Precipitation phase drives seasonal and decadal snowline changes in high mountain Asia

Snow cover is of key importance for water resources in high mountain Asia (HMA) and is expected to undergo extensive changes in a warming climate. Past studies have quantified snow cover changes with satellite products of relatively low spatial resolution (∼500 m) which are hindered by the steep topography of this mountain region. We derive snowlines from Sentinel-2 and Landsat 5, 7 and 8 images, which, thanks to their higher spatial resolution, are less sensitive to the local topography. We calculate the snow line altitude (SLA) and its seasonality for all glacierized catchments of HMA and link these patterns to climate variables corrected for topographic biases. As such, the snowline changes provide a clear proxy for climatic changes. Our results highlight a strong spatial variability in mean SLA and in its seasonal changes, including across mountain chains and between the monsoon-dominated and the westerlies-dominated catchments. Over the period 1999–2019, the western regions of HMA (Pamir, Karakoram, Western Himalaya) have undergone increased snow coverage, expressed as seasonal SLA decrease, in spring and summer. This change is opposed to a widespread increase in SLA in autumn across the region, and especially the southeastern regions of HMA (Nyainqentanglha, Hengduan Shan, South–East Himalaya). Our results indicate that the diversity of seasonal snow dynamics across the region is controlled not by temperature or precipitation directly but by the timing and partitioning of solid precipitation. Decadal snowline changes (1999–2009 vs 2009–2019) seasonally precede temperature changes, suggesting that seasonal temperature changes in the Karakoram–Pamir and Eastern Nyainqentanglha regions may have responded to snow cover changes, rather than driving them

LNCS

Two standard models for probabilistic systems are Markov chains (MCs) and Markov decision processes (MDPs). Classic objectives for such probabilistic models for control and planning problems are reachability and stochastic shortest path. The widely studied algorithmic approach for these problems is the Value Iteration (VI) algorithm which iteratively applies local updates called Bellman updates. There are many practical approaches for VI in the literature but they all require exponentially many Bellman updates for MCs in the worst case. A preprocessing step is an algorithm that is discrete, graph-theoretical, and requires linear space. An important open question is whether, after a polynomial-time preprocessing, VI can be achieved with sub-exponentially many Bellman updates. In this work, we present a new approach for VI based on guessing values. Our theoretical contributions are twofold. First, for MCs, we present an almost-linear-time preprocessing algorithm after which, along with guessing values, VI requires only subexponentially many Bellman updates. Second, we present an improved analysis of the speed of convergence of VI for MDPs. Finally, we present a practical algorithm for MDPs based on our new approach. Experimental results show that our approach provides a considerable improvement over existing VI-based approaches on several benchmark examples from the literature

Suppressed accretion onto massive black hole binaries surrounded by thin disks

We demonstrate that gas disks around binary systems might deliver gas to the binary components only when the circumbinary disk is relatively warm. We present new grid-based hydrodynamics simulations, performed with the binary on the grid and a locally isothermal equation of state, in which the binary is seen to functionally "stop accreting" if the orbital Mach number in the disk exceeds a threshold value of about 40. Above this threshold, the disk continues to extract angular momentum from the binary orbit, but it delivers very little mass to the black holes and instead piles up mass in a ring surrounding the binary. This ring will eventually become viscously relaxed and deliver mass to the binary at the large-scale inflow rate. However, we show that the timescale for such relaxation can far exceed the implied binary lifetime. We demonstrate that the ability of a binary–disk system to equilibrate is dependent on the efficiency at which accretion streams deposit mass onto the binary, which, in turn is highly sensitive to the thermodynamic conditions of the inner disk. If disks around massive black hole binaries do operate in such nonaccreting regimes, it suggests these systems may be dimmer than their single black hole counterparts but could exhibit dramatic rebrightening after the black holes inspiral and merge. This dimming begins in the UV/optical and could completely choke high-energy emission, such that these systems would likely be intrinsically X-ray weak with reddened continua, potentially resembling the spectra of "little red dots" recently identified in JWST observations

Linear-time MaxCut in multigraphs parameterized above the Poljak-Turzík bound

MaxCut is a classical NP-complete problem and a crucial building block in many combinatorial algorithms. The famousEdwards-Erdös bound states that any connected graph on n vertices with m edges contains a cut of size at least m/2 + n−1/4 . Crowston, Jones and Mnich [Algorithmica, 2015] showed that the MaxCut problem on simple connected graphs admits an FPT algorithm, where the parameter k is the difference between the desired cut size c and the lower bound given by the Edwards-Erdös bound. This was later improved by Etscheid and Mnich [Algorithmica, 2017] to run in parameterized linear time, i.e., f (k) · O(m). We improve upon this result in two ways: Firstly, we extend the algorithm to work also for multigraphs (alternatively, graphs with positive integer weights). Secondly, we change the parameter; instead of the difference to the Edwards-Erdös bound, we use the difference to the Poljak-Turzík bound. The Poljak-Turzík bound states that any weighted graph G has a cut of weight at least w(G)/2 + wMSF (G)/4 , where w(G) denotes the total weight of G, and wMSF (G) denotes the weight of its minimum spanning forest. In connected simple graphs the two bounds are equivalent, but for multigraphs the Poljak-Turzík bound can be larger and thus yield a smaller parameter k. Our algorithm also runs in parameterized linear time, i.e., f (k) · O(m + n)

A F420-dependent single domain chemogenetic tool for protein de-dimerization

Protein-protein interactions (PPIs) mediate many fundamental cellular processes. Control of PPIs through optically or chemically responsive protein domains has had a profound impact on basic research and some clinical applications. Most chemogenetic methods induce the association, i.e., dimerization or oligomerization, of target proteins, whilst the few available dissociation approaches either break large oligomeric protein clusters or heteromeric complexes. Here, we have exploited the controlled dissociation of a homodimeric oxidoreductase from mycobacteria (MSMEG_2027) by its native cofactor, F420, which is not present in mammals, as a bioorthogonal monomerization switch. Using X-ray crystallography, we found that in the absence of F420 MSMEG_2027 forms a unique domain-swapped dimer that occludes the cofactor binding site. Rearrangement of the N-terminal helix upon F420 binding results in the dissolution of the dimer. We then showed that MSMEG_2027 can be fused to proteins of interest in human cells and applied it as a tool to induce and release MAPK/ERK signalling downstream of a chimeric fibroblast growth factor receptor 1 (FGFR1) tyrosine kinase. This F420-dependent chemogenetic de-homodimerization tool is stoichiometric and based on a single domain and thus represents a novel mechanism to investigate protein complexes in situ

Destabilizing Iris

The separation logic framework Iris has been built on the premise that all assertions are stable, meaning they unconditionally enjoy the famous frame rule. This gives Iris—and the numerous program logics that build on it—very modular reasoning principles. But stability also comes at a cost. It excludes a core feature of the Viper verifier family, heap-dependent expression assertions, which lift program expressions to the assertion level in order to reduce redundancy between code and specifications and better facilitate SMT-based automation. In this paper, we bring heap-dependent expression assertions to Iris with Daenerys. To do so, we must first revisit the very core of Iris, extending it with a new form of unstable resources (and adapting the frame rule accordingly). On top, we then build a program logic with heap-dependent expression assertions and lay the foundations for connecting Iris to SMT solvers. We apply Daenerys to several case studies, including some that go beyond what Viper and Iris can do individually and others that benefit from the connection to SMT

Prospects of nanoscience with nanocrystals: 2025 edition

Nanocrystals (NCs) of various compositions have made important contributions to science and technology, with their impact recognized by the 2023 Nobel Prize in Chemistry for the discovery and synthesis of semiconductor quantum dots (QDs). Over four decades of research into NCs has led to numerous advancements in diverse fields, such as optoelectronics, catalysis, energy, medicine, and recently, quantum information and computing. The last 10 years since the predecessor perspective “Prospect of Nanoscience with Nanocrystals” was published in ACS Nano have seen NC research continuously evolve, yielding critical advances in fundamental understanding and practical applications. Mechanistic insights into NC formation have translated into precision control over NC size, shape, and composition. Emerging synthesis techniques have broadened the landscape of compounds obtainable in colloidal NC form. Sophistication in surface chemistry, jointly bolstered by theoretical models and experimental findings, has facilitated refined control over NC properties and represents a trusted gateway to enhanced NC stability and processability. The assembly of NCs into superlattices, along with two-dimensional (2D) photolithography and three-dimensional (3D) printing, has expanded their utility in creating materials with tailored properties. Applications of NCs are also flourishing, consolidating progress in fields targeted early on, such as optoelectronics and catalysis, and extending into areas ranging from quantum technology to phase-change memories. In this perspective, we review the extensive progress in research on NCs over the past decade and highlight key areas where future research may bring further breakthroughs

Multiple ionic memories in asymmetric nanochannels revealed by mem-spectrometry

Recently discovered nanofluidic memristors, have raised promises for the development of iontronics and neuromorphic computing with ions. Ionic memory effects are related to ion dynamics inside nanochannels, with timescales associated with the manifold physicochemical phenomena occurring at confined interfaces. Here, we explore experimentally the frequency-dependent current–voltage response of model nanochannels—namely glass nanopipettes—to investigate memory effects in ion transport. This characterisation, which we refer to as mem-spectrometry, highlights two characteristic frequencies, associated with short and long timescales of the order of 50 ms and 50 s in the present system. Whereas the former can be associated with ionic diffusion, very long timescales are difficult to explain with conventional transport phenomena. We develop a minimal model accounting for these mem-spectrometry results, pointing to surface charge regulation and ionic adsorption-desorption as possible origins for the long-term memory. Our work demonstrates the relevance of mem-spectrometry to highlight subtle ion transport properties in nanochannels, giving hereby new insights on the mechanisms governing ion transport and current rectification in charged conical nanopores

LNCS

We present the first supermartingale certificate for quantitative -regular properties of discrete-time infinite-state stochastic systems. Our certificate is defined on the product of the stochastic system and a limit-deterministic Büchi automaton that specifies the property of interest; hence we call it a limit-deterministic Büchi supermartingale (LDBSM). Previously known supermartingale certificates applied only to quantitative reachability, safety, or reach-avoid properties, and to qualitative (i.e., probability 1) -regular properties.We also present fully automated algorithms for the template-based synthesis of LDBSMs, for the case when the stochastic system dynamics and the controller can be represented in terms of polynomial inequalities. Our experiments demonstrate the ability of our method to solve verification and control tasks for stochastic systems that were beyond the reach of previous supermartingale-based approaches

PMLR

Observational genome-wide association studies are now widely used for causal inference in genetic epidemiology. To maintain privacy, such data is often only publicly available as summary statistics, and often studies for the endogenous covariates and the outcome are available separately. This has necessitated methods tailored to two-sample summary statistics. Current state-of-the-art methods modify linear instrumental variable (IV) regression---with genetic variants as instruments---to account for unmeasured confounding. However, since the endogenous covariates can be high dimensional, standard IV assumptions are generally insufficient to identify all causal effects simultaneously. We ensure identifiability by assuming the causal effects are sparse and propose a sparse causal effect two-sample IV estimator, spaceTSIV, adapting the spaceIV estimator by Pfister and Peters (2022) for two-sample summary statistics. We provide two methods, based on L0- and L1-penalization, respectively. We prove identifiability of the sparse causal effects in the two-sample setting and consistency of spaceTSIV. The performance of spaceTSIV is compared with existing two-sample IV methods in simulations. Finally, we showcase our methods using real proteomic and gene-expression data for drug-target discovery