Using ion beams to tune the nanostructure and optical response of co-deposited Ag : BBBN thin films

The present study is devoted to co-deposited Ag : BN nanocermet thin films and is focused on the influence of ion irradiation conditions on their structural and linear optical properties. Ion irradiation was performed in situ during the growth of the nanocermets using a 50 eV assistance beam (nitrogen/argon or nitrogen-ion assistance) and ex situ on as-grown films using a 120 keV argon-ion beam (post-irradiation). Grazing incidence small-angle x-ray scattering measurements show that (i) as-grown N-assisted films contain prolate spheroidal clusters (height-to-diameter ratio H/D ≈ 1.8), (ii) N/Ar-ion assistance leads to the formation of more elongated clusters (H/D ≈ 2.1) and (iii) post-irradiation leads to a decrease of H/D to a value close to 1. These results are discussed on the basis of atomic diffusion processes involved during the growth of the nanocermets and during the post-irradiation. The optical transmittance spectra of these films measured at normal incidence display one absorption band, due to the excitation of the (1,1) plasmon mode of the clusters. In the case of the as-grown films, an additional band appears at oblique incidence for P-polarized light, as a consequence of the excitation of the (1,0) plasmon mode of the clusters. Our results show that the spectral position of the absorption bands (which can be tuned in the 400-600 nm range) depends on the H/D ratio of the clusters, in good agreement with calculations of optical transmittance considering the nanocomposite layer as a uniaxial anisotropic medium whose dielectric tensor is described by an anisotropic Maxwell-Garnett model. © 2007 IOP Publishing Ltd.The authors would like to thank CNRS-CSIC and Picasso programmes for financial support which permitted the collaboration between the Instituto de Ciencia de Materiales de Sevilla (Spain) and the Laboratoire de Metallurgie Physique ´ de Poitiers (France). The authors also thank J P Simon and the D2AM staff at the ESRF for their support during the GISAXS measurements.Peer Reviewe

Self-organization and optical response of silver nanoparticles dispersed in a dielectric matrix

Abstract. Double ion-beam sputtering has been used to fabricate nanocermet multilayers consisting of silver nanoparticles sandwiched between Si 3 N 4 dielectric layers. The organization of the nanoparticles has been studied in detail by quantitative analysis of transmission electronic microscopy and atomic force microscopy images. Our results show that the nanoparticles deposited on a plane surface present an isotropic macroscopic in-plane organization while their vertical arrangement displays a topology-induced self-organization. The use of faceted alumina substrates with periodic hill-and-valley structures results in the formation of linear chains of silver particles along the valleys. In that case, transmission optical measurements reveal in-plane anisotropy

Cardiovascular responses during rest-exercise and exercise-exercise transients

If indeed vagal withdrawal determines the rapid response to exercise (phase I), the a large reduction, if not complete suppression, of phase I should be found, when an exercise transient starts from a previous lower steady state exercise rather than from rest. On 15 healthy young subjects we measured beat-by-beat cardiac output (Q̇, Modelflow from Portapres data) and heart rate (fH, ECG) during these cycle ergometer exercise transients: 0–50 W (transient from rest, RT) and 50–100W (transient from exercise, ET). A double exponential was used to compute amplitudes and time constants of phase I and II (A1 and A2; T1 and T2). At steady state, fH was 87.510.4, 109.312.0, and 139.617.1bpm, and Q̇ was 7.31.5, 12.61.6, and 16,11,9L/min, at rest, 50W and 100W, respectively. In RT, A1 and A2 for fH were 11.78.6 and 11.34.7bpm; the corresponding T1 and T2 were 1.61.9 and 14.421.3s. For Q̇, we had: A1=4.01.8L/min, A2=1.51.4L/min, T1=3.21.8s, T2=11.312.2s. In ET, the double exponential model provided preposterous A1 and T1 values and extremely high T2 values (>100s). Subsequent use of a mono exponential model provided, for fH, A=29.78.9bpm and T=7.74.9s, and for Q̇, A=3.58.6L/min, and T=7.05.7s. The A and T in ET did not differ from the A2 and T2 of RT. We conclude that a single exponential model is more adequate to describe ET and this single exponential corresponds to the second exponential of RT. Our results are compatible with the vagal withdrawal hypothesis

Plasma-enhanced chemical vapor deposition of SiO2 from a Si(CH3)3Cl precursor and mixtures Ar/O2 as plasma gas

Silicon dioxide thin films have been prepared at room temperature by remote plasma-enhanced chemical vapor deposition in a downstream reactor by using Si(CH3)3Cl as a volatile precursor and a microwave electron cyclotron resonance external source. Experiments are done at constant pressure by changing the relative amount of Ar species R in the plasma gas. The aim was to obtain thin films with low density and, therefore, low refractive index. Characterization of the species of the plasma is carried out by optical emission spectroscopy. The changes of the plasma conditions are correlated with the growing rate and microstructure of the films, the latter determined by atomic force microscopy and infrared spectroscopy. It is found that the growing rate of the films decreases and their roughness increases as R increases. The optical properties of SiO2 thin films are analyzed by optical ellipsometry. A decrease in the refractive index is found for the films grown with high values of R. The possible routes for activation of the precursor and the formation of the SiO2 thin films are discussed.Ministerio de Ciencia y Tecnología MAT2001-2820European Union ERK6-CT-1999-0001

LIFESTYLE ASSESSMENT AND IMPROVEMENT WITH FOCUS ON LEISURE TIME PHYSICAL ACTIVITY AMONG UNIVERSITY STUDENTS: THE #STUDIOXLAVITA PROJECT

INTRODUCTION: Sedentariness, smoking, alcohol abuse and unbalanced feeding are harmful for health, leading to chronic diseases and increasing mortality rate. For young adults, University is a new social and cultural context: parents’ imprinting could be easily altered, new lifestyles take shape and personal choices emerge. Intervention programmes to advance awareness on harmful lifestyle and promote healthy habits are essential. The #studioxlavita project, launched in 2016 by the University of Brescia with these purposes, investigated students’ lifestyle, with special emphasis on physical activity . METHODS: We developed two consecutive facultative surveys, of 15 <1st level> and 52 items <2nd level>, addressed to all the University’s students. Questions were about leisure time physical activity , use of fitness technology, relationship with friends, classmates and parents, feed, physical appearance, body self-perception, physical and mental health, use of certain substances or products , night-time rest and beliefs concerning healthy behaviours. In the 2nd level survey we also adopted the Kessler Psychological Distress Scale and the short form of the International Physical Activity Questionnaire to estimate the amount of PA carried out in the last 7 days. Students who filled in both questionnaires received a personal report including the aggregate data analysis, a comparison with other investigations and indications about healthy habits, according to recommendations and guidelines. RESULTS: 3,436 out of 15,688 students filled in the1st level survey. Of them, 778 accepted to participate in the 2nd level survey, and 456 completed it. 1st level survey revealed that 72% of the students practised LTPA <45% regularly and 27% occasionally>. LTPA is largely performed <44% of the student> in non-competitive form, with recreational and/or health purposes. According to IPAQ-SF categorical score, 24%, 34% and 42% of the students performed low, moderate and high levels of PA, respectively. In 2st level survey, 76% of the students wished to practise more PA; 42% would participate in practical sport courses. CONCLUSION: University is an ideal setting for promoting lifestyle change among a captive audience. Intervention programs to increment PA are acclaimed by students. The students from University of Brescia reported higher LTPA practice than the national average people between 18 and 34 years <47%, data from Italian National Institute of Statistics, 2015>, although this parameter was assessed with different methods

EFFECTS OF PHYSICAL ACTIVITY PROMOTION AMONG UNIVERSITY STUDENTS: THE #STUDIOXLAVITA PROJECT

INTRODUCTION: Sedentariness is a major health problem in our time and physical activity promotion is an imperative commitment for healthcare systems. Recommendations from WHO indicate a minimum of 150 minutes of moderate intensity aerobic exercise as weekly standard for adults. Strategies to increment PA practice are implemented in different settings, such as house care, school, University and workplace. The project #studioxlavita <#SXLV> was launched by the University of Brescia in 2016 with the aim of collecting data about undergraduates lifestyle and encourage healthy behaviours. In particular we focused on PA assessment and promotion in a Universitybased setting. METHODS: Two consecutive surveys were sent to all students . Q0 included the short form of the International Physical Activity Questionnaire , the Kessler Psychological Distress Scale and additional questions on several lifestyle aspects. Among responders, we selected 40 students who agreed to take part in one of the following 15-week practical sport courses: ultimate frisbee, muscle strengthening and dance fitness. Before and after being engaged in practical sport courses, students underwent cardiopulmonary exercise test and skinfold thickness measurements, in order to assess peak oxygen consumption and percent body fat . Finally, to assess possible lifestyle changes, we sent them additional surveys at the end of the practical sport courses and 30 days after . Paired t-test was used to analyse significant differences. RESULTS: 27 students <16 female, 11 male; age: 22.7±3.7> concluded sport activity courses and filled in Q1. Of them, 20 completed also Q2. Overall courses attendance was 57%. At T1 , normalized Q̇O2peak increased with respect to T0 <37.0±6.9 vs 35.2±7.4 ml/min/Kg, p=0.03>. Conversely, percent body fat decreased <16.5±6.4 vs 18.3±7.5, p=0.01>. In Q1, 20 students declared to have a more active lifestyle since the beginning of the courses. In Q2, IPAQ-SF-derived total weekly energy expenditure was higher than in Q0, although not significant <5,839 ±7,035 MET*min vs 2,770±2,457 MET*min, p=0.1>. Q2 showed a reduced K6 scale score with respect to Q0 <13.8±4.6 vs 15.8±4.9, p=0.03>. CONCLUSION: With the sport activity courses established in #SXLV we gave students the opportunity to comply with WHO recommendations. After courses, they appeared to practice more PA, have a higher maximal aerobic capacity, a lower percent body fat and a lower grade of psychological distress than before courses. Simple activities as those proposed by #SXLV are sufficient to reduce sedentariness and improve the quality of life of student

When ellipsometry works best: a case study with transparent conductive oxides

As the library of potential materials with plasmonic behavior in the infrared (IR) grows, we must carefully assess their suitability for nanophotonic applications. This assessment relies on knowledge of the materials’ optical constants, best determined via spectroscopic ellipsometry (SE). Transparent conductive oxides are great candidates for IR plasmonics due to their low carrier concentration (compared to noble metals) and the ability to tailor their carrier concentration by manipulating the defect composition. When the carrier concentration becomes low enough, phonon and defect states become the dominant mechanisms of absorption in the IR spectral range, leading to near-IR (NIR) tailing effects. These NIR tailing effects can be misinterpreted for free carrier absorption, rendering NIR-visible-ultraviolet-SE (NIR-VIS-UV-SE) incapable of reliably extracting the carrier transport properties. In this work, we report the limitations of NIR-VIS-UV and IR-SE (in terms of carrier concentration) by investigating the transport mechanisms of indium tin oxide, aluminum-doped zinc oxide and gallium-doped zinc oxide. We find regions of carrier concentration where NIR-VIS-UV-SE cannot reliably determine the transport properties and we designate material-dependent and application-specific confidence factors for this case. For IR-SE, the story is more complex, and so we investigate the multifaceted influences on the limitations, such as phonon behavior, grain size, presence of a substrate, film thickness, and measurement noise. Finally, we demonstrate the importance of identifying the IR optical constants directly via IR-SE (rather than by extrapolation from NIR-VIS-UV-SE) by means of comparing specific figures of merits (Faraday and Joule numbers), deemed useful indicators for plasmonic performance

Positioning variation modeling for aircraft panels assembly based on elastic deformation theory

Dimensional variation in aircraft panel assembly is one of the most critical issues that affects the aerodynamic performance of aircraft, due to elastic deformation of parts during the positioning and clamping process. This paper proposes an assembly deformation prediction model and a variation propagation model to predict the assembly variation of aircraft panels, and derives consecutive 3-D deformation expressions which explicitly describe the nonlinear behavior of physical interaction occurring in compliant components assembly. An assembly deformation prediction model is derived from equations of statics of elastic beam to calculate the elastic deformation of panel component resulted from positioning error and clamping force. A variation propagation model is used to describe the relationship between local variations and overall assembly variations. Assembly variations of aircraft panels due to positioning error are obtained by solving differential equations of statics and operating spatial transformations of the coordinate. The calculated results show a good prediction of variation in the experiment. The proposed method provides a better understanding of the panel assembly process and creates an analytical foundation for further work on variation control and tolerance optimization

Gravitational waves from single neutron stars: an advanced detector era survey

With the doors beginning to swing open on the new gravitational wave astronomy, this review provides an up-to-date survey of the most important physical mechanisms that could lead to emission of potentially detectable gravitational radiation from isolated and accreting neutron stars. In particular we discuss the gravitational wave-driven instability and asteroseismology formalism of the f- and r-modes, the different ways that a neutron star could form and sustain a non-axisymmetric quadrupolar "mountain" deformation, the excitation of oscillations during magnetar flares and the possible gravitational wave signature of pulsar glitches. We focus on progress made in the recent years in each topic, make a fresh assessment of the gravitational wave detectability of each mechanism and, finally, highlight key problems and desiderata for future work.Comment: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and Astrophysics of Neutron Stars", NewCompStar COST Action 1304. Minor corrections to match published versio