Vortex polarization and circulation statistics in isotropic turbulence.

We carry out an in-depth analysis of a recently introduced vortex gas model of homogeneous and isotropic turbulence. Direct numerical simulations are used to provide a concrete physical interpretation of one of the model's constituent fields: the degree of vortex polarization. Our investigations shed light on the complexity underlying vortex interactions and reveal, furthermore, that despite some striking similarities, classical and quantum turbulence exhibit distinct structural characteristics, even at inertial range scales. Crucially, these differences arise due to correlations between the polarization and circulation intensity within vortex clusters.

Statistics of extreme turbulent circulation events from multifractality breaking.

Recent numerical explorations of extremely intense circulation fluctuations at high Reynolds number flows have brought to light novel aspects of turbulent intermittency. Vortex gas modeling ideas, which are related to a picture of turbulence as a dilute system of vortex tube structures, have been introduced alongside such developments, leading to accurate descriptions of the core and the intermediate tails of circulation probability distribution functions (cPDFs), as well as the scaling exponents associated to statistical moments of circulation. We extend the predictive reach of the vortex gas picture of turbulence by emphasizing that multifractality breaking, one of its salient phenomenological ingredients, is the key concept to disclose the asymptotic form of cPDF tails. A remarkable analytical agreement is found with previous results derived within the framework of the instanton approach to circulation intermittency, a functional formalism devised to single out the statistically dominant velocity configurations associated to extreme circulation events.

Circulation statistics and the mutually excluding behavior of turbulent vortex structures.

The small-scale statistical properties of velocity circulation in classical homogeneous and isotropic turbulent flows are assessed through a modeling framework that brings together the multiplicative cascade and the structural descriptions of turbulence. We find that vortex structures exhibit short-distance repulsive correlations, which is evidenced when they are "tomographically" investigated, by means of planar cuts of the flow, as two-dimensional vortex gases. This phenomenon is suggested from model improvements which allow us to obtain an accurate multiscale description of the intermittent fluctuations of circulation. Its crucial new ingredient, the conjectured hard disk behavior of the effective planar vortices, is then found to be strongly supported from a study of their spatial distributions in direct numerical simulations of the Navier-Stokes equations.

Multifractality breaking from bounded random measures.

Multifractal systems usually have singularity spectra defined on bounded sets of Hölder exponents. As a consequence, their associated multifractal scaling exponents are expected to depend linearly on statistical moment orders at high-enough orders-a phenomenon referred to as the linearization effect. Motivated by general ideas taken from models of turbulent intermittency and focusing on the case of two-dimensional systems, we investigate the issue within the framework of Gaussian multiplicative chaos. As verified by means of Monte Carlo simulations, it turns out that the linearization effect can be accounted for by Liouville-like random measures defined in terms of upper-bounded scalar fields. The coarse-grained statistical properties of Gaussian multiplicative chaos are furthermore found to be preserved in the linear regime of the scaling exponents. As a related application, we look at the problem of turbulent circulation statistics, and obtain a remarkably accurate evaluation of circulation statistical moments, recently determined with the help of massive numerical simulations.

Vortex gas modeling of turbulent circulation statistics.

Statistical properties of circulation encode relevant information about the multiscale structure of turbulent cascades. Recent massive computational efforts have posed challenging theoretical issues, such as the dependence of circulation moments upon Reynolds numbers and length scales, and the specific shape of the heavy-tailed circulation probability distribution functions. We address these focal points in an investigation of circulation statistics for planar cuts of three-dimensional flows. The model introduced here borrows ideas from the structural approach to turbulence, whereby turbulent flows are depicted as dilute vortex gases, combined with the standard Obukhov-Kolmogorov phenomenological framework of small-scale intermittency. We are able to reproduce, in this way, key statistical features of circulation, in close agreement with empirical observations compiled from direct numerical simulations.

Magnetic dissipation of near-wall turbulent coherent structures in magnetohydrodynamic pipe flows.

Relaminarization of wall-bounded turbulent flows by means of external static magnetic fields is a long-known phenomenon in the physics of electrically conducting fluids at low magnetic Reynolds numbers. Despite the large literature on the subject, it is not yet completely clear what combination of the Hartmann (M) and the Reynolds number has to be used to predict the laminar-turbulent transition in channel or pipe flows fed by upstream turbulent flows free of magnetic perturbations. Relying upon standard phenomenological approaches related to mixing length and structural concepts, we put forward that M/R_{τ}, where R_{τ} is the friction Reynolds number, is the appropriate controlling parameter for relaminarization, a proposal which finds good support from available experimental data.

Toy model for vortex-ring-assisted particle drag in superfluid counterflow.

The interpretation of data obtained from particle image and tracking velocimetry in the study of superfluid flows has been so far a challenging task. Tracking particles (as solid hydrogen or deuterium) are attracted to the cores of quantized vortices, so that their dynamics can be strongly affected by the surrounding vortex tangle. Previous phenomenological arguments indicate that tracking particles and microsized vortex rings could form bound states (denoted here as VRP states). While a comprehensive description of the vortex ring-particle bonding mechanism has to deal with somewhat involved flow configurations, we introduce a simplified two-dimensional model of VRP states, which captures essential qualitative features of their three-dimensional counterparts. Besides an account of known experimental and numerical observations, the model proves to be of great heuristic interest. In particular, it sheds light on the important role played by viscous dissipation (due to the normal component of the fluid), the Magnus force, and topologically excited vortex rings in the stability and dynamics of VRP states.

Onset of intermittency in stochastic Burgers hydrodynamics.

We study the onset of intermittency in stochastic Burgers hydrodynamics, as characterized by the statistical behavior of negative velocity gradient fluctuations. The analysis is based on the response functional formalism, where specific velocity configurations-the viscous instantons-are assumed to play a dominant role in modeling the left tails of velocity gradient probability distribution functions. We find, as expected on general grounds, that the field-theoretical approach becomes meaningful in practice only if the effects of fluctuations around instantons are taken into account. Working with a systematic cumulant expansion, it turns out that the integration of fluctuations yields, in leading perturbative order, to an effective description of the Burgers stochastic dynamics given by the renormalization of its associated heat kernel propagator and the external force-force correlation function.

Trend of decreasing length of cervical cone excision during the last 20 years.

OBJECTIVE: The aim of the present investigation was to evaluate the cervical conizations performed in the last 20 years in a single institution, with a particular interest in analyzing the trend of the length of cone excisions. PATIENTS AND METHODS: A retrospective cohort study of women who underwent a CO2-laser cervical conization between January 1996 and December 2015. Cytological abnormalities on referral pap smear, colposcopic findings and pertinent clinical and socio-demographic characteristics of each woman were collected. In particular, the length of cone specimen was evaluated, taking into account all the factors potentially influencing the length of excision. RESULTS: A total of 1270 women who underwent cervical conization from January 1996 to December 2015 were included in the analysis. A mean cone length of 15.1 ± 5.7 mm was reported, and we observed a significant decrease in the length of cone excisions over the whole study period. Age (rpartial = 0.1543, p < 0.0001), see & treat procedure (rpartial = -0.1945, p < 0.0001) and grade II colposcopic findings (rpartial = 0.1540, p < 0.0001) were significantly associated with the length of cone excision on multivariate analysis. CONCLUSIONS: In the last 20 years, a significant decrease in the length of cone excision was observed. In our opinion, this can be due to the acquired awareness by the gynecologists of the potential disadvantages of wide cone excision in term of adverse obstetric outcomes in future pregnancies.

Predictors of malignancy in endometrial polyps: a multi-institutional cohort study.

PURPOSE OF INVESTIGATION: The risk of endometrial cancer in women with endometrial polyps (EPs) has been reported to vary between 0.3% and 4.8%. There is a lack of data about the management of asymptomatic women with incidental diagnosis of EPs. In the present study the authors correlated demographic and clinical characteristics with histopathological features of the EPs hysteroscopically removed. MATERIALS AND METHODS: An observational multi-institutional cohort study was conducted from February 2010 to December 2012 to identify all the premenopausal and postmenopausal women consecutively undergoing hysteroscopic polypectomy. The data of women were reviewed and clinical features were related to histopathologic results. RESULTS: The patients recruited were 813. The mean age was 52.5 years (range 22-87). The results showed a correlation between older age, high body mass index (BMI) and obesity, postmenopausal state, abnormal uterine bleeding (AUB), hypertension, and risk of malignant EPs. On multivariable analysis, the correlation remained only for age (OR 1.08, 95% CI 1.03 - 1.14) and AUB (OR 3.53, 95% CI 1.87 - 6.65). CONCLUSION: Older patients in postmenopausal status with AUB, a high BMI, and hypertension are at higher risk for premalignant and malignant polyps. In these patients a surgical approach should be used, consisting in hysteroscopical removing of the polyp.

Vorticity statistics and the time scales of turbulent strain.

Time scales of turbulent strain activity, denoted as the strain persistence times of first and second order, are obtained from time-dependent expectation values and correlation functions of Lagrangian rate-of-strain eigenvalues taken in particularly defined statistical ensembles. Taking into account direct numerical simulation data, our approach relies on heuristic closure hypotheses which allow us to establish a connection between the statistics of vorticity and strain. It turns out that softly divergent prefactors correct the usual "1/s" strain time-scale estimate of standard turbulence phenomenology, in a way which is consistent with the phenomenon of vorticity intermittency.

Markov chain modeling of polymer translocation through pores.

We solve the Chapman-Kolmogorov equation and study the exact splitting probabilities of the general stochastic process which describes polymer translocation through membrane pores within the broad class of Markov chains. Transition probabilities, which satisfy a specific balance constraint, provide a refinement of the Chuang-Kantor-Kardar relaxation picture of translocation, allowing us to investigate finite size effects in the evaluation of dynamical scaling exponents. We find that (i) previous Langevin simulation results can be recovered only if corrections to the polymer mobility exponent are taken into account and (ii) the dynamical scaling exponents have a slow approach to their predicted asymptotic values as the polymer's length increases. We also address, along with strong support from additional numerical simulations, a critical discussion which points in a clear way the viability of the Markov chain approach put forward in this work.

Conformal invariance in (2+1)-dimensional stochastic systems.

Stochastic partial differential equations can be used to model second-order thermodynamical phase transitions, as well as a number of critical out-of-equilibrium phenomena. In (2+1) dimensions, many of these systems are conjectured (and some are indeed proved) to be described by conformal field theories. We advance, in the framework of the Martin-Siggia-Rose field-theoretical formalism of stochastic dynamics, a general solution of the translation Ward identities, which yields a putative conformal energy-momentum tensor. Even though the computation of energy-momentum correlators is obstructed, in principle, by dimensional reduction issues, these are bypassed by the addition of replicated fields to the original (2+1)-dimensional model. The method is illustrated with an application to the Kardar-Parisi-Zhang (KPZ) model of surface growth. The consistency of the approach is checked by means of a straightforward perturbative analysis of the KPZ ultraviolet region, leading, as expected, to its c=1 conformal fixed point.

Log-Poisson cascade description of turbulent velocity-gradient statistics.

The Log-Poisson phenomenological description of the turbulent energy cascade is evoked to discuss high-order statistics of velocity derivatives and the mapping between their probability distribution functions at different Reynolds numbers. The striking confirmation of theoretical predictions suggests that numerical solutions of the flow obtained at low/moderate Reynolds numbers can play an important quantitative role in the analysis of experimental high Reynolds number phenomena, where small scales fluctuations are in general inaccessible from direct numerical simulations.

Minimalist turbulent boundary layer model.

We discuss an elementary model of a turbulent boundary layer over a flat surface given as a vertical random distribution of spanwise Lamb-Oseen vortex configurations placed over a nonslip boundary-condition line. We are able to reproduce several important features of realistic flows, such as the viscous and logarithmic boundary sublayers, and the general behavior of the first statistical moments (turbulent intensity, skewness, and flatness) of the streamwise velocity fluctuations. As an application, we advance some heuristic considerations on the boundary layer underlying kinematics that could be associated with the phenomenon of drag reduction by polymers, finding a suggestive support from its experimental signatures.

Instanton theory of Burgers shocks and intermittency.

A Lagrangian approach to Burgers turbulence is carried out along the lines of the field theoretical Martin-Siggia-Rose formalism of stochastic hydrodynamics. We derive, from an analysis based on the hypothesis of unbroken Galilean invariance, the asymptotic form of the probability distribution function of negative velocity differences. The origin of Burgers intermittency is found to rely on the dynamical coupling between shocks, identified to instantons, and noncoherent background fluctuations, which-then-cannot be discarded in a consistent statistical description of the flow.

Large-scale intermittency in the atmospheric boundary layer.

We find actual evidence, relying upon vorticity time series taken in a high-Reynolds-number atmospheric experiment, that to a very good approximation the surface boundary layer flow may be described, in a statistical sense and under certain regimes, as an advected ensemble of homogeneous turbulent systems, characterized by a log-normal distribution of fluctuating intensities. Our analysis suggests that the usual direct numerical simulations of homogeneous and isotropic turbulence, performed at moderate Reynolds numbers, may play an important role in the study of turbulent boundary layer flows, if supplemented with appropriate statistical information concerned with the structure of large-scale fluctuations.

[Census 2004 of the Italian Renal and Dialysis Units. Emilia-Romagna, Toscana]. / Censimento 2004 dei Centri di Nefrologia e Dialisi Italiani. Emilia-Romagna - Toscana.

The 2004 SIN census of the Italian nephrology and dialysis centres showed many interesting data about the epidemiology and the organization in the Regions of Emilia-Romagna (ER) and Tuscany (T). A) Epidemiology: incidence of dialysis patients 169 pmp (patients per million population) in ER, 147 ppm in T; prevalence of dialysis patients 639 pmp and 665 pmp, respectively; prevalence of transplanted patients 325 ppm in ER and 233 pmp in T; gross mortality of dialysis patients 16.3% and 13.4%, respectively; B) Type of vascular access in prevalently dialysis patients: arteriovenous fistula 83% and 78%; central venous catheter 13% and 12%; vascular graft 5% and 9%. C) Structural resources: nephrology beds 44 mp (per million population) and 50 mp; dialysis places 157 and 146 mp. D) Personnel resources : renal physicians 29 and 41 mp; renal nurses 171 and 202 mp ; each renal physician cares for 22 and 16 dialysis patients, and each renal nurse takes care of 3.7 and 3.3 dialysis patients. E) Activity: hospital admissions 1572, 1769 pmp; renal biopsies 115 and 166 pmp.

[Update of the Italian Society of Nephrology Project No. 1 of the 2004-2006 SIN programme]. / Update sul progetto SIN n. 1 del programma SIN 2004-2006: qualità e accreditamento delle strutture di nefrologia, dialisi e trapianto.

In the last few years the Italian Society of Nephrology has addressed many technical-scientific and management aspects to better patient satisfaction. Project No. 1 of the 2004-2006 programme on 'Quality and Accreditation of National Renal Units' focuses on four essential points. The first is the questionnaire mailed to all the Presidents and Regional Delegates on the relationship between Nephrology units, Local Government Health-System and the Regional Healthcare Agency. The results evidence that the 'political' decision-making power of nephrologists decreases in the absence of a national strategy. The second point, in collaboration with the National Census Group, includes the quality analysis and the standardization of resources (human and structural) and management of the Renal Units. The third point is based on 'Educational Courses for Quality and Accreditation' held in Rome (3-5 October 2005: L'Accreditamento all'Eccellenza dell'Unita' Operativa di Nefrologia, Dialisi e Trapianto; 17-19 October 2005: Il Manuale di Accreditamento della Specialità di Nefrologia). The courses aim at training members responsible for each region to hold courses in their specific region to create a network including each single Renal Unit to create an acceptable homogenous language on the models of analysis and on the correct use of 'The Guide for Excellence Accreditation'. The fourth point concerns both the on-line Guide for Excellence Accreditation and 'Peer Review Accreditation' and the NEQUASY (Nephrology Quality System) project. The manual must be 'user friendly' allowing each Centre to self-evaluate using national and regional standards.

Langevin simulation of the chirally decomposed sine-Gordon model.

A large class of quantum and statistical field theoretical models, encompassing relevant condensed matter and non-Abelian gauge systems, are defined in terms of complex actions. As the ordinary Monte Carlo methods are useless in dealing with these models, alternative computational strategies have been proposed along the years. The Langevin technique, in particular, is known to be frequently plagued with difficulties such as strong numerical instabilities or subtle ergodic behavior. Regarding the chirally decomposed version of the sine-Gordon model as a prototypical case for the failure of the Langevin approach, we devise a truncation prescription in the stochastic differential equations which yields numerical stability and is assumed not to spoil the Berezinskii-Kosterlitz-Thouless transition. This conjecture is supported by a finite size scaling analysis, whereby a massive phase ending at a line of critical points is clearly observed for the truncated stochastic model.