117,707 research outputs found
Evaluation of refraction in a statistically significant sample: changes according to age and strabismus
No full textPURPOSE: To assess possible refractive changes according to age and strabismus in a statistically significant cohort. METHODS: A population-based sample of 12,534 subjects 0.5 to 20 years old, examined between 2004 and 2006, was tested. Each subject received a complete orthoptic examination, including spherocylindrical streak retinoscopy in cycloplegia. Patients were divided into those with orthophoria (7,784) and those with strabismus (4,750), and the latter group was further divided into those with esodeviation (3,026) and those with exodeviation (1,724). A statistical analysis of the spherical equivalent, astigmatism, and anisometropia was performed with an independent samples t test or one-way analysis of variance. RESULTS: The percentage of patients with a mean spherical equivalent within +/- 1 and +/- 2 standard deviations was greater than 68% and 95%, respectively. The mean spherical equivalent of the total sample was 1.62 diopters (D) (+/- 2.88). The mean spherical equivalent was 1.10 +/- 2.94 D in the orthophoria group, 3.22 +/- 2.29 D in the esodeviation group, and 1.13 +/- 2.50 D in the exodeviation group (one-way analysis of variance; P = .000). Age-related changes in the mean spherical equivalent showed a clear and steady myopic shift, reaching mean myopic refraction at 12 to 14 years in both the total sample and the orthophoria and exodeviation groups. It assumed a more constant trend, with no myopic swing, in the esodeviation group (P = .000). Mean astigmatism was less in patients with less than 1.00 D anisometropia (0.83 +/- 0.92 D) than in those with 1.00 D or greater anisometropia (1.42 +/- 1.18 D) (t test; P = .0001). CONCLUSION: Both the age-related trend in the spherical equivalent and the high hyperopic values of the distribution peak in patients with esodeviation confirm the importance of the hypermetropic refractive component. The statistically significantly higher incidence of astigmatism in patients with 1.00 D or greater ametropia highlights its incidence in amblyopia. Copyright 2009, SLACK Incorporated
Gli strumenti di pagamento nel commercio internazionale
No full textIl contributo analizza la complessità degli scambi internazionali e gli strumenti utilizzati per ridurre questi fattori di complessità, approfondendo, in particolare, le caratteristiche degli strumenti proposti dalle banche nell'ambito dei pagamenti internazionali
Fatigue investigation at high load ratio R of a quenched and tempered chromium molybdenum steel
No full textThe fatigue behavior at high number of cycles in elastic-plastic field of quenched and tempered carbon chromium steel was experimentally investigated for high performance reciprocating compressors application. Fatigue tests on un-notched specimens were performed both under load and strain controls, by imposing different levels of stress/strain and for each of them different values of stress ratios R, especially high values. Stress and strain trends have been monitored, during the fatigue life, and either ratcheting or relaxation, respectively, was evident. The stress control tests have resulted into fatigue fractures only for low values of R with significant ratcheting and an increasing rate during the final part of the test, thus the fracture could be considered as a synergy The fatigue behavior at high number of cycles in elastic-plastic field of quenched and tempered carbon chromium steel was experimentally investigated for high performance reciprocating compressors application. Fatigue tests on un-notched specimens were performed both under load and strain controls, by imposing different levels of stress/strain and for each of them different values of stress ratios R, especially high values. Stress and strain trends have been monitored, during the fatigue life, and either ratcheting or relaxation, respectively, was evident. The stress control tests have resulted into fatigue fractures only for low values of R with significant ratcheting and an increasing rate during the final part of the test, thus the fracture could be considered as a synergy between fatigue damage and plastic failure. On the contrary, the ratcheting stabilized for high values of R and the tests were finalized without any fracture. Within an intermediate region, for medium/high values of R, a minor ratcheting and the fracture transition have been found. Similarly, for the tests under strain control, low values of R showed fatigue fractures despite a considerable relaxation, conversely for high values of R, the relaxation was limited without any fracture. After reporting the tests on the Haigh plane, the Smith-Watson-Topper equation (SWT) provided the best prediction of the fatigue strength, at least until the intersection with the ultimate stress line, both under stress and strain control loadings. The cyclic behavior of the material was then investigated through several static and cyclic tests on plain specimens. A kinematic hardening Chaboche model, with three parameter couples, was proposed and the values of these parameters derived and discussed. Finally, other tests have been conducted on notched specimens with C geometry and blunt radius, again at high R values. FE analysis allowed the prediction of the stress evolution during the loading cycling, implementing the Chaboche model, and observing a combined effect of ratcheting and relaxation at the notch tip. The stabilized stresses were finally reported on the Haigh diagram and the results were found in agreement with the plain specimen fatigue line
Oxidative stability of long-chain fatty acids with different unsaturation degrees into layered double hydroxides
No full textNowadays, there is increasing evidence that the intake of essential fatty acids (FAs) and oleic acid has high nutritional importance. However, the vulnerability of these FAs to oxidation deserves special attention. FA oxidation may be avoided or delayed by intercalation of its anionic form in inorganic matrices as layered double hydroxides (LDH). Thus, the aim of the study was to evaluate the protective effects of MgAl LDH towards oleate (O), linoleate (L) and α-linolenate (Ln) degradation. The incorporation and the loading of different FAs in anionic form in LDH was determined by X-ray diffraction and thermogravimetric analysis (TGA), respectively. In order to study the selectivity of LDH towards the FA, the inorganic solid was equilibrated with a mixture of O, L and Ln (1:1:1). TGA and gas chromatography showed that Ln was preferentially intercalated. Free FA (FFA) and intercalated FA (IFA) were heated at 40◦C in the dark and then analyzed weekly for a maximum of 42 days. Their oxidative stability was evaluated by monitoring the primary and secondary oxidative compounds. The volatile compounds were determined by solid-phase microextraction, coupled with gas chromatography–mass spectrometry. Peroxide values were higher in FFA samples than in IFA samples, such as hexanal and trans,trans-2,4-heptadienal % contents. The results showed the potential of LDH intercalation for FA preservation from oxidative modification
L'attendibilità dell'FDT nell'analisi di screening del campo visivo in età pediatrica
No full textL'attendibilità dell'FDT nell'analisi di screening del campo visivo in età pediatric
Modelling of a Parallel Hybrid Power Audio Amplifier
No full textParallel audio amplifier are hybrid amplifiers thatcouple a linear and a switching stage with a parallel connection. Aproper control must be designed so that the voltage is controlledby the linear stage, while most of the current is driven by theswitching stage. So doing the overall architecture achieves thetypical efficiency of the switching stage and the distortion of thelinear stage. In summary a nice trade-off between efficiency anddistortion can be achieved, allowing to reduce heat dissipationkeeping a pleasant sound reproduction.The above purposes can be achieved only with a proper controlthat must set accurately the balance between the two stages, andits implementation is very critical. The paper deals with the modelof the hybrid audio amplifier architecture aiming at retriving themost critical items, and at defining simple relationships for theoptimal design of the amplifier.A prototype hybrid amplifier was realized, that confirms theeffectiveness of the proposed method
L'alimentazione delle Fonti di Poiano
No full textLe Fonti di Poiano sono le più grandi sorgenti carsiche dell’Emilia Romagna (portata media superiore ai 400 l/s) e presentano, per di più, la caratteristica di essere abbastanza “salate”. Per tutti questi motivi sono state studiate da oltre 150 anni al fine di definirne le caratteristiche idrodinamiche e idrochimiche, con particolare riguardo alla origine del cloruro di sodio. I numerosi precedenti studi, che avevano definito in maniera abbastanza esaustiva il meccanismo di alimentazione, non erano stati in grado di spiegare completamente la definizione spaziale del bacino di alimentazione, i percorsi sotterranei delle acque per raggiungere le sorgenti e soprattutto l’evoluzione della concentrazione del cloruro di sodio nel tempo, a breve e nel lungo periodo.
Tra le attività speleologiche del “Progetto Trias” svolto dalla Società Speleologica Italiana, una nuova ricerca idrogeologica basata su acquisitori automatici è stata condotta dall’autunno 2005 alla primavera 2008. In questo lasso di tempo, inoltre, si è ritrovata e monitorata un’altra sorgente solfurea, sempre salata (sorgente di Montelazzo), di cui si era persa la memoria da oltre un cinquantennio. Sulla base dei risultati di queste nuove indagini è stato innanzitutto possibile limitare l’area interessata al flusso sotterraneo agli affioramenti gessosi compresi tra Lucola, Sologno e Secchia, limitare l’alimentazione alle acque del Lucola (fortemente maggioritarie) e in misura minore a quelle del Sologno e di infiltrazione diretta sulla porzione a Sud degli affioramenti gessosi.
Si è poi dimostrato che l’evoluzione della concentrazione del cloruro di sodio nella acque di Poiano è controllata, sia nel breve che nel lungo periodo, dalla risalita diapirica delle gesso-anidriti triassiche, risalita attualmente attiva nell’area limitrofa a Poiano. Per la vicina sorgente di Montelazzo, invece, la componente salina deriva dallo scioglimento di lenti residuali di salgemma ad opera della acque di infiltrazione meteorica.
Per la prima volta poi si è ipotizzata una velocità media di risalita diapirica negli ultimi 400 anni valutata come minimo tra 5 e 1 cm/anno
Olea europea L. leaves as a source of functional compounds
No full textOlea europaea L. leaves are an attractive and readily available source of biologically active compounds. In particular, olive leaf polyphenols are a complex mixture of different compounds, among which secoiridoids, phenolic alcohols and flavonoids. Oleuropein and hydroxytyrosol are generally the most represented phenolic compound in leaves of different olive cultivars.
It has been reported that olive leaves have the highest antioxidant and scavenging power among the different parts of the olive tree. Beyond the antioxidant capacity, olive leaf extract has been reported to possess antihypertensive, antiatherogenic, anti-inflammatory, hypoglycemic, and hypocholesterolemic properties (El and Karakaya, 2009). These biologically active compounds can be used for the preparation of dietary supplements, nutraceuticals, functional food ingredients or cosmeceuticals. However, the chemical composition of olive leaves varies depending on several factors among which cultivar, geographical origin, leaf age, climatic conditions, moisture content and storage conditions (Papoti and Tsimidou, 2009).
The objective of the present work was to characterize the phenolic compounds and the antioxidant capacity in leaves from some Olea europaea L. cultivars, harvested in different times of the year. First of all, optimal conditions for extraction of olive leaves were determined using the Response Surface Methodology (RSM) and the considered parameters were: solvent composition, solid to solvent ratio and temperature. The antioxidant activity was assessed using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical scavenging assays. Total phenol content was determined using Folin-Ciocalteu assay while the analysis of individual phenol compounds was performed by HPLC-DAD-MS.
The results showed some significant differences between the selected cultivars both considering the phenol compounds and the antioxidant activity. During olive harvesting period, the highest values of polyphenol content and antioxidant activity were found in the samples from Dolce Agogia cultivar while the lowest values in Frantoio cultivar samples. Some relationship were observed between phenol compounds and antioxidant properties of the extracts
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