Dedicated Laboratory Experiments Research Articles

Ultra-low work function of caesiated surfaces and impact of selected gas species

Modern high-power negative hydrogen ion sources rely predominantly on the surface production of negative hydrogen ions. Hence, low work function converter surfaces are mandatory, for which the alkali metal Cs is commonly evaporated into the ion source to lower the work function of refractory metals by surface adsorption. To study the work function behaviour upon caesiation under the typically given non-ultra-high vacuum conditions, investigations are performed at a dedicated laboratory experiment. In a vacuum environment dominated by water vapour, the work function evolution is found to be dependent on the flux ratio of Cs to H2O onto the surface. For sufficiently high flux ratios, ultra-low work functions in the range of 1.25±0.10 eV are generated with excellent reproducibility. In the absence of Cs evaporation, the work function gradually increases under the influence of the residual gases, and re-caesiation processes lead to lower quantum efficiencies and higher work functions of typically 1.9–2.1 eV. While the addition of hydrogen and deuterium gas at several Pa as well as the leakage of inert gases (argon and nitrogen) into the vacuum system have a negligible influence on the caesiation process, small amounts of oxygen with partial pressures of ∼10-2–10-1 Pa lead to an instant reduction of the Cs density in the gas phase by several orders of magnitude and to an increase in the work function of the order of 1 eV. After the oxygen exposure is terminated, however, the Cs density and work function fully recover within several minutes.

Estimation and analysis of insect population dynamics parameters via physiologically based models and hybrid genetic algorithm MCMC methods

Decision support systems are gaining importance in several fields of agriculture, forest, and ecological systems management. Their predictive potential, entrusted to mathematical models, is of fundamental importance to set up opportune strategies to control pests and adversities that may occur and that may seriously compromise the natural equilibria. Among the others, population dynamics is one of the crucial challenges in the field. Despite the scientific community in recent years providing valuable models that faithfully represent terrestrial arthropods populations, such as insects, one of the main concerns is still represented by the parameter estimation. Parameters, in fact, characterise the species and their estimation are often entrusted to dedicated laboratory experiments that require specific equipment and highly qualified personnel. In this study we propose a novel method to estimate the model parameters directly from field data, where experimental activities are less expensive and less time consuming. In this study we propose a combination of least squares methods via genetic algorithms to preliminary evaluate the best parameter values and Markov Chain Monte Carlo approach to obtain their distribution. The algorithm has been tested in the special case of Drosophila suzukii, to quantify part of the parameters of an almost validated model in two steps: i) a first pseudo-validation using perturbed numerical solutions, and ii) a validation using real field data. The results highlighted the potentialities of the algorithm in estimating model parameters and opened several perspectives for further improvements from both the computational and experimental point of view.

Laboratory insights into the effects of methane hydrate on the anisotropic joint elastic-electrical properties in fractured sandstones

Fractured hydrate-bearing reservoirs show significantly anisotropic geophysical properties. The joint application of seismic and electromagnetic explorations is expected to accurately assess hydrate resources in the fractured reservoirs. However, the anisotropic joint elastic-electrical properties in such reservoirs that are the key to the successful application of the joint explorations, remain poorly understood. To obtain such knowledge, we designed and implemented dedicated laboratory experiments to study the anisotropic joint elastic-electrical properties in fractured artificial silica sandstones (with fracture density of about 6.2%, porosity of approximately 25.7%, and mean grainsize of 0.089 mm) with evolving methane hydrate. The experimental results showed that the anisotropic compressional wave velocities respectively increased and decreased with the forming and dissociating hydrate, and the variation in the increasing trend and the decreasing extent of the velocity perpendicular to the fractures were more significant than that parallel to the fractures, respectively. The experimental results also showed that the overall decreasing trend of the electrical conductivity parallel to the fractures was steeper than that perpendicular to the fractures during hydrate formation, and the general variations of the two conductivities with complex trend were similar during hydrate dissociation. The variations in the elastic and electrical anisotropic parameters with forming and dissociating hydrate were also found to be distinct. Interpretation of the experimental results suggested that the hydrate binding to the grains evolved to bridge the surfaces of fractures when saturation exceeded 10% during hydrate formation, and the bridging hydrate gradually evolved to floating in fractures during dissociation. The experimental results further showed that the anisotropic velocities and electrical conductivities were correlated with approximately consistent trends of different slopes during hydrate formation, and the joint elastic-electrical anisotropic parameters exhibited a sharp peak at the hydrate saturation of about 10%. The results suggested that the anisotropic joint properties can be employed not only to accurately estimate hydrate saturation but also possibly to identify hydrate distribution in the fractures.

Elastic and electrical properties of calcite-cemented artificial sandstones based on a new manufacturing method

Calcite cement is widely existing in sandstones and can significantly affect the elastic and electrical properties of sandstones. Accordingly, understanding the effects of calcite cement on the elastic and electrical rock properties is of key importance for the accurate characterization of sandstone reservoirs through seismic and electromagnetic surveys. To obtain such knowledge, we design and implement dedicated laboratory experiments to investigate the effects of calcite cement and porosity on the P- and S-wave velocities and electrical resistivity of synthetic calcite-cemented sandstones made using a new recipe. The experimental results show that elastic velocities and electrical resistivity generally decrease with increasing porosity when the content of the calcite cement keeps constant, whereas the elastic and electrical rock properties exhibit complex variation with cement content in sandstones with approximately the same porosity. Analyses and interpretation of the experimental data indicate that the elastic and electrical rock properties are affected jointly by porosity, the content and distribution of the calcite cement, as well as the microstructure of the pore space resulting from the different axial stress employed for the consolidation of the rock samples. The results have revealed the mechanisms of how porosity and calcite cement affect the elastic and electrical properties of calcite-cemented sandstones, and provided a theoretical basis for the accurate characterization of sandstone reservoirs through seismic and electromagnetic surveys.

Particle energization in colliding subcritical collisionless shocks investigated in the laboratory

Context. Colliding collisionless shocks appear across a broad variety of astrophysical phenomena and are thought to be possible sources of particle acceleration in the Universe. Aims. The main goal of our experimental and computational work is to understand the effect of the interpenetration between two subcritical collisionless shocks on particle energization. Methods. To investigate the detailed dynamics of this phenomenon, we performed a dedicated laboratory experiment. We generated two counter-streaming subcritical collisionless magnetized shocks by irradiating two Teflon (C2F4) targets with 100 J, 1 ns laser beams on the LULI2000 laser facility. The interaction region between the plasma flows was pre-filled with a low-density background hydrogen plasma and initialized with an externally applied homogeneous magnetic field perpendicular to the shocks. We also modeled the macroscopic evolution of the system via hydrodynamic simulations and the microphysics at play during the interaction via particle-in-cell (PIC) simulations. Results. Here, we report our measurements of the plasma density and temperature during the formation of the supercritical shocks, their transition to subcritical, and their final interpenetration. We find that in the presence of two shocks, the ambient ions reach energies around 1.5 times of those obtained with single shocks. Both the presence of the downstream zone of the second shock and of the downstream zone common for the two shocks play a role in the different energization: the characteristics of the perpendicular electric fields in the two areas indeed allow for certain particles to continue being accelerated or, at least, to avoid being decelerated. Conclusions. The findings of our laboratory investigation are relevant for our understanding of the energy distribution of high-energy particles that populate the interplanetary space in our solar system and the very local interstellar medium around the heliopause, where observations have indicated evidence of subcritical collisionless shocks that may eventually go on to collide with one another.

Experimental and Numerical Study of the Effect of Model Geometric Distortion on Laboratory Modeling of Urban Flooding

AbstractLaboratory studies of urban flooding often use geometrically distorted scale models due to the multi‐scale nature of these specific flows. The possible bias induced by geometric distortion has never been thoroughly investigated with dedicated laboratory experiments. In this study, we combine experimental and computational modeling to systematically assess the influence of the distortion ratio, that is, the ratio of horizontal to vertical scale factors, on upscaled flow depths and discharge partition between streets. Three flow configurations were considered: a street junction, a street bifurcation, and a small synthetic urban district. When the distortion ratio is varied up to a value of about 5, the upscaled flow depths at the model inlets decrease monotonously and the flow discharge in the branch that conveys the largest portion of the flow is greatly enhanced. For equal flow depths at the model outlets and depending on the configuration, the distortion effect induces a variation of the upstream flow depth approximately from ∼4% to ∼17% and a change in outlet discharge partition up to 24 percentage points. For a distortion ratio above 5, both upscaled upstream flow depths and outlet discharge partition tend to stabilize asymptotically. Our study indicates the direction and magnitude of the bias induced by geometric distortion for a broad range of flow cases, which is valuable for offsetting these effects in practical laboratory studies of urban flooding.

Application of cloud particle sensor sondes for estimating the number concentration of cloud water droplets and liquid water content: case studies in the Arctic region

Abstract. A cloud particle sensor (CPS) sonde is an observing system attached with a radiosonde sensor to observe the vertical structure of cloud properties. The signals obtained from CPS sondes are related to the phase, size, and number of cloud particles. The system offers economic advantages including human resource and simple operation costs compared with aircraft measurements and land-/satellite-based remote sensing. However, the observed information should be appropriately corrected because of several uncertainties. Here we made field experiments in the Arctic region by launching approximately 40 CPS sondes between 2018 and 2020. Using these data sets, a better practical correction method was proposed to exclude unreliable data, estimate the effective cloud water droplet radius, and determine a correction factor for the total cloud particle count. We apply this method to data obtained in October 2019 over the Arctic Ocean and March 2020 at Ny-Ålesund, Svalbard, Norway, to compare with a particle counter aboard a tethered balloon and liquid water content retrieved by a microwave radiometer. The estimated total particle count and liquid water content from the CPS sondes generally agree with those data. Although further development and validation of CPS sondes based on dedicated laboratory experiments would be required, the practical correction approach proposed here would offer better advantages in retrieving quantitative information on the vertical distribution of cloud microphysics under the condition of a lower number concentration.

Laboratory Investigations of Acoustic Anisotropy in Artificial Porous Rock With Aligned Fractures During Gas Hydrate Formation and Dissociation

AbstractFractures can widely exist in hydrate‐bearing reservoirs and can give rise to anisotropic acoustic properties that play an important role in the accurate assessment of fractured reservoirs. However, the knowledge of the responses of acoustic anisotropy in fractured hydrate‐bearing reservoirs is still poorly understood. To obtain such understanding, we designed and implemented dedicated laboratory experiments to measure the anisotropic acoustic velocities in an artificial sandstone with aligned penny‐shaped fractures parallel to the layers during hydrate formation and dissociation at the confining pressures of 20 and 50 MPa, respectively. We showed that although the velocities at higher confining pressure were systematically greater, all the velocities at both confining pressures increased and decreased during hydrate formation and dissociation, respectively. We also showed that the velocities during hydrate formation were significantly higher than those during dissociation at hydrate saturation greater than 10%. It was found that all the velocities smoothly reduced with decreasing saturation during dissociation, while the varying velocities exhibited distinct increasing gradients during formation, where the compressional wave anisotropy reduced dramatically at saturation between 10% and 25%. Analyses of the experimental results suggested that the floating hydrate evolved to bridge the surfaces of fractures when hydrate saturation exceeded 10% during hydrate formation, and the bridging hydrate gradually transformed to floating in the pore system during dissociation. The results provide new insights into hydrate distribution and its effects on acoustic anisotropy in fractured reservoirs during hydrate formation and dissociation and will contribute to improving the accuracy of hydrate assessment in such reservoirs.

Pressure-dependent cross-property relationships between elastic and electrical properties of partially saturated porous sandstones

Successful joint inversion of seismic and electromagnetic survey data to estimate parameters and improve the characterization of the earth’s subsurface relies on the understanding of the cross-property relations between the elastic and electrical properties. Pressure-dependent cross-property relationships of rocks with varying degrees of fluid saturation remain poorly understood even though such conditions are encountered frequently. We investigate this problem by designing and undertaking dedicated laboratory experiments to simultaneously measure the elastic velocity and electrical resistivity in two Berea sandstone samples subject to varying confining pressure and water saturation, using a state-of-the-art joint elastic-electrical measurement system. P- and S-wave velocities are found to increase exponentially with increasing confining pressure at each water saturation, whereas electrical conductivity can either increase or decrease with confining pressure depending on the degree of water saturation. More interestingly, the elastic and electrical properties of the two samples are shown to be systematically correlated as functions of water saturation and the applied confining pressure. The correlations reveal the natural link between the elastic and electrical properties in the two porous sandstones with partial water saturation, and they help to better indicate the fluid flow within compliant pores in addition to the known flow between stiff and compliant pores. The results will form the theoretical basis for the successful joint interpretation of seismic and electromagnetic survey data acquired from partially saturated porous rocks in the subsurface of the earth.

A machine learning approach to filtrate loss determination and test automation for drilling and completion fluids

Drilling fluid property characterization currently involves several manually executed analytical tests, conducted in accordance with American Petroleum Institute (API) recommended practices 13B-1 and 13B-2. Standard (API) and high-pressure, high-temperature (HPHT) filter press units are used for filtrate loss (FL) measurements. However, these test methods have certain important disadvantages. FL tests are conducted at standardized conditions that generally do not reflect downhole oil and gas well conditions in terms of downhole pressure, temperature and filter medium encountered, present safety concerns due to their elevated pressure and temperature, and are performed only infrequently by a human mud engineer. The human measurement also introduces concerns around inaccuracies due to inconsistent practices and interpretation bias of the results. In addition, FL measurements are hard to automate given their manual, human-centric operating tasks.In this paper, we investigate if it is really necessary to automate FL measurements, or if the (strictly qualitative) information they provide can be obtained in a smarter, more advanced way. For this purpose, the relationship between fluid properties was investigated in detail using machine learning and deep learning techniques. Random forest (RF), XGBoost (XGB), support vector machine (SVM), multilayer perceptron (MLP) and multi-linear regression models were trained and tested to predict API and HPHT FL of water-based muds (WBM) based on fluid property readings of rheology, density, and temperature. A similar approach was also used for HPHT filtrate loss prediction of oil-based muds (OBM), taking into account their electrical stability and water content. A key advantage of this approach is that these WBM and OBM fluid properties can be obtained in real-time with measurements that are relatively simple and easy to automate (e.g. obtaining fluid density automatically and continuously from a Coriolis mass-flow meter measurement). Thus, real-time assessment of API and HPHT FL becomes possible without ever having to actually carry out any filter press measurements, thereby also eliminating the need to directly automate these measurements. The models were verified by dedicated laboratory experiments. The developed models estimated API and HPHT FL of WBM, and HPHT FL of OBM with mean absolute errors (MAE) of 0.56 ml/30min, 1.15 ml/30min and 0.79 ml/30min respectively, well within the measurement accuracy of the observations by a human mud engineer.

Modeling the Transmission of Vibrio aestuarianus in Pacific Oysters Using Experimental Infection Data.

Vibrio aestuarianus is a bacterium related to mortality outbreaks in Pacific oysters, Crassostrea gigas, in France, Ireland, and Scotland since 2011. Knowledge about its transmission dynamics is still lacking, impairing guidance to prevent and control the related disease spread. Mathematical modeling is a relevant approach to better understand the determinants of a disease and predict its dynamics in imperfectly observed pathosystems. We developed here the first marine epidemiological model to estimate the key parameters of V. aestuarianus infection at a local scale in a small and closed oyster population under controlled laboratory conditions. Using a compartmental model accounting for free-living bacteria in seawater, we predicted the infection dynamics using dedicated and model-driven collected laboratory experimental transmission data. We estimated parameters and showed that waterborne transmission of V. aestuarianus is possible under experimental conditions, with a basic reproduction number R0 of 2.88 (95% CI: 1.86; 3.35), and a generation time of 5.5 days. Our results highlighted a bacterial dose–dependent transmission of vibriosis at local scale. Global sensitivity analyses indicated that the bacteria shedding rate, the concentration of bacteria in seawater that yields a 50% chance of catching the infection, and the initial bacterial exposure dose W0 were three critical parameters explaining most of the variation in the selected model outputs related to disease spread, i.e., R0, the maximum prevalence, oyster survival curve, and bacteria concentration in seawater. Prevention and control should target the exposure of oysters to bacterial concentration in seawater. This combined laboratory–modeling approach enabled us to maximize the use of information obtained through experiments. The identified key epidemiological parameters should be better refined by further dedicated laboratory experiments. These results revealed the importance of multidisciplinary approaches to gain consistent insights into the marine epidemiology of oyster diseases.

Blazar VHE spectral alterations induced by photon–ALP oscillations

Prompted by the increasing interest of axion-like particles (ALPs) for very-high-energy (VHE) astrophysics, we have considered a full scenario for the propagation of a VHE photon/ALP beam emitted by a BL Lac and reaching us in the light of the most up-to-date astrophysical information and for energies up to above $100 \, \rm TeV$. During its trip, the beam -- generated in a small region of a BL Lac jet -- crosses a variety of magnetic structures in very different astronomical environments: the BL Lac jet, the host elliptical galaxy, the extragalactic space and the Milky Way. We have taken an effort to model all these magnetic fields in the most realistic fashion and using a new model developed by us concerning the extragalactic magnetic field. Assuming an intrinsic spectrum with a power law exponentially truncated at a fixed cut-off energy, we have evaluated the resulting observed spectra of Markarian 501, the extreme BL Lac 1ES 0229+200 and a similar source located at $z = 0.6$ up to above $100 \, \rm TeV$. We obtain interesting results: the model with photon-ALP oscillations possesses features (spectral energy oscillatory behaviour and photon excess above $20 \, \rm TeV$) which can be tested by $\gamma$-ray observatories like CTA, HAWC, GAMMA 400, LHAASO, TAIGA-HiSCORE and HERD. In addition, our ALP can be detected in dedicated laboratory experiments like the upgrade of ALPS II at DESY, the planned IAXO and STAX experiments, as well as with other techniques developed by Avignone and collaborators.

Turbulence in disks and laboratory experiments: the contribution of Jean-Paul Zahn

The activity of Jean-Paul on disks does represent only a small fraction of his total list of publications. It was however very important to its eyes. Beyond his important scientific results on the topic that I summarized, this activity launched a totally new area in the domain of astrophysics: the dedicated laboratory experiments.

Effects of aligned fractures on the dielectric properties of synthetic porous sandstones

Understanding the dielectric properties of reservoir rocks has important applications in various aspects in the petroleum industry. Fractures are common features in sedimentary porous rocks that not only provide space for the hydrocarbon to accumulate and reside but also are important pathways for the hydrocarbon to flow and therefore have a controlling impact on the formation and distribution of the hydrocarbon reservoirs. However, the dielectric properties of fractured reservoir rocks are still poorly understood. We investigated, through dedicated laboratory experiments, the dielectric behaviors of synthetic porous sandstones with aligned fractures and their relationships with the salinity of the electrolyte saturating the samples, the measurement frequency of the applied electrical field and the directions relative to the fractures. It showed that the fractures have significant effects on the dielectric properties of porous sandstones and their dependence on the brine salinity and measurement frequency reveals the various polarization mechanisms occurring at different frequency ranges. The results offer a preliminary basis for the characterization of fractured rocks using the dielectric properties, which has great potential applicability in oil and gas exploration and exploitation.

Study of the temperature-dependent nitrogen retention in tungsten surfaces using X-ray photoelectron spectroscopy

Nitrogen is foreseen as seeding species in future magnetic confinement fusion reactors in order to reduce the power load from the plasma onto the divertor target tiles by radiative cooling. As a side effect it also gets implanted into the tungsten wall and forms tungsten nitrides (WxN). The temperature-dependent WxN formation was investigated in dedicated laboratory experiments. N ions of 300 eV kinetic energy were implanted into W samples under ultra-high vacuum conditions in the temperature range 300 K to 800 K. The N retention in W was monitored and quantitatively analysed by X-ray photoelectron spectroscopy (XPS). A method to calculate the statistical error of the measured data based on Bayesian statistics was developed. Argon sputter depth profiling was combined with XPS to measure N in W depth profiles which were compared with simulated N implantation profiles. Annealing of samples implanted with N at 300 K does not cause a loss of N up to 800 K. However, the retained N amount decreases linearly with increasing implantation temperature. It was found that this reduction is due to ion-irradiation-induced N release at elevated temperatures. Over the whole temperature range N diffusion into depth was not observed. N accumulation measurements showed no evidence for a phase transition in the WxN layer. However, high resolution XPS measurements revealed that below 600 K a second photoelectron peak occurs in the N 1s signal which can be attributed to different local atomic arrangements of WxN.

Joint Elastic‐Electrical Properties of Artificial Porous Sandstone With Aligned Fractures

AbstractSeismic and electromagnetic surveys are among the most important geophysical applications to understand the subsurface Earth. Joint interpretation of the independent but complementary exploration data can provide geophysical parameters needed to better assess the rocks. However, cross‐property relationship between the elastic and electrical properties of fractured porous rocks, the key to the successful joint interpretation of seismic and electromagnetic data in anisotropic formations, is poorly understood. Here we use dedicated laboratory experiments and theoretical modeling to show how elastic velocity and electrical conductivity are linked in porous sandstone with aligned fractures and how the joint properties are affected by the fractures. The P and SH wave velocities are found to be approximately linearly correlated with electrical conductivity when measured in varying directions, and the linear trends are determined by the geometry and amount of the fractures in the rocks. The results provide a pathway to successful joint interpretation in fractured rocks.

Laboratory investigation of the effect of surface roughness on photoemission from surfaces in space

Surfaces in space collect charges due to exposure of solar ultraviolet (UV) radiation, electrons, and ions. Throughout the solar system, UV-generated photoelectrons dominate the charging balance and exposed surfaces tend to charge positively. The surface potential of exposed objects depends on the material properties of their surfaces. Composition and particle size primarily affect the quantum efficiency of photoelectron generation; however, surface roughness can also control the charging process. Here we examine the role of surface roughness in generating photoelectrons in dedicated laboratory experiments using solid and dusty surfaces of the same composition. Using Langmuir probe measurements, we explore the measured plasma conditions above insulating surfaces exposed to UV, and we show that the photoemission current from a dusty surface is largely reduced due to its higher surface roughness, which causes a significant fraction of the emitted photoelectrons to be re-absorbed within the surface.

Influence of H2 and D2 plasmas on the work function of caesiated materials

Caesium-covered surfaces are used in negative hydrogen ion sources as a low work function converter for H–/D– surface production. The work function χ of the converter surface is one of the key parameters determining the performance of the ion source. Under idealized conditions, pure bulk Cs has 2.14 eV. However, residual gases at ion source background pressures of 10−7–10−6 mbar and the plasma surface interaction with the hydrogen discharge in front of the caesiated surface dynamically affect the actual surface work function. Necessary fundamental investigations on the resulting χ are performed at a dedicated laboratory experiment. Under the vacuum conditions of ion sources, the incorporation of impurities into the Cs layer leads to very stable Cs compounds. The result is a minimal work function of χvac ≈ 2.75 eV for Cs evaporation rates of up to 10 mg/h independent of substrate material and surface temperature (up to 260 °C). Moreover, a distinct degradation behavior can be observed in the absence of a Cs flux onto the surface leading to a deterioration of the work function by about 0.1 eV/h. However, in a hydrogen discharge with plasma parameters close to those of ion sources, fluxes of reactive hydrogen species and VUV photons impact on the surface which reduces the work function of the caesiated substrate down to about 2.6 eV even without Cs supply. Establishing a Cs flux onto the surface with ΓCs ≈ 1017 m−2 s−1 further enhances the work function obtaining values around 2.1 eV, which can be maintained stable for several hours of plasma exposure. Hence, Cs layers with work functions close to that of pure bulk Cs can be achieved for both H2 and D2 plasmas. Isotopic differences can be neglected within the measurement accuracy of about 0.1 eV due to comparable plasma parameters. Furthermore, after shutting down the Cs evaporation, continuing plasma exposure helps against degradation of the Cs layer resulting in a constant low work function for at least 1 h.

A novel approach to measure photodesorption rates of interstellar ice analogues

Context. In recent years photodesorption rates have been determined in dedicated laboratory experiments for a number of different interstellar ice analogues. These rates are important in order to model non-thermal desorption processes that, for example, affect gas-phase abundances of species and determine the position of photo-induced snow lines in protoplanetary disks. However, different groups using similar experiments have found significant deviating photodesorption values.Aims. Here a new measurement concept is introduced that allows photodesorption rates to be determined following a different experimental approach. The potential of this method is demonstrated using the example of pure CO ice, the solid that gives the most striking discrepancies in the published results.Methods. The new experimental approach uses laser desorption post-ionisation time-of-flight mass spectrometry. It is based on the concept that the physical and geometrical properties of the plume obtained by laser induced desorption of the ice directly depend on the original ice thickness. This allows the ice loss to be determined as function of vacuum ultraviolet (VUV) fluence, which results in a photodesorption rate. The method has the additional advantage that it records all ice species, including photoproducts generated by the VUV irradiation. As a consequence, the method introduced here is also suited to determine the overall photodesorption rate of mixed ices.Results. The photodesorption rate for CO ice at 20 K has been determined as (1.4 ± 0.7) × 10-3 molecules per incident VUV photon. This result is compared to existing experimental and theoretical values and the astronomical relevance is discussed.

Preliminary analysis of radon time series before the Ml=6 Amatrice earthquake: possible implications for fluid migration

On August 24, 2016, a Ml=6.0 earthquake occurred in Central Apennines, Italy, between the towns of Norcia and Amatrice, causing severe destruction and casualties in a wide area around the epicenter. We present a preliminary analysis of continuous radon concentration data collected from the second half of 2012 to the day after the earthquake by a long term radon monitoring station, installed at Cittareale (Rieti, Italy), about 11 km south-west of the epicenter. We combine the field data analysis with the outcome of dedicated laboratory experiments, aimed to study real time radon emission dynamics from rock samples subject to normal and shear stress loads in absence of fluid transport and migration phenomena. Our results suggest the possibility of a minor role played by phenomena related to fluid migration for the Amatrice seismic event with respect to other recent Apennine earthquakes.