École Polytechnique

Abstract Controlled activation of defect-bound excitonic states in two-dimensional semiconductors provides a route to isolated quantum emitters and a sensitive probe of defect physics. Here we demonstrate that in situ high-temperature annealing of hBN-encapsulated monolayer WS2 on a suspended microheater leads to the emergence of spectrally isolated single-photon emitters at cryogenic temperatures. Annealing at temperatures around 1100 K produces a sharp emission line, XL, red-shifted by approximately 80 meV from the neutral exciton and exhibiting a linewidth below 200 µeV. Photoluminescence excitation spectroscopy and power-dependent measurements show that XL originates from annealing-induced defects in the WS2 monolayer, while second-order photon correlation measurements reveal clear antibunching with g (2) (0) < 0.5. These results establish high-temperature in situ annealing as a controlled means to access defect-bound excitonic states and single-photon emission in van der Waals materials.

ABSTRACT In Archaea, a prevalent class of circular RNAs corresponds to 16S and 23S ribosomal RNA intermediates (circ-pre-rRNAs). A conserved bulge-helix-bulge (BHB) motif within the 16S and 23S rRNAs processing stems and adjacent to the circularization site in Euryarchaeota and TACK superphylum suggests that pre-rRNAs circularization is widely conserved across Archaea. Using genome-wide transcriptomic data obtained on total RNAs of wild-type Thermococcus barophilus cells, we recovered the canonical circularization junctions of the 16S and 23S circ-pre-rRNAs at the predicted BHB motifs. We also identified three alternatives 23S circular junctions introducing variability at the 3’ end of the mature rRNA. We investigated the different forms of 16S and 23S by performing primer extension and RACE experiments. We showed that while the 16S rRNA has standard 5’ and 3’ extremities, the main form of 23S rRNA is circularly permuted, with helix H99 now at its 5’ end. This permutation most probably emerged from the deletion of helix H98 from the 23S circ-pre-rRNA. Interestingly, we showed that the permuted 23S rRNA is incorporated into ribosome subunits and 70S monosomes. The significance of this event in generating functional 50S particles remains to be determined.

Abstract Biomimetic tubular scaffolds hold great promise for tackling unmet clinical needs thanks to their biocompatibility and recapitulation of cellular microenvironments, conferring the ability to promote regeneration. Potential applications include small-diameter vascular implants and grafts for airway repair, for which no viable off-the-shelf solutions currently exist. The tubular materials (4 and 8 mm internal and external diameters) presented here consist purely of type I collagen, contain no chemical crosslinkers, and reproduce the multi-scale architecture of the native tissue including the presence of collagen fibrils. A novel two-step protocol provides materials with distinct concentric layers. A porous external structure, obtained by means of ice templating combined with collagen topotactic fibrillogenesis, favours oriented cell colonization. A smooth and much less porous internal layer provides mechanical and water-tightness properties relevant for in vivo implantation and promotes the formation of an endothelial monolayer under both static and flow conditions. The compliance of the double-layered materials under physiological pressure is close to that of piglet carotid arteries. The materials are also determined to be sufficiently flexible to provide the ability to perform ex vivo anastomosis with bronchi, although the relatively low value of suture retention strength remains a limitation for in vivo suturing.

In the absence of telomerase, telomere shortening triggers replicative senescence, a tumor suppressor mechanism that is also associated with oncogenic genomic instability. Yet, the precise mechanism that connects these seemingly opposing forces remains poorly understood. To directly study the complex interplay between senescence, telomere dynamics, and genomic instability, we develop a system in Saccharomyces cerevisiae to generate and track telomeres of precise length in the absence of telomerase. Using single-telomere and single-cell analyses combined with mathematical modeling, we identify a threshold length at which telomeres switch into dysfunction. A single shortest telomere below the threshold length is necessary and sufficient to trigger the onset of replicative senescence in a majority of cells. At population level, fluctuation assays establish that rare genomic instability arises predominantly in cis to the shortest telomere as Pol32-dependent non-reciprocal translocations that result in re-elongation of the shortest telomere and likely transient escape from senescence. The switch of the shortest telomere into dysfunction and subsequent processing in telomerase-negative cells thus serves as the mechanistic link between replicative senescence onset, genomic instability and the initiation of post-senescence survival.

Clouds exert multifaceted radiative effects on Earth's energy budget, acting as both insulators and reflectors that profoundly influence regional and global climate dynamics. Since 2006, spaceborne active sounders have monitored clouds with unprecedented vertical and horizontal resolution. Yet comparing cloud data from different lidars remains problematic - variations in wavelength, pulse energy, detector type, and observation times create discontinuities that complicate our understanding of long-term cloud behavior.This study presents a methodology to reconcile cloud observations from multiple spaceborne lidar platforms: CALIPSO (2006–2023), ALADIN/Aeolus (2018–2023), IceSat-2 (2018–present), ACDL/Daqi-1 (2022–present), and ATLID/EarthCARE (2024–present). We have already demonstrated this approach works for CALIOP and ALADIN (Feofilov et al., 2024); here we apply it to bridge CALIOP and ATLID. The approachWe use the Scattering Ratio at 532 nm (SR532) as our common language across all lidars. For measurements at other wavelengths, we convert the retrieved optical properties to SR532 and ATB532 (Attenuated Total Backscatter at 532 nm), enabling direct comparison. Since different signal-to-noise ratios between instruments can affect cloud detection near the detection threshold, we pay close attention to these differences.When satellites don't share the same viewing times - even with nearly identical equator crossings - we apply a diurnal cycle correction using climatology derived from CATS measurements as in (Feofilov and Stubenrauch, 2019; Feofilov et al., 2014). Since the satellites fly in opposite directions, they observe extratropical zones at different local times, and we must account for this.For missions that overlap in time, we fine-tune our cloud detection parameters until the datasets transition seamlessly. We then scrutinize collocated data across latitudes, altitudes, and seasons, hunting for differences and correcting for them where we find instrument sensitivity or noise effects.When instruments don't overlap that is the case for CALIOP and ATLID, we use a different strategy: we identify geographical zones characterized by minimal interannual variability and trends. These "stable" zones become our reference for intercalibration, allowing us to anchor ATLID to CALIOP without a shared observational period.What we getWe take ATLID's complete baseline, apply the wavelength conversion, perform diurnal cycle corrections, run our detection algorithm with the thresholds we've defined, generate global cloud distributions for the entire mission, and discuss its key properties with respect to CALIOP.

In the context of the Classification and Regression Trees (CART) algorithm, the efficient splitting of categorical features using standard criteria like GINI and Entropy is well-established. However, using the Mean Absolute Error (MAE) criterion for categorical features has traditionally relied on various numerical encoding methods. This paper demonstrates that unsupervised numerical encoding methods are not viable for MAE criteria. Furthermore, we present a novel and efficient splitting algorithm that addresses the challenges of handling categorical features with the MAE criterion. Our findings underscore the limitations of existing approaches and offer a promising solution to enhance the handling of categorical data in CART algorithms.

A bstract The vertex detector is crucial for precision measurements of the Higgs boson at the electron-positron Higgs factory. Benchmarked with $$ H\to c\overline{c} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>H</mml:mi> <mml:mo>→</mml:mo> <mml:mi>c</mml:mi> <mml:mover> <mml:mi>c</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> and $$ H\to s\overline{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>H</mml:mi> <mml:mo>→</mml:mo> <mml:mi>s</mml:mi> <mml:mover> <mml:mi>s</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> measurements in the $$ \nu \overline{\nu}H $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ν</mml:mi> <mml:mover> <mml:mi>ν</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>H</mml:mi> </mml:math> channel, we perform an optimisation study on the inner radius and spatial resolution of the vertex detector using the Jet Origin Identification (JOI) framework, which determines the parton flavour of jets using advanced Artificial Intelligence (AI) algorithm. We observe that, compared to the reference detector configuration, halving the inner radius and spatial resolution improves the transverse and longitudinal impact parameter resolution approximately by a factor of two, while increasing the accuracy and significance of the $$ H\to c\overline{c}/s\overline{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>H</mml:mi> <mml:mo>→</mml:mo> <mml:mi>c</mml:mi> <mml:mover> <mml:mi>c</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> <mml:mo>/</mml:mo> <mml:mi>s</mml:mi> <mml:mover> <mml:mi>s</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> measurement by 4% and 8%, respectively. Conversely, doubling these parameters results in comparable degradation, with variations in the inner radius being the dominant factor. Our results provide guidance for detector design and highlight promising prospects for identifying the $$ H\to s\overline{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>H</mml:mi> <mml:mo>→</mml:mo> <mml:mi>s</mml:mi> <mml:mover> <mml:mi>s</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> decay mode at future Higgs factories.

Cervical remodeling is a complex, spatially dynamic process essential for pregnancy and parturition. Studying microstructural changes, especially in collagen, requires imaging techniques sensitive to tissue organization and distribution. Most studies rely on transverse sections, which limit anatomical context and obscure gradients along the cervical canal. Here, we use polarization imaging on longitudinal sections of the mouse cervix to visualize structural changes from the internal to external os. This orientation aligns with the endocervical axis, the primary direction of mechanical loading, allowing spatial mapping of collagen alignment and anisotropy. Longitudinal sectioning improves localization of microstructural changes relative to anatomical landmarks, enhancing interpretation of tissue remodeling during gestation. This approach is especially useful in preclinical models, where regional specificity and temporal resolution are critical. By integrating polarization imaging with anatomically aligned samples, we establish a framework for evaluating both normal cervical maturation and pathological remodeling, such as in cervical insufficiency or preterm birth.

IntroductionStudies using transcranial magnetic stimulation and electromyography suggest that disrupted functional corticospinal connectivity significantly contributes to difficulty in initiating and controlling voluntary movements such as walking. In individuals with Cerebral Palsy (CP), the corticospinal tract (CST) may therefore be identified as a potential target for improving gait control. Increasing corticospinal excitability may enhance voluntary control of lower-limb muscles and improve selective activation patterns during gait. However, it remains uncertain whether this pathway can be further activated given the damage caused by the brain lesion. Moreover, muscle synergies, a cooperative activation of groups of muscles, play an essential role in efficient and adaptive locomotion. Disrupted CST projections may reduce the specificity and strength of descending commands, which can lead to the fusion or splitting of muscle synergies. This impaired descending modulation could explain the reduced number of synergies and lower variance often reported in people with CP. Understanding and improving the modulation of these synergies could lead to better rehabilitation strategies for individuals with CP. The objective of this study was to assess whether a visuomotor walking task promotes an increase in corticospinal excitability and a modulation of muscle synergies compared to a simple walking task in individuals with CP.MethodsSixteen individuals with CP were initially recruited, muscle synergy analyses were conducted in 14 participants and TMS-based corticospinal excitability assessments in 11 participants, due to contraindications to TMS or technical issues. In addition, 14 control subjects took part in this study. Each participant performed a simple walking task and a visuomotor walking task (i.e., stepping onto virtual targets) at comfortable speed, in counterbalanced order. Transcranial magnetic stimulations were delivered during walking at approximately 40% of the gait cycle (late stance phase), corresponding to minimal tibialis anterior activity. Muscle synergies were extracted from full gait cycles recorded throughout each condition. Motor evoked potentials (MEPs) in the tibialis anterior muscle were induced using transcranial magnetic stimulation. Muscle synergies were extracted from surface electromyography signals acquired from six key lower-limb muscles during both tasks. Values were expressed as (median [Q1–Q3]).ResultsIn the visuomotor task, MEPs increased by 59.4% in the CP group (simple task MEP = 1.89 [1.00–3.09] a.u vs. visuomotor task MEP = 2.70 [1.59–4.80] a.u; p ≤ 0.01) and 113.8% in the control group (simple task MEP = 1.95 [0.99–2.72] a.u vs. visuomotor task MEP = 2.91 [1.97–3.66] a.u; p ≤ 0.01). An increase in the number of synergies was observed during visuomotor task in CP group (p = 0.018).ConclusionThese results suggest that performing a visuomotor walking task allows to enhance the corticospinal excitability in both individuals with CP and control subjects. Moreover, CP individuals showed that either the number or the structure of synergies are modulated by the visuomotor task, in comparison to control subjects. Longitudinal studies are recommended to assess the impact of the integration of complex tasks in gait rehabilitation interventions.