5,961 research outputs found
Singular inextensible limit in the vibrations of post-buckled rods: Analytical derivation and role of boundary conditions
In-plane vibrations of an elastic rod clamped at both extremities are studied. The rod is modeled as an extensible planar Kirchhoff elastic rod under large displacements and rotations. Equilibrium configurations and vibrations around these configurations are computed analytically in the incipient post-buckling regime. Of particular interest is the variation of the first mode frequency as the load is increased through the buckling threshold. The loading type is found to have a crucial importance as the first mode frequency is shown to behave singularly in the zero thickness limit in the case of prescribed axial displacement, whereas a regular behavior is found in the case of prescribed axial load.This publication is based in part upon work supported by Award no. KUK-C1-013-04, made by King Abdullah University of Science and Technology (KAUST) (A.G.). A.G. is a Wolfson/Royal Society Merit Award holder. Support from the Royal Society, through the International Exchanges Scheme (Grant IE120203), is also acknowledge
Daytime is money
Based on real-time trade data from the Swiss franc overnight interbank repo market and SIX Interbank Clearing (SIC) - the Swiss real-time gross settlement (RTGS) system - we are able to gain valuable insights on the daytime value of money and its determinants: First, an implicit hourly interbank interest rate can be derived from the intraday term structure of the overnight rate. We thereby provide evidence that an implicit intraday money market exists. Second, we show that after the introduction of the foreign exchange settlement system CLS the value of intraday liquidity has increased during the hours of the CLS settlement cycle. Third, the turnover as well as the liquidity in SIC influence the intraday rate correspondingly. These facts provide evidence for the cost of immediacy. Features like RTGS, delivery-versus-payment and payment-versus-payment substitute credit risk with liquidity risk which in turn increases the value of intraday liquidity. The analysis is central bank policy relevant insofar as different designs of intraday liquidity facilities and different collateral policies result in different intraday term structures for the overnight money market.interbank money market, intraday credit, term structure
The yielding dynamics of a colloidal gel
Attractive colloidal gels display a solid-to-fluid transition as shear
stresses above the yield stress are applied. This shear-induced transition is
involved in virtually any application of colloidal gels. It is also crucial for
controlling material properties. Still, in spite of its ubiquity, the yielding
transition is far from understood, mainly because rheological measurements are
spatially averaged over the whole sample. Here, the instrumentation of creep
and oscillatory shear experiments with high-frequency ultrasound opens new
routes to observing the local dynamics of opaque attractive colloidal gels. The
transition proceeds from the cell walls and heterogeneously fluidizes the whole
sample with a characteristic time whose variations with applied stress suggest
the existence of an energy barrier linked to the gelation process. The present
results provide new test grounds for computer simulations and theoretical
calculations in the attempt to better understand the yielding transition. The
versatility of the technique should also allow extensive mesoscopic studies of
rupture mechanisms in soft solids ranging from crystals to glassy materials.Comment: 8 pages, 5 figure
Quantum-like models cannot account for the conjunction fallacy
Human agents happen to judge that a conjunction of two terms is more probable than one of the terms, in contradiction with the rules of classical probabilities—this is the conjunction fallacy. One of the most discussed accounts of this fallacy is currently the quantum-like explanation, which relies on models exploiting the mathematics of quantum mechanics. The aim of this paper is to investigate the empirical adequacy of major quantum-like models which represent beliefs with quantum states. We first argue that they can be tested in three different ways, in a question order effect configuration which is different from the traditional conjunction fallacy experiment. We then carry out our proposed experiment, with varied methodologies from experimental economics. The experimental results we get are at odds with the predictions of the quantum-like models. This strongly suggests that this quantum-like account of the conjunction fallacy fails. Future possible research paths are discussed
Vote Trading With and Without Party Leaders
Two groups of voters of known sizes disagree over a single binary decision to be taken by simple majority. Individuals have different, privately observed intensities of preferences and before voting can buy or sell votes among themselves for money. We study the implication of such trading for outcomes and welfare when trades are coordinated by the two group leaders and when they take place anonymously in a competitive market. The theory has strong predictions. In both cases, trading falls short of full efficiency, but for opposite reasons: with group leaders, the minority wins too rarely; with market trades, the minority wins too often. As a result, with group leaders, vote trading improves over no-trade; with market trades, vote trading can be welfare reducing. All predictions are strongly supported by experimental results.
Shear-induced fragmentation of Laponite suspensions
Simultaneous rheological and velocity profile measurements are performed in a
smooth Couette geometry on Laponite suspensions seeded with glass microspheres
and undergoing the shear-induced solid-to-fluid (or yielding) transition. Under
these slippery boundary conditions, a rich temporal behaviour is uncovered, in
which shear localization is observed at short times, that rapidly gives way to
a highly heterogeneous flow characterized by intermittent switching from
plug-like flow to linear velocity profiles. Such a temporal behaviour is linked
to the fragmentation of the initially solid sample into blocks separated by
fluidized regions. These solid pieces get progressively eroded over time scales
ranging from a few minutes to several hours depending on the applied shear rate
. The steady-state is characterized by a homogeneous flow with
almost negligible wall slip. The characteristic time scale for erosion is shown
to diverge below some critical shear rate and to scale as
with above
. A tentative model for erosion is discussed together with
open questions raised by the present results.Comment: 19 pages, 13 figures, submitted to Soft Matte
Local Oscillatory Rheology from Echography
Local Oscillatory Rheology from Echography (LORE) consists in a traditional
rheology experiment synchronized with high-frequency ultrasonic imaging which
gives access to the local material response to oscillatory shear. Besides
classical global rheological quantities, this method provides quantitative
time-resolved information on the local displacement across the entire gap of
the rheometer. From the local displacement response, we compute and decompose
the local strain in its Fourier components and measure the spatially-resolved
viscoelastic moduli. After benchmarking our method on homogeneous Newtonian
fluids and soft solids, we demonstrate that this technique is well suited to
characterize spatially heterogeneous samples, wall slip, and the emergence of
nonlinearity under large amplitude oscillatory stress in soft materials.Comment: 10 pages, 5 figures, submitted to Phys. Rev. Applie
Real-Time Nearfield Acoustic Holography: Implementation of the Direct and Inverse Impulse Responses in the Time-Wavenumber Domain
The aim of the study is to demonstrate that some methods are more relevant
for implementing the Real-Time Nearfield Acoustic Holography than others. First
by focusing on the forward propagation problem, different approaches are
compared to build the impulse response to be used. One of them in particular is
computed by an inverse Fourier transform applied to the theoretical transfer
function for propagation in the frequency-wavenumber domain. Others are
obtained by directly sampling an analytical impulse response in the
time-wavenumber domain or by additional low-pass filtering. To estimate the
performance of each impulse response, a simulation test involving several
monopoles excited by non stationary signals is presented and some features are
proposed to assess the accuracy of the temporal signals resulting from
reconstruction processing on a forward plane. Then several inverse impulse
responses used to solve the inverse problem, which consists in back propagating
the acoustic signals acquired by the microphone array, are built directly from
a transfer function or by using Wiener inverse filtering from the direct
impulse responses obtained for the direct problem. Another simulation test is
performed to compare the signals reconstructed on the source plane. The same
indicators as for the propagation study are used to highlight the differences
between the methods tested for solving the Holography inverse problem.Comment: 15 th International Congress on Sound and Vibration, Daejeon :
Cor\'ee, R\'epublique de (2008
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