Association of bidirectional network cores in the brain with conscious perception and cognition.

The brain comprises a complex network of interacting regions. To understand the roles and mechanisms of this complex network, its structural features related to specific cognitive functions need to be elucidated. Among such relationships, recent developments in neuroscience highlight the link between network bidirectionality and conscious perception. Given the essential roles of both feedforward and feedback signals in conscious perception, it is surmised that subnetworks with bidirectional interactions are critical. However, the link between such subnetworks and conscious perception remains unclear due to the network's complexity. In this study, we propose a framework for extracting subnetworks with strong bidirectional interactions-termed the "cores" of a network-from brain activity. We applied this framework to resting-state and task-based fMRI data to identify regions forming strongly bidirectional cores. We then explored the association of these cores with conscious perception and cognitive functions. The central cores predominantly included cerebral cortical regions, which are crucial for conscious perception, rather than subcortical regions. Furthermore, the cores were composed of previously reported regions in which electrical stimulation altered conscious perception. These results suggest a link between the bidirectional cores and conscious perception. A meta-analysis and comparison of the core structure with a cortical functional connectivity gradient suggested that the central cores were related to lower-order sensorimotor functions. An ablation study emphasized the importance of incorporating bidirectionality, not merely interaction strength for these outcomes. The proposed framework provides novel insight into the roles of network cores with strong bidirectional interactions in conscious perception and lower-order sensorimotor functions.

Pressure dependence of superconductivity in alkali-Bi compounds KBi2 and RbBi2.

The structural and superconducting properties of alkali-Bi-based compounds, KBi2 and RbBi2, were investigated over a wide pressure range for the first time. The samples of KBi2 and RbBi2 were prepared using a liquid ammonia (NH3) technique, and demonstrated superconductivity with superconducting transition temperatures, Tc, of 3.50 and 4.21 K at ambient pressure, respectively. The onset superconducting transition temperature, Tconset, of KBi2 decreased slightly; however, it suddenly jumped at 2 GPa and increased gradually with pressure, indicating the presence of two superconducting phases in the low-pressure range. The pressure-dependent X-ray diffraction patterns indicate that the KBi2 sample decomposed into KBi and Bi at pressures higher than 2.5 GPa. Moreover, a discontinuous change in Tconset was observed for KBi2 at 9 GPa, which reflects the decomposition of KBi2 into KBi and Bi. By contrast, the value of Tconset of RbBi2 was almost constant over a pressure range of 0-8 GPa. Thus, the superconducting properties and stability of alkali-Bi-based compounds against pressure were comprehensively explored in this study. In addition, the superconducting Cooper pair symmetry was investigated from the magnetic field dependence of Tc of KBi2 at 0.790 and 2.32 GPa, and of RbBi2 at 1.17 GPa, indicating the exact deviation from the simple s-wave paring model, which may be due to the complex electronic structure of Bi. The results elucidated the exotic superconducting properties of KBi2 and RbBi2 based on the pressure and magnetic field dependence of Tc and verified the chemical stability of KBi2 under pressure.

Laying down of gold nanorods monolayers on solid surfaces for surface enhanced Raman spectroscopy applications.

Laying-down gold nanorods (GNRs) of a monolayer immobilized on a solid substrate was realized with a hybrid method, a combination of three elemental technologies: surface modification, electrophoresis, and solvent evaporation. The self-assembly of CTAB-protected GNRs in the solution was induced by 0.05 mM of EDTA. The assembled GNRs were deposited in a laying-down form on the solid surface during the hybrid method. The final coverage was over 71% on the substrate with an area larger than 0.6 cm2. The spacing between the sides of the GNRs was fixed to be 4.6 ± 0.9 nm by the thermal annealing-promoted crystalline packing of the bilayer of CTAB salt-bridged with EDTA. The obtained laying-down GNRs of a monolayer on the gold substrate show a small shift of the transverse LSPR around 550-570 nm (with a width of around 100 nm) and a large red shift of the longitudinal LSPR to be 900-1050 nm (with a width of 500 nm), because of the strong electromagnetic coupling between the GNRs and gold substrate. Therefore it can be used in a wide range of wavelengths for surface enhanced Raman spectroscopy (SERS) applications. The film has a high enhancement factor with 105 for R6G.

Superconducting properties of BaBi3 at ambient and high pressures.

Herein, we report the preparation and characterization of BaBi3 clarified by DC magnetic susceptibility, powder X-ray diffraction (XRD), and electrical transport. The superconducting properties of BaBi3 were elucidated through the magnetic and electrical transport properties in a wide pressure range. The superconducting transition temperature, Tc, showed a slight decrease (or almost constant Tc) against pressure up to 17.2 GPa. The values of the upper critical field, Hc2, at 0 K, were determined to be 1.27 T at 0 GPa and 3.11 T at 2.30 GPa, using the formula, because p-wave pairing appeared to occur for this material at both pressures, indicating the unconventionality of superconductivity. This result appears to be consistent with the topological non-trivial nature of superconductivity predicted theoretically. The pressure-dependent XRD patterns measured at 0-20.1 GPa indicated no structural phase transitions up to 20.1 GPa, i.e., the structural phase transitions from the α phase to the ß or γ phase which are induced by an application of pressure were not observed, contrary to the previous report, demonstrating that the α phase is maintained over the entire pressure range. Admittedly, the lattice constants and the volume of the unit cell, V, steadily decrease with increasing pressure up to 20.1 GPa. In this study, the plots of Tcversus p and V versus p of BaBi3 are depicted over a wide pressure range for the first time.

Superconductivity of topological insulator Sb2Te3-ySeyunder pressure.

The crystal structures of Sb2Te3-ySey(y= 0.6 andy= 1.2) at 0-24 GPa were investigated by synchrotron x-ray diffraction. The stoichiometry of Sb2Te3-ySeyused in this study was determined to be Sb2Te2.19(9)Se0.7(2)fory= 0.6 and Sb2Te1.7(1)Se1.3(3)fory= 1.2, on the basis of energy-dispersive x-ray spectroscopy. The sample of Sb2Te2.19(9)Se0.7(2)showed a structural phase transition from a rhombohedral structure (space group No. 166,R3¯m) (phase I) to a monoclinic structure (space group No. 12,C2/m) (phase II), with increasing pressure up to ∼9 GPa. A new structural phase (phase II') emerged at 17.7 GPa, a monoclinic structure with the space groupC2/c(No. 15). Finally, a 9/10-fold monoclinic structure (space group No. 12,C2/m) (phase III) was observed at 21.8 GPa. In contrast, the sample of Sb2Te1.7(1)Se1.3(3)provided only phase I (space group No. 166,R3¯m) and phase II (space group No. 12,C2/m), showing one structural phase transition from 0-19.5 GPa. These samples were not superconductors at ambient pressure, but superconductivity suddenly appeared with increasing pressure. Superconductivity with superconducting transition temperatures (Tc's) of 2 and 4 K was observed above 6 GPa in phase I of Sb2Te2.19(9)Se0.7(2). In this sample, theTcvalues of 6 and 9 K were observed in phase II and phase II' or III of Sb2Te2.19(9)Se0.7(2), respectively. Superconductivity withTc's of 4 and 5 K suddenly emerged in Sb2Te1.7(1)Se1.3(3)at 13.6 GPa, which corresponds to phase II, and it evolved to 6.0 K under further increased pressure. ATcvalue of 9 K was finally found above 15 GPa. The magnetic field dependence ofTcin phase II of Sb2Te2.19(9)Se0.7(2)and Sb2Te1.7(1)Se1.3(3)followed ap-wave polar model, suggesting topologically nontrivial superconductivity.

Balanced Ambipolar Charge Transport in Phenacene/Perylene Heterojunction-Based Organic Field-Effect Transistors.

Electronic devices relying on the combination of different conjugated organic materials are considerably appealing for their potential use in many applications such as photovoltaics, light emission, and digital/analog circuitry. In this study, the electrical response of field-effect transistors achieved through the evaporation of picene and PDIF-CN2 molecules, two well-known organic semiconductors with remarkable charge transport properties, was investigated. With the main goal to get a balanced ambipolar response, various device configurations bearing double-layer, triple-layer, and codeposited active channels were analyzed. The most suitable choices for the layer deposition processes, the related characteristic parameters, and the electrode position were identified to this purpose. In this way, ambipolar organic field-effect transistors exhibiting balanced mobility values exceeding 0.1 cm2 V-1 s-1 for both electrons and holes were obtained. These experimental results highlight also how the combination between picene and PDIF-CN2 layers allows tuning the threshold voltages of the p-type response. Scanning Kelvin probe microscopy (SKPM) images acquired on picene/PDIF-CN2 heterojunctions suggest the presence of an interface dipole between the two organic layers. This feature is related to the partial accumulation of space charge at the interface being enhanced when the electrons are depleted in the underlayer.

Emergence of a Pressure-Driven Superconducting Phase in Ba0.77Na0.23Ti2Sb2O.

We investigated the pressure dependence of electric transport in a superconducting sample, Ba0.77Na0.23Ti2Sb2O, to complete the phase diagram of superconducting transition temperature (Tc) against pressure (p). This superconducting sample exhibits a Tc value of 5.8 K at ambient pressure. Here, the superconductivity of the recently reported sample was investigated over a wide pressure range. The Tc value monotonously decreased with pressure below 8 GPa. Interestingly, the Tc value rapidly increased above 8 GPa and slowly declined with pressure above 11 GPa. Thus, a new superconducting phase was discovered above ∼9 GPa. The crystal structure of Ba0.77Na0.23Ti2Sb2O was also elucidated at 0-22.0 GPa with synchrotron X-ray powder diffraction. Consequently, an evident relation between the crystal structure and the superconductivity was revealed, namely, a clear structural phase transition was observed at 8-11 GPa, where the Tc value rapidly increased against pressure. This study provides detailed information on the superconductivity of Ba0.77Na0.23Ti2Sb2O under pressure, which will lead to a comprehensive understanding of pressure-driven superconductivity.

Superconductivity in topological insulator ß-PdBi2 under pressure.

The topological insulator PdBi2 exhibits two different crystal phases at ambient pressure, i.e., 'α-PdBi2' and ' -PdBi2'. The pressure dependence of crystal structure and superconductivity of α-PdBi2 has been fully elucidated thus far. However, the physical properties of ß-PdBi2 crystals under pressure have not been sufficiently investigated. In this study, we fully investigate the crystal structure and superconductivity of ß-PdBi2 under pressure based on synchrotron x-ray diffraction (XRD) patterns. The temperature dependence of ß-PdBi2 indicates its superconductivity with a superconducting transition temperature (T c) as high as 4.10 K, and its crystal structure is tetragonal [space group of I4/mmm (no. 139)]. The XRD patterns at 0-22.0 GPa indicate no structural phase transitions, and the unit cell volume shrinks monotonically with pressure, unlike the behavior of α-PdBi2. Furthermore, α-PdBi2 transformed to ß-PdBi2 under pressure. This suggests that ß-PdBi2 is stable under pressure. The superconductivity is clearly observed at 0-11.8 GPa, and the value of T c is almost constant at ∼4.4 K. The temperature dependence of the upper critical field at ambient pressure and 10.7 GPa indicates that the superconductivity is not attributed to a simple s-wave dirty limit but an s-wave clean or p-wave polar model. This is the first systematic study of superconductivity of topological insulator ß-PdBi2 under pressure.

Superconducting behavior of BaTi2Bi2O and its pressure dependence.

A new superconducting sample, BaTi2Bi2O, was synthesized and characterized over a wide pressure range. The superconducting transition temperature, Tc, of BaTi2Bi2O was 4.33 K at ambient pressure. The crystal structure was tetragonal (space group of P4/mmm (No. 123)), according to the X-ray diffraction (XRD) pattern at ambient pressure. The XRD pattern was analyzed using the Le Bail method. The magnetic-field dependence of the magnetization at different temperatures was precisely investigated to elucidate the characteristics of the superconductivity. The pressure-dependent XRD patterns showed absence of structural phase transitions up to 19.8 GPa. The superconducting properties of BaTi2Bi2O were investigated under pressure. Tc monotonously increased with the pressure (p) up to 4.0 GPa and saturated above 4.0 GPa. The variations in the Tc-p plot were thoroughly analyzed. The Cooper pair symmetry (or superconducting pairing mechanism) was analyzed based on the magnetic field dependence of the superconductivity at ambient and high pressures, which indicated a sign of p-wave pairing for the superconductivity of BaTi2Bi2O, i.e., topologically nontrivial sign was suggested for BaTi2Bi2O.

Superconductivity in Bi2-x Sb x Te3-y Se y (x = 1.0 and y = 2.0) under pressure.

The crystal structure of BiSbTeSe2 (Bi2-x Sb x Te3-y Se y (x = 1.0 and y = 2.0)) at 0-29 GPa is investigated through synchrotron x-ray diffraction (XRD) and two structural phase transitions are discovered. The stoichiometry of BiSbTeSe2 employed in this study is Bi1.19(4)Sb0.81(4)Te0.83(4)Se2.17(4), as determined from energy-dispersive x-ray spectroscopy. The sample demonstrated structural transitions, from a rhombohedral structure (space group no 166, R [Formula: see text] m) (phase I) to a monoclinic structure (space group no 12, C2/m) (phase II), and from phase II to a 9/10-fold monoclinic structure (space group no 12, C2/m) (phase III). The temperature dependence of resistance (R-T plot) exhibited a semiconducting behavior in a low pressure range and changed from semiconducting to metallic behavior with increasing pressure. Pressure-driven superconductivity is observed above 9.1 GPa in Bi1.19(4)Sb0.81(4)Te0.83(4)Se2.17(4). The pressure phase corresponds to phase II. The superconducting transition temperature, T c, increased with pressure. The maximum T c value is 8.3 K at 19.1 GPa. The magnetic field dependence of T c in phase II of Bi1.19(4)Sb0.81(4)Te0.83(4)Se2.17(4) is proceeded by a p-wave polar model, indicating topologically nontrivial superconductivity. In addition, the emergence of superconductivity and the change in superconducting behavior are closely associated with the structural transitions.

Structure and superconducting properties of multiple phases of (NH3) y AE x FeSe (AE: Ca, Sr and Ba).

We synthesized the alkaline-earth metal-doped FeSe compounds (NH3) y AE x FeSe (AE: Ca, Sr and Ba), using the liquid NH3 technique, to determine their superconducting properties and crystal structures. Multiple superconducting phases were obtained in each sample of (NH3) y Ca x FeSe and (NH3) y Ba x FeSe, which showed two superconducting transition temperatures (T c's) as high as 37-39 K and 47-48 K at ambient pressure, hereinafter referred to as the 'low-T c phase' and 'high-T c phase', respectively. The high-T c phases in (NH3) y Ca x FeSe and (NH3) y Ba x FeSe were metastable, and rapidly converted to their low-T c phases. However, T c values of 38.4 K and 35.6 K were recorded for (NH3) y Sr x FeSe, which displayed different behavior than (NH3) y Ca x FeSe and (NH3) y Ba x FeSe. The Le Bail fitting of x-ray diffraction (XRD) patterns provided lattice constants of c = 16.899(1) Å and c = 16.8630(8) Å for the low-T c phases of (NH3) y Ca x FeSe and (NH3) y Ba x FeSe, respectively. The lattice constants of their high-T c phases could not be determined due to the disappearance of the high T c phase within a few days. The XRD pattern for (NH3) y Sr x FeSe indicated the coexistence of two phases with c = 16.899(3) Å and c = 15.895(4) Å. The former value of c in (NH3) y Sr x FeSe is almost the same as those of the low-T c phases in (NH3) y Ca x FeSe and (NH3) y Ba x FeSe. Therefore, the phase with c = 16.899(3) Å in (NH3) y Sr x FeSe must correspond to the superconducting phase with the T c of 38.4 K, while the superconducting phase with T c = 35.6 K is assigned to the crystal phase with c = 15.895(4) Å. For (NH3) y Sr x FeSe, a high-T c phase with T c = 47-48 K has not yet been obtained, but a new phase showing the T c value of 35.6 K was clearly obtained. This is the first systematic study of the preparation, crystal structure, and superconductivity of alkaline-earth metal-doped FeSe, (NH3) y AE x FeSe.

A new protocol for the preparation of superconducting KBi2.

A superconducting KBi2 sample was successfully prepared using a liquid ammonia (NH3) technique. The temperature dependence of the magnetic susceptibility (M/H) showed a superconducting transition temperature (T c) as high as 3.6 K. In addition, the shielding fraction at 2.0 K was evaluated to be 87%, i.e., a bulk superconductor was realized using the above method. The T c value was the same as that reported for the KBi2 sample prepared using a high-temperature annealing method. An X-ray diffraction pattern measured based on the synchrotron X-ray radiation was analyzed using the Rietveld method, with a lattice constant, a, of 9.5010(1) Šunder the space group of Fd3̄m (face-centered cubic, no. 227). The lattice constant and space group found for the KBi2 sample using a liquid NH3 technique were the same as those reported for KBi2 through a high-temperature annealing method. Thus, the superconducting behavior and crystal structure of the KBi2 sample obtained in this study are almost the same as those for the KBi2 sample reported previously. Strictly speaking, the magnetic behavior of the superconductivity was different from that of a KBi2 sample reported previously, i.e., the KBi2 sample prepared using a liquid NH3 technique was a type-II like superconductor, contrary to that prepared using a high-temperature annealing method, the reason for which is fully discussed. These results indicate that the liquid NH3 technique is effective and simple for the preparation of a superconducting KBi2. In addition, the topological nature of the superconductivity for KBi2 was not confirmed.

Superconducting behavior of a new metal iridate compound, SrIr2, under pressure.

Herein, we investigated the pressure dependence of electric transport in a new type of superconducting metal iridate compound, SrIr2, that exhibits a superconducting transition temperature, T c, as high as 6.6 K at ambient pressure, in order to complete the T c-pressure (p ) phase diagram. Very recently, this sample's superconductivity was discovered by our group, but the superconducting behavior has not yet been clarified under pressure. In this study, we fully investigated this sample's superconductivity in a wide pressure range. The T c value decreased with an increase in pressure, but the onset superconducting transition temperature, [Formula: see text], increased above a pressure of 8 GPa, indicating an unconventional superconductivity different from a BCS-type superconductor. The magnetic field dependence of electric resistance (R) against temperature (R - T plot) recorded at 7.94 and 11.3 GPa suggested an unconventional superconductivity, followed by a p -wave polar model, supporting the deviation from a simple s-wave pairing. Moreover, we fully investigated the pressure dependence of crystal structure in SrIr2 and discussed the correlation between superconductivity and crystal structure. This is the first systematic study on superconducting behavior of a new type of metal iridate compound, MIr2 (M: alkali-earth metal atom), under pressure.

Selective Two-Photon-Absorption-Induced Reactions of Anthracene-2-Carboxylic Acid on Tunable Plasmonic Substrate with Incoherent Light Source.

In this research, we report the development, characterization and application of various plasmonic substrates (with localized surface plasmon resonance wavelength tunable by gold nanoparticle size) for two-photon absorption (TPA)-induced photodimerization of an anthracene derivative, anthracene carboxylic acid, in both surface and solution phase under incoherent visible light irradiation. Despite the efficient photoreaction property of anthracene derivatives and the huge number of publications about them, there has never been a report of a multiphoton photoreaction involving an anthracene derivative with the exception of a reverse photoconversion of anthracene photodimer to monomer with three-photon absorption. We examined the progress of the TPA-induced photoreaction by means of surface-enhanced Raman scattering, taking advantage of the ability of our plasmonic substrate to enhance and localize both incident light for photoreaction and Raman scattering signal for analysis of photoreaction products. The TPA-induced photoreaction in the case of anthracene carboxylic acid coated 2D array of gold nanoparticles gave different results according to the properties of the plasmonic substrate, such as the size of the gold nanoparticle and also its resultant optical properties. In particular, a stringent requirement to achieve TPA-induced photodimerization was found to be the matching between irradiation wavelength, localized surface plasmon resonance of the 2D array, and twice the wavelength of the molecular excitation of the target material (in this case, anthracene carboxylic acid). These results will be useful for the future development of efficient plasmonic substrates for TPA-induced photoreactions with various materials.

Enhanced catalytic activity of self-assembled-monolayer-capped gold nanoparticles.

An unprecedented substrate-selective catalytic enhancement effect of an alkanethiol-self-assembled monolayer (SAM) on Au nanoparticles (AuNPs) is reported. In the supported 2D-array of AuNPs, the alkanethiol-SAM acts as a protein-like soft reaction space in which the substrate molecules are encapsulated through non-covalent intermolecular hydrophobic interactions, and thus catalytic reactions are accelerated at AuNP surfaces.

Simple one-step growth and parallel alignment of DNA nanofibers via solvent vapor-induced buildup.

This communication describes the growth and parallel patterning of 1D DNA nanofibers, exceeding several hundred micrometers in length and 40 nm in diameter, induced by solvent evaporation.