1,341 research outputs found
Quantum Logic with a Single Trapped Electron
We propose the use of a trapped electron to implement quantum logic
operations. The fundamental controlled-NOT gate is shown to be feasible. The
two quantum bits are stored in the internal and external (motional) degrees of
freedom.Comment: 7 Pages, REVTeX, No Figures, To appear in Phys. Rev.
CPT and Lorentz Tests in Penning Traps
A theoretical analysis is performed of Penning-trap experiments testing CPT
and Lorentz symmetry through measurements of anomalous magnetic moments and
charge-to-mass ratios. Possible CPT and Lorentz violations arising from
spontaneous symmetry breaking at a fundamental level are treated in the context
of a general extension of the SU(3) x SU(2) x U(1) standard model and its
restriction to quantum electrodynamics. We describe signals that might appear
in principle, introduce suitable figures of merit, and estimate CPT and Lorentz
bounds attainable in present and future Penning-trap experiments. Experiments
measuring anomaly frequencies are found to provide the sharpest tests of CPT
symmetry. Bounds are attainable of approximately in the
electron-positron case and of for a suggested experiment with
protons and antiprotons. Searches for diurnal frequency variations in these
experiments could also limit certain types of Lorentz violation to the level of
in the electron-positron system and others at the level of
in the proton-antiproton system. In contrast, measurements comparing
cyclotron frequencies are sensitive within the present theoretical framework to
different kinds of Lorentz violation that preserve CPT. Constraints could be
obtained on one figure of merit in the electron-positron system at the level of
, on another in the proton-antiproton system at , and on a
third at using comparisons of ions with antiprotons.Comment: 31 pages, published in Physical Review
Magnetic field stabilization for high-accuracy mass measurements on exotic nuclides
The magnetic-field stability of a mass spectrometer plays a crucial role in
precision mass measurements. In the case of mass determination of short-lived
nuclides with a Penning trap, major causes of instabilities are temperature
fluctuations in the vicinity of the trap and pressure fluctuations in the
liquid helium cryostat of the superconducting magnet. Thus systems for the
temperature and pressure stabilization of the Penning trap mass spectrometer
ISOLTRAP at the ISOLDE facility at CERN have been installed. A reduction of the
fluctuations by at least one order of magnitude downto dT=+/-5mK and
dp=+/-50mtorr has been achieved, which corresponds to a relative frequency
change of 2.7x10^{-9} and 1.5x10^{-10}, respectively. With this stabilization
the frequency determination with the Penning trap only shows a linear temporal
drift over several hours on the 10 ppb level due to the finite resistance of
the superconducting magnet coils.Comment: 23 pages, 13 figure
Context-aware music recommender system based on automatic detection of the user’s physical activity
[EN] The large amount of music that can be accessed in streaming
nowadays has led to the development of more reliable music recommenda-
tion systems. To this end, context-aware music recommendation systems,
capable of suggesting music taking into account contextual information,
have emerged. Studies have shown that music helps to improve mood
while can change the focus of attention of users during the performance
of some activity, helping to make this activity more bearable. This work
presents a music Context Aware Recommender System in order to moti-
vate users in their daily activities. Its main purpose is to suggest to the
user the most appropriate music to improve the performance of the phys-
ical activity at recommending time. The conducted experiments along a
case study prove that this system is useful and satisfactory when the
activity does not require a great deal of concentration. During activities
that required movement, most users indicated that the perceived effort
decreases when using the recommendation system proposed. They also
indicated that their mood had improved after using this system. This
demonstrates the usefulness of this recommender system while doing
physical activities
Towards a resource-based habitat approach for spatial modelling of vector-borne disease risks
Given the veterinary and public health impact of vector-borne diseases, there is a clear need to assess the suitability of landscapes for the emergence and spread of these diseases. Current approaches for predicting disease risks neglect key features of the landscape as components of the functional habitat of vectors or hosts, and hence of the pathogen. Empirical–statistical methods do not explicitly incorporate biological mechanisms, whereas current mechanistic models are rarely spatially explicit; both methods ignore the way animals use the landscape (i.e. movement ecology). We argue that applying a functional concept for habitat, i.e. the resource-based habitat concept (RBHC), can solve these issues. The RBHC offers a framework to identify systematically the different ecological resources that are necessary for the completion of the transmission cycle and to relate these resources to (combinations of) landscape features and other environmental factors. The potential of the RBHC as a framework for identifying suitable habitats for vector-borne pathogens is explored and illustrated with the case of bluetongue virus, a midge-transmitted virus affecting ruminants. The concept facilitates the study of functional habitats of the interacting species (vectors as well as hosts) and provides new insight into spatial and temporal variation in transmission opportunities and exposure that ultimately determine disease risks. It may help to identify knowledge gaps and control options arising from changes in the spatial configuration of key resources across the landscape. The RBHC framework may act as a bridge between existing mechanistic and statistical modelling approaches
Perceived environmental factors related to adults’ leisure-time physical activity : findings from Europe, Australia and the USA
This journal suppl. entitled: Be Avtive 2012Session 204B - Environments and physical activity: Adults: paper no. 524INTRODUCTION: A growing body of evidence shows that objective and perceived built environment factors are positively associated with physical activity in adults. However, built environment correlates are behavior-specific and the factors associated with leisure-time physical activity are less understood than those associated with active transportation. Furthermore, most previous studies of associations of built environment attributes with physical activity have been conducted in single countries. Limited within-country variability in environmental attributes and physical activity levels can potentially contribute to an underestimation of the strength of the associations. Therefore, the purpose of this study was to examine the strength, direction and shape of the associations of neighborhood environmental perceptions with recreational walking and leisure-time moderate-to-vigorous physical activity, using pooled data from four study sites (Baltimore [USA], Seattle [USA], Adelaide [Australia] and Ghent [Belgium]) in culturally- and environmentally-diverse countries. Moreover, site- and gender-specificity of the associations were examined. METHODS: Data from the four study sites were pooled. In total, 6,014 adults (20–65 years, 55.7% women) were randomly recruited in high-/low-walkable and high-/low-income neighborhoods in the four sites. All participants completed the Neighborhood Environmental Walkability Scale (environmental perceptions) and the International Physical Activity Questionnaire. General additive mixed models were used to estimate the strength and shape of the associations between environmental perceptions and leisure-time activity (walking and moderate-to-vigorous physical activity). RESULTS: Perceived residential density, aesthetics and reporting few barriers to physical activity in the neighborhood were included in a ‘recreational walking-friendliness’ index. This index was linearly positively related to recreational walking in all study sites except Ghent. No gender-differences were observed. The ‘leisure-time activity friendliness’ index consisted of perceived residential density, proximity to recreation facilities, aesthetics and perceiving few barriers in the neighborhood. This index had a positive linear association with leisure-time moderate-to-vigorous physical activity that was significant in all sites but Ghent. Again, no gender-differences in the associations were found. DISCUSSION: Similar environmental attributes were related to both outcome measures in men and women, but the present findings were clearly site-specific, imposing possible challenges for built environment recommendations. In Europe, interventions to promote leisure-time activity may need to target promotion of existing opportunities rather than built environment improvements. In the USA and Australia, a focus on the factors identified in this study, may be of most relevance for promoting leisure-time physical activity
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