3,987 research outputs found
Imaging of microwave fields using ultracold atoms
We report a technique that uses clouds of ultracold atoms as sensitive,
tunable, and non-invasive probes for microwave field imaging with micrometer
spatial resolution. The microwave magnetic field components drive Rabi
oscillations on atomic hyperfine transitions whose frequency can be tuned with
a static magnetic field. Readout is accomplished using state-selective
absorption imaging. Quantitative data extraction is simple and it is possible
to reconstruct the distribution of microwave magnetic field amplitudes and
phases. While we demonstrate 2d imaging, an extension to 3d imaging is
straightforward. We use the method to determine the microwave near-field
distribution around a coplanar waveguide integrated on an atom chip.Comment: 11 pages, 4 figure
Corporate tax effects on the quality and quantity of FDI
This paper measures the relative importance of quality and quantity effects of corporate taxation on foreign direct investment. Quantity is affected if corporate taxes reduce the equilibrium stock of foreign capital in a given country. Quality effects arise if taxes decrease the extent to which investment contributes to the corporate tax base and the capital intensity of production. Depending on the sign of the quality effects, the detrimental welfare effects of corporate taxation are either mitigated or aggravated. We derive a number of hypotheses how corporate tax changes may affect the quality of investment. Our hypotheses are then tested using data from a large sample of European multinationals. With regard to corporate tax effects on the corporate tax base, we find that quality effects account for up to fourty per cent of the total effect. With regard to corporate tax effects on labour income, our results suggest that quality effects mitigate the negative quantity effect by nearly sixty percent (as corporate taxes strongly increase the labor intensity of production). An important implication is that governments should not exclusively care about the size of inbound FDI flows but also about their specific characteristics, i.e. their quality
Glueball condensates as holographic duals of supersymmetric Q-balls and boson stars
We study non-spinning Q-balls and boson stars in 4-dimensional Anti-de Sitter
(AdS) space-time. We use an exponential scalar field potential that appears in
gauge-mediated supersymmetry (SUSY) breaking in the minimal supersymmetric
extension of the Standard Model (MSSM). We investigate the dependence of the
charge and mass of these non-topological solitons on the negative cosmological
constant, the frequency that appears in the periodic time-dependence as well as
on the ratio between the SUSY breaking scale and the Planck mass. Next to
fundamental solutions without nodes in the scalar field function we also
construct radially excited solutions. In the second part of the paper we put
the emphasis on the holographic interpretation of these solutions in terms of
Bose-Einstein condensates of scalar glueballs that are described by a strongly
coupled Quantum Field Theory (QFT) on the boundary of global AdS.Comment: 17 pages including 11 figures; v2: 19 pages including 13 figures,
references added, figures adde
Automorphism Groups of Graphical Models and Lifted Variational Inference
Using the theory of group action, we first introduce the concept of the
automorphism group of an exponential family or a graphical model, thus
formalizing the general notion of symmetry of a probabilistic model. This
automorphism group provides a precise mathematical framework for lifted
inference in the general exponential family. Its group action partitions the
set of random variables and feature functions into equivalent classes (called
orbits) having identical marginals and expectations. Then the inference problem
is effectively reduced to that of computing marginals or expectations for each
class, thus avoiding the need to deal with each individual variable or feature.
We demonstrate the usefulness of this general framework in lifting two classes
of variational approximation for MAP inference: local LP relaxation and local
LP relaxation with cycle constraints; the latter yields the first lifted
inference that operate on a bound tighter than local constraints. Initial
experimental results demonstrate that lifted MAP inference with cycle
constraints achieved the state of the art performance, obtaining much better
objective function values than local approximation while remaining relatively
efficient.Comment: Extended version of the paper to appear in Statistical Relational AI
(StaRAI-12) workshop at UAI '1
The impact of conventional and organic farming on soil biodiversity conservation: a case study on termites in the long-term farming systems comparison trials in Kenya
A long-term experiment at two trial sites in Kenya has been on-going since 2007 to assess the effect of organic and conventional farming systems on productivity, profitability and sustainability. During these trials the presence of significant numbers of termites (Isoptera) was observed. Termites are major soil macrofauna and within literature they are either depict as ‘pests’ or as important indicator for environmental sustainability. The extent by which termites may be managed to avoid crop damage, but improve sustainability of farming systems is worthwhile to understand. Therefore, a study on termites was added to the long-term experiments in Kenya. The objectives of the study were to quantify the effect of organic (Org) and conventional (Conv) farming systems at two input levels (low and high) on the abundance, incidence, diversity and foraging activities of termites.
The results showed higher termite abundance, incidence, activity and diversity in Org-High compared to Conv-High, Conv-Low and Org-Low. However, the termite presence in each system was also dependent on soil depth, trial site and cropping season. During the experiment, nine different termite genera were identified, that belong to three subfamilies: (i) Macrotermitinae (genera: Allodontotermes, Ancistrotermes, Macrotermes, Microtermes, Odontotermes and Pseudocanthotermes), (ii) Termitinae (Amitermes and Cubitermes) and (iii) Nasutitiermitinae (Trinervitermes).
We hypothesize that the presence of termites within the different farming systems might be influenced by the types of input applied, the soil moisture content and the occurrence of natural enemies. Our findings further demonstrate that the organic high input system attracts termites, which are an important, and often beneficial, component of soil fauna. This further increases the potential of such systems in enhancing sustainable agricultural production in Kenya
Observing cognitive processes in time through functional MRI model comparison
The temporal specificity of functional magnetic resonance imaging (fMRI) is limited by a sluggish and locally variable hemodynamic response trailing the neural activity by seconds. Here, we demonstrate for an attention capture paradigm that it is, never the less, possible to extract information about the relative timing of regional brain activity during cognitive processes on the scale of 100 ms by comparing alternative signal models representing early versus late activation. We demonstrate that model selection is not driven by confounding regional differences in hemodynamic delay. We show, including replication, that the activity in the dorsal anterior insula is an early signal predictive of behavioral performance, while amygdala and ventral anterior insula signals are not. This specific finding provides new insights into how the brain assigns salience to stimuli and emphasizes the role of the dorsal anterior insula in this context. The general analytic approach, named “Cognitive Timing through Model Comparison” (CTMC), offers an exciting and novel method to identify functional brain subunits and their causal interactions
The Solar Neighborhood. XXXIV. A Search for Planets Orbiting Nearby M Dwarfs using Astrometry
Astrometric measurements are presented for seven nearby stars with previously
detected planets: six M dwarfs (GJ 317, GJ 667C, GJ 581, GJ 849, GJ 876, and GJ
1214) and one K dwarf (BD 10 3166). Measurements are also presented for six
additional nearby M dwarfs without known planets, but which are more favorable
to astrometric detections of low mass companions, as well as three binary
systems for which we provide astrometric orbit solutions. Observations have
baselines of three to thirteen years, and were made as part of the RECONS
long-term astrometry and photometry program at the CTIO/SMARTS 0.9m telescope.
We provide trigonometric parallaxes and proper motions for all 16 systems, and
perform an extensive analysis of the astrometric residuals to determine the
minimum detectable companion mass for the 12 M dwarfs not having close stellar
secondaries. For the six M dwarfs with known planets, we are not sensitive to
planets, but can rule out the presence of all but the least massive brown
dwarfs at periods of 2 - 12 years. For the six more astrometrically favorable M
dwarfs, we conclude that none have brown dwarf companions, and are sensitive to
companions with masses as low as 1 for periods longer than two years.
In particular, we conclude that Proxima Centauri has no Jovian companions at
orbital periods of 2 - 12 years. These results complement previously published
M dwarf planet occurrence rates by providing astrometrically determined upper
mass limits on potential super-Jupiter companions at orbits of two years and
longer. As part of a continuing survey, these results are consistent with the
paucity of super-Jupiter and brown dwarf companions we find among the over 250
red dwarfs within 25 pc observed longer than five years in our astrometric
program.Comment: 18 pages, 5 figures, 4 tables, accepted for publication in A
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