High Luminescence in Small Si/SiO2 Nanocrystals: A Theoretical Study

In recent years many experiments have demonstrated the possibility to achieve efficient photoluminescence from Si/SiO2 nanocrystals. While it is widely known that only a minor portions of the nanocrystals in the samples contribute to the observed photoluminescence, the high complexity of the Si/SiO2 interface and the dramatic sensitivity to the fabrication conditions make the identification of the most active structures at the experimental level not a trivial task. Focusing on this aspect we have addressed the problem theoretically, by calculating the radiative recombination rates for different classes of Si-nanocrystals in the diameter range of 0.2-1.5 nm, in order to identify the best conditions for optical emission. We show that the recombination rates of hydrogenated nanocrystals follow the quantum confinement feature in which the nanocrystal diameter is the principal quantity in determining the system response. Interestingly, a completely different behavior emerges from the OH-terminated or SiO2-embedded nanocrystals, where the number of oxygens at the interface seems intimately connected to the recombination rates, resulting the most important quantity for the characterization of the optical yield in such systems. Besides, additional conditions for the achievement of high rates are constituted by a high crystallinity of the nanocrystals and by high confinement energies (small diameters)

The Influence of Silicon Nanoclusters on the Optical Properties of a-SiNx Samples: A Theoretical Study

By means of ab-initio calculations we investigate the optical properties of pure a-SiN$_x$ samples, with $x \in [0.4, 1.8]$, and samples embedding silicon nanoclusters (NCs) of diameter $0.5 \leq d \leq 1.0$ nm. In the pure samples the optical absorption gap and the radiative recombination rate vary according to the concentration of Si-N bonds. In the presence of NCs the radiative rate of the samples is barely affected, indicating that the intense photoluminescence of experimental samples is mostly due to the matrix itself rather than to the NCs. Besides, we evidence an important role of Si-N-Si bonds at the NC/matrix interface in the observed photoluminescence trend

Recent advances in understanding lung function development

Recent years have witnessed critical contributions to our understanding of the determinants and long-term implications of lung function development. In this article, we review studies that have contributed to advances in understanding lung function development and its critical importance for lung health into adult life. In particular, we have focused on early life determinants that include genetic factors, perinatal events, environmental exposures, lifestyle, infancy lower respiratory tract infections, and persistent asthma phenotypes. Longitudinal studies have conclusively demonstrated that lung function deficits that are established by school age may track into adult life and increase the risk of adult lung obstructive diseases, such as chronic obstructive pulmonary disease. Furthermore, these contributions have provided initial evidence in support of a direct influence by early life events on an accelerated decline of lung function and an increased susceptibility to its environmental determinants well into adult life. As such, we argue that future health-care programs based on precision medicine approaches that integrate deep phenotyping with tailored medication and advice to patients should also foster optimal lung function growth to be fully effective

Local-field effects in silicon nanoclusters

The effect of the local fields on the absorption spectra of silicon nanoclusters (NCs), freestanding or embedded in SiO2, is investigated in the DFT-RPA framework for different size and amorphization of the samples. We show that local field effects have a great influence on the optical absorption of the NCs. Their effect can be described by two separate contributions, both arising from polarization effects at the NC interface. First, local fields produce a reduction of the absorption that is stronger in the low energy limit. This contribution is a direct consequence of the screening induced by polarization effects on the incoming field. Secondly, local fields cause a blue shift on the main absorption peak that has been explained in terms of perturbation of the absorption resonance conditions. Both contributions do not depend either on the NC diameter nor on its amorphization degree, while showing a high sensitivity to the environment enclosing the NCs

General properties of overlap probability distributions in disordered spin systems. Toward Parisi ultrametricity

For a very general class of probability distributions in disordered Ising spin systems, in the thermodynamical limit, we prove the following property for overlaps among real replicas. Consider the overlaps among s replicas. Add one replica s+1. Then, the overlap q(a,s+1) between one of the first s replicas, let us say a, and the added s+1 is either independent of the former ones, or it is identical to one of the overlaps q(a,b), with b running among the first s replicas, excluding a. Each of these cases has equal probability 1/s.Comment: LaTeX2e, 11 pages. Submitted to Journal of Physics A: Mathematical and General. Also available at http://rerumnatura.zool.su.se/stefano/ms/ghigu.p

IL DIBATTITO GIUSFILOSOFICO TRA CARL SCHMITT, HANS KELSEN E RUDOLF SMEND SULLO SFONDO DELLA CRISI DELLA REPUBBLICA DI WEIMAR

Il presente lavoro di ricerca affronta il pensiero giusfilosofico di Carl Schmitt, Hans Kelsen e Rudolf Smend durante il periodo weimariano, nella prospettiva prioritaria di rendere visibile l\u2019attualit\ue0 dell\u2019esperienza costituzionale della Repubblica di Weimar, qualificata come laboratorio delle idee e dei fatti che rendono comprensibile la realt\ue0 delle costituzioni europee continentali post-belliche e la crisi delle odierne democrazie costituzionali, mostrando i pericoli, allora latenti, che oggi si palesano per lo Stato costituzionale democratico. Il dibattito giusfilosofico weimariano assume un\u2019importanza di portata universale, in quanto seppur si anima in una situazione costituzionale specifica produce riflessioni valide per ogni specie di sistema democratico-costituzionale che volti le spalle a vecchi regimi politici o che richieda, per mancanza di equilibrio fra poteri, aggiustamenti in corso d\u2019opera e solleva antichi problemi ancora irrisolti nell\u2019et\ue0 moderna. Nel rappresentare l\u2019importanza e l\u2019attualit\ue0 del laboratorio di Weimar, viene sviluppata la trattazione dei temi dello Stato, dell\u2019equilibrio dei poteri, della democrazia, del costituzionalismo, dei diritti fondamentali, del custode della costituzione, delle forme di governo e di stato e della crisi politico-costituzionale, muovendo dal contesto storico weimariano e sulla base delle teorie dei tre Autori scelti. Dunque, si intende saldare in un unico contributo scientifico i fatti con le idee propri del laboratorio Weimar, tramite un approccio interdisciplinare, s\uec da porre in relazione le teorie giuridico-filosofiche di tre giganti weimariani e il dibattito che ne \ue8 scaturito con il contesto storico, politico, costituzionale, istituzionale, culturale, economico e sociale della Repubblica di Weimar, e la relativa crisi costituzionale, la sua eredit\ue0 e le sue lezioni, la cui analisi costituisca luogo di comprensione dell\u2019attuale crisi delle democrazie costituzionali e momento di riflessione su adeguate soluzioni teoriche, andando a scorgere i pericoli per lo Stato costituzionale democratico. Un siffatto studio si configura, quindi, come un Forschungsdesiderat nel panorama giusfilosofico. La struttura del presente lavoro di ricerca poggia su un\u2019interazione fra ricostruzione storico-costituzionale, analisi teorico-costituzionale e riflessione giuridico-filosofica, coniugando diversi approcci scientifici (filosofia del diritto, diritto costituzionale, filosofia politica, storia costituzionale e teoria costituzionale). Specifica della presente trattazione \ue8 la tesi che gran parte dei temi discussi nelle teorie dei tre Autori sono i medesimi dell\u2019attuale dibattito a livello giusfilosofico e giuspubblicistico, al punto da avanzare la convinzione che i rischi per la democrazia costituzionale, gi\ue0 individuati a Weimar nella forma del totalitarismo, siano ora incombenti sotto altre forme sugli attuali sistemi democratici costituzionali

Clinical use of parnaparin in major and minor orthopedic sugery: a review

Patients undergoing arthroplasty or other orthopedic surgery show a high risk of venous thromboembolism (VTE), involving mortality, morbidity, and social costs; however, the risk for VTE in minor orthopedic surgery should not be underestimated and antithrombotic prophylaxis may be required. According to the literature, low-molecular-weight heparins (LMWHs) are more effective in preventing VTE than unfractionated heparins (UFHs) or vitamin K antagonists, and have a lower hemorrhagic risk. By comparing different prophylactic regimens, it has been shown that starting the prophylaxis near the time of the operation is the most critical point for efficacy, whether or not the first dose is administered pre- or post-operatively. Moreover, most thromboembolic complications are observed after discharge and, therefore, many clinicians advocate continuing prophylaxis for longer times (6–8 weeks) in order to further reduce the rate for VTE. The literature on parnaparin, a new LMWH, in VTE prophylaxis was reviewed. Parnaparin is equally effective as UFH, but it offers the advantages of a once-daily administration and improved tolerability, thus allowing the home management of patients with no need for laboratory coagulation tests

FACILE FUNCTIONALIZATION OF sp2 CARBON ALLOTROPES WITH A BIOBASED JANUS MOLECULE

A simple, versatile, sustainable, not expensive method for the functionalization of sp2 carbon allotropes, both nanosized and nano-structured, without altering their bulk crystalline organization, is presented. Carbon materials available at the commercial scale were used: furnace carbon black (CB), nano-sized graphite with high surface area, and multiwalled carbon nanotubes. A bio-sourced molecule, 2-(2,5-dimethyl-1H-pyrrol-1-yl)-1,3-propanediol (serinol pyrrole), was used for the functionalization. Serinol pyrrole (SP) was obtained from serinol through a reaction with atomic efficiency of about 82%, performed in the absence of solvents or catalysts. Synthesis of serinol pyrrole was performed as well on carbon allotropes as the solid support. Adducts of serinol pyrrole with a carbon allotrope were prepared with the help of either thermal or mechanical energy. Functionalization yield was in all cases larger than 90%. With such adducts, stable dispersions in water and inNRlatex were prepared.Afew layers of graphene were isolated from the water dispersions, and NR-based composites precipitated from the latex revealed very even distribution of fine graphitic particles. Composites were prepared, based on NR, IR, andBRas the rubbers andCBand silica as the fillers, with different amounts of CB–SPadduct, and were cross-linked with a sulfur-based system without observing appreciable effect of functionalization on vulcanization kinetics. The CB–SP adduct led to appreciable reduction of the Payne effect

Universal low-frequency vibrational modes in silica glasses

It was recently shown that different simple models of glass formers with binary interactions define a universality class in terms of the density of states of their quasi-localized low-frequency modes. Explicitly, once the hybridization with standard Debye (extended) modes is avoided, a number of such models exhibit a universal density of state, depending on the mode frequencies as $D(\omega) \sim \omega^4$. It is unknown however how wide is this universality class, and whether it also pertains to more realistic models of glass formers. To address this issue we present analysis of the quasi-localized modes in silica, a network glass which has both binary and ternary interactions. We conclude that in 3-dimensions silica exhibits the very same frequency dependence at low frequencies, suggesting that this universal form is a generic consequence of amorphous glassiness.Comment: 4 pages, 5 figures, Submitted in parallel to "Universality of the nonphononic vibrational spectrum across different classes of computer glasses" to arXiv on March 17th, 202