2,060 research outputs found
A trust-region method for stochastic variational inference with applications to streaming data
Stochastic variational inference allows for fast posterior inference in
complex Bayesian models. However, the algorithm is prone to local optima which
can make the quality of the posterior approximation sensitive to the choice of
hyperparameters and initialization. We address this problem by replacing the
natural gradient step of stochastic varitional inference with a trust-region
update. We show that this leads to generally better results and reduced
sensitivity to hyperparameters. We also describe a new strategy for variational
inference on streaming data and show that here our trust-region method is
crucial for getting good performance.Comment: in Proceedings of the 32nd International Conference on Machine
Learning, 201
The structure of borders in a small world
Geographic borders are not only essential for the effective functioning of
government, the distribution of administrative responsibilities and the
allocation of public resources, they also influence the interregional flow of
information, cross-border trade operations, the diffusion of innovation and
technology, and the spatial spread of infectious diseases. However, as growing
interactions and mobility across long distances, cultural, and political
borders continue to amplify the small world effect and effectively decrease the
relative importance of local interactions, it is difficult to assess the
location and structure of effective borders that may play the most significant
role in mobility-driven processes. The paradigm of spatially coherent
communities may no longer be a plausible one, and it is unclear what structures
emerge from the interplay of interactions and activities across spatial scales.
Here we analyse a multi-scale proxy network for human mobility that
incorporates travel across a few to a few thousand kilometres. We determine an
effective system of geographically continuous borders implicitly encoded in
multi-scale mobility patterns. We find that effective large scale boundaries
define spatially coherent subdivisions and only partially coincide with
administrative borders. We find that spatial coherence is partially lost if
only long range traffic is taken into account and show that prevalent models
for multi-scale mobility networks cannot account for the observed patterns.
These results will allow for new types of quantitative, comparative analyses of
multi-scale interaction networks in general and may provide insight into a
multitude of spatiotemporal phenomena generated by human activity.Comment: 9 page
Combined Palladium-Silver and Iodine-Xenon Isotope Systematics for Allegan (H5) and Dhofar 125 (Acapulcoite)
Instantons in the Double-Tensor Multiplet
The double-tensor multiplet naturally appears in type IIB superstring
compactifications on Calabi-Yau threefolds, and is dual to the universal
hypermultiplet. We revisit the calculation of instanton corrections to the
low-energy effective action, in the supergravity approximation. We derive a
Bogomolny'i bound for the double-tensor multiplet and find new instanton
solutions saturating the bound. They are characterized by the topological
charges and the asymptotic values of the scalar fields in the double-tensor
multiplet.Comment: 17 pages, LaTeX2e with amsmath.sty; v2: minor change
Is obesity policy in England fit for purpose? Analysis of government strategies and policies, 1992-2020
Context: In England, the majority of adults, and more than a quarter of children aged 2 to 15 years live with obesity or excess weight. From 1992-2020, government published fourteen obesity strategies in England, yet obesity prevalence has not been reduced. We aimed to determine whether such government strategies and policies have been fit for purpose regarding their strategic focus, nature, basis in theory and evidence, and implementation viability.
Method: We undertook a mixed-methods study, involving a document review and analysis of government strategies either wholly or partially dedicated to tackling obesity in England. We developed a theory-based analytical framework, using content analysis and applied thematic analysis (ATA) to code all policies. Interpretation drew on quantitative findings and thematic analysis.
Results: We identified and analysed fourteen government strategies published from 1992-2020 containing 689 wide-ranging policies. Policies were largely proposed in a way that would be unlikely to lead to implementation; the majority were not interventionist and made high demands on individual agency, meaning they relied on individuals to make behaviour changes rather than shaping external influences, and are thus less likely to be effective or to reduce health inequalities.
Conclusions: The absence of impact on obesity prevalence of government obesity strategies for England over almost 30 years may be due to policy design weaknesses leading to lack of effectiveness, but may also be due to failures of implementation and evaluation. This appears to have led to insufficient or no policy learning and government proposing similar or identical policies repeatedly over many years. Governments should learn from earlier policy failures. They should prioritise policies that make minimal demands on individuals and have the potential for population-wide reach so as to maximise their potential for equitable impacts. Policies should be proposed in ways that readily lead to implementation and evaluation.The research is funded by/supported by a PhD studentship awarded to DRZT by the National Institute for Health Research (NIHR) School for Public Health Research (Grant No. PD-SPH-2015-10025). MW is supported by the MRC Epidemiology Unit (Grant No. MC/UU/12015/6) and the Centre for Diet & Activity Research (CEDAR), with funding from the British Heart Foundation, Cancer Research UK, Economic & Social Research Council, Medical Research Council, NIHR and Wellcome Trust (Grant Nos. ES/G007462/1, MR/K023187/1 & 087636/Z/08/Z). The views expressed are those of the author(s) and not necessarily those of any of the above named funders
Engineering adiabaticity at an avoided crossing with optimal control
We investigate ways to optimize adiabaticity and diabaticity in the
Landau-Zener model with non-uniform sweeps. We show how diabaticity can be
engineered with a pulse consisting of a linear sweep augmented by an
oscillating term. We show that the oscillation leads to jumps in populations
whose value can be accurately modeled using a model of multiple,
photon-assisted Landau-Zener transitions, which generalizes work by Wubs et al.
[New J. Phys. 7, 218 (2005)]. We extend the study on diabaticity using methods
derived from optimal control. We also show how to preserve adiabaticity with
optimal pulses at limited time, finding a non-uniform quantum speed limit
Development of visible/infrared/microwave agriculture classification and biomass estimation algorithms, volume 2
Agricultural crop classification models using two or more spectral regions (visible through microwave) were developed and tested and biomass was estimated by including microwave with visible and infrared data. The study was conducted at Guymon, Oklahoma and Dalhart, Texas utilizing aircraft multispectral data and ground truth soil moisture and biomass information. Results indicate that inclusion of C, L, and P band active microwave data from look angles greater than 35 deg from nadir with visible and infrared data improved crop discrimination and biomass estimates compared to results using only visible and infrared data. The active microwave frequencies were sensitive to different biomass levels. In addition, two indices, one using only active microwave data and the other using data from the middle and near infrared bands, were well correlated to total biomass
Microwave remote sensing of soil moisture, volume 1
Multifrequency sensor data from NASA's C-130 aircraft were used to determine which of the all weather microwave sensors demonstrated the highest correlation to surface soil moisture over optimal bare soil conditions, and to develop and test techniques which use visible/infrared sensors to compensate for the vegetation effect in this sensor's response to soil moisture. The L-band passive microwave radiometer was found to be the most suitable single sensor system to estimate soil moisture over bare fields. The perpendicular vegetation index (PVI) as determined from the visible/infrared sensors was useful as a measure of the vegetation effect on the L-band radiometer response to soil moisture. A linear equation was developed to estimate percent field capacity as a function of L-band emissivity and the vegetation index. The prediction algorithm improves the estimation of moisture significantly over predictions from L-band emissivity alone
Multifrequency remote sensing of soil moisture
Multifrequency sensor data collected at Guymon, Oklahoma and Dalhart, Texas using NASA's C-130 aircraft were used to determine which of the all-weather microwave sensors demonstrated the highest correlation to surface soil moisture over optimal bare soil conditions, and to develop and test techniques which use visible/infrared sensors to compensate for the vegetation effect in this sensor's response to soil moisture. The L-band passive microwave radiometer was found to be the most suitable single sensor system to estimate soil moisture over bare fields. In comparison to other active and passive microwave sensors the L-band radiometer (1) was influenced least by ranges in surface roughness; (2) demonstrated the most sensitivity to soil moisture differences in terms of the range of return from the full range of soil moisture; and (3) was less sensitive to errors in measurement in relation to the range of sensor response. L-band emissivity related more strongly to soil moisture when moisture was expressed as percent of field capacity. The perpendicular vegetation index as determined from the visible/infrared sensors was useful as a measure of the vegetation effect on the L-band radiometer response to soil moisture
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