4,617 research outputs found
A new model for deflagration fronts in reactive fluids
We present a new way of modeling deflagration fronts in reactive fluids, the
main emphasis being on turbulent thermonuclear deflagration fronts in white
dwarfs undergoing a Type Ia supernova explosion. Our approach is based on a
level set method which treats the front as a mathematical discontinuity and
allows full coupling between the front geometry and the flow field. With only
minor modifications, this method can also be applied to describe contact
discontinuities. Two different implementations are described and their
physically correct behaviour for simple testcases is shown. First results of
the method applied to the concrete problems of Type Ia supernovae and chemical
hydrogen combustion are briefly discussed; a more extensive analysis of our
astrophysical simulations is given in (Reinecke et al. 1998, MPA Green Report
1122b).Comment: 11 pages, 13 figures, accepted by A&A, corrected and extended
according to referee's comment
Advanced solar concentrator mass production, operation, and maintenance cost assessment
The object of this assessment was to estimate the costs of the preliminary design at: production rates of 100 to 1,000,000 concentrators per year; concentrators per aperture diameters of 5, 10, 11, and 15 meters; and various receiver/power conversion package weights. The design of the cellular glass substrate Advanced Solar Concentrator is presented. The concentrator is an 11 meter diameter, two axis tracking, parabolic dish solar concentrator. The reflective surface of this design consists of inner and outer groups of mirror glass/cellular glass gores
Metallic single-electron transistor without traditional tunnel barriers
We report on a new type of single-electron transistor (SET) comprising two
highly resistive Cr thin-film strips (~ 1um long) connecting a 1 um-long Al
island to two Al outer electrodes. These resistors replace small-area oxide
tunnel junctions of traditional SETs. Our transistor with a total asymptotic
resistance of 110 kOhm showed a very sharp Coulomb blockade and reproducible,
deep and strictly e-periodic gate modulation in wide ranges of bias currents I
and gate voltages V_g. In the Coulomb blockade region (|V| < 0.5 mV), we
observed a strong suppression of the cotunneling current allowing appreciable
modulation curves V-V_g to be measured at currents I as low as 100 fA. The
noise figure of our SET was found to be similar to that of typical Al/AlOx/Al
single-electron transistors.Comment: 5 pages incl. 4 fig
Noise in Al single electron transistors of stacked design
We have fabricated and examined several Al single electron transistors whose
small islands were positioned on top of a counter electrode and hence did not
come into contact with a dielectric substrate. The equivalent charge noise
figure of all transistors turned out to be surprisingly low, (2.5 - 7)*10E-5
e/sqrt(Hz) at f = 10 Hz. Although the lowest detected noise originates mostly
from fluctuations of background charge, the noise contribution of the tunnel
junction conductances was, on occasion, found to be dominant.Comment: 4 pages of text with 1 table and 5 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
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