5,971 research outputs found
Internal versus External Labour Flexibility : The Role of Knowledge Codification.
This article uses a competence-based approach to the firm in order to analyse the recent destabilisation of internal labour markets. We argue that increasing knowledge codification made possible by the diffusion of information and communication technologies has made competences less dependent upon individuals. Knowledge has been increasingly embodied in firms themselves which has played an important role in lowering the relative cost of human resource management strategies based on external labour flexibility. As a consequence, recourse to external labour markets has developed, which may harm firms' innovative capabilities in the long run.Competences; knowledge codification; information technologies; internal labour markets;
Replacing Leads by Self-Energies Using Nonequilibrium Green's Functions
An open quantum system consists of leads connected to a device of interest.
Within the nonequilibrium Green's function technique, we examine the
replacement of leads by self-energies in continuum calculations. Our starting
point is a formulation of the problem for continuum systems by T.E. Feuchtwang.
In this approach there is considerable flexibility in the choice of unperturbed
Green's functions. We examine the consequences of this freedom on the treatment
of leads. For any choice the leads can be replaced by coupling self-energies
which are simple functions of energy. We find that the retarded self-energy
depends on the details of the choice of unperturbed Green's function, and can
take any value. However, the nonequilibrum self-energy or scattering function
can be taken to be independent of this choice. Expressed in terms of these
self-energies, nonequilibrium transport calculations take a particularly simple
form.Comment: 14 pages, 0 figure
Plastic Response of a 2D Amorphous Solid to Quasi-Static Shear : II - Dynamical Noise and Avalanches in a Mean Field Model
We build a minimal, mean-field, model of plasticity of amorphous solids,
based upon a phenomenology of dissipative events derived, in a preceding paper
[A. Lemaitre, C. Caroli, arXiv:0705.0823] from extensive molecular simulations.
It reduces to the dynamics of an ensemble of identical shear transformation
zones interacting via the dynamic noise due to the long ranged elastic fields
induced by zone flips themselves. We find that these ingredients are sufficient
to generate flip avalanches with a power-law scaling with system size,
analogous to that observed in molecular simulations. We further show that the
scaling properties of avalanches sensitively depend on the detailed shape of
the noise spectrum. This points out the importance of developing a realistic
coarse-grained description of elasticity in these systems
Rate-Dependent Avalanche Size in Athermally Sheared Amorphous Solids
We perform an extensive numerical study of avalanche behavior in a 2D LJ
glass at T=0, sheared at finite strain rates . From the finite size
analysis of stress fluctuations and of transverse diffusion we show that
flip-flip correlations remain relevant at all realistic strain rates. We
predict that the avalanche size scales as , with the
space dimension
Towards a Microscopic Theory for Metallic Heavy-Fermion Point Contacts
The bias-dependent resistance R(V) of NS-junctions is calculated using the
Keldysh formalism in all orders of the transfer matrix element. We present a
compact and simple formula for the Andreev current, that results from the
coupling of electrons and holes on the normal side via the anomalous Green's
function on the superconducting side. Using simple BCS Nambu-Green's functions
the well known Blonder-Tinkam-Klapwijk theory can be recovered. Incorporating
the energy-dependent quasi-particle lifetime of the heavy fermions strongly
reduces the Andreev-reflection signal.Comment: 3 pages, TeX type, 1 eps figure include, SCES96 Z\"uric
Ultrafast spherulitic crystal growth as a stress-induced phenomenon specific of fragile glass-formers
We propose a model for the abrupt emergence, below temperatures close to the
glass transition, of the ultra-fast (GC) steady mode of spherulitic crystal
growth in deeply undercooled liquids. We interpret this phenomenon as
controlled by the interplay between the generation of stresses by
crystallization and their partial release by flow in the surrounding amorphous
visco-elastic matrix. Our model is consistent with both the observed ratios
() of fast-to-slow velocities and the fact that fast growth emerges
close to the glass transition. It leads us to conclude that the existence of a
fast growth regime requires both (i) a high fragility of the glassformer; (ii)
the fine sub-structure specific of spherulites. It finally predicts that the
transition is hysteretic, thus allowing for an independent experimental test
Self-healing slip pulses and the friction of gelatin gels
We present an extensive experimental study and scaling analysis of friction
of gelatin gels on glass. At low driving velocities, sliding occurs via
propagation of periodic self-healing slip pulses whose velocity is limited by
collective diffusion of the gel network. Healing can be attributed to a
frictional instability occurring at the slip velocity . For ,
sliding is homogeneous and friction is ruled by the shear-thinning rheology of
an interfacial layer of thickness of order the (nanometric) mesh size,
containing a semi-dilute solution of polymer chain ends hanging from the
network. Inspite of its high degree of confinement, the rheology of this system
does not differ qualitatively from known bulk ones. The observed ageing of the
static friction threshold reveals the slow increase of adhesive bonding between
chain ends and glass. Such structural ageing is compatible with the existence
of a velocity-weakening regime at velocities smaller than , hence with the
existence of the healing instability.Comment: 9 pages, 16 figure
Rheological aging and rejuvenation in solid friction contacts
We study the low-velocity (0.1--100 m.s) frictional properties of
interfaces between a rough glassy polymers and smooth silanized glass, a
configuration which gives direct access to the rheology of the adhesive joints
in which shear localizes. We show that these joints exhibit the full
phenomenology expected for confined quasi 2D soft glasses: they strengthen
logarithmically when aging at rest, and weaken (rejuvenate) when sliding.
Rejuvenation is found to saturate at large velocities. Moreover, aging at rest
is shown to be strongly accelerated when waiting under finite stress below the
static threshold
Innovative Work Practices, Information Technologies, and Working Conditions : Evidence for France.
We investigate the impact of new work practices and information and communication technologies (ICT) on working conditions in France. We use a unique French dataset providing information on individual workers for the year 1998. New work practices include the use of quality norms, job rotation, collective discussions on work organization, and work time flexibility. Working conditions are captured by occupational injuries as well as indicators of mental strain. We find that individuals working under the new practices face greater mental strain than individuals who do not. They also face a higher probability of work injuries, at least for benign ones. In contrast, our results suggest that ICT contribute to make the workplace more cooperative and to reduce occupational risks and injuries.New work practices; technology; working conditions; occupational injuries; Working Conditions;
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