68 research outputs found
A laser based accelerator for ultracold atoms
We present first results on our implementation of a laser based accelerator
for ultracold atoms. Atoms cooled to a temperature of 420 nK are confined and
accelerated by means of laser tweezer beams and the atomic scattering is
directly observed in laser absorption imaging. The optical collider has been
characterized using Rb87 atoms in the |F=2,mF=2> state, but the scheme is not
restricted to atoms in any particular magnetic substates and can readily be
extended to other atomic species as well.Comment: (c) 2012 The Optical Society, 3 pages, 4 figures, 1 movie lin
Observation of Quantum Effects in sub Kelvin Cold Reactions
There has been a long-standing quest to observe chemical reactions at low
temperatures where reaction rates and pathways are governed by quantum
mechanical effects. So far this field of Quantum Chemistry has been dominated
by theory. The difficulty has been to realize in the laboratory low enough
collisional velocities between neutral reactants, so that the quantum wave
nature could be observed. We report here the first realization of merged
neutral supersonic beams, and the observation of clear quantum effects in the
resulting reactions. We observe orbiting resonances in the Penning ionization
reaction of argon and molecular hydrogen with metastable helium leading to a
sharp increase in the absolute reaction rate in the energy range corresponding
to a few degrees kelvin down to 10 mK. Our method is widely applicable to many
canonical chemical reactions, and will enable a breakthrough in the
experimental study of Quantum Chemistry
Biomarkers as Proxies to Analyse Land-Use History in Northern Jordan
In the semi-arid 'Decapolis region' in northern Jordan, due severe land degradation in the past, 'barren' and 'impoverished' landscapes can be found today. It is widely believed that land degradation in these regions was caused by ancient land use, e.g. overgrazing due to ‘Arab mismanagement'. However, the connection of degradation with land use is far from certain. The 'Decapolis region' is located in an approximately 100 km wide transition zone from Mediterranean to steppe and desert climate. Therefore, the landscape in this region is highly sensitive to climate variations. A major sedimentation phase in the late 6th century AD appears to represent a significant climate change towards more aridity, and might be connected with a cluster of heavy rainfall events in northern Jordan. In fact, more recent studies have found that periods of predominantly pastoral land use in northern Jordan were connected with natural reforestation. Since a dating of sedimentation alone does not deliver clues about the precise reason of deposition, a multidisciplinary team is analyzing the land-use history in the ‘Decapolis’ region. This presentation focusses on ongoing biomarker analyses. Samples were selected considering geoarchaeological data, including phosphorus concentrations, archaeological data, including distribution of potsherds and other fragments on ancient fields and data of further disciplines. Vegetation changes are investigated by analyses of n-alkanes and terpenoids. Manuring with faeces is analysed by specific steroids that are indicative for faeces deposition. Preliminary results showed a high input of omnivorous (pigs, humans) faeces in some areas. Manuring with faeces of herbivores seemed to be less important
Low-cost setup for generation of 3 GHz frequency difference phase-locked laser light
We have devised an all-optical setup for the generation of two phase-locked laser fields with a frequency difference of 3 GHz using only standard optics and two acousto-optical frequency shifters, that are operated at 253 MHz in sixtupel pass. The spectral width of the beat frequency is measured to be 300 Hz ͑full width at half maximum͒ limited by the resolution bandwidth of the spectrum analyzer. We routinely obtain an overall efficiency of more than 15% and demonstrate that the frequency shifted light can be further amplified by injecting it into additional ''slave'' lasers. This setup provides a low-cost alternative over conventional methods to generate laser fields with difference frequencies in the GHz domain, as for example, used in laser spectroscopy, laser cooling and trapping, and coherent manipulation of atomic quantum states
A Quantum Scattering Interferometer
The collision of two ultra-cold atoms results in a quantum-mechanical
superposition of two outcomes: each atom continues without scattering and each
atom scatters as a spherically outgoing wave with an s-wave phase shift. The
magnitude of the s-wave phase shift depends very sensitively on the interaction
between the atoms. Quantum scattering and the underlying phase shifts are
vitally important in many areas of contemporary atomic physics, including
Bose-Einstein condensates, degenerate Fermi gases, frequency shifts in atomic
clocks, and magnetically-tuned Feshbach resonances. Precise measurements of
quantum scattering phase shifts have not been possible until now because, in
scattering experiments, the number of scattered atoms depends on the s-wave
phase shifts as well as the atomic density, which cannot be measured precisely.
Here we demonstrate a fundamentally new type of scattering experiment that
interferometrically detects the quantum scattering phase shifts of individual
atoms. By performing an atomic clock measurement using only the scattered part
of each atom, we directly and precisely measure the difference of the s-wave
phase shifts for the two clock states in a density independent manner. Our
method will give the most direct and precise measurements of ultracold
atom-atom interactions and will place stringent limits on the time variations
of fundamental constants.Comment: Corrected formatting and typo
Law and Social Capital: Evidence from the Code Napoleon in Germany
Do legal institutions affect norms of cooperation? Using the introduction of the Code Napoleon during the Napoleonic Wars in Germany as a historical experiment, I show that a positive shock to the quality of legal institutions can increase social-capital long-lastingly. I find that individuals living in regions where the Code Napoleon was used display higher levels of interpersonal trust in the data of the German Socio-Economic Panel (SOEP). This result holds true conditional on past development levels, as well as in a less heterogeneous border sample, separating regions that applied the Code Napoleon from those that did not. Artificially moving the border and comparing regional pre-treatment characteristics support the interpretation of a causal treatment effect. In addition, I show immediate effects of the Code Civil on novel measures of 19th century social capital. The analysis of historical employment data furthermore suggests economic cooperation to be a potential mechanism for the relationship between legal institutions and social capital
Sediment source fingerprinting: benchmarking recent outputs, remaining challenges and emerging themes
Abstract: Purpose: This review of sediment source fingerprinting assesses the current state-of-the-art, remaining challenges and emerging themes. It combines inputs from international scientists either with track records in the approach or with expertise relevant to progressing the science. Methods: Web of Science and Google Scholar were used to review published papers spanning the period 2013–2019, inclusive, to confirm publication trends in quantities of papers by study area country and the types of tracers used. The most recent (2018–2019, inclusive) papers were also benchmarked using a methodological decision-tree published in 2017. Scope: Areas requiring further research and international consensus on methodological detail are reviewed, and these comprise spatial variability in tracers and corresponding sampling implications for end-members, temporal variability in tracers and sampling implications for end-members and target sediment, tracer conservation and knowledge-based pre-selection, the physico-chemical basis for source discrimination and dissemination of fingerprinting results to stakeholders. Emerging themes are also discussed: novel tracers, concentration-dependence for biomarkers, combining sediment fingerprinting and age-dating, applications to sediment-bound pollutants, incorporation of supportive spatial information to augment discrimination and modelling, aeolian sediment source fingerprinting, integration with process-based models and development of open-access software tools for data processing. Conclusions: The popularity of sediment source fingerprinting continues on an upward trend globally, but with this growth comes issues surrounding lack of standardisation and procedural diversity. Nonetheless, the last 2 years have also evidenced growing uptake of critical requirements for robust applications and this review is intended to signpost investigators, both old and new, towards these benchmarks and remaining research challenges for, and emerging options for different applications of, the fingerprinting approach
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