Search

The collective dynamics of topological structures.sup.1-6 are of interest from both fundamental and applied perspectives. For example, studies of dynamical properties of magnetic vortices and skyrmions.sup.3,4 have not only deepened our understanding of many-body physics but also offered potential applications in data processing and storage.sup.7. Topological structures constructed from electrical polarization, rather than electron spin, have recently been realized in ferroelectric superlattices.sup.5,6, and these are promising for ultrafast electric-field control of topological orders. However, little is known about the dynamics underlying the functionality of such complex extended nanostructures. Here, using terahertz-field excitation and femtosecond X-ray diffraction measurements, we observe ultrafast collective polarization dynamics that are unique to polar vortices, with orders-of-magnitude higher frequencies and smaller lateral size than those of experimentally realized magnetic vortices.sup.3. A previously unseen tunable mode, hereafter referred to as a vortexon, emerges in the form of transient arrays of nanoscale circular patterns of atomic displacements, which reverse their vorticity on picosecond timescales. Its frequency is considerably reduced (softened) at a critical strain, indicating a condensation (freezing) of structural dynamics. We use first-principles-based atomistic calculations and phase-field modelling to reveal the microscopic atomic arrangements and corroborate the frequencies of the vortex modes. The discovery of subterahertz collective dynamics in polar vortices opens opportunities for electric-field-driven data processing in topological structures with ultrahigh speed and density. A dynamical study shows that vortices of electrical polarization have higher frequencies and smaller size than their magnetic counterparts, properties that are promising for electric-field-driven data processing., Author(s): Qian Li [sup.1] [sup.11] , Vladimir A. Stoica [sup.1] [sup.2] , Marek Pasciak [sup.3] , Yi Zhu [sup.1] , Yakun Yuan [sup.2] , Tiannan Yang [sup.2] , Margaret R. [...]

Well-known K-pop (Korean popular music) bands have gained the status of pop music icons, owing to their widespread popularity around the world. This study explored the interrelations between a set of relevant social and psychological factors to explain how K-pop has also contributed to a one-of-a-kind transcultural communication phenomenon on the Internet via social media. An online survey was conducted with a sample of non-Asian American college students, as K-pop is highly popular among this group of music fans. A path analysis was performed to test a conceptual framework that integrated social distance theory, common ingroup identity model, and dialectical mode. The conceptual framework theorizes that perceived social distance and intergroup acceptance between individuals of non-Asian and Asian descent, as well as perceived musical similarity between Western and K-pop cultures, will underscore the intention for transcultural social media communication about K-pop. The current study contributes to advancing the literature by addressing the social-psychological domain of transcultural communication in the context of popular entertainment across social, cultural, lingusitic, and national boundaries. [ABSTRACT FROM AUTHOR]

Clinical translation of nanoparticles is limited because of their short circulation time, which hampers targeting to prolong therapeutic effects. Angiogenesis is required to regenerate damaged sites under inflammation, and CD11b+ cells turn vasculogenic under hypoxia. As a turning‐point strategy to increase the circulation time, this study explores liposomal targeting of splenic CD11b+ cells, which are gathered in the spleen and move to inflamed sites inherently. Moreover, nano‐hypoxia is strategized as a therapeutic method by loading liposomes with a hypoxic‐mimetic agent (CoCl2) to induce in situ reprogramming of splenic CD11b+ cells upon venous injection. Consequently, the vasculogenic potential of reprogrammed cells accelerates regeneration through inflammation‐responsive homing. Hydrophilic coating of liposomes improves the selectivity of splenic targeting in contrast to fast targeting without coating. Hypoxia chambers and surgical induction of splenic hypoxia are compared to validate the reprogramming effect. The strategy is validated in mouse models of inflamed skin, ischemic hindlimbs, and 70% hepatectomy compared with a conventional approach using bone marrow cells. Intravital multiphoton microscopy, 19F 2D/3D MRI, and microchannel hydrogel chips for 3D tissue culture are used as advanced tools. Overall, nanocarrier change to CD11b+ cells prolong targeting by inducing in situ reprogramming for inflammation‐responsive vasculogenic therapy. [ABSTRACT FROM AUTHOR]

Vaping has dramatically increased in recent years among young adults. To increase risk perceptions and promote preventive behaviors against vaping and secondhand e-cigarette aerosol (SHA), this study designed and tested virtual reality (VR) messages based on the theory of psychological distance. We randomly assigned 137 participants to see one of three messages: a VR message presenting SHAs impact on the self (VR-Self), a VR message showing SHAs impact on others (VR-Other), and a print advertisement. Risk perceptions and preventive intentions/behaviors were assessed at three different times: before, immediately after, and 1 week after the experimental treatment. All three messages increased desired intentions and risk perceptions immediately, reduced vaping interest both immediately and 1 week after message exposure, and increased behavior to persuade others to quit vaping after a week. Compared with the print advertisement, VR-Other generated less vaping interest immediately following message exposure (β = 1.40, p = 0.05). After 1 week, VR-Self (β = 1.62, p = 0.05) and VR-Other (β = 2.37, p = 0.01) generated less vaping interest than the print advertisement. VR-Other also generated a higher level of perceived harm of SHA (β = 1.27, p = 0.01) than the print advertisement. VRs advantage over print in reducing vaping interest was increased after 1 week. Although VR-Other generated less emotions, such as fear, than VR-Self (z = 2.48, p = 0.02) and print (z = −2.82, p = 0.02), its persuasiveness was not hindered. Disgust increased the intentions to persuade others to quit vaping immediately after the experimental treatment (β = 0.85, p = 0.02), and anger aroused by recalling the messages decreased vaping interest 1 week later (β = −2.07, p = 0.02). [ABSTRACT FROM AUTHOR]

We have designed and synthesized a multifunctional dendritic molecular probe that selectively detects Cu2+ ions via potentiometric and fluorometric techniques with low detection limits (3.5 μM in potentiometry, 15 nM in fluorometry). The selective and reversible binding of the molecule with the Cu2+ ion was used to make a solid-state microsensor (diameter of 25 μm) by incorporating the molecular probe into the carbon-based membrane as an ionophore for Cu(II). The Cu(II) microelectrode has a broad linear range of 10 μM to 1 mM with a near Nernstian slope of 30 mV/log [aCu2+] and detection limit of 3.5 μM. The Cu(II) microsensor has a fast response time (1.5 s), and it has a broad working pH range from 3.5 to 6.0. The incorporation of the hydrophobic dendritic moiety makes the ionophore less prone to leaching in an aqueous matrix for potentiometric measurement. The cinnamaldehyde component of the molecule helps detection of Cu2+ ions fluorometrically, as indicated by a change in fluorescence upon selective and reversible binding of the molecular probe to the Cu2+ ions. The strategic design of the molecular probe allows us to detect Cu2+ ions in drinking water by using this novel dendritic fluoroionophore and solid-state Cu2+ – ion-selective microelectrode. [ABSTRACT FROM AUTHOR]

The present study seeks to extend the extant body of work on media multitasking by examining the impact of second screen use (tweeting while watching television) on transportation into a narrative and enjoyment of a TV sitcom, mediated through affective experiences. In a between-subjects experiment, participants watched a TV show with or without tweeting about it. The findings support the assumption that media multitasking decreases people's experience of transportation, which then impairs their emotional responses; reduced emotions further decrease enjoyment of the show. However, trait empathy does not moderate the impact of concurrent TV-viewing and tweeting. [ABSTRACT FROM AUTHOR]

While clusterin is reportedly involved in Alzheimer's disease (AD) pathogenesis, how clusterin interacts with amyloid‐β (Aß) to cause Aß neurotoxicity remains unclear in vivo. Using 5×FAD transgenic mice, which develop robust AD pathology and memory deficits when very young, we detected interactions between clusterin and Aß in the mouse brains. The two proteins were concurrently upregulated and bound or colocalized with each other in the same complexes or in amyloid plaques. Neuropathology and cognitive performance were assessed in the progeny of clusterin‐null mice crossed with 5×FAD mice, yielding clu−/−;5×FAD and clu+/+;5×FAD. We found far less of the various pools of Aß proteins, most strikingly soluble Aß oligomers and amyloid plaques in clu−/−;5×FAD mice at 5 months of age. At that age, those mice also had higher levels of neuronal and synaptic proteins and better motor coordination, spatial learning and memory than age‐matched clu+/+;5×FAD mice. However, at 10 months of age, these differences disappeared, with Aß and plaque deposition, neuronal and synaptic proteins and impairment of behavioral and cognitive performance similar in both groups. These findings demonstrate that clusterin is necessarily involved in early stages of AD pathogenesis by enhancing toxic Aß pools to cause Aß‐directed neurodegeneration and behavioral and cognitive impairments, but not in late stage. [ABSTRACT FROM AUTHOR]

Background: The accumulation of misfolded protein aggregates is connected with neurodegenerative diseases such as Alzheimer's disease (AD), and Parkinson's disease. Because of the accumulation of amyloid β (Aβ) plaques and tau tangles (NFTs) in the brain, neurons slowly degenerate and lose their functions in AD. Recently, many clinical trials for AD therapy with single‐target drugs, especially targeted for Aβ or tau aggregates, have failed. As a therapeutic strategy for AD, we therefore propose to introduce a multifunctional anti‐AD agent to disaggregate the Aβ plaques and NFTs. Method: Hit compound was selected with disaggregation of Aβ and tau aggregates in various concentrations and half maximal effective concentration by thioflavin T (ThT) fluorescence assay. In vitro study, we examined the effects of our hit compound on the accumulation of intracellular Aβ or tau in over‐expressing cells. In vivo study, we administrated orally our hit compound to AD mouse model for 12 weeks (100mg/kg by weekly). Analysis of Aβ and tau was performed by molecular biological and histological experiments. Result: Our results show that the hit compound had dual disaggregation capacity for Aβ and tau aggregates. We observed significant decrease of Aβ and NFTs in hit compound treated AD mice compared to vehicle treated. Also, we found the restoration of cognitive decline in compound treated AD mice. Conclusion: The study demonstrate that our hit compound was identified as dual functional drug for Aβ and NFTs disaggregator. These findings may help to design the next generations of dual or selective disaggregators. [ABSTRACT FROM AUTHOR]

Zinc and apolipoprotein E (apoE) are reportedly involved in the pathology of Alzheimer's disease. To investigate the associative interaction among zinc, apoE, and amyloid-β (Aβ) and its role in amyloid pathogenesis, we performed various biochemical and immunoreactive analyses using brain tissues of Tg2576 mice and synthetic Aβ and apoE peptides. On amyloid plaques or in brain lysates of Tg2576 mice, apoE and Aβ immunoreactivities increased after zinc chelation and were restored by its subsequent replacement. Zinc depletion dissociated apoE/Aβ complexes or larger-molecular sizes of Aβ oligomers/aggregates into smaller-molecular sizes of apoE and/or Aβ monomers/complexes. In the presence of zinc, synthetic apoE and/or Aβ peptides aggregated into larger-molecular sizes of oligomers or complexes. Endogenous proteases or plasmin in brain lysates degraded apoE and/or Aβ complexes, and their proteolytic activity increased with zinc depletion. These biochemical findings suggest that zinc associates with apoE and Aβ to encourage the formation of apoE/Aβ complexes or large aggregates, raising the deposition of zinc-rich amyloid plaques. In turn, the presence of abundant zinc around and within apoE/Aβ complexes may block the access or activity of Aβ-degrading antibodies or proteases. These results support the plausibility of chelation strategy aiming at reducing amyloid pathology in Alzheimer's disease. [ABSTRACT FROM AUTHOR]

Controlling interlayer excitons in Van der Waals heterostructures holds promise for exploring Bose-Einstein condensates and developing novel optoelectronic applications, such as excitonic integrated circuits. Despite intensive studies, several key fundamental properties of interlayer excitons, such as their binding energies and interactions with charges, remain not well understood. Here we report the formation of momentum-direct interlayer excitons in a high-quality MoSe_{2}/hBN/MoSe_{2} heterostructure under an electric field, characterized by bright photoluminescence (PL) emission with high quantum yield and a narrow linewidth of less than 4 meV. These interlayer excitons show electrically tunable emission energy spanning ∼180  meV through the Stark effect, and exhibit a sizable binding energy of ∼81  meV in the intrinsic regime, along with trion binding energies of a few millielectronvolts. Remarkably, we demonstrate the long-range transport of interlayer excitons with a characteristic diffusion length exceeding 10  μm, which can be attributed, in part, to their dipolar repulsive interactions. Spatially and polarization-resolved spectroscopic studies reveal rich exciton physics in the system, such as valley polarization, local trapping, and the possible existence of dark interlayer excitons. The formation and transport of tightly bound interlayer excitons with narrow linewidth, coupled with the ability to electrically manipulate their properties, open exciting new avenues for exploring quantum many-body physics, including excitonic condensate and superfluidity, and for developing novel optoelectronic devices, such as exciton and photon routers.

Manipulating the polarization of light at the nanoscale is key to the development of next-generation optoelectronic devices. This is typically done via waveplates using optically anisotropic crystals, with thicknesses on the order of the wavelength. Here, using a novel ultrafast electron-beam-based technique sensitive to transient near fields at THz frequencies, we observe a giant anisotropy in the linear optical response in the semimetal WTe 2 and demonstrate that one can tune the THz polarization using a 50 nm thick film, acting as a broadband wave plate with thickness 3 orders of magnitude smaller than the wavelength. The observed circular deflections of the electron beam are consistent with simulations tracking the trajectory of the electron beam in the near field of the THz pulse. This finding offers a promising approach to enable atomically thin THz polarization control using anisotropic semimetals and defines new approaches for characterizing THz near-field optical response at far-subwavelength length scales.

High light absorption (∼15%) and strong photoluminescence (PL) emission in monolayer (1L) transition metal dichalcogenides (TMDs) make them ideal candidates for optoelectronic device applications. Competing interlayer charge transfer (CT) and energy transfer (ET) processes control the photocarrier relaxation pathways in TMD heterostructures (HSs). In TMDs, long-distance ET can survive up to several tens of nm, unlike the CT process. Our experiment shows that an efficient ET occurs from the 1Ls WSe 2 -to-MoS 2 with an interlayer hexagonal boron nitride (hBN), due to the resonant overlapping of the high-lying excitonic states between the two TMDs, resulting in enhanced HS MoS 2 PL emission. This type of unconventional ET from the lower-to-higher optical bandgap material is not typical in the TMD HSs. With increasing temperature, the ET process becomes weaker due to the increased electron-phonon scattering, destroying the enhanced MoS 2 emission. Our work provides new insight into the long-distance ET process and its effect on the photocarrier relaxation pathways.

Tissue regeneration requires structural holding and movement support using tissue-type-specific aids such as bone casts, skin bandages, and joint protectors. Currently, an unmet need exists in aiding breast fat regeneration as the breast moves following continuous body motion by exposing the breast fat to dynamic stresses. Here, the concept of elastic structural holding is applied to develop a shape-fitting moldable membrane for breast fat regeneration ("adipoconductive") after surgical defects are made. The membrane has the following key characteristics: (a) It contains a panel of honeycomb structures, thereby efficiently handling motion stress through the entire membrane; (b) a strut is added into each honeycomb in a direction perpendicular to gravity, thereby suppressing the deformation and stress concentration upon lying and standing; and (c) thermo-responsive moldable elastomers are used to support structural holding by suppressing large deviations of movement that occur sporadically. The elastomer became moldable upon a temperature shift above T m . The structure can then be fixed as the temperature decreases. As a result, the membrane promotes adipogenesis by activating mechanotransduction in a fat miniature model with pre-adipocyte spheroids under continuous shaking in vitro and in a subcutaneous implant placed on the motion-prone back areas of rodents in vivo., (Copyright © 2023 Hye-Seon Kim et al.)

The stemness of bone marrow mesenchymal stem cells (BMSCs) is maintained by hypoxia. The oxygen level increases from vessel-free cartilage to hypoxic bone marrow and, furthermore, to vascularized bone, which might direct the chondrogenesis to osteogenesis and regenerate the skeletal system. Hence, oxygen was diffused from relatively low to high levels throughout a three-dimensional chip. When we cultured BMSCs in the chip and implanted them into the rabbit defect models of low-oxygen cartilage and high-oxygen calvaria bone, (i) the low oxygen level (base) promoted stemness and chondrogenesis of BMSCs with robust antioxidative potential; (ii) the middle level (two times ≥ low) pushed BMSCs to quiescence; and (iii) the high level (four times ≥ low) promoted osteogenesis by disturbing the redox balance and stemness. Last, endochondral or intramembranous osteogenesis upon transition from low to high oxygen in vivo suggests a developmental mechanism-driven solution to promote chondrogenesis to osteogenesis in the skeletal system by regulating the oxygen environment.

Magnetism in topological materials creates phases exhibiting quantized transport phenomena with potential technological applications. The emergence of such phases relies on strong interaction between localized spins and the topological bands, and the consequent formation of an exchange gap. However, this remains experimentally unquantified in intrinsic magnetic topological materials. Here, this interaction is quantified in MnBi 2 Te 4 , a topological insulator with intrinsic antiferromagnetism. This is achieved by optically exciting Bi-Te p states comprising the bulk topological bands and interrogating the consequent Mn 3d spin dynamics, using a multimodal ultrafast approach. Ultrafast electron scattering and magneto-optic measurements show that the p states demagnetize via electron-phonon scattering at picosecond timescales. Despite being energetically decoupled from the optical excitation, the Mn 3d spins, probed by resonant X-ray scattering, are observed to disorder concurrently with the p spins. Together with atomistic simulations, this reveals that the exchange coupling between localized spins and the topological bands is at least 100 times larger than the superexchange interaction, implying an optimal exchange gap of at least 25 meV in the surface states. By quantifying this exchange coupling, this study validates the materials-by-design strategy of utilizing localized magnetic order to manipulate topological phases, spanning static to ultrafast timescales., (© 2022 Wiley-VCH GmbH.)

Engineering novel states of matter with light is at the forefront of materials research. An intensely studied direction is to realize broken-symmetry phases that are "hidden" under equilibrium conditions but can be unleashed by an ultrashort laser pulse. Despite a plethora of experimental discoveries, the nature of these orders and how they transiently appear remain unclear. To this end, we investigate a nonequilibrium charge density wave (CDW) in rare-earth tritellurides, which is suppressed in equilibrium but emerges after photoexcitation. Using a pump-pump-probe protocol implemented in ultrafast electron diffraction, we demonstrate that the light-induced CDW consists solely of order parameter fluctuations, which bear striking similarities to critical fluctuations in equilibrium despite differences in the length scale. By calculating the dynamics of CDW fluctuations in a nonperturbative model, we further show that the strength of the light-induced order is governed by the amplitude of equilibrium fluctuations. These findings highlight photoinduced fluctuations as an important ingredient for the emergence of transient orders out of equilibrium. Our results further suggest that materials with strong fluctuations in equilibrium are promising platforms to host hidden orders after laser excitation.

We have designed and synthesized a multifunctional dendritic molecular probe that selectively detects Cu 2+ ions via potentiometric and fluorometric techniques with low detection limits (3.5 μM in potentiometry, 15 nM in fluorometry). The selective and reversible binding of the molecule with the Cu 2+ ion was used to make a solid-state microsensor (diameter of 25 μm) by incorporating the molecular probe into the carbon-based membrane as an ionophore for Cu(II). The Cu(II) microelectrode has a broad linear range of 10 μM to 1 mM with a near Nernstian slope of 30 mV/log [ a Cu 2+ ] and detection limit of 3.5 μM. The Cu(II) microsensor has a fast response time (1.5 s), and it has a broad working pH range from 3.5 to 6.0. The incorporation of the hydrophobic dendritic moiety makes the ionophore less prone to leaching in an aqueous matrix for potentiometric measurement. The cinnamaldehyde component of the molecule helps detection of Cu 2+ ions fluorometrically, as indicated by a change in fluorescence upon selective and reversible binding of the molecular probe to the Cu 2+ ions. The strategic design of the molecular probe allows us to detect Cu 2+ ions in drinking water by using this novel dendritic fluoroionophore and solid-state Cu 2+ - ion-selective microelectrode.

Simultaneous observation of nuclear and electronic motion is crucial for a complete understanding of molecular dynamics in excited electronic states. It is challenging for a single experiment to independently follow both electronic and nuclear dynamics at the same time. Here we show that ultrafast electron diffraction can be used to simultaneously record both electronic and nuclear dynamics in isolated pyridine molecules, naturally disentangling the two components. Electronic state changes (S 1 →S 0 internal conversion) were reflected by a strong transient signal in small-angle inelastic scattering, and nuclear structural changes (ring puckering) were monitored by large-angle elastic diffraction. Supported by ab initio nonadiabatic molecular dynamics and diffraction simulations, our experiment provides a clear view of the interplay between electronic and nuclear dynamics of the photoexcited pyridine molecule., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Metal nanocrystals exhibit important optoelectronic and photocatalytic functionalities in response to light. These dynamic energy conversion processes have been commonly studied by transient optical probes to date, but an understanding of the atomistic response following photoexcitation has remained elusive. Here, we use femtosecond resolution electron diffraction to investigate transient lattice responses in optically excited colloidal gold nanocrystals, revealing the effects of nanocrystal size and surface ligands on the electron-phonon coupling and thermal relaxation dynamics. First, we uncover a strong size effect on the electron-phonon coupling, which arises from reduced dielectric screening at the nanocrystal surfaces and prevails independent of the optical excitation mechanism ( i.e., inter- and intraband). Second, we find that surface ligands act as a tuning parameter for hot carrier cooling. Particularly, gold nanocrystals with thiol-based ligands show significantly slower carrier cooling as compared to amine-based ligands under intraband optical excitation due to electronic coupling at the nanocrystal/ligand interfaces. Finally, we spatiotemporally resolve thermal transport and heat dissipation in photoexcited nanocrystal films by combining electron diffraction with stroboscopic elastic scattering microscopy. Taken together, we resolve the distinct thermal relaxation time scales ranging from 1 ps to 100 ns associated with the multiple interfaces through which heat flows at the nanoscale. Our findings provide insights into optimization of gold nanocrystals and their thin films for photocatalysis and thermoelectric applications.

Complex systems, which consist of a large number of interacting constituents, often exhibit universal behavior near a phase transition. A slowdown of certain dynamical observables is one such recurring feature found in a vast array of contexts. This phenomenon, known as critical slowing-down, is well studied mostly in thermodynamic phase transitions. However, it is less understood in highly nonequilibrium settings, where the time it takes to traverse the phase boundary becomes comparable to the timescale of dynamical fluctuations. Using transient optical spectroscopy and femtosecond electron diffraction, we studied a photoinduced transition of a model charge-density-wave (CDW) compound LaTe_{3}. We observed that it takes the longest time to suppress the order parameter at the threshold photoexcitation density, where the CDW transiently vanishes. This finding can be captured by generalizing the time-dependent Landau theory to a system far from equilibrium. The experimental observation and theoretical understanding of dynamical slowing-down may offer insight into other general principles behind nonequilibrium phase transitions in many-body systems.

The light-induced selective population of short-lived far-from-equilibrium vibration modes is a promising approach for controlling ultrafast and irreversible structural changes in functional nanomaterials. However, this requires a detailed understanding of the dynamics and evolution of these phonon modes and their coupling to the excited-state electronic structure. Here, we combine femtosecond mega-electronvolt electron diffraction experiments on a prototypical layered material, MoTe 2 , with non-adiabatic quantum molecular dynamics simulations and ab initio electronic structure calculations to show how non-radiative energy relaxation pathways for excited electrons can be tuned by controlling the optical excitation energy. We show how the dominant intravalley and intervalley scattering mechanisms for hot and band-edge electrons leads to markedly different transient phonon populations evident in electron diffraction patterns. This understanding of how tuning optical excitations affect phonon populations and atomic motion is critical for efficiently controlling light-induced structural transitions of optoelectronic devices.