102 research outputs found
Localized fluidization in granular materials: Theoretical and numerical study
We present analytical and numerical results on localized fluidization within
a granular layer subjected to a local injection of fluid. As the injection rate
increases the three different regimes previously reported in the literature are
recovered: homogeneous expansion of the bed, fluidized cavity in which
fluidization starts developing above the injection area, and finally the
chimney of fluidized grains when the fluidization zone reaches the free
surface. The analytical approach is at the continuum scale, based on Darcy's
law and Therzaghi's effective stress principle. It provides a good description
of the phenomenon as long as the porosity of the granular assembly remains
relatively homogeneous, i.e. for small injection rates. The numerical approach
is at the particle scale based on the coupled DEM-PFV method. It tackles the
more heterogeneous situations which occur at larger injection rates. The
results from both methods are in qualitative agreement with data published
independently. A more quantitative agreement is achieved by the numerical
model. A direct link is evidenced between the occurrence of the different
regimes of fluidization and the injection aperture. While narrow apertures let
the three different regimes be distinguished clearly, larger apertures tend to
produce a single homogeneous fluidization regime. In the former case, it is
found that the transition between the cavity regime and the chimney regime for
an increasing injection rate coincides with a peak in the evolution of inlet
pressure. Finally, the occurrence of the different regimes is defined in terms
of the normalized flux and aperture
Gravitational diffraction radiation
We show that if the visible universe is a membrane embedded in a
higher-dimensional space, particles in uniform motion radiate gravitational
waves because of spacetime lumpiness. This phenomenon is analogous to the
electromagnetic diffraction radiation of a charge moving near to a metallic
grating. In the gravitational case, the role of the metallic grating is played
by the inhomogeneities of the extra-dimensional space, such as a hidden brane.
We derive a general formula for gravitational diffraction radiation and apply
it to a higher-dimensional scenario with flat compact extra dimensions.
Gravitational diffraction radiation may carry away a significant portion of the
particle's initial energy. This allows to set stringent limits on the scale of
brane perturbations. Physical effects of gravitational diffraction radiation
are briefly discussed.Comment: 5 pages, 2 figures, RevTeX4. v2: References added. Version to appear
in Phys. Rev.
Shannon dimensionality of quantum channels and its application to photon entanglement
We introduce the concept of Shannon dimensionality D as a new way to quantify
bipartite entanglement as measured in an experiment. This is applied to
orbital-angular-momentum entanglement of two photons, using two state analyzers
composed of a rotatable angular-sector phase plate that is lens-coupled to a
single-mode fiber. We can deduce the value of D directly from the observed
two-photon coincidence fringe. In our experiment, D varies between 2 and 6,
depending on the experimental conditions. We predict how the Shannon
dimensionality evolves when the number of angular sectors imprinted in the
phase plate is increased and anticipate that D = 50 is experimentally within
reach.Comment: 4 pages, 3 figures, accepted for Physical Review Letter
Economic burden of diverticular disease : an observational analysis based on real world data from an Italian region
INTRODUCTION:
Diverticular disease (DD), a herniation of the colonic mucosa through the muscle layer, covers a wide variety of conditions associated with the presence of diverticula in the colon. The most serious form is an acute episode of diverticulitis, which can lead to hospitalization and surgery with various types of consequences. The main aim of this study is to evaluate the economic burden of hospitalizations arising from acute episodes of diverticulitis using data from the administrative databases used in the Marche region in Italy and, as a secondary objective of this real-world data analysis, to study patient outcome variables following initial hospitalization for diverticulitis.
METHOD:
A deterministic linkage was performed at individual user level between the different administrative sources of the Marche region through anonymous ID number for a period of analysis between 1 January, 2008 and 31 December, 2014. We enrolled all patients with at least one hospitalization for "diverticulitis of the colon without mention of haemorrhage" (ICD-9-CM code 562.11) or "diverticulitis of the colon with haemorrhage" (ICD-9-CM code 562.13) as primary or secondary diagnosis. For each patient we assessed the cost of hospitalization, of medicines and of specialist services considering a time-scale of one year or cohort analysis 365days after first admission.
RESULTS:
The total number of residents in the Marche region who had at least one hospitalization for diverticulitis in the period 2008-2014 was 2987 (427 patients a year, corresponding to about 35 patients per 100,000 adult residents); the total number of admissions was 3453 (just over 490 a year). The direct healthcare costs incurred by the Marche region for episodes of diverticulitis in 2008-2014 amounted to approximately €11.4 million (€1.6 million a year), of which €10.9 million (95.5%) for the hospitalizations, € 246,000 (2.1%) for pharmaceutical treatment and €270,000 (2.4%) for specialist outpatient services. The average annual cost per patient was €3826, of which €3653 was for hospitalization, while pharmaceutical expenditure and specialist services accounted for €83 and €90, respectively. The cohort of patients undergoing a first admission for diverticulitis between 2010 and 2013 was made up of 1729 people (54.4% women, mean age 68.9 years), of whom 1500 (86.8%) did not undergo surgery while in hospital. Hospital mortality, recorded only for the over-65 age class, averaged 1.2%; for patients not receiving surgery during the initial hospitalization it was 0.5%, reaching 5.2% in patients undergoing surgery. The percentage of patients with one or more readmissions for diverticulitis within a year of the first was on average 7.8% and in 48% of cases this resulted in surgery.
CONCLUSIONS:
Our study is the first analysis in Italy to use real-world data to measure the financial impact of diverticular disease. Assuming that the diagnostic and therapeutic behaviour identified in the Marche region could be representative of the situation nationwide, the estimated annual number of hospitalizations in Italy for acute episodes of diverticulitis is 19,000. The total amount of economic resources needed to treat patients suffering from acute episodes of diverticulitis is estimated at €63.5 million a year
Temporary Acceleration of Electrons While Inside an Intense Electromagnetic Pulse
A free electron can temporarily gain a very significant amount of energy if
it is overrun by an intense electromagnetic wave. In principle, this process
would permit large enhancements in the center-of-mass energy of
electron-electron, electron-positron and electron-photon interactions if these
take place in the presence of an intense laser beam. Practical considerations
severely limit the utility of this concept for contemporary lasers incident on
relativistic electrons. A more accessible laboratory phenomenon is
electron-positron production via an intense laser beam incident on a gas.
Intense electromagnetic pulses of astrophysical origin can lead to very
energetic photons via bremsstrahlung of temporarily accelerated electrons
Is symmetry identity?
Wigner found unreasonable the "effectiveness of mathematics in the natural
sciences". But if the mathematics we use to describe nature is simply a coded
expression of our experience then its effectiveness is quite reasonable. Its
effectiveness is built into its design. We consider group theory, the logic of
symmetry. We examine the premise that symmetry is identity; that group theory
encodes our experience of identification. To decide whether group theory
describes the world in such an elemental way we catalogue the detailed
correspondence between elements of the physical world and elements of the
formalism. Providing an unequivocal match between concept and mathematical
statement completes the case. It makes effectiveness appear reasonable. The
case that symmetry is identity is a strong one but it is not complete. The
further validation required suggests that unexpected entities might be
describable by the irreducible representations of group theory
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