9,542 research outputs found
Slow dynamics in a turbulent von K\'arm\'an swirling flow
We present an experimental study of a turbulent von K\'arm\'an flow produced
in a cylindrical container using two propellers. The mean flow is stationary up
to , where a bifurcation takes place. The new regime breaks some
symmetries of the problem, and is time-dependent. The axisymmetry is broken by
the presence of equatorial vortices with a precession movement, being the
velocity of the vortices proportional to the Reynolds number. The reflection
symmetry through the equatorial plane is broken, and the shear layer of the
mean flow appears displaced from the equator. These two facts appear
simultaneously. In the exact counterrotating case, a bistable regime appears
between both mirrored solutions and spontaneous reversals of the azimuthal
velocity are registered. This evolution can be explained using a three-well
potential model with additive noise. A regime of forced periodic response is
observed when a very weak input signal is applied.Comment: Improved model, additional results and figures, accepted in PR
Monitoring of arthropod infestations on high quality hard wheat in southern Italy
The results of a survey in 2006-2009 on high quality hard wheat, coming from 31 different storage centers located in Southern Italy, are reported. About 300 samples were analyzed by visual test, while 891 by both sieving and biological test. For the three different kinds of test the infesting species are listed and their relative incidence on the samples is reported. The most widespread species in the samples belonged to the order Coleoptera, i.e. Sitophilus granarius, Rhyzopertha dominica and Oryzaephilus spp., while Lepidoptera were less abundant. The results are discussed with the aim of providing the storage centre operators with helpful information on the correct monitoring strategies to adopt in case of arthropod infestations in high-quality hard-wheat warehouses.Keywords: Stored grain, Insects, Sampling, Coleoptera, Ital
On Randomness in Quantum Mechanics
The quantum mechanical probability densities are compared with the
probability densities treated by the theory of random variables. The relevance
of their difference for the interpretation of quantum mechanics is commented
Disinvestment in healthcare: An overview of HTA agencies and organizations activities at European level
Background: In an era of a growing economic pressure for all health systems, the interest for "disinvestment" in healthcare increased. In this context, evidence based approaches such as Health Technology Assessment (HTA) are needed both to invest and to disinvest in health technologies. In order to investigate the extent of application of HTA in this field, methodological projects/frameworks, case studies, dissemination initiatives on disinvestment released by HTA agencies and organizations located in Europe were searched. Methods: In July 2015, the websites of HTA agencies and organizations belonging to the European network for HTA (EUnetHTA) and the International Network of Agencies for HTA (INAHTA) were accessed and searched through the use of the term "disinvestment". Retrieved deliverables were considered eligible if they reported methodological projects/frameworks, case studies and dissemination initiatives focused on disinvestment in healthcare. Results: 62 HTA agencies/organizations were accessed and eight methodological projects/frameworks, one case study and one dissemination initiative were found starting from 2007. With respect to methodological projects/frameworks, two were delivered in Austria, one in Italy, two in Spain and three in U.K. As for the case study and the dissemination initiative, both came from U.K. The majority of deliverables were aimed at making an overview of existing disinvestment approaches and at identifying challenges in their introduction. Conclusions: Today, in a healthcare context characterized by resource scarcity and increasing service demand, "disinvestment" from low-value services and reinvestment in high-value ones is a key strategy that may be supported by HTA. The lack of evaluation of technologies in use, in particular at the end of their lifecycle, may be due to the scant availability of frameworks and guidelines for identification and assessment of obsolete technologies that was shown by our work. Although several projects were carried out in different countries, most remain constrained to the field of research. Disinvestment is a relatively new concept in HTA that could pose challenges also from a methodological point of view. To tackle these challenges, it is necessary to construct experiences at international level with the aim to develop new methodological approaches to produce and grow evidence on disinvestment policies and practices
mm-Wave DRW Antenna Phase Centre Determination
This document presents an approach to the phase centre determination of a dielectric rod waveguide (DRW) antenna by means of measurements obtained with a planar measuring system at millimeter wave lengths. Phase centre determination by the least squares fit technique is described in this document for different DRW antennas (silicon and sapphire). Results at different operating frequencies are offered
Quantum oscillations of self-dual Abrikosov-Nielsen-Olesen vortices
The mass shift induced by one-loop quantum fluctuations on self-dual ANO
vortices is computed using heat kernel/generalized zeta function regularization
methods. The quantum masses of super-imposed multi-vortices with vorticity
lower than five are given. The case of two separate vortices with a quantum of
magnetic flux is also discussed.Comment: RevTex, 13 pages, 4 figures, 7 tables. Minor corrections. Version to
appear in Physical Review
Quasiparticle dynamics and spin-orbital texture of the SrTiO3 two-dimensional electron gas
Two-dimensional electron gases (2DEGs) in SrTiO have become model systems
for engineering emergent behaviour in complex transition metal oxides.
Understanding the collective interactions that enable this, however, has thus
far proved elusive. Here we demonstrate that angle-resolved photoemission can
directly image the quasiparticle dynamics of the -electron subband ladder of
this complex-oxide 2DEG. Combined with realistic tight-binding supercell
calculations, we uncover how quantum confinement and inversion symmetry
breaking collectively tune the delicate interplay of charge, spin, orbital, and
lattice degrees of freedom in this system. We reveal how they lead to
pronounced orbital ordering, mediate an orbitally-enhanced Rashba splitting
with complex subband-dependent spin-orbital textures and markedly change the
character of electron-phonon coupling, co-operatively shaping the low-energy
electronic structure of the 2DEG. Our results allow for a unified understanding
of spectroscopic and transport measurements across different classes of
SrTiO-based 2DEGs, and yield new microscopic insights on their functional
properties.Comment: 10 pages including supplementary information, 4+4 figure
Safety verification of asynchronous pushdown systems with shaped stacks
In this paper, we study the program-point reachability problem of concurrent
pushdown systems that communicate via unbounded and unordered message buffers.
Our goal is to relax the common restriction that messages can only be retrieved
by a pushdown process when its stack is empty. We use the notion of partially
commutative context-free grammars to describe a new class of asynchronously
communicating pushdown systems with a mild shape constraint on the stacks for
which the program-point coverability problem remains decidable. Stacks that fit
the shape constraint may reach arbitrary heights; further a process may execute
any communication action (be it process creation, message send or retrieval)
whether or not its stack is empty. This class extends previous computational
models studied in the context of asynchronous programs, and enables the safety
verification of a large class of message passing programs
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