Observation of pi/2 modes in an acoustic Floquet system

Topological phases of matter have remained an active area of research in the last few decades. Periodic driving is known to be a powerful tool for enriching such exotic phases, which leads to various phenomena with no static analogs. One such phenomenon is the emergence of the elusive $pi/2$ modes, i.e., a type of topological boundary state pinned at a quarter of the driving frequency. The latter may lead to the formation of Floquet parafermions in the presence of interaction, which is known to support more computational power than Majorana particles. In this work, we experimentally verify the signature of $\pi/2$ modes in an acoustic waveguide array, which is designed to simulate a square-root periodically driven Su-Schrieffer-Heeger model. This is accomplished by confirming the $4T$-periodicity ($T$ being the driving period) profile of an initial-boundary excitation, which we also show theoretically to be the smoking gun evidence of $\pi/2$ modes. Our findings are expected to motivate further studies of $\pi/2$ modes in quantum systems for potential technological applications.Comment: 6 pages, 3 figure. Comments are welcom

Stiefel-Whitney topological charges in a three-dimensional acoustic nodal-line crystal

Band topology of materials describes the extent Bloch wavefunctions are twisted in momentum space. Such descriptions rely on a set of topological invariants, generally referred to as topological charges, which form a characteristic class in the mathematical structure of fiber bundles associated with the Bloch wavefunctions. For example, the celebrated Chern number and its variants belong to the Chern class, characterizing topological charges for complex Bloch wavefunctions. Nevertheless, under the space-time inversion symmetry, Bloch wavefunctions can be purely real in the entire momentum space; consequently, their topological classification does not fall into the Chern class, but requires another characteristic class known as the Stiefel-Whitney class. Here, in a three-dimensional acoustic crystal, we demonstrate a topological nodal-line semimetal that is characterized by a doublet of topological charges, the first and second Stiefel-Whitney numbers, simultaneously. Such a doubly charged nodal line gives rise to a doubled bulk-boundary correspondence: while the first Stiefel-Whitney number induces ordinary drumhead states of the nodal line, the second Stiefel-Whitney number supports hinge Fermi arc states at odd inversion-related pairs of hinges. These results establish the Stiefel-Whitney topological charges as intrinsic topological invariants for topological materials, with their unique bulk-boundary correspondence beyond the conventional framework of topological band theory.Comment: 12 pages, 10 figure

Tailoring MoS2 Valley-Polarized Photoluminescence with Super Chiral Near-Field

Transition metal dichalcogenides with intrinsic spin–valley degrees of freedom hold great potentials for applications in spintronic and valleytronic devices. MoS2 monolayer possesses two inequivalent valleys in the Brillouin zone, with each valley coupling selectively with circularly polarized photons. The degree of valley polarization (DVP) is a parameter to characterize the purity of valley-polarized photoluminescence (PL) of MoS2 monolayer. Usually, the detected values of DVP in MoS2 monolayer show achiral property under optical excitation of opposite helicities due to reciprocal phonon-assisted intervalley scattering process. Here, it is reported that valley-polarized PL of MoS2 can be tailored through near-field interaction with plasmonic chiral metasurface. The resonant field of the chiral metasurface couples with valley-polarized excitons, and tailors the measured PL spectra in the far-field, resulting in observation of chiral DVP of MoS2-metasurface under opposite helicities excitations. Valley-contrast PL in the chiral heterostructure is also observed when illuminated by linearly polarized light. The manipulation of valley-polarized PL in 2D materials using chiral metasurface represents a viable route toward valley-polaritonic devices

Initialization of nanowire or cluster growth critically controlled by the effective V/III ratio at the early nucleation stage

For self-catalyzed nanowires (NWs), reports on how the catalytic droplet initiates successful NW growth are still lacking, making it difficult to control the yield and often accompanying a high density of clusters. Here, we have performed a systematic study on this issue, which reveals that the effective V/III ratio at the initial growth stage is a critical factor that governs the NW growth yield. To initiate NW growth, the ratio should be high enough to allow the nucleation to extend to the entire contact area between the droplet and substrate, which can elevate the droplet off of the substrate, but it should not be too high in order to keep the droplet. This study also reveals that the cluster growth between NWs is also initiated from large droplets. This study provides a new angle from the growth condition to explain the cluster formation mechanism, which can guide high-yield NW growth

Improved DQN-Based Computation Offloading Algorithm in MEC Environment

Massive terminal users have brought explosive need of data residing at edge of overall network. Multiple Mobile Edge Computing (MEC) servers are built in/near base station to meet this need. However, optimal distribution of these servers to multiple users in real time is still a problem. Reinforcement Learning (RL) as a framework to solve interaction problem is a promising solution. In order to apply RL based algorithm into a multi-agent environment, we propose an iterative scheme: select individual users with priorities to interact with the environment iteratively one at a time Furthermore, we tried to optimize the overall system performance based on this scheme. Hence, we construct three objective system performance indicators: average processing cost, delay and energy consumption, improve the existing Deep Q-learning Network (DQN) by using the cost as reward function, changing the fixed exploitation rate into dynamic one that associated with reward and episode time. In order to explore the performance potential of the proposed algorithm, we have simulated the proposed algorithm, DQN algorithm and greedy algorithm under different users and data sizes. The results show that the proposed algorithm had reduced at least 12% of system average processing cost comparing to the greedy algorithm. It also outperform the greedy algorithm and DQN algorithm in delay and energy consumption significantly.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Computer Engineerin

Lateral Involvement in Different Sized Papillary Thyroid Carcinomas Patients with Central Lymph Node Metastasis: A Multi-Center Analysis

Objective: To quantitatively predict the probability of lateral lymph node metastasis (LLNM) for papillary thyroid carcinomas (PTC) patients with central lymph node metastasis (CLNM) in order to guide postoperative adjuvant treatment. Methods: Five hundred and three PTC patients with CLNM from three medical centers were retrospectively analyzed. Results: The LLNM rate for all patients was 23.9% (120 in 503), with 15.5% (45 in 291) and 35.4% (75 in 212) for patients with papillary thyroid microcarcinoma (PTMC) and large papillary thyroid carcinoma (LPTC), respectively. Patients with no fewer than five positive central lymph nodes (CLN) exhibited a higher risk of LLNM. For patients with fewer than five positive CLN, a maximum diameter of positive CLN > 0.5 cm and the presence of ipsilateral nodular goiter were identified as independent risk factors of LLNM for papillary thyroid microcarcinoma (PTMC) patients. The independent risk factors of LLNM for large papillary thyroid carcinoma (LPTC) patients included a tumor located in the upper portion of thyroid, maximum tumor diameter ≥ 2.0 cm, maximum diameter of positive CLN > 0.5 cm, and the presence of thyroid capsular invasion. Predictive nomograms were established based on these risk factors for PTMC and LPTC patients, respectively. The accuracy and validity of our newly built models were verified by C-index and calibration curves. PTMC and LPTC patients with fewer than five positive CLN were each stratified into three subgroups based on their nomogram risk scores, and a detailed risk stratification flow chart was established for a more accurate evaluation of LLNM risk in PTC patients. Conclusions: A detailed stratification flow chart for PTC patients with CLNM to quantitatively assess LLNM risk was established, which may aid in clinical decision-making for those patients

Programmable Self-Assembly of Gold Nanoarrows via Regioselective Adsorption

Programing the self-assembly of colloidal nanoparticles into predetermined superstructures represents an attractive strategy to realize functional assemblies and novel nanodevices, but it remains a challenge. Herein, gold nanoarrows (GNAs) showing a distinct convex-concave structure were employed as unique building blocks for programmable self-assembly involving multiple assembly modes. Regioselective adsorption of 1,10-decanedithiol on the vertexes, edges, and facets of GNAs allowed for programmable self-assembly of GNAs with five distinct assembly modes, and regioselective blocking with 1-dodecanethiol followed by adsorption of 1,10-decanedithiol gave rise to programmable self-assembly with six assembly modes including three novel wing-engaged modes. The assembly mode was essentially determined by regioselective adsorption of the dithiol linker dictated by the local curvature together with the shape complementarity of GNAs. This approach reveals how the geometric morphology of nanoparticles affects their regioselective functionalization and drives their self-assembly

Efficient solidification of Pb2+ by activated tungsten tailings and cement

The preparation of cementing admixture from tailings and co-solidification of Pb2+ with cement is a green way to realize the resource utilization of tailings and treatment of the lead-containing wastewater. In this paper, the tungsten tailings were activated in different ways, and the mechanical properties of the tungsten tailings-cement solidified body with different activation systems and the solidification behavior of Pb2+ were studied. The phase and microstructure of the hydrated product were characterized by XRD, FT-IR, SEM and EDS. The results showed that the curing effect of Pb2+ was obviously different of different activation systems, and the curing effect of the solidified body of the ternary composite activation system (TCAS) was the best, second only to the pure cement system (PCS). Different activation methods have a significant impact on the mechanical properties of the solidified body. With the increase of the Pb2+ content, the compressive strength of the solidified body gradually decreased, the Pb2+ leaching concentration gradually increased; with the extension of the curing age, the compressive strength gradually increased, and the Pb2+ leaching concentration gradually decreased. In particular, the compressive strength of the 28d solidified body was 31.43 MPa and the leaching concentration of Pb2+ was only 0.38 mg/L when the Pb2+ content was 5%. The phase, microstructure and EDS results of the hydration products showed that Pb2+ was mainly solidified in the C-S-H gel