Oxidation of sulphur dioxide in water droplets in the presence of ammonia

SO2 oxidation by oxygen in monodisperse water droplets was studied in a cylindrical chamber, without and in the presence of ammonia. The range of SO2 concentration was from about 1022 to 5 ppmv, while the NH3 input concentration was kept constant at about 4.731022 ppmv. The contact time between gases and droplets was 210 s. The experimental results were compared with the theoretical values predicted by the kinetics of Larson et al. (Atmos. Environ., 12 (1978) 1597) and McKay (Atmos. Environ., 5 (1971) 7). Much higher sulphate concentrations were obtained in experiments run in the presence of NH3, as opposed to those without NH3. The experimental results agree with the values predicted by McKay’s kinetics and are higher than Larson’s

Inhomogeneous mechanical losses in micro-oscillators with high reflectivity coating

We characterize the mechanical quality factor of micro-oscillators covered by a highly reflective coating. We test an approach to the reduction of mechanical losses, that consists in limiting the size of the coated area to reduce the strain and the consequent energy loss in this highly dissipative component. Moreover, a mechanical isolation stage is incorporated in the device. The results are discussed on the basis of an analysis of homogeneous and non-homogeneous losses in the device and validated by a set of Finite-Element models. The contributions of thermoelastic dissipation and coating losses are separated and the measured quality factors are found in agreement with the calculated values, while the absence of unmodeled losses confirms that the isolation element integrated in the device efficiently uncouples the dynamics of the mirror from the support system. Also the resonant frequencies evaluated by Finite-Element models are in good agreement with the experimental data, and allow the estimation of the Young modulus of the coating. The models that we have developed and validated are important for the design of oscillating micro-mirrors with high quality factor and, consequently, low thermal noise. Such devices are useful in general for high sensitivity sensors, and in particular for experiments of quantum opto-mechanics

Detection of weak stochastic force in a parametrically stabilized micro opto-mechanical system

Measuring a weak force is an important task for micro-mechanical systems, both when using devices as sensitive detectors and, particularly, in experiments of quantum mechanics. The optimal strategy for resolving a weak stochastic signal force on a huge background (typically given by thermal noise) is a crucial and debated topic, and the stability of the mechanical resonance is a further, related critical issue. We introduce and analyze the parametric control of the optical spring, that allows to stabilize the resonance and provides a phase reference for the oscillator motion, yet conserving a free evolution in one quadrature of the phase space. We also study quantitatively the characteristics of our micro opto-mechanical system as detector of stochastic force for short measurement times (for quick, high resolution monitoring) as well as for the longer term observations that optimize the sensitivity. We compare a simple, naive strategy based on the evaluation of the variance of the displacement (that is a widely used technique) with an optimal Wiener-Kolmogorov data analysis. We show that, thanks to the parametric stabilization of the effective susceptibility, we can more efficiently implement Wiener filtering, and we investigate how this strategy improves the performance of our system. We finally demonstrate the possibility to resolve stochastic force variations well below 1% of the thermal noise

An ultra-low dissipation micro-oscillator for quantum opto-mechanics

Generating non-classical states of light by opto-mechanical coupling depends critically on the mechanical and optical properties of micro-oscillators and on the minimization of thermal noise. We present an oscillating micro-mirror with a mechanical quality factor Q = 2.6x10^6 at cryogenic temperature and a Finesse of 65000, obtained thanks to an innovative approach to the design and the control of mechanical dissipation. Already at 4 K with an input laser power of 2 mW, the radiation-pressure quantum fluctuations become the main noise source, overcoming thermal noise. This feature makes our devices particularly suitable for the production of pondero-motive squeezing.Comment: 21 pages including Supplementary Informatio

SO2 oxidation in supercooled droplets in the presence of O2

Sulphur dioxide oxidation in supercooled monodisperse droplets at T4213 7C was studied in the presence of oxygen. The SO2 concentration was found to range from 0.08 to 7.1 ppmv and the contact time between gases and droplets was 210 s. The experimental results showed that sulphate concentration due to SO2 oxidation is independent of temperature, i.e. the increase of SO2 solubility in the liquid phase balances the rate constant decrease of the oxidation reaction. Following McKay’s kinetics (Atmos. Environ., 5 (1971) 7), we calculated the rate constant at T4213 7C and the activation energy. A comparison was made between experimental S(VI) oxidation concentrations due to oxygen and theoretical oxidation values due to O3, H2O2 and oxygen in the presence of catalyzers (Fe31, Mn21)

Ballistic accretion on a point seed

We carefully discuss the two-dimensional ballistic aggregation process. Studying the microscopic discrete process, we theoretically derive the probability density function describing the single-particle accretion. Using this function, we describe the properties of the “fan”, obtained for ballistic aggregation on the single seed, and we predict its mean density and its opening angle. We discuss the shadowing effect on a microscopic scale, between the single particles and, on a larger scale, between grown structures, deriving the columnar microstructure direction law. Comparisons with numerical experiments are shown

EXPERIENCING HERITAGE DYNAMIC THROUGH VISUALIZATION

Abstract. The present article aims to consider the added value attached to the usage of new technologies in a project aimed to study heritage. Indeed, multimedia devices could be used to create representations useful to develop and disseminate information integrating the architectural and territorial framework and to reach a general understanding.The processed data come from a research project, based on an interdisciplinary approach, address to the study of medieval buildings in Armenia, Vayots Dzor region, with the aim of studying and understanding the cultural heritage.Three different technologies are used to visualize and disseminate the results of the analyses carried out: the video, the hologram, and the virtual reality. These digital visualization methods enable experts to make the topics investigated accessible and comprehensible to a wider general public with a didactic and informative aim.The solid 3D-model of the site allows to virtually reproduce the reality and to provide a spatial perception of the site. Indeed, it is a neutral base, represents the morphological conformation and settlements, a landscape whose reference points are easily identified with the historical architectures, helping the public and spectators to get oriented inside the territory. These methods of representation allow to move from general view to particular, or to a different frame appropriate to the addressed topic. Thus, it binds the scientific research with the visual part, and enable communication, even in a context where it is difficult to use a common spoken or written language.</p

Measurements of atmospheric aerosol in the Salentum Peninsula and its correlation with local meteorology

In this paper the results of measurements of Total Suspended Particles (TSP), PM10 and PM2.5 and their correlation with meteorological parameters are presented. The samplings were carried out with a mobile laboratory in seven locations in the Salentum Peninsula located in the southeastern part of Italy in Puglia. Measurements were taken discontinuously during the period 2002-2005. Up to now no systematic analyses of aerosol concentrations in the Salentum Peninsula have been presented in the scientific literature. This study is therefore a useful basis for assessing the local situation and for planning future monitoring. Measurements have been performed, on a daily basis, using standard European inlet (CEN-EN12341, 1998) and successive gravimetric detection of aerosol deposited on filters. The measurement sites can be considered representative of urban background for all the cases investigated. An analysis of the random uncertainties (LOQ and LOD) for the different types of filters used is reported. Results show concentrations in good agreement with lognormal distributions, indicating that the PM10 fraction is about 66% of TSP and PM2.5 is about 67% of PM10, which allows us to evaluate that the fraction of PM2.5 is about 44% of TSP. Concentration levels were correlated with local meteorological parameters, especially with wind velocity and precipitations. Results indicate that during rainy days the average concentration is reduced of about 70% and the reduction is larger for TSP and PM10 with respect to PM2.5. There is, on average, a substantial decrease of concentration levels in high wind conditions. Results also suggest the possibility of a significant contribution of African dust to PM10 and TSP, especially in the spring and summer season, which could be responsible for some days with concentrations above the threshold imposed by the European legislation on PM10

Frequency noise cancellation in optomechanical systems for ponderomotive squeezing

Ponderomotive squeezing of the output light of an optical cavity has been recently observed in the MHz range in two different cavity optomechanical devices. Quadrature squeezing becomes particularly useful at lower spectral frequencies, for example in gravitational wave interferometers, despite being more sensitive to excess phase and frequency noise. Here we show a phase/frequency noise cancellation mechanism due to destructive interference which can facilitate the production of ponderomotive squeezing in the kHz range and we demonstrate it experimentally in an optomechanical system formed by a Fabry-P\'{e}rot cavity with a micro-mechanical mirror.Comment: 11 pages, 9 figures. Physical explanation expanded. Modified figure

Dynamical two-mode squeezing of thermal fluctuations in a cavity opto-mechanical system

We report the experimental observation of two-mode squeezing in the oscillation quadratures of a thermal micro-oscillator. This effect is obtained by parametric modulation of the optical spring in a cavity opto-mechanical system. In addition to stationary variance measurements, we describe the dynamic behavior in the regime of pulsed parametric excitation, showing enhanced squeezing effect surpassing the stationary 3dB limit. While the present experiment is in the classical regime, our technique can be exploited to produce entangled, macroscopic quantum opto-mechanical modes