127 research outputs found
Electron Counting Capacitance Standard with an improved five-junction R-pump
The Electron Counting Capacitance Standard currently pursued at PTB aims to
close the Quantum Metrological Triangle with a final precision of a few parts
in 10^7. This paper reports the considerable progress recently achieved with a
new generation of single-electron tunnelling devices. A five-junction R-pump
was operated with a relative charge transfer error of five electrons in 10^7,
and was used to successfully perform single-electron charging of a cryogenic
capacitor. The preliminary result for the single-electron charge quantum has an
uncertainty of less than two parts in 10^6 and is consistent with the value of
the elementary charge.Comment: 16 pages, 9 figures, 1 tabl
Single-charge escape processes through a hybrid turnstile in a dissipative environment
We have investigated the static, charge-trapping properties of a hybrid
superconductor---normal metal electron turnstile embedded into a high-ohmic
environment. The device includes a local Cr resistor on one side of the
turnstile, and a superconducting trapping island on the other side. The
electron hold times, t ~ 2-20s, in our two-junction circuit are comparable with
those of typical multi-junction, N >= 4, normal-metal single-electron tunneling
devices. A semi-phenomenological model of the environmental activation of
tunneling is applied for the analysis of the switching statistics. The
experimental results are promising for electrical metrology.Comment: Submitted to New Journal of Physics 201
Quantum Metrology Triangle Experiments: A Status Review
Quantum Metrology Triangle experiments combine three quantum electrical
effects (the Josephson effect, the quantum Hall effect and the single-electron
transport effect) used in metrology. These experiments allow important
fundamental consistency tests on the validity of commonly assumed relations
between fundamental constants of nature and the quantum electrical effects.
This paper reviews the history, results and the present status and perspectives
of Quantum Metrology Triangle experiments. It also reflects on the possible
implications of results for the knowledge on fundamental constants and the
quantum electrical effects.Comment: 36 pages, 8 figure
The first sub-70 minute non-interacting WD-BD system: EPIC212235321
We present the discovery of the shortest-period, non-interacting, white dwarf-brown dwarf post-common-envelope binary known. The K2 light curve shows the system, EPIC 21223532 has a period of 68.2 min and is not eclipsing, but does show a large reflection effect due to the irradiation of the brown dwarf by the white dwarf primary. Spectra show hydrogen, magnesium and calcium emission features from the brown dwarf's irradiated hemisphere, and the mass indicates the spectral type is likely to be L3. Despite having a period substantially lower than the cataclysmic variable period minimum, this system is likely a pre-cataclysmic binary, recently emerged from the common-envelope. These systems are rare, but provide limits on the lowest mass object that can survive common envelope evolution, and information about the evolution of white dwarf progenitors, and post-common envelope evolution
Population policies, programmes and the environment
Human consumption is depleting the Earth's natural resources and impairing the capacity of life-supporting ecosystems. Humans have changed ecosystems more rapidly and extensively over the past 50 years than during any other period, primarily to meet increasing demands for food, fresh water, timber, fibre and fuel. Such consumption, together with world population increasing from 2.6 billion in 1950 to 6.8 billion in 2009, are major contributors to environmental damage. Strengthening family-planning services is crucial to slowing population growth, now 78 million annually, and limiting population size to 9.2 billion by 2050. Otherwise, birth rates could remain unchanged, and world population would grow to 11 billion. Of particular concern are the 80 million annual pregnancies (38% of all pregnancies) that are unintended. More than 200 million women in developing countries prefer to delay their pregnancy, or stop bearing children altogether, but rely on traditional, less-effective methods of contraception or use no method because they lack access or face other barriers to using contraception. Family-planning programmes have a successful track record of reducing unintended pregnancies, thereby slowing population growth. An estimated 5 billion of the total, however, current donor assistance is less than a quarter of this funding target
What Can We Conclude from Death Registration? Improved Methods for Evaluating Completeness
Julie Rajaratnam and colleagues evaluate the performance of a suite of demographic methods that estimate the fraction of deaths registered and counted by civil registration systems, and identify three variants that generally perform the best
New binaries among UV-selected, hot subdwarf stars and population properties
We have measured the orbital parameters of seven close binaries, including six new objects, in a radial velocity survey of 38 objects comprising a hot subdwarf star with orbital periods ranging from ~0.17 to 3 d. One new system, GALEX J2205-3141, shows reflection on an M dwarf companion. Three other objects show significant short-period variations, but their orbital parameters could not be constrained. Two systems comprising a hot subdwarf paired with a bright main-sequence/giant companion display short-period photometric variations possibly due to irradiation or stellar activity and are also short-period candidates. All except two candidates were drawn from a selection of subluminous stars in the Galaxy Evolution Explorer ultraviolet sky survey. Our new identifications also include a low-mass subdwarf B star and likely progenitor of a low-mass white dwarf (GALEX J0805-1058) paired with an unseen, possibly substellar, companion. The mass functions of the newly identified binaries imply minimum secondary masses ranging from 0.03 to 0.39M?. Photometric time series suggest that, apart from GALEX J0805-1058 and J2205-3141, the companions are most likely white dwarfs. We update the binary population statistics: close to 40 per cent of hot subdwarfs have a companion. Also, we found that the secondary mass distribution shows a lowmass peak attributed to late-type dwarfs, and a higher mass peak and tail distribution attributed to white dwarfs and a few spectroscopic composites. Also, we found that the population kinematics imply an old age and include a few likely halo population members
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