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Thermal conductivity of powdered materials under vacuum conditions is a valuable physical parameter in the context of planetary sciences. We report results of thermal conductivity measurements of 90–106 μm and 710–1000 μm glass beads, and lunar regolith simulant using two different experimental setups for varying the compressional stress and the temperature, respectively. We found the thermal conductivity increase with the compressional stress, for example, from 0.003 to 0.008 W m −1 K −1 for the glass beads of 90–106 μm in diameter at the compressional stress less than 20 kPa. This increase of the thermal conductivity is attributed the areal enlargement of the contacts between particles due to their elastic deformation. The thermal conductivity increased also with temperature, which primarily represented enhancement of the radiative heat conduction between particles. Reduction of the estimated radiative conductivity from the effective thermal conductivity obtained in the first experiment yields the relation between the solid conductivity (conductive contribution through inter-particle contacts) and the compressional stress. We found that the solid conductivity is proportional to approximately 1/3 power of the compressional stress for the glass beads samples, while the regolith simulant showed a weaker exponent than that of the glass beads. We developed a semi-empirical expression of the thermal conductivity of the lunar regolith using our data on the lunar regolith simulant. This model enabled us to estimate a vertical distribution of the lunar subsurface thermal conductivity. Our model provides an examination for the density and compressional stress relationships to thermal conductivity observed in the in-situ measurements in Apollo 15 and 17 Heat Flow Experiments. [ABSTRACT FROM AUTHOR]

Gas bearings are popular for their high speed capabilities, low friction and clean operation, but suffer from poor damping, which poses challenges for safe operation in presence of disturbances. Feedback control can achieve enhanced damping but requires low complexity models of the dominant dynamics over its entire operating range. Models from first principles are complex and sensitive to parameter uncertainty. This paper presents an experimental technique for “in situ” identification of a low complexity model of a rotor–bearing–actuator system and demonstrates identification over relevant ranges of rotational speed and gas injection pressure. This is obtained using parameter-varying linear models that are found to capture the dominant dynamics. The approach is shown to be easily applied and to suit subsequent control design. Based on the identified models, decentralised proportional control is designed and shown to obtain the required damping in theory and in a laboratory test rig. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to develop an experimental system to apply high rates of loading, in order to characterize the behaviour of bolted steel connections subjected to accidental loads, such as impact. The work presented in this paper is part of an ongoing research project at the University of Coimbra IMPACTFIRE PTDC/ECM/110807/2009. Design/methodology/approach – The experimental set-up was designed to test under tension T-stubs and is capable to apply high strain rates. The test rig comprises a series of beams and steel elements placed horizontally, providing resistance and stiffness for the proposed tests. The loading system is operated by high-pressure nitrogen and it comprises three main components: pneumatic reservoir, pneumatic cylinder and a rapidly opening valve, which and allows the instantaneous nitrogen flow from the reservoir to the cylinder. This paper presents a detailed description of the experimental components developed, designed and fabricated at University of Coimbra. Furthermore, the data acquisition system, the methodology for analysis of the results and the results of preliminary tests are also reported. Findings – The results of the tests showed that the developed system is capable to apply an impact force in the specimens, the shape of the force and acceleration, in terms of duration and magnitude provided by the system showed that the system is capable to apply and simulate an impact force in specimens under tension. Moreover, the results reached under high rates of loading are compared with those reached under quasi-static loading; an increase of the plastic and ultimate resistances and a decrease of the deformation capacity are noticed. Originality/value – The value of this paper is to describe the development of a new experimental system to perform tests at high strain rates. The results of the experimental tests of T-stub under tension are presented herein. [ABSTRACT FROM AUTHOR]

Intense east–west winds called zonal jets are observed in the atmospheres of Jupiter and Saturn and extend in their deep interior. We present experimental results from a fully three-dimensional laboratory analog of deep gas giants zonal jets. We use a rapidly rotating deep cylindrical tank, filled with water, and forced by a small-scale hydraulic circulation at the bottom. A topographic β -effect is naturally present because of the curvature of the free surface. Instantaneous turbulent zonal jets spontaneously emerge from the small-scale forcing, equilibrate at large scale, and can contain up to 70% of the total kinetic energy of the flow once in a quasi-steady state. We show that the spectral properties of the experimental flows are consistent with the theoretical predictions in the zonostrophic turbulence regime, argued to be relevant to gas giants. This constitutes the first fully-experimental validation of the zonostrophic theory in a completely three-dimensional framework. Complementary, quasi-geostrophic (QG) simulations show that this result is not sensitive to the forcing scale. Next, we quantify the potential vorticity (PV) mixing. While PV staircasing should emerge in the asymptotic regime of the gas giants, only a moderate PV mixing occurs because of the strong forcing and dissipation, as confirmed by QG simulations at smaller Ekman number. We quantify the local PV mixing by measuring the equivalent of a Thorpe scale, and confirm that it can be used to estimate the upscale energy transfer rate of the flow, which otherwise needs to be estimated from a much more demanding spectral analysis. [Display omitted] • We present a fully three-dimensional laboratory analog of deep gas giants zonal jets. • We validate predictions made for the gas giants in a two-dimensional framework. • Local potential vorticity mixing is used to estimate the upscale transfer of energy. • Quasi-geostrophic numerical simulations allow to alleviate experimental limitations. [ABSTRACT FROM AUTHOR]

In this paper, we present an alternative to Hapke's correction for the photometric effect of macroscopic roughness of planetary surfaces (Hapke, 1984). Our model includes the effects of both single-facet scattering and multi-facet scattering. The single-facet scattering model is derived directly from the definition of bidirectional reflectance of a rough surface. We model projected shadowing by adopting an approximation published elsewhere in the literature. Monte Carlo simulations of single-facet scattering demonstrate very good agreement with the single-facet scattering component of our model. Using 3D printed molds with known roughness statistics, we prepared rough mineral surfaces consisting of quartz and olivine in the laboratory. We recorded extensive measurements of the rough surface bidirectional reflectance over a wide range of illumination and view geometries at 1751 wavelength bands ranging from 500–2250 nm. By fitting the residual between the measured bidirectional reflectance and our single-facet scattering model, we developed an empirical approximation for multi-facet scattering. Our results show that the multi-facet scattering is proportional to the surface's diffusive reflectance, RMS slope, and the cosine of the illumination angle. Furthermore, the multi-facet scattering is approximately Lambertian for phase angles less than 90° but becomes forward scattering at higher phase angles. Our empirical multi-facet scattering model incorporates all of these features. As a surface becomes more macroscopically rough, our data show that the overall reflectance distribution becomes progressively more backscattering in a way that is distinct from the shadow hiding opposition effect. We refer to this effect as the macroscopic roughness backscattering bias (MRBB), which affects the entire hemisphere rather than being localized to small phase angles. Our proposed model is more accurate than Hapke's for phase angles less than 90°, and the accuracy of the two models is comparable at higher phase angles. However, researchers should be aware of an issue regarding the roughness parameter defined in Hapke's model, namely the fact that " ϑ ¯ " is not actually equal to the mean slope angle of the surface for the probability density function used in the model. This is an issue which apparently has gone unnoticed in the literature, and has potentially caused the model to be applied incorrectly in past studies. • A new photometric correction for macroscopic roughness of soil surfaces is presented. • The proposed correction includes an empirical model for multi-facet scattering. • A spectro-gonio-radiometer is used to assess the model on rough quartz and olivine. • The proposed correction demonstrates superior RMSE over Hapke's correction. • Macroscopic roughness causes an overall bias toward backward scattering in the BRDF. [ABSTRACT FROM AUTHOR]

This paper presents a new version of the modal identification method previously proposed by the authors. The method is aimed at experimental tests of lipped channel columns but may also be applied to numerical columns. The first version of the method considered only three main deformation modes: local, symmetric distortional and minor axis flexural global modes. In this new version, anti-symmetric distortional and flexural–torsional modes are included in the formulation and original expressions for local mode are improved. The inclusion of new modes does not alter the procedure to perform the modal identification of the first version. In short, simple displacement functions are assumed for each buckling mode and through an error minimization process the participation of each mode in a generic deformed shape of the column is assessed. The new version of the method is validated against numerical results from Generalized Beam Theory (GBT) for columns undergoing D–G interaction and applied to experimental results of lipped channel columns. • A previously proposed modal identification for analysis of experimental results of lipped channel columns is expanded. • Improved displacement functions for local buckling are proposed. • The method is validated against GBT for numerical columns undergoing distortional–global​ interaction. • The method is applied to results from experimental tests allowing the identification of the main buckling modes. • Based on few experimental data, the proposed method is able to reconstruct entire deformed shape of experimental columns. [ABSTRACT FROM AUTHOR]

Bolted joints are the most common solution for joining composite components in aerospace structures. Critical structures such as wing to fuselage joints, or flight control surface fittings use bolted joining techniques. Recent research concluded that higher bearing strengths in composite bolted joints can be achieved by a CFRP/ Titanium hybrid lay-up in the vicinity of the bolted joint. The high costs of titanium motivate a similar research with the more cost competitive austenitic steel. An experimental program was performed in order to compare the apparent inter-laminar shear stress (ILSS) of a CFRP reference beam with the ILSS of hybrid CFRP/Steel beams utilizing different surface treatments in the metallic ply. The apparent ILSS was determined by short beam test, a three-point bending test. Finite element models using cohesive elements in the CFRP/Steel interface were built to simulate the short beam test in the reference beam and in the highest interlaminar shear stress hybrid beam. The main parameters for a FEM simulation of inter laminar shear are the cohesive elements damage model and appropriate value for the critical energy release rate. The results show that hybrid CFRP/Steel have a maximum ILSS very similar to the ILSS of the reference beam. Hybrid CFRP/Steel is a competitive solution when compared with the reference beam ILSS. FEM models were able to predict the maximum ILSS in each type of beam.

A recently developed dual-anneal diffusion-multiple approach is employed to the determination of the Fe-Cr-Mo phase diagram at intermediate temperatures. Diffusion multiples of Fe-Cr-Ni-Co-Mo were first annealed at 1200 °C for 500 h to create wide ranges of solid solution compositions. Subsequent annealing of the diffusion multiples at individual intermediate temperatures induced various precipitate phases. Electron probe microanalysis (EPMA) across the interface between large precipitates and the matrix phase provided local equilibrium information for the establishment of equilibrium tie-lines which are utilized to construct the Fe-rich part of the Fe-Cr-Mo isothermal sections at 900 and 800 °C. The Mo-rich part of the isothermal sections at intermediate temperatures was not obtained due to the sluggish kinetics of precipitation and growth, resulting in too small precipitates for reliable EPMA composition evaluation. A complete 1200 °C isothermal section of the Fe-Cr-Mo system is also established from EPMA data on a water quenched diffusion multiple that was annealed at 1200 °C for 500 h only without a second anneal. [ABSTRACT FROM AUTHOR]

We measured the bidirectional reflectance in the VIS–NIR spectral range of different surfaces prepared from small-grained spherical water–ice particles over a wide range of incidence and emission geometries, including opposition. We show that coherent backscattering is dominating the opposition effect on fresh sample material, but its contribution decreases when particles become more irregularly shaped and the bulk porosity increases. Strong temporal evolution of the photometric properties of icy samples, caused by particle sintering and resulting in a decrease of backscattering, is shown. The sintering of the ice particles is documented using cryo-SEM micrographs of fresh and evolved samples. To complement the photometric characterization of ices, multiple high albedo laboratory analogs were investigated to study the effects of shape, grain size distribution, wavelength and surface roughness. In addition to the main backscattering peak, the phase curves also display the effect of glory in the case of surfaces of granular surfaces formed by either spherical ice or glass particles. We show that the angular position of the glory can be used to determine accurately the average size of the particles. Reflectance data are fitted by the Hapke photometric model, the Minnaert model and three morphological models. The resulting parameters can be used to reproduce our data and compare them to the results of other laboratory experiments and astronomical observations. [ABSTRACT FROM AUTHOR]

Research in elastohydrodynamic lubrication (EHL) was, at its very beginning, essentially numerical, and even analytical. This area has, however, significantly evolved due to the necessity of validating the first models experimentally. Moreover, it soon became clear that the elastohydrodynamic (EHD) problem would be a topic of much more complex nature than the basic one involving perfectly smooth surfaces, Newtonian fluid, isothermal flow, etc. The experimental approach was the natural choice to make progress in offering the possibility of comparisons, first at the global level of the contact and, over time, at higher and higher spatial resolutions. The in situ analysis of elastohydrodynamic contacts was launched and everyone knows how much its contribution to the field has been and remains important. The present paper takes the task of reviewing the different in situ experimental techniques that have proven to be able to map the key-parameters in living EHD contacts. They are presented both in chronological order and according to the physical mechanism behind them, namely electrical, optical and acoustic methods. A last section presents some opportunities and recommendations for future works, with the aim to improve further our understanding of EHL. [ABSTRACT FROM AUTHOR]

The performance of the placenta as a gas exchanger has a direct impact on the future health of the newborn. To provide accurate estimates of respiratory gas exchange rates, placenta models need to account for both the physiology of exchange and the organ morphology. While the former has been extensively studied, accounting for the latter is still a challenge. The geometrical complexity of placental structure requires use of carefully crafted approximations. We present here the state of the art of respiratory gas exchange placenta modeling and demonstrate the influence of the morphology description on model predictions. Advantages and shortcomings of various classes of models are discussed, and experimental techniques that may be used for model validation are summarized. Several directions for future development are suggested. [ABSTRACT FROM AUTHOR]

Evaluations of the fracture toughness in metal matrix composites (Duralcan reinforced with 15% of Al(2)0(3) and SiC) are presented in this work. The application of Elastic Plastic Fracture Mechanics is discussed and the obtained values are compared with the ones obtained by means of Linear Elastic Fracture Mechanics. Results show that J IC derived K JC values are higher than the corresponding values obtained by direct application of the linear elastic methodology. The effect of a heat treatment on the material fracture toughness was also evaluated in which the analyzed approaches showed, not only different toughness values, but also opposite tendencies. A second comparison of the J IC and K JC values obtained in this work with toughness values reported in the literature is presented and discussed.

The focus of this paper is on the mixing of a conserved passive scalar for Sc = 1 (Sc is the Schmidt number) in axisymmetric turbulence for which the initial injections of turbulent kinetic energy and scalar variance are similar. Two confined-opposed-jets (COJ) are experimentally studied through simultaneous PIV (particle image velocimetry) and PLIF (planar laser induced fluorescence) measurements, for different flow regimes. One-point transport equation for the scalar variance is assessed through experimental data, along the common axis of the two opposed jets, and different physical phenomena are revealed (production, diffusion, dissipation). The production of scalar variance is equilibrated by the diffusion term (∼75%) and the mean dissipation of the scalar variance (∼25%). To further assess the scalar behaviour at each scale in this anisotropic, but axisymmetric, flow, a scale-by-scale scalar variance budget equation is derived for axisymmetric turbulence. This equation reduces to Yaglom's 4/3 law, under additional restrictions. The equation is assessed through experimental data, in the impingement region between the two COJ. In particular, the anisotropic energy transfer along different directions is quantified. It is shown that for scales smaller than the size of the central region, Δ, the cascade of the scalar variance is completely inhibited, independently of the particular direction. For scales larger than Δ, the apparent aspect of the energy transfer is that of an inverse cascade, with positive values of the scalar variance transfer. Nonetheless, inhomogeneity of the flow and mixing at those scales is directly responsible for these positive values. [ABSTRACT FROM PUBLISHER]

The single particle phase function describes the manner in which an average element of a granular material diffuses the light in the angular space usually with two parameters: the asymmetry parameter b describing the width of the scattering lobe and the backscattering fraction c describing the main direction of the scattering lobe. Hapke proposed a convenient and widely used analytical model to describe the spectro-photometry of granular materials. Using a compilation of the published data, Hapke (Hapke, B. [2012]. Icarus 221, 1079–1083) recently studied the relationship of b and c for natural examples and proposed the hockey stick relation (excluding b > 0.5 and c > 0.5 ). For the moment, there is no theoretical explanation for this relationship. One goal of this article is to study a possible bias due to the retrieval method. We expand here an innovative Bayesian inversion method in order to study into detail the uncertainties of retrieved parameters. On Emission Phase Function (EPF) data, we demonstrate that the uncertainties of the retrieved parameters follow the same hockey stick relation, suggesting that this relation is due to the fact that b and c are coupled parameters in the Hapke model instead of a natural phenomena. Nevertheless, the data used in the Hapke (Hapke, B. [2012]. Icarus 221, 1079–1083) compilation generally are full Bidirectional Reflectance Diffusion Function (BRDF) that are shown not to be subject to this artifact. Moreover, the Bayesian method is a good tool to test if the sampling geometry is sufficient to constrain the parameters (single scattering albedo, surface roughness, b , c , opposition effect). We performed sensitivity tests by mimicking various surface scattering properties and various single image-like/disk resolved image, EPF-like and BRDF-like geometric sampling conditions. The second goal of this article is to estimate the favorable geometric conditions for an accurate estimation of photometric parameters in order to provide new constraints for future observation campaigns and instrumentations. [ABSTRACT FROM AUTHOR]

Here we present our recent studies of proton-irradiated and unirradiated ammonium hydrosulfide, NH 4 SH, a compound predicted to be an important tropospheric cloud component of Jupiter and other giant planets. We irradiated both crystalline and amorphous NH 4 SH at 10–160 K and used IR spectroscopy to observe and identify reaction products in the ice, specifically NH 3 and long-chained sulfur-containing ions. Crystalline NH 4 SH was amorphized during irradiation at all temperatures studied with the rate being the fastest at the lowest temperatures. Irradiation of amorphous NH 4 SH at ∼10–75 K showed that 60–80% of the NH 4 + remained when equilibrium was reached, and that NH 4 SH destruction rates were relatively constant within this temperature range. Irradiations at higher temperatures produced different dose dependence and were accompanied by pressure outbursts that, in some cases, fractured the ice. The thermal stability of irradiated NH 4 SH was found to be greater than that of unirradiated NH 4 SH, suggesting that an irradiated giant-planet cloud precipitate can exist at temperatures and altitudes not previously considered. [ABSTRACT FROM AUTHOR]

We performed shock experiments simulating natural comet impacts in an attempt to examine the role that comet impacts play in peptide synthesis. In the present study, we selected a mixture of alanine ( dl -alanine), water ice, and silicate (forsterite) to make a starting material for the experiments. The shock experiments were conducted under cryogenic conditions (77 K), and the shock pressure range achieved in the experiments was 4.8–25.8 GPa. The results show that alanine is oligomerized into peptides up to tripeptides due to the impact shock. The synthesized peptides were racemic, indicating that there was no enantioselective synthesis of peptides from racemic amino acids due to the impact shock. We also found that the yield of linear peptides was a magnitude higher than those of cyclic diketopiperazine. Furthermore, we estimated the amount of cometary-derived peptides to the early Earth based on two models (the Lunar Crating model and the Nice model) during the Late Heavy Bombardment (LHB) using our experimental data. The estimation based on the Lunar Crating model gave 3 × 10 9 mol of dialanine, 4 × 10 7 mol of trialanine, and 3 × 10 8 mol of alanine-diketopiperazine. Those based on the Nice model, in which the main impactor of LHB is comets, gave 6 × 10 10 mol of dialanine, 1 × 10 9 mol of trialanine, and 8 × 10 9 mol of alanine-diketopiperazine. The estimated amounts were comparable to those originating from terrestrial sources (Cleaves, H.J., Aubrey, A.D., Bada, J.L. [2009]. Orig. Life Evol. Biosph. 39, 109–126). Our results indicate that comet impacts played an important role in chemical evolution as a supplier of linear peptides, which are important for further chemical evolution on the early Earth. Our study also highlights the importance of icy satellites, which were formed by comet accumulation, as prime targets for missions searching for extraterrestrial life. [ABSTRACT FROM AUTHOR]

We conducted a qualitative study to simulate the flux of volatile gases expected to occur at the lunar surface due to cometary impact or lunar outgassing events. A small sample cell containing 8.8 g of JSC-1A lunar soil simulant in a vacuum system with a base pressure of 1.5 × 10 −8 Torr was exposed to various gases using dynamic pressure dosing at room temperature to observe any retention of those gases as a function of the exposure times, temperatures and pressures used. Gases included pure argon, a five-component gas mixture (H 2 , He, Ne, N 2 , Ar), a simulated Mars atmospheric mixture (CO 2 , N 2 , Ar, CO, O 2 ), and a simulated Titan mixture (N 2 , CH 4 ). Results at exposure pressures of approximately 1.5 × 10 −8 Torr above background showed no observable retention of rare gases, slight retention of molecular gases, but surface retention of the triatomic gas CO 2 occurred at room temperature with a time to reach equilibrium of greater than 10 min, which was an unanticipated result. Despite several bakeouts and months under ultrahigh vacuum (UHV) conditions, trace levels of atmospheric gases continued to evolve from the simulant. Mechanical and optical probing of the simulant surface increased this latent gas evolution, particularly for CO 2 and CO, with some evidence also for the release of CH 4 . We assert our results are, by analogy, applicable to protocols and instrumentation needed for conducting analytical chemistry aboard future landed lunar missions. [ABSTRACT FROM AUTHOR]

The bouncing barrier, a parameter combination at which dust particles in the protoplanetary disk always rebound in mutual collisions, is one of the crucial steps of planet formation. In the past years, several experiments have been performed to determine the mass and velocity regimes at which perfect bouncing does occur and those where there is a chance of the aggregates sticking together. We conducted a microgravity experiment, which allows us to investigate free collisions of millimeter-sized SiO 2 dust aggregates at the relevant velocities. We analyzed 52 collisions in detail with velocities of 3.4 × 10 - 3 m s - 1 to 6.2 × 10 - 2 m s - 1 and found four of them leading to sticking, while the other aggregates rebounded. Three out of the four sticking collisions occurred at velocities where previously only bouncing had been predicted. Although the probability for sticking is low, this opens a new possibility for growth beyond millimeter sizes. Our setup allowed us to obtain the complete three-dimensional collision information. Since most previous experiments were interpreted based on two-dimensional information, we compare our three-dimensional values with those obtained if only one projection had been available. We find that the error of a two-dimensional analysis of the collision velocity is very small. The distribution of the coefficient of restitution in the two-dimensional view is representative of the real case, but for any given collision its value can be far off. Impact parameters always have to be analyzed three-dimensionally, because the two-dimensional values are not meaningful in any way. [ABSTRACT FROM AUTHOR]

Crowdsourcing gains momentum: In digital work places such as Amazon Mechanical Turk, oDesk, Clickworker, 99designs, or InnoCentive it is easy to distribute human work to hundreds or thousands of freelancers. In these crowdsourcing settings, one challenge is to properly incent worker effort to create value. Common incentive schemes are piece rate payments and rank-order tournaments among workers. Tournaments might or might not disclose a worker's current competitive position via a leaderboard. Following an exploratory approach, we derive a model on worker performance in rank-order tournaments and present a series of real effort studies using experimental techniques on an online labor market to test the model and to compare dyadic tournaments to piece rate payments. Data suggests that on average dyadic tournaments do not improve performance compared to a simple piece rate for simple and short crowdsourcing tasks. Furthermore, giving feedback on the competitive position in such tournaments tends to be negatively related to workers' performance. This relation is partially mediated by task completion and moderated by the provision of feedback: When playing against strong competitors, feedback is associated with workers quitting the task altogether and, thus, showing lower performance. When the competitors are weak, workers tend to complete the task but with reduced effort. Overall, individual piece rate payments are most simple to communicate and implement while incenting performance is on par with more complex dyadic tournaments. [ABSTRACT FROM AUTHOR]

A methodology to evaluate the specific heat of metallic thin films at constant pressure and 300 K hy means of the heating profile is proposed. Changes on the electrical resistance of metallic films after the application of short electric pulses (20-500 ps) are correlated with changes of temperature of the films. Electric pulses are applied on films by an implemented electronic device. A proposed analytical thermal model predicts the correlation between the duration of the electric pulses and the thermal profiles of the film!substrate systems. The analytical thermal model and the measured thermal profiles results are useful to evaluate the specific heat of films. Following this methodology. Alt and Al nanofilms evaporated on glass substrates were analyzed. Results indicate that specific heat values of Au films decrease from (229 ± 15) J/kg K to (125 ± 8) J/kg K. and for Al films from (1444 ± 89) J/kg K to (947 ± 53) J/kg K. for film thicknesses from 20 to 200 nm. [ABSTRACT FROM AUTHOR]

We present measurements of the complete scattering matrix as a function of the scattering angle of five martian dust analogs, namely montmorillonite, two palagonite (JSC-1) samples, basalt, and calcite. The measurements are performed at 488 and 647 nm, covering the scattering angle range from 3° to 177°. The experimental scattering matrices are compared with results of Lorenz–Mie calculations performed for the same size distributions and refractive indices as our analog samples. As expected, we find that scattering matrices of realistic polydispersions of dust particles cannot be replaced by such calculated matrices. In contrast, the measured phase functions for our martian dust analogs may be considered a good approximation for martian dust at the studied wavelengths. Further, because of the sensitivity of polarimetry to particle microphysics, spectro-polarimetric observations from the martian surface appear to be a powerful diagnostic tool to infer the composition of the dust in the martian atmosphere. To facilitate the use of the experimental matrices for multiple-scattering calculations with polarization included, we compute the corresponding synthetic scattering matrices based on the measurements and defined in the full angle range from 0° to 180°. [ABSTRACT FROM AUTHOR]

Surface compositional features on rocks such as coatings and weathering rinds provide important information about past aqueous environments and water–rock interactions. The search for these features represents an important aspect of the Curiosity rover mission. With its unique ability to do fine-scale chemical depth profiling, the ChemCam laser-induced breakdown spectroscopy instrument (LIBS) onboard Curiosity can be used to both identify and analyze rock surface alteration features. In this study we analyze a terrestrial manganese-rich rock varnish coating on a basalt rock in the laboratory with the ChemCam engineering model to determine the LIBS signature of a natural rock coating. Results show that there is a systematic decrease in peak heights for elements such as Mn that are abundant in the coating but not the rock. There is significant spatial variation in the relative abundance of coating elements detected by LIBS depending on where on the rock surface sampled; this is due to the variability in thickness and spatial discontinuities in the coating. Similar trends have been identified in some martian rock targets in ChemCam data, suggesting that these rocks may have coatings or weathering rinds on their surfaces. [ABSTRACT FROM AUTHOR]

High-speed spectra of hypervelocity impacts at the NASA Ames Vertical Gun Range (AVGR) captured the rapidly evolving conditions of impact-generated vapor as a function of impact angle, viewpoint, and time (within the first 50 μs). Impact speeds possible at the AVGR (<7 km/s) are insufficient to induce significant vaporization in silicates, other than the high-temperature (but low-mass) jetting component created at first contact. Consequently, this study used powdered dolomite as a proxy for surveying the evolution and distribution of chemical constituents within much longer lasting vapor. Seven separate telescopes focused on different portions of the impact vapor plume and were connected through quartz fibers to two 0.35 cm monochromaters. Quarter-space experiments reduced the thermal background and opaque phases due to condensing particles and heated projectile fragments while different exposure times isolated components passing through different the fields of view, both above and below the surface within the growing transient cavity. At early times (<5 μs), atomic emission lines dominate the spectra. At later times, molecular emission lines dominate the composition of the vapor plume along a given direction. Layered targets and target mixtures isolated the source and reveal that much of the vaporization comes from the uppermost surface. Collisions by projectile fragments downrange also make significant contributions for impacts below 60° (from the horizontal). Further, impacts into mixtures of silicates with powdered dolomite reveal that frictional heating must play a role in vapor production. Such results have implications for processes controlling vaporization on planetary surfaces including volatile release, atmospheric evolution (formation and erosion), vapor generated by the Deep Impact collision, and the possible consequences of the Chicxulub impact. [ABSTRACT FROM AUTHOR]

Pyrolysis coupled with mass spectry is among the instrumentation the most implemented in planetary exploration probes to analyze the chemical composition of extraterrestrial solid samples. It is used to analyze the volatile species which can be thermally extracted from the samples, including the organic fraction which is of primary interest for astrobiological purposes. However the thermal degradation of these organic materials, which can be very complex in nature or very different from organics commonly present on Earth, is badly known. This leads to a restriction in the optimization of space instrumentation, and in the interpretation of the measurements. In the present work we propose a complete overview of the thermal degradation processes studied on a model of complex organic material produced in an extraterrestrial environment, i.e. laboratory analogues of Titan’s atmospheric aerosols. The thermal evolution of the studied analogues is monitored by following their mass loss, the emitted heating flux, and the evolution of their chemical composition through infrared spectroscopy and elemental analysis. The gaseous products released from the material are also analyzed by mass spectrometry, allowing to better constrain the mechanisms of chemical evolution of the samples. The complex organic material analyzed is found not to be fully decomposed when heated up to about 800 °C, with the evidence that nitrogen is still deeply incorporated in the remaining graphitic carbon nitride residue. The most appropriate pyrolysis temperature to chemically probe the studied material is found to be about 450 °C because at this temperature are detected the largest gaseous molecules which should be the most representative ones of the material pyrolyzed. [ABSTRACT FROM AUTHOR]

The current inventory of recent (fresh) impacts on Mars shows a strong bias towards areas of low thermal inertia. These areas are generally visually bright, and impacts create dark scours and rays that make them easier to detect. It is expected that impacts occur at a similar rate in areas of higher thermal inertia, but those impacts are under-detected. This study investigates the use of a trained machine learning classifier to increase the detection of fresh impacts on Mars using CTX data. This approach discovered 69 new fresh impacts that have been confirmed with follow-up HiRISE images. We found that examining candidates partitioned by thermal inertia (TI) values, which is only possible due to the large number of machine learning candidates, helps reduce the observational bias and increase the number of known high-TI impacts. • Machine learning classifiers can help increase the detection of rare fresh impacts on Mars. • The most-confident machine learning candidates preserve observational biases in the manually identified training examples. • Analyzing candidates partitioned by thermal inertia bins reduces observational bias. [ABSTRACT FROM AUTHOR]

• Stress dead zone concept was assessed by advanced high-resolution optical techniques. • Electronic Speckle Pattern Interferometry (ESPI) was employed to measure the crack. • Digital Image Correlation (DIC) was used for comparable experimental solution. • Stress dead zone was geometrically evaluated by ESPI and DIC. • Stress intensity factor was calculated from stress dead zone and optical methods. The work described in this paper is a study of the stress dead zone (SDZ) concept with advanced full-field optical methods. The SDZ is a region located around the fatigue crack flanks, adding a negligible contribution to internal stresses on the global deformation energy calculation. In the analytical modelling, this area can be removed from the structural member, resulting in a geometry simplification, and in the possibility of using analytical formulations in the Stress Intensity Factor (SIF) calculation associated to the existing fatigue crack. In a fatigue-testing program, aluminium middle tension (MT) specimens were prepared and then subjected to a cyclic fatigue loading, in order to generate different crack lengths for each specimen. Then, the fatigued specimens are monotonically tested under a uniaxial tensile loading to assess the SDZ concept. The experimental data is collected and analysed through two full-field high-resolution optical techniques with different system resolutions, Digital Image Correlation (DIC), and Electronic Speckle Pattern Interferometry (ESPI). As a result, the SDZ is geometrically characterized through a set of mathematical formulations based on the compliance function for the studied specimens, and is experimentally identified through deformation fields obtained from both DIC and ESPI techniques. The obtained results from both high-resolution methods verify the validity of the concept and demonstrate that it can be used to simplify the analysis. [ABSTRACT FROM AUTHOR]

The scope of fiber metal laminates (FMLs) in the applications for shock and blastwave mitigation has been gaining a lot of focus recently. The response of the FML structures to side-on interaction with shock waves was experimentally investigated using a shock tube. The influence of incorporating ballistic grade fabrics as sandwiched plies between metallic skins in addition to low acoustic impedance materials was explored in the current work. Five sequences of laminates were fabricated employing AA6061-T6 skins, with aramid-epoxy, ultra-high molecular weight polyethylene-epoxy, and paperboard-epoxy as sandwiched layers. The deformation profiles of different sequences were investigated and the stackups with the best shock mitigation response were identified. A numerical model for the laminate transverse deformation was developed. The deformations of the faceplate and the backplate of each sequence were compared to the numerical results. Among the five sequences, BRSP-II and BRSP-IV showed the least backplate deformation of ∼ −0.25 mm after single shock impact, while the same configurations showed lowest backplate deformation ∼ −0.6 mm after the second shock impact, as compared to the other sequences. The twin shock impacted specimens of various sequences were subjected to Cone beam computed tomography (CBCT) for layerwise investigation of shock impact. The four sequences BRSP-I, BRSP-II, BRSP-III and BRSP-IV showed deformations in all the plies with no delamination. However, delamination was observed at the center in BRSP-V between the backplate and the penultimate ply. [ABSTRACT FROM AUTHOR]