561975 research outputs found
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Thin-film Al0.30Ga0.70As (111) as a ‘flat’ source of high-purity orthogonally polarized entangled photons
No full textFlat-optics platforms offer new opportunities for the generation of entangled photons by relaxing traditional phase-matching constraints, enabling the use of a broader range of nonlinear materials. Among these, gallium arsenide and aluminum gallium arsenide stand out for their exceptionally high second-order nonlinearities, but their conventional orientation (001) has limited their applicability for photon-pair generation. By transitioning to crystals with (111) surface orientation, we overcome these limitations. We demonstrate a flat-optics-based telecom-range SPDC source using Al0.30Ga0.70As that achieves a high photon-pair generation rate per pump power and bandwidth of up to 0.24 Hz/mW/nm. The choice of 30% aluminum concentration allowed us to reduce pump absorption and photoluminescence background for photon-pair generation at telecom wavelengths by at least an order of magnitude compared to that of GaAs. The specific layer orientation facilitates the generation of orthogonally polarized entangled photons, a prerequisite for polarization-entangled states. Rather than directly probing entanglement, we observe the effect of hidden polarization. Our results highlight AlGaAs (111) as a promising platform for scalable quantum photonic sources and shed light on nonclassical polarization effects accessible through flat-optics engineering
A Redox‐Active Tetrathiafulvalene‐Based 3D Covalent Organic Framework with scu Topology for Controllable Charge Transport
No full textUnlike 2D frameworks where conductivity is largely confined to in-plane transport, the scu topology offers 3D conduction pathways that enhance bulk charge mobility. When integrated with redox-active species like tetrathiafulvalene (TTF), the scu architecture promotes electron transfer across the 3D network, enabling tunable conductivity. This article presents the construction of a 3-periodic (4,8)-c covalent organic framework (COF), TU-48, adopting a twofold interpenetrated scu net, achieved through the integration of a tetratopic D2h-symmetric rectangular TTF structural motif and an octatopic D2h-symmetric quadrangular prism linker. TU-48 exhibits high structural order, well-defined porosity, and redox-responsive electrochemical behavior. The high-connectivity 3D COF configuration ensures effective access to TTF redox centers, enabling controlled iodine oxidation and resulting in electrical conductivities of 4.3 × 10−6 S cm−1 at 298 K and 1.8 × 10−4 S cm−1 at 393 K. By demonstrating how enhanced structural connectivity in TTF-bridged 3D covalent lattices enables improved charge-transport properties, this research fuels innovation in sustainable energy storage solutions and electronics
Concert formats influence how audiences experience live classical music
No full textMany people enjoy listening to live music. But what exactly does a live context contribute to people’s experience, and do different types of concerts influence the musical experience in different ways? In this study, we focus on the Western classical concert, which has been claimed to be in an existential crisis. One way in which practitioners are seeking to counter this crisis is by adapting the concert format. Our study was inspired by such artistic endeavors and conducted live concert experiments in an ecologically valid setting to explore the effects of the concert format on the audience’s aesthetic experience. Eleven chamber music concerts were organized, all of which presented the same three string quintets but differed regarding several format components. To represent the aesthetic experience of the audience (N = 802) in an exhaustive way, self-report data, physiological responses, as well as camera recordings of facial expressions were collected. The analyses revealed that each concert format variant had a unique effect on the audience. Variants that differed the most from the standard format had the strongest influence on the audience’s experience, while also one concert that represented an ideal realization of the standard format, led to particularly positive experiences. Aesthetic emotions and heart rate were particularly susceptible to format changes, whereas appreciation of the music and the musical performance were not affected by the concert format. We found that (1) a high-quality concert venue can afford a more immersed experience and a higher appreciation of the concert as a whole; (2) explanations of the meaning of the pieces in a relatable, personal way during the concert help people connect emotionally with the pieces and increase tolerance towards contemporary pieces; (3) an intense musical experience and a satisfying social experience may compete with each other. Our results do not only broaden our scientific understanding of how contexts contribute to aesthetic experiences, but can also be of use for concert practitioners
The human osteocyte lacunocanalicular network structure in osteons of the iliac crest of elderly women depends on mineral content but not individual age
No full textOsteocytes provide essential functions for the maintenance of healthy bone tissue. They are embedded in lacunar pores within the mineralised bone matrix and communicate through interconnected dendritic cell processes that are housed in canalicular channels constituting the osteocyte lacunocanalicular network (LCN). Ageing is associated with increased fracture risk and bone fragility, particularly in elderly women. Despite the LCN playing a critical role in bone remodelling, characteristics of the network in bone tissue of different individual age and mineral content is thus far largely unexplored. Confocal laser scanning microscopy was used to image the fluorescent-stained LCN of cortical osteons in iliac crest bone specimens from female donors with mean age 60 years (n = 6) and 94 years (n = 6) in 3D. Quantitative backscattered electron imaging was also used to assess osteonal mineral content to compare LCN structure in highly and lowly mineralised osteons. Network defects were identified in one-third of osteons, which were further investigated using focussed ion beam scanning electron microscopy. Assessment of the LCN revealed no influence of individual age on the canalicular density, the volume of the lacunae or the degree of the lacunae, whereas canalicular density is inversely correlated with osteonal mineral content. An increase in the volume of non-mineralised matrix is demonstrated in defective regions that are prevalent in all individuals. While relative osteon age, as characterised by mineral content, influences the density of the canaliculi in the LCN, there is no influence of the age of the individual women over 60 years. Statement of significance Osteocytes play a central and ongoing role in bone health throughout the lifespan: they orchestrate bone remodelling by regulating osteoclastic bone resorption and osteoblastic bone deposition, as well as controlling subsequent bone mineralisation. Deterioration of the osteocyte lacunocanalicular network may contribute to the decline in bone quality observed with age. Consequently, we studied this communication system in 3D in bone from middle-aged to elderly donors. Unexpectedly, individual age had no influence on network characteristics, but the density of the network was decreased in older osteons. Furthermore, we observed network defects that are surprisingly common at all ages investigated. The size of these defects increases with age, suggesting a possible link to the concurrent reduction in bone quality. Graphical abstract Download: Download high-res image (492KB) Download: Download full-size imag
Deciphering Asymmetric Induction in Photoredox Catalysis by Chiral Counteranions
No full textWe investigate the origin of stereocontrol in asymmetric counteranion-directed photoredox catalysis (ACPC) using a representative [2 + 2] cycloaddition mediated by a chiral imidodiphosphorimidate (IDPi) counteranion (Science 2023, 379, 494−499). Combining extensive conformational sampling, high-level DFT calculations, and multiscale modeling, we elucidate the mechanism and stereochemical landscape of this transformation. Both enantio- and diastereoselectivity are established in the first C−C bond-forming step: diastereoselectivity arises from intrinsic aryl−aryl interactions within the radical cation−styrene pair, whereas enantioselectivity is imposed by the confined chiral environment of the IDPi counteranion. Although electronically silent during the initial photoinduced single-electron transfer, the counteranion anchors the radical cation and organizes its cycloaddition with styrene. Atomic decomposition of the London dispersion (ADLD) and molecular dispersion potential (MDP) analyses reveal that attractive van der Waals forces, shaped by the steric and electronic architecture of the counteranion, promote reactive prealignment of the substrates and selectively stabilize the transition state, leading to the major product. Extension to substituted styrenes shows that ring substitution reconfigures the noncovalent contact map within the catalyst pocket, reshaping the energetic balance between competing pathways, in line with experiment. These findings provide a unified framework for stereocontrol in chiral ion-pair radical catalysis and offer general strategies for designing asymmetric photoredox transformations
Catalytic asymmetric activation of bicyclobutanes
No full textThe precise manipulation of unfunctionalized hydrocarbons remains a fundamental challenge for chemical synthesis and catalysis. Stereodifferentiation in strained alkanes is particularly difficult to accomplish because a catalyst has to distinguish various highly exergonic chemo- and stereoselective strain-release channels. Here we disclose an organocatalytic asymmetric hydroalkoxylation of bicyclobutanes with alcohols to efficiently access tertiary cyclopropylcarbinyl ethers with high enantioselectivity (e.r. up to 98:2). Enantiocontrol is accomplished through chiral recognition between the confined iminoimidodiphosphoric acid catalyst and the substrate, mediated by non-covalent interactions between a Lewis basic binding site of the confined anion and the polarized C–H bond of the cyclopropylcarbinyl ion intermediate. Our work establishes bicyclobutane activation by harnessing strain-release energetics while maintaining precise stereo- and regiocontrol through structural confinement
Transport evidence for chiral surface states from three-dimensional Landau bands
No full textStrong magnetic fields applied to metals confine electrons into Landau orbits, except at the boundaries at which frequent surface collisions disrupt their cyclotron motion. In two-dimensional systems, these boundary states form dissipationless chiral edge channels in the quantum Hall regime. By contrast, the quantum limit of three-dimensional (3D) metals is traditionally thought to differ fundamentally and instead contains gapless Landau bands, lacking quantized Hall conductance or dissipationless transport. Here we demonstrate enhanced surface conduction in the quantum limit of the 3D semimetal bismuth, characterized by the counterintuitive increase in conductivity as material is removed by micropatterning. The conductance of the 3D chiral boundary states—3D analogues of quantum Hall states in two dimensions—naturally accounts for this behaviour and for the highly non-local transport observed in micrometre-sized crystalline bismuth structures. These findings introduce an approach for engineering and exploiting chiral conduction on the surfaces of 3D materials, offering a design space for geometries beyond the simple one-dimensional boundary modes of two-dimensional systems
