13,437 research outputs found
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Nonlinear stability of continuously stratified quasi-geostrophic flow
Nonlinear stability theorems analogous to Arnol'd's second stability theorem are established for continuously stratified quasi-geostrophic flow with general nonlinear boundary conditions in a vertically and horizontally confined domain. Both the standard quasi-geostrophic model and the modified quasi-geostrophic model (incorporating effects of hydrostatic compressibility) are treated. The results establish explicit upper bounds on the disturbance energy, the disturbance potential enstrophy, and the disturbance available potential energy on the horizontal boundaries, in terms of the initial disturbance fields. Nonlinear stability in the sense of Liapunov is also established
Visualizing Convolutional Networks for MRI-based Diagnosis of Alzheimer's Disease
Visualizing and interpreting convolutional neural networks (CNNs) is an
important task to increase trust in automatic medical decision making systems.
In this study, we train a 3D CNN to detect Alzheimer's disease based on
structural MRI scans of the brain. Then, we apply four different gradient-based
and occlusion-based visualization methods that explain the network's
classification decisions by highlighting relevant areas in the input image. We
compare the methods qualitatively and quantitatively. We find that all four
methods focus on brain regions known to be involved in Alzheimer's disease,
such as inferior and middle temporal gyrus. While the occlusion-based methods
focus more on specific regions, the gradient-based methods pick up distributed
relevance patterns. Additionally, we find that the distribution of relevance
varies across patients, with some having a stronger focus on the temporal lobe,
whereas for others more cortical areas are relevant. In summary, we show that
applying different visualization methods is important to understand the
decisions of a CNN, a step that is crucial to increase clinical impact and
trust in computer-based decision support systems.Comment: MLCN 201
decay beyond the standard model
The decay is investigated beyond the standard
model. Interestingly, the upper limit of the CP-conserving and CP-violating
branching ratios of the decay, induced from the possible extensions of the
standard model, would be larger than the corresponding branching ratios given
in the standard model respectively, and it is expected that the CP-violating
part could be enhanced
Challenges of Primary Frequency Control and Benefits of Primary Frequency Response Support from Electric Vehicles
As the integration of wind generation displaces conventional plants, system inertia provided by rotating mass declines, causing concerns over system frequency stability. This paper implements an advanced stochastic scheduling model with inertia-dependent fast frequency response requirements to investigate the challenges on the primary frequency control in the future Great Britain electricity system. The results suggest that the required volume and the associated cost of primary frequency response increase significantly along with the increased capacity of wind plants. Alternative measures (e.g. electric vehicles) have been proposed to alleviate these concerns. Therefore, this paper also analyses the benefits of primary frequency response support from electric vehicles in reducing system operation cost, wind curtailment and carbon emissions
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Nonlinear stability of multilayer quasi-geostrophic flow
New nonlinear stability theorems are derived for disturbances to steady basic flows in the context of the multilayer quasi-geostrophic equations. These theorems are analogues of Arnol’d's second stability theorem, the latter applying to the two-dimensional Euler equations. Explicit upper bounds are obtained on both the disturbance energy and disturbance potential enstrophy in terms of the initial disturbance fields. An important feature of the present analysis is that the disturbances are allowed to have non-zero circulation. While Arnol’d's stability method relies on the energy–Casimir invariant being sign-definite, the new criteria can be applied to cases where it is sign-indefinite because of the disturbance circulations. A version of Andrews’ theorem is established for this problem, and uniform potential vorticity flow is shown to be nonlinearly stable. The special case of two-layer flow is treated in detail, with particular attention paid to the Phillips model of baroclinic instability. It is found that the short-wave portion of the marginal stability curve found in linear theory is precisely captured by the new nonlinear stability criteria
Chiral Perturbation Theory and U(3)_L\times U(3)_R Chiral Theory of Mesons
We examine low energy limit of chiral theory of mesons
through integrating out fields of vector and axial-vector mesons. The effective
lagrangian for pseudoscalar mesons at has been obtained, and five low
energy coupling constants have been revealed. They are in
good agreement with the results of CHPT's at .Comment: 20 pages, Standard LaTex file, no finger
Nonlinearly combined impacts of initial perturbation from human activities and parameter perturbation from climate change on the grassland ecosystem
Human activities and climate change are important factors that affect grassland ecosystems. A new optimization approach, the approach of conditional nonlinear optimal perturbation (CNOP) related to initial and parameter perturbations, is employed to explore the nonlinearly combined impacts of human activities and climate change on a grassland ecosystem using a theoretical grassland model. In our study, it is assumed that the initial perturbations and parameter perturbations are regarded as human activities and climate change, respectively. Numerical results indicate that the climate changes causing the maximum effect in the grassland ecosystem are different under disparate intensities of human activities. This implies the pattern of climate change is very critical to the maintenance or degradation of grassland ecosystem in light of high intensity of human activities and that the grassland ecosystem should be rationally managed when the moisture index decreases. The grassland ecosystem influenced by the nonlinear combination of human activities and climate change undergoes abrupt change, while the grassland ecosystem affected by other types of human activities and climate change fails to show the abrupt change under a certain range of perturbations with the theoretical model. The further numerical analyses also indicate that the growth of living biomass and the evaporation from soil surface shaded by the wilted biomass may be crucial factors contributing to the abrupt change of the grassland equilibrium state within the theoretical model
Low Scale Non-universal, Non-anomalous U(1)'_F in a Minimal Supersymmetric Standard Model
We propose a non-universal U(1)'_F symmetry combined with the Minimal
Supersymmetric Standard Model. All anomaly cancellation conditions are
satisfied without exotic fields other than three right-handed neutrinos.
Because our model allows all three generations of chiral superfields to have
different U(1)'_F charges, upon the breaking of the U(1)'_F symmetry at a low
scale, realistic masses and mixing angles in both the quark and lepton sectors
are obtained. In our model, neutrinos are predicted to be Dirac fermions and
their mass ordering is of the inverted hierarchy type. The U(1)'_F charges of
the chiral super-fields also naturally suppress the mu term and automatically
forbid baryon number and lepton number violating operators. While all
flavor-changing neutral current constraints in the down quark and charged
lepton sectors can be satisfied, we find that constraint from D0-D0bar turns
out to be much more stringent than the constraints from the precision
electroweak data.Comment: 21 pages, 2 figures; v2: discussion on sparticle mass spectrum
included, 27 pages, 2 figure
Evidence for line nodes in the energy gap of the overdoped Ba(FeCo)As from low-temperature specific heat measurements
Low-temperature specific heat (SH) is measured on
Ba(FeCo)As single crystals in a wide doping region under
different magnetic fields. For the overdoped sample, we find the clear evidence
for the presence of term in the data, which is absent both for the
underdoped and optimal doped samples, suggesting the presence of line nodes in
the energy gap of the overdoped samples. Moreover, the field induced electron
specific heat coefficient increases more quickly with the
field for the overdoped sample than the underdoped and optimal doped ones,
giving another support to our arguments. Our results suggest that the
superconducting gap(s) in the present system may have different structures
strongly depending on the doping regions.Comment: 5 pages, 4 figure
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