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Surging and streaming of glaciers are modulated by meltwater availability and pressure which controls mechanical coupling at their beds. Using laboratory-scale experimental modelling and palaeoglaciological mapping, we explore how subglacial drainage landsystems control meltwater drainage efficiency and ice flow velocities for terrestrial-based ice lobes resting on flat horizontal and permeable beds. Two end-members regimes, surging and streaming, appear in our experiments. The surge regime is characterised by a rapid increase of drainage efficiency through development of tunnel valleys and their tributaries, thus reducing the duration of ice flow speed-up events by lowering water pressures and increasing ice-bed coupling. Tunnel valleys connected to ice lobe margins, submarginal thrust moraines, reduced ice lobe extensions and ephemeral shear margins are the most distinctive characteristics of this regime. The stream regime is characterised by disconnected channels of smaller dimensions unable to evacuate all the meltwater: this prolonged drainage inefficiency leads to sustained high ice flow velocity and steady shear margins. Small and rectilinear meltwater channels devoid of tributaries, often disconnected from ice lobe margins, and lineation swarms are diagnostic of this regime.

We report on measurements of dissipation and frequency noise at millikelvin temperatures of nanomechanical devices covered with aluminum. A clear excess damping is observed after switching the metallic layer from superconducting to the normal state with a magnetic field. Beyond the standard model of internal tunneling systems coupled to the phonon bath, here we consider the relaxation to the conduction electrons together with the nature of the mechanical dispersion laws for stressed/unstressed devices. With these key ingredients, a model describing the relaxation of two-level systems inside the structure due to interactions with electrons and phonons with well separated timescales captures the data. In addition, we measure an excess 1/f-type frequency noise in the normal state, which further emphasizes the impact of conduction electrons., 7 pages (main text) + 9 pages (SI), same as published version

Introduction: Louth Crater is a 36 km diameter located at 70 °N, 103.2 °E (Fig. 1) less than 1000 km from the Martian North Polar Cap. At the center of Louth crater a perennial water ice cap ~10 km in diameter, ~250 m in width (Fig. 1) that undergoes phase changes (condensation / sublimation cycles) during the Martian year [1 - 4]. Some periodic structure at the surface of its perennial water ice cap have been observed [2]. The presence of smaller ice undulations superimposed on this periodic structure, comparable to the sublimation waves on the Martian North Polar Cap [5] could be formed during sublimation and condensation period of the water ice. The characterization of this ice waves could make it possible to specify environmental conditions favorable to their formation. The first part of the study consists of identifying these ice waves using orbital topography and imaging data, and then associating these results with data from the Martian Database [6-7] and with the scaling laws inherent to the formation of sublimation and condensation waves. Fig. 1: Louth crater in summer. CTX product J02_045439_2504_XN_70N256W Ls = 133.2° Geomorphological analysis: Methods: Digital Elevation Model (DEM) at ~100 m/pixel and MOLA elevation data at ~128 m/pixel have been coupled with imagery data from HRSC ~10 m/pixel, CTX at ~6 m/pixel and HiRISE images for more precise areas for up to 25 cm/pixel. Data were georeferenced in ESRI’s ArcMap GIS software to produce geomorphological map and analyzed to evaluate ice waves shape and spatial organization. Observations: Louth presents two units (Fig. 2). (a) Lower unit with dark stucco texture and stratifications (Fig. 3a). (b) Fresh ice overlies this older, stratified structure (Fig 3.a). This fresh ice is distributed in a non-uniform manner as shown by the kilometrics waves of about 560 m wavelength on which are superimposed decametrics waves of about 55 m wavelength which are both perpendicular to the prevailing wind (Fig 3.b). The crests of both wave populations show similar NW-SE. The main wind direction was assessed from barkhane field on the sand mound. Fig. 2: Louth’s geomorphological map in summer. CTX product J02_045439_2504_XN_70N256W Ls = 133.2°. Fig. 3: Boxes from Fig. 2. (a) East side of the Louth crater ice cap. Green lines represents stratifications, HiRISE product EPS_045439_2505, Ls = 133.2°. (b) decametric waves on the ice waves. Black dashes represent leeside foot of each kilometric waves. Blue lines emphasize decametric waves, same HiRISE product from (a). Transport hypothesis: Preliminary experiments studied the threshold velocity necessary to initiate a transport of ice grains in Martian Simulation Wind Tunnel [8]. These experiments were carried out for grains from a few hundred micrometers to 2 mm in diameter under atmospheric pressures of 40 to 1000 mbar. To transport ice particles under near-Martian condition is hard because the threshold velocity is ten times higher than Earth. The wind speeds estimated from the Martian Database [6-7] in Louth crater are much lower than those needed to transport ice grains at Martian pressure. We support the hypothesis of diffusion by sublimation/condensation rather than the transport of icy particles by the wind. Mass transfer hypothesis: In a recent theoretical model [5] scaling laws explain the formation of sublimation waves and have been validated on terrestrial bedforms and on the Martian North Polar Cap. These waves are periodic and oriented in accordance with a turbulent boundary layer flow that diffuse the sublimated vapor. These laws, which are superimposed on the two ice waves studied, make these waves suitable geomorphological markers for climatic predictions. This model has been adapted to study similar waves created by condensation [9] and results indicate that condensation waves would be larger with one order gap than sublimation waves. Discussion: From the wind tunnel experimentation of ice particles transport in Martian-Like environment [8], wind necessary to initiate transport of ice particles is unlikely in Louth. Friction velocities of 3 m.s-1 would be required, compared to 0.6 m.s-1 deduced from scaling laws, to transport the most mobilizable 0.3 mm ice particles [8]. Wind speed in Louth is too weak for initiating particles transport. From the scaling laws, we extract values of friction velocity and flow velocity at a given altitude that can be compared with those extracted from the Martian Data Base over two Martian periods: a period of sublimation (during the summer in the northern hemisphere) at the origin of the formation of decametric waves and a period of condensation at the end of the summer, beginning of the autumn favorable for the kilometric waves formation. Scaling laws are in agreement with the predicted ratio velocity between sublimation and condensation period from the Martian Data Base values. From the Martian Data Base, independent velocity values are larger. This can be explained by the gridding of the database which takes place on a global scale larger than the crater. Conclusion: The observations indicate kilometric bedforms on the ice cap of Louth Crater, on which decametric bedforms appear with an order of magnitude gap. Comparison with numerical results suggests that the kilometric bedforms are formed by condensation and the smaller ones by sublimation. These condensation and sublimation waves are suitable markers to constrain mesoscale climate modelling in small, complex regions such as this type of crater, where topographic and/or seasonal effects can affect climate data. These waves can also be used as geomarkers on other planetary bodies where climatic conditions are not well constrained. Acknowledgments: We acknowledge PNP (Plan National de Planétologie) for founding the project “sublimation and condensation waves”. We used Planetary Data System (PDS) for observational data. References: [1] Conway et al. (2012) Icarus. [2] Brown et al. (2008) Icarus. [3] Hofstader & Murray (1990) Icarus. [4] Appéré et al. (2011) Journal of Geophysical Research. [5] Bordiec M. et al. (2020) Earth-Science Reviews, 211, 103350.[6] Forget et al. (1999). [7] Millour et al. (2018). [8] Herny et al. (2020). 7th Mars Polar Science Conf. Abstract #2099. [9] Carpy S. et al. (2022). EGU, Abstract #5998.

Sublimation combined with wind: Volatiles (N2, CH4, CO2, H20, NH3) are very common in the solar system (Fig 1). The average pressure and temperature conditions at the surface of many bodies suggest that volatile ices are stable and we thus expect that solid bedforms may form on these surfaces by either sublimation and/or condensation. These mass transfers between ice and overlying atmospheres are already known as landforms-shaping processes at different scales. These processes are very effective on the Martian North Polar Cap [2], whose spirals of the MNPC are known to be the result of sublimation on one side and condensation on the other [3-4], and as Pluto, where the Bladed Terrain Deposits are associated with sublimation of N2 and condensation of CH4 [5]. FIGURE 1 – Superimposed phase diagrams of the predominantly represented species (N2, CH4, CO2, NH3, H2O) in the Solar System in (p,T), using the Clausius-Clapeyron relationship. Scientific goal: To understand the process of material redistribution by the wind on icy planetary surfaces subject to phase changes, we propose a theoretical model coupling of flow dynamics and mass transfer and perform a linear stability analysis [6]. As done for loose bedforms, we use solid transverse bedforms as geomarkers to identify sublimation zones and to deduce erosion rate. We aim to physically and morphologically characterise these periodic waves perpendicular to the main flow over icy substrates and we are looking for analogues to assess the validity of our model before interpreting the observations on other bodies. On Earth, field analogues could be found in extreme cold and icy environment. Similar laboratory experiments are also suggested to complete the dataset. Sublimation waves analogues: We have identified two possible analogues for sublimation patterns from the literature: in the Blue Ice areas (Fig 2a) of the Antarctic ice sheets [1] and in ice caves such as the Eisriesenwelt cave (Fig 2b) in Austria [7]. We also use new measurements made in a laboratory experiment on the sublimation of CO2 ice in an atmospheric wind tunnel (Fig 2c). FIGURE 2 – Sublimation waves analogues [6]: (left: a) Blue Ice areas (middle: b) the Eisriesenwelt ice cave (right: c) CO2 ice in an atmospheric wind tunnel. In all these environments, linear and transverse bedforms appear. However, there are quite different in scales and involve different compositions of the icy substrate and the atmosphere. Despite those differences, the winds that flow on these surfaces are always turbulent and of infinite height and the environmental conditions are favorable to sublimation of ice: the surface temperatures are lower than the triple point and the partial pressure of the species is far from pressure at saturation. These sublimation waves have been classified as net ablation areas from surface energy balance. Theoretical model for redistribution processes: We consider a simple 2D case of a wavy surface of wavelength l and small amplitude with an overlying turbulent atmospheric boundary layer, of height H much larger that the wavelength. The mass transfer rate varies along the profile and has a maximum somewhere in the troughs, shifted from the crests by a phase lag. This effect allows the growth of a range of wavelengths and their migration, depending on the location of the maximum. The flow is perturbed by the topography and modify the mass transfer in turn, which may lead to the instability of such bedforms. From the stability analysis [6] we obtain 3 scaling laws: (1) the first law can predict either the friction velocity or the wind speed from a measure of the wavelength and if the viscosity is known, (2) the second law show that the migration velocity is found to scale linearly with the average value of the sublimation rates and thus depends on the kinetics of the phase transition, (3) the third law links the characteristic time of formation with the viscous length and the sublimation rate. FIGURE 3 – Model (black line), measurements (symbols) and prediction (MNPC) for sublimation waves [6]. Sublimation bedforms as geomorphic markers: The model prediction, black line (Fig 3), is superimposed on the natural terrestrial and the experimental model. This allows us to predict either the friction velocity or the wind speed from a measurement of the wavelength for the Martian Northern Polar Cap. The values predicted are in good agreement with those obtained by the martian climate database at the same place where these sublimation waves have been detected, and those both for the frictional velocities and the wind speeds. Conclusion: We propose a formation model for the sublimation waves by coupling mass waste with the hydrodynamic instability of the overlaying turbulent flow, in the case where the flow heigh is larger than the wavelength. The subjacent objective was to determine if terrestrial analogues exist or some experimental facilities could be used. We show it is possible to link the dimension of the sublimation waves to their environment and produce three scaling laws that links the geomorphological characteristics of these bedforms (wavelengths, migration, formation time) and the flow (velocity, viscosity, flow height). The adequacy between the observations/experiments and our model allows us to validate these environments as terrestrial/experimental analogues of sublimation waves. New experiments could thus be designed in controlled atmospheric wind tunnel like Aarhus wind tunnel, Denmark to explore controlling parameters. Acknowledgments: Plan National de Planétologie. References: [1] Bintanja R. (1999) Reviews of Geophysics, 37(3) :337–359 [2] Herny C. et al. (2014) EPSL, 4013, 56-66. [3] Howard A. D. (2000)Icarus, 144(2) :267–288. [4] Smith I. et al (2010) Nature, 465(7297). [5] Moore et al (2017) Icarus, 287 :320–333, 2017. [6] Bordiec M. et al. (2020) Earth & Sci. Reviews. Sci., 103350. [7] Obleitner and Spötl, (2011) Cryosphere, 5(1) :245–25.

The specific heat of phonon cavities is investigated in order to analyze the effect of phonon confinement on thermodynamic properties. The specific heat of freestanding very thin SiN membranes in the low-dimensional limit is measured down to very low temperatures (from 6 K to 50 mK). In the whole temperature range, we measured an excess specific heat orders of magnitude bigger than the typical value observed in amorphous solids. Below 1 K, a crossover in cp to a lower power law is seen, and the value of the specific heat of thinner membranes becomes larger than that of thicker ones demonstrating a significant contribution coming from the surface. We show that this high value of the specific heat cannot be explained by the sole contribution of two-dimensional phonon modes (Lamb waves). The excess specific heat, being thickness dependent, could come from tunneling two-level systems that form in low-density regions of amorphous solids located on the surfaces. We also show that the specific heat is strongly tuned by the internal stress of the membrane by orders of magnitude, giving high values, making low-stress SiN very efficient for energy storage at very low temperature. peerReviewed

During the 20th century, the last glaciation in the Massif Central, France, was documented by several geomorphologists based on intensive field investigations. Seven paleoglaciers were identified, ranging from cirque glaciers in the Velay (4 km2) to coalescent ice caps (3500 km2) covering the Cantal, Cézallier and Monts Dore mountains. The associated glacial chronology relied mainly on morphostratigraphic observations and indirect age determination, such as radiocarbon ages from organic sediments in freshly deglaciated landscapes. Our study aims to improve this incomplete glacial chronology in order to reconstruct the paleoclimatic conditions that controlled these glaciations. We focused on the Cantal Mounts (45.0°N, 2.7°E) and Aubrac Mounts (44.6°N, 3.0°E) in the western Massif Central. Glacial landform assemblages and associated morphostratigraphy were re-investigated in the field and updated by new observations, e.g. the identification of end moraines. Three glacial stadials were recognized: the Local Last Glacier Maximum (LLGM) and two glacier re-advances. A final cirque glaciation was identified in the Cantal. We obtained an original set of exposure ages from erratic boulders and depth profiles in till at key sites using in situ produced Terrestrial Cosmogenic Nuclides 10Be, 26Al and 36Cl. Our results show comparable glacial chronologies for the Cantal ice cap and the Aubrac plateau icefield suggesting that the majority of glacial landforms and sediments were deposited during the global Last Glacial Maximum (LGM; 26.5 to 19.5 ka) and the Last Glacial-to-Interglacial Transition (LGIT; 19.5 to 11.7 ka). Advances and retreats of these two paleoglaciers were synchronous with regional climatic events reported from independant paleoclimatic proxies, especially the Heinrich Stadial 2 and the Heinrich Stadial 1. We combined two glacier modelling procedures, the theoretical glacier surface profiles and the Positive Degree-Day method, to constrain the paleoclimatic conditions (i.e. paleotemperatures and paleoprecipitations) that controlled these glacial fluctuations. The results showed changes between past and current climatic gradients with a probable enhancement of southerly moisture advection from the Mediterranean during the Heinrich Stadial 2 and drier conditions during the Heinrich Stadial 1.

Observation and modelling have long contributed to associate surging and streaming of glaciers with glacier thermal regime, variations in meltwater availability and pressure and mechanical coupling at their beds. Using experimental modelling and palaeoglaciological mapping, we explore how the development of subglacial drainage landsystems controls variations in drainage efficiency and ice flow velocities for terrestrial-based ice lobes on flat horizontal beds. We observe that the achievement or not of efficient subglacial drainage landsystems determines the fast-flow regime of these glaciers. In the surge regime, rapid increase of drainage efficiency through development of tunnel valleys and their tributaries reduces the duration of ice flow speed-up events by lowering water pressures and increasing ice-bed coupling. Tunnel valleys connected to ice lobe margins, submarginal thrust moraines, reduced ice lobe extensions and ephemeral shear margins are the most distinctive characteristics of this regime. In the stream regime, disconnected channels of smaller dimensions develop, but they are unable to evacuate all the meltwater: this prolonged drainage inefficiency leads to sustained high ice flow velocity and steady shear margins. Small and rectilinear meltwater channels devoid of tributaries, often disconnected from ice lobe margins and lineation swarms are diagnostic of this regime.

Hybrid quantum optomechanical systems offer an interface between a single two-level system and a macroscopical mechanical degree of freedom. In this work, we build a hybrid system made of a vibrating microwire coupled to a single semiconductor quantum dot (QD) via material strain. It was shown a few years ago, that the QD excitonic transition energy can thus be modulated by the microwire motion. We demonstrate here the reverse effect, whereby the wire is set in motion by the resonant drive of a single QD exciton with a laser modulated at the mechanical frequency. The resulting driving force is found to be almost 3 orders of magnitude larger than radiation pressure. From a fundamental aspect, this state dependent force offers a convenient strategy to map the QD quantum state onto a mechanical degree of freedom., Comment: 16 pages, 12 figures

Aeolian processes are at the origin of a large number of bedforms, which are topographic patterns that are spatially organised in a periodic manner and that can be observed both on Earth and on other planetary bodies. Two main categories of bedforms can be distinguished: (i) "loose" bedforms, generated on a bed of mobilisable grains by erosion, transport and deposition and (ii) "solid" bedforms, not induced by grain transport but by mass transfers such as ice sublimation or condensation under turbulent winds. Although the mechanisms involved in the growth of some solid bedforms have been studied (penitents, sublimation ripples, …), the subject remains largely less treated to date than loose bedforms, partly because of the lack of terrestrial environments favourable to sublimation. Comparison with other planetary environments has opened up new horizons for understanding these objects and the aeolian environments in which they develop.Among these bedforms, sublimation waves are transverse linear waveforms: regular and parallel ridges oriented perpendicular to the main direction of the turbulent flow interacting with the ice surface. The height of the flow is greater than their wavelength. The emergence of the bedforms is due to a hydrodynamic instability mechanism of the band-pass type which allows their growth. Our theoretical linear stability study shows that this instability appears in the laminar-turbulent transition regime, based on the near-wall Reynolds number, only if the modulation of the viscous sublayer by an effective longitudinal pressure gradient is taken into account in the turbulence model enabling to reproduce the feedback of the topography on the flow.These sublimation waves have been observed in different environments [Bordiec et al, 2020], by sublimation and diffusion of (a) water ice in air, in Antarctica or Ice caves, (b) water ice in CO2 atmosphere, on some areas of the northern polar cap of Mars, (c) and experimentally with CO2 ice in air. They are also observed on a Martian H2O glacier near the northern polar cap of Mars [Collet et al, in prep.], however, in the latter case, these sublimation waves are observed on larger icy waves. How can this difference in scale between two wavelengths be explained? What is their size selection process? To answer these questions, we investigate in our theoretical study the dependence on environmental conditions through (i) the fluid properties (wind speed, fluid viscosity) (ii) the direction of the transfer (sublimation or condensation) and (iii) the height of the flow in front of the wavelength (infinite or finite).

Molards are cones of loose debris, from ~ 50 cm to ~ 15 m in height, and are the remnants of formerly ice-cemented blocks that moved within a landslide, then degraded progressively (e.g., [1]). Thus, presence of molards in landslide deposits implies an involvement of both ice-cemented and non-ice-cemented ground within the mass movement, and so the presence of an area of discontinuous permafrost at the level of the detachment zone. Permafrost is frozen or unfrozen ground that remains < 0°C for at least two consecutive years, and it can be sensitive to temperature variations [2]. Increasing temperatures can cause its degradation, which can create areas of discontinuous permafrost and enhance slope instability (e.g. [3]), which represents a threat for populations in polar and mountainous regions [4]. Therefore, accurately identifying areas of discontinuous permafrost is a contemporary challenge for assessments of the state and evolution of permafrost, and for understanding landslide-related hazards to protect local populations. In this context, we will carry out physical modelling of the degradation of initial ice-cemented blocks made of sediments into molards. The M2C laboratory contains two cold rooms – the largest one > 12 m² – that can go down to -20°C, allowing near-field-scale simulations to be performed. We are developing an experimental protocol that consists in freezing mixes of sediment and water in 30 cm cubes, and then observing their degradation under controlled conditions. We identified grain size of the sediment and its ice content as the main two parameters that should influence the degradation process. Therefore, we will vary these parameters in the first series of experiments. We will observe the degradation processes that occur (e.g. grain falls, gravitational collapses, debris flows) using video cameras. The thaw-front propagation will be monitored by thermocouples within the frozen blocks. An array of time-lapse cameras will be used to produce time series of elevation models to monitor the 3D morphological evolution from blocks to molards. Air temperature and humidity will be monitored. Data on grain size, ice content, degradation processes and temperature/humidity will be used to calibrate a numerical model, which will allow us to explore a parameter space inaccessible/impractical for the laboratory (e.g. bigger scales, or realistic diurnal/seasonal thermal cycles). The final 3D shape (e.g. height, slope, basal area covered) of experimental molards should vary according to the initial parameters (i.e. grain size and ice content) and these measurements will inform the criteria used to distinguish molards from other similar landforms, such as hummocks or hummocky moraine, in the field and/or from remote sensing data. Acknowledgements: authors thank the Agence Nationale de la Recherche for funding the ANR-19-CE01-0010 PERMOLARDS project, which supports this experimental work. References: [1] Morino C. et al. (2019) EPSL 516, 136-147. [2] Hinzman L. D. et al. (2005) Climate Change 72, 251-298. [3] Dramis F. et al. (1995) PPP 6, 73-82. [4] Saemundsson Þ. et al. (2003) In: Rickenman, D., Chen, C.I. (Eds.), Debris-Flow Hazards Mitigation: Mechanics, Prediction, and Assessment. 1, pp. 167–178.

We investigate thin film resistive thermometry based on metal-to-insulator-transition (niobium nitride) materials down to very low temperature. The variation of the NbN thermometer resistance have been calibrated versus temperature and magnetic field. High sensitivity in tempertaure variation detection is demonstrated through efficient temperature coefficient of resistance. The nitrogen content of the niobium nitride thin films can be tuned to adjust the optimal working temperature range. In the present experiment, we show the versatility of the NbN thin film technology through applications in very different low temperature use-cases. We demonstrate that thin film resistive thermometry can be extended to temperatures below 30 mK with low electrical impedance., Comment: Article accepted for publication in JLTP

Over the three last decades, great efforts have been undertaken by the glaciological community to characterize the behaviour of ice streams and better constrain the dynamics of ice sheets. Studies of modern ice stream beds reveal crucial information on ice-meltwater-till-bedrock interactions, but are restricted to punctual observations limiting the understanding of ice stream dynamics as a whole. Consequently, theoretical ice stream landsystems derived from geomorphological and sedimentological observations were developed to provide wider constraints on those interactions on palaeo-ice stream beds. Within these landsystems, the spatial distribution and formation processes of subglacial periodic bedforms transverse to the ice flow direction – ribbed bedforms – remain unclear. The purpose of this study is (i) to explore the conditions under which these ribbed bedforms develop and (ii) to constrain their spatial organisation along ice stream beds. We performed physical experiments with silicon putty (to simulate the ice), water (to simulate the meltwater) and sand (to simulate a soft sedimentary bed) to model the dynamics of ice streams and produce analog subglacial landsystems. We compare the results of these experiments with the distribution of ribbed bedforms on selected examples of palaeo-ice stream beds of the Laurentide Ice Sheet. Based on this comparison, we can draw several conclusions regarding the significance of ribbed bedforms in ice stream contexts:Ribbed bedforms tend to form where the ice flow undergoes high velocity gradients and the ice-bed interface is unlubricated. Where the ribs initiate, we hypothesize that high driving stresses generate high basal shear stresses, accommodated through bed deformation of the active uppermost part of the bed. Ribbed bedforms can develop subglacially from a flat sediment surface beneath shear margins (i.e., lateral ribbed bedforms) and stagnant lobes (i.e., submarginal ribbed bedforms) of ice streams, while they do not develop beneath surging lobes. The orientation of ribbed bedforms reflects the local stress state along the ice-bed interface, with transverse bedforms formed by compression beneath ice lobes and oblique bedforms formed by transgression below lateral shear margins. The development of ribbed bedforms where the ice-bed interface is unlubricated reveals distinctive types of discontinuous basal drainage systems below shear and lobe margins: linked-cavities and efficient meltwater channels respectively. Ribbed bedforms could thus constitute convenient geomorphic markers for the reconstruction of palaeo-ice stream margins, palaeo-ice flow dynamics and palaeo-meltwater drainage characteristics.

The South Polar Terrain (SPT) of Enceladus is a site with eruptions of gas and water ice particle plumes, which indicate internal geodynamic activity. These eruptions are located along a series of tectonic structures, that is, the Tiger Stripe Fractures (TSF), which are composed of regularly spaced, linear depressions. The SPT is surrounded by sinuous chains of ridges and troughs (the Marginal Zone). To unravel the tectonics that affect the region and its evolution, we performed specific structural mapping and quantitative analyses of brittle features from remotely sensed images. The results are consistent with a block rotation model, in which several tectonic regimes coexist. The TSF are left-lateral strike-slip faults that bound rigid elongated blocks. The blocks rotate clockwise and are enclosed in a regional scale right-lateral kinematic framework expressed in the Marginal Zone. These two opposite and complementary kinematic regimes induce transtensional and transpressional regimes within the SPT. An evolutionary tectonic model is proposed for the past and future evolution of the SPT. This model confirms the role of tectonic-related kinematics in icy satellites and contributes to preparations for future missions.

Conceptual ice stream landsystems derived from geomorphological and sedimentological observations provide constraints on ice-meltwater-till-bedrock interactions on palaeo-ice stream beds. Within these landsystems, the spatial distribution and formation processes of ribbed bedforms remain unclear. We explore the conditions under which these bedforms develop and their spatial organisation with (i) an experimental model that reproduces the dynamics of ice streams and subglacial landsystems and (ii) an analysis of the distribution of ribbed bedforms on selected examples of paleo-ice stream beds of the Laurentide Ice Sheet. We find that a specific kind of ribbed bedforms can develop subglacially from a flat bed beneath shear margins (i.e., lateral ribbed bedforms) and lobes (i.e., submarginal ribbed bedforms) of ice streams. These bedforms initiate where the ice flow undergoes high velocity gradients and the ice-bed interface is unlubricated. We suggest that (i) their orientation reflects the local stress state along the ice-bed interface and (ii) their development reveals distinctive types of subglacial drainage patterns below these two kinds of margins: linked-cavities and efficient meltwater channels respectively. These ribbed bedforms are thus convenient geomorphic markers to reconstruct palaeo-ice stream margins and constrain palaeo-ice flow dynamics and palaeo-meltwater drainage characteristics.

Introduction: The transport of ice by wind plays a major role in the surface mass balance of polar caps [1, 2]. Ice can be redistributed by wind due to (1) transport of ice particles and/or (2) transport of water vapour associated with sublimation/condensation. On Mars, although the low atmospheric density is less favourable for the transport of particles than on Earth, both dust and sand have been observed to be transported by wind [3,4]. Despite ice aeolian landforms have been observed at the surface of the North Polar Cap of Mars [2, 5, 6], ice particle transport has not been directly observed on the Martian surface. Similarly, no laboratory studies of snow/ice particle transport under Martian-like conditions have been attempted thus far due to the complexity of the material. In this study we performed experiments of ice particle transport in a wind-flow under low temperatures and low pressures. From the experiments, threshold shear velocity of water ice particle transport is retrieved for different pressures and sizes in order to evaluate the plausibility of ice particle wind-driven transportation at the surface of Mars. The North Polar Cap of Mars: The Martian atmosphere is thin (7 mbar), cold (220 K) and dry (< 80 μm-pr) [7]. These conditions favoured ice sublimation/condensation processes. Spectral analyses [8, 9] suggested the optical ice grain sizes to vary between 10 μm to about 2000 μm for the seasonal frost and surface of the perennial North polar cap. But, the mechanisms of ice deposition are not well established. It can potentially come from vapour condensation directly onto the surface [9] or from snow fall [10]. This will affect the shape and size of ice particles and degree of ice sintering, which all influence the shear velocity threshold. The North polar cap experiences a permanent katabatic wind regime [11] with a typical friction shear velocity u* about 0.2 m.s-1. The complex interaction between the cryosphere and the wind leads to the formation of aeolian features at different scales [2, 5, 6]. Wind tunnel experiments: We performed experiments using the environmental wind tunnel AWTSII at Aarhus University. It is a cylindrical vacuum chamber, housing a recirculating wind tunnel about 8 m long, 2 m wide and 1 m high [12]. The facility can achieve a turbulent boundary layer flow at both low temperature and low pressure. The ice samples were produced by using the Setup for production of Icy Planetary Analogues [13]. The ice samples were sieved (125 - 250 μm, 250 - 500 μm, 500 - 2000 μm) as a monolayer on a plate covered with volcanic regolith (125 μm). The fan speed was increased by steps (shear velocity u* = 0 to 2 m.s-1) and the wind flow characterized by laser Doppler anemometry. The removal of ice particles was monitored by webcam. We performed the experiments for the different particle shapes and sizes for 4 different air pressures; 40, 100, 500 and 1000 mbar. The air temperature was maintained low (~-25°C) close to the sample plate to prevent the ice melting, sublimating and sintering. Threshold shear velocity calculation: The threshold shear velocity was determined from analysis of acquired images. When bright ice particles are removed from the dark volcanic regolith plate, the reflectance of the surface decreases. Black and white reference targets are placed close to the sample plate in the field of view of the webcam. The reflectance evolution of a region of interest (ROI) on the sample plate is calculated as follow: reflectance = (ROI – black target)/(white target – black target) The reflectance serves as a proxy for ice mass removal. For each image the reflectance is linked to the corresponding shear velocity. In most of the cases performed, the reflectance is constant until a certain wind speed and then decreases. To determine the threshold shear velocity uth, we set the threshold reflectance at 10% decrease from the first image at u* = 0 m.s-1. Results and conclusion: We have performed for the 1st time experiments of ice particles transportation at low pressure in a planetary wind tunnel. The averaged threshold shear velocity obtained at 1000 mbar, uth = 0.4 m.s-1, is consistent with theoretical and experimental calculation of ice/snow at terrestrial condition [14, 15], from 0.3 m.s-1 to 0.6 m.s-1 for range of ice particles sizes selected, supporting our set-up reliability. The shear velocity increases significantly as the pressure decreases. The influence of the ice grain sizes is not clear and more experiments are required. The results should then be scaled to Martian gravity in order to compare the results to wind speed simulations and conclude about the likeliness of transport of ice particles by wind at the surface of Mars. References: [1] Das I. et al. (2013) Nature Geoscience, 6, 367-371. [2] Howard A. D. (2000) Icarus, 144, 267-288. [3] Cantor B. A. et al. (2010) Icarus, 208, 61-81. [4] Bridges B. A. et al. (2012) Geology, 40, 31-34. [5] Smith I. B. and Holt J. (2010) Nature, 465, 450-453. [6] Herny C. et al. (2014) EPSL, 403, 56-66. [7] Pankine A. A. et al. (2010) Icarus, 210, 5871. [8] Langevin Y. et al. (2005) Science, 307, 1584-6. [9] Appéré T. et al. (2011) JGR : Planets, 116, E05001. [10] Spiga A. et al. (2017) Nature Geoscience, 10, 652-657. [11] Spiga A. et al. (2011) PSS, 59, 915-922. [12] Holstein-Rathlou C. et al. (2014) Am. Met. Society, 31, 447-457. [13] Pommerol A. et al. (2019) Space Sci. Rev., 215. [14] Shao Y. and Lu H. (2000) JGR, 105, 437-443. [15] Clifton A. et al. (2006) JoG, 52, 585-596. [16] Herny C. et al. (2016) 6th MPSC, Abstract #6075. [17] Bordiec M. et al. (2018) ICAR X. Acknowledgements: This work has been fund by Europlanet (Europlanet 2020 RI has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 654208). This work has been supported by the University of Bern. This work has been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation.

In this work, we propose an experimental setup to measure the thermal conductivity and specific heat of a single suspended glass fiber, as well as the thermal contact resistance between two glass fibers. By using optical lithography, wet and dry etching and thin film deposition, we prepared suspended glass fibers that are coated by niobium nitride (NbN) thin film used as room temperature thermal transducer. By using the 3ω technique, the thermal conductivity of glass fiber was measured to be 1.1 W m−1 K–1 and specific heat 0.79 J g−1 K–1 around 300 K under vacuum conditions. By introducing exchange gas into the measurement chamber, influence of the gas on the heat transfer was studied, and the convection coefficient h for all the measurement ranges from a pressure of 0.01 hPa to 1000 hPa, over more than five orders of magnitude, has been obtained. By adding a bridging glass fiber on top of two other suspended glass fibers, it was possible to estimate the thermal contact resistance between two glass fibers Rc in the range of 107–108 K W–1.

Superconductivity in two dimensions is nontrivial. One way to achieve global superconductivity is via the Berezinskii-Kosterlitz-Thouless (BKT) transition due to proliferation of vortex-antivortex pairs. This transition is expected to have a clear signature on the specific heat. The singularity at the transition temperature ${T}_{\mathrm{BKT}}$ is predicted to be immeasurable, and a broad nonuniversal peak is expected at $Tg{T}_{\mathrm{BKT}}$. Up to date, this has not been observed in two-dimensional superconductors; this work is then dedicated to investigate ${c}_{p}$ signatures in the limit of ultrathin 2d superconductors. We use a unique highly sensitive technique to measure the specific heat of quench condensed ultrathin Pb films. We find that thick films exhibit a specific heat jump at ${T}_{C}$ that is consistent with BCS theory. As the film thickness is reduced below the superconducting coherence length and the systems enter the 2D limit, the specific heat reveals BKT-like behavior in what can appear as to be a continuous BCS-BKT crossover as a function of film thickness. However, a number of problems arise with this interpretation. We discuss the experimental results and the possible significance of various scenarios involving BKT physics.

International audience; Sublimation waves are periodic, linear and transverse bedforms that grow by sublimation of icy substrates under turbulent winds. They occur in different environments of the Earth and other planets, where the climate is favorable to sublimation. Their morphological and kinematic characteristics (wavelength, migration velocity, characteristic time of formation) depend on the environmental conditions in which they develop (atmosphere viscosity, wind speed, sublimation rate). To highlight these relations, we designed a theoretical model for their formation, based on models previously designed for dissolution bedforms. From a linear stability analysis of the model, we derived a dispersion relation and three scaling laws. These are validated by comparison with measurements available for two natural terrestrial examples (Blue Ice Areas of the Antarctic ice sheets and ice caves) and with new measurements in a laboratory experiment. They are applied to linear bedforms, of hitherto unknown origin, that we identified on the Martian North Polar Cap. We thus demonstrate that sublimation waves are convenient geomorphic markers to constrain surface compositions, atmospheric properties, climates, and winds on terrestrial ice sheets and other icy planetary surfaces.

We report on microwave optomechanics measurements performed on a nuclear adiabatic demagnetization cryostat, whose temperature is determined by accurate thermometry from below 500$~\mu$K to about 1$~$Kelvin. We describe a method for accessing the on-chip temperature, building on the blue-detuned parametric instability and a standard microwave setup. The capabilities and sensitivity of both the experimental arrangement and the developed technique are demonstrated with a very weakly coupled silicon-nitride doubly-clamped beam mode of about 4$~$MHz and a niobium on-chip cavity resonating around 6$~$GHz. We report on an unstable intrinsic driving force in the coupled microwave-mechanical system acting on the mechanics that appears below typically 100$~$mK. The origin of this phenomenon remains unknown, and deserves theoretical input. It prevents us from performing reliable experiments below typically 10-30$~$mK; however no evidence of thermal decoupling is observed, and we propose that the same features should be present in all devices sharing the microwave technology, at different levels of strengths. We further demonstrate empirically how most of the unstable feature can be annihilated, and speculate how the mechanism could be linked to atomic-scale two level systems. The described microwave/microkelvin facility is part of the EMP platform, and shall be used for further experiments within and below the millikelvin range., Comment: 14 pages with appendix; plus Erratum 17, 049901 (2022)

Advances in nanomechanics within recent years have demonstrated an always expanding range of devices, from top-down structures to appealing bottom-up MoS$_2$ and graphene membranes, used for both sensing and component-oriented applications. One of the main concerns in all of these devices is frequency noise, which ultimately limits their applicability. This issue has attracted a lot of attention recently, and the origin of this noise remains elusive up to date. In this Letter we present a very simple technique to measure frequency noise in nonlinear mechanical devices, based on the presence of bistability. It is illustrated on silicon-nitride high-stress doubly-clamped beams, in a cryogenic environment. We report on the same $T/f$ dependence of the frequency noise power spectra as reported in the literature. But we also find unexpected {\it damping fluctuations}, amplified in the vicinity of the bifurcation points; this effect is clearly distinct from already reported nonlinear dephasing, and poses a fundamental limit on the measurement of bifurcation frequencies. The technique is further applied to the measurement of frequency noise as a function of mode number, within the same device. The relative frequency noise for the fundamental flexure $\delta f/f_0$ lies in the range $0.5 - 0.01~$ppm (consistent with literature for cryogenic MHz devices), and decreases with mode number in the range studied. The technique can be applied to {\it any types} of nano-mechanical structures, enabling progresses towards the understanding of intrinsic sources of noise in these devices., Comment: Published 7 may 2018

International audience; With the ever increasing energy demand, the need for miniaturized thermoelectric (TE) devices that minimize energy waste is becoming urgent. In this context, the use of thin film-based devices is a promising strategy provided that suitable materials with appropriate properties are developed. Here, for applications at temperatures ranging from 500 K to 850 K, the TE properties of the Mg2Si compound are investigated after its deposition as thin film by microwave plasma-assisted co-sputtering method. The effects of doping the Mg2Si films with different Sb contents and of the deposition temperature are assessed. Structural characterization shows that the films grown at room temperature exhibit a larger degree of texture and strains compared to those deposited at 463 K. Furthermore, the TE properties (electrical conductivity, Seebeck coefficient, thermal conductivity) are affected in a different way by the deposition temperature, resulting eventually in a higher power factor (based on in-plane characteristics) and higher thermal conductivity (measured out-of-plane) for RT depositions

Tunnel valleys are elongated hollows commonly found in formerly glaciated areas and interpreted as resulting from subglacial meltwater erosion beneath ice sheets. Over the past two decades, the number of studies of terrestrial tunnel valleys has continuously increased and their existence has been hypothesized also on Mars, but their formation mechanisms remain poorly understood. We introduce here, an innovative experimental approach to examine erosion by circulation of pressurized meltwater within the substratum and at the silicon-substratum interface. We used a permeable substratum (sand) partially covered by a viscous, impermeable and transparent lid (silicon putty), below which we applied a central injection of pure water. Low water pressures led to groundwater circulation in the substratum only, while water pressures exceeding the sum of the glaciostatic and lithostatic pressures led to additional water circulation and formation of drainage landforms at the cap-substratum interface. The formation of these drainage landforms was monitored through time and their shapes were analyzed from digital elevation model obtained by stereo-photogrammetry. The experimental landforms include valleys that are similar to natural tunnel valleys in their spatial organization and in a number of diagnostic morphological criteria, such as undulating longitudinal profiles and “tunnel” shapes. These results are consistent with the hypothesis that overpressurized subglacial water circulation controls the formation of tunnel valleys.

The contribution of paraglacial rock-slope failure (RSF) to the excavation of cirques in glacial landscapes is explored in the Tindastóll Mountain, Skagi peninsula, northern Iceland. We analyze 8 cirques that developed during the Quaternary and 13 paraglacial RSF cavities that developed during the Holocene in this paleo-plateau. From a reconstruction of the pre-Quaternary surface of the plateau, we calculate the excavated volumes of the cirques and RSF cavities and quantify the contribution of Holocene RSF to cirque growth. By extrapolating this contribution to the whole Quaternary, we find that paraglacial RSF is a first-order contributor to the development of cirques. This contribution is twofold: first, paraglacial RSF creates cavities along valley slopes, in which cirque glaciers can develop during subsequent glaciations; second, paraglacial RSF along pre-existing cirque walls promotes cirque widening and deepening. Our results also reveal that Quaternary glacial/paraglacial erosion rates range from 0.02 to 0.17 mm yr‑¹ in the studied cirques. We infer that glaciers are (i) efficient preparatory factors for the destabilization of slopes by paraglacial RSF, (ii) efficient conveyors to evacuate deposits produced by paraglacial RSF in cirques, but (iii) not necessarily predominant agents in the excavation of cirque bedrocks. La contribution des mouvements de masse rocheuse paraglaciaires au creusement de cirques dans des paysages glaciaires est explorée dans la montagne de Tindastóll, dans la péninsule de Skagi, dans le nord de l'Islande. Nous analysons 8 cirques qui se sont développés pendant le Pléistocène et 13 cavités de mouvements de masse rocheuse paraglaciaires qui se sont développées pendant l'Holocène dans ce paléo-plateau. À partir d'une reconstruction de la surface pré-quaternaire du plateau, nous calculons les volumes excavés des cirques et des cavités des mouvements de masse rocheuse et quantifions leur contribution au cours de l'Holocène à l’élargissement du cirque. En extrapolant cette contribution à l'ensemble du Quaternaire, nous constatons que les mouvements de masse rocheuse paraglaciaires sont des contributeurs de premier ordre au développement des cirques. Cette contribution est double : premièrement, les mouvements de masse rocheuse paraglaciaires créent des cavités le long des versants de la vallée, dans lesquels des glaciers de cirque peuvent se développer lors de glaciations ultérieures ; deuxièmement, les mouvements de masse rocheuse paraglaciaires le long des parois de cirque préexistants favorisent l’élargissement et l’approfondissement du cirque lui-même. Nos résultats révèlent également que les taux d’érosion glaciaire / paraglaciaire du Quaternaire varient de 0,02 à 0,17 mm par an dans les cirques étudiés. Nous en déduisons que les glaciers sont (i) des facteurs préparatoires efficaces pour la déstabilisation des pentes par les mouvements de masse rocheuse paraglaciaires, (ii) des convoyeurs efficaces pour évacuer les dépôts produits par les mouvements de masse rocheuse paraglaciaire dans les cirques, mais (iii) des agents non nécessairement prédominants dans l'excavation des planchers du cirque.

Pnictogen and chalcogenide compounds have been seen as high-potential materials for efficient thermoelectric conversion over the past few decades. It is also known that with nanostructuration, the physical properties of these pnictogen–chalcogenide compounds can be further enhanced towards a more efficient heat conversion. Here, we report the reduced thermal conductivity of a large ensemble of Bi2Te3 alloy nanowires (70 nm in diameter) with selenium for n-type and antimony for p-type (Bi2Te3−ySey and Bi2−xSbxTe3 respectively). The nanowire growth was carried out through electrodeposition in nanoporous aluminium oxide templates with high aspect ratios leading to a forest (109 per centimetre square) of nearly identical nanowires. The temperature dependence of thermal conductivity for the nanowire ensembles was acquired through a highly sensitive 3ω measurement technique. The change in the thermal conductivity of nanowires is largely affected by the roughness in addition to the size effect due to enhanced boundary scattering. The major factor that influences the thermal conductivity was found to be the ratio of the rms roughness to the correlation length of the nanowire. With a high Seebeck coefficient and electrical conductivity at room temperature, the overall thermoelectric figure of merit ZT allows the consideration of such forests of nanowires as efficient potential building blocks of future TE devices., The authors acknowledge funding and support from the ANR project MESOPHON, the Laboratoire dexcellence LANEF in Grenoble (No. ANR-10-LABX-51-01), and from the ANRT. ECA, JJF and CMST acknowledge support from the Severo Ochoa Program (MINECO, Grant SEV-2017-0706) and funding from the CERCA Programme/Generalitat de Catalunya. Funding from the Spanish Ministry MINECO/FEDER: FIS2015-70862-P PHENTOM is also acknowledged.

International audience; We report the design, elaboration and measurements of an innovative planar thermoelectric (TE) devices made of a large array of small mechanically suspended nanogenerators (nanoTEG). The miniaturized TE generators based on SiN membranes are arranged in series and/or in parallel depending on the expected final resistance adapted to the one of the load. The microstructuration allows, at the same time, a high thermal insulation of the membrane from the silicon frame and high thermal coupling to its environment (surrounding air, radiations). We show a ratio of 60% between the measured effective temperature of the membrane, (and hence of the TE junctions), and the available temperature of the heat source (air). The thermal gradient generated across the TE junction reaches a value as high as 60 kelvin per mm. Energy harvesting with this planar TE module is demonstrated through the collected voltage on the TE junctions when a temperature gradient is applied, showing a harvested power on the order of 0.3 µWatt for a 1 cm 2 chip for an effective temperature gradient of 10 K. The optimization of nanoTEGs performances will increase the power harvested significantly and permit to send a signal by a regular communication protocol and feed basic functions like temperature measurement or airflow sensing.

Saturn’s moon Titan has a dense nitrogen-rich atmosphere, with methane as its primary volatile. Titan’s atmosphere experiences an active chemistry that produces a haze of organic aerosols that settle to the surface and a dynamic climate in which hydrocarbons are cycled between clouds, rain and seas. Titan displays particularly energetic meteorology at equinox in equatorial regions, including sporadic and large methane storms. In 2009 and 2010, near Titan’s northern spring equinox, the Cassini spacecraft observed three distinctive and short-lived spectral brightenings close to the equator. Here, we show from analyses of Cassini spectral data, radiative transfer modelling and atmospheric simulations that the brightenings originate in the atmosphere and are consistent with formation from dust storms composed of micrometre-sized solid organic particles mobilized from underlying dune fields. Although the Huygens lander found evidence that dust can be kicked up locally from Titan’s surface, our findings suggest that dust can be suspended in Titan’s atmosphere at much larger spatial scale. Mobilization of dust and injection into the atmosphere would require dry conditions and unusually strong near-surface winds (about five times more than estimated ambient winds). Such strong winds are expected to occur in downbursts during rare equinoctial methane storms—consistent with the timing of the observed brightenings. Our findings imply that Titan—like Earth and Mars—has an active dust cycle, which suggests that Titan’s dune fields are actively evolving by aeolian processes. Saturn’s moon Titan may have an active dust cycle in equatorial regions driven by storm winds, Cassini observations consistent with dust suspension in Titan’s atmosphere suggest.

International audience; The mitochondrion is often referred as the cellular powerhouse because the organelle oxidizes organic acids and NADH derived from nutriments, converting around 40% of the Gibbs free energy change of these reactions into ATP, the major energy currency of cell metabolism. Mitochondria are thus microscopic furnaces that inevitably release heat as a by-product of these reactions, and this contributes to body warming, especially in endotherms like birds and mammals. Over the last decade, the idea has emerged that mitochondria could be warmer than the cytosol, because of their intense energy metabolism. It has even been suggested that our own mitochondria could operate under normal conditions at a temperature close to 50 °C, something difficult to reconcile with the laws of thermal physics. Here, using our combined expertise in biology and physics, we exhaustively review the reports that led to the concept of a hot mitochondrion, which is essentially based on the development and use of a variety of molecular thermosensors whose intrinsic fluorescence is modified by temperature. Then, we discuss the physical concepts of heat diffusion, including mechanisms like phonons scattering, which occur in the nanoscale range. Although most of approaches with thermosensors studies present relatively sparse data and lack absolute temperature calibration, overall, they do support the hypothesis of hot mitochondria. However, there is no convincing physical explanation that would allow the organelle to maintain a higher temperature than its surroundings. We nevertheless proposed some research directions, mainly biological, that might help throw light on this intriguing conundrum.

The intense plume activity at the South Pole of Enceladus together with the recent detection of libration hints at an internal water ocean underneath the outer ice shell. However, the interpretation of gravity, shape, and libration data leads to contradicting results regarding the depth of ocean/ice interface and the total volume of the ocean. Here we develop an interior structure model consisting of a rocky core, an internal ocean, and an ice shell, which satisfies simultaneously the gravity, shape, and libration data. We show that the data can be reconciled by considering isostatic compensation including the effect of a few hundred meter thick elastic lithosphere. Our model predicts that the core radius is 180–185 km, the ocean density is at least 1030 kg/m3, and the ice shell is 18–22 km thick on average. The ice thicknesses are reduced at poles decreasing to less than 5 km in the south polar region.

Sub-nanometer thickness accuracy and excellent conformity make atomic layer deposited films prevalent in modern electronics, continuously shrinking in size. The thermal resistance of these films plays a major role in the overall energy efficiency of miniaturized devices. We report very sensitive thermal conductivity measurements of amorphous Al 2O 3 thin films grown using atomic layer deposition in the temperature range of 100–300 K. The 3 ω method is used to characterize these films ranging from 17.0 to 119.4 nm in thickness, using a series-resistor model to deconvolve the intrinsic thermal conductivity of the film from thermal boundary resistances inherently present in the multilayer system. The thermal conductivity of amorphous alumina films with a density of 2.77 ± 0.14 g cm − 3 is measured to be 1.73 ± 0.08 W m − 1 K − 1 at 300 K. Measurements were carried out on germanium and sapphire substrates, leading to no substrate dependence of the films’ thermal conductivity, within experimental accuracy. On the other hand, thermal boundary resistances of the systems Pt/Al 2O 3/substrate are observed to be strongly substrate-dependent, with values ranging from 2.1 × 10 − 8 m 2 K W − 1 to 3.7 × 10 − 8 m 2 K W − 1 at 300 K for films deposited on sapphire and germanium, respectively. These results provide further insights into the significance of interfaces in thermal transport across layered materials, in particular, for potential germanium-based devices.

Here we report the design, the elaboration and the measurement of an innovative planar thermoelectric (TE) devices made of large array of suspended nanogenerators [1]. The miniaturized TE generators are arranged in serial and/or in parallel depending on the expected final resistance adapted to the charge. Devices are elaborated using MEMS clean room processes. They can produce enough power (below 100 ¼Watt) to send a signal with common communication protocol and feed basic functions, for example a temperature measurement.

with the emergence of quantum technologies mastering thermal management is required, especially at the nanoscale. It is now accepted that thermal metamaterials (phononic diodes, themo-crystals) based on phonon manipulation are made possible especially at sub-Kelvin temperatures. In these extreme limits of low temperature and low dimension, phonon heat conduction enters into a quantum regime where the phonon exchange obeys the Landauer formalism. In this regime, phonon transport is governed by the value of the transmission coefficients between the ballistic conductor and the thermal reservoirs. Here, we report an ultra-sensitive thermal experiments made on a ballistic 1D phonon conductor using a new micro-platform suspended sensor. We achieved the measurement of thermal conductance with a resolution of $\Delta \mathrm{K}=\mathrm{K}$ of 1.5% and an unprecedented power sensitivity of few attoWatts around 100 mK. We show that the ballistic thermal transport is dominated by non-ideal transmission coefficients and not by the quantized thermal conductance of the nanowire itself. The measurements reveal scattering mechanisms dominated by phonon diffusion in the reservoirs. Since amorphous silicon nitride are used in that experiment we suspect that scattering of phonons on tunneling two Level systems (TLS) may be at the origin of the reduction of thermal transport. Complementary specific heat experiments are confirming that hypothesis of significant phonon-TLS scattering. The demonstration of the breakdown of the thermal conductance quantization is a major result for the phonon physics, showing that optimized thermal coupling to reservoirs from a 1D structure might be difficult to obtain. This limitation of heat transport in the quantum regime may have significant impacts on the design of modern thermal circuits and nanoelectronics (Josephson junction, quantum solid state devices). This high resolution experimental achievement gives new insight of heat transport in the quantum regime, a scientific goal that has remained uncertain till now.

Ice streams are corridors of fast-flowing ice that control mass transfers from continental ice sheets to oceans. Their flow speeds are known to accelerate and decelerate, their activity to switch on and off, and even their locations to shift entirely. Our analogue physical experiments reveal that a lifecycle incorporating evolving subglacial meltwater routing and bed erosion can govern this complex transitory behaviour. The model ice streams switch on when subglacial water pockets drain as marginal outburst floods. Then they decelerate as basal coupling increases as a consequence of the lubricating water drainage system spontaneously organising itself into channels that erode tunnel valleys. They surge or jump in location when these water drainage systems maintain low discharge but they ultimately switch off when tunnel valleys have expanded to develop efficient drainage systems. Beyond reconciling previously disconnected observations of modern and ancient ice streams into a single lifecycle, the modelling suggests that tunnel valley development may be crucial in stabilising portions of ice sheets during periods of climate change.

International audience; Titan in a Earth-like world with active erosion processes based on the interaction of liquid methane with solid organics and ices at the surface, which shapes the landscapes over geological timescales.

The floor of Isidis Planitia, a giant impact basin located close to the martian equator, exhibits a landform assemblage, nicknamed Thumbprint Terrain, made of Arcuate Ridges, Aligned Cones, Isolated Cones, Cone Fields, associated with a peripheral network of Sinuous Ridges, Linear Depressions, and Mounds. From a new comprehensive mapping initiative of these landforms and from comparisons with terrestrial analogues (ribbed moraines, dirt cones, kettle holes, eskers, tunnel valleys and moraine plateaux), we demonstrate that this distinctive assemblage is a glacial landsystem inherited from the presence of a massive polythermal ice sheet over the basin during the Hesperian. The flow of the ice sheet was controlled by its basal thermal regime. Wet-based conditions led to the formation of Arcuate Ridges and Aligned Cones in most parts of the basin, while a negative geothermal anomaly due to impact-related crustal thinning was responsible for cold-based conditions in its central part, where only Isolated Cones and Cones Fields are present. Sinuous Ridges, Linear Depressions and Mounds at the basin margins are interpreted as relicts of a radial network of subglacial channels, which drained the glacial meltwater produced within the interior of the ice sheet across its cold-based periphery.

During the Late Weichselian deglaciation, the coastal mountains of northern central Iceland have experienced significant paraglacial readjustment processes in the form of conspicuous rock slope failures and deep-seated gravitational slope deformation (DSGSD). Local topographic slopes and ridges were deeply reshaped by these large scale paraglacial processes. Located on the eastern side of Skagafjorður, one of the largest fjords of northern Iceland, the Oslandshliðarfjoll and Hnjukar ridges (65°49N, 19°14W) exhibit geomorphic evidence of spectacular DSGDS. Several series of DSGSD-induced landforms such as crestal graben and troughs initiated by ridge-top splitting were investigated over a 30-km2 area. On the basis of geomorphological mapping we recognized: (i) a ridge-top splitting event mainly controlled by glacial debuttressing induced by a minimal 300 m lowering of the glacier surface in the Deildardalur valley; (ii) a rapid Late Weichselian deglaciation of the Deildardalur valley spanning a few thousands of years (ice-free stage probably reached around 14,000 years cal. BP); (iii) ridge-top splitting having an influence on large-scale glacial patterns by guiding and facilitating glacial erosion along ridge-top grabens, resulting in accelerated trough widening. Based on these interpretations, we propose an evolutionary sequence of both the kinematic stages of the DSGSD and the Late Weichselian deglaciation at the valley scale. This work provides new insights into (i) the patterns of the Late Weichselian deglaciation in the Skagafjorður area, especially in tributary valleys of the fjord, (ii) the timing of large-scale paraglacial ridge-top deformations in relation to the post-LGM deglaciation and (iii) the influence of paraglacial DSGSD features on large-scale glacial erosional patterns.

International audience; Thermal transport properties of amorphous materials at low temperatures are governed by the interaction between phonons and localized excitations referred to as tunneling two level systems (TLS). The temperature variation of the thermal conductivity of these amorphous materials is considered as universal and is characterized by a quadratic power law. This is well described by the phenomenological TLS model even though its microscopic explanation is still elusive. Here, by scaling down to the nanometer scale amorphous systems much below the bulk phonon-TLS mean free path, we probed the robustness of that model in restricted geometry systems. Using very sensitive thermal conductance measurements, we demonstrate that the temperature dependence of the thermal conductance of silicon nitride nanostructures remains mostly quadratic independently of the nanowire section. It is not following the cubic power law in temperature as expected in a Casimir-Ziman regime of boundary limited thermal transport. This shows a thermal transport counter intuitively dominated by phonon-TLS interactions and not by phonon-boundary scattering in the nanowires. This could be ascribed to an unexpected high density of TLS on the surfaces which still dominates the phonon diffusion processes at low temperatures and explains why the universal quadratic temperature dependence of thermal conductance still holds for amorphous nanowires.

The superconductor-insulator transition (SIT) is considered an excellent example of a quantum phase transition which is driven by quantum fluctuations at zero temperature. The quantum critical point is characterized by a diverging correlation length and a vanishing energy scale. Low energy fluctuations near quantum criticality may be experimentally detected by specific heat, $c_{\rm p}$, measurements. Here, we use a unique highly sensitive experiment to measure $c_{\rm p}$ of two-dimensional granular Pb films through the SIT. The specific heat shows the usual jump at the mean field superconducting transition temperature $T_{\rm c}^{\rm {mf}}$ marking the onset of Cooper pairs formation. As the film thickness is tuned toward the SIT, $T_{\rm c}^{\rm {mf}}$ is relatively unchanged, while the magnitude of the jump and low temperature specific heat increase significantly. This behaviour is taken as the thermodynamic fingerprint of quantum criticality in the vicinity of a quantum phase transition., 9 pages, 5 figures, 1 table

We report on experiments performed within the Knudsen boundary layer of a low-pressure gas. The non-invasive probe we use is a suspended nano-electro-mechanical string (NEMS), which interacts with $^4$He gas at cryogenic temperatures. When the pressure $P$ is decreased, a reduction of the damping force below molecular friction $\propto P$ had been first reported in Phys. Rev. Lett. Vol 113, 136101 (2014) and never reproduced since. We demonstrate that this effect is independent of geometry, but dependent on temperature. Within the framework of kinetic theory, this reduction is interpreted as a rarefaction phenomenon, carried through the boundary layer by a deviation from the usual Maxwell-Boltzmann equilibrium distribution induced by surface scattering. Adsorbed atoms are shown to play a key role in the process, which explains why room temperature data fail to reproduce it., Comment: Article plus supplementary material

Titan is an Earth-like world possessing a nitrogen-rich atmosphere covering a surface showing signs of lacustrine (lakes and depressions), fluvial (channels, valleys), aeolian (longitudinal dunes) activity. The chemistry implied in the geological processes is, however, strikingly different from that on Earth. Titan’s extremely cold environment (T ~ -180°C) only allows water to exist under the form of an icy “bedrock”. The presence of methane as the second major constituent in the atmosphere, as well as an active nitrogen-methane photochemistry, allows methane and ethane to drive a hydrocarbon cycle similar to the terrestrial hydrological cycle. A plethora of organic solids, more or less soluble in liquid hydrocarbons, is also produced in the atmosphere and can lead, by atmospheric sedimentation over geological timescales, to formation of some kind of organic geological sedimentary layer.[figure_sikun2other]Based on comparisons between Titan’s landscapes seen in the Cassini spacecraft data and terrestrial analogues, karstic-like dissolution and evaporitic crystallization have been suggested in various instances to take part in the landscape development on Titan. Dissolution has been invoked, for instance, for the development of the so-called “labyrinthic terrain”, located at high latitudes and resembling terrestrial cockpit or polygonal karst terrain. In this work, we aim at testing this hypothesis by comparing the natural landscapes visible in the Cassini/RADAR images of Titan’s surface, with those inferred from the use of a 3D Landscape Evolution Model (LEM) based on the Channel-Hillslope Integrated Landscape Development (CHILD), modified to include karstic dissolution as the major geological process. Digital Elevation Models (DEMs) are generated from an initial quasi-planar surface for a set of dissolution rates, diffusion coefficients (solute transport), and sink densities of the mesh. The landscape evolves over millions of years. Synthetic SAR images are generated from these DEMs in order to compare with Titan’s landforms seen in the actual SAR images and infer the possible thickness and degree of maturation of the Titan karst