7,084 research outputs found
Decreasing participation rates for old and young people in France
Today, working in the industrialized countries is mainly a matter of middle-aged people (25 to 54 year old). This is particularly true in France where the participation rate for the less than 25 year old people is the smallest one in OECD countries and that for men older than 54 one of the smallest. For the last thirty years, the participation rate of the youngest and oldest working people has been significantly decreasing, apart that of old women due to the increasing trending female participation rate. To illustrate the causes of these changes, we model from a descriptive point of view male and female participation rates for the following age classes: 15 to 19, 20 to 24, 55 to 59 and 60 to 64. Modelling old people participation rate allows us to illustrate the importance of political measures used over the last thirty years to deal with unemployment, in particular the development of early retirement programs and the decrease of the retirement age. Modelling young people participation rate does not give a leading part to a particular cause among the various ones we consider (development of apprenticeship, increasing number of students passing the baccalauréat, population structure, unemployment rate&). In both situations, we measure only weak, if any, response of participation rates to short-term unemployment rate changes.participation rate, unemployment, early retirement programs, apprenticeship, logistic trend
Fourfold oscillations and anomalous magnetic irreversibility of magnetoresistance in the non-metallic regime of Pr1.85Ce0.15CuO4
Using magnetoresistance measurements as a function of applied magnetic field
and its direction of application, we present sharp angular-dependent
magnetoresistance oscillations for the electron-doped cuprates in their
low-temperature non-metallic regime. The presence of irreversibility in the
magnetoresistance measurements and the related strong anisotropy of the field
dependence for different in-plane magnetic field orientations indicate that
magnetic domains play an important role for the determination of electronic
properties. These domains are likely related to the stripe phase reported
previously in hole-doped cuprates.Comment: 11 pages, 5 figure
Metal-to-Insulator Crossover in the Low-Temperature Normal State of Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta}
We measure the normal-state in-plane resistivity of La-doped Bi-2201 single
crystals at low temperatures by suppressing superconductivity with 60-T pulsed
magnetic fields. With decreasing hole doping, we observe a crossover from a
metallic to insulating behavior in the low-temperature normal state. This
crossover is estimated to occur near 1/8 doping, well inside the underdoped
regime, and not at optimum doping as reported for other cuprates. The
insulating regime is marked by a logarithmic temperature dependence of the
resistivity over two decades of temperature, suggesting that a peculiar charge
localization is common to the cuprates.Comment: 4 pages, 5 figures, accepted for publication in PR
Calculation of renormalized viscosity and resistivity in magnetohydrodynamic turbulence
A self-consistent renormalization (RG) scheme has been applied to nonhelical
magnetohydrodynamic turbulence with normalized cross helicity and
. Kolmogorov's 5/3 powerlaw is assumed in order to compute the
renormalized parameters. It has been shown that the RG fixed point is stable
for . The renormalized viscosity and resistivity
have been calculated, and they are found to be positive for all
parameter regimes. For and large Alfv\'{e}n ratio (ratio of
kinetic and magnetic energies) , and . As
is decreased, increases and decreases, untill where both and are approximately zero. For large ,
both and vary as . The renormalized parameters for
the case are also reported.Comment: 19 pages REVTEX, 3 ps files (Phys. Plasmas, v8, 3945, 2001
Spin-Charge Coupling in lightly doped NdCeCuO
We use neutron scattering to study the influence of a magnetic field on spin
structures of NdCuO. On cooling from room temperature, NdCuO
goes through a series of antiferromagnetic (AF) phase transitions with
different noncollinear spin structures. While a c-axis aligned magnetic field
does not alter the basic zero-field noncollinear spin structures, a field
parallel to the CuO plane can transform the noncollinear structure to a
collinear one ("spin-flop" transition), induce magnetic disorder along the
c-axis, and cause hysteresis in the AF phase transitions. By comparing these
results directly to the magnetoresistance (MR) measurements of
NdCeCuO, which has essentially the same AF structures
as NdCuO, we find that a magnetic-field-induced spin-flop transition,
AF phase hysteresis, and spin c-axis disorder all affect the transport
properties of the material. Our results thus provide direct evidence for the
existence of a strong spin-charge coupling in electron-doped copper oxides.Comment: 12 pages, 12 figure
Low-temperature phonon thermal conductivity of cuprate single crystals
The effect of sample size and surface roughness on the phonon thermal
conductivity of NdCuO single crystals was studied down to 50
mK. At 0.5 K, is proportional to , where is the
cross-sectional area of the sample. This demonstrates that is
dominated by boundary scattering below 0.5 K or so. However, the expected
dependence of is not observed down to 50 mK. Upon roughing the
surfaces, the dependence is restored, showing that departures from
are due to specular reflection of phonons off the mirror-like sample surfaces.
We propose an empirical power law fit, to (where
) in cuprate single crystals. Using this method, we show that
recent thermal conductivity studies of Zn doping in YBaCuO
re-affirm the universal heat conductivity of d-wave quasiparticles at .Comment: 4 pages, 4 figure
Inherent Inhomogeneities in Tunneling Spectra of BSCCO Crystals in the Superconducting State
Scanning Tunneling Spectroscopy on cleaved BSCCO(2212) single crystals reveal
inhomogeneities on length-scales of 30 . While most of the surface
yields spectra consistent with a d-wave superconductor, small regions show a
doubly gapped structure with both gaps lacking coherence peaks and the larger
gap having a size typical of the respective pseudo-gap for the same sample.Comment: 4 pages, 4 figure
Anomalous electronic structure and pseudogap effects in Nd_1.85Ce_0.15CuO_4
We report a high-resolution angle-resolved photoemission spectroscopic
(ARPES) study of the electron-doped (n-type) cuprate superconductor
Nd_1.85Ce_0.15CuO_4. We observe regions along the Fermi surface where the
near-E_F intensity is suppressed and the spectral features are broad in a
manner reminiscent of the high-energy ``pseudogap'' in the underdoped p-type
(hole doped) cuprates. However, instead of occurring near the (pi, 0) region,
as in the p-type materials, this pseudogap falls near the intersection of the
underlying Fermi surface with the antiferromagnetic Brillouin zone boundary.Comment: 5 pages, 3 figures, RevTex, submitted Phys. Rev. Lett. December 21,
200
Anomalous Thermal Diffusivity of Amorphous Semiconductor Superlattices
Since the development of amorphous semiconductor superlattice films, the great interesting in fundamental and technological is attracted by their special properties and applications. The optical and electronic properties of the films have been studied by conventional spectroscope, photoluminescence and photoconductance techniques etc. Some anomalous phenomena, such as, the quantum size effect and the permenent photoconductivity (PPC) effect, have been discovered [1–2]. Recently the investigations of the characteristics and parameters of amorphous semiconductor superlattice films by photoacoustic and photothermal techniques are being got attention [3,4]. In this paper, we describe the study of the thermal diffusivity of a series samples of amorphous semiconductor superlattices a-Si:H/a-SiNx:H. The thermal diffusivity of the samples is experimentally measured by using mirage detection technique [5,6]. Up to date, the mirage detection method has been used successfully to determine the thermal diffusivity of both transparent and opaque materials. Specially it is available to measure directly the thermal parameters of thin films which are usually difficalt to be, evaluated. In the theoretical calculation, one dimensional model with “ the thormal resistors in series “ and ” the weighted average ” is used. Comparing the experimental and theoretical results, we find that both are in good agreement for the most of the samples. However, some anomalous thermal diffusivity phenomena have been observed in some special samples
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