research outputs found
Multiquantum well structure with an average electron mobility of 4.0×10^6 cm^2/V s
We report a modulation-doped multiquantum well structure which suppresses the usual ambient light effect associated with modulation doping. Ten GaAs quantum wells 300-Å wide are symmetrically modulation doped using Si δ doping at the center of 3600-Å-wide Al0.1Ga0.9As barriers. The low field mobility of each well is 4.0×10^6 cm/V s at a density of 6.4×10^10 cm^−2 measured at 0.3 K either in the dark, or during, or after, exposure to light. This mobility is an order of magnitude improvement over previous work on multiwells
Generalised Space-time and Gauge Transformations
We consider the generalised space-time introduced by the author in 2003 in
the context of the non-linear realisation of the semi-direct product of E11 and
its first fundamental representation. For all the fields we propose gauge
transformations which are compatible with the underlying E11 structure. A
crucial role is played by the generalised vielbein that the generalised
space-time possess. We work out the explicit form of the gauge transformations,
at low levels, in four, five and eleven dimensions.Comment: 33 page
The Combined Effects of Pulsed Magnetic Radiation (Diapulse) and Chemotherapy on Tumor Bearing Mice. The Measurement of Rodent Palatal Explants as a Device for Measurement of the Biologic Effects of Nonionic Radiation (EMR)
Simultaneous treatment utilizing pulsed radiowave and cancer chemotherapy significantly extended the life span of mice with Lewis lung transplanted carcinoma. In comparison with nontreated controls, the combination of hydroxyurea and whole body nonionizing EM radiation (at 27.12 MHz) produced differential enhancement of longevity depending on hydroxyurea combined with highest power output achieved by pulsing the radiation 600 times per second; at a 3.9% duty cycle, peak watts = 975 produced the mean extension of life 67% greater than that of the group treated with hydroxyurea alone
Independently contacted two-dimensional electron systems in double quantum wells
A new technique for creating independent ohmic contacts to closely spaced two-dimensional electron systems in double quantum well (DQW) structures is described. Without use of shallow diffusion or precisely controlled etching methods, the present technique results in low-resistance contacts which can be electrostatically switched between the two-conducting layers. The method is demonstrated with a DQW consisting of two 200 Å GaAs quantum wells separated by a 175 Å AlGaAs barrier. A wide variety of experiments on Coulomb and tunnel-coupled 2D electron systems is now accessible
Field-induced resonant tunneling between parallel two-dimensional electron systems
Resonant tunneling between two high-mobility two-dimensional (2D) electron systems in a double quantum well structure has been induced by the action of an external Schottky gate field. Using one 2D electron gas as source and the other as drain, the tunnel conductance between them shows a strong resonance when the gate field aligns the ground subband edges of the two quantum wells
Precision of inventory using different edge overlap methods
Bias due to the sampling procedure may occur in estimates from forest inventory when sampled trees are close to the forest edge. The “mirage,” “walkthrough,” and “walk through and fro” methods are three practical measurement methods developed to avoid this problem. However, as an increasing proportion of the sample requires use of these methods, the precision of the population estimates made from the sample is likely to decline. Simulation studies were undertaken of forest inventory, using point sampling, to estimate mean stand basal area and stocking density in both an even-aged, monoculture radiata pine (Pinus radiata D. Don) plantation forest and an uneven-aged, multispecies, complex primary rainforest. In both forest types, bias arising from use of any of the three methods appeared to be negligible. As well, precision of estimates from the inventory was reduced only slightly, even when a high proportion of the samples required use of any one of the three methods. None of the methods appeared appreciably superior in this respect to any of the others. It was concluded that use of any of the three methods was unlikely to have any substantial effect on the overall precision of estimates made from forest inventory
The Dynamics of EEG Entropy
EEG time series are analyzed using the diffusion entropy method. The
resulting EEG entropy manifests short-time scaling, asymptotic saturation and
an attenuated alpha-rhythm modulation. These properties are faithfully modeled
by a phenomenological Langevin equation interpreted within a neural network
context
Charge metastability and hysteresis in the quantum Hall regime
We report simultaneous quasi-dc magnetotransport and high frequency surface
acoustic wave measurements on bilayer two-dimensional electron systems in GaAs.
Near strong integer quantized Hall states a strong magnetic field sweep
hysteresis in the velocity of the acoustic waves is observed at low
temperatures. This hysteresis indicates the presence of a metastable state with
anomalously high conductivity in the interior of the sample. This
non-equilibrium state is not revealed by conventional low frequency transport
measurements which are dominated by dissipationless transport at the edge of
the 2D system. We find that a field-cooling technique allows the equilibrium
charge configuration within the interior of the sample to be established. A
simple model for this behavior is discussed.Comment: 8 pages, 4 postscript figure
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