Institut de Recherche Interdisciplinaire de Grenoble

We present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet, or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates. We compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal. A moving‐window analysis of the entire seismograms, including the coda, gives δ( t ), the difference in arrival times versus running time along the seismogram. The time resolution of the method is an order of magnitude better than the digitization interval. The δ( t ) technique is illustrated with a pair of microearthquakes, M = 1.7 and 2.0, that occurred before and after the Coyote Lake, California, earthquake ( M = 5.9) of August 6, 1979, and on the same segment of the Calaveras fault that ruptured during the earthquake. The coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet, so that its seismogram appears as a stretched version of the earlier event. We interpret this systematic variation in δ( t ) along the coda as a change in the average S velocity in the upper crust in the time interval between the two doublets. S wave velocities appear to have decreased by 0.2% in an oblong region 5–10 km in radius at the south end of the aftershock zone.

abstract Green's functions for an elastic layered medium can be expressed as a double integral over frequency and horizontal wavenumber. We show that, for any time window, the wavenumber integral can be exactly represented by a discrete summation. This discretization is achieved by adding to the particular point source an infinite set of specified circular sources centered around the point source and distributed at equal radial interval. Choice of this interval is dependent on the length of time desired for the point source response and determines the discretized set of horizontal wavenumbers which contribute to the solution. Comparisons of the results obtained with those derived using the two-dimensional discretization method (Bouchon, 1979) are presented. They show the great accuracy of the two methods.

Missing values are a genuine issue in label-free quantitative proteomics. Recent works have surveyed the different statistical methods to conduct imputation and have compared them on real or simulated data sets and recommended a list of missing value imputation methods for proteomics application. Although insightful, these comparisons do not account for two important facts: (i) depending on the proteomics data set, the missingness mechanism may be of different natures and (ii) each imputation method is devoted to a specific type of missingness mechanism. As a result, we believe that the question at stake is not to find the most accurate imputation method in general but instead the most appropriate one. We describe a series of comparisons that support our views: For instance, we show that a supposedly "under-performing" method (i.e., giving baseline average results), if applied at the "appropriate" time in the data-processing pipeline (before or after peptide aggregation) on a data set with the "appropriate" nature of missing values, can outperform a blindly applied, supposedly "better-performing" method (i.e., the reference method from the state-of-the-art). This leads us to formulate few practical guidelines regarding the choice and the application of an imputation method in a proteomics context.

Multiorgan-on-a-chip (multi-OoC) platforms have great potential to redefine the way in which human health research is conducted. After briefly reviewing the need for comprehensive multiorgan models with a systemic dimension, we highlight scenarios in which multiorgan models are advantageous. We next overview existing multi-OoC platforms, including integrated body-on-a-chip devices and modular approaches involving interconnected organ-specific modules. We highlight how multi-OoC models can provide unique information that is not accessible using single-OoC models. Finally, we discuss remaining challenges for the realization of multi-OoC platforms and their worldwide adoption. We anticipate that multi-OoC technology will metamorphose research in biology and medicine by providing holistic and personalized models for understanding and treating multisystem diseases.

Ongoing global warming raises the hypothesis of an intensification of the hydrological cycle, extreme rainfall events becoming more frequent. However, the strong time–space variability of extreme rainfall makes it difficult to detect meaningful trends in the regime of their occurrence for recent years. Using an integrated regional approach, it is shown that over the last 10 years, the Sahelian rainfall regime is characterized by a lasting deficit of the number of rainy days, while at the same time the extreme rainfall occurrence is on the rise. As a consequence, the proportion of annual rainfall associated with extreme rainfall has increased from 17% in 1970–1990 to 19% in 1991–2000 and to 21% in 2001–2010. This tends to support the idea that a more extreme climate has been observed over 2001–2010: this climate is drier in the sense of a persisting deficit of rainfall occurrence compared to 1950–1969, while at the same time there is an increased probability of extreme daily rainfall.

Other| December 01, 1997 Structural mechanism of Co2+ oxidation by the phyllomanganate buserite Alain Manceau; Alain Manceau University of Grenoble, LGIT-IRIGM, Grenoble, France Search for other works by this author on: GSW Google Scholar Victor A. Drits; Victor A. Drits Search for other works by this author on: GSW Google Scholar Ewen Silvester; Ewen Silvester Search for other works by this author on: GSW Google Scholar Celine Bartoli; Celine Bartoli Search for other works by this author on: GSW Google Scholar Bruno Lanson Bruno Lanson Search for other works by this author on: GSW Google Scholar American Mineralogist (1997) 82 (11-12): 1150–1175. https://doi.org/10.2138/am-1997-11-1213 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Alain Manceau, Victor A. Drits, Ewen Silvester, Celine Bartoli, Bruno Lanson; Structural mechanism of Co2+ oxidation by the phyllomanganate buserite. American Mineralogist 1997;; 82 (11-12): 1150–1175. doi: https://doi.org/10.2138/am-1997-11-1213 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract The geochemistry of Co at the Earth's surface is closely associated with that of manganese oxides. This geochemical association results from the oxidation of highly soluble Co2+ to weakly soluble Co3+ species, coupled with the reduction of Mn4+ or Mn3+ ions, initially present in the manganese oxide sorbent, to soluble Mn2+. The structural mechanism of this Co immobilization-manganese oxide dissolution reaction was investigated at the buserite surface. Co-sorbed samples were prepared at different surface coverages by equilibrating a Na-exchanged buserite suspension in the presence of aqueous Co2+ at pH 4. The structure of Co-sorbed birnessite obtained by drying buserite samples was determined by X-ray diffraction (XRD) and powder and polarized EXAFS spectroscopy. For each sample we determined the proportion of interlayer cations and layer vacancy sites, the Co2+/(Co2+ + Co3+) ratio, the nature of Co sorption crystallographic sites, and the proportion of interlayer vs. layer Co. From this in-depth structural characterization two distinct oxidation mechanisms were identified that occur concurrently with the transformation of low pH monoclinic buserite to hexagonal H-rich birnessite (Drits et al. 1997; Silvester et al. 1997). The first mechanism is associated with the fast disproportionation of layer Mn3+ according to 2Mnlayer3+→Mnlayer4++□layer+Mnsolution2+⁠, where □ denotes a vacant site. Divalent Co sorbs above or below a vacant site (□1) and is then oxidized by the nearest Mnlayer3+⁠. The resulting Co3+ species fills the □1 position while the reduced Mn migrates to the interlayer or into solution creating a new vacant site (□2). This reaction can be written: Cosolution2++□1+Mnlayer3+→Cointerlayer2++□1+Mnlayer3+→Cointerlayer3++□1+Mnlayer2+→Colayer3++□2+Mnsol/inter2+⁠. This mechanism may replicate along a Mn3+-rich row, and, because the density of vacancies remains constant, it can result in relatively high Co concentrations, as well as domains rich in Colayer3+−Mnlayer4+⁠. During the low-pH buserite transformation, about one-half of the layer Mn3+ that does not disproportionate migrates from the layer to the interlayer space creating new vacancies, with the displaced Mn3+ residing above or below these vacancies. The second oxidation mechanism involves the replacement of Mninterlayer3+ by Cointerlayer3+⁠; the latter may eventually migrate into layer vacancies depending on the chemical composition of octahedra surrounding the vacancy. The criterion for the migration of Co3+ into layer vacancies is the need to avoid Mnlayer3+−Colayer3+−Mnlayer3+ sequences. The suite of chemical reactions for this second mechanism can be schematically written: Cosolution2++Mninterlayer3++□→Mnsolution2++Cointerlayer3++□→Mnsolution2++Colayer3+⁠, the last step being conditional. In contrast to the first mechanism, this second mechanism decreases the density of vacant sites. At high surface coverage, Co-sorbed birnessite contains a substantial amount of unoxidized Cointerlayer2+ species despite some non-reduced Mn3+ in the sorbent. This result can be explained by the sorption of Cosolution2+ onto vacant sites located in Colayer3+- and Mnlayer4+-rich domains devoid of Mn3+. The number and size of these domains increase with the extent of oxidation and the total Co concentration in the solution, and this accounts for the decreasing capacity of buserite to oxidize Co. The weight of structural evidence indicates that Co is oxidized by Mn3+ rather than Mn4+. Thermodynamic considerations indicate that under the solution pH conditions employed in this study Mn3+ is the more likely electron sink for the oxidation of Co2+. This study also shows that the high affinity of Co for manganese oxides is not only due to its oxidation to weakly soluble Co3+ species, but also because of the reducted layer strains from the substitution of Co3+ for Mn3+.Results obtained for these model compounds were compared with those for natural Co-containing asbolane and lithiophorite (Manceau et al. 1987). This comparison indicates that the different structural mechanisms explored in the laboratory can satisfactorily account for the observations made on natural samples. Specifically, the present study proves that Co substitutes for Mn in natural phyllomanganates and allows us to eliminate the possibility of precipitation of discrete CoOOH particles. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.

abstract Digital recordings of microearthquake codas from shallow and intermediate depth earthquakes in the Hindu Kush region of Afghanistan were used to determine the attenuation factors of the S-wave coda (Qc) and primary S waves (Qβ). An anomalously rapid decay of the coda shortly after the S-wave arrival, observed also in a study of coda in central Asia by Rautian and Khalturin (1978), seems to be due primarily to depth-dependent variations in Qc. In particular, we deduce the average Qc in the crust and uppermost mantle (<100-km depth) is approximately four times lower than the deeper mantle (<400-km depth) over a wide frequency range (0.4 to 24 Hz). Further, while Qc generally increases with frequency at any depth, the degree of frequency dependence of Qc depends on depth. Except at the highest frequency studied here (∼48 Hz), the magnitude of Qc at a particular frequency increases with depth while its frequency dependence decreases. For similar depths, determinations of Qβ and Qc agree, suggesting a common wave composition and attenuation mechanism for S waves and codas. Comparison of these determinations of Qc in Afghanistan with those in other parts of the world shows that the degree of frequency dependence of Qc correlates with the expected regional heterogeneity. Such a correlation supports the prejudice that Qc is primarily influenced by scattering and suggests that tectonic processes such as folding and faulting are instrumental in creating scattering environments.

Abstract This roadmap presents the transformational research ideas proposed by “BATTERY 2030+,” the European large‐scale research initiative for future battery chemistries. A “chemistry‐neutral” roadmap to advance battery research, particularly at low technology readiness levels, is outlined, with a time horizon of more than ten years. The roadmap is centered around six themes: 1) accelerated materials discovery platform, 2) battery interface genome, with the integration of smart functionalities such as 3) sensing and 4) self‐healing processes. Beyond chemistry related aspects also include crosscutting research regarding 5) manufacturability and 6) recyclability. This roadmap should be seen as an enabling complement to the global battery roadmaps which focus on expected ultrahigh battery performance, especially for the future of transport. Batteries are used in many applications and are considered to be one technology necessary to reach the climate goals. Currently the market is dominated by lithium‐ion batteries, which perform well, but despite new generations coming in the near future, they will soon approach their performance limits. Without major breakthroughs, battery performance and production requirements will not be sufficient to enable the building of a climate‐neutral society. Through this “chemistry neutral” approach a generic toolbox transforming the way batteries are developed, designed and manufactured, will be created.

The Human Proteome Organization (HUPO) launched the Human Proteome Project (HPP) in 2010, creating an international framework for global collaboration, data sharing, quality assurance and enhancing accurate annotation of the genome-encoded proteome. During the subsequent decade, the HPP established collaborations, developed guidelines and metrics, and undertook reanalysis of previously deposited community data, continuously increasing the coverage of the human proteome. On the occasion of the HPP's tenth anniversary, we here report a 90.4% complete high-stringency human proteome blueprint. This knowledge is essential for discerning molecular processes in health and disease, as we demonstrate by highlighting potential roles the human proteome plays in our understanding, diagnosis and treatment of cancers, cardiovascular and infectious diseases.

Multiplets, i.e. events with similar waveforms, are selected from shallow earthquakes recorded on Merapi volcano (Indonesia) before the eruption of February 2nd, 1992. Two multiplet families are found with their sources close to the summit. Their seismograms are analyzed using the Moving Window Cross Spectrum technique which measures the precise time delay between seismic phases in the entire seismogram. For both families of multiplets, a gradual decrease in the arrival times of coda waves is observed as a function of the date prior to the eruption: coda waves are becoming progressively faster (up to 1.2 per cent) as the time interval to the eruption shortens. This observation is interpreted as the consequence of an increase in the seismic velocity inside the volcano. The increase in velocity started in May 1991 and was observed until September 1991, 4 months before the eruption. This velocity increase may be related to an increase in pressure in the magma chamber or in the conduits and to the resulting closure of the surrounding cracks.

Tectonic and seismological data collected in the field following the September 13, 1986, Kalamata earthquake (south Peloponnesus) are presented and analyzed to discuss the earthquake rupture process and the regional tectonics. The event occurred on the Kalamata normal fault whose trace was mapped with SPOT images and topographic and field observations. This fault is part of an approximately NNW‐SSE en échelon system cutting through the Hellenic nappes. The fault striking N15°E on the average, with a dip of about 50°, has a minimum cumulated Quaternary throw of the order of 1 km. The measured coseismic slip is 6–18 cm over a length of 6 km. The main shock focal mechanism obtained from long‐period waveform modeling (strike=201° (+10°,−20°), dip=45°±5°, rake=283° (+10°,−25°)) represents almost pure east‐west extension and is in good agreement with tectonic observations. The centroid depth is constrained to 5±3 km and the seismic moment to 7.0±2.5×10 17 N m. Over 700 aftershocks, located by a 16‐station network installed after the earthquake for a period of 2 weeks, define two clusters separated by a “gap” of aftershock activity, from the surface to a depth of about 10 km. The main cluster, to the south, defines a 45° west dipping plane which lies on the downward extension of the fault mapped at the surface. Focal mechanisms of aftershocks on this fault plane are homogeneous and represent E‐W extension as the main shock. In contrast, the majority of focal mechanisms in the uppermost part of the foot wall show more or less E‐W compression, probably corresponding to postseismic stress release. The northern cluster of aftershocks is very dense and located away from the surface rupture, within a relay zone between the Kalamata and the next en échelon faults to the NW, the Thouria faults. There focal mechanisms represent extension from about N115° to N70° and N20°, corresponding mostly to fault reactivation in an area where nonrigid deformations prevail. The main shock probably initiated in this relay zone 3–4 s before the rupture front reached the main fault plane and released most of the energy there, the rupture presumably propagating southward. The focal mechanism of the Kalamata earthquake and that of the April 27, 1965, earthquake located to the northwest of Crete, as well as the regional active normal fault pattern, imply that E‐W extension oblique to the Hellenic arc is presently the dominant tectonic regime. E‐W stretching occurs partly on reactivated NW‐SE faults parallel to the Hellenic structures but mostly on newly formed N‐S normal faults across those structures. The latter faults are responsible for the apparent segmentation of the Hellenic belt from southern Peloponnesus to Crete. The existence of active E‐W extension in this region implies a recent change in the tectonic regime and consequently a change in boundary conditions at the subduction zone, probably in response to the incoming margin of Africa.

The linear, large‐scale and small‐scale amplification effects in the Mexico City valley, related to both the surficial clay layer and the underlying thick sediments, are investigated with two‐dimensional (2D) models and compared with the results of simple one‐dimensional (1D) models. The deep sediments are shown to be responsible, on their own, for an amplification ranging between 3 and 7, a part of which is due to the 2D effects in case of low damping and velocity gradient. This result is consistent with the observed relative amplification around 0.5 Hz at CU stations with respect to TACY station. The amplification due to the clay layer is much larger (above 10), and the corresponding 2D effects have very peculiar characteristics. On the one hand, the local surface waves generated on any lateral heterogeneity exhibit a strong spatial decay, even in case of low damping (2%), and the motion at a given site is therefore affected only by lateral heterogeneities lying within a radius smaller than 1 km. On the other hand, these local 2D effects may be extremely large, either on the very edges of the lake‐bed zone, or over localized thicker areas, where they induce a duration increase and an overamplification. The main engineering consequences of these results are twofold: i) microzoning studies in Mexico City should take into account the effects of deep sediments, and ii) as the surface motion in the lake‐bed zone is extremely sensitive to local heterogeneities, 1D models are probably inappropriate in many parts of Mexico City.

Models are pivotal for assessing future forest dynamics under the impacts of changing climate and management practices, incorporating representations of tree growth, mortality, and regeneration. Quantitative studies on the importance of mortality submodels are scarce. We evaluated 15 dynamic vegetation models (DVMs) regarding their sensitivity to different formulations of tree mortality under different degrees of climate change. The set of models comprised eight DVMs at the stand scale, three at the landscape scale, and four typically applied at the continental to global scale. Some incorporate empirically derived mortality models, and others are based on experimental data, whereas still others are based on theoretical reasoning. Each DVM was run with at least two alternative mortality submodels. Model behavior was evaluated against empirical time series data, and then, the models were subjected to different scenarios of climate change. Most DVMs matched empirical data quite well, irrespective of the mortality submodel that was used. However, mortality submodels that performed in a very similar manner against past data often led to sharply different trajectories of forest dynamics under future climate change. Most DVMs featured high sensitivity to the mortality submodel, with deviations of basal area and stem numbers on the order of 10-40% per century under current climate and 20-170% under climate change. The sensitivity of a given DVM to scenarios of climate change, however, was typically lower by a factor of two to three. We conclude that (1) mortality is one of the most uncertain processes when it comes to assessing forest response to climate change, and (2) more data and a better process understanding of tree mortality are needed to improve the robustness of simulated future forest dynamics. Our study highlights that comparing several alternative mortality formulations in DVMs provides valuable insights into the effects of process uncertainties on simulated future forest dynamics.

Nickel enzymes, present in archaea, bacteria, plants, and primitive eukaryotes are divided into redox and nonredox enzymes and play key functions in diverse metabolic processes, such as energy metabolism and virulence. They catalyze various reactions by using active sites of diverse complexities, such as mononuclear nickel in Ni-superoxide dismutase, glyoxylase I and acireductone dioxygenase, dinuclear nickel in urease, heteronuclear metalloclusters in [NiFe]-carbon monoxide dehydrogenase, acetyl-CoA decarbonylase/synthase and [NiFe]-hydrogenase, and even more complex cofactors in methyl-CoM reductase and lactate racemase. The presence of metalloenzymes in a cell necessitates a tight regulation of metal homeostasis, in order to maintain the appropriate intracellular concentration of nickel while avoiding its toxicity. As well, the biosynthesis and insertion of nickel active sites often require specific and elaborated maturation pathways, allowing the correct metal to be delivered and incorporated into the target enzyme. In this review, the phylogenetic distribution of nickel enzymes will be briefly described. Their tridimensional structures as well as the complexity of their active sites will be discussed. In view of the latest findings on these enzymes, a special focus will be put on the biosynthesis of their active sites and nickel activation of apo-enzymes.

The snow cover is a key component of land surface hydrology, especially in mountain areas where it governs the amount and timing of water availability in downstream areas. It is involved in relevant climate feedbacks and natural hazards such as avalanches and floods. Monitoring and forecasting snow cover characteristics is challenging. While snow cover extent is relatively easy to retrieve from satellite data, remote sensing retrievals of the snow water equivalent (SWE) is often inaccurate, particularly in complex mountainous terrain. Model-based snow cover estimates, driven by meteorological data, often bear significant uncertainties due to both input data and model errors. Data assimilation can combine both approaches to improve SWE estimates. In this paper, we review current state-of-the-art data assimilation methodologies used to optimally combine measurements with snow cover models in order to reduce uncertainties. The suitability of a given data assimilation method varies with the numerical complexity of snow models as well as the availability and the type of observations. This review describes the issues and challenges associated with data assimilation applied to the mountain snow cover, providing recommendations for existing and upcoming monitoring and prediction systems of snow hydrology in mountainous regions.

Abstract Particulate matter (PM) induces oxidative stress in vivo , leading to adverse health effects. Oxidative potential (OP) of PM is increasingly studied as a relevant metric for health impact (instead of PM mass concentration) as much of the ambient particle mass do not contribute to PM toxicity. Several assays have been developed to quantify PM oxidative potential and a widely used one is the acellular dithiothreitol (DTT) assay. However in such assays, particles are usually extracted with methanol or Milli-Q water which is unrepresentative of physiological conditions. For this purpose, OP DTT measurements after simulated lung fluids (SLF) extraction, in order to look at the impact of simulated lung fluid constituents, were compared to Milli-Q water extraction measurements. Our major finding is a significant decrease of the OP DTT when the artificial lysosomal fluid (ALF) solution was used. Indeed, ligand compounds are present in the SLF solutions and some induce a decrease of the OP when compared to water extraction. Our results suggest that the effect of ligands and complexation in lining fluids towards PM contaminants probably has been underestimated and should be investigated further.

Abstract Bioaerosols represent up to 15–25% of PM by mass, but there is currently no assessment of their impact on Oxidative Potential (OP), or capacity of particulate matter (PM) to produce damaging oxidative reactions in the human lungs. Here, the OP of selected bioaerosols (bacteria cells vs fungal spores) was assessed through the cell-free DTT assay. Results show that bioaerosols induce Reactive Oxygen Species (ROS) production, varying along the microorganism type, species, and concentration. Fungal spores show up to 10 times more ROS generation than bacterial cells. At the highest concentrations, fungal spores present as much oxidative reactivity as the most redox-active airborne chemicals (Copper, Naphtoquinone). Moreover, bioaerosols substantially influence OP of ambient PM and that of its chemical constituents: in presence of A . fumigatus spores, the OP of Cu/NQ is increased by a factor of 2 to 5, whereas, 10 4 and 10 5 S . epidermidis bacterial cells.mL −1 halves the OP of Cu/NQ. Finally, viable and gamma-rays-killed model bioaerosols present similar oxidative reactivity, suggesting a metabolism-independent cellular mechanism. These results reveal the importance of bioaerosols for PM reactivity. PM toxicity can be modified due to bioaerosols contribution or by their ability to modulate the OP of toxic chemicals present in PM.

The grain‐size dependent behavior of pyrrhotite during a magnetic LT‐transition at 34 K is suitable for granulometric purposes. Cycling down to liquid Helium temperature suppresses soft MD J rs more than hard SD J rs , so that it may be effective in removing soft secondary NRM components. The domain structure of large pyrrhotite grains changes from MD at room temperature to SD or PSD below the LT‐transition.

Abstract. Steep mountain catchments typically experience large sediment pulses from hillslopes which are stored in headwater channels and remobilized by debris-flows or bedload transport. Event-based sediment budget monitoring in the active Manival debris-flow torrent in the French Alps during a two-year period gave insights into the catchment-scale sediment routing during moderate rainfall intensities which occur several times each year. The monitoring was based on intensive topographic resurveys of low- and high-order channels using different techniques (cross-section surveys with total station and high-resolution channel surveys with terrestrial and airborne laser scanning). Data on sediment output volumes from the main channel were obtained by a sediment trap. Two debris-flows were observed, as well as several bedload transport flow events. Sediment budget analysis of the two debris-flows revealed that most of the debris-flow volumes were supplied by channel scouring (more than 92%). Bedload transport during autumn contributed to the sediment recharge of high-order channels by the deposition of large gravel wedges. This process is recognized as being fundamental for debris-flow occurrence during the subsequent spring and summer. A time shift of scour-and-fill sequences was observed between low- and high-order channels, revealing the discontinuous sediment transfer in the catchment during common flow events. A conceptual model of sediment routing for different event magnitude is proposed.

Abstract Janus single-layer transition metal dichalcogenides, in which the two chalcogen layers have a different chemical nature, push chemical composition control beyond what is usually achievable with van der Waals heterostructures. Here, we report such a Janus compound, SPtSe, which is predicted to exhibit strong Rashba spin–orbit coupling. We synthetized it by conversion of a single-layer of PtSe 2 on Pt(111) via sulfurization under H 2 S atmosphere. Our in situ and operando structural analysis with grazing incidence synchrotron X-ray diffraction reveals the process by which the Janus alloy forms. The crystalline long-range order of the as-grown PtSe 2 monolayer is first lost due to thermal annealing. A subsequent recrystallization in presence of a source of sulfur yields a highly ordered SPtSe alloy, which is isostructural to the pristine PtSe 2 . The chemical composition is resolved, layer-by-layer, using angle-resolved X-ray photoelectron spectroscopy, demonstrating that Se-by-S substitution occurs selectively in the topmost chalcogen layer.