Giant enhancement of cryogenic thermopower by polar structural instability in the pressurized semimetal MoTe2

We found that a high mobility semimetal 1T'-MoTe2 shows a significant pressure-dependent change in the cryogenic thermopower in the vicinity of the critical pressure, where the polar structural transition disappears. With the application of a high pressure of 0.75 GPa, while the resistivity becomes as low as 10 {\mu}{\Omega}cm, thermopower reached the maximum value of 60 {\mu}VK-1 at 25 K, leading to a giant thermoelectric power factor of 300 {\mu}WK-2cm-1. Based on semiquantitative analyses, the origin of this behavior is discussed in terms of inelastic electron-phonon scattering enhanced by the softening of zone center phonon modes associated with the polar structural instability.Comment: 13 pages, 4 figures Physical review B (accepted

Unveiling the orbital-selective electronic band reconstruction through the structural phase transition in TaTe2_2

Tantalum ditelluride TaTe$_2$ belongs to the family of layered transition metal dichalcogenides but exhibits a unique structural phase transition at around 170 K that accompanies the rearrangement of the Ta atomic network from a "ribbon chain" to a "butterfly-like" pattern. While multiple mechanisms including Fermi surface nesting and chemical bonding instabilities have been intensively discussed, the origin of this transition remains elusive. Here we investigate the electronic structure of single-crystalline TaTe$_2$ with a particular focus on its modifications through the phase transition, by employing core-level and angle-resolved photoemission spectroscopy combined with first-principles calculations. Temperature-dependent core-level spectroscopy demonstrates a splitting of the Ta $4f$ core-level spectra through the phase transition indicative of the Ta-dominated electronic state reconstruction. Low-energy electronic state measurements further reveal an unusual kink-like band reconstruction occurring at the Brillouin zone boundary, which cannot be explained by Fermi surface nesting or band folding effects. On the basis of the orbital-projected band calculations, this band reconstruction is mainly attributed to the modifications of specific Ta $5d$ states, namely the $d_{XY}$ orbitals (the ones elongating along the ribbon chains) at the center Ta sites of the ribbon chains. The present results highlight the strong orbital-dependent electronic state reconstruction through the phase transition in this system and provide fundamental insights towards understanding complex electron-lattice-bond coupled phenomena.Comment: 21 pages, 5 figure

Turning motion generation of peristaltic crawling robot using two-dimensional dynamic model and numerical optimization

Peristaltic crawling robots inspired by the earthworm's motion have been attracting attention as robots for working in hazardous environments or confined spaces. The peristaltic crawling robots need turning motion to move in winding piping or in spaces with obstacles. In this study, we propose a model-based motion generation method for peristaltic crawling robots to realize a turning motion suitable for the robot’s dynamics and the friction characteristics of the environment. For realizing the motion generation, a two-dimensional dynamic model is constructed by combining the robot’s kinematics and a dynamic friction model, and motion patterns are generated by applying numerical optimization based on the particle optimization method. The contributions of this study are the construction of the model that enables detailed motion analysis on two-dimensional plane and the realization of the model-based method for generating efficient turning motions and turning movements at specified angles for peristaltic crawling robots. As a result of generating the turning motions, it was confirmed that the turning angle was increased by combining the stretching and bending motion. In addition, the validities of the constructed a two-dimensional dynamic model and motion generation method were confirmed from experimental verifications

Progressive Alteration of UCP and ANT in Skeletal Muscle of Fasted Chickens

Avian uncoupling protein (avUCP), sharing 71-73% amino acid homology with both UCP2 and UCP3, is one of the mitochondrial anion carrier proteins. Its precise physiological roles in the cell remain elusive. A confusing aspect of these UCP variants (namely, UCP2, UCP3 and avUCP), is that their expression is enhanced in response to fasting ; that is, in response to basal metabolic state in which such energy expenditure would be expected to be depressed. In this study, we examined progressive alterations in the expression of genes encoding for mitochondrial uncoupling proteins, not only UCP but also avian adenine nucleotide translocator (avANT), in the skeletal muscle tissue of fasted chickens. The expression of avUCP gene was markedly enhanced after 12h of fasting and then diminished slightly but remained elevated after 96h of fasting compared to time 0 levels. In contrast, avANT was up-regulated only after 24h of fasting but continued to be further increased after 96h. Taken together, these results demonstrate that transcription of each of the mitochondrial anion carriers, avUCP and avANT, is independently up-regulated during fasting periods, implying different control mechanisms and consequences of each in metabolic adaptations involved in prolonged fasting

A Stimulus-Responsive Shape-Persistent Micelle Bearing a Calix[4]arene Building Block: Reversible pH-Dependent Transition between Spherical and Cylindrical Forms

A series of cationic calix[4]­arene-based lipids with alkyl chains of varying length were newly synthesized, and the ones with propyl and hexyl tails, denoted by CaL[4]­C3 and C6, respectively, were found to form spherical micelles at low pH (protonated state of the amine headgroup). Upon deprotonation with increasing pH, CaL[4]­C3 showed a sphere-to-cylinder transition, while CaL[4]­C6 changed from sphere, to cylinder, to monolayer vesicle. Synchrotron small-angle X-ray scattering (SAXS) patterns from both spherical and cylindrical CaL[4]­C3 micelles exhibited a sharp intensity minimum, indicating shape monodispersity. The monodispersity of the CaL[4]­C3 spherical micelles was further confirmed by analytical ultracentrifugation (AUC). SAXS, AUC, and static light scattering agreeingly indicated an aggregation number of 6. In contrast, CaL[4]­C6 exhibited polydispersity with an average aggregation number of 12. When the number of carbons of the alkyl chain was increased to 9 (CaL[4]­C9), cylinder formed at low pH, while at high pH, no clear morphology could be observed. The present results indicate that a very precise combination of tail length, head volume, and rigidity of the building block is required to produce shape-persistent micelles and that the shape-persistence can be maintained upon a structural transition. An attempt to reconstruct a molecular model for the spherical CaL[4]­C3 micelle was made with an ab initio shape determining program

Anisotropic Crystals Based on a Main-Group Coordination Polymer with Alignment of Rigid π Skeletons

We succeeded in the alignment of π skeletons, resulting in the formation of anisotropic crystals. The combination of plumbacyclopentadienylidene, which has a divalent lead atom incorporated into the π skeleton, and 1,4-dioxane afforded a coordination polymer, where the π skeletons are completely aligned in the same direction. The resulting plumbylene chains are also aligned in the same direction in the solid state, and therefore the crystals are noncentrosymmetric, showing second-harmonic generation (SHG) properties. Using pyrazine instead of 1,4-dioxane afforded an adduct composed of three plumbole units and two pyrazine molecules, and the crystals are symmetric and exhibit no SHG properties. The solid-state structures and optical properties are highly dependent on the Lewis base utilized. The present findings spotlight the use of group 14 divalent species incorporated into a π skeleton as a novel, useful method for the creation of a π-aligned coordination polymer with NLO properties

X‑ray Scattering from Immunostimulatory Tetrapod-Shaped DNA in Aqueous Solution To Explore Its Biological Activity–Conformation Relationship

We carried out synchrotron X-ray scattering experiments from four DNA supermolecules designed to form tetrapod shapes; these supermolecules had different sequences but identical numbers of total base pairs, and each contained an immunostimulatory CpG motif. We confirmed that the supermolecules did indeed form the expected tetrapod shape. The sample that had the largest radius of gyration (<i>R</i>_g) induced the most cytokine secretion from cultured immune cells. Structural analysis in combination with a rigid tetrapod model and an atomic scale DNA model revealed that the larger <i>R</i>_g can be ascribed to dissociation of the DNA double strands in the central connecting portion of the DNA tetrapod. This finding suggests that the biological activity is related to the ease with which single DNA strands can be formed