@article{12605, abstract = {Snow depth patterns over glaciers are controlled by precipitation, snow redistribution due to wind and avalanches, and the exchange of energy with the atmosphere that determines snow ablation. While many studies have advanced the understanding of ablation processes, less is known about winter snow patterns and their variability over glaciers. We analyze snow depth on Haut Glacier d'Arolla, Switzerland, in the two winter seasons 2006–2007 and 2010–2011 to (1) understand whether snow depth over an alpine glacier at the end of the accumulation season exhibits a behavior similar to the one observed on single slopes and vegetated areas; and (2) investigate the snow pattern consistency over the two accumulation seasons. We perform this analysis on a data set of high-resolution lidar-derived snow depth using variograms and fractal parameters. Our first main result is that snow depth patterns on the glacier exhibit a multiscale behavior, with a scale break around 20 m after which the fractal dimension increases, indicating more autocorrelated structure before the scale break than after. Second, this behavior is consistent over the two years, with fractal parameters and their spatial variability almost constant in the two seasons. We also show that snow depth patterns exhibit a distinct behavior in the glacier tongue and the upper catchment, with longer correlation distances on the tongue in the direction of the main winds, suggesting spatial distinctions that are likely induced by different processes and that should be taken into account when extrapolating snow depth from limited samples.}, author = {Clemenzi, I. and Pellicciotti, Francesca and Burlando, P.}, issn = {1944-7973}, journal = {Water Resources Research}, keywords = {Water Science and Technology}, number = {10}, pages = {7929--7945}, publisher = {American Geophysical Union}, title = {{Snow depth structure, fractal behavior, and interannual consistency over Haut Glacier d'Arolla, Switzerland}}, doi = {10.1029/2017wr021606}, volume = {54}, year = {2018}, } @article{12606, abstract = {Ice cliffs within a supraglacial debris cover have been identified as a source for high ablation relative to the surrounding debris-covered area. Due to their small relative size and steep orientation, ice cliffs are difficult to detect using nadir-looking space borne sensors. The method presented here uses surface slopes calculated from digital elevation model (DEM) data to map ice cliff geometry and produce an ice cliff probability map. Surface slope thresholds, which can be sensitive to geographic location and/or data quality, are selected automatically. The method also attempts to include area at the (often narrowing) ends of ice cliffs which could otherwise be neglected due to signal saturation in surface slope data. The method was calibrated in the eastern Alaska Range, Alaska, USA, against a control ice cliff dataset derived from high-resolution visible and thermal data. Using the same input parameter set that performed best in Alaska, the method was tested against ice cliffs manually mapped in the Khumbu Himal, Nepal. Our results suggest the method can accommodate different glaciological settings and different DEM data sources without a data intensive (high-resolution, multi-data source) recalibration.}, author = {Herreid, Sam and Pellicciotti, Francesca}, issn = {1994-0424}, journal = {The Cryosphere}, keywords = {Earth-Surface Processes, Water Science and Technology}, number = {5}, pages = {1811--1829}, publisher = {Copernicus Publications}, title = {{Automated detection of ice cliffs within supraglacial debris cover}}, doi = {10.5194/tc-12-1811-2018}, volume = {12}, year = {2018}, } @article{12607, abstract = {Supraglacial ice cliffs exist on debris-covered glaciers worldwide, but despite their importance as melt hot spots, their life cycle is little understood. Early field observations had advanced a hypothesis of survival of north-facing and disappearance of south-facing cliffs, which is central for predicting the contribution of cliffs to total glacier mass losses. Their role as windows of energy transfer suggests they may explain the anomalously high mass losses of debris-covered glaciers in High Mountain Asia (HMA) despite the insulating debris, currently at the center of a debated controversy. We use a 3D model of cliff evolution coupled to very high-resolution topographic data to demonstrate that ice cliffs facing south (in the Northern Hemisphere) disappear within a few months due to enhanced solar radiation receipts and that aspect is the key control on cliffs evolution. We reproduce continuous flattening of south-facing cliffs, a result of their vertical gradient of incoming solar radiation and sky view factor. Our results establish that only north-facing cliffs are recurrent features and thus stable contributors to the melting of debris-covered glaciers. Satellite observations and mass balance modeling confirms that few south-facing cliffs of small size exist on the glaciers of Langtang, and their contribution to the glacier volume losses is very small (∼1%). This has major implications for the mass balance of HMA debris-covered glaciers as it provides the basis for new parameterizations of cliff evolution and distribution to constrain volume losses in a region where glaciers are highly relevant as water sources for millions of people.}, author = {Buri, Pascal and Pellicciotti, Francesca}, issn = {1091-6490}, journal = {PNAS}, number = {17}, pages = {4369--4374}, publisher = {Proceedings of the National Academy of Sciences}, title = {{Aspect controls the survival of ice cliffs on debris-covered glaciers}}, doi = {10.1073/pnas.1713892115}, volume = {115}, year = {2018}, } @article{13, abstract = {We propose a new method for fabricating digital objects through reusable silicone molds. Molds are generated by casting liquid silicone into custom 3D printed containers called metamolds. Metamolds automatically define the cuts that are needed to extract the cast object from the silicone mold. The shape of metamolds is designed through a novel segmentation technique, which takes into account both geometric and topological constraints involved in the process of mold casting. Our technique is simple, does not require changing the shape or topology of the input objects, and only requires off-the- shelf materials and technologies. We successfully tested our method on a set of challenging examples with complex shapes and rich geometric detail. © 2018 Association for Computing Machinery.}, author = {Alderighi, Thomas and Malomo, Luigi and Giorgi, Daniela and Pietroni, Nico and Bickel, Bernd and Cignoni, Paolo}, journal = {ACM Trans. Graph.}, number = {4}, publisher = {ACM}, title = {{Metamolds: Computational design of silicone molds}}, doi = {10.1145/3197517.3201381}, volume = {37}, year = {2018}, } @misc{13055, abstract = {Dataset for manuscript 'Social network plasticity decreases disease transmission in a eusocial insect' Compared to previous versions: - raw image files added - correction of URLs within README.txt file }, author = {Stroeymeyt, Nathalie and Grasse, Anna V and Crespi, Alessandro and Mersch, Danielle and Cremer, Sylvia and Keller, Laurent}, publisher = {Zenodo}, title = {{Social network plasticity decreases disease transmission in a eusocial insect}}, doi = {10.5281/ZENODO.1322669}, year = {2018}, } @misc{13059, abstract = {This dataset contains a GitHub repository containing all the data, analysis, Nextflow workflows and Jupyter notebooks to replicate the manuscript titled "Fast and accurate large multiple sequence alignments with a root-to-leaf regressive method". It also contains the Multiple Sequence Alignments (MSAs) generated and well as the main figures and tables from the manuscript. The repository is also available at GitHub (https://github.com/cbcrg/dpa-analysis) release `v1.2`. For details on how to use the regressive alignment algorithm, see the T-Coffee software suite (https://github.com/cbcrg/tcoffee).}, author = {Garriga, Edgar and di Tommaso, Paolo and Magis, Cedrik and Erb, Ionas and Mansouri, Leila and Baltzis, Athanasios and Laayouni, Hafid and Kondrashov, Fyodor and Floden, Evan and Notredame, Cedric}, publisher = {Zenodo}, title = {{Fast and accurate large multiple sequence alignments with a root-to-leaf regressive method}}, doi = {10.5281/ZENODO.2025846}, year = {2018}, } @article{131, abstract = {XY systems usually show chromosome-wide compensation of X-linked genes, while in many ZW systems, compensation is restricted to a minority of dosage-sensitive genes. Why such differences arose is still unclear. Here, we combine comparative genomics, transcriptomics and proteomics to obtain a complete overview of the evolution of gene dosage on the Z-chromosome of Schistosoma parasites. We compare the Z-chromosome gene content of African (Schistosoma mansoni and S. haematobium) and Asian (S. japonicum) schistosomes and describe lineage-specific evolutionary strata. We use these to assess gene expression evolution following sex-linkage. The resulting patterns suggest a reduction in expression of Z-linked genes in females, combined with upregulation of the Z in both sexes, in line with the first step of Ohno’s classic model of dosage compensation evolution. Quantitative proteomics suggest that post-transcriptional mechanisms do not play a major role in balancing the expression of Z-linked genes. }, author = {Picard, Marion A and Cosseau, Celine and Ferré, Sabrina and Quack, Thomas and Grevelding, Christoph and Couté, Yohann and Vicoso, Beatriz}, journal = {eLife}, publisher = {eLife Sciences Publications}, title = {{Evolution of gene dosage on the Z-chromosome of schistosome parasites}}, doi = {10.7554/eLife.35684}, volume = {7}, year = {2018}, } @article{132, abstract = {Pancreas development involves a coordinated process in which an early phase of cell segregation is followed by a longer phase of lineage restriction, expansion, and tissue remodeling. By combining clonal tracing and whole-mount reconstruction with proliferation kinetics and single-cell transcriptional profiling, we define the functional basis of pancreas morphogenesis. We show that the large-scale organization of mouse pancreas can be traced to the activity of self-renewing precursors positioned at the termini of growing ducts, which act collectively to drive serial rounds of stochastic ductal bifurcation balanced by termination. During this phase of branching morphogenesis, multipotent precursors become progressively fate-restricted, giving rise to self-renewing acinar-committed precursors that are conveyed with growing ducts, as well as ductal progenitors that expand the trailing ducts and give rise to delaminating endocrine cells. These findings define quantitatively how the functional behavior and lineage progression of precursor pools determine the large-scale patterning of pancreatic sub-compartments.}, author = {Sznurkowska, Magdalena and Hannezo, Edouard B and Azzarelli, Roberta and Rulands, Steffen and Nestorowa, Sonia and Hindley, Christopher and Nichols, Jennifer and Göttgens, Berthold and Huch, Meritxell and Philpott, Anna and Simons, Benjamin}, journal = {Developmental Cell}, number = {3}, pages = {360 -- 375}, publisher = {Cell Press}, title = {{Defining lineage potential and fate behavior of precursors during pancreas development}}, doi = {10.1016/j.devcel.2018.06.028}, volume = {46}, year = {2018}, } @inproceedings{133, abstract = {Synchronous programs are easy to specify because the side effects of an operation are finished by the time the invocation of the operation returns to the caller. Asynchronous programs, on the other hand, are difficult to specify because there are side effects due to pending computation scheduled as a result of the invocation of an operation. They are also difficult to verify because of the large number of possible interleavings of concurrent computation threads. We present synchronization, a new proof rule that simplifies the verification of asynchronous programs by introducing the fiction, for proof purposes, that asynchronous operations complete synchronously. Synchronization summarizes an asynchronous computation as immediate atomic effect. Modular verification is enabled via pending asynchronous calls in atomic summaries, and a complementary proof rule that eliminates pending asynchronous calls when components and their specifications are composed. We evaluate synchronization in the context of a multi-layer refinement verification methodology on a collection of benchmark programs.}, author = {Kragl, Bernhard and Qadeer, Shaz and Henzinger, Thomas A}, issn = {1868-8969}, location = {Beijing, China}, publisher = {Schloss Dagstuhl - Leibniz-Zentrum für Informatik}, title = {{Synchronizing the asynchronous}}, doi = {10.4230/LIPIcs.CONCUR.2018.21}, volume = {118}, year = {2018}, } @article{21096, abstract = {By using a combination of readily accessible experimental and computational experiments in water, we explored the factors governing the association between polyanionic dyn[4]arene and a series of α,ω-alkyldiammonium ions of increasing chain length. We found that the lock-and-key concept based on the best match between the apolar and polar regions of the molecular partners failed to explain the observed selectivities. Instead, the dissection of the energetic and structural contributions demonstrated that the binding events were actually guided by two crucial solvent-related phenomena as the chain length of the guest increases: the expected decrease of the enthalpic cost of guest desolvation and the unexpected increase of the favourable enthalpy of complex solvation. By bringing to light the decisive enthalpic impact of complex solvation during the binding of polyelectrolytes by inclusion, this study may provide a missing piece to a puzzle that one day could display the global picture of molecular recognition in water.}, author = {Jeamet, Emeric and Septavaux, Jean and Héloin, Alexandre and Donnier-Maréchal, Marion and Dumartin, Melissa and Ourri, Benjamin and Mandal, Pradeep K and Huc, Ivan and Bignon, Emmanuelle and Dumont, Elise and Morell, Christophe and Francoia, Jean-Patrick and Perret, Florent and Vial, Laurent and Leclaire, Julien}, issn = {2041-6539}, journal = {Chemical Science}, number = {1}, pages = {277--283}, publisher = {Royal Society of Chemistry}, title = {{Wetting the lock and key enthalpically favours polyelectrolyte binding}}, doi = {10.1039/c8sc02966k}, volume = {10}, year = {2018}, } @article{21533, abstract = {Recent advances in the fabrication of nanostructures and nanoscale features in metasurfaces offer new prospects for generating visible light emission from low-energy electrons. Here we present the experimental observation of visible light emission from low-energy free electrons interacting with nanoscale periodic surfaces through the Smith–Purcell (SP) effect. We demonstrate SP light emission from nanoscale gratings with periodicity as small as 50 nm, enabling the observation of tunable visible radiation from low-energy electrons (1.5 to 6 keV), an order of magnitude lower in energy than previously reported. We study the emission wavelength and intensity dependence on the grating pitch and electron energy, showing agreement between experiment and theory. Our results open the way to the production of SP-based nanophotonics integrated devices. Built inside electron microscopes, SP sources could enable the development of novel electron–optical correlated spectroscopic techniques and facilitate the observation of new quantum effects in light sources.}, author = {Massuda, Aviram and Roques-Carmes, Charles and Yang, Yujia and Kooi, Steven E. and Yang, Yi and Murdia, Chitraang and Berggren, Karl K. and Kaminer, Ido and Soljačić, Marin}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {light−matter interactions, periodic structures, nanophotonics, free-electron light sources}, number = {9}, pages = {3513--3518}, publisher = {American Chemical Society }, title = {{Smith–Purcell radiation from low-energy electrons}}, doi = {10.1021/acsphotonics.8b00743}, volume = {5}, year = {2018}, } @article{21545, abstract = {Free-electron radiation such as Cerenkov1, Smith–Purcell2 and transition radiation3,4 can be greatly affected by structured optical environments, as has been demonstrated in a variety of polaritonic5,6, photonic-crystal7 and metamaterial8,9,10 systems. However, the amount of radiation that can ultimately be extracted from free electrons near an arbitrary material structure has remained elusive. Here we derive a fundamental upper limit to the spontaneous photon emission and energy loss of free electrons, regardless of geometry, which illuminates the effects of material properties and electron velocities. We obtain experimental evidence for our theory with quantitative measurements of Smith–Purcell radiation. Our framework allows us to make two predictions. One is a new regime of radiation operation—at subwavelength separations, slower (non-relativistic) electrons can achieve stronger radiation than fast (relativistic) electrons. The other is a divergence of the emission probability in the limit of lossless materials. We further reveal that such divergences can be approached by coupling free electrons to photonic bound states in the continuum11,12,13. Our findings suggest that compact and efficient free-electron radiation sources from microwaves to the soft X-ray regime may be achievable without requiring ultrahigh accelerating voltages.}, author = {Yang, Yi and Massuda, Aviram and Roques-Carmes, Charles and Kooi, Steven E. and Christensen, Thomas and Johnson, Steven G. and Joannopoulos, John D. and Miller, Owen D. and Kaminer, Ido and Soljačić, Marin}, issn = {1745-2481}, journal = {Nature Physics}, pages = {894--899}, publisher = {Springer Nature}, title = {{Maximal spontaneous photon emission and energy loss from free electrons}}, doi = {10.1038/s41567-018-0180-2}, volume = {14}, year = {2018}, } @article{21563, abstract = {Quantum electrodynamics (QED) is one of the most precisely tested theories in the history of science, giving accurate predictions to a wide range of experimental observations. Recent experimental advances allow for the ability to probe physics on extremely short attosecond timescales, enabling ultrafast imaging of quantum dynamics. It is of great interest to extend our understanding of short-time quantum dynamics to QED, where the focus is typically on long-time observables such as 𝑆 matrices, decay rates, and cross sections. That said, solving the short-time dynamics of the QED Hamiltonian can lead to divergences, making it unclear how to arrive at physical predictions. We present an approach to regularize QED at short times and apply it to the problem of free-electron radiation into a medium, known as Cherenkov radiation. Our regularization method, which can be extended to other QED processes, is performed by subtracting the self-energy in free space from the self-energy calculated in the medium. Surprisingly, we find a number of previously unknown phenomena yielding corrections to the conventional Cherenkov effect that could be observed in current experiments. Specifically, the Cherenkov velocity threshold increases relative to the famous conventional theory. This modification to the conventional theory, which can be non-negligible in realistic scenarios, should result in the suppression of spontaneous emission in readily available experiments. Finally, we reveal a bifurcation process creating radiation into new Cherenkov angles, occurring in the strong-coupling regime, which would be realizable by considering the radiation dynamics of highly charged ions. Our results shed light on QED phenomena at short times and reveal surprising new physics in the Cherenkov effect.}, author = {Roques-Carmes, Charles and Rivera, Nicholas and Joannopoulos, John D. and Soljačić, Marin and Kaminer, Ido}, issn = {2160-3308}, journal = {Physical Review X}, number = {4}, publisher = {American Physical Society}, title = {{Nonperturbative quantum electrodynamics in the Cherenkov effect}}, doi = {10.1103/physrevx.8.041013}, volume = {8}, year = {2018}, } @inproceedings{21619, abstract = {The Smith-Purcell effect is observed when an electron beam passes in the vicinity of a periodic structure. We propose a method to shape the spatial and spectral far-field radiation using complex periodic and aperiodic gratings.}, author = {Remez, Roei and Shapira, Niv and Roques-Carmes, Charles and Tirole, Romain and Yang, Yi and Lereah, Yossi and Soljačić, Marin and Kaminer, Ido and Arie, Ady}, booktitle = {Conference on Lasers and Electro-Optics}, location = {San Jose, CA, United States}, publisher = {Optica Publishing Group}, title = {{Spectral and spatial shaping of Smith-Purcell radiation}}, doi = {10.1364/cleo_qels.2018.fw4h.3}, year = {2018}, } @article{13374, abstract = {Confining molecules to volumes only slightly larger than the molecules themselves can profoundly alter their properties. Molecular switches—entities that can be toggled between two or more forms upon exposure to an external stimulus—often require conformational freedom to isomerize. Therefore, placing these switches in confined spaces can render them non-operational. To preserve the switchability of these species under confinement, we work with a water-soluble coordination cage that is flexible enough to adapt its shape to the conformation of the encapsulated guest. We show that owing to its flexibility, the cage is not only capable of accommodating—and solubilizing in water—several light-responsive spiropyran-based molecular switches, but, more importantly, it also provides an environment suitable for the efficient, reversible photoisomerization of the bound guests. Our findings pave the way towards studying various molecular switching processes in confined environments.}, author = {Samanta, Dipak and Galaktionova, Daria and Gemen, Julius and Shimon, Linda J. W. and Diskin-Posner, Yael and Avram, Liat and Král, Petr and Klajn, Rafal}, issn = {2041-1723}, journal = {Nature Communications}, keywords = {General Physics and Astronomy, General Biochemistry, Genetics and Molecular Biology, General Chemistry, Multidisciplinary}, publisher = {Springer Nature}, title = {{Reversible chromism of spiropyran in the cavity of a flexible coordination cage}}, doi = {10.1038/s41467-017-02715-6}, volume = {9}, year = {2018}, } @article{13376, abstract = {Efficient molecular switching in confined spaces is critical for the successful development of artificial molecular machines. However, molecular switching events often entail large structural changes and therefore require conformational freedom, which is typically limited under confinement conditions. Here, we investigated the behavior of azobenzene—the key building block of light-controlled molecular machines—in a confined environment that is flexible and can adapt its shape to that of the bound guest. To this end, we encapsulated several structurally diverse azobenzenes within the cavity of a flexible, water-soluble coordination cage, and investigated their light-responsive behavior. Using UV/Vis absorption spectroscopy and a combination of NMR methods, we showed that each of the encapsulated azobenzenes exhibited distinct switching properties. An azobenzene forming a 1:1 host–guest inclusion complex could be efficiently photoisomerized in a reversible fashion. In contrast, successful switching in inclusion complexes incorporating two azobenzene guests was dependent on the availability of free cages in the system, and it involved reversible trafficking of azobenzene between the cages. In the absence of extra cages, photoswitching was either suppressed or it involved expulsion of azobenzene from the cage and consequently its precipitation from the solution. This finding was utilized to develop an information storage medium in which messages could be written and erased in a reversible fashion using light.}, author = {Samanta, Dipak and Gemen, Julius and Chu, Zonglin and Diskin-Posner, Yael and Shimon, Linda J. W. and Klajn, Rafal}, issn = {1091-6490}, journal = {Proceedings of the National Academy of Sciences}, keywords = {Multidisciplinary}, number = {38}, pages = {9379--9384}, publisher = {Proceedings of the National Academy of Sciences}, title = {{Reversible photoswitching of encapsulated azobenzenes in water}}, doi = {10.1073/pnas.1712787115}, volume = {115}, year = {2018}, } @article{13377, abstract = {Confining organic molecules to the surfaces of inorganic nanoparticles can induce intermolecular interactions between them, which can affect the composition of the mixed self-assembled monolayers obtained by co-adsorption from solution of two different molecules. Two thiolated ligands (a dialkylviologen and a zwitterionic sulfobetaine) that can interact with each other electrostatically were coadsorbed onto gold nanoparticles. The nanoparticles favor a narrow range of ratios of these two molecules that is largely independent of the molar ratio in solution. Changing the solution molar ratio of the two ligands by a factor of 5 000 affects the on-nanoparticle ratio of these ligands by only threefold. This behavior is reminiscent of the formation of insoluble inorganic salts (such as AgCl), which similarly compensate positive and negative charges upon crystallizing. Our results pave the way towards developing well-defined hybrid organic–inorganic nanostructures.}, author = {Chu, Zonglin and Han, Yanxiao and Král, Petr and Klajn, Rafal}, issn = {1521-3773}, journal = {Angewandte Chemie International Edition}, keywords = {General Chemistry, Catalysis}, number = {24}, pages = {7023--7027}, publisher = {Wiley}, title = {{“Precipitation on nanoparticles”: Attractive intermolecular interactions stabilize specific ligand ratios on the surfaces of nanoparticles}}, doi = {10.1002/anie.201800673}, volume = {57}, year = {2018}, } @article{13379, author = {Bléger, David and Klajn, Rafal}, issn = {1521-3927}, journal = {Macromolecular Rapid Communications}, keywords = {Materials Chemistry, Polymers and Plastics, Organic Chemistry}, number = {1}, publisher = {Wiley}, title = {{Integrating macromolecules with molecular switches}}, doi = {10.1002/marc.201700827}, volume = {39}, year = {2018}, } @article{134, abstract = {The current state of the art in real-time two-dimensional water wave simulation requires developers to choose between efficient Fourier-based methods, which lack interactions with moving obstacles, and finite-difference or finite element methods, which handle environmental interactions but are significantly more expensive. This paper attempts to bridge this long-standing gap between complexity and performance, by proposing a new wave simulation method that can faithfully simulate wave interactions with moving obstacles in real time while simultaneously preserving minute details and accommodating very large simulation domains. Previous methods for simulating 2D water waves directly compute the change in height of the water surface, a strategy which imposes limitations based on the CFL condition (fast moving waves require small time steps) and Nyquist's limit (small wave details require closely-spaced simulation variables). This paper proposes a novel wavelet transformation that discretizes the liquid motion in terms of amplitude-like functions that vary over space, frequency, and direction, effectively generalizing Fourier-based methods to handle local interactions. Because these new variables change much more slowly over space than the original water height function, our change of variables drastically reduces the limitations of the CFL condition and Nyquist limit, allowing us to simulate highly detailed water waves at very large visual resolutions. Our discretization is amenable to fast summation and easy to parallelize. We also present basic extensions like pre-computed wave paths and two-way solid fluid coupling. Finally, we argue that our discretization provides a convenient set of variables for artistic manipulation, which we illustrate with a novel wave-painting interface.}, author = {Jeschke, Stefan and Skrivan, Tomas and Mueller Fischer, Matthias and Chentanez, Nuttapong and Macklin, Miles and Wojtan, Christopher J}, journal = {ACM Transactions on Graphics}, number = {4}, publisher = {ACM}, title = {{Water surface wavelets}}, doi = {10.1145/3197517.3201336}, volume = {37}, year = {2018}, } @article{13473, abstract = {Stripped-envelope stars form in binary systems after losing mass through Roche-lobe overflow. They bear astrophysical significance as sources of UV and ionizing radiation in older stellar populations and, if sufficiently massive, as stripped supernova progenitors. Binary evolutionary models predict that they are common, but only a handful of subdwarfs with B-type companions are known. The question is whether a large population of such systems has evaded detection as a result of biases, or whether the model predictions are wrong. We reanalyze the well-studied post-interaction binary φ Persei. Recently, new data have improved the orbital solution of the system, which contains an ~1.2M⊙ stripped-envelope star and a rapidly rotating ~9.6M⊙ Be star. We compare with an extensive grid of evolutionary models using a Bayesian approach and constrain the initial masses of the progenitor to 7.2 ± 0.4M⊙ for the stripped star and 3.8 ± 0.4M⊙ for the Be star. The system must have evolved through near-conservative mass transfer. These findings are consistent with earlier studies. The age we obtain, 57 ± 9 Myr, is in excellent agreement with the age of the α Persei cluster. We note that neither star was initially massive enough to produce a core-collapse supernova, but mass exchange pushed the Be star above the mass threshold. We find that the subdwarf is overluminous for its mass by almost an order of magnitude, compared to the expectations for a helium core burning star. We can only reconcile this if the subdwarf resides in a late phase of helium shell burning, which lasts only 2–3% of the total lifetime as a subdwarf. Assuming continuous star formation implies that up to ~50 less evolved, dimmer subdwarfs exist for each system similar to φ Persei, but have evaded detection so far. Our findings can be interpreted as a strong indication that a substantial population of stripped-envelope stars indeed exists, but has so far evaded detection because of observational biases and lack of large-scale systematic searches.}, author = {Schootemeijer, A. and Götberg, Ylva Louise Linsdotter and de Mink, S. E. and Gies, D. and Zapartas, E.}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, publisher = {EDP Sciences}, title = {{Clues about the scarcity of stripped-envelope stars from the evolutionary state of the sdO+Be binary system φ Persei}}, doi = {10.1051/0004-6361/201731194}, volume = {615}, year = {2018}, }