823 research outputs found
Optimization of thermochromic VO2 based structures with tunable thermal emissivity
In this paper, we design and simulate VO2/metal multilayers to obtain a large tunability of the thermal emissivity of infrared (IR) filters in the typical mid wave IR window of many infrared cameras. The multilayer structure is optimized to realise a low emissivity filter at high temperatures useful for military purposes. The values of tunability found for VO2/metal multilayers are larger than the value for a single thick layer of VO2. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4739489
Bound and free waves in non-collinear second harmonic generation
We analyze the relationship between the bound and the free waves in the
noncollinear SHG scheme, along with the vectorial conservation law for the
different components arising when there are two pump beams impinging on the
sample with two different incidence angles. The generated power is
systematically investigated, by varying the polarization state of both
fundamental beams, while absorption is included via the Herman and Hayden
correction terms. The theoretical simulations, obtained for samples which are
some coherence length thick show that the resulting polarization mapping is an
useful tool to put in evidence the interference between bound and free waves,
as well as the effect of absorption on the interference patternComment: 10 pages, 7 figure. to be published on Optics Expres
Heterotopic Pregnancy, It is Such a Rare Finding?
Heterotopic pregnancy is a multiple pregnancy with simultaneous implantation of the embryos at two or more distinct locations. Risk factors, epidemiology, signs, symptoms, sonographic findings and management options are reviewed. Literature data indicates an increase of the prevalence of heterotopic pregnancy and a trend increase toward sonographic diagnosis at an earlier stage, before rupture. In order to facilitate early diagnosis, the dictum âthink heterotopicâ is never overemphasized also in the sonographic evi- dence for an intrauterine pregnancy. Diagnostic vigilance is particularly recommended in in-vitro fertilization with multiple embryo transfer even in the case of intrauterine twin visualization. Finally management options are examined
Second harmonic generation from ZnO films and nanostructures.
Zinc oxide ZnO is a n-type semiconductor having a wide direct band gap (3.37 eV) as well as a
non-centrosymmetric crystal structure resulting from hexagonal wurtzite phase. Its wide transparency
range along with its second order nonlinear optical properties make it a promising material
for efficient second harmonic generation processes and nonlinear optical applications in general. In
this review, we present an extensive analysis of second harmonic generation from ZnO films and
nanostructures. The literature survey on ZnO films will include some significant features affecting
second harmonic generation efficiency, as crystalline structure, film thickness, surface contributes,
and doping. In a different section, the most prominent challenges in harmonic generation from ZnO
nanostructures are discussed, including ZnO nanowires, nanorods, and nanocrystals, to name a few.
Similarly, the most relevant works regarding third harmonic generation from ZnO films and nanostructures
are separately addressed. Finally, the conclusion part summarizes the current standing of
published values for the nonlinear optical coefficients and for ZnO films and nanostructures,
respectively
Severe Fetal Distress and Umbilical Cord Strangulation
We describe an extreme case of amniotic band syndrome, presented with fetal stress during labor and associated with strangulation of umbilical cord
Detection of second-order nonlinear optical magnetization by mapping normalized Stokes parameters
A measurable magnetic (nonlocal) contribution to the second harmonic generation (SHG) of nonmagnetic materials is an intriguing issue related to chiral materials, such as biomolecules. Here we report the detection of an intensity-dependent optically induced magnetization of a chiral bacteriorhodopsin film under femtosecond pulse excitation (830 nm) and far from the material's resonance. The analysis of the pump intensity-dependent noncollinear SHG signal, by means of the polarization map of normalized Stokes parameters, allows one to improve the detection of the nonlinear optical magnetization M (2 omega) contribution to the SHG signal. (c) 2013 Optical Society of Americ
On the compatibility of porous surfaces with cryogenic vacuum in future high-energy particle accelerators
Recently, pulsed laser processing of Cu samples has been demonstrated to produce rough surfaces whose structuring at the nanoscale ensures an impressive reduction of the secondary electron yield. This feature has an undoubted appealing for applications in future high energy particle accelerators. However, the effective application of such laser treated surfaces in this context requires a rigorous evaluation of their vacuum behavior, especially when used at cryogenic temperatures. To this aim, here, we compare thermal programmed desorption between 20 and 70âK by dosing Ar multilayers of different thicknesses on a laser treated copper substrate and on its flat counterpart. Our results highlight that the spongelike structural features confer to the laser treated sample's non-negligible effects due to the gas-substrate interaction. This results in a much vaster and higher desorption temperature range with respect to what is observed from the flat substrates. This evidence could render it very difficult to find temperature intervals for which detrimental vacuum transients could be avoided in the cryogenic beam pipes. On these bases, although the electron cloud mitigation efficiency has been settled, before definitely including porous surfaces in any cryogenic machine design, all the consequences of having a rough rather than a flat wall should be carefully evaluated
Produzione scientifica durante il dottorato di ricerca in medicina prenatale
Nellâelaborato finale del Dottorato di Ricerca in Medicina Prenatale ho seguito principalmente due rami di ricerca clinica: 1. La ricerca sullâutilizzo e lo sviluppo della plicometria ultrasonogrfica fetale. 2. Lo studio delle associazioni tra mutazioni (o condizioni) trombofiliche e lâinsorgere di patologie della gravidanza.
Nella prima applicazione ho studiato alcuni dei nuovi parametri plicometrici fetali proposti in letteratura negli ultimi anni. Ho implementato la tecnica di misura, contribuendo alla sua standardizzazione. In seguito ho prodotto tavole biometriche di riferimento nelle successive epoche di gravidanza, sia in condizioni di normalitĂ , sia in pazienti con diabete gestazionale. Ho condotto uno studio sui cambiamenti dei compartimenti corporei fetali in caso di ritardo di crescita. Ho inoltre studiato il potenziale beneficio (in termini di accuratezza diagnostica) dellâuso dei parametri plicometrici fetali nei preesistenti modelli di stima del peso fetale. Da ultimo ho prodotto un algoritmo per la predizione del peso alla nascita, introducendovi anche uno dei parametri plicometrici da me studiati. I risultati della mia ricerca in questo campo vengono esposti in 4 articoli editati su stampa internazionale dal 2003 al 2007, proprio in corso del Dottorato di Ricerca in oggetto.
Nella seconda applicazione ho studiato lâassociazione tra trombofilia ed esiti avversi della gravidanza. I due lavori presentati nel seguente documento hanno timbro epidemiologico e mostrano in comune lo stesso set di pazienti, ma differente analisi statistica. In questo attuale campo la mia ricerca sta procedendo. Due manoscritti sono in coso di valutazione e trattano dellâassociazione tra trombofilia ed alterata funzione renale in gravidanza.
Sempre nella stessa tesi di Dottorato di Ricerca mi preme mostrare alcuni case report relativi ad interessanti casi clinici occorsi alla mia visione nel corso di studi in oggetto, ed aventi come tema principale la patologia cordonale.
Da ultimo presento gli atti del congresso ISUOG (International Society of Ultrasounds in Obst/Gyn) riguardanti nuove tecniche ecografiche di monitoraggio per interventi endoscopici in pazienti infertili.The results and conclusive reports of my Phellowship in Perinatal Medicine are enclosed within the final manuscript of the following thesis.
My main research application fields were: 1. The study of fetal skinfolds by means of ultrasound evaluation. 2. The study of the impact of thrombophilias in pregnancy.
My former research field dealed with the study of the fetal subcutaneous tissues and their detection by ultrasounds. I spent part of my Phellowship analyzing whether these innovative ultrasound parameters could add more informations to the worldwide used birthweight estimating conventional algorithms. Thus, the targets of my research in this first field were: to analyze the behaviour of fetal compartments in different physiological or pathological gestational conditions; to analyze the usefulness of the fetal skinfolds in ameliorating pre-existing birthweight estimating formulae; to build-up a mathematical model to predict term neonatal weight as a result of an integration between traditional and innovative fetal US parameters.
The sum of my findings is elucidated in 4 published papers edited from year 2003 to year 2007.
The latter research field deals with the correlation between connatal thrombophilias and the occurrence of adverse pregnancy outcomes. In fact by now I can show the result of this research by presenting two works that share the same setting with a different statistical viewpoint. The research is going on and other 2 manuscripts are away to be evaluated by the referees.
Moreover, within the same document I show some clinical cases published as case reports (with or without a review), most of them dealing with umbilical cord pathologies.
Eventually I bring also some proceedings from Congresses from the International Society of Ultrasound in Obstetrics and Gynaecology, also edited by the ISUOG official magazine
SEY and low-energy SEY of conductive surfaces
Abstract The study of Secondary Electron Yield (SEY) is widely performed to address important properties of materials to be used in a very wide spectrum of applications. It is, therefore, extremely important to understand the SEY dependence on material type, surface contaminants, structural quality and surface damage. We review here our recent studies of such items performed by looking at some representative conductive materials as noble metals and carbon based surfaces. Polycrystalline Ag, Au and Cu samples have been studied as introduced in the ultra-high vacuum chamber (therefore with an significant surface contamination) and after having been cleaned by ion sputtering. The comparison between the curves confirms that the SEY behavior is strongly influenced by the chemical state of the metal surfaces. We demonstrate the ability of SEY to determine work function values with high accuracy if the experimental system allows using very slow primary electrons. We also investigated, for the Cu sample, the effect on SEY of minimal amount of contaminants in the sub-monolayer regime showing that SEY is highly sensitive to the presence of adsorbates even at such very low coverages, specially for low energy primary electrons. In the case of C surfaces we summarize here the effect that the structural ordering of the C lattice has on the macroscopic SEY properties of ultrathin C layers. In particular we followed the SEY evolution during the thermal graphitization of thin amorphous carbon layers and during the amorphization of highly oriented pyrolytic graphite by means of Ar+ bombardment. In the first case the SEY decrease observed with the progressive conversion of sp3 hybrids into six-fold aromatic domains was related to the electronic structure of the C-films close to the Fermi level. We found that a moderate structural quality of the C layer, corresponding to aromatic clusters of limited size, is sufficient to obtain a SEY as low as âŒ1. For the bombarded graphite, the strong lattice damage remains limited to the near surface layer, where the high density of defects reduces the transport of incoming and secondary electrons. Then, the SEY curves resulted differently modified in the low and high primary energy regions, but their maximal values remained favorably low. Our findings demonstrate that SEY, besides being an indispensable mean to qualify technical materials in many technological fields, can be also used as a flexible and advantageous diagnostics to probe surfaces and interfaces
The Chemical Origin of SEY at Technical Surfaces
The secondary emission yield (SEY) properties of colaminated Cu samples for
LHC beam screens are correlated to the surface chemical composition determined
by X-ray photoelectron spectroscopy. The surface of the "as received" samples
is characterized by the presence of significant quantities of contaminating
adsorbates and by the maximum of the SEY curve (dmax) being as high as 2.2.
After extended electron scrubbing at kinetic energy of 10 and 500 eV, the dmax
value drops to the ultimate values of 1.35 and 1.1, respectively. In both cases
the surface oxidized phases are significantly reduced, whereas only in the
sample scrubbed at 500 eV the formation of a graphitic-like C layer is
observed. We find that the electron scrubbing of technical Cu surfaces can be
described as occurring in two steps, where the first step consists in the
electron induced desorption of weakly bound contaminants that occurs
indifferently at 10 and at 500 eV and corresponds to a partial decrease of
dmax, and the second step, activated by more energetic electrons and becoming
evident at high doses, which increases the number of graphitic-like C-C bonds
via the dissociation of adsorbates already contaminating the "as received"
surface or accumulating on this surface during irradiation. Our results
demonstrate how the kinetic energy of impinging electrons is a crucial
parameter when conditioning technical surfaces of Cu and other metals by means
of electron induced chemical processing.Comment: 6 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop
on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba,
Italy; CERN Yellow Report CERN-2013-002, pp.99-10
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