We study strain localization as an enhanced velocity weakening mechanism on earthquake faults. Fault friction is modeled using Shear Transformation Zone (STZ) Theory, a microscopic physical model for ...non‐affine rearrangements in granular fault gouge. STZ Theory is implemented in spring slider and dynamic rupture models of faults. We compare dynamic shear localization to deformation that is uniform throughout the gouge layer, and find that localized slip enhances the velocity weakening of the gouge. Localized elastodynamic ruptures have larger stress drops and higher peak slip rates than ruptures with homogeneous strain.
We incorporate shear strain localization into spontaneous elastodynamic rupture simulations using a shear transformation zone (STZ) friction law. In the STZ model, plastic strain in the granular ...fault gouge occurs in local regions called STZs. The number density of STZs is governed by an effective disorder temperature, and regions with elevated effective temperature have an increased strain rate. STZ theory resolves the dynamic evolution of the effective temperature across the width of the fault zone. Shear bands spontaneously form in the model due to feedbacks amplifying heterogeneities in the initial effective temperature. In dynamic earthquake simulations, strain localization is a mechanism for dynamic fault weakening. A shear band dynamically forms, reduces the sliding stress, and decreases the frictional energy dissipation on the fault. We investigate the effect of the dynamic weakening due to localization in generating pulse‐like, crack‐like, and supershear rupture. Our results illustrate that the additional weakening and reduction of on‐fault energy dissipation due to localization have a significant impact on the initial shear stress required for supershear or pulse‐like rupture to propagate on a fault.
We present several methods to improve the resolution of human brain mapping by combining information obtained from surface electroencephalography (EEG) and functional magnetic resonance imaging ...(fMRI) of the same participants performing the same task in separate imaging sessions. As an initial step in our methods we used independent component analysis (ICA) to obtain task-related sources for both EEG and fMRI. We then used that information in an integrated cost function that attempts to match both data sources and trades goodness of fit in one regime for another. We compared the performance and drawbacks of each method in localizing sources for a dual visual evoked response experiment, and we contrasted the results of adding fMRI information to simple EEG-only inversion methods. We found that adding fMRI information in a variety of ways gives superior results to classical minimum norm source estimation. Our findings lead us to favor a method which attempts to match EEG scalp dynamics along with voxel power obtained from ICA-processed blood oxygenation level dependent (BOLD) data; this method of joint inversion enables us to treat the two data sources as symmetrically as possible.
Diversity of T-cell responses Stromberg, Sean P; Carlson, Jean M
Physical biology,
04/2013, Letnik:
10, Številka:
2
Journal Article
Recenzirano
Using a dynamic model we study the adaptive immune response to a sequence of two infections. We incorporate lymphocyte diversity by modeling populations as continuous distributions in a ...multi-dimensional space. As expected, memory cells generated by the primary infection invoke a rapid response when the secondary infection is identical (homologous). When the secondary infection is different (heterologous), the memory cells have a positive effect or no effect at all depending on the similarity of the infections. This model displays 'original antigenic sin' where the average effector affinity for the heterologous infection is lower than it would be for a naive response, but in cases with original antigenic sin we see a reduction in pathogen density. We model pathology resulting from the immune system itself (immunopathology) but find that in cases of original antigenic sin, immunopathology is still reduced. Average effector affinity is not an accurate measure of the quality of an immune response. The effectivity, which is the total pathogen killing rate, provides a direct measure of quality. This quantity takes both affinity and magnitude into account.
Friction and deformation in granular fault gouge are among various dynamic interactions associated with seismic phenomena that have important implications for slip mechanisms on earthquake faults. To ...this end, we propose a mechanistic model of granular fault gouge subject to acoustic vibrations and shear deformation. The grain‐scale dynamics is described by the Shear‐Transformation‐Zone theory of granular flow, which accounts for irreversible plastic deformation in terms of flow defects whose density is governed by an effective temperature. Our model accounts for stick‐slip instabilities observed at seismic slip rates. In addition, as the vibration intensity increases, we observe an increase in the temporal advancement of large slip events, followed by a plateau and gradual decrease. Furthermore, slip becomes progressively slower upon increasing the vibration intensity. The results shed important light on the physical mechanisms of earthquake triggering and slow slip and provide essential elements for the multiscale modeling of earthquake ruptures. In particular, the results suggest that slow slip may be triggered by tremors.
Key Points
We proposed a physics‐based model for granular flow and stick‐slip failure on faults
Vibration advances slip events
Slip becomes progressively slower upon increase in vibration intensity
This paper explores the environmental factors that drive the southern California chaparral fire regime. Specifically, we examined the response of three fire regime metrics (fire size distributions, ...fire return interval maps, cumulative total area burned) to variations in the number of ignitions, the spatial pattern of ignitions, the number of Santa Ana wind events, and live fuel moisture, using the HFire fire spread model. HFire is computationally efficient and capable of simulating the spatiotemporal progression of individual fires on a landscape and aggregating results for fully resolved individual fires over hundreds or thousands of years to predict long-term fire regimes. A quantitative understanding of the long-term drivers of a fire regime is of use in fire management and policy.
Sacrificial bonds and hidden length in structural molecules account for the greatly increased fracture toughness of biological materials compared to synthetic materials without such structural ...features by providing a molecular-scale mechanism for energy dissipation. One example is in the polymeric glue connection between collagen fibrils in animal bone. In this paper we propose a simple kinetic model that describes the breakage of sacrificial bonds and the release of hidden length, based on Bell's theory. We postulate a master equation governing the rates of bond breakage and formation. This enables us to predict the mechanical behavior of a quasi-one-dimensional ensemble of polymers at different stretching rates. We find that both the rupture peak heights and maximum stretching distance increase with the stretching rate. In addition, our theory naturally permits the possibility of self-healing in such biological structures.
Momentum transport in granular flows Lois, Gregg; Lemaître, Anaël; Carlson, Jean M.
Computers & mathematics with applications (1987),
2008, 2008-01-00, 20080101, Letnik:
55, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We investigate the error induced by considering only binary collisions in the momentum transport of hard-sphere granular materials, as is done in kinetic theories. In this process, we first present a ...general microscopic derivation of the momentum transport equation and compare it to the kinetic theory derivation, which relies on the binary collision assumption. These two derivations yield different microscopic expressions for the stress tensor, which we compare by using numerical simulations. This provides a quantitative bound on the regime where binary collisions dominate momentum transport and reveals that most realistic granular flows occur in the region of phase space where the binary collision assumption does not apply.
The ipd072Aa gene from Pseudomonas chlororaphis encodes the IPD072Aa protein which confers protection against certain coleopteran pests when expressed in genetically modified (GM) plants. A weight of ...evidence approach was used to assess the safety of the IPD072Aa protein. This approach considered the history of safe use of the source organism and bioinformatic comparison of the protein sequence with known allergenic and toxic proteins. The IPD072Aa protein was assessed for resistance to degradation in the presence of simulated gastric fluid containing pepsin as well as heat stability. There was no hazard identified with the IPD072Aa protein. Furthermore, an acute oral toxicity study found no evidence of adverse effects. Collectively, these studies support the human health safety assessment of the IPD072Aa protein.
•IPD072Aa is a novel insecticidal protein obtained from Pseudomonas chlororaphis active on certain Coleoptera.•IPD072Aa protein in genetically modified maize offers a new mode of action of protection against western corn rootworm.•A weight of evidence approach was used to assess the safety of the IPD072Aa protein.•No toxin or allergen hazard was identified therefore the IPD072Aa protein is not expected to adversely impact human health.
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