2,545 research outputs found
Ethnic Concentration, Cultural Identity and Immigrant Self-Employment in Switzerland
Immigrant self-employment rates vary considerably across regions in Switzerland. Business ownership seems to provide an alternative to wage labour, where immigrants have to face structural barriers such as the limited knowledge of the local language, or difficulties in fruitfully making use of their own human capital. Despite the historically high unemployment rates with respect to natives, immigrants in Switzerland are less entrepreneurial. It is therefore important to uncover the determinants that may facilitate the transition from the status of immigrant to the one of economic agent. Among others factors, concentration in ethnic enclaves, as well as accumulated labour market experience and time elapsed since immigration, have been associated to higher business ownership rates. In this paper we use a cross-section of 2,490 Swiss municipalities in order to investigate the role played by the ethnic concentration of immigrants, as well as cultural factors, in determining self-employment rates.self-employment, immigrants, Switzerland, ethnic concentration, cultural identity
Motility fractionation of bacteria by centrifugation
Centrifugation is a widespread laboratory technique used to separate mixtures
into fractions characterized by a specific size, weight or density. We
demonstrate that centrifugation can be also used to separate swimming cells
having different motility. To do this we study self-propelled bacteria under
the influence of an external centrifugal field. Using dynamic image correlation
spectroscopy we measure the spatially resolved motility of bacteria after
centrifugation. A significant gradient in swimming-speeds is observed for
increasing centrifugal speeds. Our results can be reproduced by a model that
treats bacteria as "hot" colloidal particles having a diffusion coefficient
that depends on the swimming speed.Comment: 7 pages, 5 figures (in press
An optical reaction micro-turbine
To any energy flow there is an associated flow of momentum, so that recoil forces arise every time an object absorbs or deflects incoming energy. This same principle governs the operation of macroscopic turbines as well as that of microscopic turbines that use light as the working fluid. However, a controlled and precise redistribution of optical energy is not easy to achieve at the micron scale resulting in a low efficiency of power to torque conversion. Here we use direct laser writing to fabricate 3D light guiding structures, shaped as a garden sprinkler, that can precisely reroute input optical power into multiple output channels. The shape parameters are derived from a detailed theoretical analysis of losses in curved microfibers. These optical reaction micro-turbines can maximally exploit lightâs momentum to generate a strong, uniform and controllable torque
Multidimensional Stationary Probability Distribution for Interacting Active Particles
We derive the stationary probability distribution for a non-equilibrium
system composed by an arbitrary number of degrees of freedom that are subject
to Gaussian colored noise and a conservative potential. This is based on a
multidimensional version of the Unified Colored Noise Approximation. By
comparing theory with numerical simulations we demonstrate that the theoretical
probability density quantitatively describes the accumulation of active
particles around repulsive obstacles. In particular, for two particles with
repulsive interactions, the probability of close contact decreases when one of
the two particle is pinned. Moreover, in the case of isotropic confining
potentials, the radial density profile shows a non trivial scaling with radius.
Finally we show that the theory well approximates the "pressure" generated by
the active particles allowing to derive an equation of state for a system of
non-interacting colored noise-driven particles.Comment: 5 pages, 2 figure
Generalized energy equipartition in harmonic oscillators driven by active baths
We study experimentally and numerically the dynamics of colloidal beads
confined by a harmonic potential in a bath of swimming E. coli bacteria. The
resulting dynamics is well approximated by a Langevin equation for an
overdamped oscillator driven by the combination of a white thermal noise and an
exponentially correlated active noise. This scenario leads to a simple
generalization of the equipartition theorem resulting in the coexistence of two
different effective temperatures that govern dynamics along the flat and the
curved directions in the potential landscape.Comment: 4 pages, 3 figure
The relevance of Giddens' structuration theory for organizational research
Anthony Giddens' Structuration Theory is probably one of the sociological theories more directly referenced and more widely used, in a variety of ways, in organizational research. Why is that, and what does it mean for organizational research? In this paper we explore this issue by reviewing some early, influential contributions, within the organizational field, that used Giddens' theory as the main reference. We will show that the actual utilizations of such theory are very heterogeneous in many relevant concepts, although they are all moved by similar theoretical needs. We also propose that in order to properly answer to those needs, organizational research should focus on some key elements that, while being central in Giddens' contribution, are not always interpreted consistently by "Giddensian" organization scholars. Finally, we will argue that it is possible for the organization reflection, even when it is not built upon Structuration Theory, to share and realize Giddens' main "message" to the organizational discipline: the need for an organization theory truly based on an epistemological view that allows to overcome the objectivist / subjectivist dilemma
Invariance properties of bacterial random walks in complex structures
Motile cells often explore natural environments characterized by a high
degree of structural complexity. Moreover cell motility is also intrinsically
noisy due to spontaneous random reorientation and speed fluctuations. This
interplay of internal and external noise sources gives rise to a complex
dynamical behavior that can be strongly sensitive to details and hard to model
quantitatively. In striking contrast to this general picture we show that the
mean residence time of swimming bacteria inside artificial complex
microstructures, can be quantitatively predicted by a generalization of a
recently discovered invariance property of random walks. We find that
variations in geometry and structural disorder have a dramatic effect on the
distributions of path length while mean values are strictly constrained by the
sole free volume to surface ratio. Biological implications include the
possibility of predicting and controlling the colonization of complex natural
environments using only geometric informations
Additional diagnostic value of implantable loop recorder in patients with initial diagnosis of real or apparent transient loss of consciousness of uncertain origin
Aims Non-syncopal transient loss of consciousness (T-LOC) encompasses disorders that sometimes resemble syncope, and the differential diagnosis with true syncope may be challenging. The implantable loop recorder (ILR) is potentially useful, but has never been systematically assessed. The aim of the study is to evaluate the diagnostic value of ILR in distinguishing syncope from non-syncopal forms of T-LOC. Methods and results We implanted an ILR in 58 patients (mean age 71 ± 17 years, 25 males) who had had 4.6 ± 2.3 episodes of real or apparent T-LOC, in order to distinguishing epilepsy from syncope (#28), unexplained fall from syncope (#29), or functional pseudo-syncope from syncope (#1). During 20 ± 13 months of follow-up, 33 patients (57%) had a spontaneous event documented by ILR. A diagnosis of syncope was established by ILR documentation of an arrhythmia in 15 (26%) patients: an asystole of 6 s (IQR 4â10 s) duration was documented at the time of the spontaneous event in seven patients with initial suspicion of epilepsy and in five patients with unexplained fall; atrial tachyarrhythmia was documented at the time of the spontaneous event in 1 and 1 patient, respectively, and ventricular tachycardia in 1 patient with unexplained fall. Conversely, in another 18 patients, ILR monitoring documented no significant rhythm abnormalities at the time of T-LOC recurrence, thus excluding an arrhythmic syncope. Finally, ILR was unable to document any syncopal episode in 25 (43%) patients. Among the 15 patients with an established diagnosis of arrhythmic syncope, syncope recurred during follow-up in 2 of 11 patients who were on pacemaker therapy and in 3 of 4 patients who were on other therapies. Conclusion Implantable loop recorder monitoring provides additional diagnostic value in 'difficult' patients with an initial diagnosis of non-syncopal real or apparent T-LOC
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