1,460 research outputs found
Predicting the failure of ultrasonic spot welds by pull-out from sheet metal
AbstractA methodology for determining the cohesive fracture parameters associated with pull-out of spot welds is presented. Since failure of a spot weld by pull-out occurs by mixed-mode fracture of the base metal, the cohesive parameters for ductile fracture of an aluminum alloy were determined and then used to predict the failure of two very different spot-welded geometries. The fracture parameters (characteristic strength and toughness) associated with the shear and normal modes of ductile fracture in thin aluminum alloy coupons were determined by comparing experimental observations to numerical simulations in which a cohesive-fracture zone was embedded within a continuum representation of the sheet metal. These parameters were then used to predict the load–displacement curves for ultrasonically spot-welded joints in T-peel and lap-shear configurations. The predictions were in excellent agreement with the experimental data. The results of the present work indicate that cohesive-zone models may be very useful for design purposes, since both the strength and the energy absorbed by plastic deformation during weld pull-out can be predicted quite accurately
Corrigendum to “Rapid vacuum-driven monolayer assembly of microparticles on the surface of perforated microfluidic devices” [Powder Technology 390 (2021), 330–338] (Powder Technology (2021) 390 (330–338), (S0032591021004885), (10.1016/j.powtec.2021.05.079))
Properties of hyperkahler manifolds and their twistor spaces
We describe the relation between supersymmetric sigma-models on hyperkahler
manifolds, projective superspace, and twistor space. We review the essential
aspects and present a coherent picture with a number of new results.Comment: 26 pages. v2: Sign mistakes corrected; Kahler potential explicitly
calculated in example; references added. v3: Published version--several small
clarifications per referee's reques
A Photographic Composition Assistant for Intelligent Virtual 3D Camera Systems
Abstract. A human photographer can frame an image and enhance its composi-tion by visualizing how elements in the frame could be better sized or posi-tioned. The photographer resizes elements in the frame by changing the zoom lens or by varying his or her distance to the subject. The photographer moves elements by panning. An intelligent virtual photographer can apply a similar process. Given an initial 3D camera view, a user or application specifies high-level composition goals such as Rule of Thirds or balance. Each objective de-fines either a One-D interval for image scaling or a Two-D interval for transla-tion. Two-D projections of objects are translated and scaled in the frame ac-cording to computed optima. These Two-D scales and translates are mapped to matching changes in the 3D field of view (zoom), dolly-in or out varying sub-ject distance, and rotating the aim direction to improve the composition.
D-brane Solitons in Supersymmetric Sigma-Models
Massive D=4 N=2 supersymmetric sigma models typically admit domain wall
(Q-kink) solutions and string (Q-lump) solutions, both preserving 1/2
supersymmetry. We exhibit a new static 1/4 supersymmetric `kink-lump' solution
in which a string ends on a wall, and show that it has an effective realization
as a BIon of the D=4 super DBI-action. It is also shown to have a
time-dependent Q-kink-lump generalization which reduces to the Q-lump in a
limit corresponding to infinite BI magnetic field. All these 1/4 supersymmetric
sigma-model solitons are shown to be realized in M-theory as calibrated, or
`Q-calibrated', M5-branes in an M-monopole background.Comment: 16 pages, 3 figures, Late
Nonstationary Stochastic Resonance in a Single Neuron-Like System
Stochastic resonance holds much promise for the detection of weak signals in
the presence of relatively loud noise. Following the discovery of nondynamical
and of aperiodic stochastic resonance, it was recently shown that the
phenomenon can manifest itself even in the presence of nonstationary signals.
This was found in a composite system of differentiated trigger mechanisms
mounted in parallel, which suggests that it could be realized in some
elementary neural networks or nonlinear electronic circuits. Here, we find that
even an individual trigger system may be able to detect weak nonstationary
signals using stochastic resonance. The very simple modification to the trigger
mechanism that makes this possible is reminiscent of some aspects of actual
neuron physics. Stochastic resonance may thus become relevant to more types of
biological or electronic systems injected with an ever broader class of
realistic signals.Comment: Plain Latex, 7 figure
Twistors and Black Holes
Motivated by black hole physics in N=2, D=4 supergravity, we study the
geometry of quaternionic-Kahler manifolds M obtained by the c-map construction
from projective special Kahler manifolds M_s. Improving on earlier treatments,
we compute the Kahler potentials on the twistor space Z and Swann space S in
the complex coordinates adapted to the Heisenberg symmetries. The results bear
a simple relation to the Hesse potential \Sigma of the special Kahler manifold
M_s, and hence to the Bekenstein-Hawking entropy for BPS black holes. We
explicitly construct the ``covariant c-map'' and the ``twistor map'', which
relate real coordinates on M x CP^1 (resp. M x R^4/Z_2) to complex coordinates
on Z (resp. S). As applications, we solve for the general BPS geodesic motion
on M, and provide explicit integral formulae for the quaternionic Penrose
transform relating elements of H^1(Z,O(-k)) to massless fields on M annihilated
by first or second order differential operators. Finally, we compute the exact
radial wave function (in the supergravity approximation) for BPS black holes
with fixed electric and magnetic charges.Comment: 47 pages, v2: typos corrected, reference added, v3: minor change
Comparison of dust related respiratory effects in Dutch and Canadian grain handling industries: a pooled analysis.
Out-of-equilibrium singlet-triplet Kondo effect in a single C_60 quantum dot
We have used an electromigration technique to fabricate a
single-molecule transistor (SMT). Besides describing our electromigration
procedure, we focus and present an experimental study of a single molecule
quantum dot containing an even number of electrons, revealing, for two
different samples, a clear out-of-equilibrium Kondo effect. Low temperature
magneto-transport studies are provided, which demonstrates a Zeeman splitting
of the finite bias anomaly.Comment: 6 pages, 4 figure
Emission spectra and intrinsic optical bistability in a two-level medium
Scattering of resonant radiation in a dense two-level medium is studied
theoretically with account for local field effects and renormalization of the
resonance frequency. Intrinsic optical bistability is viewed as switching
between different spectral patterns of fluorescent light controlled by the
incident field strength. Response spectra are calculated analytically for the
entire hysteresis loop of atomic excitation. The equations to describe the
non-linear interaction of an atomic ensemble with light are derived from the
Bogolubov-Born-Green-Kirkwood-Yvon hierarchy for reduced single particle
density matrices of atoms and quantized field modes and their correlation
operators. The spectral power of scattered light with separated coherent and
incoherent constituents is obtained straightforwardly within the hierarchy. The
formula obtained for emission spectra can be used to distinguish between
possible mechanisms suggested to produce intrinsic bistability.Comment: 18 pages, 5 figure
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