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 $S$, and we then derive tradeoffs between the performance of resilient algorithmic techniques and the size of the safe memory. Let $\delta$ and $\alpha$ denote, respectively, the maximum amount of faults which can happen during the execution of an algorithm and the actual number of occurred faults, with $\alpha \leq \delta$. We propose a resilient algorithm for sorting $n$ entries which requires $O\left(n\log n+\alpha (\delta/S + \log S)\right)$ time and uses $\Theta(S)$ safe memory words. Our algorithm outperforms previous resilient sorting algorithms which do not exploit the available safe memory and require $O\left(n\log n+ \alpha\delta\right)$ time. Finally, we exploit our sorting algorithm for deriving a resilient priority queue. Our implementation uses $\Theta(S)$ safe memory words and $\Theta(n)$ faulty memory words for storing $n$ keys, and requires $O\left(\log n + \delta/S\right)$ amortized time for each insert and deletemin operation. Our resilient priority queue improves the $O\left(\log n + \delta\right)$ 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

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