414 research outputs found
A study of methods of prediction and measurement of the transmission of sound through the walls of light aircraft
The acoustic intensity technique was applied to the sound transmission loss of panel structures (single, composite, and stiffened). A theoretical model of sound transmission through a cylindrical shell is presented
Electric properties of the Beryllium-11 system in Halo EFT
We compute E1 transitions and electric radii in the Beryllium-11 nucleus
using an effective field theory that exploits the separation of scales in this
halo system. We fix the leading-order parameters of the EFT from measured data
on the 1/2+ and 1/2- levels in Be-11 and the B(E1) strength for the transition
between them. We then obtain predictions for the B(E1) strength for Coulomb
dissociation of the Be-11 nucleus to the continuum. We also compute the charge
radii of the 1/2+ and 1/2- states. Agreement with experiment within the
expected accuracy of a leading-order computation in this EFT is obtained. We
also discuss how next-to-leading-order (NLO) corrections involving both s-wave
and p-wave neutron-Be-10 interactions affect our results, and display the NLO
predictions for quantities which are free of additional short-distance
operators at this order. Information on neutron-Be-10 scattering in the
relevant channels is inferred.Comment: 27 pages, 8 figures, final versio
Finite-size effects in heavy halo nuclei from effective field theory
Halo/Cluster Effective Field Theory describes halo/cluster nuclei in an expansion in the small ratio of the size of the core(s) to the size of the system. Even in the point-particle limit, neutron-halo nuclei have a finite charge radius, because their center of mass does not coincide with their center of charge. This point-particle contribution decreases as 1 / Ac, where Ac is the mass number of the core, and diminishes in importance compared to other effects, e.g., the size of the core to which the neutrons are bound. Here we propose that for heavy cores the EFT expansion should account for the small factors of 1 / Ac. As a specific example, we discuss the implications of this organizational scheme for the inclusion of finite-size effects in expressions for the charge radii of halo nuclei. We show in particular that a short-range operator could be the dominant effect in the charge radius of one-neutron halos bound by a P-wave interaction. The point-particle contribution remains the leading piece of the charge radius for one-proton halos, and so Halo EFT has more predictive power in that case
Recent advances in the theory of nuclear forces
After a brief historical review, we present recent progress in our
understanding of nuclear forces in terms of chiral effective field theory.Comment: 6 pages, 2 figures; talk at International Symposium on Correlations
Dynamics in Nuclei, University of Tokyo, Japan, 31 January-4 February, 200
A study of methods of prediction and measurement of the transmission sound through the walls of light aircraft
Several aspects were studied. The SEA theory was used to develop a theoretical model to predict the transmission loss through an aircraft window. This work mainly consisted of the writing of two computer programs. One program predicts the sound transmission through a plexiglass window (the case of a single partition). The other program applies to the case of a plexiglass window window with a window shade added (the case of a double partition with an air gap). The sound transmission through a structure was measured in experimental studies using several different methods in order that the accuracy and complexity of all the methods could be compared. Also, the measurements were conducted on the simple model of a fuselage (a cylindrical shell), on a real aircraft fuselage, and on stiffened panels
Hinge-Wasserstein: Mitigating Overconfidence in Regression by Classification
Modern deep neural networks are prone to being overconfident despite their
drastically improved performance. In ambiguous or even unpredictable real-world
scenarios, this overconfidence can pose a major risk to the safety of
applications. For regression tasks, the regression-by-classification approach
has the potential to alleviate these ambiguities by instead predicting a
discrete probability density over the desired output. However, a density
estimator still tends to be overconfident when trained with the common NLL
loss. To mitigate the overconfidence problem, we propose a loss function,
hinge-Wasserstein, based on the Wasserstein Distance. This loss significantly
improves the quality of both aleatoric and epistemic uncertainty, compared to
previous work. We demonstrate the capabilities of the new loss on a synthetic
dataset, where both types of uncertainty are controlled separately. Moreover,
as a demonstration for real-world scenarios, we evaluate our approach on the
benchmark dataset Horizon Lines in the Wild. On this benchmark, using the
hinge-Wasserstein loss reduces the Area Under Sparsification Error (AUSE) for
horizon parameters slope and offset, by 30.47% and 65.00%, respectively
Evaluation of Machine Learning Methods to Predict Coronary Artery Disease Using Metabolomic Data
Metabolomic data can potentially enable accurate, non-invasive and low-cost prediction of coronary artery disease. Regression-based analytical approaches however might fail to fully account for interactions between metabolites, rely on a priori selected input features and thus might suffer from poorer accuracy. Supervised machine learning methods can potentially be used in order to fully exploit the dimensionality and richness of the data. In this paper, we systematically implement and evaluate a set of supervised learning methods (L1 regression, random forest classifier) and compare them to traditional regression-based approaches for disease prediction using metabolomic data
A Contraction Based Solution for the Improvement of Fish Ladder Attraction Flow
A new, potentially cost efficient, concept for improving the attraction flow to a fish ladder has been investigated in a case study. For the upstream migrating Atlantic salmon to reach the fish ladder and by-pass the case study hydropower plant, it must be able to localize the attraction flow where it enters the main flow from the tailrace of the hydropower plant in the so-called confluence area. Here the comparatively small and limited attraction flow from the old river channel must be improved in order to be able compete with the substantially larger main flow. The objective of the present study is to investigate the feasibility of a new concept for further improvement of the attraction flow using guiding walls forming a contraction channel. Field measurements were performed tracing tagged fish in the confluence area downstream of the case study hydropower plant in order to understand the movement pattern of the fish. Based on the results, and results from bathymetry measurements in the same area, a physical scale model was constructed where it was experimentally demonstrated that it is hydraulically feasible to construct guiding walls, forming a contraction, which accelerate the attraction flow and generate a concentrated turbulent jet with a higher velocity, while keeping the flow rate unchanged. The attraction flow penetrates about half-way (70 m) into the main flow and reaches the position where most fish are positioned according to fish position measurements and therefore potentially has a good ability to attract upstream migrating fish. There is no negative impact on the water level in the confluence area and thereby not on electricity production. It was shown that the results can be scaled up to prototype conditions and the strategy can presumably be generalized to similar flow situations, existing at other hydropower plants, allowing for improved upstream fish migration in coexistence with a sound hydropower production
The ab initio no-core shell model
This contribution reviews a number of applications of the ab initio no-core
shell model (NCSM) within nuclear physics and beyond. We will highlight a
nuclear-structure study of the A = 12 isobar using a chiral NN + 3NF
interaction. In the spirit of this workshop we will also mention the new
development of the NCSM formalism to describe open channels and to approach the
problem of nuclear reactions. Finally, we will illustrate the universality of
the many-body problem by presenting the recent adaptation of the NCSM
effective-interaction approach to study the many-boson problem in an external
trapping potential with short-range interactions.Comment: 4 pages. Article based on the presentation by C. Forssen at the Fifth
Workshop on Critical Stability, Erice, Sicily. Published in Few-Body System
Urban background noise mapping: the general model
Surveys show that inhabitants of dwellings exposed to high noise levels benefit from having access to a quiet side. However, current practice in noise prediction often underestimates the noise levels at a shielded facade. Multiple reflections between facades in street canyons and inner yards are commonly neglected and facades are approximated as perfectly flat surfaces yielding only specular reflection. In addition, sources at distances much larger than normally taken into account in noise maps might still contribute significantly. Since one of the main reasons for this is computational burden, an efficient engineering model for the diffraction of the sound over the roof tops is proposed, which considers multiple reflections, variation in building height, canyon width, facade roughness and different roof shapes. The model is fitted on an extensive set of full-wave numerical calculations of canyon-to-canyon sound propagation with configurations matching the distribution of streets and building geometries in a typical historically grown European city. This model allows calculating the background noise in the shielded areas of a city, which could then efficiently be used to improve existing noise mapping calculations. The model was validated by comparison to long-term measurements at 9 building facades whereof 3 were at inner yards in the city of Ghent, Belgium. At shielded facades, a strong improvement in prediction accuracy is obtained
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