Icy Surfaces Research Articles

Efficacy of a rubber outsole with a hybrid surface pattern for preventing slips on icy surfaces

Conventional winter-safety footwear devices, such as crampons, can be effective in preventing slips on icy surfaces but the protruding studs can lead to other problems such as trips. A new hybrid (rough and smooth) rubber outsole was designed to provide high slip resistance without use of protruding studs or asperities. In the present study, we examined the slip resistance of the hybrid rubber outsole on both dry (−10 °C) and wet (0 °C) icy surfaces, in comparison to three conventional strap-on winter anti-slip devices: 1) metal coils (“Yaktrax Walker”), 2) gritted (sandpaper-like) straps (“Rough Grip”), and 3) crampons (“Altagrips-Lite”). Drag tests were performed to measure static (SCOF) and dynamic (DCOF) coefficients of friction, and gait trials were conducted on both level and sloped ice surfaces (16 participants). The drag-test results showed relatively high SCOF (≧0.37) and DCOF (≧0.31) values for the hybrid rubber sole, at both temperatures. The other three footwear types exhibited lower DCOF values (0.06–0.20) when compared with the hybrid rubber sole at 0 °C (p < 0.01). Slips were more frequent when wearing the metal coils, in comparison to the other footwear types, when descending a slope at −10 °C (6% of trials vs 0%; p < 0.05). There were no other significant footwear-related differences in slip frequency, distance or velocity. These results indicate that the slip-resistance of the hybrid rubber sole on icy surfaces was comparable to conventional anti-slip footwear devices. Given the likely advantages of the hybrid rubber sole (less susceptibility to tripping, better slip resistance on non-icy surfaces), this type of sole should contribute to a decrease in fall accidents; however, further research is needed to confirm its effectiveness under a wider range of test conditions.

Thickness of Saturn’s B ring as derived from seasonal temperature variations measured by Cassini CIRS

Structural and thermal properties of Saturn’s B ring and its particles are derived from orbital and seasonal temperatures variations observed by the Cassini CIRS spectrometer between 2004 and 2009 equinox. Our multiscale thermal model (Ferrari, C., Reffet, E. [2013]. Icarus 223, 28–39), which assumes negligible heat transfer by vertical motion of particles in dense rings, is adjusted to the data. Most observations were focused on the center of the B ring, at 105,000km from Saturn. A very good fit is obtained for conductive particles embedded in a moderately conductive ring medium. Assuming a bulk composition of water ice, the thermal inertia of particles is found to be Γ1=160–200J/m2/K/s1/2 and to vary with seasons as part of the heat transfer is radiative, then temperature-dependent. For the same reason, the thermal inertia of the ring, Γ0, varies with seasons, between 30 and 35J/m2/K/s1/2. It is very comparable to the thermal inertia of icy satellite surfaces. The porosity of particles p1 found to fit this thermal inertia is very high (0.93) and may emphasize an inappropriate modeling of particles by an effective porous medium. The ring filling factor is fairly high, D=0.34±0.01, but stays typical of a compact medium and compatible with the output of numerical simulations of dense ring dynamics. The thickness of the B ring at 105,000km from Saturn is estimated at HS=2.2±0.2m. The observed correlation of its optical depth with the thermal gradient between lit and unlit sides is easily reproduced by the model if the radial variations in optical depth are due to varying thickness HS(a) with constant filling factor. This thickness varies between 1 and 3m across theB2,B3 and B4 regions. It is thinner than the neighboring C ring and Cassini Division. This can be understood as a consequence of self-gravity. The ring surface mass density Σ=(1-p1)ρ0DHS(a) derived from these structural parameters is too low for a self-gravitating ring, due to the high porosity found. But its radial variations, if deduced from coupling HS(a) with known aspect-ratios H/λ of self-gravity wakes, range between 300 in the inner B ring and most certainly exceed 1000kg/m2 in the B3 ring, values compatible with a self-gravitating ring. The inferred minimum total mass of Saturn's rings is MR=1.4±0.2·1019kg, close to the mass expected for a viscous disk evolving over the age of the Solar System and compatible with current higher estimates.

Interplay of gas and ice during cloud evolution

During the evolution of diffuse clouds to molecular clouds, gas-phase molecules freeze out on surfaces of small dust particles to form ices. On dust surfaces, water is the main constituent of the icy mantle in which a complex chemistry is taking place. We aim to study the formation pathways and the composition of the ices throughout the evolution of diffuse clouds. For this purpose, we use time-dependent rate equations to calculate the molecular abundances in both gas phase and on solid surfaces (onto dust grains). We fully consider the gas-dust interplay by including the details of freeze-out, chemical and thermal desorption, as well as the most important photo-processes on grain surfaces. The difference in binding energies of chemical species on bare and icy surfaces is also incorporated into our equations. Using the numerical code FLASH, we perform a hydrodynamical simulation of a gravitationally bound diffuse cloud and follow its contraction. We find that while the dust grains are still bare, water formation is enhanced by grain surface chemistry which is subsequently released into the gas phase, enriching the molecular medium. The CO molecules, on the other hand, tend to freeze out gradually on bare grains. This causes CO to be well mixed and strongly present within the first ice layer. Once one monolayer of water ice has formed, the binding energy of the grain surface changes significantly and an immediate and strong depletion of gas-phase water and CO molecules occur. While hydrogenation converts solid CO into formaldehyde (H$_2$CO) and methanol (CH$_3$OH), water ice becomes the main constituent of the icy grains. Inside molecular clumps formaldehyde is more abundant than water and methanol in the gas phase owing its presence in part to chemical desorption.

Linking Europa’s plume activity to tides, tectonics, and liquid water

Much of the geologic activity preserved on Europa’s icy surface has been attributed to tidal deformation, mainly due to Europa’s eccentric orbit. Although the surface is geologically young (30–80Myr), there is little information as to whether tidally-driven surface processes are ongoing. However, a recent detection of water vapor near Europa’s south pole suggests that it may be geologically active. Initial observations indicated that Europa’s plume eruptions are time-variable and may be linked to its tidal cycle. Saturn’s moon, Enceladus, which shares many similar traits with Europa, displays tidally-modulated plume eruptions, which bolstered this interpretation. However, additional observations of Europa at the same time in its orbit failed to yield a plume detection, casting doubt on the tidal control hypothesis. The purpose of this study is to analyze the timing of plume eruptions within the context of Europa’s tidal cycle to determine whether such a link exists and examine the inferred similarities and differences between plume activity on Europa and Enceladus. To do this, we determine the locations and orientations of hypothetical tidally-driven fractures that best match the temporal variability of the plumes observed at Europa. Specifically, we identify model faults that are in tension at the time in Europa’s orbit when a plume was detected and in compression at times when the plume was not detected. We find that tidal stress driven solely by eccentricity is incompatible with the observations unless additional mechanisms are controlling the eruption timing or restricting the longevity of the plumes. The addition of obliquity tides, and corresponding precession of the spin pole, can generate a number of model faults that are consistent with the pattern of plume detections. The locations and orientations of these hypothetical source fractures are robust across a broad range of precession rates and spin pole directions. Analysis of the stress variations across the fractures suggests that the plumes would be best observed earlier in the orbit (true anomaly ∼120°). Our results indicate that Europa’s plumes, if confirmed, differ in many respects from the Enceladean plumes and that either active fractures or volatile sources are rare.

A laboratory study of ion-induced erosion of ice-covered carbon grains

Context. It has been confirmed that solid carbon dioxide (CO2) is abundantly present along the line of sight to quiescent clouds and star-forming regions via space IR observations with ISO-SWS and Spitzer Space Telescope. Since CO2 has low abundance in the gas-phase, the assumption is that it is synthesized on grains after energetic processing of icy mantles and surface reactions. Aims. The role of solid carbon is investigated as a reservoir for molecule formation and structural modifications of the material with and without an ice layer upon ion bombardment. Methods. A gas-phase condensation technique was used to prepare a layer of 13 C amorphous grains. These grains were covered with H2 Oa nd O 2 ice and finally bombarded with 200 keV protons. The formation of new molecular species was analyzed using IR spectroscopy. The formation cross sections of solid 13 CO and 13 CO2 were determined from the increase in the column density as a function of the fluence. In addition, bare carbon grains were bombarded with a comparable fluence of protons to study the processing of the grains without ice layer. Imaging techniques such as transmission electron microscopy were used to monitor the changes in the structure. Results. CO and CO2 were formed efficiently at the interface between ice and solid carbon grains at the expense of solid carbon, leading to strong grain erosion. Given the initial thickness of our C-samples (about 120 nm), this resulted in an erosion of about 50% after 200 keV proton bombardment with 6.76 × 10 16 ions/cm 2 . The column density of CO and CO2 follows an exponential trend as a function of the irradiation fluence. The asymptotic values obtained when O2 ice is deposited on top of the carbon grains are about one order of magnitude higher than the values obtained when H2O ice is deposited on the solid carbon layer. The carbon grains were strongly graphitized upon ion bombardment in a surface layer. Less graphitization accompanied by the formation of fullerene molecules and structures from cage fragments present in the original material were observed beneath the graphitic layer. Conclusions. The formation of CO and CO2 at the expense of solid carbon strongly restricts the lifetime of the solid carbon material and may influence the formation of more complex molecules in astrophysical environments. Graphitization of carbonaceous grains upon ion bombardment affect the spectral properties of the carbon grains in particular in the far-IR range.

Penetration of solar radiation into pure and Mars-dust contaminated snow

Rock and soil surface layers absorb and reflect incoming solar radiation immediately at the surface. Ices on the other hand, whilst opaque in the infrared, are partially transparent in the visible spectral range. These properties are responsible for the “solid-state greenhouse effect” (SSGE), which may play an important role in the energy balance of icy surfaces in the Solar System. To model the SSGE, we need to know not only thermal properties but also optical properties such as the albedo and the absorption scale length of the ice. We have investigated the absorption scale length, also known as e-folding scale, of snow/dust mixtures within the scope of a project directed at investigating the behaviour of the martian polar caps. After measuring the e-folding scale of recrystallized snow we can now also relate the dust content of contaminated snow to the penetration depth of sunlight into the mixture. Equally important, however, is our observation that light penetration through the mixture is dramatically affected by small-scale inhomogeneities.

Theory of Time-Dependent Freezing. Part II: Scheme for Freezing Raindrops and Simulations by a Cloud Model with Spectral Bin Microphysics

Abstract The time-dependent process of raindrop freezing is described in a general form, including thermodynamic effects from the accretion of cloud liquid and cloud ice. Freezing drops (FDs) larger than 80 μm (and their water mass) are represented explicitly in a cloud model with spectral bin microphysics. FDs consist of interior water covered by ice initially. Possibilities of both dry (icy surface) and wet growth (surface covered by liquid) of FDs are accounted for. Schemes of time-dependent freezing for rain (discussed in this paper) and wet growth of hail and graupel (discussed in Part I) were implemented in a spectral bin microphysics cloud model. The model predicted that accretion of liquid produces giant FDs of 0.5–2 cm in diameter, far larger than purely liquid drops can become. This growth of FDs is promoted by recirculation from the downdraft back into the updraft and by cessation of internal freezing from some accreted liquid remaining unfrozen (wet growth of FDs). Significant contents of FDs reach a height level of 7 km (−29°C) in the simulated storm. After FDs finish freezing and become hailstones, wet growth may resume. The critical diameter separating wet- and dry-growth regimes is predicted to increase with height for FDs and is more vertically uniform for hail. A sensitivity test shows that time-dependent freezing initially delays the formation of hail but later in the mature stage of the storm boosts it. Convection is invigorated. Hail and freezing drops are upwelled to higher levels, causing hail to grow to sizes up to 100% larger than without time-dependent freezing.

INVESTIGATION OF AUTOMOBILE ACTIVE SAFETY CONTROL SYSTEMS EFFICIENCY AND THEIR IMPACT ON THE DRIVER’S BEHAVIOUR

The paper deals with the influence of active car safety systems on driver‘s behavior in emergency situations, i.e. emergency braking, steering angle, etc. Several models of real vehicles have been tested in order to analyse the ABS and ESP systems operation efficiency. The results of emergency braking and stability in real vehicle testing with ABS and ESP stability control systems switched on and off are presented in detail. In order to get the maximum impact of ABS and ESP systems (full activated) the real vehicles were tested on the asphalt paved road covered with wet snow. Tests were also carried out on the road sections with different pavement and state. The XL Meter Pro Beta measurement device was used for the real vehicle testing. The brakes and active safety systems of the vehicles have been tested for their effectiveness at different conditions: when the vehicle is braking on horizontal wet asphalt, and on an icy gravel surface, at a different initial running speed: 40km/h, 70 km/h and 100 km/h. During the real vehicle testing the stability during emergency braking resulted in the assessment of influence of active safety systems on handling the vehicle and its stability, and the driver‘s behaviour in emergency situations i.e. on a slippery road, or at sharp steering angle. The results of real vehicle testing have been presented in the paper in the form of charts. Examination of a vehicle emergency braking and stability systems results in the conclusions concerned with handling of the vehicle ad application of the above systems.

Non-thermal ion desorption from an acetonitrile (CH3CN) astrophysical ice analogue studied by electron stimulated ion desorption.

The incidence of high-energy radiation onto icy surfaces constitutes an important route for leading new neutral or ionized molecular species back to the gas phase in interstellar and circumstellar environments, especially where thermal desorption is negligible. In order to simulate such processes, an acetonitrile ice (CH3CN) frozen at 120 K is bombarded by high energy electrons, and the desorbing positive ions are analyzed by time-of-flight mass spectrometry (TOF-MS). Several fragment and cluster ions were identified, including the Hn=1-3(+), CHn=0-3(+)/NHn=0-1(+); C2Hn=0-3(+)/CHn=0-3N(+), C2Hn=0-6N(+) ion series and the ion clusters (CH3CN)n=1-2(+) and (CH3CN)n=1-2H(+). The energy dependence on the positive ion desorption yield indicates that ion desorption is initiated by Coulomb explosion following Auger electronic decay. The results presented here suggest that non-thermal desorption processes, such as desorption induced by electronic transitions (DIET) may be responsible for delivering neutral and ionic fragments from simple nitrile-bearing ices to the gas-phase, contributing to the production of more complex molecules. The derived desorption yields per electron impact may contribute to chemical evolution models in different cold astrophysical objects, especially where the abundance of CH3CN is expected to be high.

Spectroscopy and viability of Bacillus subtilis spores after ultraviolet irradiation: implications for the detection of potential bacterial life on Europa.

One of the most habitable environments in the Solar System outside of Earth may exist underneath the ice on Europa. In the near future, our best chance to look for chemical signatures of a habitable environment (or life itself) will likely be at the inhospitable icy surface. Therefore, it is important to understand the ability of organic signatures of life and life itself to persist under simulated europan surface conditions. Toward that end, this work examined the UV photolysis of Bacillus subtilis spores and their chemical marker dipicolinic acid (DPA) at temperatures and pressures relevant to Europa. In addition, inactivation curves for the spores at 100 K, 100 K covered in one micron of ice, and 298 K were measured to determine the probability for spore survival at the surface. Fourier transform infrared spectra of irradiated DPA showed a loss of carboxyl groups to CO2 as expected but unexpectedly showed significant opening of the heterocyclic ring, even for wavelengths>200 nm. Both DPA and B. subtilis spores showed identical unknown spectral bands of photoproducts after irradiation, further highlighting the importance of DPA in the photochemistry of spores. Spore survival was enhanced at 100 K by ∼5× relative to 298 K, but 99.9% of spores were still inactivated after the equivalent of ∼25 h of exposure on the europan surface.

Perceived risks for slipping and falling at work during wintertime and criteria for a slip-resistant winter shoe among Swedish outdoor workers

The leading cause of work related accidents in Sweden is falls. Many slips and falls occur on icy and snowy surfaces, but there is limited knowledge about how to prevent accidents during outdoor work in winter conditions.The purpose of this study was to describe risk factors of slips and falls and criteria for slip-resistant winter shoes from a user perspective. The result is based on focus group interviews with 20 men and women working in mail delivery, construction and home care in Sweden. The data was analyzed with qualitative content analysis.Risk factors described were related to physical work environment, risky work situations, individual and organizational factors. User criteria for winter work shoes focused on safety, adaptation to the environment, usability and own priorities.The mechanisms of slips and falls during outdoor work are complex. There is a need for more functional and user friendly work shoes than those available and user preferences should be considered by shoe designers. Future challenges include finding ways to make individually adapted shoes suitable for changing work environments, situations and tasks.

Fragmentation and Ion Desorption from Condensed Pyrimidine by Electron Impact: Implications for Cometary and Interstellar Heterocyclic Chemistry

The desorption process induced by photons, electrons, or ions onto icy surfaces is an important mechanism for leading neutral or ionized molecular species to the gas phase in interstellar and circumstellar environments. In this work, we report the results of high energy electron impact onto a condensed pyrimidine ice by means of electron-stimulated ion desorption (ESID). Desorbed cations from the icy surface were analyzed by time-of-flight mass spectrometry (TOF-MS). The most abundant desorbed ions are H+ and H2+, although several other fragments, such as C2H2+, HCN+, C3H3+, CHN2+, C2H2N2H+, and C4H4N2H+, have also been identified. The fragmentation pattern of pyrimidine was found to be characterized by six distinct regions on its desorption spectra, containing ionic fragments bearing one to six members of the original pyrimidine ring. Five-membered fragment ions were observed for the first time in electron impact experiments. Absolute values of desorption yield for several ions were determined. Desorbed ions observed in this experiment are in agreement with observations of the comet Halley coma composition and may act as markers of the presence of pyrimidine in the interstellar medium.

Finding planets and life among the stars: For the first time in history, mankind has the tools to look for other planets and whether these might host life.

Are we alone in the universe? How can we find out? What would happen if we made contact with extraterrestrial life forms, intelligent or otherwise? These questions have fascinated humans ever since we understood that there is a universe beyond our pale blue dot. As the British physicist and author Arthur C Clarke put it: “Two possibilities exist: either we are alone in the universe or we are not. Both are equally frightening”. > Two possibilities exist: either we are alone in the universe or we are not. Both are equally frightening Speculation about the existence and nature of extraterrestrial life—and how humans might find and interact with it—has gone on for several millennia, but we live in the first age where the tools are available to collect, analyze and understand the potential evidence. The fundamental question “Are we alone?” drives the field of astrobiology, whose researchers tackle everything from microbes that thrive in extreme environments, to the origin of Earth's moon and oceans, to the potential for ecosystems under the icy surfaces of Mars and Jupiter's moon Europa. Momentum is also gathering for the search for habitable Earth‐like worlds orbiting other stars. However, the detection of “exo‐Earths”, and the discovery of any life signs thereupon, is one of the most technically and scientifically challenging feats ever attempted by astronomers. The journey begins with an understanding of our own home. To the Apollo astronauts, the Earth looked like a shiny glass marble suspended above a moonscape of gray and black. In December 1972, the Apollo 17 crew captured on film a view of Earth that can only be seen from a spaceship aligned between the Earth and the sun: in its fully illuminated glory, suspended in endless black space (Fig 1). This so‐called Blue Marble image went on to become one …

Evidence for subduction in the ice shell of Europa

Despite widespread evidence for extension, there have been few signs of contraction on the icy surface of Jupiter’s Europa. Evidence for a subduction-like convergent boundary suggests that Europa may have active plate tectonics.

Iapetus’ near surface thermal emission modeled and constrained using Cassini RADAR Radiometer microwave observations

Since its arrival at Saturn, the Cassini spacecraft has had only a few opportunities to observe Iapetus, Saturn’s most distant regular satellite. These observations were all made from long ranges (>100,000km) except on September 10, 2007, during Cassini orbit 49, when the spacecraft encountered the two-toned moon during its closest flyby so far. In this pass it collected spatially resolved data on the object’s leading side, mainly over the equatorial dark terrains of Cassini Regio (CR). In this paper, we examine the radiometry data acquired by the Cassini RADAR during both this close-targeted flyby (referred to as IA49-3) and the distant Iapetus observations. In the RADAR’s passive mode, the receiver functions as a radiometer to record the thermal emission from planetary surfaces at a wavelength of 2.2-cm. On the cold icy surfaces of Saturn’s moons, the measured brightness temperatures depend both on the microwave emissivity and the physical temperature profile below the surface down to a depth that is likely to be tens of centimeters or even a few meters. Combined with the concurrent active data, passive measurements can shed light on the composition, structure and thermal properties of planetary regoliths and thus on the processes from which they have formed and evolved. The model we propose for Iapetus’ microwave thermal emission is fitted to the IA49-3 observations and reveals that the thermal inertias sensed by the Cassini Radiometer over both CR and the bright mid-to-high latitude terrains, namely Ronceveaux Terra (RT) in the North and Saragossa Terra (ST) in the South, significantly exceed those measured by Cassini’s CIRS (Composite Infrared Spectrometer), which is sensitive to much smaller depths, generally the first few millimeters of the surface. This implies that the subsurface of Iapetus sensed at 2.2-cm wavelength is more consolidated than the uppermost layers of the surface. In the case of CR, a thermal inertia of at least 50Jm−2K−1s−1/2, and most probably >200Jm−2K−1s−1/2 is inferred. This suggests a gradient in density with depth or, more likely, that the Radiometer has probed the icy substrate underlying the dark layer. Furthermore, the measured thermal emission is found to arise from the upper few meters of the subsurface, which points to tholins, rather than iron oxide compounds, as the primary contaminants of the dark material. We also find that, although there is a latitudinal decrease probably related to the thinning of the dark layer away from the Equator, the CR region exhibits a high 2.2-cm emissivity, 0.87 in average, which is close to the emissivity of Phoebe, a putative source of the dark matter. In the case of RT+ST, model fitting points to a mean thermal inertia of ∼160Jm−2K−1s−1/2 along with the possible presence of an absorbing compound in the regolith of the bright terrains. Nevertheless, this layer is transparent enough for the Radiometer to capture the seasonal contrast between the northern and southern hemispheres. Lastly, a global decline of the microwave emissivity with latitude is revealed; it is probably indicative of a progressive increase of the water ice content in the near surface.

On the continued search for an infrared spectroscopic identification of OH radicals in water-ice

The chemistry of hydroxyl (OH) radicals plays a key role in the radiolysis and photolysis of water-rich ices of astrochemical origin. Other radical species such as hydroperoxy (HO2) radicals are also potentially important in oxygen cycles that exist on icy satellite surfaces due to the stoichiometric loss of H from radiation-processed water-ices. Both OH and HO2 are likely key intermediates in the formation of H2O in the ISM. Despite the importance of such species, laboratory measurements of OH and HO2 in water-ices are sparse. This is due to a combination of low abundances and overlapping spectral features that makes detection using infrared spectroscopy difficult. There have been several reports in the literature claiming detection of both OH and HO2 in laboratory water-ices. In the present work OH radicals are formed in the gas-phase prior to deposition with water to attempt to trap them stably in water-ice at 6 K. The present work does not find any IR spectral detection of OH in ices prepared by this method. Chemical reactions are likely the sink of OH that limits detection in additiontospectraloverlapwithH2O.Theimplicationsofthisforastrochemistryarediscussed herein. Additional experiments have been performed using the matrix-isolation technique to determine the intrinsic band strengths of the infrared absorption of the OH radical and the related H2O–HO complex. These could be used to quantify OH radical in non-water-ices where spectral interference from H2O is absent.

Challenges in modelling the reaction chemistry of interstellar dust.

Studies aiming to understand the physicochemical properties of interstellar dust and the chemical reactions that occur on and in it have traditionally been the preserve of astronomical observation and experimental attempts to mimic astronomically relevant conditions in the laboratory. Increasingly, computational modelling in its various guises is establishing a complementary third pillar of support to this endeavour by providing detailed insights into the complexities of interstellar dust chemistry. Inherently, the basis of computational modelling is to be found in the details (e.g. atomic structure/composition, reaction barriers) that are difficult to probe accurately from observation and experiment. This bottom-up atom-based theoretical approach, often itself based on deeper quantum mechanical principles, although extremely powerful, also has limitations when systems become too large or complex. In this Perspective, after first providing a general background to the current state of observational-based knowledge, we introduce a number of computational modelling methods with reference to recent state-of-the-art studies, in order to highlight the capabilities of such approaches in this field. Specifically, we first outline the use of computational chemistry methods for dust nucleation, structure, and individual reactions on bare and icy dust surfaces. Later, we review kinetic modelling of networks of reactions relevant to dust chemistry and how to take into account quantum tunnelling effects in the low temperature reactions in the interstellar medium. Finally, we point to the future challenges that need to be overcome for computational modelling to provide even more detailed and encompassing perspectives on the nature and reaction chemistry of interstellar dust.

New experimental sublimation energy measurements for some relevant astrophysical ices

Context. The knowledge of the sublimation energy of ices allows us to better understand the dynamics between surfaces and atmospheres of different environments of astrophysical interest where ices are present. Aims. This work is intended to provide sublimation energy values for a set of pure ices (CO, CH4 ,C O 2 ,N 2 ,a nd NH 3 )u sing an ew experimental procedure. The results were compared to some values obtained by other authors under different conditions and/or methods, to check the reliability of this new method. Methods. We used the frequency variation obtained from a quartz crystal microbalance to calculate the sublimation energy from the Polany-Wigner equation for the first time. Results. The results obtained are relevant since there are few previous values of sublimation energy reported on these molecules in these conditions of pressure and temperature, which are representative of astrophysical regions. These values are needed in models used to interpret dynamics of icy surfaces. In general, our results compare well to other ones obtained by different methods and complement those previously available.

SWIR Cameras for the Automotive Field: Two Test Cases

This paper presents the results obtained by the 2WIDE_SENSE Project, an EU funded project aimed at developing a low cost camera sensor able to acquire the full spectrum from the visible bandwidth to the Short Wave InfraRed one (from 400 to 1700 nm). Two specific applications have been evaluated, both related to the automotive field: one regarding the possibility of detecting icy and wet surfaces in front of the vehicle and the other regarding the pedestrian detection capability. The former application relies on the physical fact that water shows strong electromagnetic radiation absorption capabilities in the SWIR band around 1450 nm and thus an icy or wet pavement should be seen as dark; the latter is based on the observation that the amount of radiation in the SWIR band is quite high even at night and in case of poor weather conditions. Results show that even the use of SWIR and visible spectrum seems to be a promising approach; the use in outdoor environment is not always effective.

Librational response of a deformed 3-layer Titan perturbed by non-Keplerian orbit and atmospheric couplings

The analyses of Titan׳s gravity field obtained by Cassini space mission suggest the presence of an internal ocean beneath its icy surface. The characterization of the geophysical parameters of the icy shell and the ocean is important to constrain the evolution models of Titan. The knowledge of the librations, that are periodic oscillations around a uniform rotational motion, can bring a piece of information on the interior parameters.The objective of this paper is to study the librational response in longitude from an analytical approach for Titan composed of a deep atmosphere, an elastic icy shell, an internal ocean, and an elastic rocky core perturbed by the gravitational interactions with Saturn. We start from the librational equations developed for a rigid satellite in synchronous spin–orbit resonance. We introduce explicitly the atmospheric torque acting on the surface computed from the Titan IPSL GCM (Institut Pierre Simon Laplace General Circulation Model) and the periodic deformations of elastic solid layers due to the tides. We investigate the librational response for various interior models in order to compare and to identify the influence of the geophysical parameters and the impact of the elasticity.The main librations arise at two well-separated forcing frequency ranges: low forcing frequencies dominated by the Saturnian annual and semi-annual frequencies, and a high forcing frequency regime dominated by Titan׳s orbital frequency around Saturn. At low forcing frequency, the librational response is dominated by the Saturnian gravitational torque and the atmospheric torque has a small effect. In addition, the libration amplitude in that case is almost equal to the magnitude of the perturbation. The modulation of the gravitational torque amplitude at the orbital frequency with periodic deformation induces long-period terms in the librational response which contain information on the internal structure. At high forcing frequency the libration depends on the inertia of the layers and the elasticity can strongly reduce its amplitude at orbital frequency. For example, the amplitude of diurnal libration for oceanic models goes from about 320–390m if the icy shell is purely rigid to 60–85m when the elasticity is included, i.e. a reduction of about 80%. For models without ocean, diurnal libration goes from 52m in a rigid case to 50m for an elastic case, a very low reduction due to the weak deformation of an entirely solid satellite compared to the deformation of a thin icy shell. Oceanic models with elastic solid layers have the same order of libration amplitude than the oceanless models, which makes more challenging to differentiate them by the interpretation of librational motion.