Valence-bond-solid order in antiferromagnets with spin-lattice coupling

We propose that a valence-bond-solid (VBS) order can be stabilized in certain two-dimensional antiferromagnets due to spin-lattice coupling. In contrast to the VBS state of the Affleck-Kennedy-Lieb-Tesaki (AKLT) type in which the spin $2S$ and the lattice coordination $z$ must be commensurate, the spin-lattice coupling-induced VBS state can occur when $2S$ is not an integer multiple of $z$. As a concrete example, S=2 spins on the triangular network with $z=6$ is discussed. Within the Schwinger boson mean-field theory it is shown that the ground state is given by the $\sqrt{3}\times\sqrt{3}$ modulation of the valence bond amplitudes for sufficiently strong spin-lattice coupling. Using the corresponding AKLT wave function, we work out the excitation spectrum for this state within the single-mode approximation. The calculated spectrum should provide a new type of collective mode which is distinct from the spin wave excitations of the magnetically ordered ground state

Spin-polarization coupling in multiferroic transition-metal oxides

A systematic microscopic theory of magnetically induced ferroelectricity and lattice modulation is presented for all electron configurations of Mott-insulating transition-metal oxides. Various mechanisms of polarization are identified in terms of a strong-coupling perturbation theory. Especially, the spin-orbit interaction acting on the ligand p orbitals is shown to give the ferroelectric polarization of the spin-current form, which plays a crucial role particularly in eg systems. Semiquantitative agreements with the multiferroic TbMnO3 are obtained. Predictions for X-ray and neutron scattering experiments are proposed to clarify the microscopic mechanism of the spin-polarization coupling in different materials

Lattice-coupled Antiferromagnet on Frustrated Lattices

Lattice-coupled antiferromagnetic spin model is analyzed for a number of frustrated lattices: triangular, Kagome, and pyrochlore. In triangular and Kagome lattices where ground state spins are locally ordered, the spin-lattice interaction does not lead to a static deformation of the lattice. In the pyrochlore structure, spin-lattice coupling supports a picture of the hexagon spin cluster proposed in the recent experiment[S. H. Lee et al. Nature, 418, 856 (2002)]. Through spin-lattice interaction a uniform contraction of the individual hexagons in the pyrochlore lattice can take place and reduce the exchange energy. Residual hexagon-hexagon interaction takes the form of a 3-states Potts model where the preferred directions of the spin-loop directors for nearby hexagons are mutually orthogonal

Locally Adaptive and Differentiable Regression

Over-parameterized models like deep nets and random forests have become very popular in machine learning. However, the natural goals of continuity and differentiability, common in regression models, are now often ignored in modern overparametrized, locally-adaptive models. We propose a general framework to construct a global continuous and differentiable model based on a weighted average of locally learned models in corresponding local regions. This model is competitive in dealing with data with different densities or scales of function values in different local regions. We demonstrate that when we mix kernel ridge and polynomial regression terms in the local models, and stitch them together continuously, we achieve faster statistical convergence in theory and improved performance in various practical settings

Design, Modelling, and Control of a Reconfigurable Rotary Series Elastic Actuator with Nonlinear Stiffness for Assistive Robots

In assistive robots, compliant actuator is a key component in establishing safe and satisfactory physical human-robot interaction (pHRI). The performance of compliant actuators largely depends on the stiffness of the elastic element. Generally, low stiffness is desirable to achieve low impedance, high fidelity of force control and safe pHRI, while high stiffness is required to ensure sufficient force bandwidth and output force. These requirements, however, are contradictory and often vary according to different tasks and conditions. In order to address the contradiction of stiffness selection and improve adaptability to different applications, we develop a reconfigurable rotary series elastic actuator with nonlinear stiffness (RRSEAns) for assistive robots. In this paper, an accurate model of the reconfigurable rotary series elastic element (RSEE) is presented and the adjusting principles are investigated, followed by detailed analysis and experimental validation. The RRSEAns can provide a wide range of stiffness from 0.095 Nm/deg to 2.33 Nm/deg, and different stiffness profiles can be yielded with respect to different configuration of the reconfigurable RSEE. The overall performance of the RRSEAns is verified by experiments on frequency response, torque control and pHRI, which is adequate for most applications in assistive robots. Specifically, the root-mean-square (RMS) error of the interaction torque results as low as 0.07 Nm in transparent/human-in-charge mode, demonstrating the advantages of the RRSEAns in pHRI

A sensitive electrochemical sensor based on polypyrrole/electrochemically reduced graphene oxide for the determination of imidacloprid

The glassy carbon electrode (GCE) was modified by electrochemically reduced graphene oxide (ERGO) and polypyrrole (PPy) prepared by simple cyclic voltammetry (CV) electropoly­merization. The PPy/ERGO modified electrode (PPy/ERGO/GCE) was used as a platform of electrochemical sensor to detect imidacloprid (IMI) insecticide. CV and differential pulse voltammetry (DPV) were chosen as the methods to investigate of the electrochemical behavior of IMI on PPy/ERGO/GCE surface. Scanning electron microscopy (SEM) and Raman spectra were utilized to describe the morphology and structure of the modified electrode. Experimental parameters were optimized, such as the number of polymerization cycles, scan rate and the pH value of electrolyte. Under the optimized conditions, when the concentration of IMI was in the range of 1-10 μM and 10-60 μM, the increase of reduction peak current was linear with the concentration of IMI, and the low detection limit was found to be 0.18 μM (S/N = 3). Results showed that PPy/ERGO/GCE demonstrated satisfactory reproducibility and stability, and has great potential in actual sample testing

27630 Assessing signs and symptoms of hidradenitis suppurativa from the patient perspective

Background: Qualitative research was conducted to develop a patient reported outcome (PRO) measure assessing symptoms/signs of hidradenitis suppurativa (HS), the HS Symptom Diary (HSSD). Methods: Concept elicitation (CE) and combined CE/cognitive debriefing (CD) interviews were conducted with adult patients with moderate-to-severe HS from 5 dermatology practices in North America. The CE portion of the interview sought to fully understand important concepts of HS. Subjects then completed the draft HSSD, and answered questions to evaluate its content, clarity, and relevance. Revisions were made iteratively to the HSSD. The study received institutional review board approval; subjects provided written informed consent. Results: 36 subjects were interviewed [6 = CE and 30 = CE/CD, 65% female; mean age = 39]. The most commonly reported lesion locations were armpits (81%), groin (75%), or under the breasts (31%). Subjects reported pain (100%), drainage (100%), itching (100%), swelling/ inflammation (94%), odor (86%), tenderness (81%), heat (64%), and pressure (64%) related to their lesions. The most bothersome symptoms were pain (94%), drainage (50%), swelling/inflammation (42%), and itching (33%). Pain was the most difficult symptom to manage (53%). In general, respondents were able to paraphrase each item and found the content to be clear and relevant. The final HSSD, developed as a daily diary with a 24-hour recall period, contains 8 items evaluating severity of each symptom/sign using an 11-point numeric rating scale. A 7-day version was also developed. Conclusion: Content validity of the HSSD in patients with moderate-to-severe HS has been demonstrated. Its measurement properties will be assessed using data from upcoming clinical studies

Geological and evolutionary characteristics of the Gagarin Region on the far side of the Moon

Objective  This study focuses on the Gagarin region on the far side of the Moon, aiming to reveal the geological characteristics, distribution features, and genesis of typical areas on the lunar far side. Additionally, it seeks to explore the regional geological evolution history of the Gagarin region.  Methods  The study primarily employs methods such as multi-source remote sensing data interpretation, regional geological mapping, and quantitative analysis of geological elements' quantity and distribution characteristics.  Results  (1) 656 impact craters were discovered in the study area, of which 552 have diameters greater than 20 kilometers. Approximately 71.5% of the Gagarin region is covered by ancient basins and their ejecta from the Aitken period. Based on comprehensive area and diameter data, the Aitken period is identified as the geological era with the largest proportion of large impact craters (diameter greater than 70 kilometers) and the largest average diameter. From the Aitken period to the Copernican period, the total area of impact craters in each geological era shows a decreasing trend from old to new. (2) In the study area, six parallel lunar grabens, 62 lobate scarps, one sinuous rille , 50 crater floor fractures, and 70 shallow faults were discovered. It also includes parts of the two longest inferred deep faults on the Moon, originating from the South Pole–Aitken tectonic zone and almost spanning the entire highland tectonic zone. According to Bouguer gravity anomalies and crustal thickness data, linear crustal thickness anomalies extending outward from the South Pole–Aitken basin reach the major basins on the near side of the Moon. (3) The Gagarin region is primarily located in the anorthositic highlands on the far side of the Moon. The rocks mainly consist of ferroan anorthosite (fa) suites, with some crater floors showing magnesium anorthosite (ma) suites. In the central and southern parts of the Gagarin region, low-titanium (TiO2 > 1.5 and < 4.5) and very low-titanium (TiO2 < 1.5) basalts are sparsely distributed on the floors of certain impact craters and basins. (4) For this study, we selected impact craters such as Aitken and Van der Graaf, with diameters ranging from 350 to 1400 m, for dating analysis. The results of crater size-frequency distribution dating indicate ages of 3.47 GA and 3.32 GA, respectively. (5) The quantitative statistics of impact craters and the dating results of basalt units indicate that the Aitkenian to Imbrian periods were active periods of external dynamic geological processes in the Gagarin region, while the Imbrian period was an active period of internal dynamic geological processes.   Conclusion  (1) The region’s longest and deepest faults are the result of the combined effects of the South Pole–Aitken impact event and internal and external stresses, including lunar thermal expansion. (2) The variations in the number and size of impact craters in the Gagarin region on the far side of the Moon are related to the evolution of the Earth–Moon system and the solar system. (3) Based on the quantitative statistical results of impact craters and the dating results of basalt units, this study elucidates the regional geological evolution history, and different stages of the geological processes in the Gagarin region were divided according to the active periods and stage characteristics of internal and external dynamic geological processes.   Significance  The study revealed the geological features of key areas on the far side of the moon, delving into the geological history of the Gagarin region and tentatively establishing a correlation between its geological traits and the lunar evolutionary history