Unique State Research Articles

Electronic and magnetic excitations in La3Ni2O7.

High-temperature superconductivity was discovered in the pressurized nickelate La3Ni2O7 which has a unique bilayer structure and mixed valence state of nickel. The properties at ambient pressure contain crucial information of the fundamental interactions and bosons mediating superconducting pairing. Here, using X-ray absorption spectroscopy and resonant inelastic X-ray scattering, we identified that Ni 3 , Ni 3 , and ligand oxygen 2p orbitals dominate the low-energy physics with a small charge-transfer energy. Well-defined optical-like magnetic excitations soften into quasi-static spin-density-wave ordering, evidencing the strong electronic correlation and rich magnetic properties. Based on an effective Heisenberg spin model, we extract a much stronger inter-layer effective magnetic superexchange than the intra-layer ones and propose two viable magnetic structures. Our findings emphasize that the Ni 3 orbital bonding within the bilayer induces novel electronic and magnetic excitations, setting the stage for further exploration of La3Ni2O7 superconductor.

Robustness meets co-jumps: optimal consumption and portfolio choice with derivatives

In this paper, we study a robust, dynamic, continuous-time optimal consumption and portfolio allocation problem for investors with recursive preferences who have access to both stock and derivatives markets. We assume the stock price process follows a stochastic volatility model, with instantaneous precision as the unique state variable, allowing for discontinuities in all the dynamics. We obtain a closed-form approximate solution up to a system of ODEs to the optimization problem for a non-unitary value of the elasticity of intertemporal substitution of consumption, being able to derive an exact solution as a particular case. Our theoretical findings show that the optimal policies are remarkably affected by the ambiguity-aversion parameters to diffusive and jump risks. A detailed numerical analysis confirms the effectiveness of our theoretical results on real data. Finally, we prove that investors who do not believe in ambiguity may suffer considerable wealth losses.

Phylogeographic analysis of Y-chromosomal haplogroup C2a-M48-F8472, a minor paternal lineage of Han populations with possible ancestry of Xiongnu

Background Y-chromosome haplogroup C2a-M48-F8472, a unique paternal line in the ancient Xiongnu population, is concentrated in the modern Han people. The most closely related lineage of this paternal lineage is mainly distributed in Tungusic-, Mongolic-, and Turkic-speaking populations. Aim To investigate the formation process of this unique distribution state. Subjects and methods In total, 36 sequences of haplogroup C2a-M48-F8472 were analysed to generate a revised phylogenetic tree with age estimation and to explore the geographic distribution pattern. Results The results suggested that northern China is likely the diffusion centre of this paternal haplogroup. This lineage is concentrated in the Liu clan (刘姓) of Han populations and may have originated in the Tuge tribe (屠各) of Xiongnu populations. The initial expansion (∼2,600 years ago) and the second phase of expansion (∼1,570 years ago) of haplogroup C2a-M48-F8472 coincide with the earlier appearance and later disappearance of the Tuge tribe. As a sub-clade of M48, the history of F8472 suggested that ancient peoples related to Tungusic-speaking populations were intricately connected with the demographic history of populations in the Mongolian Plateau. Conclusion The appearance of this paternal line in the Han population is helpful for understanding the mixed history of ancient and modern people in the Mongolian Plateau and Central China.

Overcoming problematic growth phenotypes in organoids from patients with monogenic GI disease.

Patient-derived organoids provide a unique model system to explore disease-causing mutations ex vivo. By using organoids from duodenal or colonic biopsies of pediatric patients with intestinal epithelial disorders, we can directly assay the patient cells to tailor treatment to their unique disease state. The advent of organoid technology from patients with severe intestinal disorders such as Congenital Diarrhea Enteropathies (CoDE) and Very-Early-Onset Inflammatory Bowel Disease (VEO-IBD) has allowed for rapid advances in the understanding of and the treatment of these monogenic disorders. Still, the expansion of these lines for scalable studies is not trivial, and success rates of expansion are variable between groups, and even lab members within the same group. These protocols have been validated on patients with CoDE or VEO-IBD and age-matched control patients. Here, we present our recommended protocols for the cultivation of organoids from pediatric patients with CoDE and VEO-IBD. These protocols have been validated on organoids generated from the duodenum (duodenoids), ileum (ileoids), colon (colonoids) and iPSC-derived intestinal colonoids from pediatric healthy donors or donors with CoDE or VEO-IBD (Gwilt et al., 2023). Using our modified culture media, extended culture times from biopsy preparation and thawing frozen lines, gentle passaging techniques with the incomplete removal of the organoids from the matrigel, and modified monolayer protocols (Maeda et al., 2023; Maeda et al., 2022), we have been able to successfully culture and expand several lines for more than 5 years. The conditions and protocols used here provide a basis for reproducible phenotypes, scaling for larger functional studies on patient lines, and for reproducibility of results between several investigators. We provide a useful starting point and troubleshooting guidelines for the optimization of culturing organoids from any patient with novel disease pathology.

Dimensionally Extending from 1D MX-Chain to Ladder and Nanotube Systems: Structural and Electronic Properties.

Molecular one-dimensional (1D) electron systems have attracted much attention due to their unique electronic state, physical and chemical properties derived from high-aspect-ratio structures. Among 1D materials, mixed-valence halogen-bridged transition-metal chain complexes (MX-chains) based on coordination assemblies are currently of particular interest because their electronic properties, such as mixed-valence state and band gap, can be controlled by substituting components and varying configurations. In particular, chemistry has recently noted that dimensionally extending MX-chains through organic rung ligands can introduce and modulate electronic coupling of metal atoms between chains, i. e., interchain interactions. In this review, for the first time, we highlight the recent progress on MX systems from the viewpoint of dimensionally extending from 1D chain to ladder and nanotube, mainly involving structural design and electronic properties. Overall, dimensional extension can not only tune the electronic properties of MX-chain, but also build the unique platform for studying transport dynamics in confined space, such as proton conduction. Based on these features, we envision that the MX-chain systems provide valuable insights into deep understanding of 1D electron systems, as well as the potential applications such as nanoelectronics.

Reaction dynamics of the nonvalence bound states of the anions

Nonvalence bound state (NBS) is a unique anionic state where an excess electron is loosely bound to a neutral molecule in long-range potentials. Since Fermi and Teller first proposed that an electron could be bound in the dipolar field of a molecule, the physical and chemical properties of NBS in a variety of chemical systems have been investigated over recent decades. In this short review, recent notable studies aimed at thoroughly understanding the dynamics of NBS in various anionic chemical systems are elaborated. Photodetachment and photoelectron spectroscopic methods, particularly applied to cryogenically cooled anions, have been highly successful in providing detailed rovibronic structures of the NBS in many interesting chemical systems. Furthermore, real-time pump-probe photoelectron spectroscopy unraveled new dynamic aspects of anion physics and chemistry, offering deep insight into mode-specific autodetachment dynamics and the role of metastable NBS as a doorway into anionic chemical reactions. Autodetachment and/or nonvalence-to-valence (or vice versa) electron-transfer dynamics of NBS are found to be strongly mode-specific, presenting a challenge for theoretical explanations of their quantum-mechanical nature. The outlook for further exploration of NBS in various chemical or biological contexts as well as its potential exploitation in controlling chemical reaction is also provided.

An Inventory of Proposed and Enacted Sugar-Sweetened Beverage Policies at the State, Local, and Tribal Levels in the United States, 2014‒2023.

Objectives. To inventory and describe trends in proposal and enactment of US sugar-sweetened beverage (SSB) policies at state, local, and Tribal levels, 2014-2023. Methods. We systematically searched 6 policy databases in 2021 (updated May 2023) using SSB-related search terms, identifying additional policies through snowball and online searches and a survey of food-policy experts. We reviewed 10 821 policies for inclusion and quantitatively coded included policies. Results. The inventory included 400 (321 unique [i.e., excluding companion]) policies meeting criteria: 335 (256 unique) state-, 63 local-, and 2 Tribal-level policies. From 2014 to 2023, 11% of unique state-, 92% of local-, and 100% of Tribal-level proposed policies were enacted. Across jurisdictions, the most frequently proposed policies related to excise taxes, restaurant children's meals, nutrition standards, and the Supplemental Nutrition Assistance Program, while the largest proportions of enacted policies related to restaurant children's meals, nutrition standards, education, and procurement. More policies were proposed and enacted in California and New York than other states, and in 2017 (proposed) and 2016 (enacted). Conclusions. This comprehensive inventory of US SSB policies provides information to inform future SSB policy development and diffusion. (Am J Public Health. Published online ahead of print October 17, 2024:e1-e10. https://doi.org/10.2105/AJPH.2024.307855).

Mutually Activated 2D Ti0.87O2/MXene Monolayers Through Electronic Compensation Effect as Highly Efficient Cathode Catalysts of Li–O2 Batteries

Abstract2D materials exhibit remarkable electrochemical performance as the cathode catalyst in lithium–oxygen batteries (LOBs). Their catalytic capability mainly derives from their 2D surface with tunable surface chemistry and unique electronic states. Herein, Ti0.87O2 and Ti3C2 MXene monolayers are applied to construct a face/face 2D heterostructure to enhance the catalytic performance in LOBs. It is demonstrated that electronic compensation from the O‐terminated MXene to Ti0.87O2 side is achieved through the built‐in electric field and the overlap of Ti 3d and O 2p orbitals between Ti0.87O2 and MXene units. As a result, the ORR/OER catalytic activity is improved in Ti0.87O2/MXene heterojunction due to the modulated p‐band center that optimizes the s–p coupling with the key intermediate LiO2. The Ti0.87O2/MXene cathode presents a structural stability and long‐term cycling life of 425 cycles (2534 h) at 200 mA g−1 and 407 cycles at 1000 mA g−1 with a fixed capacity of 600 mAh g−1, being nearly five and three times higher than that of pure Ti0.87O2 and MXene cathodes, respectively.

Extracting dynamical maps of non-Markovian open quantum systems.

The most general description of quantum evolution up to a time τ is a completely positive tracing preserving map known as a dynamical mapΛ̂(τ). Here, we consider Λ̂(τ) arising from suddenly coupling a system to one or more thermal baths with a strength that is neither weak nor strong. Given no clear separation of characteristic system/bath time scales, Λ̂(τ) is generically expected to be non-Markovian; however, we do assume the ensuing dynamics has a unique steady state, implying the baths possess a finite memory time τm. By combining several techniques within a tensor network framework, we directly and accurately extract Λ̂(τ) for a small number of interacting fermionic modes coupled to infinite non-interacting Fermi baths. First, we use an orthogonal polynomial mapping and thermofield doubling to arrive at a purified chain representation of the baths whose length directly equates to a time over which the dynamics of the infinite baths is faithfully captured. Second, we employ the Choi-Jamiolkowski isomorphism so that Λ̂(τ) can be fully reconstructed from a single pure state calculation of the unitary dynamics of the system, bath and their replica auxiliary modes up to time τ. From Λ̂(τ), we also compute the time local propagator L̂(τ). By examining the convergence with τ of the instantaneous fixed points of these objects, we establish their respective memory times τmΛ and τmL. Beyond these times, the propagator L̂(τ) and dynamical map Λ̂(τ) accurately describe all the subsequent long-time relaxation dynamics up to stationarity. These timescales form a hierarchy τmL≤τmΛ≤τre, where τre is a characteristic relaxation time of the dynamics. Our numerical examples of interacting spinless Fermi chains and the single impurity Anderson model demonstrate regimes where τre ≫ τm, where our approach can offer a significant speedup in determining the stationary state compared to directly simulating the long-time limit. Our results also show that having access to Λ̂(τ) affords a number of insightful analyses of the open system thus far not commonly exploited.

Nearly linear orbital molecules on a pyrochlore lattice.

The interplay of spin-orbit coupling with other relevant parameters gives rise to the rich phase competition in complex ruthenates featuring octahedrally coordinated Ru4+. While locally, spin-orbit coupling stabilizes a nonmagnetic Jeff = 0 state, intersite interactions resolve one of two distinct phases at low temperatures: an excitonic magnet stabilized by the magnetic exchange of upper-lying Jeff = 1 states or Ru2 molecular orbital dimers driven by direct orbital overlap. Pyrochlore ruthenates A2Ru2O7 (A = rare earth, Y) are candidate excitonic magnets with geometrical frustration. We synthesized In2Ru2O7 with covalent In─O bonds. This pyrochlore ruthenate hosts a local Jeff = 0 state at high temperatures; however, at low temperatures, it forms a unique nonmagnetic ground state with nearly linear Ru─O─Ru molecules, in stark contrast to other A2Ru2O7 compounds. The disproportionation of covalent In─O bonds drives Ru2O molecule formation, quenching not only the local spin-orbit singlet but also geometrical frustration.

Quadrupolar dinuclear hypervalent tin(iv) compounds with near-infrared emission consisting of Schiff bases based on π-conjugated scaffolds.

Since π-conjugated molecules are commonly used as a scaffold for constructing optoelectronic and functional materials, much effort has been devoted to exploring novel molecular scaffolds for obtaining superior properties. This study focuses on dinuclear hypervalent tin(iv) compounds prepared by the ladderization of Schiff bases using hypervalent tin units. The optical measurements found that introducing hypervalent tin atoms can reinforce the D-π-A system. We synthesized two types of dinuclear hypervalent compounds by simple condensation reactions and observed near-infrared (NIR) emission. Also, depending on the direction of the imine bonds, these molecules had different quadrupolar orientations with D-π-A-π-D and A-π-D-π-A systems followed by negative solvatochromism, which is the unique behavior of quadrupolar-derived absorption. Furthermore, the π-conjugated polymers involving dinuclear compounds showed NIR emission in the wavelength range over 800 nm owing to the distinct expansion of π-conjugation. Our findings could be useful not only for constructing electronic structures with narrow energy gaps but also for designing molecules with unique electronic states and environmental responsiveness.

Diagnostic and therapeutic approaches to a case of pregnancy complicated by bilateral adrenocortical adenomas with primary aldosteronism and Cushing's syndrome.

Aldosterone/cortisol co-secreting adenomas (A/CPA) are a rare type of primary aldosteronism(PA), and cases of aldosterone/cortisol co-secreting adenomas during pregnancy are extremely rare, with no reported cases to date. The unique physiological state of pregnancy increases cortisol secretion through the hypothalamic-pituitary-adrenal (HPA) axis and leads to elevated levels of all components of the renin-angiotensin-aldosterone system (RAAS). This can cause overlapping symptoms with abnormal cortisol and aldosterone secretion, making diagnosis very challenging. This case involves a 29-year-old woman who developed hypercortisolism at 33 weeks of pregnancy. Despite receiving treatment for her symptoms and having a successful delivery, she continued to experience hypertension and hypokalaemia after giving birth. Eventually, she was diagnosed with ACTH-independent Cushing's syndrome and primary aldosteronism due to independent cortisol and aldosterone secretion from bilateral adrenal adenomas. Following a thorough diagnosis, classification, treatment, and follow-up, the patient achieved a clinical cure while preserving normal adrenal function. Further investigation revealed that both diseases were caused by KCNJ5 and PRKACA mutations found in the bilateral adrenal adenomas.

Single-cell heterogeneity in ribosome content and the consequences for the growth laws.

Across species and environments, the ribosome content of cell populations correlates with population growth rate. The robustness and universality of this correlation have led to its classification as a "growth law." This law has fueled theories about how evolution selects for microbial organisms that maximize their growth rate based on nutrient availability, and it has informed models about how individual cells regulate their growth rates and ribosomal content. However, due to methodological limitations, this growth law has rarely been studied at the level of individual cells. While populations of fast-growing cells tend to have more ribosomes than populations of slow-growing cells, it is unclear whether individual cells tightly regulate their ribosome content to match their environment. Here, we employ recent groundbreaking single-cell RNA sequencing techniques to study this growth law at the single-cell level in two different microbes, S. cerevisiae (a single-celled yeast and eukaryote) and B. subtilis (a bacterium and prokaryote). In both species, we observe significant variation in the ribosomal content of single cells that is not predictive of growth rate. Fast-growing populations include cells exhibiting transcriptional signatures of slow growth and stress, as do cells with the highest ribosome content we survey. Broadening our focus to non-ribosomal transcripts reveals subpopulations of cells in unique transcriptional states suggestive that they have evolved to do things other than maximize their rate of growth. Overall, these results indicate that single-cell ribosome levels are not finely tuned to match population growth rates or nutrient availability and cannot be predicted by a Gaussian process model that assumes measurements are sampled from a normal distribution centered on the population average. This work encourages the expansion of growth law and other models that predict how growth rates are regulated or how they evolve to consider single-cell heterogeneity. To this end, we provide extensive data and analysis of ribosomal and transcriptomic variation across thousands of single cells from multiple conditions, replicates, and species.

Optimal impulse control problems with time delays: An illustrative example

For impulse control systems described by a measure driven differential equation, depending linearly on the measure, it is customary to interpret the state trajectory corresponding to an impulse control, specified by a measure, as the limit of state trajectories associated with some sequence of conventional controls approximating the measure. It is known that, when the measure is vector valued, it is possible that different choices of approximating sequences for the measure give rise to different limiting state trajectories. If the measure is scalar valued, however, there is a unique limiting trajectory. Now consider impulse control systems, in which the right side of the measure driven differential equation depends on both the current and delayed states. In recent work by the authors it has been shown that, for such impulse control systems with time delay, the state trajectory corresponding to a given measure may be non-unique, even when the measure is scalar valued. It was also shown that each limiting state trajectory can be identified with the unique state trajectory associated with some measure together with a family of ‘attached controls’. (The attached controls capture the nature of the measure approximation.) The authors also derived a maximum principle governing minimizers for a general class of impulse optimal control problems with time delay, in which the domain of the optimization problem comprises measures coupled with a family of ‘attached controls’. The purpose of this paper is both to illustrate, by means of an example, this newly discovered non-uniqueness phenomenon and to provide the first application of the new maximum principle, to investigate minimizers for scalar input impulse optimal control problems with time delay, in circumstances when limiting state trajectories associated with a given measure control are not unique. The example is an optimal control problem, for which the underlying control system is a forced harmonic oscillator, with scalar impulse control, in which the control gain is a nonlinear function of the current and delayed states.

Data-driven inverse design of a multiband second-order phononic topological insulator

Second-order phononic topological insulators (SPTIs) have sparked vast interest in manipulating elastic waves, owing to their unique topological corner states with robustness against geometric perturbations. However, it remains a challenge to develop multiband SPTIs that yield multi-frequency corner states using prevailing forward design approaches via trial and error, and most inverse design approaches substantially rely on time-consuming numerical solvers to evaluate band structures of phononic crystals (PnCs), showing low efficiency particularly when applied to different optimization tasks. In this study, we develop and validate a new inverse design framework, to enable the multiband SPTI by integrating data-driven machine learning (ML) with genetic algorithm (GA). The relationship between shapes of scatterers and frequency bounds of multi-order bandgaps of PnCs is mapped via developing artificial neural networks (ANNs), and a multiband SPTI with multi-frequency topological corner states is cost-effectively designed using the proposed inverse optimization framework. Our results indicate that the data-driven approach can provide a high-efficiency solution for on-demand inverse designs of multiband second-order topological mechanical devices, enabling diverse application prospects including multi-frequency robust amplification and confinement of elastic waves.

Boron-bridged bis(tetrathiafulvalene) zwitterionic neutral radical conductors: substituent effects on intramolecular and intermolecular electronic interactions and physical properties

Abstract We have recently proposed a new molecular design for neutral radical molecular conductors, based on the chemical composition of D2X-type charge-transfer salts (D = π-electron donor molecule, X = monovalent anion). Namely, we connected two tetrathiafulvalene (TTF)-based π-electron skeletons having a charge of +0.5 via a boron anion B–, to obtain a purely organic zwitterionic neutral radical {[(PDT-TTF-Cat)2]+B–}• that shows unique electronic states and properties in the crystal due to the intramolecular and intermolecular interactions of the +0.5-charged π-skeletons. In order to further explore the structural and electronic features of this kind of zwitterionic neutral radical conductor, in this study, we have examined chemical modifications to {[(PDT-TTF-Cat)2]+B–}•. As a result, an analog molecule {[(BMT-TTF-Cat)2]+B–}•, in which propylenedithio (PDT) groups on the TTF terminals in {[(PDT-TTF-Cat)2]+B–}• are replaced by bis(methylthio) ones, was successfully synthesized as air-stable single crystals. Interestingly, this chemical modification causes intramolecular charge disproportionation between the two TTF-based π-skeletons (i.e. the monovalent cation radical TTF+• and the neutral TTF0) coupled to the modulation of the intermolecular distances and interactions between these π-skeletons, leading to electrical and magnetic properties significantly different from those of the crystal of {[(PDT-TTF-Cat)2]+B–}•.

Exploring hypnotist trance: the experiences of skilled practitioners

ABSTRACT Milton Erickson first conceptualized the hypnotist trance (HT) as a unique psychological state developed in clinicians during hypnosis sessions. This qualitative study aimed to investigates HT through the experiences of 12 skilled Clinician Hypnosis Specialists (CHS). Data were collected via semi-structured face-to-face interviews, exploring participants’ attitudes toward HT, its impact on their practice, and their strategies for developing and regulating it. Thematic analysis revealed that most CHS view HT as enhancing empathy, communication, and therapeutic effectiveness. However, challenges such as time distortion, hypnotic regression, and countertransference issues were also noted. The study highlights HT’s dual nature – offering significant therapeutic benefits while presenting challenges that need careful management. These findings emphasize the importance of comprehensive HT training in hypnotherapy education and advocate for further research to explore HT across diverse contexts and expertise levels to deepen understanding of this complex phenomenon.

Measurement and assignment of J = 5 to 9 rotational energy levels in the 9070-9370cm-1 range of methane using optical frequency comb double-resonance spectroscopy.

We use optical-optical double-resonance spectroscopy with a continuous wave (CW) pump and a cavity-enhanced frequency comb probe to measure the energy levels of methane in the upper part of the triacontad polyad (P6) with higher rotational quantum numbers than previously assigned. A high-power CW optical parametric oscillator, tunable around 3000 cm-1, is consecutively locked to the P(7, A2), Q(7, A2), R(7, A2), and Q(6, F2) transitions in the ν3 band, and a comb covering the 5800-6100cm-1 range probes sub-Doppler ladder-type transitions from the pumped levels with J' = 6 to 8, respectively. We report 118 probe transitions in the 3ν3 ← ν3 spectral range with uncertainties down to 300kHz (1 × 10-5cm-1), reaching 84 unique final states in the 9070-9370cm-1 range with rotational quantum numbers J between 5 and 9. We assign these states using combination differences and by comparison with theoretical predictions from a new abinitio-based effective Hamiltonian and dipole moment operator. This is the first line-by-line experimental verification of theoretical predictions for these hot-band transitions, and we find a better agreement of transition wavenumbers with the new calculations compared to the TheoReTS/HITEMP and ExoMol databases. We also compare the relative intensities and find an overall good agreement with all three sets of predictions. Finally, we report the wavenumbers of 27 transitions in the 2ν3 spectral range, observed as V-type transitions from the ground state, and compare them to the new Hamiltonian, HITRAN2020, ExoMol, and the WKMLC line lists.

Uncovering an Interfacial Band Resulting from Orbital Hybridization in Nickelate Heterostructures.

The interaction of atomic orbitals at the interface of perovskite oxide heterostructures has been investigated for its profound impact on the band structures and electronic properties, giving rise to unique electronic states and a variety of tunable functionalities. In this study, we conducted an extensive investigation of the optical and electronic properties of epitaxial NdNiO3 synthesized on a series of single-crystal substrates. Unlike nanofilms synthesized on other substrates, NdNiO3 on SrTiO3 (NNO/STO) gives rise to a unique band structure featuring an additional unoccupied band situated above the Fermi level. Our comprehensive investigation, which incorporated a wide array of experimental techniques and density functional theory calculations, revealed that the emergence of the interfacial band structure is primarily driven by orbital hybridization between the Ti 3d orbitals of the STO substrate and the O 2p orbitals of the NNO thin film. Furthermore, exciton peaks have been detected in the optical spectra of the NNO/STO film, attributable to the pronounced electron-electron (e-e) and electron-hole (e-h) interactions propagating from the STO substrate into the NNO film. These findings underscore the substantial influence of interfacial orbital hybridization on the electronic structure of oxide thin films, thereby offering key insights into tuning their interfacial properties.

Structural basis for adhesin secretion by the outer-membrane usher in type 1 pili

Gram-negative bacteria produce chaperone-usher pathway pili, which are extracellular protein fibers tipped with an adhesive protein that binds to a receptor with stereochemical specificity to determine host and tissue tropism. The outer-membrane usher protein, together with a periplasmic chaperone, assembles thousands of pilin subunits into a highly ordered pilus fiber. The tip adhesin in complex with its cognate chaperone activates the usher to allow extrusion across the outer membrane. The structural requirements to translocate the adhesin through the usher pore from the periplasm to the extracellular space remains incompletely understood. Here, we present a cryoelectron microscopy structure of a quaternary tip complex in the type 1 pilus system from Escherichia coli, which consists of the usher FimD, chaperone FimC, adhesin FimH, and the tip adapter FimF. In this structure, the usher FimD is caught in the act of secreting its cognate adhesin FimH. Comparison with previous structures depicting the adhesin either first entering or having completely exited the usher pore reveals remarkable structural plasticity of the two-domain adhesin during translocation. Moreover, a piliation assay demonstrated that the structural plasticity, enabled by a flexible linker between the two domains, is a prerequisite for adhesin translocation through the usher pore and thus pilus biogenesis. Overall, this study provides molecular details of adhesin translocation across the outer membrane and elucidates a unique conformational state adopted by the adhesin during stepwise secretion through the usher pore. This study elucidates fundamental aspects of FimH and usher dynamics critical in urinary tract infections and is leading to antibiotic-sparing therapeutics.