17,419 research outputs found
The business firm: the bureaucracy and the clan
This paper establishes a parallel between Max Weber's bureaucratic and traditional forms of domination, on the one hand, and the distinction between Western and Japanese management, on the other. Just as bureaucracy, so Western management theory and practice have been fundamentally guided by Zweckrationalität, often called instrumental rationality; and just as the traditional organization, so Japanese management is quickened by the kinship spirit. The parallel ceases, however, where this paper maintains that the traditional (kinship) organization is both rational and modern, or 'modernizable', without having to mutate into Weber's impersonal bureaucracy. Weber's instrumental-rationalism reduced the ideal-type of the traditional organization to a residual, counter-concept of the bureaucracy and the bureaucracy, in its turn, to a dehumanized 'thing'. In the current scene, despite clear and express efforts at overcoming the admitted inadequacies of the bureaucratic mind-set, Western management theory and practice seem unable to escape the grip of instrumental rationality. Even though the efforts at moving away from the bureaucracy are efforts at being more 'traditional', the debunking language against the 'traditional' continues. There is a need to supplement the critique of instrumental rationality that is currently taking place in some quarters with a positive reconstruction of the traditional (kinship) organization. The two-pronged approach may open up more management and organization alternatives on the micro-level of the modem business firm which is the immediate concern of this paper. Th.ere are signs that the need is beginning to be felt and, more importantly, to be addressed. --
The non-zero energy of 2+1 Minkowski space
We compute the energy of 2+1 Minkowski space from a covariant action
principle. Using Ashtekar and Varadarajan's characterization of 2+1 asymptotic
flatness, we first show that the 2+1 Einstein-Hilbert action with
Gibbons-Hawking boundary term is both finite on-shell (apart from past and
future boundary terms) and stationary about solutions under arbitrary smooth
asymptotically flat variations of the metric. Thus, this action provides a
valid variational principle and no further boundary terms are required. We then
obtain the gravitational Hamiltonian by direct computation from this action.
The result agrees with the Hamiltonian of Ashtekar and Varadarajan up to an
overall addititve constant. This constant is such that 2+1 Minkowski space is
assigned the energy E = -1/4G, while the upper bound on the energy is set to
zero. Any variational principle with a boundary term built only from the
extrinsic and intrinsic curvatures of the boundary is shown to lead to the same
result. Interestingly, our result is not the flat-space limit of the
corresponding energy -1/8G of 2+1 anti-de Sitter space.Comment: 16 pages, minor change
Directed transport of active particles over asymmetric energy barriers
We theoretically and numerically investigate the transport of active colloids
to target regions, delimited by asymmetric energy barriers. We show that it is
possible to introduce a generalized effective temperature that is related to
the local variance of particle velocities. The stationary probability
distributions can be derived from a simple diffusion equation in the presence
of an inhomogeneous effective temperature resulting from the action of external
force fields. In particular, transitions rates over asymmetric energy barriers
can be unbalanced by having different effective temperatures over the two
slopes of the barrier. By varying the type of active noise, we find that equal
values of diffusivity and persistence time may produce strongly varied
effective temperatures and thus stationary distributions
Correlation of inflation-produced magnetic fields with scalar fluctuations
If the conformal invariance of electromagnetism is broken during inflation,
then primordial magnetic fields may be produced. If this symmetry breaking is
generated by the coupling between electromagnetism and a scalar field---e.g.
the inflaton, curvaton, or the Ricci scalar---then these magnetic fields may be
correlated with primordial density perturbations, opening a new window to the
study of non-gaussianity in cosmology. In order to illustrate, we couple
electromagnetism to an auxiliary scalar field in a de Sitter background. We
calculate the power spectra for scalar-field perturbations and magnetic fields,
showing how a scale-free magnetic field spectrum with rms amplitude of ~nG at
Mpc scales may be achieved. We explore the Fourier-space dependence of the
cross-correlation between the scalar field and magnetic fields, showing that
the dimensionless amplitude, measured in units of the power spectra, can grow
as large as ~500 H_I/M, where H_I is the inflationary Hubble constant and M is
the effective mass scale of the coupling.Comment: 11 pages, 3 pdf figure
Aging under Shear: Structural Relaxation of a Non-Newtonian Fluid
The influence of an applied shear field on the dynamics of an aging colloidal
suspension has been investigated by the dynamic light scattering determination
of the density autocorrelation function. Though a stationary state is never
observed, the slow dynamics crosses between two different non-equilibrium
regimes as soon as the structural relaxation time approaches the inverse shear
rate. In the shear dominated regime (at high shear rate values) the structural
relaxation time is found to be strongly sensitive to shear rate while aging
proceeds at a very slow rate. The effect of shear on the detailed shape of the
density autocorrelation function is quantitatively described assuming that the
structural relaxation process arises from the heterogeneous superposition of
many relaxing units each one independently coupled to shear with a parallel
composition rule for timescales.Comment: 5 pages, 5 figure
Run-and-tumble particles in speckle fields
The random energy landscapes developed by speckle fields can be used to
confine and manipulate a large number of micro-particles with a single laser
beam. By means of molecular dynamics simulations, we investigate the static and
dynamic properties of an active suspension of swimming bacteria embedded into
speckle patterns. Looking at the correlation of the density fluctuations and
the equilibrium density profiles, we observe a crossover phenomenon when the
forces exerted by the speckles are equal to the bacteria's propulsion
Effective run-and-tumble dynamics of bacteria baths
{\it E. coli} bacteria swim in straight runs interrupted by sudden
reorientation events called tumbles. The resulting random walks give rise to
density fluctuations that can be derived analytically in the limit of non
interacting particles or equivalently of very low concentrations. However, in
situations of practical interest, the concentration of bacteria is always large
enough to make interactions an important factor. Using molecular dynamics
simulations, we study the dynamic structure factor of a model bacterial bath
for increasing values of densities. We show that it is possible to reproduce
the dynamics of density fluctuations in the system using a free run-and-tumble
model with effective fitting parameters. We discuss the dependence of these
parameters, e.g., the tumbling rate, tumbling time and self-propulsion
velocity, on the density of the bath
Colloidal attraction induced by a temperature gradient
Colloidal crystals are of extreme importance for applied research, such as
photonic crystals technology, and for fundamental studies in statistical
mechanics. Long range attractive interactions, such as capillary forces, can
drive the spontaneous assembly of such mesoscopic ordered structures. However
long range attractive forces are very rare in the colloidal realm. Here we
report a novel strong and long ranged attraction induced by a thermal gradient
in the presence of a wall. Switching on and off the thermal gradient we can
rapidly and reversibly form stable hexagonal 2D crystals. We show that the
observed attraction is hydrodynamic in nature and arises from thermal induced
slip flow on particle surfaces. We used optical tweezers to directly measure
the force law and compare it to an analytic prediction based on Stokes flow
driven by Marangoni forces.Comment: 4 pages, 4 figure
First-passage time of run-and-tumble particles
We solve the problem of first-passage time for run-and-tumble particles in
one dimension. Exact expression is derived for the mean first-passage time in
the general case, considering external force-fields and chemotactic-fields,
giving rise to space dependent swim-speed and tumble rate. Agreement between
theoretical formulae and numerical simulations is obtained in the analyzed case
studies -- constant and sinusoidal force fields, constant gradient chemotactic
field. Reported findings can be useful to get insights into very different
phenomena involving active particles, such as bacterial motion in external
fields, intracellular transport, cell migration, animal foraging
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