1,720,982 research outputs found
On the Cauchy Problem for a Class of Linear Weakly Hyperbolic Operators
No full textWe study a class of linear weakly hyperbolic operators with anisotropic degeneracy on their characteristic manifold and we give sufficient conditions for the well-posedness of the related Cauchy problem
An interpolation problem in the Denjoy–Carleman classes
Full text linkInspired by some iterative algorithms useful for proving the real analyticity (or the Gevrey regularity) of a solution of a linear partial differential equation with real-analytic coefficients, we consider the following question. Given a smooth function defined on [a,b]subset of R and given an increasing divergent sequence dn of positive integers such that the derivative of order dn of f has a growth of the type Mdn, when can we deduce that f is a function in the Denjoy-Carleman class CM([a,b])C<^>M([a,b])? We provide a positive result and show that a suitable condition on the gaps between the terms of the sequence dn is needed
Weyl calculus for a class of subelliptic operators
No full textWeyl-Hörmander calculus is used to get a parametrix in OPS 1/2.1/21-m(Ω) for a class of subelliptic pseudodifferential operators in OPS1.0m(Ω) with real nonnegative principal symbol
Gevrey regularity for a class of sums of squares of monomial vector fields
Full text linkAnalytic or Gevrey hypoellipticity is proved for a class of sums of squares of vector fields having a symplectic characteristic manifold of dimension 2 and arbitrary (even) codimension. We note that this class contains examples for which the Treves stratification seems to work as well as examples for which the Treves stratification does not identify properly the non symplectic stratum
Parametrix construction for a class of anisotropic operators
No full textWe set Boutet de Monvel's Calculus for hypoelliptic operators (in the case of flat symplectic characteristic manifold) in a Weyl-Hörmander framework that also contains anisotropically vanishing symbols. In this context we construct a parametrix for the related operators. © 2003 Università degli Studi di Ferrara
ANALYTIC HYPOELLIPTICITY for SUMS of SQUARES in the PRESENCE of SYMPLECTIC NON TREVES STRATA
Full text linkIn Albano, Bove and Mughetti [J. Funct. Anal. 274(10) (2018), 2725-2753]; Bove and Mughetti [Anal. PDE 10(7) (2017), 1613-1635] it was shown that Treves conjecture for the real analytic hypoellipticity of sums of squares operators does not hold. Models were proposed where the critical points causing a non-analytic regularity might be interpreted as strata. We stress that up to now there is no notion of stratum which could replace the original Treves stratum. In the proposed models such 'strata' were non-symplectic analytic submanifolds of the characteristic variety. In this note we modify one of those models in such a way that the critical points are a symplectic submanifold of the characteristic variety while still not being a Treves stratum. We show that the operator is analytic hypoelliptic
On the positive parts of second order symmetric pseudo-differential operators
No full textUsing microlocalization, the positive and the negative parts for a class of second order formally self-adjoint pseudodifferetial operators are constructe
Valutazione ecografia delle manovre di reclutamento nei pazienti affetti da ARDS
No full textPrima di applicare la ventilazione meccanica (PEEP) è indispensabile valutarne l'effettiva utilità mediante le manovre di reclutamento[1, 2, 3].
I risultati vengono valutati con varie metodiche: attualmente lo standard di riferimento è rappresentato dall'emogasanalisi e dalla TC [7, 8].
La TC permette la diretta voisualizzazione dei risultati, tuttavia richiede di trasportare un paziente critico e permette solo un approccio statico al reclutamento che è invece un processo dinamico [9, 10, 11].
Abbiamo confrontato la valutazione ecograficadelle MR con quella emogasanalitica in 23 pazienti.
L'ecografia fornisce una valutazione attendibile, diretta, dinamica, rapida, semplice ed economica delle MR, senza l'impiego di radiazioni ionizzanti
Ecographic evaluation of pronation manoeuvre efficacy in neonatal respiratory distress syndrome: Report of 15 cases
No full text1. Purpose
Prone position is a non-invasive way of increasing oxygenation in infants and children hospitalised with acute respiratory distress (RDS) [1].
In particular when consolidated areas are present in RDS, they are usually in the declivous regions of the lung and recruiting them by changing the patient’s position (in particular from supine to prone position) may be useful.
The aim of this therapeutic approach treating RDS is “to open a closed lung” [2, 3].
Accidental tracheal extubation or withdrawal of vascular catheter may occur during pronation manoeuvre (PM) and there is a well known association between prone position and sudden infant death syndrome (SIDS) [1].
For these reasons an evaluation of the effectiveness of PM is necessary before its employed.
We analysed lung echography (LE) efficacy and usefulness in the evaluation of PM in RDS.
2. Methods and Materials
A group of 65 premature neonates, suffering from RDS, treated in neonatal intensive care unit, have been preliminarly studied with direct thorax radiogram and LE.
15 (9 males, 7 females) of these patients, which presented significant consolidation areas (maximum diameter more than 2,5 cm) underwent PM: the procedure efficacy was evaluated echographically.
A portable echograph: MyLab 25®, Esaote Spa, Florence, with a 7,5- 13 MHz linear probe was used. Our approach was transthoracic by using longitudinal, transversal and coronal scans.
Echographic evaluation of PM was compared with variations in arterial partial pressure of oxygen (PaO2) and of carbon dioxide (PaCO2) and to the differnt radiographic aspect of the thorax before and after PM.
3. Results
All the 65 infants we preliminarly studied showed a diffused echographic B-line pattern without spared areas and pleural iperhechoic line irregularly thickened wich permitted to confirm clinical diagnoses.
Always minimal, subpleural areas of parenchymal consolidation were present but only in 15 patients we found significant consolidation areas (maximum diameter more than 2,5 cm).
In 11 patients LE showed complete recruitment of consolidated areas.
In 2 pts affected by 2 areas of basal consolidation we had only a partial recruitment.
In 2 pts we didn’t have neither echographic signs of recruitment, nor changes in PaO2 and PaCO2.
In the patients in which PM was effective, we made a comparison between LE and increase in arterial partial pressure of oxygen (PaO2) or of carbon dioxide (PaCO2) and we found a correlation between echographic changes and improvement in the partial pressures of the 2 gasses.
Furthermore we found some correlations between ultrasound changes and different radiological aspect before and after PM.
4. Conclusion
LE allows an accurate evaluation of results of pronation manoevre.
Unfortunately echography provides a limited field of view, so it may be difficult to measure the real extension of the consolidations.
A further limit in this kind of approach may be the fact that only parenchymal abnormalities adjacent to the visceral pleura are evaluable with ultrasounds.
When PM repetition is necessary, the study should be performed by the same operator because there is a well-known operator-dependance in echotomography.
This is a preliminary study and it didn't allow us to determine LE sensitivity in the evaluation of RM, as the gold standard is CT, which cannot be routinely used for obvious ethical reasons.
A larger number of patients should be evaluated in order to define the usefulness and the limits of the methods employed.
This particular application of LE is quite easy to learn but, in our opinion, a good knowledge of lung sonography is advisable.
REFERENCES
[1] Wells DA, Gillies D, Fitzgerald DA. Positioning for acute respiratory distress in hospitalised infants and children. Cochrane Database Syst Rev. 2005:18; 2.
[2] Barbas CS, de Matos GF, Pincelli MP (2005) Mechanical ventilation in acute respiratory failure: recruitment and high positive end-expiratory pressure are necessary. Curr Opin Crit Care. 11(1):18-28.
[3] Papadakos PJ, Lachmann B. (2007) The open lung concept of mechanical ventilation: the role of recruitment and stabilization. Crit Care Clin. 23(2):241-250
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