4,610 research outputs found
Gaugino Condensation and the Vacuum Expectation Value of the Dilaton
The mechanism of gaugino condensation has emerged as a prime candidate for
supersymmetry breakdown in low energy effective supergravity (string) models.
One of the open questions in this approach concerns the size of the gauge
coupling constant which is dynamically fixed through the vev of the dilaton. We
argue that a nontrivial gauge kinetic function could solve the potential
problem of a runaway dilaton. The actual form of might be constrained by
symmetry arguments.Comment: 10 pages, 1 postscript figure, uses eps
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
Storage capabilities of a 4-junction single electron trap with an on-chip resistor
We report on the operation of a single electron trap comprising a chain of
four Al/AlOx/Al tunnel junctions attached, at one side, to a memory island and,
at the other side, to a miniature on-chip Cr resistor R=50 kOhm which served to
suppress cotunneling. At appropriate voltage bias the bi-stable states of the
trap, with the charges differing by the elementary charge e, were realized. At
low temperature, spontaneous switching between these states was found to be
infrequent. For instance, at T=70 mK the system was capable of holding an
electron for more than 2 hours, this time being limited by the time of the
measurement.Comment: 3 pages of text and 2 figure
Gain Dependence of the Noise in the Single Electron Transistor
An extensive investigation of low frequency noise in single electron
transistors as a function of gain is presented. Comparing the output noise with
gain for a large number of bias points, it is found that the noise is dominated
by external charge noise. For low gains we find an additional noise
contribution which is compared to a model including resistance fluctuations. We
conclude that this excess noise is not only due to resistance fluctuations. For
one sample, we find a record low minimum charge noise of qn = 9*10^-6
e/sqrt(Hz) in the superconducting state and qn = 9*10^-6 e/sqrt(Hz) in the
normal state at a frequency of 4.4 kHz.Comment: 10 pages, LaTex 2.09, 4 figures (epsfig
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
Automatic extraction of faults and fractal analysis from remote sensing data
Object-based classification is a promising technique for image classification. Unlike pixel-based methods, which only use the measured radiometric values, the object-based techniques can also use shape and context information of scene textures. These extra degrees of freedom provided by the objects allow the automatic identification of geological structures. In this article, we present an evaluation of object-based classification in the context of extraction of geological faults. Digital elevation models and radar data of an area near Lake Magadi (Kenya) have been processed. We then determine the statistics of the fault populations. The fractal dimensions of fault dimensions are similar to fractal dimensions directly measured on remote sensing images of the study area using power spectra (PSD) and variograms. These methods allow unbiased statistics of faults and help us to understand the evolution of the fault systems in extensional domains. Furthermore, the direct analysis of image texture is a good indicator of the fault statistics and allows us to classify the intensity and type of deformation. We propose that extensional fault networks can be modeled by iterative function system (IFS)
Event-Based Haptics and Acceleration Matching: Portraying and Assessing the Realism of Contact
Contact in a typical haptic environment resembles the experience of tapping on soft foam, rather than on a hard object. Event-based, high-frequency transient forces must be superimposed with traditional proportional feedback to provide realistic haptic cues at impact. We have developed a new method for matching the accelerations experienced during real contact, inverting a dynamic model of the device to compute appropriate force feedback transients. We evaluated this haptic rendering paradigm by conducting a study in which users blindly rated the realism of tapping on a variety of virtually rendered surfaces as well as on three real objects. Event-based feedback significantly increased the realism of the virtual surfaces, and the acceleration matching strategy was rated similarly to a sample of real wood on a foam substrate. This work provides a new avenue for achieving realism of contact in haptic interactions
Bounds on the cosmological abundance of primordial black holes from diffuse sky brightness: single mass spectra
We constrain the mass abundance of unclustered primordial black holes (PBHs),
formed with a simple mass distribution and subject to the Hawking evaporation
and particle absorption from the environment. Since the radiative flux is
proportional to the numerical density, an upper bound is obtained by comparing
the calculated and observed diffuse background values, (similarly to the Olbers
paradox in which point sources are considered) for finite bandwidths. For a
significative range of formation redshifts the bounds are better than several
values obtained by other arguments ; and they apply
to PBHs which are evaporating today.Comment: 20 pages, 5 figures, to appear in PR
- …