468 research outputs found
Causes of the 1980s Slump in Europe
macroeconomics, slump, unemployment, Europe, EEC, macroeconomic theory
Roots of the Recent Recoveries: Labor Reforms or Private Sector Forces?.
It is widely agreed that the natural unemployment rate recovered strongly in several OECD economies in the 1990s while not yet in the others. This paper draws on models by the authors endogenizing the path of the natural rate in order to trace the causes and apportion the credit. The results suggest that the five structural reforms of the labor market urged by the OECD Secretariat were effective and account for some of the recovery where adopted. However, the paper sees most of the recoveries as largely the emergence from structural slump to a structural boom--a boom brought by revived investment in employees, customers and fixed capital. Behind this revival is a recovery of business-asset valuations resulting from improved expectations for productivity growth and, judging by the stock market, hopes for a future lift in business earnings that exceeds extrapolations of the past--both driven by the "new economy."
The Search for Supernova-produced Radionuclides in Terrestrial Deep-sea Archives
An enhanced concentration of 60Fe was found in a deep ocean's crust in 2004
in a layer corresponding to an age of ~2 Myr. The confirmation of this signal
in terrestrial archives as supernova-induced and detection of other
supernova-produced radionuclides is of great interest. We have identified two
suitable marine sediment cores from the South Australian Basin and estimated
the intensity of a possible signal of the supernova-produced radionuclides
26Al, 53Mn, 60Fe and the pure r-process element 244Pu in these cores. A finding
of these radionuclides in a sediment core might allow to improve the time
resolution of the signal and thus to link the signal to a supernova event in
the solar vicinity ~2 Myr ago. Furthermore, it gives an insight on
nucleosynthesis scenarios in massive stars, the condensation into dust grains
and transport mechanisms from the supernova shell into the solar system
Search for supernova-produced 60Fe in a marine sediment
An 60Fe peak in a deep-sea FeMn crust has been interpreted as due to the
signature left by the ejecta of a supernova explosion close to the solar system
2.8 +/- 0.4 Myr ago [Knie et al., Phys. Rev. Lett. 93, 171103 (2004)]. To
confirm this interpretation with better time resolution and obtain a more
direct flux estimate, we measured 60Fe concentrations along a dated marine
sediment. We find no 60Fe peak at the expected level from 1.7 to 3.2 Myr ago.
However, applying the same chemistry used for the sediment, we confirm the 60Fe
signal in the FeMn crust. The cause of the discrepancy is discussed.Comment: 15 pages, 5 figures, submitted to PR
Discovery Prospects for a Supernova Signature of Biogenic Origin
Approximately 2.8 Myr before the present our planet was subjected to the
debris of a supernova explosion. The terrestrial proxy for this event was the
discovery of live atoms of 60Fe in a deep-sea ferromanganese crust. The
signature for this supernova event should also reside in magnetite Fe3O4
microfossils produced by magnetotactic bacteria extant at the time of the
Earth-supernova interaction, provided the bacteria preferentially uptake iron
from fine-grained iron oxides and ferric hydroxides. Using estimates for the
terrestrial supernova 60Fe flux, combined with our empirically derived
microfossil concentrations in a deep-sea drill core, we deduce a conservative
estimate of the ^{60}{Fe} fraction as 60Fe/Fe ~ 3.6 x 10^{-15}. This value sits
comfortably within the sensitivity limit of present accelerator mass
spectrometry capabilities. The implication is that a biogenic signature of this
cosmic event is detectable in the Earth's fossil record.Comment: As it appears in Icaru
Geophysical and geochemical constraints on geoneutrino fluxes from Earth's mantle
Knowledge of the amount and distribution of radiogenic heating in the mantle
is crucial for understanding the dynamics of the Earth, including its thermal
evolution, the style and planform of mantle convection, and the energetics of
the core. Although the flux of heat from the surface of the planet is robustly
estimated, the contributions of radiogenic heating and secular cooling remain
poorly defined. Constraining the amount of heat-producing elements in the Earth
will provide clues to understanding nebula condensation and planetary formation
processes in early Solar System. Mantle radioactivity supplies power for mantle
convection and plate tectonics, but estimates of mantle radiogenic heat
production vary by a factor of more than 20. Recent experimental results
demonstrate the potential for direct assessment of mantle radioactivity through
observations of geoneutrinos, which are emitted by naturally occurring
radionuclides. Predictions of the geoneutrino signal from the mantle exist for
several established estimates of mantle composition. Here we present novel
analyses, illustrating surface variations of the mantle geoneutrino signal for
models of the deep mantle structure, including those based on seismic
tomography. These variations have measurable differences for some models,
allowing new and meaningful constraints on the dynamics of the planet. An ocean
based geoneutrino detector deployed at several strategic locations will be able
to discriminate between competing compositional models of the bulk silicate
Earth.Comment: 34 pages, 6 tables, 5 figures, 2 supplementary figures; revised
version submitted to Earth Planet. Sci. Let
Beyond the Short Term A Study of Past Productivityâs Trends and an Evaluation of Future Ones
This is the second report to be issued by a group of international economists brought together under the auspices of LUISS. LIGEP stands for LUISS International Group on Economic Policy. Its mandate was to consider problems of economic policy in the aftermath of the Global Crisis in the World, Europe and Italy
Effect of a Post-Fatigue Damage on the Residual Dynamic Behavior of Advanced-SMC Composites
The purpose of this article is to investigate the effect of an initial pre-damage induced by a fatigue loading on the tensile dynamic behavior of Advanced Sheet Molding Compounds (A-SMC). Tension-tension fatigue preloading at a frequency of 30 Hz is performed at various applied stress levels prior to subject the A-SMC specimens to tensile tests at different strain rates, namely: 10 â3 s â1 (quasi-static), 1 s â1 and 60 s â1 . The developed experimental approach provided significant findings in terms of residual behavior and damage accumulation in relation to the applied pre-fatigue loading conditions. Indeed, it has been shown that the overall quasi-static and the dynamic responses are strongly affected by the level of fatigue number of cycles reached prior to applying the high strain loading. The effect of fatigue pre-damage is found also strongly strain-rate dependent. Experimental results showed that the damage threshold in terms of stress and strain increased with strain rate. However, for a given strain-rate the damage stress threshold depends on the number of cycles applied during the fatigue preloading
Sheet Molding Compound Automotive Component Reliability Using a Micromechanical Damage Approach
The mastering of product reliability is essential for industrial competitiveness. If for metallic materials the topic is well-known, especially in automotive industry, Original Equipment Manufacturers are expecting strong support of their suppliers to full-fill the lack data. This paper presents a new original approach, using a micromechanical based on damage model to address the problem of reliability of Sheet Molding Compound (SMC) components. The first part demonstrates the inadequacy of the standard method of reliability on SMC material through its application on the new Peugeot 3008. In fact, the very flat S-N curve of SMC, and in general, composite materials is not appropriate for acceleration effect. The proposed model correlates the stress, damage and strength with both cycle number and slamming velocity. It emphasizes the relation between the effective distribution with the slamming velocity effect. Then, a new reliability approach based on a micromechanical fatigue/damage model was developed. The definition of new probability distributions based on damage was necessary to apply properly the stress-resistance approach. It allows taking into account the velocity effect by switching in damage space. Finally, applying this new methodology on the Peugeot 3008, leads to the definition of the optimal validation laboratory tests to ensure the reliability. Indeed, the required number of cycles to ensure reliability has been reduced significantly. Micromechanical damage reliability approach could be an efficient way to ensure the reliability of short fiber reinforcement composite components used in industrial context.Authors address a strong acknowledgment to E. FEIGE and Y. HAMOY, from PSA, for the data provided. Their comments and advices were also very useful.We are grateful to Mr. OZOUF for teaching and advices on the general topic of reliability
Fast fatigue life prediction of short fiber reinforced composites using a new hybrid damage approach: Application to SMC
Industrial design of Short Fiber Reinforced Composites (SFRC) structures is subject to several compounding and processing steps of optimization. Moreover, these structures are often submitted to fatigue loading. Therefore, SN curves have to be established for each new composite formulation and for several type of microstructure involved in the real component due to processing. While these preliminary characterizations are time and money consuming, this paper propose a new hybrid methodology for fast fatigue life prediction. Moreover, both monotonic and fatigue behavior of SMC composites is essentially determined by local damage propagation. Therefore, the key idea of the proposed approach is to use a Mori and Tanaka based micromechanical model in order to establish an equation of state relating local damage rate to macroscopic residual stiffness rate. The generalization of this relation to fatigue damage multi-scale description leads to the SN curve fast determination of each considered microstructure. Very limited experimental characterization is required in such a way that SN curve could be established in just one day. Comparison between experimental and simulated Whöler curves highlights a very good agreement for several microstructure configurations in the case of a SMC composite material
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