25 research outputs found
Practical quantum realization of the ampere from the electron charge
One major change of the future revision of the International System of Units
(SI) is a new definition of the ampere based on the elementary charge \emph{e}.
Replacing the former definition based on Amp\`ere's force law will allow one to
fully benefit from quantum physics to realize the ampere. However, a quantum
realization of the ampere from \emph{e}, accurate to within in
relative value and fulfilling traceability needs, is still missing despite many
efforts have been spent for the development of single-electron tunneling
devices. Starting again with Ohm's law, applied here in a quantum circuit
combining the quantum Hall resistance and Josephson voltage standards with a
superconducting cryogenic amplifier, we report on a practical and universal
programmable quantum current generator. We demonstrate that currents generated
in the milliampere range are quantized in terms of
( is the Josephson frequency) with a measurement uncertainty of
. This new quantum current source, able to deliver such accurate
currents down to the microampere range, can greatly improve the current
measurement traceability, as demonstrated with the calibrations of digital
ammeters. Beyond, it opens the way to further developments in metrology and in
fundamental physics, such as a quantum multimeter or new accurate comparisons
to single electron pumps.Comment: 15 pages, 4 figure
Quantum Hall effect in exfoliated graphene affected by charged impurities: metrological measurements
Metrological investigations of the quantum Hall effect (QHE) completed by
transport measurements at low magnetic field are carried out in
a-few--wide Hall bars made of monolayer (ML) or bilayer (BL)
exfoliated graphene transferred on substrate. From the
charge carrier density dependence of the conductivity and from the measurement
of the quantum corrections at low magnetic field, we deduce that transport
properties in these devices are mainly governed by the Coulomb interaction of
carriers with a large concentration of charged impurities. In the QHE regime,
at high magnetic field and low temperature (), the Hall
resistance is measured by comparison with a GaAs based quantum resistance
standard using a cryogenic current comparator. In the low dissipation limit, it
is found quantized within 5 parts in (one standard deviation, ) at the expected rational fractions of the von Klitzing constant,
respectively and in the ML and BL
devices. These results constitute the most accurate QHE quantization tests to
date in monolayer and bilayer exfoliated graphene. It turns out that a main
limitation to the quantization accuracy, which is found well above the
accuracy usually achieved in GaAs, is the low value of the QHE
breakdown current being no more than . The current dependence
of the longitudinal conductivity investigated in the BL Hall bar shows that
dissipation occurs through quasi-elastic inter-Landau level scattering,
assisted by large local electric fields. We propose that charged impurities are
responsible for an enhancement of such inter-Landau level transition rate and
cause small breakdown currents.Comment: 14 pages, 9 figure
Experimental based experiences with the introduction of a water safety plan for a multi-located university clinic and its efficacy according to WHO recommendations
BACKGROUND: Due to the high number of immunosuppressed and other predisposed patients hospitals have to control and ensure the microbiological water quality. The origin for the occurrence of pathogenic microorganisms in water pipes is the formation of biofilm. METHODS: For the permanent control of water safety a water safety plan (WSP) was realized as recommended by the WHO following the principle "search and destroy". The WSP is based on an established HACCP concept due to the special focus. The most important measures include the concept for sample taking depending on patient risk. 3 different categories) are distinguished: risk area1 (high infection risk), risk 2 (moderate infection risk), and risk area 3 (not increased infection risk). Additionally to the threshold value of the German law for the quality of drinking water (TrinkwV) three more limiting values were defined (warning, alert, and worst case) for immediate risk adapted reaction. Additional attention has to be focussed on lavatory sinks, which are an open bacterial reservoir. Therefore continuous disinfecting siphons were installed as part of the WSP in high risk areas. If extended technical equipment is not available, especially for immunocompromised patients the following measures are easy to realize: boiled (or sun exposed) water for nursing procedures as well alimentary use, no showering. RESULTS: Comparing data over 3 years the microbial water quality was significantly improved resulting in no new case of nosocomial Legionella pneumoniae and decrease in neonatal sepsis. CONCLUSION: According to average situations with highly contaminated water system the management must be defined with implementation of water task force, immediate providing of special equipment, information of patients and staff and control of the water quality, an example for successful decontamination of the hospital within 24 hours is given