118 research outputs found
Positive 2-bridge knots and chirally cosmetic surgeries
In this paper we verify that with the exception of the torus
knots, positive 2-bridge knots up to 31 crossings do not admit chirally
cosmetic surgeries. A knot admits chirally cosmetic surgeries if there
exist surgeries and with distinct slopes and such
that , where the negative represents an
orientation reversal. To verify this, we use the obstruction formula from
arXiv:2112.03144 which relates classical knot invariants to the existence of
chirally cosmetic surgeries. To check the formula, we develop a Python program
that computes the classical knot invariants , , , , and
of a positive 2-bridge knot.Comment: 25 pages, 22 figures, code developed can be found at
https://github.com/zl830/chiral_cosmetic_surgery_for_pos_2_bridge_knot
Trait Mindfulness Is Associated With the Self-Similarity of Heart Rate Variability
Previous studies have linked trait mindfulness with better self-regulation and adaptation. Heart rate variability (HRV) is a good physiological indicator of the capacity for self-regulation and adaptation. The present study explored the relationship between trait mindfulness and HRV from the viewpoint of crosstalking between different HRV parameter pairs, which would reflect the dynamic interactions between each pair of HRV parameters in different processes. We measured the trait mindfulness of seventy-four undergraduate students and recorded nine HRV parameters during the following four consecutive experimental phases: (1) calming phase, (2) mental arithmetic task phase, (3) recovery phase, and (4) mindfulness practice phase. The relationship between trait mindfulness and HRV was explored at the following three levels: (1) the absolute level, i.e., HRV parameters in four different states, (2) the difference-change level, i.e., differences in HRV parameters between different states, and (3) the crosstalking level, i.e., self-similarity of crosstalking HRV parameter pairs. The results supported the following hypothesis: trait mindfulness, as measured by the Mindful Attention Awareness Scale (MAAS), was significantly and positively correlated with the self-similarity of crosstalking HRV parameter pairs but was not significantly correlated with the HRV parameters at the difference-change and absolute levels. These findings indicate that as trait mindfulness increases, the ability to maintain ANS function homeostasis improves.HIGHLIGHTS-Trait mindfulness is associated with better self-regulation and adaptation.-Heart rate variability (HRV) is a good physiological indicator of the capacity for self-regulation and adaptation.-Trait mindfulness is significantly correlated with self-similarity of crosstalking HRV parameter pairs but not with the HRV parameters at the difference-change or absolute levels
Boosting Oxygen and Peroxide Reduction Reactions on PdCu Intermetallic Cubes
Palladium‐based nanocatalysts have the potential to replace platinum‐based catalysts for fuel‐cell reactions in alkaline electrolytes, especially PdCu intermetallic nanoparticles with high electrochemical activity and stability. However, unlike the synthetic methods for obtaining the nanoparticles, the effect of PdCu shape on the performance is relatively less well studied. Here, we demonstrate the facet dependence of PdCu intermetallics on the oxygen reduction reaction (ORR) and peroxide reduction, and reveal that the {100} dominant PdCu cubes have a much higher ORR mass activity and specific activity than spheres at 0.9 V vs. RHE, which is four and five times that of commercial Pd/C and Pt/C catalysts, respectively, and show only a 31.7 % decay after 30 000 cycles in the stability test. Moreover, cubic PdCu nanoparticles show higher peroxide electroreduction activity than Pd cubes and PdCu spheres. Density functional theory (DFT) calculation reveals that the huge difference originates from the reduction in oxygen adsorption energy and energy barrier of peroxide decomposition on the ordered {100} PdCu surface. Given the relationship between the shape and electrochemical performance, this study will contribute to further research on electrocatalytic improvements of catalysts in alkaline environments.Shape the future: PdCu intermetallic cubes and spheres are synthesized to investigate the facet dependence on the oxygen reduction reaction and peroxide reduction. The cubes show large improvements in mass activity towards both reactions, compared with the spheres. DFT calculation uncovers that the dominant {100} faces of the cubes offer more appropriate oxygen adsorption and are thermodynamically favorable for peroxide reduction compared to the surface of spheres.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155903/1/celc202000381.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155903/2/celc202000381_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155903/3/celc202000381-sup-0001-misc_information.pd
Prominent Size Effects without a Depolarization Field Observed in Ultrathin Ferroelectric Oxide Membranes
The increasing miniaturization of electronics requires a better understanding of material properties at the nanoscale. Many studies have shown that there is a ferroelectric size limit in oxides, below which the ferroelectricity will be strongly suppressed due to the depolarization field, and whether such a limit still exists in the absence of the depolarization field remains unclear. Here, by applying uniaxial strain, we obtain pure in-plane polarized ferroelectricity in ultrathin SrTiO3 membranes, providing a clean system with high tunability to explore ferroelectric size effects especially the thickness-dependent ferroelectric instability with no depolarization field. Surprisingly, the domain size, ferroelectric transition temperature, and critical strain for room-temperature ferroelectricity all exhibit significant thickness dependence. These results indicate that the stability of ferroelectricity is suppressed (enhanced) by increasing the surface or bulk ratio (strain), which can be explained by considering the thickness-dependent dipole-dipole interactions within the transverse Ising model. Our study provides new insights into ferroelectric size effects and sheds light on the applications of ferroelectric thin films in nanoelectronics
Lattice-contraction triggered synchronous electrochromic actuator.
Materials with synchronous capabilities of color change and actuation have prospects for application in biomimetic dual-stealth camouflage and artificial intelligence. However, color/shape dual-responsive devices involve stimuli that are difficult to control such as gas, light or magnetism, and the devices show poor coordination. Here, a flexible composite film with electrochromic/actuating (238° bending angle) dual-responsive phenomena, excellent reversibility, high synchronization, and fast response speed (< 5 s) utilizes a single active component, W18O49 nanowires. From in situ synchrotron X-ray diffraction, first principles calculations/numerical simulations, and a series of control experiments, the actuating mechanism for macroscopic deformation is elucidated as pseudocapacitance-based reversible lattice contraction/recovery of W18O49 nanowires (i.e. nanostructure change at the atomic level) during lithium ion intercalation/de-intercalation. In addition, we demonstrate the W18O49 nanowires in a solid-state ionic polymer-metal composite actuator that operates stably in air with a significant pseudocapacitive actuation
Multistep Synthesis of a Radiolabeled Imaging Probe Using Integrated Microfluidics
Microreactor technology has shown potential for optimizing synthetic efficiency, particularly in preparing sensitive compounds. We achieved the synthesis of an [^(18)F]fluoride-radiolabeled molecular imaging probe, 2-deoxy-2-[18F]fluoro-d-glucose ([^(18)F]FDG), in an integrated microfluidic device. Five sequential processes—[^(18)F]fluoride concentration, water evaporation, radiofluorination, solvent exchange, and hydrolytic deprotection—proceeded with high radio-chemical yield and purity and with shorter synthesis time relative to conventional automated synthesis. Multiple doses of [^(18)F]FDG for positron emission tomography imaging studies in mice were prepared. These results, which constitute a proof of principle for automated multistep syntheses at the nanogram to microgram scale, could be generalized to a range of radiolabeled substrates
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