Microrollers Flow Uphill as Granular Media

Pour sand into a container and only the grains near the top surface move. The collective motion associated with the translational and rotational energy of the grains in a thin flowing layer is quickly dissipated as friction through multibody interactions. Alternatively, consider what will happen to a bed of particles if one applies a torque to each individual particle. In this paper, we demonstrate an experimental system where torque is applied at the constituent level through a rotating magnetic field in a dense bed of microrollers. The net result is the grains roll uphill, forming a heap with a negative angle of repose. Two different regimes have been identified related to the degree of mobility or fluidization of the particles in the bulk. Velocimetry of the near surface flowing layer reveals the collective motion of these responsive particles scales in a similar way to flowing bulk granular flows. A simple granular model that includes cohesion accurately predicts the apparent negative coefficient of friction. In contrast to the response of active or responsive particles that mimic thermodynamic principles, this system results in macroscopic collective behavior that has the kinematics of a purely dissipative granular system

Experiential Learning Programs for the Future of Engineering Education

The need for 21st century engineers to be educated as creative innovators is discussed. Three complementary experiential learning programs that help engineering students learn to stretch beyond their comfort zones are described: a multidisciplinary design program; an entrepreneurship program; and an international engineering program. These three interdisciplinary programs each address common educational needs: to create flexible, creative, self-actualized change agents. The approaches we are taking to implement and institutionalize these in a large, comprehensive, research oriented university are described.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86757/1/Sick5.pd

Input states for quantum gates

We examine three possible implementations of non-deterministic linear optical cnot gates with a view to an in-principle demonstration in the near future. To this end we consider demonstrating the gates using currently available sources such as spontaneous parametric down conversion and coherent states, and current detectors only able to distinguish between zero or many photons. The demonstration is possible in the co-incidence basis and the errors introduced by the non-optimal input states and detectors are analysed

Neurophysiological signatures of Alzheimer's disease and frontotemporal lobar degeneration : pathology versus phenotype

The disruption of brain networks is characteristic of neurodegenerative dementias. However, it is controversial whether changes in connectivity reflect only the functional anatomy of disease, with selective vulnerability of brain networks, or the specific neurophysiological consequences of different neuropathologies within brain networks. We proposed that the oscillatory dynamics of cortical circuits reflect the tuning of local neural interactions, such that different pathologies are selective in their impact on the frequency spectrum of oscillations, whereas clinical syndromes reflect the anatomical distribution of pathology and physiological change. To test this hypothesis, we used magnetoencephalography from five patient groups, representing dissociated pathological subtypes and distributions across frontal, parietal and temporal lobes: amnestic Alzheimer's disease, posterior cortical atrophy, and three syndromes associated with frontotemporal lobar degeneration. We measured effective connectivity with graph theory-based measures of local efficiency, using partial directed coherence between sensors. As expected, each disease caused large-scale changes of neurophysiological brain networks, with reductions in local efficiency compared to controls. Critically however, the frequency range of altered connectivity was consistent across clinical syndromes that shared a likely underlying pathology, whilst the localization of changes differed between clinical syndromes. Multivariate pattern analysis of the frequency-specific topographies of local efficiency separated the disorders from each other and from controls (accuracy 62% to 100%, according to the groups' differences in likely pathology and clinical syndrome). The data indicate that magnetoencephalography has the potential to reveal specific changes in neurophysiology resulting from neurodegenerative disease. Our findings confirm that while clinical syndromes have characteristic anatomical patterns of abnormal connectivity that may be identified with other methods like structural brain imaging, the different mechanisms of neurodegeneration also cause characteristic spectral signatures of physiological coupling that are not accessible with structural imaging nor confounded by the neurovascular signalling of functional MRI. We suggest that these spectral characteristics of altered connectivity are the result of differential disruption of neuronal microstructure and synaptic physiology by Alzheimer's disease versus frontotemporal lobar degeneration.Peer reviewe

A physics-based earthquake simulator replicates seismic hazard statistics across California

Seismic hazard models are important for society, feeding into building codes and hazard mitigation efforts. These models, however, rest on many uncertain assumptions and are difficult to test observationally because of the long recurrence times of large earthquakes. Physics-based earthquake simulators offer a potentially helpful tool, but they face a vast range of fundamental scientific uncertainties. We compare a physics-based earthquake simulator against the latest seismic hazard model for California. Using only uniform parameters in the simulator, we find strikingly good agreement of the long-term shaking hazard compared with the California model. This ability to replicate statistically based seismic hazard estimates by a physics-based model cross-validates standard methods and provides a new alternative approach needing fewer inputs and assumptions for estimating hazard

Photon number resolution using a time-multiplexed single-photon detector

Photon number resolving detectors are needed for a variety of applications including linear-optics quantum computing. Here we describe the use of time-multiplexing techniques that allows ordinary single photon detectors, such as silicon avalanche photodiodes, to be used as photon number-resolving detectors. The ability of such a detector to correctly measure the number of photons for an incident number state is analyzed. The predicted results for an incident coherent state are found to be in good agreement with the results of a proof-of-principle experimental demonstration.Comment: REVTeX4, 6 pages, 8 eps figures, v2: minor changes, v3: changes in response to referee report, appendix added, 1 reference adde

Fas signaling induces raft coalescence that is blocked by cholesterol depletion in human RPE cells undergoing apoptosis

PURPOSE. To investigate whether the signaling events occurring in Fas-mediated apoptosis alter raft membrane formation in human RPE cells. METHODS. Formation of lipid rafts in cultured human retinal pigment epithelial cells (ARPE-19) was studied by confocal microscopy, with fluorescein-labeled cholera toxin subunit B binding protein (BODIPY)-labeled ganglioside GM1 lipid after Fas-L induction of apoptosis. Apoptosis was assessed by fluorescein-labeled annexin V detection of phosphatidylserine externalization and quadrant analysis with flow cytometry. Membrane rafts were localized into membrane vesicles by passing BODIPY-labeled GM1 RPE cells through a 2-m-pore polycarbonate membrane using an extruder device. The labeled fractions, containing vesicles enriched in GM1, were detected by flow cytometry and then analyzed for the presence of Fas protein. RESULTS. Differential punctate staining of membrane rafts was demonstrated in normal and FasL-induced apoptotic human ARPE-19 cells in culture by confocal microscopy, using cholera toxin B and GM1 labeling of extruded vesicles. The lipid raftassociated vesicles were derived by plasma membrane dissociation, via a newly developed whole-cell extrusion technique that produced 2-m vesicles with both GM1 lipid and Fas protein abundance enriched in a subpopulation of the membrane-derived vesicles. The amount of Fas protein in the vesicles containing raft domains markedly increased in FasL-treated cells. Treatment of human ARPE 19 cells with methyl ␤-cyclodextrin after FasL induction of apoptosis resulted in cellular cholesterol depletion and markedly reduced the incidence of Fas-receptor localization in GM1 rafts. CONCLUSIONS. Human ARPE-19 cells in culture contain membrane rafts with apoptotic signaling effectors uniformly distributed in the native state. The cells stimulated to undergo apoptosis appear to use membrane rafts in the death-signaling process by mobilization of rafts to localized regions of the membrane that are now enriched with apoptotic signaling effectors. Fas signaling induces apoptotic raft formation that results in polar condensation, or capping, of the rafts in the late stages of apoptosis. A novel extrusion technique is described that allows localization and enrichment of rafts into membrane vesicles, which can be assayed by flow cytometry. Cholesterol depletion, after Fas ligand activation of apoptosis, reduced raft formation in cells induced to undergo apoptosis. Therapeutic implications for the treatment of retinal disorders are discussed. (Invest Ophthalmol Vis Sci

Flux front penetration in disordered superconductors

We investigate flux front penetration in a disordered type II superconductor by molecular dynamics (MD) simulations of interacting vortices and find scaling laws for the front position and the density profile. The scaling can be understood performing a coarse graining of the system and writing a disordered non-linear diffusion equation. Integrating numerically the equation, we observe a crossover from flat to fractal front penetration as the system parameters are varied. The value of the fractal dimension indicates that the invasion process is described by gradient percolation.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Let