19 research outputs found
Privacy-Preserving Identification via Layered Sparse Code Design: Distributed Servers and Multiple Access Authorization
We propose a new computationally efficient privacy-preserving identification
framework based on layered sparse coding. The key idea of the proposed
framework is a sparsifying transform learning with ambiguization, which
consists of a trained linear map, a component-wise nonlinearity and a privacy
amplification. We introduce a practical identification framework, which
consists of two phases: public and private identification. The public untrusted
server provides the fast search service based on the sparse privacy protected
codebook stored at its side. The private trusted server or the local client
application performs the refined accurate similarity search using the results
of the public search and the layered sparse codebooks stored at its side. The
private search is performed in the decoded domain and also the accuracy of
private search is chosen based on the authorization level of the client. The
efficiency of the proposed method is in computational complexity of encoding,
decoding, "encryption" (ambiguization) and "decryption" (purification) as well
as storage complexity of the codebooks.Comment: EUSIPCO 201
River-bed armoring as a granular segregation phenomenon
Gravel-river beds typically have an "armored" layer of coarse grains on the
surface, which acts to protect finer particles underneath from erosion. River
bed-load transport is a kind of dense granular flow, and such flows are known
to vertically segregate grains. The contribution of granular physics to
river-bed armoring, however, has not been investigated. Here we examine these
connections in a laboratory river with bimodal sediment size, by tracking the
motion of particles from the surface to deep inside the bed, and find that
armor develops by two distinct mechanisms. Bed-load transport in the
near-surface layer drives rapid segregation, with a vertical advection rate
proportional to the granular shear rate. Creeping grains beneath the bed-load
layer give rise to slow but persistent segregation, which is diffusion
dominated and insensitive to shear rate. We verify these findings with a
continuum phenomenological model and discrete element method simulations. Our
results suggest that river beds armor by granular segregation from below ---
rather than fluid-driven sorting from above --- while also providing new
insights on the mechanics of segregation that are relevant to a wide range of
granular flows
Acoustically-induced slip in sheared granular layers: application to dynamic earthquake triggering
A fundamental mystery in earthquake physics is ``how can an earthquake be
triggered by distant seismic sources?'' Here, we use discrete element method
simulations of a granular layer, during stick-slip, that is subject to
transient vibrational excitation to gain further insight into the physics of
dynamic earthquake triggering. Using Coulomb friction law for grains
interaction, we observe delayed triggering of slip in the granular gouge. We
find that at a critical vibrational amplitude (strain) there is an abrupt
transition from negligible time-advanced slip (clock advance) to full clock
advance, {\it i.e.}, transient vibration and triggered slip are simultaneous.
The critical strain is order of , similar to observations in the
laboratory and in Earth. The transition is related to frictional weakening of
the granular layer due to a dramatic decrease in coordination number and the
weakening of the contact force network. Associated with this frictional
weakening is a pronounced decrease in the elastic modulus of the layer. The
study has important implications for mechanisms of triggered earthquakes and
induced seismic events and points out the underlying processes in response of
the fault gouge to dynamic transient stresses
E-Mobility -- Advancements and Challenges
Mobile platforms cover a broad range of applications from small portable electric devices, drones, and robots to electric transportation, which influence the quality of modern life. The end-to-end energy systems of these platforms are moving toward more electrification. Despite their wide range of power ratings and diverse applications, the electrification of these systems shares several technical requirements. Electrified mobile energy systems have minimal or no access to the power grid, and thus, to achieve long operating time, ultrafast charging or charging during motion as well as advanced battery technologies are needed. Mobile platforms are space-, shape-, and weight-constrained, and therefore, their onboard energy technologies such as the power electronic converters and magnetic components must be compact and lightweight. These systems should also demonstrate improved efficiency and cost-effectiveness compared to traditional designs. This paper discusses some technical challenges that the industry currently faces moving toward more electrification of energy conversion systems in mobile platforms, herein referred to as E-Mobility, and reviews the recent advancements reported in literature
Discrete element modeling of triggered slip in faults with granular gouge: Application to dynamic earthquake triggering
Data for Shields stress 4.7
small and large grains number ratio time-series for Shields stress 4.7. Concentration map of large grains can be made using the following contour plot commands in MATLAB or other data analysis packages:<div><br></div><div>%%%%</div><div><p>nlratio_tot = nlg./(nsm+nlg);</p><p>for i=1:458</p><p>time_ts(i,:)=time;</p><p>end</p><p>y_pos = (1:1:458)*(25/458);</p><p>for i=1:length(time)</p><p>y_mesh(:,i)=y_pos;</p><p>end</p><p>[xq,yq] = meshgrid(0:0.0005:1,0:0.175:25);</p><p>vq = griddata(time_ts(1:458,1:length(time)),25-y_mesh(1:458,1:length(time)),nlratio_tot(1:458,1:length(time)),xq,yq);</p><p>figure; [C,h] = contourf(xq,yq,vq,'LineStyle', 'none','LevelStep', 0.01);</p><p>colormap parula;</p><p>%%%%</p></div