14,289 research outputs found
Some interactions among driver, vehicle, and roadway variables in normal driving
Effects of road and vehicle conditions, visual warning signs, direction of turns, night time, and skill on automobile driver performance are studied in several experiments. Considered criteria are variability in speed and acceleration
Solution to the problem of the poor cyclic fatigue resistance of bulk metallic glasses
The recent development of metallic glass-matrix composites represents a particular milestone in engineering materials for structural applications owing to their remarkable combination of strength and toughness. However, metallic glasses are highly susceptible to cyclic fatigue damage, and previous attempts to solve this problem have been largely disappointing. Here, we propose and demonstrate a microstructural design strategy to overcome this limitation by matching the microstructural length scales (of the second phase) to mechanical crack-length scales. Specifically, semisolid processing is used to optimize the volume fraction, morphology, and size of second-phase dendrites to confine any initial deformation (shear banding) to the glassy regions separating dendrite arms having length scales of ≈2 μm, i.e., to less than the critical crack size for failure. Confinement of the damage to such interdendritic regions results in enhancement of fatigue lifetimes and increases the fatigue limit by an order of magnitude, making these “designed” composites as resistant to fatigue damage as high-strength steels and aluminum alloys. These design strategies can be universally applied to any other metallic glass systems
The Dependence of Coronal Loop Heating on the Characteristics of Slow Photospheric Motions
The Parker hypothesis (Parker (1972)) assumes that heating of coronal loops
occurs due to reconnection, induced when photospheric motions braid field lines
to the point of current sheet formation. In this contribution we address the
question of how the nature of photospheric motions affects heating of braided
coronal loops. We design a series of boundary drivers and quantify their
properties in terms of complexity and helicity injection. We examine a series
of long-duration full resistive MHD simulations in which a simulated coronal
loop, consisting of initially uniform field lines, is subject to these
photospheric flows. Braiding of the loop is continually driven until
differences in behaviour induced by the drivers can be characterised. It is
shown that heating is crucially dependent on the nature of the photospheric
driver - coherent motions typically lead to fewer large energy release events,
while more complex motions result in more frequent but less energetic heating
events
Fracture toughness and crack-resistance curve behavior in metallic glass-matrix composites
Nonlinear-elastic fracture mechanics methods are used to assess the fracture toughness of bulk metallic glass (BMG) composites; results are compared with similar measurements for other monolithic and composite BMG alloys. Mechanistically, plastic shielding gives rise to characteristic resistance-curve behavior where the fracture resistance increases with crack extension. Specifically, confinement of damage by second-phase dendrites is shown to result in enhancement of the toughness by nearly an order of magnitude relative to unreinforced glass
Designing prevention programmes to reduce incidence of dementia: prospective cohort study of modifiable risk factors
Objective To estimate the percentage reduction in incidence of dementia that would be obtained if specific risk factors were eliminated
The effect of screening long-range Coulomb interactions on the metallic behavior in two-dimensional hole systems
We have developed a technique utilizing a double quantum well heterostructure
that allows us to study the effect of a nearby ground-plane on the metallic
behavior in a GaAs two-dimensional hole system (2DHS) in a single sample and
measurement cool-down, thereby maintaining a constant disorder potential. In
contrast to recent measurements of the effect of ground-plane screening of the
long-range Coulomb interaction in the insulating regime, we find surprisingly
little effect on the metallic behavior when we change the distance between the
2DHS and the nearby ground-plane.Comment: 5 pages, 4 figures, accepted for publication in PR
An Effective Membrane Model of the Immunological Synapse
The immunological synapse is a patterned collection of different types of
receptors and ligands that forms in the intercellular junction between T Cells
and antigen presenting cells (APCs) during recognition. The synapse is
implicated in information transfer between cells, and is characterized by
different spatial patterns of receptors at different stages in the life cycle
of T cells. We obtain a minimalist model that captures this experimentally
observed phenomenology. A functional RG analysis provides further insights.Comment: 6 pages, 3 figures, submitted for publicatio
Kondo Effect in a Quantum Antidot
We report Kondo-like behaviour in a quantum antidot (a submicron depleted
region in a two-dimensional electron gas) in the quantum-Hall regime. When both
spin branches of the lowest Landau level encircle the antidot in a magnetic
field ( T), extra resonances occur between extended edge states via
antidot bound states when tunnelling is Coulomb blockaded. These resonances
appear only in alternating Coulomb-blockaded regions, and become suppressed
when the temperature or source-drain bias is raised. Although the exact
mechanism is unknown, we believe that Kondo-like correlated tunnelling arises
from skyrmion-type edge reconstruction. This observation demonstrates the
generality of the Kondo phenomenon.Comment: 9 pages, 3 figures (Fig.3 in colour), to appear in Phys. Rev. Let
Experimental position-time entanglement with degenerate single photons
We report an experiment in which two-photon interference occurs between
degenerate single photons that never meet. The two photons travel in opposite
directions through our fibre-optic interferometer and interference occurs when
the photons reach two different, spatially separated, 2-by-2 couplers at the
same time. We show that this experiment is analogous to the conventional
Franson-type entanglement experiment where the photons are entangled in
position and time. We measure wavefunction overlaps for the two photons as high
as 94 3%.Comment: Updated to published version, new fig. 4., corrected typo
Quantum key distribution using a triggered quantum dot source emitting near 1.3 microns
We report the distribution of a cryptographic key, secure from photon number
splitting attacks, over 35 km of optical fiber using single photons from an
InAs quantum dot emitting ~1.3 microns in a pillar microcavity. Using below
GaAs-bandgap optical excitation, we demonstrate suppression of multiphoton
emission to 10% of the Poissonian level without detector dark count
subtraction. The source is incorporated into a phase encoded interferometric
scheme implementing the BB84 protocol for key distribution over standard
telecommunication optical fiber. We show a transmission distance advantage over
that possible with (length-optimized) uniform intensity weak coherent pulses at
1310 nm in the same system.Comment: 4 pages, 4 figure
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