341 research outputs found
Exploiting non-constant safe memory in resilient algorithms and data structures
We extend the Faulty RAM model by Finocchi and Italiano (2008) by adding a
safe memory of arbitrary size , and we then derive tradeoffs between the
performance of resilient algorithmic techniques and the size of the safe
memory. Let and denote, respectively, the maximum amount of
faults which can happen during the execution of an algorithm and the actual
number of occurred faults, with . We propose a resilient
algorithm for sorting entries which requires time and uses safe memory words. Our
algorithm outperforms previous resilient sorting algorithms which do not
exploit the available safe memory and require time. Finally, we exploit our sorting algorithm for
deriving a resilient priority queue. Our implementation uses safe
memory words and faulty memory words for storing keys, and
requires amortized time for each insert and
deletemin operation. Our resilient priority queue improves the amortized time required by the state of the art.Comment: To appear in Theoretical Computer Science, 201
Numerical study of wind-wave interfacial phenomena
A DNS simulation has been performed in order to study the wind-wave interaction, especially focusing the attention on the interfacial phenomena. The numerical model is founded to reproduce gravity waves generation under the action of a turbulent wind. The VOF (volume of fraction) method is used in order to capture and model the free surface, while the wind is generated by imposing an external pressure gradient. This last choice, in contrast with the usual ways of simulating wind by a moving wall, turned out to be very effective from both the computational and the physical point of view.
The simulation can be described by two fundamental parameters: the friction Reynolds number is about 330 and the wave age is 35. The wave age has been calculated by a spectral analysis of the free surface: through this analysis the wavelength of the main ripple is found to be about 5 cm, while its phase speed results to be 0.7 m/s. This wavelength and phase speed seems reasonable by comparing it with experiments and observations.
The turbulent boundary layer is significantly modified by waves in a way that resembles rough turbulence. The spatially and time averaged mean velocity profile is affected by the roughness of waves as much as the fluctuating field. In this study a sea surface roughness of 0.017 is founded by observing the behaviour of the wind close to the free surface. This similarity between a rough wall and waves, can be relevant for modelling flows over wavy walls or predicting wind and wave currents, especially in the Geophysical fluid dynamic field.
Finally, the Phillips mechanism (turbulent pressure fluctuations along the free surface) and the sheltering mechanism (positive and negative pressure fluctuations respectively in front and on the leeside of the wave due to the boundary layer separation) have been clearly observed
Coherent multi-mode dynamics in a Quantum Cascade Laser: Amplitude and Frequency-modulated Optical Frequency Combs
We cast a theoretical model based on Effective Semiconductor Maxwell-Bloch
Equations and study the dynamics of a multi-mode mid-Infrared Quantum Cascade
Laser in Fabry Perot with the aim to investigate the spontaneous generation of
optical frequency combs. This model encompasses the key features of a
semiconductor active medium such as asymmetric,frequency-dependent gain and
refractive index as well as the phase-amplitude coupling of the field dynamics
provided by the linewidth enhancement factor. Our numerical simulations are in
excellent agreement with recent experimental results, showing broad ranges of
comb formationin locked regimes, separated by chaotic dynamics when the field
modes unlock. In the former case, we identify self-confined structures
travelling along the cavity, while the instantaneous frequency is characterized
by a linear chirp behaviour. In such regimes we show that OFC are characterized
by concomitant and relevant amplitude and frequency modulation
Retrieval of the Dielectric Properties of a Resonant Material in the Terahertz Region via Self-Detection Near Field Optical Microscopy
We present a numerical and analytical study of the self-detection scattering type near field optical microscopy (SD s-SNOM), a recently demonstrated technique based on a combination of self-mixing interferometry and scattering near-field microscopy. This scheme, which exploits a terahertz (THz) quantum cascade laser as both a laser source and detector, allows to investigate the optical properties of resonant materials in the THz range with resolution far beyond the diffraction limit. Our study, developed by using a modified version of the Lang-Kobayashi model, is focused on the weak feedback regime (Acket parameter C approximate to 10(-1)), where we derive an approximated method for the retrieval of the scattering coefficient of the SD s-SNOM configuration applied to a sample of Cesium Bromide (CsBr). These results were used in turn to derive the dielectric permittivity of the sample, reporting a good accuracy in the estimation of its phonon resonances
Workplace violence in different settings and among various health professionals in an Italian general hospital: a cross-sectional study
Background: Workplace violence (WPV) against health professionals is a global problem with
an increasing incidence. The aims of this study were as follows: 1) to examine the frequency
and characteristics of WPV in different settings and professionals of a general hospital and 2)
to identify the clinical and organizational factors related to this phenomenon.
Methods: The study was cross-sectional. In a 1-month period, we administered the “Violent
Incident Form” to 745 professionals (physicians, head nurses, nurses, nursing assistants), who
worked in 15 wards of a general hospital in northern Italy.
Results: With a response rate of 56%, 45% of professionals reported WPV. The most frequently
assaulted were nurses (67%), followed by nursing assistants (18%) and physicians
(12%). The first two categories were correlated, in a statistically significant way, with the risk of
WPV (P=0.005, P=0.004, multiple logistic regression). The violent incidents more frequently
occurred in psychiatry department (86%), emergency department (71%), and in geriatric wards
(57%). The assailants more frequently were males whereas assaulted professionals more often
were females. Men committed physical violence more frequently than women, in a statistically
significant way (P=0.034, chi-squared test). Verbal violence (51%) was often committed by
people in a lucid and normal state of consciousness; physical violence (49%) was most often
perpetrated by assailants affected by dementia, mental retardation, drug and substance abuse,
or other psychiatric disorders. The variables positively related to WPV were “calling for help
during the attack” and “physical injuries suffered in violent attack” (P=0.02, P=0.03, multiple
logistic regression).
Conclusion: This study suggests that violence is a significant phenomenon and that all health
workers, especially nurses, are at risk of suffering aggressive assaults. WPV presented specific
characteristics related to the health care settings, where the aggression occurred. Prevention
programs tailored to the different care needs are necessary to promote professional awareness
for violence risk
Dynamics of Optical Frequency Combs in Ring and Fabry-Perot Quantum Cascade Lasers
Since the demonstration that multimode Quantum Cascade Lasers (QCLs) can operate as sources of Optical Frequency Combs (OFC) [1] , an extended class of theoretical models, based on standard two or three level Maxwell-Bloch equations, has been proposed to interpret such phenomenology
Digital ulcers secondary to Sneddon's syndrome successfully treated with Bosentan: not only useful in Systemic Sclerosis
Interferon free antiviral treatment of chronic hepatitis C in patients affected by β-thalassemia major
Chronic hepatitis C (CHC) significantly affects the prognosis
of liver disease [1] and health related quality of life (HRQOL)
in patients with β-thalassemia major [2, 3]. CHC cure is a
crucial event in the prognosis of the disease, since prevents
fibrosis progression, decreases the risk of hepatocellular carcinoma (HCC), and improves survival. Standard antiviral
therapy with Pegylated Interferon (PEG-IFN) and Ribavirin
(RBV) has long been the standard of care, despite its limited
efficacy and increased ribavirin induced hematological adverse events in thalassemic patients [4]. Recently, several novel highly effective direct antiviral agents (DAAs) have been
approved for HCV treatment, with impressive cure rates,
higher than 90%, after 8–12 weeks of therapy and mild adverse events [5], but there are no published reports
documenting the efficacy, safety and impact on QOL of available interferon-free antiviral regimens in patients with βthalassemia majo
Flocking and turning: a new model for self-organized collective motion
Birds in a flock move in a correlated way, resulting in large polarization of
velocities. A good understanding of this collective behavior exists for linear
motion of the flock. Yet observing actual birds, the center of mass of the
group often turns giving rise to more complicated dynamics, still keeping
strong polarization of the flock. Here we propose novel dynamical equations for
the collective motion of polarized animal groups that account for correlated
turning including solely social forces. We exploit rotational symmetries and
conservation laws of the problem to formulate a theory in terms of generalized
coordinates of motion for the velocity directions akin to a Hamiltonian
formulation for rotations. We explicitly derive the correspondence between this
formulation and the dynamics of the individual velocities, thus obtaining a new
model of collective motion. In the appropriate overdamped limit we recover the
well-known Vicsek model, which dissipates rotational information and does not
allow for polarized turns. Although the new model has its most vivid success in
describing turning groups, its dynamics is intrinsically different from
previous ones in a wide dynamical regime, while reducing to the hydrodynamic
description of Toner and Tu at very large length-scales. The derived framework
is therefore general and it may describe the collective motion of any strongly
polarized active matter system.Comment: Accepted for the Special Issue of the Journal of Statistical Physics:
Collective Behavior in Biological Systems, 17 pages, 4 figures, 3 video
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