7,986 research outputs found
Gold-induced nanowires on the Ge(100) surface yield a 2D, and not a 1D electronic structure
Atomic nanowires on semiconductor surfaces induced by the adsorption of
metallic atoms have attracted a lot of attention as possible hosts of the
elusive, Tomonaga-Luttinger liquid. The Au/Ge(100) system in particular is the
subject of controversy as to whether the Au-induced nanowires do indeed host
exotic, 1D metallic states. We report on a thorough study of the electronic
properties of high quality nanowires formed at the Au/Ge(100) surface. High
resolution ARPES data show the low-lying Au-induced electronic states to
possess a dispersion relation that depends on two orthogonal directions in
k-space. Comparison of the E(k,k) surface measured using ARPES to
tight-binding calculations yields hopping parameters in the two different
directions that differ by a factor of two. We find that the larger of the two
hopping parameters corresponds, in fact, to the direction perpendicular to the
nanowires (t). This, the topology of the = contour in
k, and the fact that / proves that the
Au-induced electron pockets possess a 2D, closed Fermi surface, this firmly
places the Au/Ge(100) nanowire system outside being a potential hosts of a
Tomonaga-Luttinger liquid. We combine these ARPES data with STS measurements of
the spatially-resolved electronic structure and find that the spatially
straight conduction channels observed up to energies of order one electron volt
below the Fermi level do not originate from the Au-induced states seen in the
ARPES data. The former are more likely to be associated with bulk Ge states
that are localized to the subsurface region. Despite our proof of the 2D nature
of the Au-induced nanowire and sub-surface Ge-related states, an anomalous
suppression of the density of states at the Fermi level is observed in both the
STS and ARPES data, this phenomenon is discussed in the light of the effects of
disorder.Comment: 17 pages, 8 figure
Memristors for the Curious Outsiders
We present both an overview and a perspective of recent experimental advances
and proposed new approaches to performing computation using memristors. A
memristor is a 2-terminal passive component with a dynamic resistance depending
on an internal parameter. We provide an brief historical introduction, as well
as an overview over the physical mechanism that lead to memristive behavior.
This review is meant to guide nonpractitioners in the field of memristive
circuits and their connection to machine learning and neural computation.Comment: Perpective paper for MDPI Technologies; 43 page
Appropriate methods to analyse power conversion harmonics
Nowadays, non-linear loads represent the majority of the
residential electrical consumers. The limits on emission and
immunity are imposed by IEC- standards, however there is a lack in the domain 2 – 150 kHz. Where power quality standards focus on the current, EMC standards use voltage limits. An appropriate method for measuring high frequency grid disturbances is explored. Measurement techniques described by the existing standards for power quality and EMC are investigated. The aim of this work is to find a robust measurement method for the considered frequency range 2 - 150 kHz. Experimental results are presented in order to validate the analyzed methods
Reactive control and reasoning assistance for scientific laboratory instruments
Scientific laboratory instruments that are involved in chemical or physical sample identification frequently require substantial human preparation, attention, and interactive control during their operation. Successful real-time analysis of incoming data that supports such interactive control requires: (1) a clear recognition of variance of the data from expected results; and (2) rapid diagnosis of possible alternative hypotheses which might explain the variance. Such analysis then aids in decisions about modifying the experiment protocol, as well as being a goal itself. This paper reports on a collaborative project at the NASA Ames Research Center between artificial intelligence researchers and planetary microbial ecologists. Our team is currently engaged in developing software that autonomously controls science laboratory instruments and that provides data analysis of the real-time data in support of dynamic refinement of the experiment control. the first two instruments to which this technology has been applied are a differential thermal analyzer (DTA) and a gas chromatograph (GC). coupled together, they form a new geochemicstry and microbial analysis tool that is capable of rapid identification of the organiz and mineralogical constituents in soils. The thermal decomposition of the minerals and organics, and the attendance release of evolved gases, provides data about the structural and molecular chemistry of the soil samples
Design of a fast computer-based partial discharge diagnostic system
Partial discharges cause progressive deterioration of insulating materials working in high voltage conditions and may lead ultimately to insulator failure. Experimental findings indicate that deterioration increases with the number of discharges and is consequently proportional to the magnitude and frequency of the applied voltage. In order to obtain a better understanding of the mechanisms of deterioration produced by partial discharges, instrumentation capable of individual pulse resolution is required. A new computer-based partial discharge detection system was designed and constructed to conduct long duration tests on sample capacitors. This system is capable of recording large number of pulses without dead time and producing valuable information related to amplitude, polarity, and charge content of the discharges. The operation of the system is automatic and no human supervision is required during the testing stage. Ceramic capacitors were tested at high voltage in long duration tests. The obtained results indicated that the charge content of partial discharges shift towards high levels of charge as the level of deterioration in the capacitor increases
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