262,170 research outputs found
The Dirichlet problem for fully nonlinear degenerate elliptic equations with a singular nonlinearity
No full textWe investigate the homogeneous Dirichlet problem in uniformly convex domains for a large class of degenerate elliptic equations with singular zero order term. In particular we establish sharp existence and uniqueness results of positive viscosity solutions
Existence Issues for a Large Class of Degenerate Elliptic Equations with Nonlinear Hamiltonians
No full textFor degenerate elliptic equations with a nonlinear gradient term H, in bounded uniformly convex domains Ω, we give sufficient conditions for the existence and uniqueness of solutions in terms of the size of Ω, of the forcing term f and of H. The results apply to a wide class of equations, having as principal part significant examples, e.g. linear degenerate operators, weighted partial trace operators and the homogeneous Monge-Ampère operator
Existence through convexity for the truncated Laplacians
No full textWe study the Dirichlet problem on a bounded convex domain of RN, with zero boundary data, for truncated Laplacians Pk±, which are degenerate elliptic operators, for k< N, defined by the upper and respectively lower partial sum of k eigenvalues of the Hessian matrix. We establish a necessary and sufficient condition (Theorem 1) in terms of the “flatness” of domains for existence of a solution for general inhomogeneous term. This result, in particular, shows that the strict convexity of the domain is sufficient for the solvability of the Dirichlet problem. The result and related ideas are applied to the solvability of the Dirichlet problem for the operator Pk+ with lower order term when the domain is strictly convex and the existence of principal eigenfunctions for the operator P1+. An existence theorem is presented with regard to the principal eigenvalue for the Dirichlet problem with zero-th order term for the operator P1+. A nonexistence result is established for the operator Pk+ with first order term when the domain has a boundary portion which is nearly flat. Furthermore, when the domain is a ball, we study the Dirichlet problem, with a constant inhomogeneous term and a possibly sign-changing first order term, and the associated eigenvalue problem
Fractional truncated Laplacians: representation formula, fundamental solutions and applications
No full textWe introduce some nonlinear extremal nonlocal operators that approximate the, so called, truncated Laplacians. For these operators we construct representation formulas that lead to the construction of what, with an abuse of notation, could be called “fundamental solutions”. This, in turn, leads to Liouville type results. The interest is double: on one hand we wish to “understand” what is the right way to define the nonlocal version of the truncated Laplacians, on the other, we introduce nonlocal operators whose nonlocality is on one dimensional lines, and this dramatically changes the prospective, as is quite clear from the results obtained that often differ significantly with the local case or with the case where the nonlocality is diffused. Surprisingly this is true also for operators that approximate the Laplacian
Towards a reversed Faber–Krahn inequality for the truncated Laplacian
No full textWe consider the nonlinear eigenvalue problem, with Dirichlet boundary condition, for the very degenerate elliptic operator P1+ mapping a function u to the maximum eigenvalue of its Hessian matrix. The aim is to show that, at least for square type domains having fixed volume, the symmetry of the domain maximizes the principal eigenvalue, contrary to what happens for the Laplacian
Existence results for fully nonlinear equations in radial domains
No full textWe consider the fully nonlinear problem
-F(x,D^2u)=|u|^{p-1}u in Ω
u=0 on partial Ω
where F is uniformly elliptic, p>1 and Ω is either an annulus or a ball in Rn, n≥2.
We prove the following results:
i. existence of a positive/negative radial solution for every exponent p > 1, if Ω is an annulus;
ii. existence of infinitely many sign changing radial solutions for every p > 1, characterized by the number of nodal regions, if Ω is an annulus;
iii. existence of infinitely many sign changing radial solutions characterized by the number of nodal regions if Ω is a ball and p is subcritical
Analisi geografica a livello subcomunale del rischio di incidenza del tumore al polmone a Taranto 1999-2001
No full textIntroduzione: l’area metropolitana di Taranto è stata oggetto di diversi studi di epidemiologia descrittiva che hanno evidenziato diversi eccessi per patologie che la letteratura riporta come associate all’inquinamento ambientale, in particolare malattie dell’apparato respiratorio, neoplastiche e non. I dati di monitoraggio delle diverse matrici ambientali prodotti negli ultimi anni mostrano effettivamente una situazione di elevata criticità, soprattutto per quanto riguarda le emissioni in atmosfera di inquinanti quali idrocarburi policiclici aromatici e diossine, noti cancerogeni del polmone. La contaminazione ambientale sembra interessare prevalentemente le aree più a ridosso dell’area industriale. La revisione dei dati epidemiologici e ambientali suggerisce pertanto l’opportunità di valutare la distribuzione geografica del rischio di tumore polmonare nel comune di Taranto. Obiettivi: realizzare mappe di rischio del tumore al polmone a livello sub-comunale, allo scopo di valutare eventuali discontinuità territoriali in prossimità dell’area industriale di Taranto, tenendo in considerazione lo stato di deprivazione socio-economica. Metodi: sono stati utilizzati i dati di incidenza del tumore al polmone del comune di Taranto del Registro Tumori Jonico Salentino (RTJS) relativi al triennio 1999-2001. L’indice di deprivazione (ID) è stato calcolato secondo il metodo proposto da Caranci e coll. per ogni sezione di censimento, sulla base dei dati censuari ISTAT del 2001 e standardizzato sulla città di Taranto. Effettuata la georeferenziazione dei casi incidenti attraverso un linkage con l’anagrafe sanitaria, è stato calcolato il rapporto standardizzato di incidenza (SIR), utilizzando come popolazione di riferimento quella coperta dal RTJS (province di Taranto e Brindisi), sia a livello di quartiere che secondo la categoria di deprivazione. Successivamente, allo scopo di ridurre l’instabilità dovuta alla bassa numerosità di casi osservati e tener conto di eventuali strutture di aggregazione spaziale, si è applicato un modello bayesiano di tipo gerarchico e sono stati calcolati i rapporti bayesiani di incidenza (BIR). In tale modello è stato poi inserito l’indice di deprivazione calcolato, per ogni quartiere, come media pesata per la popolazione residente. Risultati: il tumore al polmone risulta in eccesso tra i soggetti di sesso maschile residenti nei quartieri della fascia di deprivazione media (SIR 1.29, IC 95% 1.02-1.61) e nei quartieri molto deprivati (SIR 1.7, IC 95% 1.35-2.11). Si evidenziano per il sesso maschile eccessi di rischio significativi o al limite della significatività in tutti i quartieri, e in particolare nel quartiere Solito-Corvisea (SIR 1.42, IC 95% 1.04-1.88; BIR 1.19, IC 95% 1.03-1.42; BIR aggiustato per ID 1.17, IC 95% 0.97-1.45), nel Borgo antico (BIR 1.17, IC 95% 1.00-1.37; BIR aggiustato per ID 1.176, IC 95% 1.00-1.38), a Paolo VI (BIR 1.185, IC 95% 1.00-1.44), senza peculiari eterogeneità geografiche del rischio in funzione della prossimità con l’area industriale. Si riscontra analogo quadro per il sesso femminile, con un eccesso di rischio nel quartiere Paolo VI (SIR 3.06, IC 95% 1.12-6.66; BIR 1.48, IC 95% 0.78-3.46; BIR aggiustato per ID 1.74, IC 95% 0.68-3.95). Conclusioni: l’analisi ha confermato l’attesa associazione tra condizione socio-economica più deprivata e un più elevato rischio di incidenza di tumore del polmone. La distribuzione geografica del rischio mostra eccessi più evidenti nell’area sud/sud-ovest della città di Taranto. Per una corretta interpretazione dei risultati è necessario integrare i dati di epidemiologia descrittiva con informazioni circa la dispersione degli inquinanti dalle principali sorgenti industriali e dati meteo climatici relativi all’intensità e alla direzione dei venti prevalenti
Formaldehyde Exposure and Irritative Effects on Medical Examiners, Pathologic Anatomy Post-Graduate Students and Technicians
No full textAbstract
Background: Exposure to formaldehyde (FA) causes irritative effects and induces nasopharyngeal cancer; the International
Agency for Research on Cancer (IARC, Lyon) classified FA as carcinogenic to humans, Group 1. Many studies
have been published so far concerning the occupational exposure of industrial workers, embalmers, pathologists and
anatomists to FA but very few data regarding medical examiners are available.
Methods: To assess the extent to which subjects were exposed to FA, airborne concentrations of this chemical were
measured by High Performance Liquid Chromatography (HPLC). In September-October 2006 we examined the personnel,
which worked in an autopsy room (medical examiners) and in three laboratories of pathologic anatomy of the University
Medical School of Bari, Policlinico Hospital, Southern Italy. Irritative effects were also investigated.
Results: All the personal exposure data obtained exceeded the National Institute for Occupational Safety and Health
Threshold Limit Value-Time Weighted Average (NIOSH TLV-TWA: 0.02 mg/m3) and, in a few cases, even the American
Conference of Industrial Hygienists Threshold Limit Value-Ceiling level (ACGIH TLV-C: 0.37 mg/m3).
Conclusion: Irritative effects in more than 50% of the workers enrolled, increasing the risk of injuries
Individuazione e caratterizzazione delle sorgenti di Benzo(a)pirene nel comune di Taranto e stima del rischio cancerogeno associato all’esposizione della popolazione generale
No full textIn 2009 the limit value of benzo(a)pyrene (BaP) in ambient air of 1.0 ng/m3 has been exceeded in the urban district of Taranto near to the industrial area, where a several large plants are located, including an integrated cycle steel plant.
To identify emission sources and quantify relative contribution to the PAHs levels; to estimate health impact associated to PAHs exposure in general population.
Multivariate receptor models have been used. Concentration of PAHs measured in 4 location in Taranto in 2008-2009 have been analyzed. 5 different models estimated profiles of unknown sources and identified significant chemical species. To compute the lung cancer risk the WHO unit risk estimate for BaP (8.7 x 10(5) ng/m3) has been adopted.
Models employed identify 3 to 4 emission sources. Estimated profiles have been compared with measured ones. Based on the average annual BaP level measured (1.3 ng/m3), 2 attributable cancer cases in the district Taranto population are estimated to result from a life-time exposure.
Among different emissive sources, the analysis identifies theoretical sources whose profiles, compared with observed data, allow to identify dominant contributions to PAHs pollution and to design corrective actions to reduce environmental and health impact
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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