New-particle formation events in a continental boundary layer: first results from the SATURN experiment

International audienceDuring the SATURN experiment, which took place from 27 May to 14 June 2002, new particle formation in the continental boundary layer was investigated. Simultaneous ground-based and tethered-balloon-borne measurements were performed, including meteorological parameters, particle number concentrations and size distributions, gaseous precursor concentrations and SODAR and LIDAR observations. Newly formed particles were observed inside the residual layer, before the break-up process of the nocturnal inversion, and inside the mixing layer throughout the break-up of the nocturnal inversion and during the evolution of the planetary boundary layer.</p

Steps in the Negative-Differential-Conductivity Regime of a Superconductor

Current-voltage characteristics were measured in the mixed state of Y1Ba2Cu3O(7-delta) superconducting films in the regime where flux flow becomes unstable and the differential conductivity dj/dE becomes negative. Under conditions where its negative slope is steep, the j(E) curve develops a pronounced staircase like pattern. We attribute the steps in j(E) to the formation of a dynamical phase consisting of the succesive nucleation of quantized distortions in the local vortex velocity and flux distribution within the moving flux matter.Comment: 5 pages, 3 figure

Ultrafast Spin Dynamics in Nickel

The spin dynamics in Ni is studied by an exact diagonalization method on the ultrafast time scale. It is shown that the femtosecond relaxation of the magneto-optical response results from exchange interaction and spin-orbit coupling. Each of the two mechanisms affects the relaxation process differently. We find that the intrinsic spin dynamics occurs during about 10 fs while extrinsic effects such as laser-pulse duration and spectral width can slow down the observed dynamics considerably. Thus, our theory indicates that there is still room to accelerate the spin dynamics in experiments.Comment: 4 pages, Latex, 4 postscript figure

Ultrafast optical generation of coherent phonons in CdTe1-xSex quantum dots

We report on the impulsive generation of coherent optical phonons in CdTe0.68Se0.32 nanocrystallites embedded in a glass matrix. Pump probe experiments using femtosecond laser pulses were performed by tuning the laser central energy to resonate with the absorption edge of the nanocrystals. We identify two longitudinal optical phonons, one longitudinal acoustic phonon and a fourth mode of a mixed longitudinal-transverse nature. The amplitude of the optical phonons as a function of the laser central energy exhibits a resonance that is well described by a model based on impulsive stimulated Raman scattering. The phases of the coherent phonons reveal coupling between different modes. At low power density excitations, the frequency of the optical coherent phonons deviates from values obtained from spontaneous Raman scattering. This behavior is ascribed to the presence of electronic impurity states which modify the nanocrystal dielectric function and, thereby, the frequency of the infrared-active phonons

Acoustic signals in air and water generated by very shallow marine seismic sources: An experimental study

When a marine seismic source, like an airgun, is fired close to the water surface the oscillating bubble interacts with the water–air interface. The main interest for seismic applications is how this effect impacts the acoustic signal propagating into the water. It is known that the sound transmission into air is abnormally strong when the sound source is very close to the sea surface relative to the emitted wavelength. Detailed insight into how the acoustic signal changes when the source depth is changed is useful in seismic data analysis and processing. Two experiments are conducted in a water tank with two different types of seismic sources. In experiment A the source is a small cavity that is sufficiently far away from the water–air interface so that it can be assumed that no interaction between the cavity and water surface occurs. In experiment B the source is a larger air bubble that is very close to the water–air interface, and hence interaction between the bubble and water surface occurs. The effects on the water surface, oscillating bubble, and emitted acoustic pressure into air are discussed. It is demonstrated that the moving surface contributes significantly to the acoustic signal measured in air.publishedVersionVC 2020 Acoustical Society of Americ

Size-resolved measurement of the mixing state of soot in the megacity Beijing, China: diurnal cycle, aging and parameterization

Soot particles are the most efficient light absorbing aerosol species in the atmosphere, playing an important role as a driver of global warming. Their climate effects strongly depend on their mixing state, which significantly changes their light absorbing capability and cloud condensation nuclei (CCN) activity. Therefore, knowledge about the mixing state of soot and its aging mechanism becomes an important topic in the atmospheric sciences. &lt;br&gt;&lt;br&gt; The size-resolved (30–320 nm diameter) mixing state of soot particles in polluted megacity air was measured at a suburban site (Yufa) during the CAREBeijing 2006 campaign in Beijing, using a volatility tandem differential mobility analyzer (VTDMA). Particles in this size range with non-volatile residuals at 300 &amp;deg;C were considered to be soot particles. On average, the number fraction of internally mixed soot in total soot particles (&lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt;), decreased from 0.80 to 0.57 when initial &lt;i&gt;D&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt; increased from 30 to 320 nm. Further analysis reveals that: (1) &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; was well correlated with the aerosol hygroscopic mixing state measured by a CCN counter. More externally mixed soot particles were observed when particles showed more heterogeneous features with regard to hygroscopicity. (2) &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; had pronounced diurnal cycles. For particles in the accumulation mode (&lt;i&gt;D&lt;/i&gt;&lt;sub&gt;p&lt;/sub&gt; at 100–320 nm), largest &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; were observed at noon time, with "apparent" turnover rates (&lt;i&gt;k&lt;/i&gt;&lt;sub&gt;ex &amp;rarr; in&lt;/sub&gt;) up to 7.8% h&lt;sup&gt;−1&lt;/sup&gt;. (3) &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; was subject to competing effects of both aging and emissions. While aging increases &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; by converting externally mixed soot particles into internally mixed ones, emissions tend to reduce &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; by emitting more fresh and externally mixed soot particles. Similar competing effects were also found with air mass age indicators. (4) Under the estimated emission intensities, actual turnover rates of soot (&lt;i&gt;k&lt;/i&gt;&lt;sub&gt;ex &amp;rarr; in&lt;/sub&gt;) up to 20% h&lt;sup&gt;−1&lt;/sup&gt; were derived, which showed a pronounced diurnal cycle peaking around noon time. This result confirms that (soot) particles are undergoing fast aging/coating with the existing high levels of condensable vapors in the megacity Beijing. (5) Diurnal cycles of &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; were different between Aitken and accumulation mode particles, which could be explained by the faster growth of smaller Aitken mode particles into larger size bins. &lt;br&gt;&lt;br&gt; To improve the &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; prediction in regional/global models, we suggest parameterizing &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; by an air mass aging indicator, i.e., &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; = &lt;i&gt;a&lt;/i&gt; + &lt;i&gt;bx&lt;/i&gt;, where &lt;i&gt;a&lt;/i&gt; and &lt;i&gt;b&lt;/i&gt; are empirical coefficients determined from observations, and &lt;i&gt;x&lt;/i&gt; is the value of an air mass age indicator. At the Yufa site in the North China Plain, fitted coefficients (&lt;i&gt;a&lt;/i&gt;, &lt;i&gt;b&lt;/i&gt;) were determined as (0.57, 0.21), (0.47, 0.21), and (0.52, 0.0088) for &lt;i&gt;x&lt;/i&gt; (indicators) as [NO&lt;sub&gt;z&lt;/sub&gt;]/[NO&lt;sub&gt;y&lt;/sub&gt;], [E]/[X] ([ethylbenzene]/[m,p-xylene]) and ([IM] + [OM])/[EC] ([inorganic + organic matter]/[elemental carbon]), respectively. Such a parameterization consumes little additional computing time, but yields a more realistic description of &lt;i&gt;F&lt;/i&gt;&lt;sub&gt;in&lt;/sub&gt; compared with the simple treatment of soot mixing state in regional/global models

Composability in quantum cryptography

In this article, we review several aspects of composability in the context of quantum cryptography. The first part is devoted to key distribution. We discuss the security criteria that a quantum key distribution protocol must fulfill to allow its safe use within a larger security application (e.g., for secure message transmission). To illustrate the practical use of composability, we show how to generate a continuous key stream by sequentially composing rounds of a quantum key distribution protocol. In a second part, we take a more general point of view, which is necessary for the study of cryptographic situations involving, for example, mutually distrustful parties. We explain the universal composability framework and state the composition theorem which guarantees that secure protocols can securely be composed to larger applicationsComment: 18 pages, 2 figure

Active machine learning for transmembrane helix prediction

Abstract Background About 30% of genes code for membrane proteins, which are involved in a wide variety of crucial biological functions. Despite their importance, experimentally determined structures correspond to only about 1.7% of protein structures deposited in the Protein Data Bank due to the difficulty in crystallizing membrane proteins. Algorithms that can identify proteins whose high-resolution structure can aid in predicting the structure of many previously unresolved proteins are therefore of potentially high value. Active machine learning is a supervised machine learning approach which is suitable for this domain where there are a large number of sequences but only very few have known corresponding structures. In essence, active learning seeks to identify proteins whose structure, if revealed experimentally, is maximally predictive of others. Results An active learning approach is presented for selection of a minimal set of proteins whose structures can aid in the determination of transmembrane helices for the remaining proteins. TMpro, an algorithm for high accuracy TM helix prediction we previously developed, is coupled with active learning. We show that with a well-designed selection procedure, high accuracy can be achieved with only few proteins. TMpro, trained with a single protein achieved an F-score of 94% on benchmark evaluation and 91% on MPtopo dataset, which correspond to the state-of-the-art accuracies on TM helix prediction that are achieved usually by training with over 100 training proteins. Conclusion Active learning is suitable for bioinformatics applications, where manually characterized data are not a comprehensive representation of all possible data, and in fact can be a very sparse subset thereof. It aids in selection of data instances which when characterized experimentally can improve the accuracy of computational characterization of remaining raw data. The results presented here also demonstrate that the feature extraction method of TMpro is well designed, achieving a very good separation between TM and non TM segments

Primary Versus Secondary Contributions to Particle Number Concentrations in the European Boundary Layer

It is important to understand the relative contribution of primary and secondary particles to regional and global aerosol so that models can attribute aerosol radiative forcing to different sources. In large-scale models, there is considerable uncertainty associated with treatments of particle formation (nucleation) in the boundary layer (BL) and in the size distribution of emitted primary particles, leading to uncertainties in predicted cloud condensation nuclei (CCN) concentrations. Here we quantify how primary particle emissions and secondary particle formation influence size-resolved particle number concentrations in the BL using a global aerosol microphysics model and aircraft and ground site observations made during the May 2008 campaign of the European Integrated Project on Aerosol Cloud Climate Air Quality Interactions (EUCAARI). We tested four different parameterisations for BL nucleation and two assumptions for the emission size distribution of anthropogenic and wildfire carbonaceous particles. When we emit carbonaceous particles at small sizes (as recommended by the Aerosol Intercomparison project, AEROCOM), the spatial distributions of campaign-mean number concentrations of particles with diameter >50 nm (N50) and >100 nm (N100) were well captured by the model (R2≥0.8) and the normalised mean bias (NMB) was also small (−18% for N50 and −1% for N100). Emission of carbonaceous particles at larger sizes, which we consider to be more realistic for low spatial resolution global models, results in equally good correlation but larger bias (R2≥0.8, NMB = −52% and −29%), which could be partly but not entirely compensated by BL nucleation. Within the uncertainty of the observations and accounting for the uncertainty in the size of emitted primary particles, BL nucleation makes a statistically significant contribution to CCN-sized particles at less than a quarter of the ground sites. Our results show that a major source of uncertainty in CCN-sized particles in polluted European air is the emitted size of primary carbonaceous particles. New information is required not just from direct observations, but also to determine the "effective emission size" and composition of primary particles appropriate for different resolution models.JRC.H.2-Air and Climat

Enacting the Soft Automaton: Empirical Ontologies of Two Soft Robots from Technical Research and Media Art

This paper examines two soft robots from technical research and media art respectively and the practices through which they come into being. Departing from a juxtaposition of video presentations of the two robots, the empirical ontologies of a soft robot enacted in practice are analysed. The paper argues that two different versions of softness are being done and that the two sets of practices concomitantly respecify “knowledge” and “autonomy” as concepts, with different ethical and political implications.This paper examines two soft robots from technical research and media art respectively and the practices through which they come into being. Departing from a juxtaposition of video presentations of the two robots, the empirical ontologies of a soft robot enacted in practice are analysed. The paper argues that two different versions of softness are being done and that the two sets of practices concomitantly respecify “knowledge” and “autonomy” as concepts, with different ethical and political implications