43,222 research outputs found
Straightening of a wavy strip: An elastic-plastic contact problem including snap-through
The nonlinear behavior of a wave like deformed metal strip during the levelling process were calculated. Elastic-plastic material behavior as well as nonlinearities due to large deformations were considered. The considered problem lead to a combined stability and contact problem. It is shown that, despite the initially concentrated loading, neglecting the change of loading conditions due to altered contact domains may lead to a significant error in the evaluation of the nonlinear behavior and particularly to an underestimation of the stability limit load. The stability was examined by considering the load deflection path and the behavior of a load-dependent current stiffness parameter in combination with the determinant of the current stiffness matrix
Radiant heat exchange in a space environment Scientific technical report, 1 Feb. - 31 Jul. 1970
Spectral and directional surface property effects on radiant heat transfer in space environmen
Radiant heat exchange in a space environment Scientific technical report, 1 Aug. 1969 - 31 Jan. 1970
Spectral surface property effects on radiant heat transfer in aerospace environmen
Characterization of the domain chaos convection state by the largest Lyapunov exponent
Using numerical integrations of the Boussinesq equations in rotating cylindrical domains with realistic boundary conditions, we have computed the value of the largest Lyapunov exponent lambda1 for a variety of aspect ratios and driving strengths. We study in particular the domain chaos state, which bifurcates supercritically from the conducting fluid state and involves extended propagating fronts as well as point defects. We compare our results with those from Egolf et al., [Nature 404, 733 (2000)], who suggested that the value of lambda1 for the spiral defect chaos state of a convecting fluid was determined primarily by bursts of instability arising from short-lived, spatially localized dislocation nucleation events. We also show that the quantity lambda1 is not intensive for aspect ratios Gamma over the range 20<Gamma<40 and that the scaling exponent of lambda1 near onset is consistent with the value predicted by the amplitude equation formalism
Radiant heat exchange in a space environment Scientific technical report, 1 Feb. - 31 Jul. 1969
Analytical methods development for predicting radiant heat transfer and temperature of engineering surfaces in space environmen
Dicke quantum spin glass of atoms and photons
Recent studies of strongly interacting atoms and photons in optical cavities
have rekindled interest in the Dicke model of atomic qubits coupled to discrete
photon cavity modes. We study the multimode Dicke model with variable
atom-photon couplings. We argue that a quantum spin glass phase can appear,
with a random linear combination of the cavity modes superradiant. We compute
atomic and photon spectral response functions across this quantum phase
transition, both of which should be accessible in experiment.Comment: 4 pages, 3 figures, v2: described quantum optics set-up in more
detail; extended discussion on photon correlation functions and experimental
signatures; added reference
Traveling waves in rotating Rayleigh-Bénard convection: Analysis of modes and mean flow
Numerical simulations of the Boussinesq equations with rotation for realistic no-slip boundary conditions and a finite annular domain are presented. These simulations reproduce traveling waves observed experimentally. Traveling waves are studied near threshhold by using the complex Ginzburg-Landau equation (CGLE): a mode analysis enables the CGLE coefficients to be determined. The CGLE coefficients are compared with previous experimental and theoretical results. Mean flows are also computed and found to be more significant as the Prandtl number decreases (from sigma=6.4 to sigma=1). In addition, the mean flow around the outer radius of the annulus appears to be correlated with the mean flow around the inner radius
A formal definition and a new security mechanism of physical unclonable functions
The characteristic novelty of what is generally meant by a "physical
unclonable function" (PUF) is precisely defined, in order to supply a firm
basis for security evaluations and the proposal of new security mechanisms. A
PUF is defined as a hardware device which implements a physical function with
an output value that changes with its argument. A PUF can be clonable, but a
secure PUF must be unclonable. This proposed meaning of a PUF is cleanly
delineated from the closely related concepts of "conventional unclonable
function", "physically obfuscated key", "random-number generator", "controlled
PUF" and "strong PUF". The structure of a systematic security evaluation of a
PUF enabled by the proposed formal definition is outlined. Practically all
current and novel physical (but not conventional) unclonable physical functions
are PUFs by our definition. Thereby the proposed definition captures the
existing intuition about what is a PUF and remains flexible enough to encompass
further research. In a second part we quantitatively characterize two classes
of PUF security mechanisms, the standard one, based on a minimum secret
read-out time, and a novel one, based on challenge-dependent erasure of stored
information. The new mechanism is shown to allow in principle the construction
of a "quantum-PUF", that is absolutely secure while not requiring the storage
of an exponentially large secret. The construction of a PUF that is
mathematically and physically unclonable in principle does not contradict the
laws of physics.Comment: 13 pages, 1 figure, Conference Proceedings MMB & DFT 2012,
Kaiserslautern, German
Towards Functional Flows for Hierarchical Models
The recursion relations of hierarchical models are studied and contrasted
with functional renormalisation group equations in corresponding
approximations. The formalisms are compared quantitatively for the Ising
universality class, where the spectrum of universal eigenvalues at criticality
is studied. A significant correlation amongst scaling exponents is pointed out
and analysed in view of an underlying optimisation. Functional flows are
provided which match with high accuracy all known scaling exponents from
Dyson's hierarchical model for discrete block-spin transformations.
Implications of the results are discussed.Comment: 17 pages, 4 figures; wording sharpened, typos removed, reference
added; to appear with PR
Four-point measurements of n- and p-type two-dimensional systems fabricated with cleaved-edge overgrowth
We demonstrate a contact design that allows four-terminal magnetotransport
measurements of cleaved-edge overgrown two-dimensional electron and hole
systems. By lithographically patterning and etching a bulk-doped surface layer,
finger-shaped leads are fabricated, which contact the two-dimensional systems
on the cleave facet. Both n- and p-type two-dimensional systems are
demonstrated at the cleaved edge, using Si as either donor or acceptor,
dependent on the growth conditions. Four-point measurements of both gated and
modulation-doped samples yield fractional quantum Hall features for both n- and
p-type, with several higher-order fractions evident in n-type modulation-doped
samples.Comment: 3 pages, 3 figure
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